Pulsed radiofrequency ablation

PULSED RADIOFREQUENCY ABLATION

CROSS-REFERENCE TO RELATED APPLICATIONS

0003[0001] This application claims priority to U.S. Prov. App. No. 62/330,395, filed May 2, 2016, U.S. Prov. App. No. 62/357,704, filed July 1, 2016, U.S. Prov. App. No. 62/399,632, filed September 26, 2016, U.S. Prov. App. No. 62/399,625, filed September 26, 2016, U.S. Prov. App. No. 62/420,610, filed November 11, 2016, U.S. Prov. App. No. 62/424,736, filed November 21, 2016, U.S. Prov. App. No. 62/428,406, filed November 30, 2016, U.S. Prov. App. No.

000462/434,073, filed December 14, 2016, U.S. Prov. App. No. 62/468,339, filed March 7, 2017, and U.S. Prov. App. No. 62/468,873, filed March 8, 2017, with the entire contents of each of these applications hereby incorporated herein by reference.

0005[0002] This application is also related to the following commonly-owned U.S. patent

0006applications filed on even date herewith: Attorney Docket Number AFRA-0001-P01, entitled "CATHETER SENSING AND IRRIGATING"; Attorney Docket Number AFRA-0009-P01, entitled "LESION FORMATION"; Attorney Docket Number AFRA-00011-POl, entitled "THERAPEUTIC CATHETER WITH IMAGING"; and Attorney Docket Number AFRA-0013- P01, entitled "CATHETER INSERTION." Each of the foregoing applications is hereby incorporated herein by reference in its entirety.

BACKGROUND

0008[0003] Abnormal rhythms generally referred to as arrhythmia can occur in the heart. Cardiac arrhythmias develop when abnormal conduction in the myocardial tissue modifies the typical heartbeat pattern. Radio frequency ("RF") catheter ablation can be used to form lesions that interrupt the mechanism of abnormal conduction to terminate certain arrhythmias.

SUMMARY

0010[0004] Ablation systems and methods of the present disclosure are directed toward delivering pulsed radiofrequency (RF) energy to target tissue. The pulsations of the RF energy, combined with cooling at a surface of the target tissue, can advantageously promote local heat transfer in the target tissue to form lesions having dimensions larger than those that can be safely formed in tissue using non-pulsed RF energy under similar conditions.

0011[0005] According to one aspect, a method includes placing an ablation electrode at an interface between tissue and blood in an anatomic structure of a patient, delivering RF energy to the ablation electrode at the interface during a period of lesion formation, and delivering an irrigation fluid to the interface during at least a portion of the period of lesion formation. The RF energy delivered to the ablation electrode at the interface is pulsed to cycle between a first energy phase and a second energy phase during the period of lesion formation, the RF energy in the first energy phase being greater than the RF energy in the second energy phase, and a combination of irrigation fluid and blood moves through the ablation electrode to cool the ablation electrode at the interface during the period of lesion formation.

0012[0006] In certain implementations, a rate of cooling of the interface by the combination of blood and irrigation fluid moving through the ablation electrode at the interface is greater than a rate of heating of the interface by the RF energy during the second energy phase.

0013[0007] In some implementations, the second energy phase can be an off phase.

0014[0008] In certain implementations, during each second energy phase, tissue at the interface can undergo more cooling than tissue at a depth from the interface.

0015[0009] In some implementations, during the period of lesion formation, the RF energy can be cycled between at least two cycles, with each cycle including a second energy phase and a first energy phase.

0016[0010] In certain implementations, each second energy phase can have a duration greater than 0 seconds and less than about 6 seconds.

0017[0011] In some implementations, each second energy phase has a predetermined duration.

0018[0012] In certain implementations, each first energy phase can have a predetermined duration.

0019[0013] In some implementations, the method can further include receiving, from a temperature sensor disposed at the interface, a signal indicative of temperature of the interface, wherein a duration of one or more of the first energy phase and the second energy phase is based on the signal indicative of temperature of the interface. [0014] In certain implementations, the method can further include detecting a change in an electrical signal associated with the RF energy delivered to the ablation electrode at the interface, wherein a duration of one or more of the first energy phase and the second energy phase is based on the detected change in the electrical signal.

0020[0015] In some implementations, the first phase of the RF energy can be about ten seconds.

0021[0016] In certain implementations, the period of lesion formation can be about 1 minute to about three minutes.

0022[0017] In some implementations, the anatomic structure can be a heart cavity. For example, the tissue can be the endocardium of the heart cavity.

0023[0018] In certain implementations, a volumetric flow rate of the irrigation fluid delivered to the interface can be based on one or more signals indicative of temperature at the interface. For example, the volumetric flow rate can be decreased in response to the one or more signals indicative of temperature being below a first predetermined threshold, and the volumetric flow rate is increased in response to the one or more signals indicative of temperature being above a second predetermined threshold. The first predetermined threshold can be, in certain instances, different from the second predetermined threshold. Additionally, or alternatively, increasing the volumetric flow rate, decreasing the volumetric flow rate, or both can occur over a temperature range corresponding to a range of the one or more signals indicative of temperature. Further, or instead, the volumetric flow rate can be increased according to a first predetermined function of the one or more signals indicative of temperature and the volumetric flow rate can be decreased according to a second predetermined function of the one or more signals indicative of temperature. The first predetermined function can be, in certain instances, different from the second predetermined function. Additionally, or alternatively, at least one of the first

0024predetermined function and the second predetermined function can be continuous. Further, or instead, at least one of the first predetermined function of the one or more signals indicative of temperature and the second predetermined function of the one or more signals indicative of temperature can be discontinuous (e.g., at least one of the first predetermined function and the second predetermined function can include a respective step change in the volumetric flow rate).

0025[0019] In some implementations, the method can further include receiving, from respective sensors disposed along the ablation electrode, a plurality of signals indicative of respective sensed temperatures. Increasing the volumetric flow rate, decreasing the volumetric flow rate, or both can be based on a signal of the plurality of signals corresponding to a maximum sensed temperature. Additionally, or alternatively, the method can further include processing each signal of the plurality of signals based on an inverse Laplacian operator, wherein increasing the volumetric flow rate, decreasing the volumetric flow rate, or both can be based on a maximum signal of the processed signals.

0026[0020] In certain implementations, a volumetric flow rate of the irrigation fluid delivered to the interface can be based on the RF energy delivered to the ablation electrode at the interface.

0027[0021] In some implementations, a volumetric flow rate of the irrigation fluid can be pulsed between a first volumetric flow rate and a second volumetric flow rate less than the first volumetric flow rate. For example, the volumetric flow rate of the irrigation fluid can be pulsed substantially in phase with the pulsation of the RF energy such that the first volumetric flow rate can be substantially in phase with the first energy phase and the second volumetric flow rate can be substantially in phase with the second energy phase.

0028[0022] In certain implementations, delivering the irrigation fluid to the interface can include mixing the irrigation fluid with blood moving through the ablation electrode at the interface.

0029[0023] In some implementations, the irrigation fluid can be saline.

0030[0024] In certain implementations, placing the ablation electrode at the interface between the tissue and blood can include moving the ablation electrode into the anatomic structure through vasculature of the patient. For example, the ablation electrode can be coupled to a distal portion of a catheter shaft and placing the ablation electrode at the interface between tissue and blood in the anatomic structure can include moving the distal portion of the catheter shaft through vasculature of the patient and into the anatomic structure.

0031[0025] According to another aspect, a method includes placing an ablation electrode at an interface between tissue and blood in an anatomic structure of a patient such that fluid in the anatomic structure moves through the ablation electrode placed at the interface, delivering RF energy to the ablation electrode at the interface during a period of lesion formation, delivering an irrigation fluid to the interface during at least a portion of the period of lesion formation such that the fluid moving through the ablation electrode includes the irrigation fluid, and monitoring tissue at the interface, wherein monitoring tissue at the interface includes reducing the RF energy and reducing the volumetric flow rate of the irrigation fluid during a measurement phase of the period of lesion formation, receiving one or more signals indicative of temperature at the interface, and determining a temperature at the interface based on the one or more signals received during the measurement phase of the period of lesion formation.

0032[0026] In certain implementations, determining the temperature at the interface can be further based on the one or more signals received during a portion of the period of lesion formation other than the measurement phase.

0033[0027] In some implementations, the method can further include displaying the determined temperature on a graphical user interface.

0034[0028] In certain implementations, the method can further include, based on the determined temperature, titrating the RF energy delivered to the ablation electrode.

0035[0029] In some implementations, the method can further include adjusting the volumetric flow rate of the irrigation fluid based on the determined temperature.

0036[0030] In some implementations, the volumetric flow rate can be decreased in response to the determined temperature being below a first predetermined threshold. Additionally, or alternatively volumetric flow rate can be increased in response to the determined temperature being above a second predetermined threshold.

0037[0031] In certain implementations, receiving the one or more signals indicative of temperature at the interface can include receiving, from respective sensors disposed along the ablation electrode, a plurality of signals indicative of a respective plurality of sensed temperatures. For example, increasing the volumetric flow rate, decreasing the volumetric flow rate, or both can be based on a signal of the plurality of signals corresponding to a maximum sensed temperature. Additionally, or alternatively, each signal of the plurality of signals can be based on an inverse Laplacian operator, wherein increasing the volumetric flow rate, decreasing the volumetric flow rate, or both is based on a maximum signal of the processed signals.

0038[0032] In some implementations, the method can further include increasing the RF energy following reduction of the RF energy, and increasing the volumetric flow rate of the irrigation fluid following reduction of the volumetric flow rate of the irrigation fluid. [0033] In certain implementations, the RF energy can be pulsed to cycle between a first energy phase and a second energy phase during the period of lesion formation, the delivered RF energy in the first energy phase can be greater than the delivered RF energy in the second energy phase.

0039[0034] According to still another aspect, a method includes placing an ablation electrode at an interface between tissue and blood in an anatomic structure of a patient such that fluid in the anatomic structure moves through the ablation electrode placed at the interface, delivering RF energy to the ablation electrode at the interface during a period of lesion formation, delivering an irrigation fluid to the interface during at least a portion of the period of lesion formation such that the fluid moving through the ablation electrode includes irrigation fluid, and monitoring tissue at the interface, wherein monitoring tissue at the interface includes receiving one or more signals indicative of temperature at the interface, determining a temperature at the interface based on the one or more received signals, and increasing the volumetric flow rate based on the determined temperature exceeding a predetermined threshold (e.g., about 55 °C).

0040[0035] According to still another aspect a system includes an ablation electrode, an irrigation element, a generator, and a controller. The ablation electrode is positionable at an interface between endocardium tissue and blood in a heart cavity of a patient such that fluid in the heart cavity is movable through the ablation electrode at the interface to cool the ablation electrode during a period of lesion formation. The irrigation element defines at least one orifice positioned to direct irrigation fluid toward the ablation electrode such that the fluid movable through the ablation electrode at the interface includes irrigation fluid. The generator is in electrical communication with the ablation electrode to deliver RF energy to the ablation electrode during the period of lesion formation. The controller is in communication with the generator, the controller including one or more processors and a non-transitory, computer-readable storage medium having stored thereon computer executable instructions for causing the one or more processors to control energy delivered from the generator to the ablation electrode at the interface between the endocardium tissue and blood during the period of lesion formation, wherein the RF energy delivered to the ablation electrode at the interface is pulsed to alternate between a first energy phase and a second energy phase during the period of lesion formation, the delivered RF energy in the first energy phase being greater than the delivered RF energy in the second energy phase. [0036] In certain implementations, the ablation electrode can be positionable at the interface such that blood is movable through the ablation electrode at the interface to cool the ablation electrode during the period of lesion formation.

0041[0037] In some implementations, the at least one orifice of the irrigation element can be positioned to direct irrigation fluid toward the ablation electrode such that the fluid movable past the ablation electrode is a mixture of the irrigation fluid and blood in the heart cavity.

0042[0038] In certain implementations, the controller can be in communication with a source of irrigation fluid in fluid communication with the at least one orifice of the irrigation element to control a volumetric flow rate of irrigation fluid moving from the source of irrigation fluid and through the at least one orifice. Additionally, or alternatively, the computer executable instructions can further include instructions for causing the one or more processors to control a volumetric flow rate of irrigation fluid delivered from the source of irrigation fluid and through the at least one orifice. For example, the computer executable instructions can further include instructions for causing the one or more processors to control the volumetric flow rate of irrigation fluid based on the RF energy delivered to the ablation electrode. As an additional, or alternative example, the computer executable instructions can further include instructions for causing the one or more processors to pulse the volumetric flow rate of irrigation fluid between a first volumetric flow rate and a second volumetric flow rate less than the first volumetric flow rate. As an example, the computer executable instructions can further include instructions for causing the one or more processors to pulse the volumetric flow rate of irrigation fluid substantially in phase with the pulsation of the RF energy such that the first volumetric flow rate is substantially in phase with the first energy phase and the second volumetric rate is

0043substantially in phase with the second energy phase.

0044[0039] In some implementations, each second energy phase can have a duration greater than 0 seconds and less than about 6 seconds.

0045[0040] In certain implementations, the first energy phase of the RF energy can be about ten seconds.

0046[0041] In some implementations, the ablation electrode can be movable through vasculature of the patient and into the heart cavity of the patient. For example, the system can further include a catheter including a proximal portion and a distal portion, the ablation electrode coupled to the distal portion of the catheter.

0047[0042] According to yet another aspect, a system includes an ablation electrode, at least one sensor, a generator, an irrigation pump, and a controller. The ablation electrode is positionable at an interface between endocardium tissue and blood in a heart cavity of a patient. The at least one sensor is disposed along the ablation electrode. The irrigation element defines at least one orifice positioned to direct an irrigation fluid toward the ablation electrode. The generator is in electrical communication with the ablation electrode. The irrigation pump is in mechanical communication with a fluid line to deliver the irrigation fluid through the at least one orifice. The controller is in communication with the generator, the at least one sensor, and the irrigation pump, the controller including one or more processors and a non-transitory, computer-readable storage medium having stored thereon computer executable instructions for causing the one or more processors to deliver RF energy from the generator to the ablation electrode at the interface between the endocardium tissue and blood during a period of lesion formation, deliver the irrigation fluid to the interface during at least a portion of the period of lesion formation, reduce the RF energy and reduce the volumetric flow rate of the irrigation fluid during a measurement phase of the period of lesion formation, receive from the at least one sensor one or more signals indicative of temperature at the interface, and determine a temperature at the interface based on the one or more signals received during the measurement phase of the period of lesion formation.

0048[0043] In certain implementations, the computer executable instructions for causing the one or more processors to determine the temperature at the interface further can include instructions for causing the one or more processors to determine the temperature at the interface further based on the one or more signals received during a portion of the period of lesion formation other than the measurement phase.

0049[0044] In some implementations, the computer executable instructions can further include instructions for causing the one or more processors to display the determined temperature on a graphical user interface.

0050[0045] In certain implementations, the computer executable instructions can further include instructions for causing the one or more processors to titrate the RF energy delivered to the ablation electrode based on the determined temperature. [0046] In some implementations, the ablation electrode can be positionable at the interface such that blood is movable through the ablation electrode at the interface to cool the ablation electrode during the period of lesion formation.

0051[0047] In certain implementations, the at least one orifice of the irrigation element can be positioned to direct irrigation fluid toward the ablation electrode such that the fluid movable through the ablation electrode is a mixture of the irrigation fluid and blood in the heart cavity.

0052[0048] In some implementations, the computer executable instructions can further include instructions for causing the one or more processors to control the volumetric flow rate of irrigation fluid based on the RF energy delivered to the ablation electrode.

0053[0049] In certain implementations, the computer executable instructions can further include instructions for causing the one or more processors to pulse the volumetric flow rate of irrigation fluid between a first volumetric flow rate and a second volumetric flow rate less than the first volumetric flow rate.

0054[0050] In some implementations, the RF energy delivered to the ablation electrode at the interface can be pulsed to alternate between a first energy phase and a second energy phase during the period of lesion formation, the delivered RF energy in the first energy phase being greater than the delivered RF energy in the second energy phase. Additionally, or alternatively, the computer executable instructions can further include instructions for causing the one or more processors to pulse the volumetric flow rate of irrigation fluid substantially in phase with the pulsation of the RF energy such that the first volumetric flow rate is substantially in phase with the first energy phase and the second volumetric rate is substantially in phase with the second energy phase. For example, each second energy phase can have a duration greater than 0 seconds and less than about 6 seconds. Additionally, or alternatively, the first energy phase of the RF energy can be about ten seconds.

0055[0051] According to still another aspect, a system includes an ablation electrode, at least one sensor, an irrigation pump, a generator, and a controller. The ablation electrode is positionable at an interface between endocardium tissue and blood in a heart cavity of a patient such that fluid in the heart cavity is movable through the ablation electrode at the interface to cool the ablation electrode during a period of lesion formation. The at least one sensor is disposed along the ablation electrode. The irrigation element defines at least one orifice positioned to direct irrigation fluid toward the ablation electrode. The generator is in electrical communication with the ablation electrode to deliver RF energy to the ablation electrode during the period of lesion formation. The irrigation pump is in mechanical communication with a fluid line to deliver irrigation fluid through the at least one orifice. The controller is in communication with the generator, the at least one sensor, and the irrigation pump, the controller including one or more processors and a non-transitory, computer-readable storage medium having stored thereon computer executable instructions for causing the one or more processors to control energy delivered from the generator to the ablation electrode at the interface between the endocardium tissue and blood during a period of lesion formation, based on the one or more signals from the at least one sensor, determine a temperature at the interface, deliver irrigation fluid to the interface such that the fluid moving through the ablation electrode includes the irrigation fluid, increase the volumetric flow rate of the irrigation fluid based on the determined temperature exceeding a predetermined threshold.

0056[0052] In certain implementations, the computer-executable instructions to deliver irrigation fluid to the interface can include instructions to decrease the volumetric flow rate of the irrigation fluid in response to the determined temperature being below the predetermined threshold.

0057[0053] In some implementations, the computer-executable instructions to control energy delivered from the generator to the ablation electrode can include instructions to pulse RF energy to cycle between a first energy phase and a second energy phase during the period of lesion formation, the delivered RF energy in the first energy phase being greater than the delivered RF energy in the second energy phase.

0058[0054] Other aspects, features, and advantages will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

0060[0055] FIG. 1 is a schematic representation of an ablation system during an ablation treatment.

0061[0056] FIG. 2 is a perspective view of a catheter of the ablation system of FIG. 1.

0062[0057] FIG. 3 is a perspective view of a distal end portion of the catheter of the ablation system of FIG. 1. [0058] FIG. 4 is a cross-sectional perspective view along cross-section A-A of FIG. 3.

0063[0059] FIG. 5 is a schematic representation of a jet of irrigation fluid moving from an irrigation element to an inner portion of an ablation electrode of the catheter of FIG. 2.

0064[0060] FIG. 6 is a side view of an ablation electrode of the ablation system of FIG. 1.

0065[0061] FIG. 7 is a perspective view of the ablation electrode of the ablation system of FIG. 1.

0066[0062] FIG. 8 is a cross-sectional view, taken along line B-B in FIG. 7, of the ablation electrode of the ablation system of FIG. 1.

0067[0063] FIG. 9 is an exemplary graph of force as a function of displacement of a deformable portion of the ablation electrode of the ablation system of FIG. 1.

0068[0064] FIG. 10 is a perspective view of sensors and the ablation electrode of the ablation system of FIG. 1, with the sensors shown mounted to the ablation electrode.

0069[0065] FIG. 11 is a perspective view of a sensor of the ablation system of FIG. 1.

