Abstract:
An electrophysiology catheter includes a tube having a proximal end, a distal end, and a lumen therebetween. The tube is preferably comprised of multiple sections of different flexibility, arranged so that the flexibility of the catheter increases from the proximal end to the distal end. There is a first generally hollow electrode member at the distal end. A magnetically responsive element is disposed at least partially in the hollow end electrode, for aligning the distal end of the catheter with an externally applied magnetic field. The hollow end electrode can have openings for delivering irrigating fluid, and/or a sleeve can be provided around the tube to create an annular space for the delivering of irrigating fluid. A temperature sensor can be provided to control the operation of the catheter. A localization coil can also be provided to sense the position and orientation of the catheter.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This Application is a continuation-in-part application of U.S. patent application Ser. No. 09/771,954, filed Jan. 29, 2001 (incorporated herein by reference). 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to electrophysiology catheters, and in particular to a magnetically guidable electrophysiology catheter. 
     Electrophysiology catheters are elongate medical devices that are introduced into the body and are used for sensing electrical properties of tissues in the body; applying electrical signals to the body for example for cardiac pacing; and/or applying energy to the tissue for ablation. Electrophysiology catheters have a proximal end, a distal end, and two or more electrodes on their distal end. Recently, electrophysiology catheters have been made with electrodes having openings in their distal ends for passage of normal saline solution which cools the surface tissues to prevent blood clotting. These electrodes can be difficult to navigate into optimal contact with the tissues using conventional mechanical pull wires. 
     SUMMARY OF THE INVENTION 
     The electrophysiology catheter of this invention is particularly adapted for magnetic navigation. The electrophysiology catheter comprises a tube having a proximal end and a distal end, and a lumen therebetween. The tube is preferably comprised of multiple sections of different flexibility, each section being more flexible than its proximal neighbor, so that the flexibility of the catheter increases from the proximal end to the distal end. A first generally hollow electrode member is located at the distal end of the tube. The first electrode has a generally cylindrical sidewall and a dome shaped distal end. There is a second electrode spaced proximally from the first electrode, and in general there are multiple ring electrodes spaced at equal distances proximal to the first electrode. In accordance with the principles of this invention, a magnetically responsive element is positioned at least partially, and preferably substantially entirely, within the hollow electrode member. The magnetically responsive element can be a permanent magnet or a permeable magnet. The magnet is sized and shaped so that it can orient the distal end of the catheter inside the body under the application of a magnetic field from an external source magnet. The magnet is preferably responsive to a magnetic field of 0.1 T, and preferably less. The magnet allows the distal end of the electrophysiology catheter to be oriented in a selected direction with the applied magnetic field, and advanced. Because the magnet is disposed in the hollow electrode, the distal end portion of the catheter remains flexible to facilitate orienting and moving the catheter within the body. 
     In accordance with one embodiment of the present invention, a temperature sensor, such as a thermistor or thermocouple is mounted in the distal end of the catheter for sensing the temperature at the distal end, for controlling the temperature of the catheter tip during ablation. With this embodiment, the rf energy delivered to the electrode can be adjusted to maintain a pre-selected tip temperature. 
     In accordance with another embodiment of the present invention, the end electrode is provided with a plurality of outlet openings, the magnetically responsive element has at least one passage therethrough, and a conduit is provided in the lumen to conduct irrigating fluid to the passage in the magnetically responsive element, which conducts the irrigating fluid to the end electrode where the fluid flows out the openings in the end electrode. 
     In accordance with another embodiment of the present invention, a sleeve is also provided around the tube, creating an annular space for conducting irrigating fluid to a point adjacent the end electrode. 
