Method for displaying catheter electrode-tissue contact in electro-anatomic mapping and navigation system

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Method for displaying catheter electrode-tissue contact in electro-anatomic mapping andnavigation system

St. Jude Medical, Atrial FibrillationDivision, Inc. C.184123 191733/2

BACKGROUND OF THE INVENTION a. Field of the Invention [0002] The instant invention is directed toward an electrode catheter and a method forusing the electrode catheter for tissue ablation. In particular, the electrode catheter of thepresent invention may comprise a circuit to assess electrode-tissue contact and electricalcoupling for applying ablative energy (e.g., RF energy) to target tissue. b. Background Art [0003] It is well known that benefits may be gained by forming lesions in tissue if thedepth and location of the lesions being formed can be controlled. In particular, it can bedesirable to elevate tissue temperature to around 50°C until lesions are formed viacoagulation necrosis, which changes the electrical properties of the tissue. For example,lesions may be formed at specific locations in cardiac tissue via coagulation necrosis tolessen or eliminate undesirable atrial fibrillations.

[0004] Several difficulties may be encountered, however, when attempting to formlesions at specific locations using some existing ablation electrodes. One such difficultyencountered with existing ablation electrodes is how to ensure adequate tissue contact andelectrical coupling. Electrode-tissue contact is not readily determined using conventionaltechniques such as fluoroscopy. Instead, the physician determines electrode-tissue contactbased on his/her experience using the electrode catheter. Such experience only comeswith time, and may be quickly lost if the physician does not use the electrode catheter ona regular basis. In addition, when forming lesions in a heart, the beating of the heart 1 191733/3 further complicated matters, making it difficult to determine and maintain sufficientcontact pressure between the electrode and the tissue for a sufficient length of time toform a desired lesion. If the contact between the electrode and the tissue cannot beproperly maintained, a quality lesion is unlikely to be formed. Similarly, information onelectrical coupling between the electrode and the target tissue is not readily available apriori to determine how much ablative energy may be absorbed in the tissue duringablation. Instead, the physician uses generalized pre-determined ablation parameters, suchas power and duration, based on his/her experience to perform ablation procedures withthe electrode catheter. Such experience may lead to deficiencies, inefficiencies andcomplications, such as inadequate lesion formation, premature high impedance shut-off,tissue charring, and thrombus formation.

[0005] Previous systems have attempted to provide information that allows a physician tomonitor tissue contact of an electrode catheter. For instance, U.S. Patent No. 5,673,704to Marchlinski allows for making a binary determination of tissue contact between anelectrode and patient tissue based on an impedance measurement. U.S. Patent No.6,490,474 to Willis utilizes an ultrasound monitoring system to extrapolate a position ofcatheter, which includes an ultrasound transducer, relative to patient tissue. EP 1,586,281and US 6,569,160 to Goldin utilizes a differential electrical response between twoelectrodes of a catheter to determine contact between an electrode and tissue.WO98/46149 is directed to a catheter system that identifies a maximum impedancemeasurement as a condition of maximum mechanical contact between a catheter electrodeand patient tissue. However, none of these references differentiate between differentlevels of electrical coupling between an electrode catheter and patient tissue.

BRIEF SUMMARY OF THE INVENTION

[0006] The present invention relates to providing an indication to the physician, via thenavigation system, concerning the electrical coupling of an electrode, such as an ablativeelectrode or mapping electrode, with the patient. During an electrode catheter procedure,a physician uses the navigation system for monitoring electrode position. The navigationsystem may provide real-time visualization of electrode movements and position inrelation to physiological structure of the patient.

[0007] It has been recognized that it is desirable to provide an indication concerningelectrode coupling with minimal distraction to the physician. This is particularly the casewhere the system is used not only for initially establishing a desired electrode position for 01841238\56-01 2 191733/2 a procedure, but also for monitoring electrode procedure during the procedure. This canbe accomplished, in accordance with the present invention, by providing an indication viaa monitor of the navigation system. In this manner, the physician can receivecontinuously or periodically (occasionally) updated electrode coupling information duringa medical procedure while the physician’s attention remains substantially fully directed tothe medical procedure.

[0008] In accordance with one aspect of the present invention, a method and apparatus(“utility”) is provided that supplies an indication to the physician, via the navigationsystem, concerning the electrical coupling of an electrode. The utility involvesestablishing an electrical coupling monitoring system for evaluating a tissue couplingrelationship. Any suitable monitoring system may be used in this regard, includingsystems based on impedance, phase angle, mechanical vibration or mechanicaldeformation measurements. The monitoring system is operative to distinguish between atleast two different electrode coupling levels (e.g., insufficient or sufficient coupling forthe procedure at issue) and may distinguish between more than two electrode couplinglevels (e.g., insufficient coupling, sufficient coupling and elevated coupling). In oneimplementation, the electrical coupling monitoring system employs a phase angletechnology where different electrode coupling levels are associated with different phaseangle ranges. The utility further involves operating said electrode coupling assessmentsystem in connection with a medical procedure to identify a level of electrode coupling.For example, the assessment system may be operated prior to initiation of an ablative ormapping procedure to analyze electrode coupling. Additionally or alternatively, theassessment system may be operated continuously or periodically during a medicalprocedure to monitor electrode coupling. An output is then provided indicating theidentified level of electrode coupling. In particular, the output is provided via thenavigation system used by the physician in monitoring the electrode. For example, thecolor or other display parameter of a representation of the electrode may be altered toindicate the level of electrode coupling. Additionally or alternatively, a waveformreflecting values of electrode coupling versus time may be provided in connection with adisplay of the navigation system.

[0009] In accordance with a still further aspect of the present invention, an electrodecatheter system is provided that allows for providing electrode coupling information with 01841238\56-01 3 191733/2 minimal distraction. An associated utility involves: an electrode adapted to applyelectrical energy; a catheter for enabling the electrode to be remotely operated by aphysician; guidance instrumentation for guiding the electrode relative to the physiologicalstructure of a patient; and a processor for receiving signal information and determining alevel of electrical coupling between the electrode and the patient. The guidanceinstrumentation includes at least a navigation system for use in monitoring a position ofthe electrode. The processor is further operative to control the navigation system toprovide an indication of the level of electrode coupling. In this regard, the processor candistinguish between a least two different levels of electrode coupling. In oneimplementation, the processor can distinguish between multiple levels of electrodecoupling, including a level indicating elevated coupling that may be associated with thepotential for penetrating tissue of interest. Such penetration may be desired or undesired.In either event, an indication of such elevated coupling can be useful to a physician. Thevarious levels of electrode coupling may be determined by any suitable technology. Inone implementation, the levels are distinguished based on a phase angle analysis.

[0010] The foregoing and other aspects, features, details, utilities, and advantages of thepresent invention will be apparent from reading the following description and claims, andfrom reviewing the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Fig. 1 is a diagrammatic illustration of an exemplary tissue ablation system whichmay be implemented to assess electrode-tissue contact during a tissue ablation procedurefor a patient.

[0012] Fig. la is a detailed illustration of the patient’s heart in Fig. 1, showing theelectrode catheter after it has been moved into the patient’s heart.

[0013] Fig. 2a illustrates exemplary levels of electrical contact or coupling between theelectrode catheter and a target tissue.

[0014] Fig. 2b illustrates exemplary levels of mechanical contact or coupling between theelectrode catheter and a target tissue.

[0015] Fig. 3 is a high-level functional block diagram showing the exemplary tissueablation system of Fig. 1 in more detail.

[0016] Fig. 4 is a model of the electrode catheter in contact with (or coupled to) targettissue. 01841238\56-01 4 191733/2 [0017] Fig. 4a is a simplified electrical circuit for the model shown in Fig. 4.

[0018] Fig. 5 is an exemplary phase detection circuit which may be implemented in thetissue ablation system for assessing electrode-tissue contact or coupling.

[0019] Fig. 6 is an exemplary block diagram showing phase angle measurement forcontact sensing and tissue sensing.

[0020] Fig. 7 is an exemplary block diagram showing phase angle measurement duringablation with both ablation energy and a contact sensing signal applied to the ablationelectrode at the same time.

[0021] Fig. 8 is an exemplary block diagram showing phase angle measurement duringablation with switching between a sensing signal and ablation power.

[0022] Fig. 9a illustrates one embodiment of a protocol that may be used to assess acoupling between an electrode and tissue based upon a phase angle comparison.

[0023] Fig. 9b illustrates one embodiment of a protocol that may be used to assess acoupling between an electrode and tissue based upon a reactance comparison.

[0024] Fig. 9c illustrates one embodiment of a protocol that may be used to assess acoupling between an electrode and tissue based upon an impedance components ratiocomparison.

[0025] Fig. 10 illustrates a representative, schematic representation of an electricalcoupling between an electrode and tissue.

[0026] Fig. 11a illustrates a schematic of one embodiment of an ablation system that usestwo power sources operating at different frequencies, where only one of these powersources is interconnected with the ablation electrode at any one time, and where one ofthese power sources is used for assessing a coupling between an electrode and tissue.[0027] Fig. 1 lb illustrates a schematic of one embodiment of an ablation system that usestwo power sources operating at different frequencies, where both power sources arealways interconnected with the ablation electrode, and where one of these power sourcesis used for assessing a coupling between an electrode and tissue.

[0028] Fig. 11c illustrates a schematic of one embodiment of an ablation system that usestwo power sources operating at least generally at the same frequency, where only one ofthese power sources is interconnected with the ablation electrode at any one time, andwhere each of these power sources may be used for assessing a coupling between anelectrode and tissue. 01841238\56-01 5 191733/2 [0029] Fig. 12a illustrates one embodiment of a system for assessing a coupling betweenan electrode and tissue.

[0030] Fig. 12b illustrates one embodiment of a protocol that may be used to assess acoupling between an electrode and tissue based upon identifying a baseline couplingcondition.

Fig. 12c illustrates one embodiment of a protocol that may be used to assess a couplingbetween an electrode and tissue based upon identifying a target frequency.

[0031] Fig. 13 is a schematic diagram of an electrode catheter system in accordance withthe present invention.

[0032] Fig. 14 is a schematic diagram of an electrode coupling output system inaccordance with the present invention.

[0033] Fig. 15 illustrates a handle set based electrode coupling output system inaccordance with the present invention.

