Dual-purpose lasso catheter with irrigation using circumferentially arranged ring bump electrodes

212307/2

FIELD OF THE INVENTION

This invention relates to cardiac mapping and ablation systems. More particularly, this invention relates to a lasso catheter for use in a cardiac mapping and ablation system.

BACKGROUND OF THE INVENTION

Cardiac arrhythmia, such as atrial fibrillation, occurs when regions of cardiac tissue abnormally conduct electric signals to adjacent tissue, thereby disrupting the normal cardiac cycle and causing asynchronous rhythm. Important sources of undesired signals are located in the tissue region along the pulmonary veins of the left atrium and in the superior pulmonary veins. In this condition, after unwanted signals are generated in the pulmonary veins or conducted through the pulmonary veins from other sources, they are conducted into the left atrium where they can initiate or continue arrhythmia.

Procedures for treating arrhythmia include surgically disrupting the origin of the signals causing the arrhythmia, as well as disrupting the conducting pathway for such signals. More recently, it has been found that by mapping the electrical properties of the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy, it is sometimes possible to cease or modify the propagation of unwanted electrical signals from one portion of the heart to another. The ablation process destroys the unwanted electrical pathways by formation of non-conducting lesions .

In this two-step procedure--mapping followed by ablation--electrical activity at points in the heart is typically sensed and measured by advancing a catheter 1 212307/2 containing one or more electrical sensors into the heart, and acquiring data at a multiplicity of points. These data are then utilized to select the target areas at which ablation is to be performed. U.S. Pat. No. 6,063,022 to Ben-Haim, which is assigned to the assignee of the present patent application, describes an invasive probe including two position sensors in a fixed, known relation to the distal end of the probe. The position sensors generate signals responsive to their respective position coordinates and at least one contact sensor along a radial surface of the probe for generating a signal representing its contact with body tissue to be ablated by electrodes on the probe. U.S. Pat. No. 6,272,371 to Ben-Haim, which is assigned to the assignee of the present patent application, describes an invasive probe including a flexible portion that assumes a predetermined curve form when a force is applied thereto. Two position sensors, fixed to the distal portion of the probe in known positions, are used to determine position and orientation coordinates of at least one of the sensors, and to determine the locations of a plurality of points along the length of the distal portion of the probe. PCT Patent Publication WO 96/05768 and corresponding U.S. Patent Application Publication 2002/0065455 to Ben-Haim et al. , which are assigned to the assignee of the present patent application, describe a system that generates sixdimensional position and orientation information regarding the tip of a catheter. This system uses a plurality of sensor coils adjacent to a locatable site in the catheter, for example near its distal end, and a plurality of radiator 2 212307/3 patent application, describe a system that generates sixdimensional position and orientation information regarding the tip of a catheter. This system uses a plurality of sensor coils adjacent to a locatable site in the catheter, for example near its distal end, and a plurality of radiator coils fixed in an external reference frame. These coils generate signals in response to magnetic fields generated by the radiator coils, which signals allow for the computation of six position and orientation dimensions, so that the position and orientation of the catheter are known without the need for imaging the catheter. A lasso catheter is disclosed in commonly assigned U.S. Patent No. 6,973,339. The lasso catheter is particularly adapted for pulmonary vein mapping and ablation. This catheter comprises: a curved section having a first position sensor that is capable of generating fewer than six dimensions of position and orientation information, one or more electrodes, adapted to measure an electrical property of the pulmonary vein; and a base section attached to a proximal end of the curved section. Disposed on the base section within 3 mm of the distal end thereof is a second position sensor, capable of generating six dimensions of position and orientation information. U.S. Patent 5,730,127 describes a recording and ablation catheter including an array of electrode arcuate shapes.

SUMMARY OF THE INVENTION

Lasso catheters are generally used for ablating tissue along an arc surrounding an anatomical structure, such as the ostium of a pulmonary vein. Conventionally, the curved section or loop of the lasso catheter is generally thin and "floppy," for purposes of maneuverability, while ring 3 BIO5203USCIP1 electrodes disposed on the lasso are relatively large in order to minimize electrical resistance.