0070[0066] FIGS. 12A-12C are schematic representations of a method of forming the ablation electrode of the ablation system of FIG. 1.

0071[0067] FIGS. 13A-13E are schematic representations of a method of inserting the catheter of FIG. 2 into a patient.

0072[0068] FIGS. 14A-C are schematic representations of a method of positioning the ablation electrode of the ablation system of FIG. 1 at a treatment site of a patient.

0073[0069] FIGS. 15A-B are schematic representations of a method of irrigating the ablation electrode of the ablation system of FIG. 1.

0074[0070] FIG. 16 is a schematic representation of a side view of a helical irrigation element of a catheter of an ablation system.

0075[0071] FIG. 17 is a side view of an irrigation element of a catheter of an ablation system, the irrigation element including a porous membrane.

0076[0072] FIG. 18 is a perspective view of a distal end portion of a catheter of an ablation system. [0073] FIG. 19 is a cross-sectional perspective view along cross-section C-C of FIG. 18. [0074] FIG. 20 is a perspective view of a distal end portion of a catheter of an ablation system. [0075] FIG. 21 is a cross-sectional perspective view along cross-section D-D of FIG. 20.

0077[0076] FIG. 22 is a perspective view of a distal end portion of a catheter of an ablation system.

0078[0077] FIG. 23 is a cross-sectional side view of the catheter of FIG. 22 along cross-section E-E. of FIG. 22.

0079[0078] FIG. 24 is a schematic representation of a trajectory around an outer surface of an ablation electrode of the catheter of FIG. 22, the trajectory used to present simulation results of current density associated with the ablation electrode.

0080[0079] FIG. 25 is a graph of percentage change in simulated current density along the trajectory shown in FIG. 24, at a fixed distance of 1 mm from an outer surface of the ablation electrode.

0081[0080] FIG. 26 is a graph of depth and width of lesions applied to chicken breast meat using the ablation electrode of FIG. 22 in axial and lateral orientations relative to the chicken breast meat.

0082[0081] FIG. 27 is a graph of RF energy as a function of time for a pulsed RF energy profile having a first energy phase greater than a second energy phase.

0083[0082] FIG. 28 is a schematic representation of a lesion formed in tissue receiving non-pulsed RF energy.

0084[0083] FIGS. 29A-B are schematic representations of heat transfer in tissue as the pulsed RF energy profile of FIG. 27 is applied to tissue.

0085[0084] FIG. 30 is a flowchart of an exemplary process of pulsing RF energy to ablate target tissue.

0086[0085] Like reference symbols in the various drawings indicate like elements. DETAILED DESCRIPTION

0087[0086] The present disclosure is generally directed to systems and methods of ablating tissue of a patient during a medical procedure being performed on an anatomic structure of the patient. By way of non-limiting example and for the sake of clarity of explanation, the systems and methods of the present disclosure are described with respect to ablation of tissue in a heart cavity of the patient as part of an ablation treatment associated with the treatment of cardiac arrhythmia. However, it should be appreciated that, unless otherwise specified, the systems and methods of the present disclosure can be used for any of various different medical procedures, such as procedures performed on a hollow anatomic structure of a patient, in which ablation of tissue is part of a medical treatment.

0088[0087] As used herein, the term "physician" should be considered to include any type of medical personnel who may be performing or assisting a medical procedure.

0089[0088] FIG. 1 is a schematic representation of an ablation system 100 during a cardiac ablation treatment being performed on a patient 102. The ablation system 100 includes a catheter 104 connected, via an extension cable 106, to a catheter interface unit 108. The catheter interface unit 108 can be a computing device that includes a processing unit 109a, a non-transitory, computer readable storage medium 109b, and a graphical user interface 110. The processing unit 109a can be a controller including one or more processors, and the storage medium 109b can have stored thereon computer executable instructions for causing the one or more processors of the processing unit 109a to carry out one or more portions of the various methods described herein, unless otherwise indicated or made clear from the context.

0090[0089] A mapping system 112, a recording system 111, an irrigation pump 114, and a generator 116 can be connected to the catheter interface unit 108. The irrigation pump 114 can be removably and fluidly connected to the ablation catheter 104 via fluid line 115. The generator 116 can also, or instead, be connected, via one or more wires 117, to one or more return electrodes 118 attached to the skin of the patient 102. The recording system 111 can be used throughout the ablation treatment, as well as before or after the treatment. The mapping system 112 can be used prior to and/or during an ablation treatment to map the cardiac tissue of the patient 102 and determine which region or regions of the cardiac tissue require ablation.

0091[0090] Referring now to FIGS. 2-4, the catheter 104 can include a handle 120, a catheter shaft 122, an ablation electrode 124, sensors 126, and an irrigation element 128. The handle 120 is coupled to a proximal end portion 130 of the catheter shaft 122, and a distal end portion 132 of the catheter shaft 122 can be coupled to the irrigation element 128 and to the ablation electrode 124, which supports the sensors 126 in some implementations. The handle 120 can, further or instead, be coupled to the fluid line 115 and to one or more of the wires 117 for delivery of irrigation fluid and electrical energy, respectively, along the catheter shaft 122, to the ablation electrode 124. [0091] As described in further detail below, in a deployed state of the ablation electrode 124, irrigation fluid exits irrigation holes 134 defined by the irrigation element 128 and is directed toward an inner portion 136 of the ablation electrode 124 while an outer portion 138 (opposite the inner portion 136) of the ablation electrode 124 is in contact with tissue as part of an ablation treatment. Spacing between the irrigation holes 134 and the inner portion 136 of the ablation electrode 124 can facilitate heat transfer between the irrigation fluid and the ablation electrode 124. For example, in the spacing between the irrigation holes 134 and the inner portion 136 of the ablation electrode 124, the respective jets of irrigation fluid can develop turbulent characteristics. Without wishing to be bound by theory, it is believed that, as compared to non- turbulent or less turbulent flow of irrigation fluid, increased turbulence can improve local heat transfer from the ablation electrode 124 (e.g., from the inner portion 136 of the ablation electrode 124) to the irrigation fluid. Additionally, or alternatively, blood can flow through the spacing between the irrigation holes 134 and the inner portion 136 of the ablation electrode 124. As compared to configurations in which the flow of blood away from the treatment site is impeded, the flow of blood through the spacing between the irrigation holes 134 and the inner portion 136 of the ablation electrode 124 can, additionally or alternatively, improve further the local heat transfer from the outer portion 138 of the ablation electrode 124. In general, it should be appreciated that such improved local heat transfer can reduce the likelihood of blood clot or charring.

0092[0092] As also described in further detail below, the ablation electrode 124 can include a coupling portion 140 and a deformable portion 142. As used herein, the terms "expandable" and "deformable" are used interchangeably, unless otherwise specified or made clear from the context. Thus, for example, it should be understood that the deformable portion 142 is expandable unless otherwise specified.

0093[0093] The coupling portion 140 is secured to the distal end portion 132 of the catheter shaft 122, and the deformable portion 142 can extend distally from the coupling portion 140. The deformable portion 142 of the ablation electrode 142 can be deformed for delivery (e.g., through an introducer sheath, such as an 8F introducer sheath) and expanded at a treatment site to have a cross-sectional dimension larger than a cross-sectional dimension of the catheter shaft 122. As compared to smaller ablation electrodes, the ablation electrode 124 can provide wider lesions within a shorter period of time, facilitating the creation of a pattern of overlapping lesions (e.g., reducing the likelihood of arrythmogenic gaps, and reducing the time and number of lesions required for an overlapping pattern, or both). Additionally, or alternatively, a larger tip can facilitate the delivery of more power for providing wider and deeper lesions.

0094[0094] Further, in an expanded state, the deformable portion 142 of the ablation electrode 124 is deformable upon sufficient contact force with tissue, and the shape and extent of the deformation can be detected based, at least in part, upon signals received from the sensors 126 on the deformable portion 142 of the ablation electrode 124. As described in greater detail below, the sensors 126 can be used in one or more modes of parameter measurement and, for example, can include one or more of an electrode, a thermistor, an ultrasound transducer, and an optical fiber. Additionally, or alternatively, the deformable portion 142 can be radiopaque such that deformation of the deformable portion 142 as a result of contact with tissue is observable, for example, through X-ray or similar visualization techniques. The detection and/or observation of the deformation of the deformable portion 142 of the ablation electrode 124 can, for example, provide improved certainty that an intended treatment is, in fact, being provided to tissue. It should be appreciated that improved certainty of positioning of an ablation electrode with respect to tissue can reduce the likelihood of gaps in a lesion pattern and, also or instead, can reduce the time and number of ablations otherwise required to avoid gaps in a lesion pattern.

0095[0095] The handle 120 can include a housing 145 and an actuation portion 146. In use, the actuation portion 146 can be operated to deflect the distal end portion 132 of the catheter shaft 122 to facilitate positioning the ablation electrode 124 into contact with tissue at a treatment site. The handle 120 can include a fluid line connector 148 (e.g., a luer connector) and an electrical connector 149. The fluid line 115 can be connectable to the fluid line connector 148 and, in use, irrigation fluid (e.g., saline) can be delivered from the irrigation pump 114 to the catheter 104 where, as described in further detail below, the irrigation fluid is ultimately deliverable through the irrigation holes 134 of the irrigation element 128 to the inner portion 136 of the ablation electrode 124. The extension cable 106 is connectable to the electrical connector 149. In use, electrical energy can be delivered from the ablation generator 116 to the catheter 104 where, as described in further detail below, the electrical energy is ultimately deliverable to the ablation electrode 124 to ablate tissue in contact with the outer portion 138 of the ablation electrode 124. [0096] The handle 120 can be attached to the proximal end portion 130 of the catheter shaft 122 through any of various techniques, including one or more of adhesive bonds, thermal bonds, and mechanical connections.

0096[0097] The catheter shaft 122 defines a lumen 151 extending from the proximal end portion 130 of the catheter shaft 122 to the distal end portion 132 of the catheter shaft 122. The lumen 151 can be in fluid communication with the irrigation pump 114, via the fluid line 115 and the fluid line connector 148 of the handle 120, such that irrigation fluid can be pumped from the irrigation pump 114 to the irrigation holes 134 defined by the irrigation element 128. The catheter shaft 122 can also, or instead, include electrical wires (such as any one or more of the wires 117 shown in FIG. 1) extending along the catheter shaft 122 to carry signals between the sensors 126 and the catheter interface unit 108 and that carry electrical power from the ablation generator 116 to the ablation electrode 124.

0097[0098] The catheter shaft 122 can be formed of any of various different biocompatible materials that provide the catheter shaft 122 with sufficient sturdiness and flexibility to allow the catheter shaft 122 to be navigated through blood vessels of a patient. Examples of suitable materials from which the catheter shaft 122 can be formed include polyether block amides (e.g., Pebax®, available from Arkema of Colombes, France), nylon, polyurethane, Pellethane®, available from The Lubrizol Corporation of Wickliffe, Ohio), and silicone. In certain implementations, the catheter shaft 122 includes multiple different materials along its length. The materials can, for example, be selected to provide the catheter shaft 122 with increased flexibility at the distal end, when compared to the proximal. The catheter shaft 122 can also, or instead, include a tubular braided element that provides torsional stiffness while maintaining bending flexibility to one or more regions of the catheter shaft 122. Further, or in the alternative, the shaft material can include radiopaque agents such as barium sulfate or bismuth, to facilitate fluoroscopic visualization.

0098[0099] The catheter shaft 122 can further include pull wires (not shown) mechanically coupled (e.g., via a ring secured to the catheter shaft 122) to the distal end portion 132 of the catheter shaft 122 and mechanically coupled to the actuation portion 146 of the handle 120, as is well known in the art. During use, tension may be applied to the wires to deflect the distal end portion 132 of the catheter shaft 122 to steer the catheter shaft 122 toward a treatment site. [0100] The irrigation element 128 can include a stem 154 and a bulb 156. The stem 154 can be coupled to the distal end portion 132 of the catheter shaft 122 in fluid communication with the lumen 151 of the catheter shaft 122 and, ultimately, with the irrigation pump 114. The bulb 156 defines the irrigation holes 134 and is in fluid communication with the stem 154. Accordingly, irrigation fluid can pass through the lumen 151, through the stem 154, and can exit the irrigation element 128 through the irrigation holes 134 defined by the bulb 156.

0099[0101] The stem 154 can be substantially rigid and extend from the distal end portion 132 of the catheter shaft 122 in a direction having a distal component and/or a radial component. For example, a radial extent of the stem 154 can direct irrigation fluid from an off-center position of the lumen 151 to a position along a center axis defined by the catheter shaft 122. Additionally, or alternatively, a distal extent of the stem 154 can facilitate clearance of the catheter shaft 122 such that a portion of the irrigation holes 134 directed in the proximal direction have a substantially unobstructed path to a portion of the inner portion 136 of the ablation electrode 124 that is proximal to the irrigation element 128. Thus, more generally, it should be understood that the size and shape of one or more of the stem 154, the bulb 156, and the irrigation holes 134 can be varied to achieve desired directionality of the irrigation fluid toward the inner portion 136 of the ablation electrode 124.

0100[0102] The bulb 156 can be substantially rigid and, in certain implementations, formed of the same material as the stem 154. Additionally, or alternatively, the bulb 156 can be substantially spherical to facilitate directing irrigation fluid toward substantially the entire inner portion 136 of the ablation electrode 124. It should be appreciated, however, that the bulb 156 can be any of various different shapes that facilitate multi-directional dispersion of irrigation fluid toward the inner portion 136 of the ablation electrode 124.

0101[0103] In certain implementations, the irrigation holes 134 can be spaced circumferentially and axially along the irrigation element. For example, the irrigation holes 134 can be spatially distributed along the bulb 156 with at least a portion of the irrigation holes 134 arranged to direct irrigation fluid in a distal direction with respect to the ablation electrode 124 and at least a portion of the irrigation holes 134 arranged to direct irrigation fluid in a proximal direction with respect to the ablation electrode 124. More generally, the irrigation holes 134 can be distributed to produce a relatively uniform dispersion of irrigation fluid along the inner portion 136 of the ablation electrode 124 enveloping the irrigation element 128.

0102[0104] The overall radial extent of the irrigation element 128 can be less than the outer diameter of the catheter shaft 122. For example, the irrigation element 128 can remain in the same orientation in a delivery configuration of the catheter 104 to the treatment and during treatment at the treatment site while, as described in further detail below, the ablation electrode 124 expands from a compressed state during delivery to an expanded state during treatment at the treatment site. As also described in further detail below, the fixed orientation of the irrigation element 128 can facilitate using the irrigation element 128 to act as a sensor or to carry a sensor. For example, a sensor can be added to the irrigation element 128 to act as a sensor, in

0103cooperation with the sensors 126 such that the sensor on the irrigation element 128 can act as a center electrode and the sensors 126 can act as surface electrodes, as described in greater detail below.

0104[0105] While the irrigation element 128 can extend distal to the catheter shaft 122, distal extent of the irrigation element 128 can be limited by the inner portion 136 of the ablation electrode 124. For example, the irrigation element 128 can be spaced proximal to the inner portion 136 of the ablation electrode 124 such that the irrigation holes 134 direct irrigation fluid toward the inner portion 136 of the ablation electrode 124 in an expanded state. In particular, given that the deformable portion 142 of the ablation electrode 124 is intended to contact tissue during ablation, the irrigation holes 134 can be oriented toward the deformable portion 142 of the ablation electrode 124 to direct fluid toward the inner portion 136 of the ablation electrode 124 along the deformable portion 142 in contact with the tissue. Directing the irrigation fluid toward the deformable portion 142 of the ablation electrode 124 in this way can, for example, reduce the likelihood of unintended tissue damage resulting from the ablation treatment.

0105[0106] Referring now to FIG. 5, a schematic representation of a jet 158 of irrigation fluid exiting one of the irrigation holes 134 and moving toward the inner portion 136 of the ablation electrode 124 is shown just prior to impact between the jet 158 and the inner portion 136. A distance "L" is a perpendicular distance between the irrigation hole 134 and the inner portion 136 of the ablation electrode 124 when the ablation electrode 124 is in an undeformed state (e.g., in the absence of an external force applied to the ablation electrode 124). For the sake of clarity, a two- dimensional cross-section of a single jet is shown. However, it should be understood that, in use, a respective three-dimensional jet issues from each of the irrigation holes 134 and the plurality of jets may interact with one another and/or with the patient's blood, along the distance "L," to create additional turbulence at the inner portion 136 of the ablation electrode 124.

0106[0107] In implementations in which the irrigation holes 134 have a circular cross-section, the ratio of a diameter "D" of each of the irrigation holes 134 to the respective distance "L" between the respective irrigation hole 134 and the inner portion 136 of the ablation electrode 124 can be greater than about 0.02 and less than about 0.2 (e.g., greater than about 0.03 and less than about 0.06). Given other design considerations (e.g., manufacturability of hole sizes of the irrigation holes 134, acceptable pressure drop in the system, the influence of blood flow between the irrigation element 128 and the ablation electrode 124, or a combination thereof), this range of ratios will result in turbulent flow of irrigation fluid at the inner portion 136 of the ablation electrode 124. Without wishing to be bound by theory, it is believed that, as compared to configurations with laminar flow and/or less turbulent flow of irrigation fluid past the inner portion 136 of the ablation electrode 124, the turbulent flow of irrigation fluid moving from the irrigation holes 134 to the inner portion 136 of the ablation electrode 124 results in increased heat transfer, which can reduce unintended tissue damage during ablation.

0107[0108] The size and number of the irrigation holes 134 defined by the irrigation element 128 are selected such that the pressure of irrigation fluid in the irrigation element 128 is sufficient to prevent blood from entering the irrigation holes 134. For example, providing for some margin of variation in pressure of the irrigation fluid, the size and number of the irrigation holes 134 defined by the irrigation element 128 can be selected such that the pressure of the irrigation fluid in the irrigation element 128 is at least about 0.5 psi greater than the pressure of the blood of the patient 102. Further, in implementations in which the irrigation element 128 is expandable (e.g., a balloon), the positive pressure difference between the irrigation fluid within the irrigation element 128 and the blood of the patient 102 can allow the irrigation element 128 to maintain an expanded shape. The size and number of the irrigation holes 134 can be, additionally or alternatively, selected to provide substantially uniform coverage of the irrigation fluid on the deformable portion 142 of the ablation electrode 124. [0109] In certain implementations, the irrigation holes 134 defined by the irrigation element 128 have a total open area of greater than about 0.05 mm² and less than about 0.5 mm². In implementations in which the irrigation element 128 is substantially rigid (e.g., formed of stainless steel and/or platinum iridium), the irrigation holes 134 can be drilled into the irrigation element 128. In implementations in which the irrigation element 127 is formed of an elastomer, the irrigation holes 134 can be formed through the use of a laser.

0108[0110] Referring now to FIGS. 1-11, the ablation electrode 124 is a continuous structure that acts as one electrode in the monopolar electrode configuration of the ablation system 100, shown in FIG. 1. It should be appreciated, however, that the ablation electrode 124 can include electrically isolated portions such that the ablation electrode 124 includes two electrodes of a bipolar electrode configuration.