     In accordance with still another embodiment of the present invention, the end electrode is provided with a plurality of openings. The magnetically responsive element has a plurality of passages therein for conducting irrigating fluid delivered through a sleeve around the tube to the distal electrode tip, where it is discharged through holes in the tip. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a longitudinal cross section of a first embodiment of a catheter constructed according to the principles of this invention; 
     FIG. 2 is a longitudinal cross section of a first alternate construction of the first embodiment of a catheter constructed according to the principles of this invention, adapted to deliver irrigating fluid to the distal end; 
     FIG. 3 is a longitudinal cross sectional view of a second alternate construction of the first embodiment of a catheter constructed according to the principles of this invention, showing a separate line for providing irrigating fluid to the distal end; 
     FIG. 4 is a longitudinal cross-sectional view of a second embodiment of an electrophysiology catheter constructed according to the principles of this invention; 
     FIG. 5 is a an enlarged longitudinal cross-sectional view of the distal end portion of the electrophysiology catheter of the second embodiment; 
     FIG. 6 is a side elevation view of the magnetically responsive element of the electrophysiology catheter of the second embodiment; 
     FIG. 7 is an end elevation view of the magnetically responsive element of the electrophysiology catheter of the second embodiment; 
     FIG. 8 is a longitudinal cross-sectional view of a third embodiment of an electrophysiology catheter constructed according to the principles of this invention; 
     FIG. 9 is an enlarged longitudinal cross-sectional view of the distal end portion of the electrophysiology catheter of the third embodiment; 
     FIG. 10 is an enlarged side elevation view of the end electrode of the third embodiment; 
     FIG. 11 is an enlarged rear end elevation view of the end electrode of the third embodiment; 
     FIG. 12 is a longitudinal cross-sectional view of a fourth embodiment of an electrophysiology catheter constructed according to the principles of this invention; 
     FIG. 13 is a an enlarged longitudinal cross-sectional view of the distal end portion of the electrophysiology catheter of the fourth embodiment; 
     FIG. 14 is an enlarged side elevation view of the end electrode of the fourth embodiment; 
     FIG. 15 is an enlarged rear end elevation view of the end electrode of the fourth embodiment; 
     FIG. 16 is a longitudinal cross-sectional view of a fifth embodiment of an electrophysiology catheter constructed according to the principles of this invention; 
     FIG. 17 is a an enlarged longitudinal cross-sectional view of the distal end portion of the electrophysiology catheter of the fifth embodiment; 
     FIG. 18 is an enlarged side elevation view of the magnetically responsive element of the fifth embodiment; 
     FIG. 19 is an enlarged end elevation view of the magnetically responsive element of the fifth embodiment; 
     FIG. 20 is an enlarged longitudinal cross-sectional view of the end electrode of the fifth embodiment; and 
     FIG. 21 is an enlarged rear elevation view of the end electrode of the fifth embodiment. 
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     A first embodiment of an electrophysiology catheter constructed according to the principles of this invention is indicated generally as  20  in FIG.  1 . The electrophysiology catheter  20  has a proximal end  22  and a distal end  24 . The catheter  20  is preferably a hollow flexible tubular member comprising a sidewall  26  with a lumen  28  therethrough. The catheter  20  can be made from Pebax™. 
     The electrophysiology catheter  20  of the first embodiment has a first generally hollow electrode member  30  on its distal end  24 . The electrode member  30  has a generally cylindrical sidewall  32  and a blunt, rounded dome-shaped distal end  34 . In the preferred embodiment, the electrode member  30  is preferably about 0.250 inches long, and has an external diameter of about 0.1044 inches. According to the principles of this invention, the electrode member  30  is hollow, opening to the proximal end  22 . In the preferred embodiment the electrode member has a cavity that is about 0.205 to about 0.210 inches long, with a diameter of between about 0.091 and 0.095 inches. A magnet member  36  is disposed substantially entirely within the electrode member  30 . The magnet member  36  is preferably a solid cylindrical mass of a permanent magnetic material, such as Neodymium-Iron-Boron (Nd—Fe—B) or Samarium-Cobalt, or a permeable magnetic material, such as hiperco. 
     The proximal end portion  38  of the electrode  30  has a recessed diameter, facilitating joining the electrode  30  to the tube forming the catheter. In the preferred embodiment this recessed proximal d end portion  38  is about 0.05 inches long, and has an outside diameter of about 0.103 inches. 
     In a first alternate construction of the first preferred embodiment indicated generally as  20 ′ in FIG. 2, there are a plurality of openings  40  in the dome  34 , and there is at least one passage through the magnet member  36 , such as passage  42  extending axially through the center of the magnet member  36 , for the passage of irrigation fluid. The fluid can be provided through the lumen  28  of the catheter  20 ′ as shown in FIG. 2, or in accordance with a second alternate construction  20 ″ of the first preferred embodiment, a separate line  44  can be provided to provide irrigating fluid to the distal end  34  of the electrode  30  as shown in FIG.  3 . 