Embodiments of the present invention provide a lasso catheter that may be used for both ablation and sensing, and which has other advantageous features. Its distal curved portion, sometimes referred to herein as a "loop" or "loop segment", is typically thicker and stiffer than that of conventional lasso catheters. Rather than ring electrodes, the lasso catheter has relatively small, raised protuberant electrodes. The small size of these electrodes is advantageous in permitting measurement of local electrical activity with good spatial resolution. The bulges of the electrodes increase the surface area that is in contact with the heart tissue, and thus reduces the electrical resistance when the electrodes are used for ablation .

In order to provide local cooling and prevent adhesion during ablation, the electrodes may be fenestrated by multiple perforations. The perforations are in fluid contact with a lumen, which carries irrigation fluid from within the catheter to the outer surfaces of the electrodes and thence to the adjacent tissues. Another lumen may contain wires connected to each of the electrodes.

An embodiment of the invention provides a catheter, including an insertion tube and a resilient distal section fixed to the distal end of the insertion tube. The distal section has an inner irrigating lumen and a plurality of electrodes that bulge above the outer surface. The electrodes have a plurality of perforations formed therethrough, and the outer surface is in fluid communication with the irrigating lumen via the perforations. 4 BIO5203USCIP1

According to an aspect of the catheter, the insertion tube is configured for insertion through a blood vessel into a heart of a subject, and wherein the resilient distal section defines an open loop when deployed within the heart.

An embodiment of the invention provides a method for locating an arrhythmogenic area in a heart of a living subject, The method is further carried out by inserting a catheter into a chamber of the heart, the catheter including an insertion tube and a resilient distal section that has an inner irrigating lumen and is fixed to the distal end of the insertion tube. The distal section also includes a plurality of electrodes that bulge above the outer surface, the electrodes having a plurality of perforations formed there-through. The outer surface of the distal section is in fluid communication with the irrigating lumen via the perforations, The method is further carried out by locating the catheter in proximity to a target in the chamber, analyzing electrical signals received from the target via the catheter to make a determination that the electrical signals are indicative of abnormal electrical conduction within the heart, and responsively to the determination, conducting energy into the heart to thereby affect the abnormal electrical conduction.

According to another preferred embodiment, the present invention is a catheter comprising an insertion tube having a distal end and a resilient distal section fixed to the distal end of the insertion tube. The distal section can also be in the form of a "loop" or "loop segment". The distal section has an outer surface and an inner irrigating lumen and comprises a plurality of ring electrodes that bulge above the outer surface and are circumferen-5 BIO5203USCIP1 tially arranged around the entire circumference of the outer surface. Each ring electrode defines a cavity thereunder. The ring electrodes have a plurality of perforations formed there-through and the outer surface has a breach hole (or holes) therein positioned beneath each ring electrode and in fluid communication with the irrigating lumen. The cavity and the perforations of each ring electrode facilitate dispensing of irrigating fluid from the distal section through each ring electrode.

According to the present invention, the diameter of the breach hole for each ring electrode varies in size. For example, in one embodiment, the diameter of the breach hole for each ring electrode varies in size from smaller to larger from proximal to distal along the resilient distal section. Alternatively, in another embodiment according o the present invention, the diameter of the breach hole for each ring electrode varies in size from larger to smaller from proximal to distal along the resilient distal section.

Breach hole (or holes) could be of circular or other shape (for example: rectangular).

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference is made to the detailed description of the invention, by way of example, which is to be read in conjunction with the following drawings, wherein like elements are given like reference numerals, and wherein: 6 BIO5203USCIP1

Fig. 1 is a pictorial illustration of a system for detecting areas of abnormal electrical activity and performing ablative procedures on a heart of a living subject in accordance with a disclosed embodiment of the invention;

Fig. 2 is a side elevation of a lasso catheter that is constructed and operative in accordance with a disclosed embodiment of the invention;

Fig. 3 is a cross section through the catheter shown in Fig. 2 taken through line 3-3;

Fig. 4 a fragmentary elevational view of the shaft of a catheter that is constructed and operative in accordance with a disclosed embodiment of the invention;