0109[0111] The ablation electrode 124 can have an outer diameter of greater than about 4 mm and less than about 16 mm (e.g., about 8 mm) and, additionally or alternatively, a thickness of greater than about 0.07 mm and less than about 0.25 mm (e.g., about 0.17 mm). In certain

0110implementations, the ablation electrode 124 can have greater than about 50 percent open area and less than about 95 percent open area (e.g., about 80 percent open area). As used herein, the percentage of open area of the ablation electrode 124 should be understood to be the ratio of the area through which fluid can flow from the outer portion 138 of the ablation electrode 124 to the surface area of a convex hull that includes the outer portion 138 of the ablation electrode 124 and the structural elements defining the outer portion 138 of the ablation electrode, with the ratio expressed as a percentage. It should be appreciated that the open area of the ablation electrode 124 can facilitate the flow of irrigation fluid and blood through ablation electrode 124 during treatment. As compared to ablation electrodes that impede the flow of blood, the open area of the ablation electrode 124 can reduce the likelihood of local heating of blood at the treatment site as ablation energy is delivered to the tissue. It should be appreciated that the delivery of irrigation fluid to the inner portion 136 of the ablation electrode 124 can augment the cooling that occurs through the flow of only blood through the open area.

0111[0112] In general, it should be appreciated that the dimensions of the ablation electrode 124, including the dimensions related to the diameter, thickness, and/or open area, can facilitate retraction of the ablation electrode 124. That is, the force required to retract the ablation electrode 124 into a sheath (e.g., at the end of a procedure) are such that the ablation electrode 124 can be retracted by a physician without requiring assistance of a separate mechanism to provide a mechanical advantage. Further, or instead, the dimensions of the ablation electrode 124 can facilitate adequate expansion of the electrode 124. For example, in instances in which the electrode 124 is formed of nitinol, the ablation electrode 124 can be dimensioned such that, in the compressed state (e.g., for delivery), strain in the ablation electrode 124 is less than about ten percent. As a more general example, the ablation electrode 124 can be dimensioned such that the ablation electrode 124 is compressible to a size suitable for delivery (e.g., through an 8 French sheath) using a force that avoids, or at least limits, plastic deformation of the material of the ablation electrode 124. It should be appreciated that avoiding, or at least limiting, plastic deformation in this way can facilitate expansion of the ablation electrode 124 in a predictable manner (e.g., to a full extent) in the absence of an applied force.

0112[0113] The coupling portion 140 of the ablation electrode 124 can be directly or indirectly mechanically coupled to the catheter shaft 122. For example, the coupling portion 140 can include struts 144a directly coupled to the catheter shaft 122 or coupled to a transition part coupled to the catheter shaft 122. Each strut 144a can include a portion extending parallel to the catheter shaft 122 with the coupling portion 140 coupled to the catheter shaft 122 along the portion of the strut 144a extending parallel to the catheter shaft 122. Alternatively, or in addition, the coupling portion 140 can include a complete ring directly or indirectly mechanically coupled to the catheter shaft 122.

0113[0114] The coupling portion 140 can be electrically coupled to the generator 116 via one or more of the wires 117 (shown in FIG. 1) and/or other conductive paths extending from the generator 116, along the length of the catheter shaft 122, and to the coupling portion 140. For example, the coupling portion 140 can be fitted into the distal end portion 132 of the catheter shaft 122, connected to wires extending to the generator 116, and potted within an adhesive in the distal end portion 132 of the catheter shaft 122. In use, electrical energy provided at the generator 116 can be delivered to the coupling portion 140 and, thus, to the deformable portion 142 of the ablation electrode 124, where the electrical energy can be delivered to tissue of the patient 102.

0114[0115] The deformable portion 142 of the ablation electrode 124 can include struts 144b mechanically coupled to one another at joints 141a to define collectively a plurality of cells 147 of the ablation electrode 124. Additionally, or alternatively, the struts 144b can be mechanically coupled to one another by a fastener 141b. Accordingly, each end of the struts 144b can be coupled to an end of another strut 144b, to the fastener 141b, or a combination thereof to define the deformable portion 142 of the ablation electrode 124. For example, the struts 144b along the deformable portion 142 of the ablation electrode can be coupled to one another, to the fastener 141b, or to a combination thereof to define a closed shape along the deformable portion 142. Also, or instead, at least some of the struts 144b can be coupled to the struts 144a to transition between the deformable portion 142 and the coupling portion 140 of the ablation electrode 124. In certain implementations, the struts 144b can be coupled to the struts 144a such that the coupling portion 140 defines an open shape along the coupling portion 140 to facilitate, for example, securing the struts 144a to the distal end portion 132 of the catheter shaft 122.

0115[0116] The catheter shaft 122 defines a center axis CL-CL extending from the proximal end portion 130 to the distal end portion 132 of the catheter shaft 122. The cells 147 can have a generally axial orientation relative to the center axis CL-CL. For example, each of the cells 147 can have a respective symmetry plane passing through a distal end of the cell 147, a proximal end of the cell 147, and the center axis CL-CL. Such an orientation can advantageously preferentially expand and contract the cells 147 relative to the center axis CL-CL, which can facilitate compressing the deformable portion 142 of the ablation electrode 124 to a size suitable for delivery to a treatment site.

0116[0117] The center axis CL-CL can, for example, extend through the fastener 141b in the absence of an external force applied to the ablation electrode. Such alignment of the fastener 141b can facilitate, in certain instances, location of the distal end portion 142 of the ablation electrode 124 (e.g., by locating the fastener 141b at a treatment site).

0117[0118] The fastener 141b can be formed of a first material (e.g., a polymer) and the struts 144b can be formed of a second material (e.g., a nitinol) different from the first material. It should be appreciated that the material of the fastener 141b can be selected for a combination of strength and electrical properties suitable for maintaining the struts 144b coupled to one another while achieving a current density distribution suitable for a particular application. The closed shape of the deformable portion 142 can, for example, facilitate the delivery of substantially uniform current density through the ablation electrode 124 in a manner that, as compared to an electrode with an open shape, is less dependent on the orientation of the ablation electrode 124 relative to tissue, as described in greater detail below.

0118[0119] In general, each cell 147 can be defined by at least three struts 144b. Also, or instead, each strut 144b can define a portion of at least two of the cells 147. The inner portion 136 of the ablation electrode 124 can be in fluid communication with the outer portion 138 of the ablation electrode 124 through the plurality of cells 147 such that, in use, irrigation fluid, blood, or a combination thereof can move through the plurality of cells 147 to cool the ablation electrode 124 and tissue in the vicinity of the ablation electrode 124.

0119[0120] At least some of the plurality of cells 147 can be flexible in the axial and lateral directions such that the open framework formed by the plurality of cells 147 along the deformable portion 142 of the ablation electrode 124 is similarly flexible. For example, at least some of the plurality of cells can be substantially diamond-shaped in the uncompressed state of the deformable portion 142 of the ablation electrode 124. As used herein, substantially diamond- shaped includes shapes including a first pair of joints substantially aligned along a first axis and a second pair of joints substantially aligned along a second axis, different from the first axis (e.g., perpendicular to the first axis).

0120[0121] The flexibility of the open framework formed by the plurality of cells 147 along the deformable portion 142 of the ablation electrode 124 can, for example, advantageously resist movement of the deformable portion 142 in contact with tissue during a medical procedure. That is, the deformable portion 142 can deform upon contact with tissue and the deformable portion 142 can engage the tissue through one or more of the cells 147 to resist lateral movement of the deformable portion 142 relative to the tissue. That is, as compared to a closed surface in contact with tissue, the deformable portion 142 will resist unintended movement (e.g., sliding with respect to the tissue) with which it is in contact. It should be appreciated that such resistance to movement can facilitate, for example, more accurate placement of lesions.

0121[0122] The struts 144a, 144b can have dimensions that differ from corresponding dimensions of other ones of the struts 144a, 144b. For example, the struts 144b can have a dimension (e.g., width) that differs from a corresponding dimension of another one of the struts 144b. Varying dimensions of the struts 144a, 144b, for example, for delivery of substantially uniform current density through the deformable portion 142 of the ablation electrode 124, as described in greater detail below. Additionally, or alternatively, the struts 144a can be wider than the struts 144b to facilitate fixing the struts 144a directly or indirectly to the distal end portion 132 of the catheter shaft 122.

0122[0123] In general, the struts 144b can be dimensioned and arranged relative to one another for delivery of substantially uniform current density through the deformable portion 142 of the ablation electrode 124, as described in greater detail below. By way of non-limiting example, a first set of the struts 144b can have a first width, and a second set of the struts 144b can have a second width, different from the first width. Continuing with this example, the first set of the struts 144b can be axially spaced relative to the second set of the struts 144b. Such axial distribution of the material of the struts can be useful, for example, for achieving a desired current density profile (e.g., a substantially uniform current density profile). As another non- limiting example, at least some of the struts 144b can have a non-uniform width along a length of the respective strut 144b such that the amount of material along a given strut is varied, resulting in an associated distribution in current density. For example, at least some of the struts 144b can include a width increasing along the length of the respective strut 144b in a direction from a proximal region to a distal region of the ablation electrode 124.

0123[0124] In general, the plurality of cells 147 can be disposed circumferentially and axially about the ablation electrode 124. More specifically, as described in greater detail below, the plurality of cells 147 can be arranged about the ablation electrode 124 (e.g., along the deformable portion 142 of the ablation electrode 124) to facilitate contraction and expansion of the deformable portion 142 and/or to facilitate substantially uniform distribution of current density along the deformable portion 142.

0124[0125] Each cell 147 can be bounded. In particular, as used herein, a bounded cell 147 includes a cell entirely defined by the struts 144b, the joints 141a, sensors 126 disposed along the struts 144b or the joints 141a, or a combination thereof. As described in further detail below, the struts 144b can be connected to one another at the joints 141a as part of a unitary or substantially unitary structure. Additionally, or alternatively, as also described in greater detail below, the struts 144b can be connected to one another through welds, fasteners, or other mechanical connections at one or more of the joints 141a. [0126] The stmts 144b can be movable relative to one another through flexing at the joints 141a. More specifically, the struts 144b can be flexible relative to one another to move the deformable portion 142 between a compressed state, in the presence of an external force, and an

0125uncompressed state, in the absence of the external force. For example, a maximum radial dimension (alternatively referred to herein as a lateral dimension) of the ablation electrode can increase by at least a factor of 2 as the coupled struts 144b move relative to one another to transition the ablation electrode 124 from a compressed state, in the presence of external force, to an uncompressed state, in the absence of external force. This ratio of increase in size is achieved through the use of the open framework of cells 147 formed by the struts 144b, which makes use of less material than would otherwise be required for a solid shape of the same size. Further, or instead, it should be appreciated that the ratio of the increase in size achieved through the use of the open framework of cells 147 is useful for delivery to a treatment site through an 8 French sheath while also facilitating the formation of large lesions at the treatment site.

0126[0127] Through flexing at the joints 141a and associated movement of the struts 144b, the deformable portion 142 can be resiliently flexible in an axial direction relative to the catheter shaft 122 and/or in a radial direction relative to the catheter shaft 122. Additionally, or alternatively, the deformable portion 142 can be expandable (e.g., self-expandable) from the compressed state to the uncompressed state. For example, the struts 144b can be biased to move in one or more directions away from one another to self-expand the deformable portion 142 from the compressed state to the uncompressed state.

0127[0128] In the uncompressed state, the struts 144b, the joints 141a, and the cells 147 together can form an open framework having a conductive surface along the deformable portion 142 of the ablation electrode 124. For example, the open framework formed by the struts 144b, the joints 141a, and the cells 147 can have greater than about 50 percent open area along the outer portion 138 of the ablation electrode 124 when the deformable portion 142 of the ablation electrode 124 is in the uncompressed state. Continuing with this example, in the uncompressed state, the combined open area of the cells 147 can be greater than the combined area of the struts 144b and the joints 141a along the outer portion 138 of the ablation electrode 124. Further, or instead, at least some of the cells 147 can have a larger area in the uncompressed state of the deformable portion 142 than in the compressed state of the deformable portion 142. [0129] More generally, the open area defined by the cells 147 can have a magnitude and spatial distribution sufficient to receive the struts 144b and, optionally the sensors 126, as the deformable portion 142 collapses from the uncompressed state to the compressed state.

0128Accordingly, it should be appreciated that the magnitude of the ratio of the combined open area of the cells 147 to the combined area of the struts 144b and the joints 141a can, among other things, be useful for varying the degree of expansion of a deformable portion 142 of the ablation electrode 124 relative to a delivery state in which the deformable portion 142 is in a compressed state. That is, the ratio of the combined open area of the cells 147 to the combined area of the struts 144b and the joints 141a can facilitate minimally invasive delivery (e.g., delivery through an 8 Fr sheath) of the ablation electrode 124.

0129[0130] By way of example, a maximum radial dimension of the ablation electrode 124 can increase by at least a factor of 2 as the struts 144b move relative to one another to transition the ablation electrode 124 (e.g., the deformable portion 142 of the ablation electrode 124) from a compressed state, in the presence of an external force (e.g., a radial force), to an uncompressed state, in the absence of an external force. Additionally, or alternatively, the struts 144b can be movable relative to one another such that a maximum radial dimension of the deformable portion 142, in the uncompressed state, is at least about 20 percent greater than a maximum radial dimension of the catheter shaft 122 (e.g., greater than a maximum radial dimension of the distal end portion 132 of the catheter shaft 122). It should be appreciated that the extension of the deformable portion 142 beyond the maximum radial dimension of the catheter shaft 122 can facilitate creation of a lesion having a large width, as compared to an ablation electrode constrained by a radial dimension of a catheter shaft.

0130[0131] In certain implementations, the ablation electrode 124 has a maximum axial dimension that changes by less than about 33 percent (e.g., about 20 percent) as the struts 144b expand (e.g., self-expand) from the uncompressed state to the compressed state upon removal of an external radial force applied to the ablation electrode 124.

0131[0132] At least some of the struts 144b extend in a direction having a circumferential dimensional component with respect to an axis defined by the catheter shaft 122 (e.g., an axis defined by the proximal end portion 130 and the distal end portion 132 of the catheter shaft 122). That is, the struts 144b extending in a direction having a circumferential dimensional component with respect to an axis defined by the catheter shaft 122 are nonparallel to the axis defined by the catheter shaft 122. In some implementations, at least some of the struts 144b include a nonuniform width along a length of the respective strut 144b. Because current density at a given point along the ablation electrode 124 is a function of surface area at the given point along the ablation electrode 124, the non-uniform width of a given one of the struts 144b can facilitate balancing current density to achieve a target current density profile along the deformable portion 142 of the ablation electrode 124. As described in greater detail below, the circumferential extension and/or the non-uniform width along the length of at least some of the struts 144b can facilitate substantially uniform distribution of current density along the deformable portion 142 during a medical procedure.

0132[0133] While a large surface area of the struts 144b can be advantageous for the delivery of energy to tissue, an upper boundary of the area of the struts 144b can be the geometric configuration that will allow the struts 144b to collapse into the compressed state (e.g., during delivery to the treatment site and/or during contact with tissue at the treatment site) without interfering with one another. Additionally, or alternatively, the struts 144b can be twisted towards the inner portion 136 of the ablation electrode 124. It should be appreciated that, as compared to struts that are not twisted, the twisted struts 144b can be wider while still being collapsible into the compressed state without interfering with one another. Further in addition or further in the alternative, an upper boundary of the area of the struts 144b can be the amount of open area of the deformable portion 142 that will facilitate appropriate heat transfer (e.g., during ablation) at the ablation electrode 124 through the movement of irrigation fluid and/or blood through the deformable portion 142.

0133[0134] As used herein, the uncompressed state of the deformable portion 142 refers to the state of the deformable portion 142 in the absence of a substantial applied force (e.g., an applied force less than about 5 grams). Thus, the uncompressed state of the deformable portion 142 includes a state of the ablation electrode 124 in the absence of external forces. Additionally, the uncompressed state of the deformable portion 142 includes a state of the ablation electrode 124 in which a small applied force (e.g., less an about 5 grams) is present, but is insufficient to create a significant deformation in the deformable portion 142.

0134[0135] In the uncompressed state of the deformable portion 142, the ablation electrode 124 can be bulbous. For example, in the uncompressed state, the deformable portion 142 can be a shape having symmetry in a radial direction and/or an axial direction relative to the catheter shaft 122. For example, in the uncompressed state the deformable portion 142 can be an ellipsoidal shape such as, for example, a substantially spherical shape (e.g., an arrangement of the struts 144b, each strut 144b having a planar shape, relative to one another to approximate a spherical shape). Additionally, or alternatively, in the uncompressed state, the deformable portion 142 can be a symmetric shape (e.g., a substantially ellipsoidal shape or another similar shape contained between a first radius and a perpendicular second radius, the first radius and the second radius within 30 percent of one another in magnitude). Symmetry of the deformable portion 142 can, for example, facilitate symmetric delivery of ablation energy to the tissue in a number of orientations of the deformable portion 142 relative to the tissue being ablated.

0135[0136] At least when the deformable portion 142 is in the uncompressed state, the deformable portion 142 can envelop the irrigation element 128 such that the irrigation element 128 directs irrigation fluid toward the inner portion 136 of the ablation electrode 124. Accordingly, in implementations in which the deformable portion 142 is symmetric, the irrigation element 128 can provide a substantially uniform distribution of irrigation fluid along the inner portion 136 of the ablation electrode 124, as the deformable portion 142 in the uncompressed state envelops the irrigation element 128.

0136[0137] In certain implementations, the largest cross-sectional dimension of the deformable portion 142 in the uncompressed state is larger than the largest cross-sectional dimension of the catheter shaft 122. Thus, because the deformable portion 142 is expandable to extend beyond the catheter shaft 122, the deformable portion 142 can create a lesion that is larger than the largest dimension of the catheter shaft 122 such that the resulting lesions are wider and deeper than lesions created by ablation electrodes that do not expand. For example, in the uncompressed state, the deformable portion 142 can be substantially circular at the largest cross-sectional dimension of the deformable portion, and the catheter shaft 122 can be substantially circular at the largest cross-sectional dimension of the catheter shaft 122. Thus, continuing with this example, the outer diameter of the deformable portion 142 is larger than the outer diameter of the catheter shaft 122 such that the size of the ablation created by the ablation electrode 124 is larger than the outer diameter of the catheter shaft 122.

0137[0138] The compressed state of the ablation electrode 124, as used herein, refers to the state of the ablation electrode in the presence of a force (e.g., a force of about 5 grams or greater) sufficient to cause the deformable portion 142 to flex (e.g., through flexing of one or more of the joints 141a) to a significant extent. Thus, for example, the compressed state of the ablation electrode 124 includes the reduced size profile of the ablation electrode 124 during introduction of the catheter 104 to the treatment site, as described in further detail below. The compressed state of the ablation electrode 124 also includes one or more states of deformation and/or partial deformation resulting from an external force exerted along one or more portions of the deformable portion 142 of the ablation electrode 124 as a result of contact between the deformable portion 142 and tissue at the treatment site.

0138[0139] The compressed state of the ablation electrode 124 can have a predetermined relationship with respect to an applied force. For example, the compressed state of the ablation electrode 124 can have a substantially linear (e.g., within ± 10 percent) relationship with applied forces in the range of forces typically applied during an ablation procedure (e.g., about 1 mm deformation in response to 60 grams of force). It should be appreciated that such a predetermined relationship can be useful, for example, for determining the amount of applied force on the ablation electrode 124 based on a measured amount of deformation of the ablation electrode 124. That is, given the predetermined relationship between deformation of the ablation electrode 124 and an amount of an applied force, determining the amount of deformation of the ablation electrode 124 can provide an indication of the amount of force being applied by the ablation electrode 124 on tissue at the treatment site. As such, the determined amount of deformation of the ablation electrode 124 can be used, for example, as feedback to control the amount of force applied to tissue at the treatment site. Methods of determining the amount of deformation of the ablation electrode 124 are described in greater detail below.