[0034] Fig. 16 illustrates a handle set incorporated various types of output devices inaccordance with the present invention.

[0035] Fig. 17 illustrates a handle set incorporating a vibration device in accordance withthe present invention.

[0036] Fig. 18 is a schematic diagram of a navigation system based electrode couplingoutput system in accordance with the present invention.

[0037] Figs. 19A-20D illustrate graphical representations of an electrode in a navigationsystem display in accordance with the present invention.

[0038] Fig. 21 illustrates a navigation system display in accordance with the presentinvention.

[0039] Fig. 22 is a flow chart illustrating a process for outputting electrode couplinginformation via guidance instrumentation in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION 01841238\56-01 6 191733/2 [0040] The present invention relates to providing an indication regarding a condition ofinterest, e.g., a level of electrode coupling, to a physician via guidance instrumentation ofan electrode catheter system. While such an indication may be provided in connectionwith various parameters of interest in connection with an electrode catheter procedureand, specifically, in connection with a variety of electrode coupling assessmenttechnologies, certain advantage are achieved by using an assessment technology capableof accurately identifying multiple electrode coupling levels such as a phase angletechnology. In the following description, certain phase angle-related technologies arefirst described. Thereafter, various mechanisms for outputting information to thephysician are described in detail.

[0041] Fig. 1 is a diagrammatic illustration of an exemplary electrode catheter system 10which may be implemented to assess electrode-tissue contact during a tissue ablationprocedure for a patient 12. Catheter system 10 may include an electrode catheter 14,which may be inserted into the patient 12, e.g., for forming ablative lesions inside thepatient’s heart 16. During an exemplary ablation procedure, a user (e.g., the patient’sphysician or a technician) may insert the electrode catheter 14 into one of the patient’sblood vessels 18, e.g., through the leg (as shown in Fig. 1) or the patient’s neck. The user,guided by a real-time fluoroscopy imaging device (not shown), moves the electrodecatheter 14 into the patient’s heart 16 (as shown in more detail in Fig. la).

[0042] When the electrode catheter 14 reaches the patient’s heart 16, electrodes 20 at thetip of the electrode catheter 14 may be implemented to electrically map the myocardium22 (i.e., muscular tissue in the heart wall) and locate a target tissue 24. After locating thetarget tissue 24, the user must move the electrode catheter 14 into contact and electricallycouple the catheter electrode 14 with the target tissue 24 before applying ablative energyto form an ablative lesion or lesions. The electrode-tissue contact refers to the conditionwhen the catheter electrode 14 physically touches the target tissue 24 thereby causing amechanical coupling between the catheter electrode 14 and the target tissue 24. Electricalcoupling refers to the condition when a sufficient portion of electrical energy passes fromthe catheter electrode 14 to the target tissue 24 so as to allow efficient lesion creationduring ablation. For target tissues with similar electrical and mechanical properties,electrical coupling includes mechanical contact. That is, mechanical contact is a subset ofelectrical coupling. Thus, the catheter electrode may be substantially electrically coupledwith the target tissue without being in mechanical contact, but not vice-versa. In other 01841238X56-01 7 191733/2 words, if the catheter electrode is in mechanical contact, it is also electrically coupled.The range or sensitivity of electrical coupling, however, changes for tissues with differentelectrical properties. For example, the range of electrical coupling for electricallyconductive myocardial tissue is different from the vessel walls. Likewise, the range orsensitivity of electrical coupling also changes for tissues with different mechanicalproperties, such as tissue compliance. For example, the range of electrical coupling forthe relatively more compliant smooth atrial wall is different from the relatively lesscompliant pectinated myocardial tissue. The level of contact and electrical coupling areoften critical to form sufficiently deep ablative lesions on the target tissue 24 withoutdamaging surrounding tissue in the heart 16. The catheter system 10 may be implementedto measure impedance at the electrode-tissue interface and assess the level of contact(illustrated by display 11) between the electrode catheter 14 and the target tissue 24, asdescribed in more detail below.

[0043] Fig. 2a illustrates exemplary levels of electrical contact or coupling between anelectrode catheter 14 and a target tissue 24. Fig. 2b illustrates exemplary levels ofmechanical contact or coupling between an electrode catheter 14 and a target tissue 24.Exemplary levels of contact or coupling may include “little or no contact” as illustratedby contact condition 30a, “light to medium contact” as illustrated by contact condition30b, and “hard contact” as illustrated by contact condition 30c. In an exemplaryembodiment, the catheter system 10 may be implemented to display or otherwise outputthe contact condition for the user, e.g., as illustrated by light arrays 31a-c correspondingto contact conditions 30a-c, respectively.

[0044] Contact condition 30a (“little or no contact”) may be experienced before theelectrode catheter 14 comes into contact with the target tissue 24. Insufficient contact mayinhibit or even prevent adequate lesions from being formed when the electrode catheter14 is operated to apply ablative energy. However, contact condition 30c (“hard contact”)may result in the formation of lesions which are too deep (e.g., causing perforations in themyocardium 22) and/or the destruction of tissue surrounding the target tissue 24.Accordingly, the user may desire contact condition 30b (“light to medium contact”).[0045] It is noted that the exemplary contact or coupling conditions 30a-c in Fig. 2a-b areshown for purposes of illustration and are not intended to be limiting. Other contact orcoupling conditions (e.g., finer granularity between contact conditions) may also existand/or be desired by the user. The definition of such contact conditions may depend at 01841238\56-01 8 191733/2 least to some extent on operating conditions, such as, the type of target tissue, desireddepth of the ablation lesion, and operating frequency of the RF radiation, to name only afew examples.

[0046] Fig. 3 is a high-level functional block diagram showing the catheter system 10 inmore detail as it may be implemented to assess contact or coupling conditions for theelectrode catheter 14. It is noted that some of the components typical of conventionaltissue ablation systems are shown in simplified form and/or not shown at all in Fig. 1 forpurposes of brevity. Such components may nevertheless also be provided as part of, or foruse with the catheter system 10. For example, electrode catheter 14 may include a handleportion, a fluoroscopy imaging device, and/or various other controls, to name only a fewexamples. Such components are well understood in the medical devices arts and thereforefurther discussion herein is not necessary for a complete understanding of the invention.[0047] Exemplary catheter system 10 may include a generator 40, such as, e.g., a radiofrequency (RF) generator, and a measurement circuit 42 electrically connected to theelectrode catheter 14 (as illustrated by wires 44 to the electrode catheter). The electrodecatheter 14 may also be electrically grounded, e.g., through grounding patch 46 affixed tothe patient’s arm or chest (as shown in Fig. 1).

[0048] Generator 40 may be operated to emit electrical energy (e.g., RF current) near thetip of the electrode catheter 14. It is noted that although the invention is described hereinwith reference to RF current, other types of electrical energy may also be used forassessing contact conditions.

[0049] In an exemplary embodiment, generator 40 emits a so-called “pinging” (e.g., low)frequency as the electrode catheter 14 approaches the target tissue 24. The “pinging”frequency may be emitted by the same electrode catheter that is used to apply ablativeenergy for lesion formation. Alternatively, a separate electrode catheter may be used forapplying the “pinging” frequency. In such an embodiment, the separate electrode may bein close contact with (or affixed to) the electrode for applying ablative energy so that acontact or coupling condition can be determined for the electrode which will be applyingthe ablative energy.

[0050] The resulting impedance at the electrode-tissue interface may be measured duringcontact or coupling assessment (or “pinging”) using a measurement circuit 42. In anexemplary embodiment, the measurement circuit 42 may be a conventionally availableresistance-capacitance-inductance (RCL) meter. Another exemplary measurement circuit 0I841238\56-01 9 191733/2 which may be implemented for determining the phase angle component is also describedin more detail below with reference to Fig. 5. Still other measurement circuits 42 may beimplemented and the invention is not limited to use with any particular type orconfiguration of measurement circuit.

[0051] The reactance and/or phase angle component of the impedance measurements maybe used to determine a contact or coupling condition. The contact or coupling conditionmay then be conveyed to the user in real-time for achieving the desired level of contact orcoupling for the ablation procedure. For example, the contact or coupling condition maybe displayed for the user on a light array (e.g., as illustrated in Fig. 2a-b).

[0052] After the user has successfully guided the electrode catheter 14 into the desiredcontact or coupling condition with the target tissue 24, a generator, such as generator 40or a second generator, may be operated to generate ablative (e.g., high frequency) energyfor forming an ablative lesion or lesions on the target tissue 24. In an exemplaryembodiment, the same generator 40 may be used to generate electrical energy at variousfrequencies both for the impedance measurements (e.g., “pinging” frequencies) and forforming the ablative lesion. In alternative embodiments, however, separate generators orgenerating units may also be implemented without departing from the scope of theinvention.

[0053] In an exemplary embodiment, measurement circuit 42 may be operativelyassociated with a processor 50 and memory 52 to analyze the measured impedance. Byway of example, processor 50 may determine a reactance and/or phase angle componentof the impedance measurement, and based on the reactance component and/or phaseangle, the processor 50 may determine a corresponding contact or coupling condition forthe electrode catheter 14. In an exemplary embodiment, contact or coupling conditionscorresponding to various reactance and/or phase angles may be predetermined, e.g.,during testing for any of a wide range of tissue types and at various frequencies. Thecontact or coupling conditions may be stored in memory 52, e.g., as tables or othersuitable data structures. The processor 50 may then access the tables in memory 42 anddetermine a contact or coupling condition corresponding to impedance measurementbased on the reactance component and/or phase angle. The contact or coupling conditionmay be output for the user, e.g., at display device 54.

[0054] It is noted, that the catheter system 10 is not limited to use with processor 50 andmemory 52. In other embodiments, analog circuitry may be implemented for assessing 01841238\56-01 10 191733/2 contact conditions based on the impedance measurement and for outputting acorresponding contact condition. Such circuitry may be readily provided by one havingordinary skill in the electronics arts after having become familiar with the teachingsherein, and therefore further discussion is not needed.