Fig. 5 is a fragmentary elevational view of the shaft of a catheter that is constructed and operative in accordance with an alternate embodiment of the invention;

Fig. 6 is a fragmentary elevational view of the shaft of a catheter that is constructed and operative in accordance with an alternate embodiment of the invention;

Fig. 7 is a schematic view of a cardiac catheter in accordance with an alternate embodiment of the invention;

Fig. 8 is a fragmentary elevational view of a shaft of a catheter having a plurality of linear electrode arrays that is constructed and operative in accordance with an alternate embodiment of the invention;

Fig. 9 is a fragmentary elevational view of the shaft of a catheter that is constructed and operative in accordance with an alternate embodiment of the invention;

Fig. 10 is a cross section through the catheter shown in Fig. 9 taken through a circumferential ring bump electrode in accordance with the invention; and

Fig. 11 is a side elevation view in longitudinal cross section through a circumferential ring bump electrode of the catheter shown in Fig. 9 in accordance with the invention . 7 212307/2

DETAILED

DESCRIPTION OF THE INVENTION

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the various principles of the present invention. It will be apparent to one skilled in the art, however, that not all these details are necessarily always needed for practicing the present invention. In this instance, well-known circuits, control logic, and the details of computer program instructions for conventional algorithms and processes have not been shown in detail in order not to obscure the general concepts unnecessarily.

Turning now to the drawings, reference is initially made to FIG. 1, which is a pictorial illustration of a system 10 for detecting areas of abnormal electrical activity and performing ablative procedures on a heart 12 of a living subject in accordance with a disclosed embodiment of the invention. The system comprises a lasso catheter 14, which is percutaneously inserted by an operator 16, who is typically a physician, through the or vascular brings the patient's vascular system into a chamber structure of the heart. The operator 16 catheter’s distal tip 18 ("18" has to be moved closer to the loop-the way it is looks that indicates a heart chamber rather than the distal tip (loop} of the catheter) into contact with the heart wall at a target site that is to be evaluated. Electrical activation maps are then prepared, according to the methods disclosed in the above-noted U.S. Patent Nos. 6,226,542, and 6,301,496, and in commonly assigned U.S. Patent No. 6,892,091. 8 212307/2

The energy is point (typically

Areas determined to be abnormal by evaluation of the electrical activation maps can be ablated by application of electrical energy, e.g., by passage of radiof requency electrical current through wires in the catheter to one or more electrodes at the distal tip 18, which apply the radiofrequency energy to the myocardium absorbed in the tissue, heating it to a about 50 °C} at which it permanently loses its electrical excitability. When successful, this procedure creates nonconducting lesions in the cardiac tissue, which disrupt the abnormal electrical pathway caus ing the arrhythmia. Alternatively, other known methods of applying ablative energy can be used, e.g., ultrasound energy, as disclosed in U.S. Patent Application Publication No. 2004/0102769. The principles of the invention can be applied to different heart chambers, and to mapping in sinus rhythm, and when many different cardiac arrhythmias are present.

The catheter 14 typically comprises a handle 20, the the handle to enable having suitable controls on operator 16 to steer, position and orient the distal end of the catheter as desired for the ablation. To aid the operator 16, the distal portion of the catheter 14 contains position sensors (not shown) that provide signals to a positioning processor 22, located in a console 24. The console 24 typically contains an ablation power generator 25. The catheter 14 may be adapted to conduct ablative energy to the heart using any known ablation technique, e.g., radiofrequency energy, ultrasound energy, and laser energy. Such methods are disclosed in commonly assigned U.S. Patent Nos. 6,814,733, 6,997,924, and 7,156,816.

The positioning processor 22 is an element of a positioning system 26 that measures location and 9 212307/2 orientation coordinates of the catheter 14. Throughout this patent application, the term "location" refers to the and the term spatial coordinates of the catheter, "orientation" refers to its angular coordinates. The term "position" refers to the full positional information of the catheter, comprising both location and orientation coordinates .

In one embodiment, the positioning system 26 comprises a magnetic position tracking system that determines the position and orientation of the catheter 14. The positioning system 26 generates magnetic fields in a predefined working volume its vicinity and senses these fields at the catheter. The positioning system 26 typically comprises a set of external radiators, such as field generating coils 28, which are located in fixed, known positions external to the patient. The coils 28 generate fields, typically electromagnetic fields, in the vicinity of the heart 12.