0139[0140] FIG. 9 is a graph of an exemplary relationship between force and displacement for different amounts of force applied to the deformable portion 142 of the ablation electrode 124. The deformable portion 142 of the ablation electrode 124 can have different force-displacement responses, depending on the direction of the force applied to the deformable portion 142 of the ablation electrode 124. For example, as shown in the exemplary relationship in FIG.9, the deformable portion 142 of the ablation electrode 124 can have an axial force-displacement response 143a and a lateral force-displacement response 143b. That is, the response of the deformable portion 142 to the application of force can depend on the direction of the applied force. In the specific example of FIG. 9, the deformable portion 142 can be stiffer in the axial direction than in the lateral direction.

0140[0141] In general, the axial force-displacement 143a and the lateral force-displacement response 143b can be reproducible and, thus, the amount of force applied to the deformable portion 142 of the ablation electrode 124 in the axial and/or lateral direction can be reliably determined based on respective displacement of the deformable portion 142. Accordingly, as described in greater detail below, the determined displacement of the deformable portion 142 can be used to determine the amount and direction of force applied to the deformable portion 142. More generally, because the deformable portion 142 is movable between a compressed state and an uncompressed state in a reproducible manner in response to applied force, the deformable portion 142 of the ablation electrode can be useful as a contact force sensor and, thus, can facilitate application of appropriate force during ablation treatment.

0141[0142] In certain implementations, at least a portion of the ablation electrode 124 is radiopaque, with the deformable portion 142 observable through the use of fluoroscopy or other similar visualization techniques. For example, the deformable portion 142 of the ablation electrode 124 can be radiopaque such that fluoroscopy can provide an indication of the deformation and/or partial deformation of the deformable portion 142 and, therefore, provide an indication of whether the deformable portion 142 is in contact with tissue.

0142[0143] A material for forming the ablation electrode 124 can include nitinol, which is weakly radiopaque and is repeatably and reliably flexible between a compressed state and an

0143uncompressed state. Additionally, or alternatively, the material for forming the ablation electrode 124 can be coated with one or more of gold or tantalum. Thus, continuing with this example, the deformable portion 142 of the ablation electrode 124 (e.g., the struts 144b) can be formed of nitinol, either alone or coated, such that ablation energy is delivered through the nitinol forming the deformable portion 142 for delivery to tissue to create lesions.

0144[0144] As described in further detail below, the deformation and/or partial deformation of the deformable portion 142 in the compressed state can be additionally, or alternatively, detected by the sensors 126 to provide feedback regarding the extent and direction of contact between the deformable portion 142 of the ablation electrode 124 and the tissue at the treatment site. [0145] Referring now to FIGS. 10 and 11, the sensors 126 can be mounted along the deformable portion 142 of the ablation electrode 124. Each sensor 126 can be electrically insulated from the ablation electrode 124 and mounted on one of the struts 144b of the deformable portion 142. For example, each sensor 126 can be mounted to the deformable portion 142 using a compliant adhesive (e.g., a room temperature vulcanized (RTV) silicone), any of various different mechanical retaining features (e.g., tabs) between the sensor 126 and the ablation electrode 124, and/or molding or overmolding of the sensor 126 to the ablation electrode 124. Because the struts 144b do not undergo significant flexing as the deformable portion 142 moves between the compressed state and the uncompressed state, mounting the sensors 126 on the struts 144b can reduce physical strain on the sensors 126, as compared to mounting the sensors 126 on sections of the deformable portion 142 that experience larger amounts of flexing as the deformable portion 142 moves between the compressed state and the uncompressed state.

0145[0146] In general, the sensors 126 can be positioned along one or both of the inner portion 136 and the outer portion 138 of the ablation electrode 124. Wires 148 extend from each sensor 126, along the inner portion 136 of the ablation electrode 124, and into the catheter shaft 122 (FIG. 2). The wires 148 are in electrical communication with the catheter interface unit 108 (FIG. 1) such that, as described in further detail below, each sensor 126 can send electrical signals to and receive electrical signals from the catheter interface unit 108 during use.

0146[0147] The sensors 126 can be substantially uniformly spaced from one another (e.g., in a circumferential direction and/or in an axial direction) along the deformable portion 142 of the ablation electrode 124 when the deformable portion 142 of the ablation electrode 124 is in an uncompressed state. Such substantially uniform distribution of the sensors 126 can, for example, facilitate determining an accurate deformation and/or temperature profile of the deformable portion 142 during use.

0147[0148] Each sensor 126 can act as an electrode to detect electrical activity of the heart in an area local to the sensor 126 and, further or instead, each sensor 126 can include a flexible printed circuit 150, a thermistor 152 secured between portions of the flexible printed circuit 150, and a termination pad 155 opposite the thermistor 152. As an example, the sensor 126 can be mounted on the deformable portion 142 of the ablation electrode 124 with the thermistor 152 disposed along the outer portion 138 of the deformable portion 142 and the termination pad 154 disposed along the inner portion 136 of the deformable portion 142. In certain instances, the thermistor 152 can be disposed along the outer portion 138 to provide an accurate indication of tissue temperature. A thermally conductive adhesive or other conductive material can be disposed over the thermistor 152 to secure the thermistor 152 to the flexible printed circuit 150.

0148[0149] In some implementations, each sensor 126 can include a radiopaque portion and/or a radiopaque marker. The addition of radi opacity to the sensor 126 can, for example, facilitate visualization (e.g., using fluoroscopy) of the sensor 126 during use. Examples of radiopaque material that can be added to the sensor 126 include: platinum, platinum iridium, gold, radiopaque ink, and combinations thereof. The radiopaque material can be added in any pattern that may facilitate visualization of the radiopaque material such as, for example, a dot and/or a ring.

0149[0150] In use, each sensor 126 can, further or instead, act as an electrode to detect electrical activity in an area of the heart local to the respective sensor 126, with the detected electrical activity forming a basis for an electrogram associated with the respective sensor 126 and, further or instead, can provide lesion feedback. The sensors 126 can be arranged such that electrical activity detected by each sensor 126 can form the basis of unipolar electrograms and/or bipolar electrograms. Additionally, or alternatively, the sensors 126 can cooperate with a center electrode (e.g., an electrode associated with an irrigation element, such as a center electrode 235 in FIG. 22, or the irrigation element itself, such as the irrigation element 128 in FIG. 3) to provide near-unipolar electrograms, as described in greater detail below. It should be

0150appreciated that the sensors 126 and a center electrode can cooperate to provide near-unipolar electrograms in addition, or as an alternative, to any one or more of the various different methods of determining contact, shape, force, and impedance described herein, each of which may include further or alternative cooperation between the sensors 126 and a center electrode.

0151[0151] FIGS. 12A-12C are a schematic representation of an exemplary method of making the ablation electrode 124 from a sheet 156 of material.

0152[0152] As shown in FIG. 12A, the sheet 156 of material is flat. As used herein, a flat material includes a material exhibiting flatness within normal manufacturing tolerances associated with the material. The material of the sheet 156 is conductive and, optionally, also radiopaque. For example, the sheet 156 can be nitinol. [0153] The thickness of the sheet 156 can correspond to the thickness of the ablation electrode 124. For example, the thickness of the sheet 156 can be greater than about 0.1 mm and less than about 0.20 mm. In certain implementations, however, the thickness of the sheet 156 can be larger than at least a portion of the thickness of the ablation electrode 124 such that the removal of material from the flat sheet includes removal of material in a thickness direction of the sheet 156. For example, material can be selectively removed in the thickness direction of the sheet 156 to produce the ablation electrode 124 with a variable thickness (e.g., the ablation electrode 124 can be thinner along the joints 141a (FIGS. 6-8) to facilitate flexing).

0153[0154] As shown in FIG. 12B, material can be removed from the sheet 156 to define the open area of the deformable portion 142 and to define the coupling portion 140. In particular, the removal of material along the deformable portion 142 can define the struts 144b and the joints 141a.

0154[0155] The material of the sheet 156 can be removed, for example, by using any of various different subtractive manufacturing processes. As an example, the material of the sheet 156 can be removed using chemical etching (also known as photo etching or photochemical etching) according to any one or more methods that are well known in the art and generally include removing material by selectively exposing the material to an acid to remove the material.

0155Additionally, or alternatively, the material of the sheet 156 can be removed by laser cutting the material. The removal of material can be done to create openings in the sheet 156 and/or to thin selected portions of the sheet 156.

0156[0156] Because the sheet 156 is flat, removing material from the sheet 156 to form the deformable portion 142 can have certain advantages. For example, as compared to removing material from a curved workpiece, removing material from the sheet 156 can facilitate controlling geometric tolerances. Additionally, or alternatively, as compared to removing material from a curved workpiece, removing material from the sheet 156 can facilitate placement of sensors (e.g., while the sheet 156 is flat). In certain implementations, as compared to removing material from a curved workpiece, removing material from the sheet 156 can reduce, or even eliminate, the need to shape set the sheet 156, as the distal and proximal sections can be put together to form the shape of the ablation electrode 124 (e.g., a substantially spherical shape). [0157] In certain implementations, the material removed from the sheet 156 can define eyelets 157 disposed at one end of at least a portion of the struts 144b. The eyelets 157 can be, for example, defined at the intersection of two or more of the struts 144b.

0157[0158] In general, the material forming the ablation electrode 124 can be processed at any of various different stages of fabrication of the ablation electrode 124. For example, with the material removed from the sheet to define the struts 144a, 144b and the joints 141a as shown in FIG. 12B, one or more surfaces of the material can be electropolished. Such electropolishing can, for example, be useful for smoothing surfaces and/or otherwise producing fine adjustments in the amount of material along the ablation electrode 124.

0158[0159] As shown in FIG. 12C, with the material removed from the sheet 156 to define the struts 144a, 144b and the joints 141a, the sections 158 are bent into proximity with one another and joined to one another to form a unitary three-dimensional structure having the overall shape of the ablation electrode 124. For example, the struts 144b can be bent toward one another and the fastener 141b can couple the portion of the struts 144b to one another at the eyelets 157, thus defining a closed distal end of the deformable portion 142 of the ablation electrode 124. With the deformable portion 142 defined, the fastener 141b can be at a distalmost portion of the deformable portion 142.

0159[0160] In certain implementations, the fastener 141b can be a rivet. In such implementations, the eyelets 157 can be, for example, aligned with one another such that the fastener 141b passes through the aligned eyelets 157 to hold them together through force exerted on the eyelets 157 by the fastener 141b. Additionally, or alternatively, a secondary operation such as welding can secure the fastener 141b to the struts 144b at the eyelets 157.

0160[0161] Referring now to FIGS. 13A-E, to perform a cardiac ablation treatment, the distal end portion 132 of the catheter shaft 122 and, thus, the ablation electrode 124 can be first introduced into the patient, typically via a femoral vein or artery. FIGS. 13A-E schematically illustrate a series of steps carried out to introduce the ablation electrode 124 into the patient.

0161[0162] In a first step, shown in FIG. 13 A, an introducer sheath 162 is positioned within a blood vessel of the patient (e.g., the femoral artery of the patient) and the ablation electrode 124 is positioned for insertion into the introducer sheath 162. [0163] In a second step, shown in FIG. 13B, the user grasps the handle 120 of the catheter 104 and distally advances an insertion sheath 164 along the catheter shaft 122 until the insertion sheath 164 surrounds the ablation electrode 124. As the insertion sheath 164 is advanced over the ablation electrode 124, the ablation electrode 124 collapses to a diameter capable of being inserted into the introducer sheath 162.

0162[0164] In a third step, shown in FIG. 13C, the user inserts the insertion sheath 164 (containing the ablation electrode 124) into the introducer sheath 162 and distally advances the catheter 104.

0163[0165] In a fourth step, shown in FIG. 13D, after positioning the ablation electrode 124 within the introducer sheath 162, the ablation electrode 124 is advanced out of the insertion sheath 164 that is then left surrounding the proximal end portion 130 of the catheter shaft 122 throughout the remainder of the treatment.

0164[0166] In a fifth step, shown in FIG. 13E, the catheter 104 is advanced through the introducer sheath 162 and the patient's vasculature until the ablation electrode 124 reaches the treatment site in the heart of the patient. As the ablation electrode 124 is extended distally beyond the introducer sheath 162, the ablation electrode 124 can expand to the uncompressed state.

0165[0167] Because the ablation electrode 124 is collapsible, the introducer sheath 162 can have a small diameter that can be inserted through a correspondingly small insertion site. In general, small insertion sites are desirable for reducing the likelihood of infection and/or reducing the amount of time required for healing. In certain implementations, the introducer sheath 162 can have an 8 French diameter, and the deformable portion 142 (FIG.3) of the ablation electrode 124 can be collapsible to a size deliverable through the introducer sheath 162 of this size. In some implementations, the irrigation element 128 is additionally collapsible to a size smaller than the size of the ablation electrode 124 such that the irrigation element 128 and the ablation electrode 124 are, together, deliverable through the introducer sheath 162 of this size.

0166[0168] FIGS. 14A-C schematically represent an exemplary method of positioning the deformable portion 142 of the ablation electrode 124 into contact with tissue "T" at the treatment site. It should be appreciated that, because the delivery of ablation energy to the tissue "T" at the treatment site is enhanced by contact between the ablation electrode 124 and the tissue "T," such contact is established prior to delivery of ablation energy. [0169] In a first step, shown in FIG. 14A, the deformable portion 142 of the ablation electrode 124 is away from the tissue "T" and, thus, in an uncompressed state. In certain instances, this uncompressed state is observable through fluoroscopy. That is, the shape of the deformable portion 142 can be observed in the uncompressed state.

0167[0170] In a second step, shown in FIG. 14B, the deformable portion 142 of the ablation electrode 124 makes initial contact with the tissue "T." Depending on the nature of the contact between the tissue "T" and the deformable portion 142 of the ablation electrode 124, deformation of the deformable portion 142 may or may not be observable through fluoroscopy alone. For example, the contact force on the deformable portion 142 may be insufficient to compress the deformable portion 142 to an extent observable using fluoroscopy. Additionally, or alternatively, the contact may not be observable, or may be difficult to observe, in the direction of observation provided by fluoroscopy.

0168[0171] In a third step, shown in FIG. 14C, the deformable portion 142 of the ablation electrode 124 is moved further into contact with the tissue "T" such that sufficient contact is established between the deformable portion 142 and the tissue "T" to deform the deformable portion 142. While such deformation may be observable using fluoroscopy, the degree and/or direction of the deformation is not readily determined using fluoroscopy alone. Further, as is also the case with initial contact, the contact and/or degree of contact may not be observable, or may be difficult to observe, in the direction of observation provided by fluoroscopy. Accordingly, as described in greater detail below, determining apposition of the deformable portion 142 to the tissue "T" can, additionally or alternatively, include sensing the position of the deformable portion 142 based on signals received from the sensors 126.

0169[0172] Referring again to FIGS. 1 and 3, the sensors 126 can be used to determine the shape of the deformable portion 142 of the ablation electrode 124 and, thus, determine whether and to what extent certain regions of the deformable portion 142 are in contact with the tissue "T." It should be appreciated, however, that the sensing methods described herein can be carried out using the sensors 126, alone or in combination with another electrode, such as an electrode carried on an irrigation element, as described in greater detail below.

0170[0173] For example, the processing unit 109a can control the generator 116 and/or another electrical power source to drive an electrical signal between any number and combination of electrode pairs formed by any combination of electrodes associated with the ablation electrode 124, and the processing unit 109 can receive a signal (e.g., a signal indicative of voltage) from another electrode pair or the same electrode pair. For example, the processing unit 109a can control the generator 116 to drive one or more of the sensors 126, the ablation electrode 124, the irrigation element 128, and a center electrode (e.g., a center electrode 235 shown in FIG. 22). Additionally, or alternatively, multiple pairs can be driven in a multiplexed manner using time division, frequency division, code division, or combinations thereof. The processing unit 109a can also, or instead, receive one or more measured electrical signals from one or more of the sensors 126, the ablation electrode 124, the irrigation element 128, and a center electrode (e.g., the center electrode 235 shown in FIG. 22). The driven electrical signal can be any of various, different forms, including, for example, a prescribed current or a prescribed voltage. In certain implementations, the driven electrical signal is an 8kHz alternating current applied between one of the sensors 126 and the irrigation element 128.

0171[0174] In an exemplary method, the impedance detected by an electrode pair can be detected (e.g., as a signal received by the processing unit 109a) when an electrical signal is driven through the electrode pair. The impedance detected for various electrode pairs can be compared to one another and relative distances between the members of each electrode pair determined. For example, if the sensors 126 are identical, each sensor 126 can be driven as part of a respective electrode pair including the irrigation element 128. For each such electrode pair, the measured impedance between the electrode pair can be indicative of relative distance between the particular sensor 126 and the irrigation element 128 forming the respective electrode pair. In implementations in which the irrigation element 128 is stationary while electrical signals are driven through the electrode pairs, the relative distance between each sensor 126 and the irrigation element 128 can be further indicative of relative distance between each sensor 126 and each of the other sensors 126. In general, driven electrode pairs with lower measured impedance are closer to one another than those driven electrode pairs with higher measured impedance. In certain instances, electrodes associated with the ablation electrode 124 (e.g., one or more of the sensors 126) that are not being driven can be measured to determine additional information regarding the position of the driven current pair.

0172[0175] The current measurements received by the processing unit 109a and associated with the driven current pairs alone, or in combination with the current measurements at the sensors 126 that are not being driven, can be fit to a model and/or compared to a look-up table to determine displacement of the deformable portion 142 of the ablation electrode 124. For example, the determined displacement of the deformable portion 142 of the ablation electrode 124 can include displacement in at least one of an axial direction or a lateral (radial) direction. It should be appreciated that, because of the spatial separation of the current pairs in three dimensions, the determined displacement of the deformable portion 142 of the ablation electrode 124 can be in more than one direction (e.g., an axial direction, a lateral direction, and combinations thereof). Additionally, or alternatively, the determined displacement of the deformable portion 142 of the ablation electrode 124 can correspond to a three-dimensional shape of the deformable portion 142 of the ablation electrode 124.

0173[0176] Based on the determined displacement of the deformable portion 142 of the ablation electrode 124, the processing unit 109a can send an indication of the shape of the deformable portion 142 of the ablation electrode 124 to the graphical user interface 110. Such an indication of the shape of the deformable portion 142 can include, for example, a graphical representation of the shape of the deformable portion 142 corresponding to the determined deformation.

0174[0177] In implementations in which the force-displacement response of the deformable portion 142 is reproducible (e.g., as shown in FIG. 9), the processing unit 109a can determine force applied to the deformable portion 142 based on the determined displacement of the deformable portion 142. For example, using a lookup table, a curve fit, or other predetermined relationship, the processing unit 109a can determine the direction and magnitude of force applied to the deformable portion 142 based on the magnitude and direction of the displacement of the deformable portion 142, as determined according to any one or more of the methods of determining displacement described herein. It should be appreciated, therefore, that the reproducible relationship between force and displacement along the deformable portion 142, coupled with the ability to determine displacement using the sensors 126 disposed along the deformable portion 142, can facilitate determining whether an appropriate amount of force is being applied during an ablation treatment and, additionally or alternatively, can facilitate determining appropriate energy and cooling dosing for lesion formation.

0175[0178] FIGS. 15A-B schematically represent an exemplary method of cooling the ablation electrode 124 at the treatment site with irrigation fluid from the irrigation element 128. For the sake of clarity of illustration, a single jet of irrigation fluid is shown. It should be appreciated, however, that a plurality of jets issue from the irrigation element 128 during use. In certain implementations, the irrigation fluid is substantially uniformly directed to the inner portion 136 of the ablation electrode 124. Additionally, or alternatively, a portion of the irrigation fluid can be directed in a direction distal to the irrigation element 128 and a portion of the irrigation fluid can be directed in a direction proximal to the irrigation element 128.