     A second annular electrode  46  is positioned on the exterior sidewall  26  of the catheter  20 , spaced proximally from the first electrode member  30 . Lead wires  48  and  50  extend proximally from the electrodes  30  and  46 . These lead wires can pass through the lumen  28  of the catheter (as shown in FIG.  3 ), or they can be embedded in the sidewall  26  (as shown in FIG.  2 ). The proximal ends of the lead wires  48  and  50  can be electrically connected to an apparatus for sensing the electrical potential between the electrodes, or to a device for applying an electric charge to the tissue between the electrodes, or to a device for applying electrical energy to the tissue for ablation between the tip electrode and a grounding pad on the patient. 
     By providing the magnet inside the first electrode, the distal end of the catheter remains more flexible, making it easier to navigate. 
     A second embodiment of a magnetically guidable electrophysiology catheter constructed according to the principles of this invention is indicated generally as  120  in FIGS. 4 and 5. The catheter  120  comprises a tube  122 , having a sidewall  124 , with a proximal end  126 , a distal end  128 , and a lumen  130  extending therebetween. The tube  122  is preferably comprised of a plurality of sections of different flexibility along its length. In this preferred embodiment, there are four sections  132 ,  134 ,  136 , and  138 , from the proximal end  126  to the distal end  128 . Each section is preferably more flexible than the next most proximal section, so that the flexibility of the tube  122 , and thus of the catheter  120 , increases from the proximal end to the distal end. The sections  132 ,  134 ,  136 , and  138  may be separate segments, joined together by ultrasonic welding or adhesive or other suitable means, or the sections  132 ,  134 ,  136  and  138  may be extruded in one continuous piece using a variable durometer extrusion process. 
     There is an end electrode  140  on the distal end of the electrophysiology catheter  120 , and at least one ring electrode  142  on the distal end portion of the catheter, proximal to the end electrode. The end electrode  140  is preferably hollow, having a dome-shaped distal end  144 . The proximal end of the electrode  140  has a section  146  of reduced outside diameter. The at least one ring electrode  142  is preferably a ring-shaped element extending circumferentially around the distal end portion of the tube  122 . A lead wire  148  extends proximally from the end electrode  140 , and a lead wire  150  extends proximally from the ring electrode  142 . The lead wires extend to the proximal end of the catheter  120  through lumen  130  of tube  122  where they can be connected to devices for measuring electric signals in the tissue in contact with the electrodes, for providing pacing signals to the tissue in contact with the electrodes, and to apply ablative energy to the tissues in contact with the electrodes. 
     There is a temperature sensor, such as thermistor  152 , on the distal end  126  of the catheter  120 , for measuring the temperature at the distal end  144  of the end electrode  140 . The thermistor  152  can be secured on an inside surface of the electrode  140  with an adhesive, and allows the temperature of the distal end of the electrode to be measured, and thus controlled. Lead wires  154  and  155  extend proximally from the thermistor  152  to the proximal end of the catheter  120  through lumen  130  of the tube  122  to provide temperature information for controlling the catheter tip temperature. 
     There is also at least one localization coil  156  in the distal end portion of the catheter  120  for locating the distal end of the catheter. The localization coil  156  is preferably disposed distally of the distal end  128  of the tube  122 , and proximally of the end electrode  140 . The localization coil  156  is enclosed in a jacket  158 , that extends between the distal end  128  of the tube  122 , and the proximal section  146  of the end electrode  140 . The proximal end of the jacket  158  may be secured to the distal end  128  of the tube  122  by ultrasonic welding or an adhesive or other suitable means. The distal end of the jacket is friction fit over the proximal end of the electrode  140 , and can be secured with a bead  159  of adhesive. The localization coil  156  receives electromagnetic signals from an array of transmitter coils located outside the patient. (Of course the transmitter coils could alternatively be located inside the patient, for example on a reference catheter, or the coils on the catheter could be transmitter coils, and the coils outside the patient or on the reference catheter could be receiver coils). Lead wires  160  and  162  extend proximally from the localization coil  156  to carry signals to the proximal end of the catheter  120 , through lumen  130  in tube  122 , to be processed to provide three dimensional location and orientation of the coil, and thus the distal end of the catheter  120 . 