In an alternative embodiment, a radiator in the catheter 14, such as a coil, generates electromagnetic fields, which are received by sensors (not shown) outside the patient's body.

Some position tracking systems that may be used for this purpose are described, for example, in the above-noted U.S. Patents 6,690,963, and in commonly assigned U.S. Patent Nos. 6,618,612 and 6,332,089, and U.S. Patent Application Publications 2004/0147920, and 2004/0068178. Although the positioning system 26 shown in FIG. 1 uses magnetic fields, the methods described below may be 10 BIO5203USCIP1 implemented using any other suitable positioning system, such as systems based on electromagnetic fields, acoustic or ultrasonic measurements. The positioning system 26 may be realized as the CARTO XP EP Navigation and Ablation System, available from Biosense Webster, Inc., 3333 Diamond Canyon Road, Diamond Bar, CA 91765.

As noted above, the catheter 14 is coupled to the console 24, which enables the operator 16 to observe and regulate the functions of the catheter 14. Console 24 includes a processor, preferably a computer with appropriate signal processing circuits. The processor is coupled to drive a monitor 29. The signal processing circuits typically receive, amplify, filter and digitize signals from the catheter 14, including signals generated by the sensors 31, 33 and a plurality of sensing electrodes 35. The digitized signals are received and used by the console 24 to compute the position and orientation of the catheter 14 and to analyze the electrical signals from the electrodes. The information derived from this analysis is used to generate an electrophysiological map of at least a portion of the heart 12 or structures such as the pulmonary venous ostia, for diagnostic purposes such as locating an arrhythmogenic area in the heart or to facilitate therapeutic ablation.

Typically, the system 10 includes other elements, which are not shown in the figures for the sake of simplicity. For example, the system 10 may include an electrocardiogram (ECG) monitor, coupled to receive signals from one or more body surface electrodes, so as to provide an ECG synchronization signal to the console 24. As mentioned above, the system 10 typically also includes a reference position sensor, either on an externally-applied 11 BIO5203USCIP1 reference patch attached to the exterior of the subject's body, or on an internally-placed catheter, which is inserted into the heart 12 maintained in a fixed position relative to the heart 12. By comparing the position of the 5 catheter 14 to that of the reference catheter, the coordinates of catheter 14 are accurately determined relative to the heart 12, irrespective of heart motion. Alternatively, any other suitable method may be used to compensate for heart motion. 10

Reference is now made to Fig. 2, which is a side elevation of a lasso catheter 37 that is constructed and operative in accordance with a disclosed embodiment of the invention. The catheter 37 is a steerable device. Its han- 15 die, control and steering mechanisms (not shown) are conventional and are omitted from Fig. 2 for simplicity. The catheter 37 features a base segment 39, which is bendable responsively to forces applied by the steering mechanisms. A distal curved section, referred to herein as loop seg- 20 ment 41, completes the lasso configuration. The loop segment 41 is joined to the base segment 39 by a range-restricted angle 0( at a joint 43. The angle 0( between the loop segment 41 and the base segment 39 optimally is about 90 decrees. The joint 43 may define a point where two 25 initially-separate members (base segment 39; loop segment 41) are joined, or, alternatively, the joint 43 may define a point on the catheter 37 where a single member is bent, so as to form the base segment 39 and the loop segment 41. The loop segment 41 is of a known fixed length, 30 having a curvature dimensioned to a particular medical application. The curvature may be adjustable using the steering and control mechanisms (not shown) of the catheter. A radius 45 of adjustable between 7-15 mm is suita- 12 BIO5203USCIP1 ble for cardiac applications. However, the vary up to 25 mm in some applications. In loop segment 41 may be dimensioned so as structures such as the ostia of pulmonary coronary sinus. radius 45 may any case, the to conform to veins or the

The loop segment 41 is constructed of a material that preferably is twistable but not stretchable when subjected to typical forces encountered in medical practice. Preferably, the loop segment 41 is sufficiently resilient so as to assume a predetermined curved form, i.e., an open circular or semicircular form when no force is applied thereto, and to be deflected from the predetermined curved form when a force is applied thereto. Preferably, the loop segment 41 has an elasticity that is generally constant over at least a portion of its length, for example, because of internal reinforcement of the curved section with a resilient longitudinal member, as is known in the art. The loop segment 41 is generally thicker and stiffer than conventional lassos. For example, the loop segment 41 may be made from polyurethane and be at least one mm in diameter.