[0055] It is also noted that display device 54 is not limited to any particular type ofdevice. For example, display device 54 may be a computer monitor such as a liquid-crystal display (LCD). Alternatively, display device may be implemented as a light array,wherein one or more light emitting diodes (LED) are activated in the light array toindicate a contact condition (e.g., more lights indicating more contact). Indeed, anysuitable output device may be implemented for indicating contact conditions to a user,and is not limited to a display device. For example, the contact condition may be output tothe user as an audio signal or tactile feedback (e.g., vibrations) on the handle of theelectrode catheter.

[0056] It is further noted that the components of catheter system 10 do not need to beprovided in the same housing. By way of example, measurement circuit 42 and/orprocessor 50 and memory 52 may be provided in a handle portion of the electrodecatheter 14. In another example, at least part of the measurement circuit 42 may beprovided elsewhere in the electrode catheter 14 (e.g., in the tip portion). In still otherexamples, processor 50, memory 52, and display device 54 may be provided as a separatecomputing device, such as a personal desktop or laptop computer which may beoperatively associated with other components of the catheter system 10.

[0057] Assessing a contact or coupling condition between the electrode catheter 14 andtarget tissue 24 based on impedance measurements at the electrode-tissue interface maybe better understood with reference to Figs. 4 and 4a. Fig. 4 is a model of the electrodecatheter 14 in contact with (or coupled to) target tissue 24. The electrode catheter 14 iselectrically connected to the generator 40 (e.g., an RF generator). In an exemplaryembodiment, the circuit may be completed through the target tissue 24, showing thatcurrent flows through the blood, myocardium, and other organs to the reference electrode,such as a grounding patch 46 on the patient’s body (Fig. 1).

[0058] As described above, the generator 40 may be operated to generate electricalenergy for emission by the electrode catheter 14. Emissions are illustrated in Fig. 4 byarrows 60. Also as described above, generator 40 may emit a “pinging” frequency as theelectrode catheter 14 approaches the target tissue 24 for assessing electrode-tissue contact 01841238\56-01 11 191733/2 or coupling. In an exemplary embodiment, this “pinging” frequency may be selected suchthat inductive, capacitive, and resistive effects other than those at the blood-tissueinterface do not appreciably affect the impedance measurements.

[0059] In an exemplary application, capacitive effects of the blood and at the electrode-blood interface (e.g., between the metal electrode catheter and the blood) were found beminimal or even non-existent at frequencies higher than about 50 kHz. Stray inductance(e.g., due to the relatively thin catheter wires), capacitance and resistance at the electrodeinterface, and capacitance effects of other organs (e.g., the lungs) were also found to beminimal or even non-existent at frequencies higher than about 50 kHz.

[0060] In addition, it was found that resistive effects dominate at the blood-tissueinterface for frequencies below 50 kHz because the current flows into the target tissue 24primarily via the interstitial fluid spaces 23, and the cell membranes 25 (e.g., bi-lipids or“fat”) act as an insulator. However, at frequencies greater than about 50 kHz, the cellmembranes 25 become conductive, and electrical current penetrates the target tissue 24through both the interstitial fluid spaces 23 and the cell membranes 25. Accordingly, thecell membranes act as “capacitors” and the resistive effects are reduced at frequenciesabove about 50 kHz.

[0061] To avoid a risk of creating an ablation lesion during contact or couplingassessment, it can be desirable to use a low amount of current and power. A presentlypreferred range for a current of less than 1mA is a working frequency in the 50~500 kHzrange.

[0062] The frequency choice is mostly based on physiological aspect and engineeringaspect and is within the purview of one of ordinary skill in the art. For physiologicalaspect, lower frequencies can introduce measurement errors due to electrode-electrolyteinterface. When frequency goes higher to MHz range or above, the parasitic capacitancecan become significant. It is noted, however, that the invention is not limited to use at anyparticular frequency or range of frequencies. The frequency may depend at least to someextent on operational considerations, such as, e.g., the application, the type of targettissue, and the type of electrical energy being used, to name only a few examples.

[0063] Assuming, that a desired frequency has been selected for the particularapplication, the model shown in Fig. 4 may be further expressed as a simplified electricalcircuit 62, as shown in Fig. 4a. In the circuit 62, generator 40 is represented as an ACsource 64. As discussed above, capacitance and resistance at the blood-tissue interface 01841238\56-01 12 191733/2 dominate impedance measurements at low frequency operation such as may be used forassessing electrode-tissue contact. Accordingly, other capacitive, inductive, and resistiveeffects may be ignored and the capacitive-resistive effects at the blood-tissue interfacemay be represented in circuit 62 by a resistor-capacitor (R-C) circuit 66.

[0064] The R-C circuit 66 may include a resistor 68 representing the resistive effects ofblood on impedance, in parallel with a resistor 70 and capacitor 72 representing theresistive and capacitive effects of the target tissue 24 on impedance. When the electrodecatheter 14 has no or little contact with the target tissue 24, resistive effects of the bloodaffect the R-C circuit 66, and hence also affect the impedance measurements. As theelectrode catheter 14 is moved into contact with the target tissue 24, however, theresistive and capacitive effects of the target tissue 24 affect the R-C circuit 66, and hencealso affect the impedance measurements.

[0065] The effects of resistance and capacitance on impedance measurements may bebetter understood with reference to a definition of impedance. Impedance (Z) may beexpressed as:

Z=R + jX where: R is resistance from the blood and/or tissue; j an imaginary number indicating the term has a phase angle of +90degrees; and X is reactance from both capacitance and inductance.

[0066] It is observed from the above equation that the magnitude of the reactancecomponent responds to both resistive and capacitive effects of the circuit 62. Thisvariation corresponds directly to the level of contact or coupling at the electrode-tissueinterface, and therefore may be used to assess the electrode-tissue contact or coupling. Byway of example, when the electrode catheter 14 is operated at a frequency of 100 kHz andis primarily in contact with the blood, the impedance is purely resistive and the reactance(X) is close to 0 Ohms. When the electrode catheter 14 contacts the target tissue, thereactance component becomes negative. As the level of contact or coupling is increased,the reactance component becomes more negative. 01841238\56-01 13 191733/2 [0067] Alternatively, contact or coupling conditions may be determined based on thephase angle. Indeed, determining contact or coupling conditions based on the phase anglemay be preferred in some applications because the phase angle is represented as atrigonometric ratio between reactance and resistance. Although the magnitude of thereactance component may be different under varying conditions (e.g., for differentpatients), the phase angle is a relative measurement which tends to be insensitive toexternal conditions.

[0068] In an exemplary embodiment, the phase angle may be determined from theimpedance measurements (e.g., by the processor 50 in Fig. 3). That is, impedance may beexpressed as: Z=|Z|Z<z} where: |Z| is the magnitude of the impedance; andφ is the phase angle.

[0069] The terms |Z| and φ may further be expressed as: |Z| = vlR2+X2 ; and tan φ = —

R

[0070] The phase angle also corresponds directly to the level of contact or coupling at theelectrode-tissue interface, and therefore may be used to assess the electrode-tissue contactor coupling. By way of example, when the electrode catheter 14 is operated at afrequency of 100 kHz and is primarily in contact with the blood, the phase angle is closeto zero (0). When the electrode catheter 14 contacts the target tissue, the phase anglebecomes negative, and the phase angle becomes more negative as the level of contact orcoupling is increased. An example is shown in Table 1 for purposes of illustration. TABLE 1: Phase Angle Relation to Contact Conditions

Phase Angle Contact Condition φ>-3° little or no contact or coupling 01841238\56-01 14 191733/2 -3° < φ < -7° medium contact or coupling -7°< φ <-10° high contact or coupling φ <-10° excessive contact or coupling [0071] Although impedance measurements may be used to determine the phase angle, inan alternative embodiment, the measurement circuit 42 may be implemented as a phasedetection circuit to directly determine the phase angle. An exemplary phase detectioncircuit 80 is shown in Fig. 5. Phase detection circuit 80 is shown and described withreference to functional components. It is noted that a particular hardware configuration isnot necessary for a full understanding of the invention. Implementation of the phasedetection circuit 80 in digital and/or analog hardware and/or software will be readilyapparent to those having ordinary skill in the electronics art after becoming familiar withthe teachings herein.

[0072] Exemplary phase detection circuit 80 may include a current sensor 82 and voltagesensor 84 for measuring current and voltage at the electrode-tissue interface. The currentand voltage measurements may be input to a phase comparator 86. Phase comparator 86provides a direct current (DC) output voltage proportional to the difference in phasebetween the voltage and current measurements.

[0073] In one embodiment, the current sensor 82 may be used to measure the ablationcurrent. The sensor can be in series with ablation wire. For example, a Coilcraft CST1current sensing transformer may be placed in series with the ablation wire. Alternatively,the current wire can pass through holes of a current sensor, with or without physicalconnection. In addition, the voltage between the ablation electrode and the ground patchcan be sensed. This voltage can be attenuated so that it can be fed into a phase sensingcircuit. The phase sensing circuit then measures the current and voltage and determinesthe phase angle between them, which is then correlated to a coupling level. In this waythe ablation current can be used to measure the phase angle rather than injecting anadditional current for the coupling sensing purpose.

[0074] Optionally, current measurements may be phase shifted by phase shift circuit 88to facilitate operation of the phase comparator 86 by “correcting” phase lag between themeasured current and the measured voltage. Also optionally, output from the phasecomparator 86 may be “corrected” by phase adjustment circuit 90 to compensate forexternal factors, such as the type of grounding patch 46 being used. A signal scaling 01841238\56-01 15 191733/2 circuit 92 may also be provided to amplify the output (e.g., from milli-volts to volts) foruse by various devices (e.g., the processor 50 and display device 54 in Fig. 3).

[0075] During ablation, the measured impedance, and its component’s resistance andreactance, change with tissue temperature. In such conditions, the change due to changesin tissue temperature provides a measure of lesion formation during ablation.

[0076] It is noted that phase detection circuit 80 shown in Fig. 5 is provided as oneexample, and is not intended to be limiting. Other implementations may also be readilyprovided by those having ordinary skill in the electronics arts after becoming familiarwith the teachings herein without departing from the scope of the invention.