     There is a magnetically responsive element  164  in the distal end portion of the catheter  120 . The magnetically responsive element  164  is preferably disposed at least partially, and preferably substantially entirely, inside the hollow end electrode  140 . This reduces the stiffness of the distal end portion of the catheter  120 . The magnetically responsive element  164  may be a body of a permanent magnetic material, such as neodymium-iron-boron (Nd—Fe—B), or a magnetically permeable material, such as iron. As shown in FIGS. 6 and 7, the magnetically responsive element  164  is preferably hollow, having a generally central passage  166 . The lead wires  154  and  155  from the thermistor  152  extend through the passage  166  in the magnetically responsive element  164 . There are a plurality of longitudinal grooves  168  in the exterior surface of the magnetically responsive element  164 . As shown in FIG. 7, there are preferably three grooves  168  in the magnetically responsive element  164 . The lead wire  148  passes through one of these grooves  168  to the end electrode  140 . In the first preferred embodiment the magnetically responsive element is a generally cylindrical Nd—Fe—B magnet 0.240 inches long and 0.0885 inches in diameter. The passage  166  has a diameter of 0.023 inches. 
     A third embodiment of a magnetically guidable electrophysiology catheter constructed according to the principles of this invention is indicated generally as  220  in FIGS. 8 and 9. The catheter  220  comprises a tube  222 , having a sidewall  224 , with a proximal end  226 , a distal end  228 , and a lumen  230  extending therebetween. The tube  222  is preferably comprised of a plurality of sections of different flexibility along its length. In this preferred embodiment, there are four sections  232 ,  234 ,  236 , and  238 , from the proximal end  226  to the distal end  228 . Each section is preferably more flexible than the next most proximal section,  50  that the flexibility of the tube  222 , and thus of the catheter  220 , increases from the proximal end to the distal end. The sections  232 ,  234 ,  236 , and  238  may be separate segments, joined together by ultrasonic welding or adhesive or other suitable means, or the sections  232 ,  234 ,  236  and  238  may be extruded in one continuous piece using a variable durometer extrusion process. 
     There is an end electrode  240  on the distal end of the electrophysiology catheter  220 , and at least one ring electrode  242  on the distal end portion of the catheter, proximal to the end electrode. The end electrode  240  is preferably hollow, having a dome-shaped distal end  244 . The proximal end of the electrode  240  has a section  246  of reduced outside diameter. There are a plurality of openings  270  in the distal end  244  of the electrode  240 . As shown in FIGS. 10 and 11 there are preferably three openings  270 , extending generally axially through the end electrode  240 . In this preferred embodiment, the end electrode  240  is about 0.250 inches long, with an outside diameter of about 0.104 inches, and an internal diameter of 0.0895 inches. The outside diameter of section  246  has an outside diameter of 0.096 inches, and is 0.050 inches long. 
     The at least one ring electrode  242  is preferably a ring-shaped element extending circumferentially around the distal end portion of the tube  222 . A lead wire  248  extends proximally from the end electrode  240 , and a lead wire  250  extends proximally from the ring electrode  242 . The lead wires extend to the proximal end of the catheter  220 , embedded in the sidewall  224  of the tube  222 , where they can be connected to devices for measuring electric signals in the tissue in contact with the electrodes, for providing pacing signals to the tissue in contact with the electrodes, and to apply ablative energy to the tissues in contact with the electrodes  240  and  242 . 
     There is a temperature sensor, such as thermistor  252 , on the distal end of the catheter  220 , for measuring the temperature adjacent the distal end  244  of the end electrode  240 . The thermistor  252  can be secured on an inside surface of the electrode  240  with an adhesive, and allows the temperature of the electrode to be measured. Lead wires  254  and  255  extend proximally from the thermistor  252  to the proximal end of the catheter  220  through the lumen  230  of the tube  222  to provide temperature information for controlling the catheter. 
     There is also at least one localization coil  256  in the distal end portion of the catheter  220  for locating the distal end of the catheter. The localization coil  256  is preferably disposed distally of the distal end  228  of the tube  222 , and proximally of the end electrode  240 . The localization coil  256  is enclosed in a jacket  258 , that extends between the distal end  228  of the tube  222 , and the proximal section  246  of the end electrode  240 . The proximal end of the jacket  258  may be secured to the distal end  228  of the tube  222  by ultrasonic welding or an adhesive or other suitable means. The distal end of the jacket is friction fit over the proximal end of the electrode  240 , and can be secured with a bead  259  of adhesive. The localization coil  256  preferably receives electromagnetic signals from an array of transmission coils located outside the patient. Lead wires  260  and  262  extend proximally from the localization coil  256  in lumen  230  of tube  222  to carry signals to the proximal end of the catheter  220 , to be processed to provide three dimensional location and orientation of the coil, and thus the distal end of the catheter  220 . 