One or more electrodes 35, adapted for sensing electrical characteristics of cardiac tissue, are fixed to the loop segment 41. Reference is now made to Fig. 3, which is a cross section through the catheter 37 (Fig. 2) taken through line 3-3, illustrating one of the electrodes 35. The electrodes 35 may bulge between about 0.1-0.5 mm above the outer surface 47 and have a generally rounded profile, forming a cap on the surface 47. In some embodiments the electrodes 35 may have a larger bulge, up to 1 mm above the surface. The electrodes 35 may extend over 25-270 per cent of the circumference of the surface 47, as contrasted with a conventional ring electrode, which covers 100% of 13 BIO5203USCIP1 the circumference. The electrodes 35 may have a circular border. Alternatively, they may be elliptical in contour, as further described below. These configurations provide substantial contact between the electrodes 35 and the cardiac tissue, lowering electrical resistance as compared with conventional electrodes. The electrodes 35 may be 2-5 mm in dimension. The electrodes 35 may also be used for ablation, in which case the reduced electrical resistance is particularly advantageous. In one embodiment, two of the electrodes 35 are selected for performing bi-polar ablation, e.g., radiofrequency ablation in which case a cable 57 may include wires individually leading to the electrodes 35.

The exterior surface of the electrodes 35 is fenestrated by multiple small perforations 49 formed therethrough. Typically there are between 1 and 50 perforations having diameters of 0.05-0.4 mm. Perforations could also be any other shape area (not circular) , for example rectangular, wherein these other shaped areas are equivalent to the area of circular perforations of diameter 0.05-0.4 mm. The perforations 49 are in fluid communication with an irrigating lumen 51 through a channel 53. A second lumen 55 carries cable 57 comprising one or more electrically conductive wires that link the electrodes 35 to the console 24 (Fig. 1), for example wire 59. The lumen 55 may also conduct additional wires as described below.

Reference is now made to Fig. 4, which is a fragmentary elevational view of a shaft 61 of a catheter that is constructed and operative in accordance with a disclosed embodiment of the invention. Electrodes 63 are circular in contour, and the surface distribution of perforations 49 is substantially uniform. 14 BIO5203USCIP1

Reverting to Fig. 2, at least a first single-coil position sensor 31 is fixed to loop segment 41. Preferably, the sensor 31 is fixed to the distal end of the loop segment 41 (distal with respect to the base segment 39), and a second single-coil position sensor 33 is fixed to the approximate center of the loop segment 41. Optionally, one or more additional single-coil position sensors (not shown) are fixed to the loop segment 41. Additionally, a multi-coil position sensor 65 is preferably fixed near the distal end of the base segment 39, in the vicinity of the joint 43, typically within 10 mm of the distal end. The sensor 65 is preferably able to generate six position and orientation dimensions, using techniques described in the above-cited PCT Patent Publications to Ben-Haim et al., or other techniques known in the art. The sensor 65 preferably comprises two or three coils, which are generally sufficient for generating six dimensions of position information. The sensors 31, 33 are preferably able to generate five position and orientation dimensions. A preferred electromagnetic mapping sensor is manufactured by Biosense Webster (Israel) Ltd., (Tirat Hacarmel, Israel) and marketed under the trade designation NOGA.TM. Alternatively, the sensors 31, 33, 65 comprise field sensors other than coils, such as Hall effect devices or other antennae, in which case the sensors 31, 33 are preferably smaller than the sensor 65.