[0077] Having described exemplary systems for electrode contact assessment, exemplaryoperational modes may now be better understood with reference to the block diagramsshown in Fig. 6-8. Fig. 6 is an exemplary block diagram 100 showing phase anglemeasurement for sensing contact or coupling. Fig. 7 is an exemplary block 200 diagramshowing phase angle measurement during ablation with both ablation energy and acontact sensing signal applied to the ablation electrode at the same time. Fig. 8 is anexemplary block diagram 300 showing phase angle measurement during ablation withswitching between sensing signal and ablation power. It is noted that 200-series and 300-series reference numbers are used in Fig. 7 and Fig. 8, respectively, to denote similarelements and these elements may not be described again with reference to Fig. 7 and Fig.8.

[0078] As noted above, the phase angle method of sensing contact or coupling is basedon the fact that (1) tissue is both more resistive and capacitive than blood, and (2)measured electrode impedance is mostly dependant on the immediate surroundingmaterials. Thus, when an electrode moves from blood to myocardium, the measuredimpedance value increases and phase angles change from 0° to negative values(capacitive). Phase angle may be used to represent the contact or coupling levels becausephase angle is a relative term of both resistance and reactance. That is, it provides a 0°base line when the electrode is in contact with blood, and becomes increasingly morenegative as more contact or coupling is established. It also minimizes the influence of thecatheter, instrumentation, and physiological variables.

[0079] The phase angle measurement may be made by sampling both electrical voltage(V) 102 and current (I) 104 of a load and calculating the lag between those signals as thephase angle. As shown in Fig. 6, a sensing signal 106 is applied between the ablation 01841238\56-01 16 191733/2 electrode 108 and a reference electrode 110. This sensing signal 106 can, for example, bebetween 50 to 500 kHz at a small amplitude (&lt;1 mA).

[0080] Exemplary instruments may be operated as frequencies of, for example but notlimited to, 100 kHz, 400 kHz and 485 kHz, depending on the reference electrodeconfiguration. Both current 104 and voltage 102 are sensed. These two signals aretransmitted to a phase comparator 112 to calculate phase angle, which corresponds to thecontact or coupling condition of the electrode 108. The raw phase angle signal is adjustedin block 114 to compensate for external influence on the phase angle, e.g., caused by thecatheter, instrumentation, and physiological variables. It is also conditioned for easyinterpretation and interface and then output in block 116 to other equipments for displayor further processing.

[0081] The phase compensation may be achieved at the beginning of an ablationprocedure. First, the catheter electrode is maneuvered to the middle of the heart chamber(e.g., the right atrium or left atrium) so that the electrode 108 only contacts blood. Thesystem measures the phase angle and uses this value as a baseline for zero contact level.This adjustment compensates the fixed phase angles caused by catheter and patient suchas catheter wiring, location of the reference electrode and skin or adiposity if externalpatch is used.

[0082] After the initial zero adjustment, the user may maneuver the catheter electrode toone or more desired sites to ablate arrhythmic myocardium. In an exemplary embodiment,the phase angle starts to change when the electrode 108 approaches to say within 3mmfrom the myocardium and becomes increasingly more negative as more contact orcoupling is established. The user may judge the quality of electrode contact or couplingbefore administering the ablation energy based on phase angle output. In an exemplaryembodiment, this phase angle value is about -3° when a 4mm ablation electrode actuallycontacts the myocardium. It is noted that there are at least two methods to measure phaseangle during ablation, as described in more detail now with reference to Fig. 7 and Fig. 8.[0083] In Fig. 7, ablation power 218 is applied to the electrode 208 while the sensingsignal 206 is applied as well. The ablation and contact sensing operate at differentfrequencies. Accordingly, with filtering, the phase angle can be measured during ablationwithout disturbing the ablation of the myocardium.

[0084] Another option is to switch the phase measurement between the sensing signal306 and ablation power 318, as indicated by switch 320 in Fig. 8. When the ablation 01841238\56-01 17 191733/2 power 318 is switched off during approach, the small amplitude sensing signal 306 isswitched on and used to measure phase angle for sensing contact or coupling. When theablation power 318 is switched on for the ablation procedure, the voltage and current ofthe large amplitude ablation power 318 are sensed and used as the contact or couplingindicator during ablation.

[0085] Fig. 9a illustrates one embodiment of an electrode coupling assessmentprotocol 400 (hereafter "assessment protocol 400") that may be used to assess thecoupling of an electrode (e.g., a catheter electrode) with any appropriate tissue, where thisassessment is phase angle based. Therefore, the protocol 400 may be used in relation tothe embodiments discussed above in relation to Figs. 6-8. In any case, "coupling" mayinclude an electrical coupling of an electrode with a target tissue, a mechanical couplingbetween an electrode and the target tissue, or both.

[0086] Step 402 of the assessment protocol 400 of Fig. 9a is directed to sending anelectrical signal to an electrode. Typically this will be after the electrode has beenpositioned at least in the general vicinity of the target tissue (e.g., within a heart chamber,such as the left atrium). A phase angle is thereafter determined at step 404, and theelectrode coupling is thereafter assessed at step 408 based upon this phase angle. Theelectrode coupling assessment from step 408 may be categorized through execution ofstep 410. However, the categorization of step 410 may not be required in all instances.In any case, the result of the assessment from step 408 is output pursuant to step 412.[0087] The electrical signal that is sent pursuant to step 402 of the protocol 400 may be atany appropriate frequency. However, only a single frequency is required to make theassessment for purposes of the protocol 400. The phase angle associated with step 404may be the phase angle of the impedance. This phase angle may be determined in anyappropriate manner, for instance using a phase sensing circuit of any appropriateconfiguration. In one embodiment and using the electrical signal associated with step402, the phase angle is determined by measuring the current at the electrode, measuringthe voltage between the electrode and another electrode (e.g., a return electrode), and thendetermining the phase angle between these current and voltage measurements. Anotheroption would be to measure/determine the reactance and impedance in an appropriatemanner, and to then determine the phase angle from these values (e.g., the sine of thephase angle being the ratio of the reactance to the impedance). 01841238\56-01 18 191733/2 [0088] The phase angle may be determined using an RCL meter or a phase detectioncircuit (e.g., having an oscillator, multiplexer, filter, phase detection circuit), and may bereferred to as a phase module. This phase module (measurement and/or detection) maybe disposed at any appropriate location, such as by being incorporated into or embeddedin the catheter handle set, by being in the form of a standalone unit between the ablationcatheter and the power generator, by being incorporated into or embedded in the powergenerator, by being incorporated into an electrophysiology or EP mapping system, or bybeing part of an electrophysiology recording system.

[0089] Assessment of the coupling of the electrode with the tissue (step 408 of theprotocol 400) may be undertaken in any appropriate manner. For instance, the phaseangle determined through step 404 may be compared with one or more benchmark phaseangle values (e.g., using a phase angle comparator). These benchmark phase angle valuesmay be determined/set in any appropriate manner, for instance empirically. Thesebenchmark phase angle values may be stored in an appropriate data structure, for instanceon a computer-readable data storage medium, or otherwise may be made available to aphase angle comparator. Generally and in one embodiment, the phase angle decreases asmore electrode-tissue (e.g., myocardium) coupling exists.

[0090] There may be one or more benchmark phase angle values (e.g., a singlebenchmark phase angle value or a range of benchmark phase angle values) for one ormore of the following conditions for purposes of the categorization of step 410 of theassessment protocol 400 of Fig. 9a: 1) insufficient electrode coupling (e.g., an electrodecoupling where the associated phase angle being less than "A" is equated -with aninsufficient electrode coupling); 2) sufficient electrode coupling (e.g., an electrodecoupling with an associated phase angle greater than "A" and less than "B" being equatedwith a sufficient electrode coupling); and 3) elevated or excessive electrode coupling(e.g., an electrode coupling where the associated phase angle being greater than "B" isequated with an elevated or excessive electrode coupling). One embodiment equates thefollowing phase angle values with the noted conditions: insufficient electrode coupling: Φ > -5° sufficient electrode coupling: -5° > Φ > -10° elevated/excessive electrode coupling: Φ < -10° 01841238\56-01 19 191733/2 [0091] An "elevated" or "excessive" electrode coupling may be elevated/excessive inrelation to the electrical coupling, the mechanical coupling, or both (the coupling betweenthe electrode and the target tissue). In one embodiment, an elevated/excessive or hardelectrode coupling means an elevated/excessive mechanical contact between the electrodeand the target tissue. It may be desirable to know when an elevated or excessivemechanical contact exists between the electrode and tissue for a variety of reasons. Forinstance, it may be desirable to avoid an elevated or excessive mechanical contactbetween the electrode and the target tissue (e.g., to reduce the likelihood of directing theelectrode through a tissue wall, membrane, or the like). However, it may also bedesirable to know when a sufficient mechanical force is being exerted on the target tissueby the electrode (e.g., to increase the likelihood of directing the electrode through a tissuewall, membrane, or the like to gain access to a desired region on the other side of thistissue wall or membrane).

[0092] The result of the assessment of step 408 may be output in any appropriate mannerpursuant to step 412 of the electrode coupling assessment protocol 400 of Fig. 9a. Anyappropriate output may be utilized, for instance visually (e.g., a bar graph or any otherappropriate display at any appropriate location or combination of locations), audibly (e.g.,an alarm), physically (e.g., by vibrating a handle being held by a physician that isperforming an electrode-based procedure, and as discussed in more detail herein), or anycombination thereof. A single output may be provided. A combination of two or moreoutputs may also be utilized. One or more outputs may be issued to a single location or tomultiple locations.

[0093] Fig. 9b illustrates one embodiment of an electrode coupling assessment protocol400' that may be used to assess the coupling of an electrode (e.g., a catheter electrode)with any appropriate tissue, where this assessment is reactance based. As the protocol400' is a variation of the protocol 400 of Fig. 9a, a "single prime" designation is used inrelation the reference numerals that identify the individual steps of the protocol 400' ofFig. 9b.

[0094] Step 402' of the assessment protocol 400' of Fig. 9b is directed to sending anelectrical signal. Only a single frequency is required for the protocol 400' to provide itsassessment. That is, the electrode coupling assessment may be provided using a singlefrequency in the case of the assessment protocol 400'. Typically this will be after theelectrode has been positioned at least in the general vicinity of the target tissue (e.g., 01841238\56-01 20 191733/2 within a heart chamber). A reactance of the electrical circuit that includes the electrodeand the target tissue is thereafter determined at step 404'. This reactance may bedetermined in any appropriate manner. For instance, the phase angle may be measured(e.g., in accordance with the foregoing), the impedance may be measured, and thereactance may be calculated from these two values (e.g., the sine of the phase angle isequal to the ratio of the reactance to the impedance). Another option for determining thereactance would be to determine the phase or frequency response of a pulse wave .