0176[0179] In a first step, shown in FIG. 15A, the ablation electrode 124 is positioned at the treatment site with the outer portion 138 disposed toward tissue. A baseline flow of irrigation fluid is delivered to the irrigation element 128 prior to delivery of ablation energy to the ablation electrode 124. The baseline flow of irrigation fluid can be, for example, about 0.5 psi above the patient's blood pressure to reduce the likelihood that blood will enter the irrigation element 128 and clot. Further, as compared to always delivering irrigation fluid at a higher pressure, the delivery of this lower pressure of irrigation fluid when ablation energy is not being delivered to the ablation electrode 124 can reduce the amount of irrigation fluid delivered to the patient during treatment.

0177[0180] In a second step, shown in FIG. 15B, ablation energy is directed to at least some of the outer portion 138 of the ablation electrode 124 in contact with the tissue "T". As the ablation energy is delivered to the ablation electrode 124, the pressure of the irrigation fluid can be increased, resulting in a higher pressure flow directed from the irrigation element 128 toward the inner portion 136 of the ablation electrode 124. The higher flow of irrigation fluid at the inner portion 136 can result in turbulent flow which, compared to laminar flow, can improve heat transfer away from the ablation electrode 124. For example, each jet of irrigation fluid issuing from the irrigation element 128 can have a Reynolds number above about 2000 (e.g., greater than about 2300) at the inner portion 136 of the ablation electrode 124 when the deformable portion 142 is in the uncompressed state.

0178[0181] While certain embodiments have been described, other embodiments are additionally or alternatively possible.

0179[0182] For example, while forming the deformable portion of an ablation electrode has been described as including removal of material from a flat sheet, other methods of forming a deformable portion of an ablation electrode are additionally or alternatively possible. For example, a deformable portion of an ablation electrode can be formed by removing material (e.g., by laser cutting) from a tube of material (e.g., a tube of nitinol). With the material removed, the tube can be bent into a substantially enclosed shape such as the substantially spherical shapes described herein.

0180[0183] As another example, while the deformable portion of an ablation electrode has been described as being formed by removing material from a unitary structure of material (e.g., from a plate and/or from a tube), other methods of forming a deformable portion of an ablation electrode are additionally or alternatively possible. For example, a deformable portion of an ablation electrode can include a mesh and/or a braid having greater than about 5 percent and less than about 50 percent open area along an inner portion of the ablation electrode. The mesh material can be, for example, nitinol. It should be appreciated that this mesh and/or braided portion of the ablation electrode can move between a compressed and uncompressed state.

0181[0184] As yet another example, while an ablation electrode has been described as having a deformable portion, along which sensors are disposed for determining displacement of the deformable portion, other configurations for determining displacement are additionally or alternatively possible. For example, a plurality of coils can be disposed along a deformable portion of an ablation electrode. In use, some coils in the plurality can be used to emit a magnetic field while other coils in the plurality can be used to measure the resultant magnetic field. The signals measured can be used to determine displacement of the deformable portion. This determined displacement of the deformable portion can be used, for example, to determine shape of the deformable portion and, additionally or instead, to determine the force applied to the deformable portion according to any one or more of the methods described herein. Further, or instead, a plurality of ultrasound transducers can be disposed along a deformable portion of an ablation electrode, on an irrigation element enveloped by the deformable portion, or a combination thereof. The signals measured by the ultrasound transducers can be used to determine displacement of the deformable portion.

0182[0185] As still another example, while the deformable portion of an ablation electrode has been described as being self-expandable from the compressed state to the uncompressed state, the deformable portion of the ablation electrode can be additionally or alternatively expanded and/or contracted through the application of external force. For example, a catheter such as any one or more of the catheters described herein can include a sliding member extending from the handle, though a catheter shaft, and to an ablation electrode. The sliding member can be coupled (e.g., mechanically coupled) to the ablation electrode such that axial movement of the sliding member relative to the catheter shaft can exert compression and/or expansion force on the deformable portion of the ablation electrode. For example, distal movement of the sliding member can push the ablation electrode in a distal direction relative to the catheter shaft such that the deformable portion of the ablation electrode collapses to a compressed state (e.g., for retraction, delivery, or both). In addition, or as an alternative, proximal movement of the sliding member can pull the ablation electrode in a proximal direction relative to the catheter shaft such that the deformable portion of the ablation electrode expands to an uncompressed state (e.g., for the delivery of treatment). In certain implementations, the sliding member can be mechanically coupled to a portion of the handle such that movement of the sliding member can be controlled at the handle. It should be appreciated that the sliding member can be an elongate member (e.g., a wire) that is sufficiently flexible to bend with movement of the shaft while being sufficiently rigid to resist buckling or other types of deformation in response to the force required to move the deformable portion of the ablation electrode.

0183[0186] As yet another example, while the irrigation element has been described as including a substantially rigid stem and bulb configuration, other configurations of the irrigation element are additionally or alternatively possible. For example, referring now to FIG. 16, an irrigation element 128a can include an axial portion 166 and a helical portion 168. The irrigation element 128a can be used in any one or more of the catheters described herein. For example, the irrigation element 128a can be used in addition to or instead of the irrigation element 128, as described with respect to FIGS. 3-5.

0184[0187] The axial portion 166 and the helical portion 168 are in fluid communication with one another and, in certain implementations, with an irrigation lumen defined by the catheter shaft. At least the helical portion 168 and, optionally, the axial portion 166 define a plurality of irrigation holes 134a along at least a portion of the length of the irrigation element 128a. In use, the delivery of irrigation fluid through the irrigation holes 134a can result in an axially, circumferentially, and/or radially distributed pattern. Unless otherwise indicated or made clear from the context, the irrigation element 128a can be used in addition to or instead of the irrigation element 128 (FIG. 3). Thus, for example, it should be understood that the irrigation element 128a can provide substantially uniform cooling along the inner portion 136 of the ablation electrode 124 (FIG. 3).

0185[0188] The irrigation holes 134a can be similar to the irrigation holes 134 defined by the irrigation element 128 (FIG. 3). For example, the irrigation holes 134a can be the same size and shape as the irrigation holes 134 defined by the irrigation element 128. Additionally, or alternatively, the irrigation holes 134a can have the same open area as the irrigation holes 134 defined by the irrigation element 128.

0186[0189] The axial portion 166 of the irrigation element 128 can be coupled to a catheter shaft (e.g., to a distal end portion of the catheter shaft such as the distal end portion 132 of the catheter shaft 122 described with respect to FIGS. 2-4). Additionally, or alternatively, the axial portion 166 can extend distally from the catheter shaft. For example, the axial portion 166 can extend distally from the catheter shaft, along an axis defined by the irrigation lumen.

0187[0190] In general, the helical portion 168 extends in a radial direction away from the axial portion 166. In certain implementations, a maximum radial dimension of the helical portion 168 is less than an outer diameter of the catheter shaft. In such implementations, the helical portion 168 can remain in the same orientation during delivery and use of the catheter (e.g., during any of the delivery and/or use methods described herein). In some implementations, however, the helical portion 168 can be resiliently flexible (e.g., a nitinol tube shape set in a helical configuration) such that the maximum radial extent of the helical portion 168 is less than an outer diameter of the catheter shaft during delivery to the treatment site and expands such that the maximum radial extent of the helical portion 168 is greater than the outer diameter of the catheter shaft in a deployed position. It should be appreciated that, in the deployed position, the helical portion can be positioned closer to the inner surface of an ablation electrode, which can facilitate delivery of irrigation fluid to the inner surface of the ablation electrode.

0188[0191] In addition to extending in a radial direction away from the catheter shaft, the helical portion 168 extends in a circumferential direction relative to the axial portion 166. For example, the helical portion 168 can extend circumferentially about the axial portion 166 through at least one revolution. Such circumferential extension of the helical portion through at least one revolution can facilitate substantially uniform dispersion of irrigation fluid about an inner surface of a substantially spherical ablation electrode enveloping the helical portion 168. [0192] Optionally, the helical portion 168 can further extend in an axial direction relative to the axial portion 166. Thus, as used herein, the helical portion 168 should be understood, in the most general sense, to include any of various different helical patterns that are substantially planar and/or various different helical patterns that extend axially relative to the axial portion 166.

0189[0193] As another example, while the irrigation element has been described as having a discrete number of uniform irrigation holes, other implementations are additionally or alternatively possible. For example, referring now to FIG. 17, an irrigation element 128b can be a porous membrane defining a plurality of openings 170. In general, the plurality of openings 170 are a property of the material forming the irrigation element 128c and are, therefore, distributed (e.g., non-uniformly distributed and/or uniformly distributed) along the entire surface of the irrigation element 128b. Because the openings 170 are a property of the material forming the irrigation element 128b, the plurality of openings 170 can be substantially smaller than irrigation holes formed in an irrigation element through laser drilling or other similar secondary processes. Unless otherwise indicated or made clear from the context, the irrigation element 128b can be used in addition to or instead of the irrigation element 128 (FIG. 3) and/or the irrigation element 128a (FIG. 16). Thus, for example, it should be understood that the irrigation element 128b can provide substantially uniform cooling along the inner portion 136 of the ablation electrode 124 (FIG. 3).

0190[0194] In certain implementations, the irrigation element 128b can include an arrangement of one or more polymers. Such an arrangement can be porous and/or microporous and, as an example, can be formed of polytetrafluoroethylene (PTFE). In such implementations, the openings 170 can be defined by spaces between polymeric fibers or through the polymeric fibers themselves and are generally distributed along the entire surface of the irrigation element 128b. It should be appreciated that the large number of the openings 170 and the distribution of the openings 170 along the entire surface of the irrigation element 128b can produce a substantially uniform spray of irrigation fluid. Further, the large number of the openings 170 and the distribution of the openings 170 along the entire surface of the irrigation element 128b can facilitate interaction of multiple different fluid jets and, thus, the development of turbulent flow of irrigation fluid. [0195] The size and distribution of the openings 170 defined between or through polymeric fibers can allow the irrigation element 128b to act as a selective filter. For example, because blood molecules are substantially larger than water molecules, the size (e.g., the average size) of the openings 170 can be smaller than blood molecules but larger than water molecules. It should be appreciated that such sizing of the openings 170 can permit egress of irrigation fluid from the irrigation element 128b while preventing ingress and, thus, clotting of blood molecules into the irrigation element 128b.

0191[0196] The arrangement of one or more polymers of the irrigation element 128b can include electrospun polytetrafluorethylene and/or expanded polytetrafluoroethylene (ePTFE). In certain implementations, the arrangement of one or more polymers is nonwoven (as shown in FIG. 17) resulting in the spacing between the fibers being substantially non-uniform such that the openings 170 defined by the spacing between the fibers are of non-uniform size and/or nonuniform distribution. In some implementations, the irrigation element 128b can include a woven or fabric arrangement of polymers through which irrigation fluid can be directed. For example, the fabric can be formed of one or more polymers or other biocompatible materials woven together to form a substantially uniform porous barrier through which, in use, irrigation fluid may pass. Examples of polymers that can be arranged together into a fabric suitable for forming the irrigation element 128c include, but are not limited to, one or more of the following:

0192polyester, polypropylene, nylon, PTFE, and ePTFE.

0193[0197] In some implementations, the irrigation element 128b can include an open cell foam such that the openings 170 are defined by cells of the open cell foam along the surface of the irrigation element 128b. In such implementations, irrigation fluid can move through tortuous paths defined by the open cell foam until the irrigation fluid reaches the openings 170 along the surface of the irrigation element 128b, where the irrigation fluid exits the irrigation element 128b. It should be appreciated that, in such implementations, the openings 170 are distributed along the entire surface of the irrigation element 128b, resulting in spray of irrigation fluid issuing from the irrigation element 128b in a substantially uniform and substantially turbulent pattern.

0194[0198] As yet another example, while irrigation elements have been described as including a resilient, expandable helical portion, other types of resilient, expandable irrigation elements are additionally or alternatively possible. For example, referring now to FIGS. 18 and 19, an irrigation element 128c can be a resilient, inflatable structure, such as balloon, disposed along a distal end portion 132' of a catheter shaft 122' and in fluid communication with a lumen 15 . In certain implementations, the irrigation element 128c and the ablation electrode 124' can each be coupled to the distal end portion 132' of the catheter shaft 122' . Unless otherwise indicated or made clear from the context, an element designated with a primed (') element number in FIGS. 18 and 19 is similar to a corresponding element designated with an unprimed number in other figures of the present disclosure and, thus, should be understood to include the features of the corresponding element designated with an unprimed number. As one example, therefore, the ablation electrode 124' should be understood to correspond to the ablation electrode 124 (FIG. 3), unless otherwise specified.

0195[0199] In certain implementations, the irrigation element 128c is expandable. For example, the irrigation element 128c can be uninflated and/or underinflated in a delivery state of the distal end portion 132' of the catheter shaft 122' to a treatment site according to any of the methods described herein. In such a delivery state, the irrigation element 128c can be delivered to the treatment site with a low profile (e.g., a profile that is less than or equal to a maximum outer dimension of the catheter shaft 122'). At the treatment site, the irrigation element 128c can be inflated to expand from the delivery state to an expanded state. For example, the irrigation element 128c can expand in a radial direction beyond an outermost dimension of the catheter shaft 122').

0196[0200] The irrigation element 128c can be a non-compliant balloon or a semi-compliant balloon. In such implementations, the irrigation element 128c can be substantially resistant to

0197deformation when in an inflated state. Thus, in instances in which the irrigation element 128c is non-compliant or semi-compliant, the irrigation element 128c can resist deformation when contacted by an inner portion 136' of the deformable portion 142' of the ablation electrode 124' . As compared to a compliant balloon, this resistance to deformation by the irrigation element 128c can facilitate, for example, control over the flow of irrigation fluid through the irrigation element 128c.

0198[0201] In some implementations, the irrigation element 128c is a balloon formed of one or more polymers. Polymers can be, for example, sufficiently flexible to expand from the delivery state to the expanded state while withstanding forces created by the movement of irrigation fluid through the irrigation element 128c. In instances in which the irrigation element 128c is formed of one or more polymers, irrigation holes can be formed in polymers through laser drilling or other similar secondary processes. Examples of polymers that can be used to form the irrigation element 128c include one or more of: thermoplastic polyurethane, silicone, poly(ethylene terephthalate), and polyether block amide.

0199[0202] The irrigation element 128c can define a plurality of irrigation holes 134c. The irrigation holes 134c can be similar to the irrigation holes 134 defined by the irrigation element 128 (FIG. 3). For example, the irrigation holes 134c can be the same size and shape as the irrigation holes 134 defined by the irrigation element 128. Additionally, or alternatively, the irrigation holes 134c can have the same open area as the irrigation holes 134 defined by the irrigation element 128.

0200[0203] In use, irrigation fluid can flow from the lumen 15 , into the irrigation element 128c, and can exit the irrigation element 128c through the plurality of irrigation holes 134c. In general, the plurality of irrigation holes 134c can have a combined area that is less than the cross- sectional area of the lumen 15 such that fluid pressure can build in the inflatable element 128c as the irrigation fluid moves through the irrigation element 128c. It should be appreciated, then, that the pressure in the inflatable element 128c, resulting from the flow of irrigation fluid through the irrigation element 128c, can inflate the irrigation element 128c (e.g., from the delivery state to the expanded state).

0201[0204] In certain implementations, the volume defined by an inner portion 136' of the ablation electrode 124' in an expanded or uncompressed state is larger than the volume defined by the irrigation element 128c in an expanded state. Thus, for example, the inner portion 136' of the ablation electrode 124' (e.g., along the deformable portion 142') can be spatially separated from at least a portion of the surface area of the irrigation element 128c when the irrigation element 128c is in the expanded state. This spatial separation can be advantageous, for example, for developing turbulence of irrigation fluid issuing from the irrigation holes 134c prior to reaching the inner portion 136' of the ablation electrode 124' . It should be appreciated that, as compared to less turbulent flow and/or laminar flow, such turbulence of the flow of irrigation fluid at the inner portion 136' of the ablation electrode 124' can facilitate efficient cooling of the ablation electrode 124' . [0205] The irrigation element 128c can be enveloped by the ablation electrode 124' in an uncompressed state to facilitate, for example, cooling substantially the entire inner portion 136' of the ablation electrode 124' . Additionally, or alternatively, enveloping the irrigation element 128c with the ablation electrode 124' can reduce the likelihood of exposing the irrigation element 128c to undesirable forces such as, for example, forces that can be encountered as the ablation electrode 124' and the irrigation element 128c are moved to the treatment site.

0202[0206] In the expanded state, the irrigation element 128c can include a substantially ellipsoidal portion. As used herein, a substantially ellipsoidal portion can include a substantially spherical shape and deformations of a substantially spherical shape.

0203[0207] In certain implementations, the irrigation holes 134c are defined on this ellipsoidal portion of the irrigation element 128c. Thus, in such implementations, the ellipsoidal portion of the irrigation element 128c can facilitate directing irrigation fluid in multiple, different axial and radial directions. For example, the irrigation holes 134c can be spaced circumferentially (e.g., about the entire circumference) about the ellipsoidal portion of the irrigation element 128c such that irrigation fluid can be directed toward the inner portion 136' of the ablation electrode 142' along various different radial directions. As an additional or alternative example, the irrigation holes 134c can be spaced axially (e.g., along an entire axial dimension of the ellipsoidal portion of the irrigation element 128c ) such that the irrigation fluid can be directed toward the inner portion 136' of the ablation electrode 142' along proximal and/or distal axial directions.

0204[0208] A plurality of sensors 126' can be supported on the deformable portion 142' of the ablation electrode 124'. In use, the plurality of sensors 126' can be used to detect deformation of the deformable portion 142'. For example, the irrigation element 128c can include a sensor 172 and electrical signals can be driven between the one or more electrodes on the irrigation element 128c and each of the plurality of sensors 126' according to any of the methods described herein.

0205[0209] While the plurality of sensors 126' can be used in cooperation with the sensor 172 on the irrigation element 128c, other configurations for sensing deformation of the deformable portion 142' are also or instead possible. For example, referring now to FIGS. 20 and 21, a plurality of sensors 174 can be supported along an ablation electrode 124" at least partially enveloping an irrigation element 128c". Unless otherwise indicated or made clear from the context, an element designated with a double primed (") element number in FIGS. 20 and 21 is similar to a corresponding element designated with an unprimed number and/or with a primed number in other figures of the present disclosure and, thus, should be understood to include the features of the corresponding element designated with an unprimed number and/or with a primed number. As one example, the irrigation element 128c" should be understood to include the features of the irrigation element 128c (FIGS. 18 and 19), unless otherwise specified or made clear from the context. As another example, the ablation electrode 124" should be understood to include the features of the ablation electrode 124 (FIG. 3 and 4) and/or of the ablation electrode 124' (FIGS. 18 and 19), unless otherwise specified or made clear from the context.

0206[0210] Each sensor 174 can include a flexible printed circuit and/or a thermistor similar to any of the flexible printed circuits and/or thermistors described herein, including the flexible printed circuit 150 and/or thermistor 152 described above with respect to FIGS. 10 and 11.

0207[0211] In the uncompressed state of the ablation electrode 124", the inner portion 136" of the ablation electrode 124" is spatially separated from a least a portion of a surface of the irrigation element 128c" such that, for example, at least one of the plurality of sensors 174 is not in contact with the irrigation element 128c". In certain implementations, the ablation electrode 124" in the uncompressed state is not in contact with any of the plurality of sensors 174. That is, in such implementations in which the ablation electrode 124", in the uncompressed state, is spatially separated from one or more of the sensors 126", the default arrangement of the sensors 126" is away from the irrigation element 128c.