The sensors 31, 33, 65 are fixed to the catheter 37 by any suitable method, for example, using polyurethane glue or the like. The sensors 31, 33, 65 are electrically connected to the cable 57 (Fig. 3), which extends through the catheter body and into a control handle (not shown) of the catheter 37. The cable 57 preferably comprises multiple wires encased within a plastic covered sheath. Within the 15 BIO5203USCIP1 catheter body, the cable 57 may be enclosed within a protective sheath along with wire 59 (Fig. 3). Preferably, in the control handle, the wires of the sensor cable are connected to a circuit board (not shown), which amplifies the signals received from the position sensors and transmits them to a computer housed in the console 24 (Fig. 1), in a form understandable to the computer. Alternatively, amplifying circuitry is included at the distal end of catheter 37, so as to reduce the effect of noise.

Reference is again made to Fig. 1. In order to use the position sensors 31, 33, 65, the subject is placed in a magnetic field that is generated, for example, by situating under the subject a pad containing field generator coils 28 for generating a magnetic field. A reference electromagnetic sensor (not shown) is preferably fixed relative to the subject, e.g., taped to the subject's back, and the catheter 37 is advanced into the subject's heart and into a desired location in or near one of the cardiac chambers, for example one of the pulmonary veins. Reverting now to Fig. 2, the coils in the sensors 31, 33, 65 generate weak electrical signals indicative of their position in the magnetic field. Signals generated by both the fixed reference sensor and the sensors 31, 33, 65 sensors in the heart are amplified and transmitted to coils 28 (Fig. 1), which analyzes the signals so as to facilitate the determination and visual display of the precise location of the sensors 31, 33, 65 relative to the reference sensor.

Each of the sensors 31, 33 preferably comprises one coil, and the sensor 65 preferably comprises three non- concentric, typically mutually orthogonal coils, such as those described in the above-cited PCT Patent Publication 16 BIO5203USCIP1 WO 96/05768. The coils sense magnetic fields generated by the coils 28, which are driven by driver circuits in the generator 25 (Fig. 1). Alternatively, the sensors may generate fields, which are detected by fixed sensing coils (not shown), in which case the coils 28 can be omitted. The system 10 thus achieves continuous generation of five dimensions of position and orientation information with respect to each of the sensors 31, 33, and six dimensions with respect to position the sensor 65.

Reference is now made to Fig. 5, which is a fragmentary elevational view of a shaft 67 of a catheter that is constructed and operative in accordance with an alternate embodiment of the invention. Electrodes 69 are elliptical in contour. The longitudinal axis 71 of the shaft 67 is aligned with the major axes of the elliptical electrodes. As in the previous embodiment, the surface distribution of perforations 49 is substantially uniform.

Reference is now made to Fig. 6, which is a fragmentary elevational view of a shaft 73 of a catheter that is constructed and operative in accordance with an alternate embodiment of the invention. Electrodes 75 are elliptical in contour. The longitudinal axis 71 of the shaft 73 is aligned with the minor axes of the elliptical electrodes. As in the previous embodiments, the surface distribution of perforations 49 is substantially uniform.

The irrigated bump electrodes shown in the figure may also be arrayed along the length of catheters or probes of other types than lasso catheters. Reference is now made to Fig. 7, which is a schematic view of a cardiac catheter 77 in accordance with an alternate embodiment of the invention . 17 212307/2

The catheter 77 includes a flexible body 79. An electrode 81 is at a distal portion 83 disposed for measuring the electrical properties of the heart tissue or for ablating defective cardiac tissue. The distal portion 83 further includes an array of non-contact electrodes 85 for measuring far field electrical signals in the heart chamber. The electrodes 85 may be constructed in accordance with any of the preceding embodiments. The details are not repeated in the interest of brevity.

Electrodes 38 are arranged in a linear array in that the non-contact electrodes 38 are linearly arranged along the longitudinal axis of the distal portion 83. The distal portion 83 further includes at least one position sensor 89 that generates signals used to determine the position and orientation of the distal tip 91 within the body. The position sensor 89 is preferably adjacent to the tip 91. There is a fixed positional and orientational relationship of the position sensor 89, the tip 91 and the electrode 81. A handle 93 of the catheter 14 includes controls 95 to steer or deflect the distal portion 83, or to orient it as desired. A cable 97 comprises a receptacle 99, which connects to the handle 93 . The cable 97 may one or more isolation transformers (not shown), which electrically isolate the catheter 77 from the console 24 (FIG. 1) . Alternatively, the isolation transformers may be contained in the receptacle 99 or in the system electronics of the console 24.