[0095] The electrode coupling is assessed at step 408' of the protocol 400' based upon theabove-noted reactance. This electrode coupling from step 408' may be categorizedthrough execution of step 410'. However, the categorization of step 410' may not berequired in all instances. In any case, the result of the assessment is output pursuant tostep 412'. Step 412' may correspond with step 412 of the electrode coupling assessmentprotocol 400 of Fig. 9a.

[0096] Assessment of the electrode coupling with the tissue (step 408' of the protocol400') may be undertaken in any appropriate manner. For instance, the reactancedetermined through step 404' may be compared with one or more benchmark reactancevalues (e.g., using a reactance comparator). These benchmark reactance values may bedetermined/set in any appropriate manner, for instance empirically. These benchmarkreactance values may be stored in an appropriate data structure, for instance a computer -readable data storage medium, or otherwise may be made available to a reactancecomparator. Generally and in one embodiment, the reactance decreases as moreelectrode-tissue (e.g., myocardium) coupling exists.

[0097] There may be one or more benchmark reactance values (e.g., a single benchmarkreactance value or a range of benchmark reactance values) for one or more of thefollowing conditions for purposes of the categorization of step 410': 1) insufficient electrode coupling (e.g., an electrode coupling where the associated reactance being lessthan "A" is equated with insufficient electrode coupling); 2) sufficient electrode coupling(e.g., an electrode coupling with an associated reactance greater than "A" and less than"B" being equated with a sufficient electrode coupling); and 3) elevated or excessiveelectrode coupling (e.g., an electrode coupling where the associated reactance beinggreater than "B" is equated with an elevated or excessive electrode coupling). Oneembodiment equates the following reactance values for the noted conditions: insufficient electrode coupling: X > -5 01841238X56-01 21 191733/2 sufficient electrode coupling: -5 > X > -15 elevated/excessive electrode coupling: X < -15 [0098] One benefit of basing the electrode coupling assessment upon phase angle is thatthe phase angle is more insensitive to changes from patient to patient, or operation setup,than both impedance or reactance when considered alone or individually. Other ways ofrealizing less sensitivity to changes from tissue to tissue or such other conditions may beutilized to provide an electrode coupling assessment. Fig. 9c illustrates such anembodiment of an electrode coupling assessment protocol 480 — a protocol 480 that maybe used to assess the coupling of an electrode (e.g., a catheter electrode) with anyappropriate tissue. Step 482 of the assessment protocol 480 is directed to sending anelectrical signal to an electrode at a certain frequency. At least one electrical parameter ismeasured at step 484. What may be characterized as an "impedance components ratio" isthen determined from this measurement at step 486. The phrase "impedance componentsratio" means any term that is a ratio of two individual components of the impedance, suchas the phase angle (the tangent of the phase angle being equal to the ratio of reactance toresistance). The impedance components ratio may be determined in any appropriatemaimer, such as by simply measuring a phase angle. Other ways for determining theimpedance components ratio include without limitation determining a resistance andreactance at the frequency encompassed by step 482, and calculating the impedancecomponents ratio from these two parameters. Using a ratio of two components that relateto impedance may provide less sensitivity to changes from tissue to tissue for an electrodecoupling assessment - an assessment of the coupling between an electrode and the targettissue.

[0099] The electrode coupling is assessed at step 488 of the protocol 480. This electrodecoupling from step 488 may be categorized through execution of step 490, where step 490may be in accordance with step 410 of the electrode coupling assessment protocol 400discussed above in relation to Fig. 9a. As such, the categorization of step 490 may not berequired in all instances. In any case, the result of the assessment is output pursuant tostep 492. Step 492 may be in accordance step 412 of the electrode coupling assessmentprotocol 400 discussed above in relation to Fig. 9a.

[00100] Each of the protocols of Figs. 9a-c encompasses the electrode coupling beinga mechanical coupling between the electrode and the target tissue (i.e., physical contact),as well as an electrical coupling (e.g., a condition when a sufficient portion of the 01841238\56-01 22 191733/2 electrical energy passes from the electrode to the target tissue). Any time there is amechanical coupling, there is an electrical coupling. The reverse, however, is not true.There may be an electrical coupling without the electrode being in contact with the targettissue. Fig. 10 illustrates a representative example of where there is an electrical couplingwithout having mechanical contact between an electrode 414 and the target tissue 416.Here, the electrode 414 is disposed within a cavity 418 on the surface of the tissue 416,and which provides an electrical coupling between the electrode 414 and the target tissue416. Therefore, each of the protocols of Figs. 9a-c may provide an indication of electricalcoupling without requiring mechanical contact between the electrode and the target tissue.[00101] Figs, lla-c schematically present various configurations that may be used inrelation to providing an electrode coupling assessment. Although each of these systemswill be discussed in relation to an ablation electrode, this electrode coupling assessmentmay be used for any appropriate application where an electrode provides any appropriatefunction or combination of functions. Each of the systems of Figs, lla-c may be used toprovide the assessment protocols discussed above in relation to Figs. 9a-c. It should alsobe appreciated that it may be desirable to utilize various other components tocommercially implement these configurations, such as filters (e.g., as there may be acurrent from one or more other sources that should be isolated from the current beingused to make the coupling assessment), one or more components to "electrically protect"the patient and/or the electrical circuitry used to make the electrode coupling assessment.[00102] Fig. 11a illustrates an ablation system 420 that includes an ablation powersource 424, an ablation electrode 422, and a return electrode 426. Any appropriatefrequency may be used by the ablation power source 424. Each of the ablation electrode422 and return electrode 426 may be of any appropriate size, shape, and/or configuration.Typically the ablation electrode 422 will be in the form of a catheter electrode that isdisposed within the patient's body. The return electrode 426 may be disposed at anyappropriate location (e.g., a ground patch disposed on the skin of a patient; a catheterelectrode disposed within the body of a patient).

[00103] Additional components of the ablation system 420 include an electrodecoupling assessment power source 428 (hereafter the "assessment power source 428"), anassessment return electrode 430, and an electrode coupling assessment module 432(hereafter the "assessment module 432"). Any appropriate frequency may be used by the 01841238\56-01 23 191733/2 assessment power source 428. Typically, the ablation power source 424 will also use asignificantly higher current than the assessment power source 428.

[00104] The assessment return electrode 430 may be of any appropriate size, shape,and/or configuration, and may be disposed at any appropriate location. One embodimenthas the return electrode 426 and the assessment return electrode 430 being in the form ofseparate structures that are disposed at different locations. Another embodiment has thefunctionality of the return electrode 426 and the functionality of the assessment returnelectrode 430 be provided by a single structure (a single unit that functions as both areturn electrode 426 and as an assessment return electrode 430).

[00105] The ablation electrode 422 either receives power from the ablation powersource 424 or the assessment power source 428, depending upon the position of a switch434 for the ablation system 420. That is, ablation operations and electrode couplingassessment operations may not be simultaneously conducted in the case of the ablationsystem 420 of Fig. 11a. During electrode coupling assessment operations, the switch 434is of course positioned to receive power from the assessment power source 428. Thisallows the assessment module 432 to assess the coupling between the ablation electrode422 and the target tissue. Any appropriate configuration may be utilized by theassessment module 432 to provides its electrode coupling assessment function, includingwithout limitation the various configurations addressed herein (e.g., assessment basedupon phase angle comparisons; assessment based upon reactance comparisons;assessment based upon impedance components ratio comparisons; assessment based uponidentifying the frequency associated with a 0° phase frequency or a 0 inductancefrequency as will be discussed below in relation to Figs. 12a-b). The assessment module432 may provide the electrode coupling assessment using any of the protocols of Figs. 9a-c from a single frequency.

[00106] Fig. 1 lb illustrates an ablation system 440 that includes an ablation powersource 444, an ablation electrode 442, and a return electrode 446. Any appropriatefrequency may be used by the ablation power source 444. Each of the ablation electrode442 and return electrode 446 may be of any appropriate size, shape, and/or configuration.Typically the ablation electrode 442 will be in the form of a catheter electrode that isdisposed within the patient's body. The return electrode 446 may be disposed at anyappropriate location (e.g., a ground patch disposed on the skin of a patient; a catheterelectrode disposed within the body of a patient). 01841238\56-01 24 191733/2 [00107] Additional components of the ablation system 440 include an electrodecoupling assessment power source 448 (hereafter the "assessment power source 448"), anassessment return electrode 450, and an electrode coupling assessment module 452(hereafter the "assessment module 452"). Any appropriate frequency may be used by theassessment power source 448. However, the ablation power source 444 and theassessment power source 448 operate at different frequencies in the case of the ablationsystem 440 in order to accommodate the simultaneous execution of ablation and electrodecoupling assessment operations. Moreover, typically the ablation power source 444 willalso use a significantly higher current than the assessment power source 448.

[00108] The assessment return electrode 450 may be of any appropriate size, shape,and/or configuration, and may be disposed at any appropriate location. One embodimenthas the return electrode 446 and the assessment return electrode 450 being in the form ofseparate structures that are disposed at different locations. Another embodiment has thefunctionality of the return electrode 446 and the functionality of the assessment returnelectrode 450 be provided by a single structure (a single unit that functions as both areturn electrode 446 and as an assessment return electrode 450).

[00109] The ablation electrode 442 may simultaneously receive power from theablation power source 444 and the assessment power source 448. That is, ablationoperations and electrode coupling assessment operations may be simultaneously executedin the case of the ablation system 440 of Fig. lib. In this regard, the ablation powersource 444 and the assessment power source 448 again will operate at differentfrequencies. The assessment module 452 may provide the electrode coupling assessmentusing any of the protocols of Figs. 9a-c from a single frequency. In any case, theassessment module 452 assesses the coupling between the ablation electrode 442 and thetarget tissue. The discussion presented above with regard to the assessment module 432for the ablation system 420 of Fig. 11a is equally applicable to the assessment module452 for the ablation system 440 of Fig. 1 lb.