     There is a magnetically responsive element  264  in the distal end portion of the catheter  220 . The magnetically responsive element  264  is preferably disposed at least partially, and preferably substantially entirely, inside the hollow end electrode  240 . This reduces the stiffness of the distal end portion of the catheter  220 . The magnetically responsive element  264  may be a body of a permanent magnetic material, such as neodymium-iron-boron (Nd—Fe—B), or a magnetically permeable material, such as iron. The magnetically responsive element  264  is preferably hollow, having a generally central passage  266 . A conduit  272  extends through the lumen  230  of the tube  222  and connects to the generally central passage  266  of the magnetically responsive element  264  to deliver irrigating fluid to the distal end of the catheter  220 , where it exits through the openings  270 . If the lead wires from the electrodes, thermistor, and localization coil are embedded in the wall  224 , then conduit  272  may not be necessary, as irrigation fluid can flow to the distal end of the catheter without contacting the lead wires, conversely, if the conduit  272  is present, the wires can pass through the lumen  230 . The irrigating fluid cools the electrode  240  and the tissue in contact with the electrode  240 . There are a plurality of longitudinal grooves in the exterior surface of the magnetically responsive element  264  (similar to grooves  168 ). There are preferably three grooves in the magnetically responsive element  264 . The lead wire  248  passes through one of these grooves to the end electrode  240 . The magnetically responsive element may be coated with an electrically thermally insulating material which also prevents fluid contact with the magnet surfaces. For this purpose, the tube  272  may pass through lumen  266  to insulate the inner surface of the magnetically responsive element. The lead wires  254  and  255  pass through another of the grooves. The magnetically responsive element  264  may be the same size and shape as the magnetically responsive element  164 , described above. 
     A fourth embodiment of a magnetically guidable electrophysiology catheter constructed according to the principles of this invention is indicated generally as  320  in FIGS. 12 and 13. The catheter  320  comprises a tube  322 , having a sidewall  324 , with a proximal end  326 , a distal end  328 , and a lumen  330  extending therebetween. The tube  322  is preferably comprised of a plurality of sections of different flexibility along its length. In this preferred embodiment, there are four sections  332 ,  334 ,  336 , and  338 , from the proximal end  326  to the distal end  328 . Each section is preferably more flexible than the next most proximal section, so that the flexibility of the tube  322 , and thus of the catheter  320 , increases from the proximal end to the distal end. The sections  332 ,  334 ,  336 , and  338  may be separate segments, joined together by ultrasonic welding or adhesive or other suitable means, or the sections  332 ,  334 ,  336  and  338  may be extruded in one continuous piece using a variable durometer extrusion process. 
     There is an end electrode  340  on the distal end of the electrophysiology catheter  320 , and at least one ring electrode  342  on the distal end portion of the catheter, proximal to the end electrode. The end electrode  340  is preferably hollow, having a dome-shaped distal end  344 . The proximal end of the electrode  340  has a section  346  of reduced outside diameter. As shown in FIGS. 14 and 15, there are preferably a plurality of longitudinally extending grooves  374  in the external surface of the end electrode  340 . In this preferred embodiment, there are six grooves  374  equally spaced about the circumference of the end electrode  340 . In this preferred embodiment, the end electrode  340  is about 0.250 inches long, with an outside diameter of about 0.104 inches, and an internal diameter of 0.0895 inches. The outside diameter of section  346  has an outside diameter of 0.096 inches, and is 0.050 inches long. 
     The at least one ring electrode  342  is preferably a ring-shaped element extending circumferentially around the distal end portion  328  of the tube  322 . A lead wire  348  extends proximally from the end electrode  340 , and a lead wire  350  extends proximally from the ring electrode  342 . Ring electrode  342  could be disposed on the outside of the sleeve  376  (discussed in more detail below). In that case the lead wire  350  extends through the wall  376 , and the wall of the tube  322 , into the lumen  330 . The lead wires  348  and  350  extend to the proximal end  326  of the catheter  320  through the lumen  330  of the tube  322  where they can be connected to devices for measuring electric signals in the tissue in contact with the electrodes, for providing pacing signals to the tissue in contact with the electrodes, and to apply ablative energy to the tissues in contact with the electrodes. 