In embodiments in which there are three or more electrodes 85, they may be aligned as a single linear array along the shaft of the distal portion 83 as shown in FIG. 7. 18 BIO5203USCIP1

Reference is now made to Fig. 8, which is a fragmentary elevational view of a shaft 103 of a catheter that is constructed and operative in accordance with an alternate embodiment of the invention. Alternatively, the elec- 5 trodes 85 may be disposed as one or more arrays that spiral about the having circumferentially aligned or staggered electrodes that are distributed about the circumference of the shaft 103, and may forming a plurality of linear arrays. For example, as shown in Fig. 8, electrodes 105, 107 10 form a portion of a first linear array along broken line 109. Electrodes 111, 113 form a portion of a second linear array along broken line 115.

Fig. 9 is a fragmentary elevational view of the 15 shaft or loop segment 41 of the catheter 37 in an unfurled configuration and depicted along a longitudinal axis for illustration purposes in accordance with an alternate embodiment of the present invention. As shown in Fig. 9, loop section 41 has a plurality of circumferential ring 20 ("rings" are "circumferential" by definition) bump electrodes 36A - 36J extending circumferentially 360° around outersurface or loop lumen 47 of the lasso catheter 37, 77 (Fig. 2 and Fig. 7) as best depicted in Fig. 10. 25 In this embodiment, loop section 41 has ten (10) separate circumferential ring bump electrodes 36A - 36J ex tending circumferentially 360° around the entire outer surface or loop lumen 47. 30 As best shown in Fig. 10 and Fig. 11, each circumfe rential ring bump electrode 36 (depicted collectively as 36A-36J in Fig. 9) is made of 90% platinum, 10% iridium by weight in a preferred embodiment and 80% palladium, 20% platinum by weight in an alternative embodiment. 19 BIO5203USCIP1

Each circumferential ring bump electrode 36 has a plurality of perforations 49 made in the material of each ring 36 wherein each perforation 49 is in fluid communication with cavity or chamber 38 circumferentially surrounding the outer surface or loop lumen 47. Preferably, there are anywhere between 2 and 25 separate perforations 49 in each ring 36 and more preferably ten (10) distinct perforations 49 circumferentially arranged throughout each ring 36.

The cavity or chamber 38 in each ring electrode 36 is in fluid communication with a channel or breach hole 53 in order for fluid like saline solution to be channeled through irrigating lumen 51 into breach hole 53 which feeds fluid directly into chamber 38 of the bump ring electrode 36 and ultimately dispensed through the bump ring electrode 36 through the perforations 49 dispersed or arranged circumferentially around the ring electrode 36, i.e. the saline can leave from the breach hole 53 and circulate around the chamber 38 and then leave the catheter 37, 77 via the perforations 49 in the ring 36. Preferably, one or more breach holes 53 are used for each ring electrode 36.

As best depicted in Fig. 9, the loop segment 41 of the catheter 37, 77 has a breach hole pattern (53A-53J) ranging proximally to distally along the segment 41 from approximately .005" to .375" in OD (outer diameter) . More preferably, breach hole pattern (53A-53J) ranges proximally to distally along the segment 41 from approximately .012" OD to .025" OD. 20 BIO5203USCIP1

For example, breach hole 53A in circumferential ring bump electrode 36A is approximately .0120" OD, breach hole 53 B in circumferential ring bump electrode 36B is approximately .0128" OD, breach hole 53C in circumferential ring bump electrode 36C is approximately .0136" OD, breach hole 53 D in circumferential ring bump electrode 36D is approximately .0142" OD, breach hole 53E in circumferential ring bump electrode 36E is approximately .0154" OD, breach hole 53 F in circumferential ring bump electrode 36F is approximately .0174 OD, breach hole 53G in circumferential ring bump electrode 36G is approximately .0192" OD, breach hole 53H in circumferential ring bump electrode 36H is approximately .0214" OD, breach hole 531 in circumferential ring bump electrode 361 is approximately .0236" OD and breach hole 53J in circumferential ring bump electrode 36J is approximately .0250" OD (all breach holes 53A - 53J with OD tolerance or variance +/- .0005").