[00110] Fig. 11c illustrates an ablation system 460 that includes an ablation powersource 464, an ablation electrode 462, and a return electrode 466. Any appropriatefrequency may be used by the ablation power source 464. Each of the ablation electrode462 and return electrode 466 may be of any appropriate size, shape, and/or configuration.Typically the ablation electrode 462 will be in the form of a catheter electrode that isdisposed within the patient's body. The return electrode 466 may be disposed at any 01841238\56-01 25 191733/2 appropriate location (e.g., a ground patch disposed on the skin of a patient; a catheterelectrode disposed within the body of a patient).

[00111] Additional components of the ablation system 460 include an electrodecoupling assessment power source 468 (hereafter the "assessment power source 468").Any appropriate frequency may be used by the assessment power source 468. Typically,the ablation power source 464 will also use a significantly higher current than theassessment power source 468.

[00112] The ablation system 460 further includes a pair of electrode couplingassessment modules 472a, 472b (hereafter the "assessment module 472a" and "theassessment module 472b"). The assessment module 472a is associated with theassessment power source 468, while the assessment module 472b is associated with theablation power source 464. Both ablation operations and electrode coupling assessmentoperations utilize the return electrode 466 in the illustrated embodiment, although it maybe possible to utilize separate return electrodes as in the case of the embodiments of Figs.11a and lib discussed above.

[00113] The ablation electrode 462 either receives power from the ablation powersource 464 or the assessment power source 468, depending upon the position of a switch474 for the ablation system 460. However, electrode coupling assessment operations maybe executed regardless of the position of the switch 474, unlike the embodiment of Fig.11a. When the ablation electrode 462 is electrically interconnected with the assessmentpower source 468 through the switch 474, the assessment module 472a is used to assessthe coupling between the ablation electrode 462 and the target tissue. When the ablationelectrode 462 is electrically interconnected with the ablation power source 464 throughthe switch 474, the assessment module 472b is used to assess the coupling between theablation electrode 462 and the target tissue. The assessment modules 427a, 472b mayeach provide an electrode coupling assessment using any of the protocols of Figs. 9a-cfrom a single frequency.

[00114] Any appropriate configuration may be utilized by each of the assessmentmodule 472a, 472b to provide their respective electrode coupling assessment functions,including without limitation the various configurations addressed herein. The discussionpresented above with regard to the assessment module 432 for the ablation system 420 ofFig. 11a is equally applicable to the assessment modules 472a, 472b for the ablationsystem 460 of Fig. 11c. Typically, the assessment modules 472a, 472b will be of the 01841238\56-01 26 191733/2 same configuration for assessing electrode coupling, although such may not be requiredin all instances. When the assessment modules 472a, 472b are the same configuration,the ablation power source 464 and the assessment power source 468 will typically operateat the same frequency. Therefore, the ablation system 460 accommodates the assessmentof electrode coupling prior to initiating ablation operations (e.g., using an assessmentcurrent and the assessment module 472a), and further accommodates the assessment ofelectrode coupling during ablation operations (e.g., using the actual ablation currentversus a smaller current, and using the assessment module 472b). The ablation system440 of Fig. lib also accommodates the assessment of electrode coupling during ablationoperations, but it uses a separate assessment current versus the actual ablation current.[00115] One of the electrodes used by the assessment module in each of theembodiments of Figs, lla-c is of course the ablation or "active" electrode. Both theelectrode coupling assessment module and the ablation electrode need another electrodethat interfaces with the patient in some manner to provide their respective functions. Fig.la illustrates one embodiment where the return electrode used by the assessment moduleand the return electrode that cooperates with the ablation electrode to provide electricalenergy to the tissue for providing one or more desired functions are integrated into acommon structure. More specifically, an ablation electrode 20 (e.g., a catheter electrode)is disposed in a chamber of the heart 16 (e.g., the left atrium), and is in the form of acatheter electrode 20. A return electrode 20a (e.g., a catheter electrode) is also disposedin the same chamber of the heart 16 and may be used by each of the assessment modulesof Figs, lla-c (to assess coupling of the ablation electrode 20 with the target tissue 24)and the ablation electrode 20 (to deliver electrical energy to the target tissue 24 to providea desired medical function). Therefore, the ablation electrode 20 and the return electrode20a may be associated with different catheters, and thereby may be independently movedor manipulated. In one embodiment, the return electrode 20a has a larger surface areathan the ablation electrode 20. Each of the ablation electrode 20 and the return electrode20a have electrode tips that are spaced from each other.

[00116] The configuration shown in Fig. la provides two electrodes 20, 20a in acommon heart chamber. Another option would be to have two or more electrodes beassociated with a common catheter, but where the catheter has two separated distalportions each with an electrode on a separate electrode tip on a distal end thereof suchthat the electrode tips are spaced from each other. 01841238\56-01 27 191733/2 [00117] One or more ways of using a phase angle to assess the coupling between anactive electrode and the target tissue have been presented above. Another way in which aphase angle may be used to assess electrode coupling is illustrated in Figs. 12a-b. Fig.12a presents a schematic of an electrode coupling assessment system 500 which includesa variable frequency source 502, an electrical parameter measurement module 504, anelectrode coupling assessment module 506, and an electrode 508 that is to be coupledwith tissue 510 to provide a desired function or combination of functions (e.g., ablation).The return electrode is not illustrated in Fig. 12a, but may be of any appropriate type anddisposed at any appropriate location. Generally, the variable frequency source 502provides an electrical signal to the electrode 508 for purposes of transmitting electricalenergy to the tissue 510. The electrical parameter measurement module 504 may be ofany appropriate type and/or configuration, measures one or more electrical parameters,and provides information used by the electrode coupling assessment module 506. Theelectrode coupling assessment module 506 assesses the coupling between the electrode508 and the tissue 510.

[00118] Fig. 12b presents one embodiment of an electrode coupling protocol 520 thatmay be used by the electrode coupling assessment module 506 of Fig. 12a. One or moreelectrical signals are sent to the electrode 508 through execution of step 524. A baselinecoupling condition can be assessed. For example, the baseline coupling condition can bedefined pursuant to steps 524-528 of protocol 520. The term "baseline couplingcondition" encompasses a zeroed phase angle or zeroed reactance at a desired frequencyin a medium (e.g., blood).

[00119] A determination is made through execution of step 525 to determine when theelectrode is in the desired medium, e.g., the blood. Next, through the execution of step526, the baseline coupling condition is established. For example, the physician canactivate an input device to indicate the establishment of the baseline coupling condition.Then protocol 520 adjusts to the baseline coupling condition in step 528 by correcting thephase angle or the reactance to zero.

[00120] In an alternative to zeroing the baseline coupling condition, the value(s) of thebaseline coupling condition established in step 526 may be stored and used to determinean electrode coupling condition relative to such a baseline coupling condition.

In a second alternative, the baseline coupling condition may be determined by comparingthe determined phase angle with one or more predetermined benchmark values. These 01841238\56-01 28 191733/2 benchmark values may be determined/set in any appropriate manner, for instanceempirically through in vitro, ex vivo, or in vivo studies. These benchmark values may bestored in an appropriate data structure, for instance on a computer-readable data storagemedium, or otherwise may be made available to a phase comparator.

[00121] The electrode coupling may be assessed pursuant to step 532 of the protocol520 using the baseline coupling condition from step 528. One or more electricalparameters may be determined in any appropriate manner and compared with thecorresponding value of the baseline coupling condition from step 528. For instance, thefollowing categories may be provided: 1) insufficient electrode coupling (e.g., anelectrode coupling where the value(s) associated with a baseline coupling condition beingless than "A" is equated with insufficient electrode coupling); 2) sufficient electrodecoupling (e.g., an electrode coupling where the value(s) associated with a baselinecoupling condition greater than "A" and less than "B" is equated with a sufficientelectrode coupling); and 3) elevated or excessive electrode coupling (e.g., an electrodecoupling where the value(s) associated with a baseline coupling condition being greaterthan "B" is equated with an elevated or excessive electrode coupling).

[00122] In another embodiment, the electrical coupling is measured as a function of a“target frequency” - a frequency that corresponds to a preset value for an electricalparameter (e.g., a preset reactance or a phase angle value). Fig. 12c presents oneembodiment of an electrode coupling protocol 620 that may be used by the electrodecoupling assessment module 506 of Fig. 12a. Electrical signals are sent to the electrode508 through execution of step 624. The electrical signals are sent at varying frequencies.At each frequency sent, step 626 measures the reactance and/or phase. Step 628compares the measured reactance or phase with a preset value. The frequency at whichthe reactance or phase matches the preset value is the “target frequency.” Anyappropriate value may be used for the preset value for purposes of step 628, including apositive value, zero, or a negative value (e.g., a zero phase angle, such that the targetfrequency may be referred to as a 0° phase frequency; or a zero inductance, such that thetarget condition frequency may be referred to as a 0 inductance frequency).

[00123] When the protocol 620 determines that the target frequency exists, theprotocol 620 proceeds to step 630 where the coupling of the electrode 508 with the tissue510 is assessed using the information provided by step 628, and the result of this 01841238\56-01 29 191733/2 assessment is output pursuant to step 636 of the protocol 620. Step 636 may be inaccordance with step 412 of the protocol discussed above in relation to Fig. 9a.

[00124] Assessment of the electrode coupling with the tissue is provided through step630 of the protocol 620 of Fig. 12c. The target frequency from step 628 may becompared with one or more benchmark frequency values (e.g., using a comparator).These benchmark frequency values may be determined/set in any appropriate manner.The values can be predetermined, for instance empirically through in vitro, ex vivo, or invivo studies. These benchmark frequency values may be stored in an appropriate datastructure, for instance on a computer-readable data storage medium. The benchmarkfrequency values can also be determined during the procedure by a physician. Forexample, a determination can be made when the electrode is in the desired medium, e.g.,the blood. At that point the physician can activate an input device to set the benchmarkvalue for the existing coupling relevant condition.