0208[0212] The ablation electrode 124" can include a deformable portion 142" that is resiliently flexible from a compressed state (e.g., in which the inner portion 136" of the ablation electrode 124" is in contact with the irrigation element 128c") to an uncompressed state (e.g., in which the inner portion 136" of the ablation electrode 124" is spatially separated from at least a portion of the surface of the irrigation element 128c"). Thus, in such implementations, deformation of the deformable portion 142" can place one or more of the plurality of sensors 174 into contact with the irrigation element 128c" and sensing this contact can be used to determine the shape of the deformable portion 142" in response to a deformation force, such as a force exerted through contact with tissue.

0209[0213] The sensors 174 can be axially and/or circumferentially spaced from one another along the deformable portion 142" of the ablation electrode 124". For example, a first set of the sensors 174 can be disposed distal to a second set of the sensors 174 along the inner portion 136" of the ablation electrode 124" (e.g., along the deformable portion 142"). It should be appreciated that the spatial resolution of the detected deformation of the deformable portion 142" can be a function of the number and spatial distribution of the sensors 174, with a larger number of uniformly spaced sensors 174 generally providing increased spatial resolution as compared to a smaller number of clustered sensors 174.

0210[0214] In use, an electrical signal can be driven between at least one of the sensors 174 and another one of the sensors 174. Measured electrical signals generated between at least one of the sensors 174 and another of the sensors 174 can be received at a processing unit such as any of the processing units described herein (e.g., processing unit 109a described with respect to FIG. 1).

0211[0215] Based at least in part on the measured electrical signals generated between at least one of the sensors 174 and another of the sensors 174, deformation of the deformable portion 142" of the ablation electrode 124" can be detected. For example, as the deformable portion 142" of the ablation electrode 124" deforms, one or more of the sensors 174 can be brought into contact with the irrigation element 128c". It should be appreciated that a certain amount of force is required to deform the deformable portion 142" by an amount sufficient to bring the one or more sensors 174 into contact with the irrigation element 128c". As used herein, this force can be considered a threshold at least in the sense that forces below this threshold are insufficient to bring the one or more sensors 174 into contact with the irrigation element 128c" and, therefore, are not detected as contact between the one or more sensors 174 and the irrigation element 128c".

0212[0216] Contact between the one or more sensors 174 and the irrigation element 128c" can be detected, for example, as a change in the measured electrical signal received, by the processing unit, from the respective one or more sensors 174. As a non-limiting example, contact between one or more of the sensors 174 and the irrigation element 128c can be detected as a rise in impedance of a respective one or more electrical signals associated with the one or more sensors 174 in contact with the irrigation element 128c.

0213[0217] The detection of deformation of the deformable portion 142" of the ablation electrode 124" can, for example, include a determination of whether one or more of the sensors 174 is in contact with the irrigation element 128c. In addition, or instead, the detection of deformation of the deformable portion 142" based on the measured electrical signals can include a detection of a degree and/or direction of deformation of the deformable portion 142". That is, a degree and/or direction of deformation of the deformable portion 142" can be determined based on the number and/or position of the one or more sensors 174 detected as being in contact with the irrigation element 128c.

0214[0218] An indication of a determined state of the deformable portion 142" can be sent to a graphical user interface, such as any one or more of the graphical user interfaces described herein (e.g., the graphical user interface 110 described with respect to FIG. 1). In certain

0215implementations, the degree and/or orientation of deformation of the deformable portion 142" can be sent to the graphical user interface. For example, based on which sensors 174 are detected as being in contact with the irrigation element 128c, a corresponding representation of the compressed state of the deformable portion 142" can be sent to the graphical user interface. The corresponding representation of the compressed state of the deformable portion 142" can be based on, for example, a look-up table of shapes corresponding to different combinations of sensors 174 detected as being in contact with the irrigation element 128c.

0216[0219] An exemplary method of making a catheter including the irrigation element 128c" can include coupling (e.g., using an adhesive) the irrigation element 128c" to a distal end portion 132" of a catheter shaft 122". The deformable portion 142" can be formed according to any one or more of the methods described herein, and the deformable portion 142" can be positioned relative to the irrigation element 128c" such that the inner portion 136" of the ablation electrode 124" envelops the irrigation element 128c". The deformable portion 142" can be coupled to the catheter shaft 122" relative to the irrigation element 128c" such that, in a compressed state, the inner portion 136" of the ablation electrode 124" is in contact with the irrigation element 128c" and, in an uncompressed state, the inner portion 136" of the ablation electrode 124" along the deformable portion 142" is spatially separated from the irrigation element 128c".

0217[0220] As another example, while certain arrangements of struts to form cells along a deformable portion of an ablation electrode have been described, other configurations are additionally or alternatively possible. For example, referring now to FIGS. 22 and 23, a catheter 204 can include an ablation electrode 224 having struts 244b defining a plurality of cells 247, with the struts 244b progressively ganged together in a direction from a proximal region to a distal region of a deformable portion 242 of the ablation electrode 224. For the sake of efficient and clear description, elements designated by 200-series element numbers in FIGS. 22 and 23 are analogous to or interchangeable with elements with 100-series element numbers (including primed and double-primed element numbers) described herein, unless otherwise explicitly indicated or made clear from the context, and, therefore, are not described separately from counterpart elements having 100-series element numbers, except to note differences or to describe features that are more easily understood with reference to FIGS. 22 and 23. Thus, for example, catheter 204 in FIGS. 22 and 23 should generally be understood to be analogous to the catheter 104 (FIGS. 1-4), unless otherwise explicitly indicated or made clear from the context.

0218[0221] As used herein, a progressively ganged together configuration of the struts 244b can include an arrangement of the struts 244b in which the number of cells 247 in the plurality of cells 247 decreases in a given direction. Thus, for example, the struts 244b can be progressively ganged together in the direction toward the distal end of the deformable portion 242 such that the number of cells 247 defined by the struts decreases in the direction toward the distal end of the deformable portion 242. Thus, as compared to a configuration in which struts are uniformly disposed about a shape, the closed end of the deformable portion 242 of the ablation electrode 224 can be formed by joining together relatively few of the struts 244b. This can be

0219advantageous with respect to, for example, achieving acceptable manufacturing tolerances or, further or instead, facilitating substantially uniform distribution of current density along the deformable portion 242.

0220[0222] In some implementations, the cells in the plurality of cells 247 can be bounded by different numbers of struts 244b, which can facilitate achieving a target distribution of current density along the deformable portion 242. For example, a first set of cells of the plurality of cells 247 can be bounded by struts 244b defining eyelets (e.g., eyelets 157 in FIG. 12B), and a second set of cells 247 can be bounded by fewer struts than the first set of cells. For example, the first set of cells of the plurality of cells 247 can be bounded by at least four struts 244b.

0221[0223] In certain implementations, at least some of the cells of the plurality of cells 247 are symmetric. Such symmetry can, for example, facilitate achieving substantially uniform current density in a deformable portion 242 of the ablation electrode 224. Additionally, or alternatively, such symmetry can be useful for achieving suitable compressibility of the deformable portion for delivery to a treatment site (e.g., through a sheath) while also achieving suitable expansion of the deformable portion for use at the treatment site.

0222[0224] At least some of the cells 247 can have mirror symmetry. As used herein, a mirror symmetric shape includes a shape that is substantially symmetric about a plane intersecting the shape, with the substantial symmetry allowing for the presence or absence of a sensor 226 on one or both sides of the plane intersecting the shape. For example, at least some of the cells 247 can have mirror symmetry about a respective mirror symmetry plane passing through the respective cell 247 and containing a center axis CL' -CL' defined by a catheter shaft 222 and extending from a proximal end portion to a distal end portion of the catheter shaft 222. In the side view shown in FIG. 23, a mirror symmetry plane for some of the cells of the plurality of cells 247 is directed perpendicularly into the page and passes through the center axis CL'-CL'. Additionally, or alternatively, it should be appreciated that the overall deformable portion 242 of the ablation electrode 224 can be symmetric about a plane including the center axis CL'-CL', such as the plane directed perpendicularly into the page and passing through the center axis CL' -CL' .

0223[0225] The mirror symmetry of at least some of the cells of the plurality of cells 247 and/or the overall deformable portion 242 can be useful, for example, for uniform distribution of current density. Additionally, or alternatively, symmetry can facilitate expansion and contraction of the deformable portion 242 of the ablation electrode 224 in a predictable and repeatable manner (e.g., with little to no plastic deformation). For example, each of the cells of the plurality of cells 247 can be symmetric about its respective symmetry plane in the compressed state and in the uncompressed state of the deformable portion 242 of the ablation electrode 224. With such symmetry in the compressed state and in the uncompressed state of the deformable portion 242, the deformable portion 242 can expand with little to no circumferential translation of the deformable portion 242 during expansion, which can facilitate accurate knowledge of the position of the deformable portion 242 during delivery and deployment of the deformable portion 242.

0224[0226] The catheter 204 can be formed according to any one or more of the various different methods described herein. For example, the ablation electrode 224 can be formed from a flat sheet or from a tube, as described herein, such that the ablation electrode 224 has two open ends. A fastener 241b can be inserted through an end of at least some of the struts 244b according to any of the various different methods described herein to couple ends of the struts 244b to close one of the two open ends of the ablation electrode 224. An open end of ablation electrode 224 (e.g., an end opposite the fastener 241b) can be coupled to a distal end portion 232 of the catheter shaft 222 to form the catheter 204.

0225[0227] The following simulation and experiment describe the uniformity of current density associated with the ablation electrode 224 in the uncompressed state. It is to be understood that the simulation and experiment described below are set forth by way of example only, and nothing in the simulation or experiment shall be construed as a limitation on the overall scope of this disclosure.

0226[0228] Referring now to FIG. 24, current density through the deformable portion 242 of the ablation electrode 224 (FIG. 22) in the uncompressed state was simulated using a finite difference method. In the simulation, the ablation electrode 224 was assumed to have uniform voltage (e.g., 1 V), with the medium set at uniform resistivity. The return electrode was assumed to be the edge of the domain and was set to another uniform voltage (e.g., 0 V). It is believed that the variation in simulated current density along a trajectory (shown as the arc extending from position 0 to position 450) at a fixed distance away from an outer surface of the deformable portion 242 is a proxy for the actual variation in current density along the respective trajectory of the deformable portion 242.

0227[0229] Referring now to FIGS. 24 and 25, the simulated current density through the deformable portion 242 varies by less than about ±10 percent along the trajectory at 1 mm away from an outer surface of the deformable portion 242 in the uncompressed state. Thus, the current density at a fixed distance near the deformable portion 242 in the uncompressed state is believed to be relatively uniform. Thus, more generally, current density near the surface of the deformable portion 242 is substantially insensitive to the orientation of the deformable portion 242 relative to tissue. Further, given that the deformable portion 242 in the expanded state is larger than a maximum lateral dimension of the catheter shaft 222 (FIG. 22), the deformable portion 242 can reliably deliver wide lesions in any of various different orientations relative to tissue. This can be useful, for example, for reducing treatment time and/or increasing the likelihood that applied ablation energy is sufficient to treat a targeted arrhythmia. [0230] While the results shown in FIG. 25 are based on a simulation using a finite difference method, the general observations drawn from these simulations are supported by the

0228experimental results described below.

0229[0231] FIG. 26 is a graph of depth of lesions applied to chicken breast meat using the ablation electrode 224 in axial and lateral orientations relative to the chicken breast meat. Each lesion was performed on chicken breast meat and 0.45% saline solution at body temperature and, for each lesion, the deformable portion 242 of the ablation electrode 224 was in contact with the chicken breast meat with 10 g of force and 8 ml/min of irrigation was used. For each ablation, 2 amperes were delivered to the tissue through the deformable portion 242 (FIG. 22) for ten seconds. Lesion depth was determined using a ruler to measure the depth of tissue discolored from pink to white.

0230[0232] Five of the lesions were created with the deformable portion 242 (FIG. 22) in an axial orientation in which the catheter shaft 222 (FIG. 22) was perpendicular to the chicken breast, and five of the lesions were created with the deformable portion 242 in a lateral orientation perpendicular to the axial orientation. As shown in FIG. 26, although the lesions were created using different orientations, the lesion depths were similar, with lesion depth varying by less than about ± 20 percent, indicating that the amount of energy ablating tissue in both orientations is similar. This experimental finding is consistent with the results of the simulation. That is, lesions corresponding to multiple different angles between the deformable portion 242 (FIG. 22) and tissue have similar depth at each of the multiple different angles. Such uniform distribution of current density can facilitate controlling lesion size, which can be particularly useful for ablating thin tissue.

0231[0233] Referring again to FIGS. 22 and 23, an irrigation element 228 is enveloped by the deformable portion 242 of the ablation electrode 224 such that the deformable portion 242 forms an enclosure about the irrigation element 228. The irrigation element 228 can be any of the various different irrigation elements described herein and can be in fluid communication with a catheter shaft 222. For example, the irrigation element 228 can be disposed substantially along the center axis CL' -CL', can extend distally from a distal end portion 232 of the catheter shaft 222, and, also or instead, can define a plurality of irrigation holes 234 disposed along the irrigation element 228 to direct irrigation fluid toward the deformable portion 242 of the ablation electrode 224. Additionally, or alternatively, a center electrode 235 can be disposed along the irrigation element 228 and directly or indirectly coupled to the distal end portion 232 of the catheter shaft 222.

0232[0234] In the absence of force applied to the deformable portion 242 of the ablation electrode 224, the center electrode 235 is spaced apart from the sensors 226. As the deformable portion 242 is brought into contact with tissue through application of force applied to the deformable portion 242, it should be appreciated that, independent of orientation of the deformable portion 242 relative to tissue, the deformable portion 242, and thus the sensors 226, makes initial contact with the tissue before the center electrode 235 makes initial contact with the tissue. In certain implementations, the center electrode 235 remains spaced from tissue under normal operation. That is, the deformable portion 242 of the ablation electrode 224 can be sufficiently rigid to maintain spacing of the center electrode 235 from tissue under a normal range of contact forces, which are less than about 100 g (e.g., less than about 50 g).

0233[0235] Electrical activity detected (e.g., passively detected) by the center electrode 235 and the sensors 226 (acting as surface electrodes) can form the basis of respective electrograms associated with each unique pairing of the center electrode 235 and the sensors 226. For example, in implementations in which there are six sensors 226, the center electrode 235 can form six electrode pairs with the sensors 226 which, in turn, form the basis for six respective electrograms.

0234[0236] An electrogram formed by electrical signals received from each respective electrode pair (i.e., the center electrode 235 and a respective one of the sensors 226) can be generated through any of various different methods. In general, an electrogram associated with a respective electrode pair can be based on a difference between the signals from the electrodes in the pair and, thus more specifically, can be based on a difference between an electrical signal received from the center electrode 235 and an electrical signal received from a respective one of the sensors 226. Such an electrogram can be filtered or otherwise further processed to reduce noise and/or to emphasize cardiac electrical activity, for example.

0235[0237] Because the center electrode 235 remains spaced at an intermediate distance from the sensors 226 and tissue in the range of forces experienced through contact between tissue and the deformable portion 242 of the ablation electrode 224, the electrogram formed from each electrode pair can advantageously be a near-unipolar electrogram. As used herein, a near- unipolar electrogram includes an electrogram formed based on the difference between two electrodes that are greater than about 2 mm apart and less than about 6 mm apart and oriented such that one of the electrodes remains spaced away from tissue. In certain implementations, in the absence of force applied to the deformable portion 242 of the ablation electrode 224, the center electrode 235 is spaced apart from the sensors 226 by distance greater than about 2 mm and less than about 6 mm.

0236[0238] The near-unipolar electrograms associated with the center electrode 235 spaced from the sensors 226 can provide certain advantages over unipolar configurations (i.e., configurations having electrode spacing greater than 6 mm) and over bipolar configurations (i.e., configurations having electrode spacing equal to or less than 2.5 mm and/or allowing both electrodes to be spaced close to tissue). For example, as compared to unipolar electrograms, the near-unipolar electrograms formed based on signals received from the center electrode 235 and the sensors 226 are less noisy and, additionally or alternatively, less susceptible to far-field interference from electrical activity away from the tissue of interest. Also, as compared to unipolar electrograms, a near-unipolar electrogram does not require a reference electrode on a separate catheter or other device. As a further or alternative example, as compared to bipolar electrograms, a near-unipolar electrogram formed based on signals received from the center electrode 235 and the sensors 226 is generated from an electrode pair with only one electrode in the electrode pair in contact with tissue such that the resulting electrogram waveform arises from one tissue site, making it less complex to interpret. Also, or instead, as compared to bipolar electrograms generated from a pair of electrodes in contact with tissue, the signal of a near-unipolar electrogram formed based on signals received from the center electrode 235 and the sensor 226 in contact with tissue can have a more consistent morphology and/or a larger amplitude at least because the center electrode 235 is always oriented away from tissue as compared to the sensor 226 in the electrode pair touching tissue.

0237[0239] The sensors 226 can be any of the various different sensors described herein and, in addition or in the alternative, can be arranged on the deformable portion 242 of the ablation electrode 224 according to any of the various different arrangements described here. For example, in the absence of external force applied to the deformable portion 242 of the ablation electrode 224 enveloping the center electrode 235, the sensors 226 can be noncoplanar relative to one another. It should be appreciated that, as compared to a planar arrangement, the electrograms generated from the sensors 226 arranged in such a noncoplanar configuration can be useful for providing improved directional information regarding electrical activity in tissue.

0238[0240] The sensors 226 can be electrically isolated from the deformable portion 242 of the ablation electrode 224 with the sensors 226, acting as surface electrodes, passively detecting electrical activity in tissue in proximity to each respective sensor 226 without interference from the deformable portion 242 of the ablation electrode 224. At least some of the sensors 226 can be disposed on an outer portion of the deformable portion 242 of the ablation electrode 224 with the deformable portion 242 of the ablation electrode between the center electrode 235 and at least a portion of each respective one of the sensors 226 on the outer portion. Additionally, or alternatively, at least some of the sensors 226 can be disposed on an inner portion of the deformable portion 242 of the ablation electrode 224. In such implementations, each sensor 226 can be in proximity to tissue without touching tissue as the deformable portion 242 of the ablation electrode 224 touches tissue.

0239[0241] Referring now to FIGS. 1, 22, and 23, the catheter 204 can replace the catheter 104 in FIG. 1. Accordingly, electrical signals from the sensors 226 and the center electrode 235 can be directed to the catheter interface unit 108. For example, the signals can be sent to an electrical input stage associated with the catheter interface unit 108. In certain implementations, the difference between electrical signals is determined through electronic circuitry (e.g., a voltage amplifier with a differential input). Additionally, or alternatively, the difference between electrical signals can be determined by the processing unit 109a of the catheter interface unit 108.

0240[0242] In general, the storage medium 109b of the catheter interface unit 108 can have stored thereon computer-executable instructions for causing the processing unit 109a to acquire a plurality of electrograms (e.g., an electrogram for each electrode pair formed by the center electrode 235 and each respective sensor 226). The storage medium 109b be can, also or instead, have stored thereon instructions for causing the processing unit 109a to display a representation of at least one of the plurality of electrograms on the graphical user interface 110. In certain implementations, the storage medium 109b can have stored thereon instructions for causing the processing unit 109a to determine a voltage map associated with the plurality of electrograms, the voltage map corresponding, for example, to electrical activity of a heart of a patient. In some implementations, the storage medium 109b can have stored thereon instructions for causing the processing unit 109a to display the voltage map on the graphical user interface 110. The displayed electrograms, alone or in combination with a displayed voltage map, can be useful for selectively treating tissue of the heart (e.g., delivering ablation energy from the deformable portion 242 of the ablation electrode 224 to tissue in a cavity of the heart).