As shown in Fig. 9 and described, this pattern has the OD for each breach hole 53A-53J of each ring 36A-36J ranging from smaller to larger size in diameter from proximal to distal along the length of the loop segment 41. This pattern was experimentally proven to give a relatively balanced flow out of each ring 36 when the pump (not shown) of system 10 (Fig. 1) is operated at the 60ml/min. range. The breach hole pattern (53A-53J) shown in Fig. 9 is just one example according to the present invention as the pattern (53A-53J) can be biased further to provide preferential flow to the distal rings, for example rings 36F-36J).

As best shown in Fig. 10 and Fig. 11, breach holes 53 are precisely drilled through the outer surface or loop lumen 47 through to the irrigation lumen 51 of the loop lumen 47 and through to the cavity/chamber 38 created by 21 BIO5203USCIP1 the bump of the circumferential ring electrode 36. The change in size of the breach holes 53A-53J under or beneath each ring 36A-36J (in general, larger size breach holes 53 ranging proximal to distal) in order to control how much flow each ring 36A - 36J will receive and ultimately dispense through its respective perforations 49.

Thus, it is important to note that the adjusting of the size of breach holes 53A-53J in the manner prescribed by the present invention eliminates the need to adjust the perforations 49 on the rings themselves, thereby allowing the catheter to be built with all the same ring components. This is more cost effective and efficient for manufacturing and pricing.

It is also important to note that the breach holes 53A - 53J can be adjusted to balance the flow (as shown in Fig. 9 and described above) in any desired manner or to bias the flow proximally for those applications that require greater fluid volume near the proximal end of the loop segment 41 if necessary. Thus, breach holes 53A-53J will be arranged with larger size breach hole OD more proximal and smaller size breach holes more distal, i.e. an opposite arrangement to that shown and described in Fig. 9.

Accordingly, the distal section or loop segment 41 has a breach hole pattern (53A-53J) that is customized in any desired manner in order to bias or provide preferential flow of irrigating fluid to one end of loop segment 41 or the opposite end of loop segment 41. Moreover, in accordance with the present invention, breach holes at or near the middle portion of loop segment 41, for example breach 22 BIO5203USCIP1 holes 53D-53J, can have similar sized holes for an even distribution of irrigating flow at the middle portion of the loop segment 41 while the breach holes 53A-53C and 53H-53J can have either larger or smaller sized holes than the centrally located breach holes 53D-53J for those medical applications that require this type of pattern of irrigating fluid.

Alternatively, a single ring electrode 36 is supplied with irrigating fluid by more than one breach hole 53. The shape of the hole 53 can be any desired shape, such as a rectangular shape, elliptical shape, triangular, square, etc. wherein any shape which is other than circular has an area equivalent to areas of the circular holes with OD mentioned previously above.

In accordance with a preferred embodiment, as shown in Fig. 10, the loop segment 41 has position sensor lumen 50 for at least one position sensor 89 (Fig. 2) and a third lumen 52 for a nitinol deflection wire and puller wire (not shown) . The nitinol wire is allows the catheter 27, 77 to take on its "lasso" or circular shape. Since the wire through lumen 52 is made of nitinol, it is super elastic which allows distal segment 41 to be straightened in order to facilitate movement of distal segment 41 into a guiding catheter sheath and then take its circular shape as it leaves the sheath without permanently bending. Distal segment 41 is a variable loop that easily adjusts to fit any size vein, for example, a vein sized between 25 and 15 mm in diameter. The puller wire in third lumen 52 is used to contract the diameter of the circular distal segment 41 (lasso) in order to accommodate the diameter of the vein and ensure good contact of the circumferential ring bump electrodes 36 with the inner surface of the vein 23 BIO5203USCIP1 (or other intended tissue target within the heart chamber) .

It will be appreciated by persons skilled in the art 5 that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications 10 thereof that are not in the prior art, which would occur to persons skilled in the art upon reading the foregoing description . 24