[00125] There may be one or more benchmark frequency values (e.g., a singlebenchmark frequency value or a range of benchmark frequency values) for one or more ofthe following conditions for purposes of the categorization for the assessment protocol620 of Fig. 12c: 1) insufficient electrode coupling (e.g., an electrode coupling where thetarget frequency being less than "A" is equated with insufficient electrode coupling); 2)sufficient electrode coupling (e.g., an electrode coupling where the target frequency isgreater than "A" and less than "B" is equated with sufficient electrode coupling); and 3)excessive electrode coupling (e.g., an electrode coupling where the target frequency beinggreater than "B" is equated with an excessive electrode coupling). One embodimentequates the following target frequency values for the noted conditions (where Ft is thetarget frequency for the noted condition): insufficient electrode coupling: sufficient electrode coupling:elevated/excessive electrode coupling:

Ft&lt;120kHz 120 kHz &lt; Ft &lt;400 kHz

Ft >400 kHz

The protocol 620 of Fig. 12c may be implemented in any appropriate manner. Forinstance, the impedance may be monitored to obtain the target phase frequency bysweeping the signal frequency (e.g., in accordance with the system 500 of Fig. 12a).This frequency sweep could be provided between two appropriate values (e.g., 50 kHzand 1 MHz) and using any appropriate incremental change between these values for the 01841238\56-01 30 191733/2 sweep (e.g., 10-20 kHz increments). This approach uses what may be referred to asfrequency switching, which involves measuring the impedance one frequency at a timeand rotating the frequencies by a frequency synthesizer or the like. Another approachwould be to combine multiple frequencies together, and to determine the impedance ateach of the individual frequencies from the combined signal through filtering. It shouldbe appreciated that it may be such that interpolation will be required to determine thefrequency associated with the target frequency condition in some cases (e.g., where thefrequency associated with the target frequency condition is determined to exist betweentwo frequencies used by the protocol 620).

[00126] The discussion above describes various implementations for determining alevel of electrode coupling to a patient based on certain impedance related measurementssuch as phase angle. It will be appreciated that, while this is believed to be a particularlyeffective mechanism for obtaining electrode coupling information, other mechanisms maybe utilized. Some of these mechanisms include other impedance-based measurement,mechanical vibration measurements (such as obtained from piezoelectric devices) ormechanical deformation measurements (such as obtained via a strain gauge). Thus, anindication of electrode positioning may be based on electrical, mechanical or otherproperties.

[00127] In any event, once an indication of electrode position has been obtained, it isdesirable to convey this information to the physician. Moreover, as discussed above, it isuseful to provide this information to the physician in a manner that minimizes distraction.

[00128] One aspect of the present invention relates to providing electrode couplinginformation or other information to a physician via electrode guidance instrumentation.

In the following discussion, this is set forth in the context of providing outputs via thecatheter handle set and/or a navigation system that can indicate any of multiple levels ofelectrode coupling such as insufficient coupling, sufficient coupling or elevated coupling.However, it will be appreciated that the invention is not limited to these specific contextsor implementations.

[00129] Referring to Fig. 13, a catheter system 1300 in accordance with the presentinvention is shown. The system 1300 generally includes an electrode catheter 1302 thatis operatively associated with a navigation system display 1312 and a user interface 1314. 01841238\56-01 31 191733/2

The illustrated electrode catheter 1302 includes an electrode 1308 for interacting withfluids and tissue of a patient, a handle set 1304 that can be gripped by a physician toadvance withdraw, rotate or otherwise position the electrode 1308, and a catheter body1306 extending between the handle set 1304 and the electrode 1308. The illustratedelectrode catheter 1302 further includes an output device 1310 such as an LED array forproviding an output concerning a level of electrode coupling, as will be discussed in moredetail below.

[00130] The navigation system display 1312 provides visual information for assistingthe physician in positioning the electrode 1308 in a desired position in relation to thepatient. The navigation system will be described in more detail below. However,generally, the navigation system displays certain physiological structure of the patient,such as cardiac structure, based on electrical mapping, fluoroscopic and/or otherinformation. Moreover, the position of the electrode 1308 is generally depicted on thedisplay 1312 in relation to the physiological structure in order to assist the physician indirecting the electrode 1308 to a desired position. It will thus be appreciated that thephysician’s visual attention is largely directed to the display during a medical procedureinvolving the electrode catheter 1302. However, skilled physicians will also deducecertain information regarding the electrode position based on tactile feedback through thehandle set 1304.

[00131] The illustrated system also includes a user interface 1314 that the physiciancan utilize to input certain information regarding a procedure. For example, the physicianmay input information identifying the patient, the equipment utilized, the procedure beingperformed and the like. In addition, the physician may use the user interface 1314 toidentify locations of interest, e.g., for ablation or the like. Thus, the user interface mayinclude a keyboard, a graphical user interface or other input mechanisms.

[00132] Fig. 14 is a schematic diagram of an electrode coupling output system 1400 inaccordance with the present invention. The system 1400 receives an input 1401indicative of a level of electrode coupling. For example, in implementations as discussedabove, this input may provide information regarding phase angle. The system 1400includes a coupling assessment module 1402, an output drive module 1404 and an outputdevice 1406. 01841238X56-01 32 191733/2 [00133] The coupling assessment module 1402 receives the input 1401 anddetermines a level of electrode coupling based on the input 1401. Depending on theimplementation, the coupling assessment module 1402 may be capable of distinguishingbetween two or more levels of electrode coupling. The module 1402 may be embodied ina processor for executing logic to implement electrode coupling calculation as describedabove. The processor has appropriate I/O structure including an input interface forreceiving the noted input 1401 and an output interface for transmitting control signals tothe output drive module 1404. Thus, in certain implementations, the module 1402 maydistinguish between insufficient coupling (e.g., corresponding to electrode contact withblood) and sufficient coupling (e.g., associated with tissue contact or electrical couplingsufficient for the desired procedure, such as ablation or mapping, regardless of physicalcontact). Alternatively, the module may distinguish between insufficient contact,sufficient contact and elevated contact (e.g., associated with potential penetration of theelectrode through a chamber wall, which may or may not be desired). It will beappreciated that more levels may be defined, for example, representing additional contactlevels or finer resolution between the noted contact levels.

[00134] Based on the determined coupling level, the coupling assessment module1402 provides an output signal 1403 to the output drive module 1404. The output drivemodule generates a drive signal 1405 to drive an output device 1406 that provides anoutput to the physician, indicating the determined level of electrode coupling. As will bediscussed in more detail below, various types of output devices may be utilized to providethis output to the physician. For example, an audio, visual or mechanical (e.g., vibration)indication may be provided via the handle set of the electrode catheter. Alternatively, anaudio, visual or other indication may be provided to the physician via the navigationsystem. Accordingly, the nature of the output device 1406 varies depending on thespecific implementation. Relatedly, the nature of the drive signal 1405 provided by theoutput drive module 1404 varies depending on the application, as will be described inmore detail below.

[00135] As discussed above, an output indicating the determined level of electrodecoupling may be provided to the physician via, for example, the handle set or thenavigation system. Fig. 15 is a schematic diagram of a catheter system 1500 forproviding such an output via the catheter handle set 1504. The illustrated system 1500 01841238X56-01 33 191733/2 includes the handle set 1504 and a coupling detection module 1502. Although thecoupling detection module 1502 is schematically illustrated as being separate from thehandle set 1504, it will be appreciated that the module 1502 may be physicallyincorporated into the handle set 1504. In the illustrated system 1500, the handle set 1504,which is associated with the electrode of the electrode catheter, provides a sensing signal 1501 to the coupling detection module 1502. For example, in the case of a phase angleimplementation, the sensing signal 1501 may include information sufficient to indicatephase angle relative to movement of the electrode. In that case, the detection module 1502 executes logic as described above to determine an electrode coupling level based onthe phase angle information.

[00136] Based on this determination, a contact indication signal 1503 is provided tothe handle set 1504. The handle set 1504 is then operative to provide an output 1505 tothe physician, indicating the coupling level. Any suitable type of output may be used inthis regard. For example, a mechanical output, such as a vibration of the handle set 1504,a visual output, such as an LED or LED bar graph, or an audio output, such as a variabletone (e.g., variable in pitch, volume or other audio parameter) may be utilized in thisregard. Moreover, combinations of these types of outputs may be utilized. For example,a visual or audio output may be utilized to indicate an insufficient or sufficient level ofelectrode coupling, whereas a mechanical output may be used to indicate elevatedelectrode coupling. The type of output may be selected to minimize distraction to thephysician or enhance physician awareness of the output. Again, it will be appreciated thatthe physician’s visual attention may be primarily directed to a display of a navigationsystem during the medical procedure.

[00137] Fig. 16 is a partially schematic illustration of a handle set 1600 incorporatingmultiple output devices. The handle set receives an input signal 1601 from a couplingdetection module. This signal 1601 is used to drive one or more of a vibration device1602, an audio output device 1604, such as a tone generator, and a display 1606, in thiscase an LED bar graph. In this regard, the signal 1601 can be either a digital or analogsignal. In the case of a digital signal, the signal may indicate yes/no information withregard to one or more coupling levels, e.g.: (1) insufficient contact (yes/no); (2) sufficientcontact (yes/no); and (3) elevated contact (yes/no). Alternatively, the digital signal mayindicate any of multiple coupling levels in step-wise fashion. That is, the digital signal 01841238X56-01 34 191733/2 may be encoded with information indicating the coupling level where such coding isbased on a current level, voltage level, pulse sequence or other signal characteristic. Inthe case of an analog signal, the analog signal may be continuously variable to representthe electrode coupling level.

[00138] The vibration source 1602 is operative in response to the input signal 1601 tocause vibration of the handle set 1600 so as to provide electrode coupling information tothe physician. For example, the device 1602 may be activated to indicate a particularcoupling level, such as elevated contact. Alternatively, the vibration device may beoperated at different frequencies or other parameters to indicate different electrodecoupling levels.

[00139] The audio output device can output any suitable audio indication to identifythe electrode coupling level. Thus, for example, where the input signal 1601 is an analogsignal, the current, voltage or other parameter of the signal 1601 can be correlated to anelectrode contact parameter such as phase angle. In response to the signal 1601, the pitch,volume or other parameter of a tone generated by the audio output device 1604 can bevaried to directly correspond to the electrode coupling level.