0241[0243] While the center electrode 235 has been described as being disposed on the irrigation element 228, it should be appreciated that the center electrode 235 can additionally or alternatively be located at any of various different positions within the deformable portion 242 of the ablation electrode 224. For example, the center electrode 235 can be positioned on the distal end portion 232 of the catheter shaft 222. Additionally, or alternatively, the irrigation element 228 itself can be used as a center electrode.

0242[0244] Referring now to FIGS. 1, 22, 23, and 27, various different parameters of the RF energy delivered by the ablation generator 116 to the ablation electrode 224 (e.g., at an interface between endocardial tissue and blood in a heart cavity of a patient) can be controlled during a period of lesion formation to achieve desired characteristics of the resulting lesions formed in tissue in contact with the ablation electrode 224 (e.g., in contact with the deformable portion 242 of the ablation electrode 224). For example, as described in greater detail below, the RF energy delivered by the ablation electrode 224 to the tissue can be controlled to interact advantageously with local heat transfer patterns to produce large lesions.

0243[0245] The RF energy, shown as electric current in FIG. 27, delivered to the ablation electrode 224 can be pulsed to cycle (e.g., repeatedly) between a first energy phase 310 and a second energy phase 320 during a period of lesion formation (e.g., when the ablation electrode 224 is in contact with tissue). For the sake of clarity of explanation, pulsation of RF energy is described herein with reference to electric current. It should be readily understood, however, that any one or more of the systems and methods described herein can additionally, or alternatively, include pulsation of voltage, unless otherwise specified or made clear from the context.

0244[0246] The first energy phase 310 is greater than the second energy phase 320 such that repeated cycling between the first energy phase 310 and the second energy phase 320 results in a pulse wave 330 having an amplitude 332 and a period 334. One or more of the amplitude 332 and the period 334 of the pulse wave 330 can be varied during the formation of a given lesion to control, for example, the size of the lesion produced by the introduction of the RF energy into the tissue. Additionally, or alternatively, the percentage of time spent in the first energy phase 310 relative to the second energy phase 320 can be varied to achieved a target duty cycle of energy delivered to tissue at a treatment site. In certain instances, however, the amplitude 332, the period 334, and/or the duty cycle of the pulse wave 330 can be fixed, which can be useful, for example, for simplifying the software and/or hardware used to generate the pulse wave 330. Additionally, or alternatively, the parameters of the pulse wave 330 during the first energy phase 310 and/or the second energy phase 320 can be a function of a sensed parameter, a computed parameter, or a combination thereof. As an example, the energy delivered to the ablation electrode 224 during the first energy phase 310 can be controlled to maintain a known temperature (e.g., a temperature of about 70 °C) for a given amount of time and, because the first energy phase 310 is greater than the second energy phase 320, the duration of the second energy phase 320 can be controlled to maintain temperature of the tissue below a predetermined threshold for a given amount of time.

0245[0247] The repeated cycling between the first energy phase 310 and the second energy phase 320 can result in corresponding cycling of ablation energy delivered to tissue in contact with the ablation electrode 224. More specifically, the first energy phase 310 can correspond to energy suitable to ablate tissue in contact with the ablation electrode 224, and the second energy phase 320 can correspond to an energy level that does not result in ablation of the same tissue in contact with the ablation electrode 224. For example, the second energy phase 320 can correspond to an "off state in which no energy is delivered to the ablation electrode 224.

0246Additionally, or alternatively, the second energy phase 320 can correspond to a low energy state, such as a state that might be useful for sensing tissue parameters.

0247[0248] In general, the hottest point in tissue receiving RF energy from the ablation electrode 224 is a point away from the surface in contact with the ablation electrode 224 because the surface in contact with the ablation electrode 224 is irrigated through the movement of blood, irrigation fluid, or both. Without wishing to be bound by theory, and as described in greater detail below, it is believed that pulsed RF energy produces lesion sizes larger than those produced by non- pulsed RF energy of the same amplitude at least because, as compared to cooling that occurs when non-pulsed RF energy of the same amplitude is used, the hottest point in the tissue is cooled differently when pulsed RF energy is used to ablate tissue. [0249] Referring now to FIG. 28, when RF energy is delivered to the ablation electrode 224, heat is generated in the blood, at the surface of the tissue "T," and within the tissue "T," through, for example, Joule heating. In general, more heat is generated near the ablation electrode 224, where current density is highest, and generated heat decreases with distance away from the ablation electrode. In the case in which non-pulsed RF energy is directed from the ablation electrode 224 into the tissue "T," heat is transferred into a portion of the tissue "T" defined by a lesion boundary "L" at a rate, Qin, while heat is transferred away from the portion of tissue "T" defined by the lesion boundary "L" at a rate, Qout. The rate of heat carried away, Qout, can be a combination of conduction below the surface of tissue "T" and convective cooling by blood and/or irrigation fluid moving past the surface of tissue "T" in the anatomic structure. Initially, Qin is greater than Qout such that the lesion boundary "L" will continue to grow (e.g., move away from the surface of tissue "T") as non-pulsed RF energy is directed into the tissue "T." Under conditions in which the non-pulsed RF energy is applied by the ablation electrode 224 to tissue "T" for a sufficiently long period of time (e.g., about 1-2 minutes in cardiac tissue), however, thermal equilibrium is eventually reached in tissue "T." As used herein, such a thermal equilibrium condition includes a condition in which the heat transfer rate, Qin, into the tissue within the lesion boundary "L" substantially equals the heat transfer rate away, Qout, from the tissue within the lesion boundary "L". Once thermal equilibrium is established in tissue "T," the delivery of more non-pulsed RF energy of the same amplitude will not result in substantial further propagation of the lesion boundary "L." Thus, at a given amplitude of non-pulsed RF energy delivered to tissue "T" by the ablation electrode 224, the lesion boundary "L" has an approximate maximum depth and maximum width under conditions in which thermal equilibrium is established in tissue "T."

0248[0250] In general, the maximum depth and maximum width of the lesion boundary "L" is limited by the amplitude of the non-pulsed RF energy that can be delivered safely to tissue "T" without damaging tissue "T" (e.g., without causing steam-pop to occur in tissue "T") at a hottest point "H" and without overheating blood (e.g., without causing thrombus formation). The surface of tissue "T" is cooled by the flow of blood and/or irrigation fluid and, thus, the hottest point "H" is generally at a position below the surface of tissue "T." The temperature of the surface of tissue "T" can be used as a proxy for the temperature of the hottest point "FT' such that, by maintaining temperature of the surface of tissue "T" below a threshold, the hottest point "H" can be maintained below a temperature associated with tissue damage. That is, temperature feedback from the surface of tissue "T" (e.g., from one or more sensors 246 carried by the ablation electrode 224) can be used as a feedback parameter to control the amplitude of the non- pulsed RF energy applied to tissue "T" such that the temperature of the hottest point "H" of tissue "T" can be maintained at a safe temperature.

0249[0251] Referring now to FIGS. 27, 29A, and 29B, RF energy delivered to tissue "T" by ablation electrode 224 can be pulsed to cycle repeatedly between the first energy phase 310 and the second energy phase 320. In general, the pulsation of RF energy delivered to tissue "T" by the ablation electrode 224 can decouple lesion size from thermal equilibrium and temperature constraints associated with non-pulsed RF energy. As shown in FIGS. 29A and 29B, a point "K" below the surface of tissue "T" is the hottest point during delivery of pulsed RF energy, and a point "P" is representative of cooler tissue further into tissue "T" than the point "K." As described in greater detail below, the heat directed at the point "K" advantageously changes as the RF energy is pulsed from the first energy phase 310 to the second energy phase 320, with the resulting change facilitating delivery of thermal ablation energy to the point "P" while the temperature of the point "K" is maintained at a safe temperature. More generally, the change in the heat directed at the point "K" as the RF energy is pulsed from the first energy phase 310 to the second energy phase 320 can facilitate the creation of lesions larger than those achievable by delivering of non-pulsed RF energy until thermal equilibrium is established in tissue "T."

0250[0252] During the first energy phase 310 of pulsed RF energy delivered to tissue "T," shown in FIG. 29A, heat is directed into point "K" at a rate, Qin_p, greater than a rate at which heat is carried away from tissue "T" and away from point "K," Qout_p. The rate of heat carried away from point "K," Qout_p, is a function of conduction from point "K" to cooler portions of tissue "T" and convective cooling by fluid moving past the surface of tissue "T." As described in greater detail below, the convective cooling of the surface of tissue "T" can be achieved through the flow of blood past the surface of tissue "T" and, additionally or alternatively, through the flow of irrigation fluid (e.g., saline) delivered by the irrigation element 228 toward the surface of tissue "T" according to any one or more of the systems and methods of irrigation described herein. [0253] In general, the duration of the first energy phase 310 is less than a duration required for establishing thermal equilibrium at point "K" and, thus, the temperature of point "K" can increase during the duration of the first energy phase 310. For example, amplitude and/or duration of the RF energy directed into tissue "T" during the first energy phase 310 can be such that the point "K" and, optionally, nearby tissue (e.g., tissue at a point "P") undergoes thermal ablation during the first energy phase 310.

0251[0254] During the second energy phase 320 of pulsed RF energy delivered to tissue "T," shown in FIG. 29B, heat directed into point "K" can be sufficiently low (e.g., approximately zero) such that point "K" undergoes net cooling by a combination of heat conducted into cooler portions (e.g., the point "P") of tissue "T" and convective cooling through blood, irrigation fluid, or a combination thereof moving past the surface of tissue "T." For example, during the second energy phase 320, the point "K" can be cooled as heat moves into the point "P" from the point "K" through conductive cooling. Further, or in the alternative, because the distance between the point "K" and the surface of tissue "T" is less than the distance between the point "P" and the surface of tissue "T," the point "K" undergoes a greater amount of convective cooling than the point "P" during the second energy phase 320. Thus, the point "K" cools more rapidly than the point "P" during the second energy phase 320.

0252[0255] In general, because the temperature of the point "K" is a limiting factor in the amount of heat that can be safely provided to tissue "T," the preferential cooling of the point "K" during the second energy phase 320 can facilitate delivery of more heat to the point "P" during the first phase 310 of pulsed RF energy than would otherwise be possible without damaging the tissue "T" at the point "K." The pulsed RF energy can be cycled between the first energy phase 310 and the second energy phase 320 to deliver additional heat to the point "P" without exceeding a threshold temperature at the point "K." It should be appreciated that a higher temperature at the point "P" results in higher temperatures in tissue "T" adjacent to the point "P" and, thus, more generally, results in lesion sizes larger than those achievable with non-pulsed RF energy.

0253[0256] Referring now to FIGS. 1, 22, 23, and 27, the ablation electrode 224 can be positioned in an anatomic structure, at an interface between tissue and blood (e.g., at an interface between endocardial tissue and blood in a heart cavity of a patient) such that fluid (e.g., blood, irrigation fluid, or a combination thereof) in the anatomic structure can move past the ablation electrode 224 at the interface to cool the ablation electrode 224, according to any of the various different methods described herein, during a period of lesion formation. For example, the storage medium 109b can have stored thereon computer executable instructions for causing the processing unit 109a to control the ablation generator 116 to pulse the RF energy delivered from the ablation generator 1 16 to the ablation electrode 224 according to any one or more of the various different methods described herein. Additionally, or alternatively, it should be appreciated that the ablation generator 116 can include circuitry to pulse the RF energy delivered from the ablation generator 116 to the ablation electrode 224 according to any one or more of the various different methods described herein. Unless otherwise indicated, each of the following exemplary methods can be implemented using the ablation system 100 and/or one or more components thereof, including any of the various different catheters described herein.

0254[0257] Referring now to FIG. 30, an exemplary method 350 of delivering RF energy to target tissue can include placing 352 an ablation electrode at an interface between tissue and blood in an anatomic structure (e.g., at an interface between endocardial tissue and blood in a heart cavity of a patient), and delivering 354 RF energy to the ablation electrode at the interface.

0255[0258] Placing 352 the ablation electrode at the interface between tissue and blood in the anatomic structure can include any one or more of the various different methods of placement of an ablation electrode described herein. Thus, for example, placing 352 the ablation electrode at the interface between tissue and blood can include moving the ablation electrode into the anatomic structure by moving a distal portion of a catheter shaft, coupled to the ablation electrode, through vasculature of the patient. Additionally, or alternatively, placing 352 the ablation electrode at the interface between tissue and blood can include inserting a catheter into a patient according to the methods described with respect to FIGS. 13A-13E. Also, or instead, placing 352 the ablation electrode at the interface between tissue and blood can include positioning the ablation electrode at the interface according to the methods described with respect to FIGS. 14A-C.

0256[0259] Placing 352 the ablation electrode at the interface between tissue and blood can include expanding the at least a portion of the ablation electrode, according to any one or more of the various different methods described herein, such that blood, other fluids, or a combination thereof can move through the ablation electrode to provide cooling at the interface between tissue and blood. In addition, or instead, placing 352 the ablation electrode at the interface between tissue and blood can include positioning an outer surface of the ablation electrode in contact with fluid moving through the ablation electrode to provide cooling at the interface between tissue and blood.

0257[0260] Delivering 354 pulsed RF energy to the ablation electrode at the interface can include providing the first energy phase to ablate tissue at the interface and the second energy phase to cool tissue at the interface. Pulsing between the first energy phase and the second energy phase can create an alternating pattern of heating and cooling at a surface of the tissue. As described with respect to FIGS. 29A and 29B, for example, such an alternating pattern of heating and cooling can result in heat transfer patterns in tissue that facilitate formation of lesions larger than those that can otherwise be formed through the use of non-pulsed RF energy under similar conditions.

0258[0261] The parameters of the pulsed RF energy delivered 354 to the ablation electrode at the interface can impact local heat transfer at the interface and, therefore, can impact the size of the lesion formed in the presence of such local heating. Further, it should be understood that the impact of these parameters on local heat transfer at the interface can depend on a number of factors, including the type of tissue being treated, the amount of cooling provided at the interface, contact area between the ablation electrode and tissue at the interface, etc. In certain applications, however, delivering 354 pulsed RF energy can include repeatedly cycling between at least two cycles (with each cycle including at least the first energy phase and the second energy phase) to establish a local heat transfer pattern facilitating the formation of large lesions. Additionally, or alternatively, in some applications (e.g., ablation of endocardial tissue), the total period of lesion formation can be about 30 seconds to about three minutes.

0259[0262] During the first energy phase, the rate of heating of the interface by the ablation electrode can be greater than the rate of cooling at the interface by the fluid moving through the ablation electrode at the interface. In general, the first energy phase can have a duration sufficient to provide significant heat to tissue such that the lesion can progress (e.g., grow in size) during the first energy phase. In certain applications, such as forming lesions in endocardial tissue, the first phase of the pulsed RF energy can be greater than about 5 seconds and less than about 20 seconds (e.g., about ten seconds). [0263] In some implementations, the initial first energy phase can be longer than subsequent first energy phases. For example, the duration of each first energy phase can be based on exposing tissue to a predetermined target temperature for a given period of time. In such instances, because the initial first energy phase is initially applied to tissue at a baseline temperature (e.g., body temperature) and subsequent first energy phases are applied to tissue at a temperature above the baseline temperature, the initial first energy phase can be longer than the subsequent first energy phases to account for the additional time required to heat the tissue from the baseline temperature to the predetermined target temperature.

0260[0264] During the second energy phase, the rate of cooling at the interface by the fluid moving through the ablation electrode at the interface can be greater than the rate of heating of the interface by the ablation electrode. For example, the second energy phase can correspond to an off phase in which energy to the ablation electrode is interrupted during the second energy phase. Additionally, or alternatively, the second energy phase can correspond to low energy insufficient to heat the tissue in the presence of fluid moving through the ablation electrode. More generally, it should be appreciated that the duration of the second energy phase can impact the amount of cooling occurring at the interface. As an example, the duration of the second energy phase can be greater than 0 seconds and less than about 6 seconds to achieve suitable cooling after the first energy phase of a first cycle while maintaining the tissue at a sufficient temperature to resume ablating upon exposure to the first energy phase of a second, subsequent cycle of RF energy delivery.

0261[0265] In certain instances, one or both of the first energy phase and the second energy phase can have a predetermined duration. A predetermined duration of one or both of the first energy phase and the second energy phase can be useful, for example, for simplifying the software and/or hardware required to control of the pulsed RF energy delivered 354 to the interface.

0262[0266] In certain implementations, the exemplary method 350 can further include monitoring 356 tissue at the interface between tissue and blood in the anatomic structure of the patient. The monitoring 356 can be based, for example, on a signal measured at or near a point of contact between the ablation electrode and tissue. For example, monitoring 356 tissue can include directly or indirectly detecting a change in tissue. In general, a detected change in tissue can be used as feedback to control any one or more of various different parameters of the delivered 354 pulsed RF energy. Examples of parameters of the pulsed RF energy that can be controlled based at least in part on a detected change in tissue can include amplitude of the pulsed RF energy, duration of one or both of the first energy phase and the second energy phase, and duration of the lesion formation. As described in greater detail below, a detected change in tissue can be, additionally or alternatively, used as feedback to control any one or more of various different parameters associated with delivery of irrigation fluid to the ablation electrode.

0263[0267] Monitoring 356 tissue at the interface of tissue and blood in the anatomic structure can include, for example, receiving one or more signals indicative of temperature of the interface. The one or more signals can be any of various different temperature signals described herein. For example, the one or more signals can be received from a temperature sensor disposed at the interface (e.g., a thermistor of one or more of the sensors 126 in FIG. 3 and/or one or more thermocouples disposed along a deformable portion of the ablation electrode). In certain instances, a duration of one or more of the first energy phase and the second energy phase can be based on the received signal indicative of temperature at the interface. For example, if the received signal indicative of temperature is at or above an upper threshold value, the delivered 354 pulsed RF energy can be adjusted to switch from the first energy phase to the second energy phase. Additionally, or alternatively, if the received signal indicative of temperature is at or below a lower threshold value, the delivered 354 pulsed RF energy can be adjusted to switch from the second energy phase to the first energy phase. More generally, it should be appreciated that the received signal indicative of temperature at the interface can be used to maintain the tissue within a desired temperature range for a given amount of time.

0264[0268] Monitoring 356 tissue at the interface of tissue and blood in the anatomic structure can, additionally or alternatively, include detecting a change in an electrical signal associated with the RF energy delivered to the ablation electrode at the interface. The change in the electrical signal associated with the RF energy delivered to the ablation electrode can include, for example, detecting a change in tissue impedance, which can be indicative of lesion progress. In general, the impedance can be, for example, measured between two electrodes associated with the ablation electrode. For example, the impedance can be measured between a surface electrode (e.g., carried on a deformable portion of the ablation electrode) and a center electrode (e.g., carried on an irrigation element enveloped by the deformable portion of the ablation electrode), such as any of the various different surface electrodes and center electrodes described herein. Additionally, or alternatively, the impedance can be measured between the ablation electrode and an ablation return (e.g., a patch positioned outside of the body of the patient as a return path). In certain instances, the duration of one or more of the first energy phase and the second energy phase can be based on the detected change in the electrical signal. For example, a switch from the first energy phase to the second energy phase can be based on detecting a change in the electrical signal. While detecting a change in an electrical signal has been described as detecting a change in impedance, it should be appreciated, that a change in voltage or current can similarly be detected as an indication of lesion progress.

0265[0269] Monitoring 356 tissue at the interface of tissue and blood in the anatomic structure can, further or instead, include determining parameters of a model of the tissue and blood (e.g., one or more of a thermal model and an electrical model of the tissue and blood). Such a model can be useful, for example, for adjusting parameters of a controller for delivery of RF energy, delivery of irrigation fluid, or a combination thereof. Also, or instead, such a model can be useful for estimating temperature below the surface of the tissue, in certain instances.

0266[0270] In some implementations, monitoring 356 tissue at the interface of tissue and blood in the anatomic structure can include determining temperature response of the tissue to RF energy delivery and, independently, determining temperature response of the tissue to irrigation rate. For example, such independent determination of temperature response to RF energy delivery and to irrigation rate can be facilitated by delivering RF energy and irrigation fluid according to profiles that produce step changes in RF energy and irrigation fluid at different times. That is, continuing with this example, a step change in RF energy can be delivered to tissue while the irrigation rate is substantially constant, and a step change in the irrigation rate can be delivered to tissue while the RF energy delivered to tissue is substantially constant. As an additional or alternative example, independent determination of temperature response to RF energy delivery and irrigation rate can include adjusting one or more of RF energy delivery and irrigation rate with other orthogonal signals such as sinusoids or combinations of sinusoids. As a more specific example, the RF energy can be adjusted above and below a nominal value using a sine wave of a first frequency, while irrigation rate can be adjusted above and below a nominal value using a sine wave of a second frequency different from the first frequency. In general, it should be appreciated that, through independent variation of RF energy and irrigation rate, the impact of these parameters on tissue temperature can be substantially isolated to facilitate accurate control of tissue temperature.

0267[0271] In certain implementations, the exemplary method 350 further includes delivering 358 irrigation fluid (e.g., saline) to the interface between tissue and blood. In general, the irrigation fluid can be delivered 358 such that fluid moving through the ablation electrode during at least a portion of the period of lesion formation includes the delivered irrigation fluid (e.g., a combination of irrigation fluid and blood moves through the ablation electrode to cool the ablation electrode at the interface). In certain implementations, delivering 358 irrigation fluid to the interface between tissue and blood can provide more cooling to the interface between tissue and blood than would otherwise be achievable through only the flow of blood past the interface between tissue and blood. For example, the rate of cooling of the interface by a combination of blood and irrigation fluid moving through the ablation electrode at the interface can be greater than a rate of heating of the interface by the RF energy during the second energy phase.

0268Additionally, or alternatively, delivering 358 irrigation fluid to the interface between tissue and blood can facilitate controlling of the amount of cooling occurring at the interface between tissue and blood, as compared to cooling using only the flow of blood past the interface between tissue and blood.

0269[0272] Delivering 358 irrigation fluid to the interface between tissue and blood can include controlling, based on the monitored 356 tissue at the interface, a volumetric flow rate of irrigation fluid moving from a source of irrigation fluid through at least one orifice defined by an irrigation element. That is, control of the volumetric flow rate of irrigation fluid moving from the source of irrigation fluid through at least one orifice defined by an irrigation element can be based on a control loop including monitoring 356 tissue at the interface and delivering 358 irrigation fluid at the interface. The irrigation element can be, for example, any one or more of the various different irrigation elements described herein. Controlling the volumetric flow rate of irrigation fluid can include any of various different known methods of controlling volumetric flow rate of a fluid, including, for example, controlling rotational speed of a peristaltic pump arranged to move the irrigation fluid from the source of irrigation fluid through the at least one orifice defined by the irrigation element. [0273] In certain instances, delivering 358 irrigation fluid to the interface between tissue and blood can include, for example, cooling a surface of the ablation electrode in contact with the tissue at the interface. In general, delivering 358 irrigation fluid to the interface can include any one or more methods of providing irrigation fluid described herein and, thus, can include any one or more of various different methods of directing irrigation fluid from an irrigation element toward an inner surface of the ablation electrode, as described herein. It should be appreciated that directing irrigation fluid from the irrigation element toward the inner surface of the ablation electrode can facilitate convective cooling of the ablation electrode which, in turn, can promote conductive cooling of the outer surface of the ablation electrode in contact with tissue.

0270Additionally, or alternatively, at least a portion of the irrigation fluid can flow into direct contact with the outer surface of the ablation electrode in contact with tissue. It should be further appreciated that delivering 358 irrigation fluid to the interface can include mixing the irrigation fluid with blood moving through the ablation electrode and, thus, the combination of irrigation fluid and blood can provide convective cooling of the ablation electrode.

0271[0274] A flow rate (e.g., a volumetric flow rate) of the irrigation fluid delivered to the interface between tissue and blood can be controlled based on one or more parameters associated with ablation. Such control of the flow rate of irrigation fluid can be useful, for example, for balancing considerations of effective cooling with those of systemic limits of irrigation fluid in the body of the patient.

0272[0275] The flow rate of the irrigation fluid delivered to the interface can be based on the RF energy delivered to the ablation electrode at the interface. For example, the flow rate of the irrigation fluid can be changed from a low flow rate when RF energy is not being delivered to the ablation electrode to one or more higher flow rates when RF energy is being delivered to the ablation electrode. Additionally, or alternatively, the irrigation fluid can be pulsed between a first flow rate and a second flow rate less than the first flow rate. These pulsations can be timed to match substantially the cycling of the pulsed RF energy from between the first energy phase and the second energy phase. That is, the irrigation fluid can be delivered to the ablation electrode at the first flow rate substantially in phase with the first energy phase and at the second volumetric flow rate substantially in phase with the second energy phase. As used herein, a volumetric flow rate substantially in phase with an energy phase includes flow that occurs over more than half of the duration of the corresponding energy phase. Thus, for example, a volumetric flow rate should be understood to be substantially in phase with a corresponding energy phase when differences in delay between a fluid control system and an RF energy control system are accounted for.

0273[0276] The volumetric flow rate of irrigation fluid delivered to the interface can, further or instead, be based on sensed temperature (e.g., a sensed temperature at the interface). In general, it should be appreciated that controlling the flow rate of irrigation fluid based on sensed temperature can be useful for reducing the likelihood of overcooling at the onset of delivering ablation energy to tissue. More specifically, controlling the flow rate of irrigation fluid based on measured temperature can be useful for reducing the likelihood of cooling to such an extent that tissue is not ablated. In implementations in which the tissue is endocardial tissue, reducing the likelihood of such overcooling can have an associated advantage of reducing the likelihood of unintended endocardial sparing. As used herein, sensed temperature can be based on one or more received signals indicative of temperature sensed in an anatomic structure. For example, a plurality of signals indicative of sensed temperatures can be received from respective sensors disposed along the ablation electrode, according to any of the various different systems and methods described herein.

0274[0277] In implementations in which the flow rate of the irrigation fluid is delivered to the interface based on sensed temperature, the volumetric flow rate of the irrigation fluid can be decreased in response to one or more signals indicative of temperature being below a first predetermined threshold. Additionally, or alternatively, the volumetric flow rate can be increased in response to the one or more signals indicative of temperature being above a second predetermined threshold. The first predetermined threshold can be, for example, different from the second predetermined threshold. Such a difference in respective predetermined thresholds used as the basis for increasing and decreasing the volumetric flow rate of the irrigation fluid can be useful, for example, for introducing hysteresis into the temperature control loop. Such hysteresis can reduce the likelihood of unintended oscillation between high and low flow rates as the tissue responds to change in the volumetric flow rates.

0275[0278] It should be appreciated that the likelihood of unintended oscillation between high and low flow rates can further, or instead, be reduced by controlling a change in the volumetric flow rate (e.g., an increase, a decrease, or both) to occur over a temperature range corresponding to a range of the one or more signals indicative of temperature. As an example of a change in the volumetric flow rate over a range of temperatures, the volumetric flow rate can be increased according to a first predetermined function of the one or more signals indicative of temperature. Additionally, or alternatively, the volumetric flow rate can be decreased according to a second predetermined function of the one or more signals indicative of temperature. The first predetermined function and the second predetermined function can be, for example, the same over at least a portion of the temperature range associated with the change in the volumetric flow rate. In some instances, the first predetermined function and the second predetermined function can be different over at least a portion of the temperature range associated with the change in the volumetric flow rate. It should be appreciated that the first predetermined function and the second predetermined function can be any of various different types of functions over the temperature range and, thus, can include functions that are continuous or discontinuous (e.g., including a step change in the volumetric flow rate) over the temperature range. For example, one or more of the first predetermined function and the second predetermined function can be based on, for example, a continuous time derivative of temperature. Additionally, or

0276alternatively, one or more of the first predetermined function and the second predetermined function can be based on present and previous temperature values.

0277[0279] In general, the position of the maximum temperature of tissue at the interface is not known. Accordingly, in certain implementations the exemplary method 350 can include estimating the maximum temperature. For example, the exemplary method 350 can include receiving a plurality of signals from a respective plurality of sensors disposed along the ablation electrode. As compared to sensing temperature using only a single sensor, the use of a plurality of sensors (e.g., spatially separated from one another) can provide a better estimate of a maximum temperature at the interface, even if none of the sensors is directly located at the position of the maximum temperature. Additionally, or alternatively, the temperature of tissue as a function of depth below the tissue surface can be approximated with a parameterized model, such as a polynomial. For example, switching between the first phase and the second phase, with at least one of RF energy and irrigation rate differing between the first phase and the second phase, can cause temperature measured at the surface of the tissue to change. The rate of change in temperature can depend, for example, on the temperature below the surface of the tissue. Thus, the parameters of the parameterized model can be estimated using the rate of change in temperature measured at the surface of the tissue. Continuing with this example, the parameterized model can be used to adjust energy delivery to achieve a target temperature below the surface of the tissue.

0278[0280] In certain implementations, increasing the volumetric flow rate, decreasing the volumetric flow rate, or both can be based on a single signal of the plurality of signals, with the single signal corresponding to a maximum sensed temperature. This maximum sensed temperature, it should be understood, may or may not correspond to the actual maximum temperature at the interface between the ablation electrode and tissue. Nevertheless, this maximum sensed temperature can serve as a useful proxy for the actual maximum temperature. Further, or instead, the maximum sensed temperature can advantageously serve as a robust feedback parameter for controlling the volumetric flow rate.

0279[0281] In some implementations, increasing the volumetric flow rate, decreasing the volumetric flow rate, or both can be, further or instead, based on more complex processing of each signal of the plurality of signals. For example, without wishing to be bound by theory, heat transfer at the interface of the ablation electrode and tissue occurs according to Laplace's equation of heat transfer under conditions of uniform cooling. Thus, in implementations in which this approximation of uniform cooling is a suitable approximation, processing each signal of the plurality of signals indicative of temperature can be based on an inverse Laplacian operator. In such implementations, increasing the volumetric flow rate, decreasing the volumetric flow rate, or both can be based on, for example, a maximum signal of the processed signals indicative of temperature. Further, or instead, increasing the volumetric flow rate, decreasing the volumetric flow rate, or both can be based on one or more of a maximum time derivative of the respective signal (e.g., in the case of continuous time) and a time difference (e.g., in the case of discrete time).

0280[0282] While controlling volumetric flow has been described as being used to provide cooling as RF energy is pulsed, it should be more generally understood that the volumetric flow rate can be controlled through any of various different combinations of monitoring 356 tissue at the interface and delivering 358 irrigation fluid and, additionally or alternatively, as a function of any variation of the RF energy during the period of lesion formation. Thus, in addition to, or as an alternative to, controlling the volumetric flow rate of the irrigation fluid based on RF energy pulsation, the volumetric flow rate of the irrigation fluid can be controlled to facilitate monitoring temperature during a portion of the period of lesion formation according to any one or more of the methods described herein. For example, the response of measured temperature to RF energy delivery can be approximated (e.g., for small changes in RF energy delivery), as a linear system. By switching between the first phase and the second phase, with the RF energy delivery different between the first phase and the second phase, the RF energy delivery input to the system can undergo a step change. Using system identification techniques known in the art, the parameters of a linear system can be estimated based on the temperature response to this step change in RF energy. The parameters of the linear system can be used to adjust control parameters. Additionally, or alternatively, the response of the measured temperature to irrigation flow rate can be approximated, for small changes in irrigation flow rate, as a linear system. The parameters of the linear system can be estimated in a similar way, and these parameters can be used to adjust controller parameters.

0281[0283] As an example of controlling volumetric flow rate of the irrigation fluid based on RF energy pulsation, monitoring 356 tissue at the interface can include reducing the RF energy and reducing the volumetric flow rate of the irrigation fluid can be reduced during a measurement phase of the period of the lesion formation to provide a useful tool for accurately sensing temperature during lesion formation. In general, irrigation fluid can interfere with accurate sensing of temperature at the interface of the ablation electrode and tissue because the irrigation fluid is cooling the area in which temperature is to be measured. Accordingly, reducing the volumetric flow rate of the irrigation fluid can reduce interference with temperature sensing. Because the volumetric flow rate of the irrigation fluid is reduced and, thus, less cooling is provided at the interface, the reduction in the volumetric flow rate of the irrigation fluid can be accompanied by an associated reduction in RF energy to decrease the likelihood of overheating the tissue during a temperature measurement.

0282[0284] With the RF energy and the volumetric flow rate of the irrigation fluid reduced during the measurement phase of the period of lesion formation, monitoring 356 tissue at the interface can include receiving one or more signals indicative of temperature at the interface. These signals can be any one or more of the various signals described herein with respect to temperature sensing. Based on these one or more signals received during the measurement phase of the period of lesion formation, a temperature at the interface can be determined according to any one or more of the various methods described herein. Additionally, or alternatively, the temperature at the interface can be based on one or more signals indicative of temperature and received during a portion of the period of lesion formation other than the measurement phase in which the RF energy and the volumetric flow of the irrigation fluid are reduced. The determination of temperature can include estimation based on, for example, a plurality of signals received from a respective plurality of sensors disposed along the ablation electrode. The determined

0283temperature, it should be appreciated, can be used as a feedback parameter to control one or more of the volumetric flow rate of the irrigation fluid and the RF energy. For example, the determined temperature can form a basis for increasing or decreasing the volumetric flow rate to remain within a predetermined temperature range according to any of the various different methods of increasing and decreasing the volumetric flow rate described herein. Additionally, or alternatively, the determined temperature can form a basis for switching the RF energy between energy phases, such as the first energy phase and the second energy phase described herein. Further, or instead, the determined temperature can form a basis for titrating the RF energy delivered to the ablation electrode. Still further or in the alternative, the determined temperature can be displayed on a graphical user interface (e.g., as feedback to a physician).

0284[0285] Following the reduction of RF energy and the volumetric flow rate of the irrigation fluid to measure temperature, the RF energy and the volumetric flow rate of the irrigation fluid can be increased such that lesion formation continues. To the extent it is desirable in a given implementation to determine temperature again during lesion formation, it should be appreciated that the RF energy and the volumetric flow rate of the irrigation fluid can again be reduced and temperature determined. More generally, it should be understood that reduction of RF energy and irrigation fluid to determine temperature during a period of lesion formation can be done multiple times, as necessary, to control temperature at the interface of the ablation electrode and tissue.

0285[0286] While pulsed RF ablation has been described as being delivered through an ablation electrode including a deformable portion expandable to have a maximum cross-sectional dimension greater than a maximum cross-sectional dimension of a catheter shaft, other implementations are additionally or alternatively possible. For example, it should be understood that any one or more of the methods of delivering pulsed RF ablation to tissue described herein can be carried out using an RF ablation electrode with a closed tip (e.g., a tip that is impervious to the passage of blood), unless otherwise specified or made clear from the context. Further, or instead, it should be understood that any one or more of the methods of delivering pulsed RF ablation to tissue described herein can be carried out using an RF ablation electrode having a maximum cross-sectional dimension substantially equal to a maximum cross-sectional dimension of a catheter shaft on which the RF ablation electrode is carried. Thus, for example, lesion formation using pulsed RF ablation, as described herein, can be carried out using an RF ablation electrode including a closed tip and having a maximum cross-sectional dimension substantially equal to a maximum cross-sectional dimension of a catheter shaft.

0286[0287] The above systems, devices, methods, processes, and the like may be realized in hardware, software, or any combination of these suitable for a particular application. The hardware may include a general-purpose computer and/or dedicated computing device. This includes realization in one or more microprocessors, microcontrollers, embedded

0287microcontrollers, programmable digital signal processors or other programmable devices or processing circuitry, along with internal and/or external memory. This may also, or instead, include one or more application specific integrated circuits, programmable gate arrays, programmable array logic components, or any other device or devices that may be configured to process electronic signals.

0288[0288] It will further be appreciated that a realization of the processes or devices described above may include computer-executable code created using a structured programming language such as C, an object oriented programming language such as C++, or any other high-level or low level programming language (including assembly languages, hardware description languages, and database programming languages and technologies) that may be stored, compiled or interpreted to run on one of the above devices, as well as heterogeneous combinations of processors, processor architectures, or combinations of different hardware and software. In another aspect, the methods may be embodied in systems that perform the steps thereof, and may be distributed across devices in a number of ways. At the same time, processing may be distributed across devices such as the various systems described above, or all of the functionality may be integrated into a dedicated, standalone device or other hardware. In another aspect, means for performing the steps associated with the processes described above may include any of the hardware and/or software described above. All such permutations and combinations are intended to fall within the scope of the present disclosure. [0289] Embodiments disclosed herein may include computer program products comprising computer-executable code or computer-usable code that, when executing on one or more computing devices, performs any and/or all of the steps thereof. The code may be stored in a non-transitory fashion in a computer memory, which may be a memory from which the program executes (such as random access memory associated with a processor), or a storage device such as a disk drive, flash memory or any other optical, electromagnetic, magnetic, infrared or other device or combination of devices.

0289[0290] In another aspect, any of the systems and methods described above may be embodied in any suitable transmission or propagation medium carrying computer-executable code and/or any inputs or outputs from same.

0290[0291] The method steps of the implementations described herein are intended to include any suitable method of causing such method steps to be performed, consistent with the patentability of the following claims, unless a different meaning is expressly provided or otherwise clear from the context. So, for example performing the step of X includes any suitable method for causing another party such as a remote user, a remote processing resource (e.g., a server or cloud computer) or a machine to perform the step of X. Similarly, performing steps X, Y and Z may include any method of directing or controlling any combination of such other individuals or resources to perform steps X, Y and Z to obtain the benefit of such steps. Thus, method steps of the implementations described herein are intended to include any suitable method of causing one or more other parties or entities to perform the steps, consistent with the patentability of the following claims, unless a different meaning is expressly provided or otherwise clear from the context. Such parties or entities need not be under the direction or control of any other party or entity, and need not be located within a particular jurisdiction.

0291[0292] It should further be appreciated that the methods above are provided by way of example. Absent an explicit indication to the contrary, the disclosed steps may be modified, supplemented, omitted, and/or re-ordered without departing from the scope of this disclosure.

0292[0293] It will be appreciated that the methods and systems described above are set forth by way of example and not of limitation. Numerous variations, additions, omissions, and other modifications will be apparent to one of ordinary skill in the art. In addition, the order or presentation of method steps in the description and drawings above is not intended to require this order of performing the recited steps unless a particular order is expressly required or otherwise clear from the context. Thus, while particular embodiments have been shown and described, it will be apparent to those skilled in the art that various changes and modifications in form and details may be made therein without departing from the spirit and scope of this disclosure and are intended to form a part of the invention as defined by the following claims, which are to be interpreted in the broadest sense allowable by law.