[00140] The visual display 1606 can provide any suitable visual indication of theelectrode coupling level. Thus, for example, the display 1606 may include a single LED,multiple LEDs or an LED bar graph. In the illustrated embodiment, the displaycomprises an LED bar graph, including multiple light segments 1608. Thus, for example,the voltage of the input signal 1601 can raise as a function of increasing electrodecoupling. This raising voltage results in increased lighting of the light segments 1608 toprovide a direct visual indication of electrode coupling level. Although Fig. 16 showsthree separate output devices 1602,1604 and 1606 in a single handle set 1600, it will beappreciated that a single type of output device may be utilized to indicate the electrodecoupling level. Moreover, any combination of the illustrated output device types or otheroutput device types may be utilized in this regard.

[00141] Fig. 17 illustrates one embodiment of a mechanical vibration output devicethat may be utilized to indicate the electrode coupling level. It will be appreciated thatvibration devices are well known and are used, for example, in connection with cellphones, pagers, control pads of video games and other existing products. A handle set 01841238\56-01 35 191733/2 1700 incorporating such a vibration device is illustrated in Fig. 17. The vibration deviceof the handle set 1700 includes a motor 1702 that rotates an output shaft 1704. Anunbalanced load 1706 is mounted on the output shaft 1704. Accordingly, operation of themotor 1702 to rotate the output shaft 1704 results in reciprocating forces associated withrotational movement of the unbalanced load 1706. The motor 1702 is mounted on asupport structure 1708 that allows the motor 1702 to reciprocate in response to theseforces. This, in turn, causes the handle set 1700 to vibrate. Accordingly, the motor 1702receives an input signal 1701 indicating a level of electrode coupling. The motor 1702can be activated or its operating parameters can be varied based on the input signal 1701to provide an indication of the electrode coupling level. For example, the motor may beoperative to vibrate the handle set 1700 only when a particular level of electrode couplingis indicated, such as elevated coupling. Alternatively, the operating speed of the motor1702 or another parameter may be varied to indicate multiple levels of electrode coupling.

[00142] As noted above, during a medical procedure performed using the electrodecatheter, the physician’s visual attention is primarily directed to the navigation system.Accordingly, it has been recognized that an indication regarding the electrode couplinglevel may be provided (e.g., visually) via the navigation system in lieu of, or in additionto, the handle set indications described above. Certain implementations of such a systemare described below.

[00143] Fig. 18 is a block diagram illustrating an electrode coupling assessmentsystem 1800 that provides an indication of the electrode coupling level via a navigationsystem display. Although the level of electrode coupling may be determined in anyappropriate manner, the illustrated system utilizes a phase angle measurement, asdescribed above. The system 1800 includes a signal generator 1802 for generating asignal 1803 useful for making the phase angle measurement. As described above, thesignal generator may be a dedicated signal generator for providing the electrode couplingassessment signal and/or a signal generator for providing a mapping, ablation or otherprocedure signal. The signal 1803 is applied to the patient via an electrode 1804 such asan ablation or mapping electrode.

[00144] The resulting current signal 1806 and voltage signal 1808 are compared by aphase comparator 1812. The phase comparator 1812 therefore provides an output signal1813 indicative of a time series of phase angle values. Optionally, current measurements 01841238\56-01 36 191733/2 may be shifted by a phase shift circuit to facilitate operation of the phase comparator1812 by “correcting” phase lag between the measured current and the measured voltage.Also optionally, output from the phase comparator 1812 may be “corrected” by a phaseadjustment circuit to compensator for external factors, such as the type of groundingpatch being used. The result is a phase angle signal 1815 indicative of the level ofelectrode coupling.

[00145] This signal 1815 can be displayed as a waveform and/or interpreted as anelectrode contact level by an electro-anatomic mapping and navigation (EAMN) systemor other procedure monitoring system (generically, “navigation system”). Examples ofcommercially available EAMN systems include the NAVX system of St. Jude Medicaland the CARTO system of Johnson and Johnson. Fluoroscopic or other systems may alsobe used for procedure monitoring in this regard. The signal 1815 may therefore be scaledor otherwise processed by a signal scaling module 1816 to provide an input that can beproperly handled by the navigation system. For example, the resulting signal 1817 maybe voltage signal scaled to a range of 0-1V, a current signal scaled to 4-20mA, or anyother signal as required by the navigation system. In the illustrated implementation, thissignal 1817 is used to provide a phase angle versus time waveform 1820 and isinterpreted as a graphical electrode representation 1822 reflecting a level of electrodecoupling.

[00146] In the latter regard, the graphical electrode representation may reflect any oftwo or more levels of electrode coupling depending on the specific implementation. Figs.19A and 19B depict an exemplary implementation for indicating two possible electrodecoupling levels, for example, indicating no physical tissue contact (e.g., the electrode isdisposed in the patient’s blood within a cardiac chamber) or tissue contact (e.g., theelectrode is directly contacting cardiac tissue). Such two-state systems have beenproposed by various parties.

[00147] Figs. 19A and 19B show how these two electrode coupling conditions may bedepicted on a display of a navigation system in accordance with the present invention.Specifically, Fig. 19A shows a condition where there is no physical contact between theelectrode 1900 of catheter 1902 and the cardiac tissue 1904 of interest. This condition isdetected by an electrode coupling detection system (a phase angle based system asdescribed above or other system), and the associated electrode coupling level is 01841238\56-01 37 191733/2 communicated to the navigation system. The navigation system then uses this electrodecoupling level to select a display parameter (e.g., a color) for the electrode 1900. Forexample, the electrode may be depicted in blue (represented as lighter shading in Fig. 19A) for the no contact condition and in red (represented as darker shading in Fig. 19B)for the direct physical contact condition.

[00148] Other systems may be capable of detecting and indicating more than twolevels of electrode coupling, as shown in Figs. 20A-20D. In this case, four levels ofcoupling, which may be designated no coupling (Fig. 20A), light coupling (Fig. 20B),hard coupling (Fig. 20C) and elevated coupling (Fig. 20D) are detected and shown in thedisplay as different electrode colors (represented by different shading in Figs. 20A-20D).Any colors can be used to designate the levels no coupling, light coupling, hard couplingand elevated coupling, such as white, green, yellow and red, respectively. In the case of aphase angle implementation, theses levels may be defined by corresponding phase angleranges. Although the increasing electrode coupling levels of Figs. 20A-20D are shown ascorresponding to increasing levels of physical contact, it is noted that electrode coupling,including significant levels of coupling, can be achieved without physical contact.

[00149] Other types of display representations may be used to provide the electrodecoupling level information in connection with a navigation system display. For example,physicians in this field tend to be comfortable with and to derive a substantial amount ofinformation from waveform data. Indeed, it is common to provide an ECG waveform orother waveforms on the navigation system display. Fig. 21 illustrates a display screen2100, including imaging portion 2102 depicting a catheter 2104 with an electrode 2106(which may change colors to indicate the electrode coupling level) and a waveformportion 2108 showing various waveforms 2110a-21 lOd. For example, these waveformsmay include an ECG waveform 2110a, a waveform showing the signal detected by anablation electrode 2110b (which can be the same as electrode 2106), a waveform detectedby a reference electrode 2110c (e.g., another electrode on the catheter 2104, an electrodeon another catheter or an external return electrode patch) and a phase angle waveform2110d.

[00150] In this case, the phase angle waveform 21 lOd shows not only the magnitudeof the phase angle at a given time, but also the trend or change in magnitude over timewhich may assist a physician in evaluating the electrode coupling level or provide other 01841238\56-01 38 191733/2 useful information (e.g., to evaluate the quality of a lesion formed by ablation). Thewaveform may be a raw waveform reflecting each successive determined value of phaseangle. Alternatively, the waveform 21 lOd may be filtered to remove noise such asartifact associated with patient motion or provide averaging. Thus, in the illustratedexample, the waveform includes plethysmographic features reflecting variations inelectrode coupling due to movement of the beating heart. This may be useful to aphysician in evaluating the electrode coupling (e.g., the level or modulation in this regard,as visually discerned by the physician or calculated, for example, by spectral analysis,may be indicative of the level of electrode coupling) or otherwise. Alternatively, suchwaveform features may be eliminated by applying an appropriate low pass filter toremove these components and provide a degree of averaging. Such filtering or averagingmay also be desired in relation to outputting electrode coupling level information (e.g.,via displayed electrode color) so as to avoid elevated output flicker.

[00151] A number of implementations for providing an indication of electrode contactlevel via electrode guidance instrumentation (e.g., the handle set and/or the navigationsystem) have thus been described. The associated functionality can be summarized byreference to the flow chart of Fig. 22. The illustrated process 2200 is initiated byreceiving (2202) current and voltage signals associated with the electrode underconsideration and determining a phase angle value. This value can then be used todetermine (2204) an electrode coupling level. Information regarding this coupling levelcan be provided to the physician in various ways via the handset (an audio, visual and/ormechanical output) and/or via a navigation system display. Accordingly, an appropriatedrive signal is established (2206) depending on the nature of the output device. In anyevent, the output indicates an electrode cooling level of two or more possible couplinglevels. The output device is thereby operated (2208) to provide an output indicating thedetermined electrode coupling level.

Although a number embodiments of this invention have been described above with acertain degree of particularity, those skilled in the art could make numerous alterations tothe disclosed embodiments without departing from the spirit or scope of this invention.

For example, the levels of electrode coupling may be determined via varioustechnologies. Moreover, certain aspects of the invention are applicable in other contexts.For example, an output device may be incorporated into an electrode catheter to provide 01841238X56-01 39 191733/2 any information of interest and is not limited to providing electrode coupling information.All directional references (e.g., upper, lower, upward, downward, left, right, leftward,rightward, top, bottom, above, below, vertical, horizontal, clockwise, andcounterclockwise) are only used for identification purposes to aid the reader’sunderstanding of the present invention, and do not create limitations, particularly as to theposition, orientation, or use of the invention. Joinder references (e.g., attached, coupled,connected, and the like) are to be construed broadly and may include intermediatemembers between a connection of elements and relative movement between elements.

As such, joinder references do not necessarily infer that two elements are directlyconnected and in fixed relation to each other. It is intended that all matter contained inthe above description or shown in the accompanying drawings shall be interpreted asillustrative only and not limiting. Changes in detail or structure may be made withoutdeparting from the spirit of the invention as defined in the appended claims. 01841238\56-01 40