     There is a temperature sensor, such as thermistor  352 , on the distal end  328  of the catheter  320 , for measuring the temperature at the distal end  344  of the end electrode  340 . The thermistor  352  can be secured on an inside surface of the electrode  340  with an adhesive, and allows the temperature of the distal end of the electrode to be measured. Lead wires  354  and  355  extend proximally from the thermistor  352 , through the lumen  330  of the tube  322 , to the proximal end of the catheter  320  to provide temperature information for controlling the catheter. 
     There is also at least one localization coil  356  in the distal end portion of the catheter  320  for locating the distal end of the catheter  320 . The localization coil  356  is preferably disposed distally of the distal end  328  of the tube  322 , and proximally of the end electrode  340 . The localization coil  356  is enclosed in a jacket  358 , that extends between the distal end  328  of the tube  322 , and the proximal section  346  of the end electrode  340 . The proximal end of the jacket  358  may be secured to the distal end  328  of the tube  322  by ultrasonic welding or an adhesive or other suitable means. The distal end of the jacket  358  is friction fit over the proximal end of the electrode  340 . The localization coil  356  preferably receives electromagnetic signals from an array of transmitter coils located outside of the patient. Lead wires  360  and  362  extend proximally from the localization coil  356 , through the lumen  330  of the tube  322 , to carry signals to the proximal end of the catheter  320 , to be processed to provide three dimensional location and orientation of the coil, and thus the distal end of the catheter  320 . 
     There is a magnetically responsive element  364  in the distal end portion of the catheter  320 . The magnetically responsive element  364  is preferably disposed at least partially, and preferably substantially entirely, inside the hollow end electrode  340 . This reduces the stiffness of the distal end portion of the catheter  320 . The magnetically responsive element  364  may be a body of a permanent magnetic material, such as neodymium-iron-boron (Nd—Fe—B), or a magnetically permeable material, such as iron. The magnetically responsive element  364  is preferably hollow, having a generally central passage  366 . The lead wire  354  from the thermistor  352  extends through the passage  366  in the magnetically responsive element  364 . There are a plurality of longitudinal grooves in the exterior surface of the magnetically responsive element  364 . There are preferably three grooves in the magnetically responsive element  364 . The lead wire  348  passes through one of these grooves to the end electrode  340 . The magnetically responsive element  364  may be the same size and shape as the magnetically responsive element  64 , described above. 
     A sleeve  376  surrounds all but the distal-most portion of the catheter  320 , creating an annular space  378  through which irrigating fluid can be passed to cool the end electrode  340 . The fluid passes through the annular space  378 , and exits through the spaces formed between the grooves  374  in the end electrode  340  and the sleeve  376 . Passage of fluid through the grooves  374  provides a more uniform distribution of cooling fluid, than if the grooves are omitted. 
     A fifth embodiment of a magnetically guidable electrophysiology catheter constructed according to the principles of this invention is indicated generally as  420  in FIGS. 16 and 17. The catheter  420  comprises a tube  422 , having a sidewall  424 , with a proximal end  426 , a distal end  428 , and a lumen  430  extending therebetween. The tube  422  is preferably comprised of a plurality of sections of different flexibility along its length. In this preferred embodiment, there are four sections  432 ,  434 ,  436 , and  438 , from the proximal end  426  to the distal end  428 . Each section is preferably more flexible than the next most proximal section, so that the flexibility of the tube  422 , and thus of the catheter  420 , increases from the proximal end to the distal end. The sections  432 ,  434 ,  436 , and  438  may be separate segments, joined together by ultrasonic welding or adhesive or other suitable means, or the sections  432 ,  434 ,  436  and  438  may be extruded in one continuous piece using a variable durometer extrusion process. 
     There is an end electrode  440  on the distal end of the electrophysiology catheter  420 , and at least one ring electrode  442  on the distal end portion of the catheter, proximal to the end electrode. The end electrode  440  is preferably hollow, having a dome-shaped distal end  444 . The proximal end of the electrode  440  has a section  446  of reduced outside diameter. As shown in FIGS. 20 and 21, there are a plurality of openings  480  in the side of the end electrode  440  and openings  482  in the distal end  444  of the end electrode. 
     The at least one ring electrode  442  is preferably a ring-shaped element and can extend circumferentially around the distal end portion of the. In that case the lead wire  448  extends proximally from the end electrode  440 , and a lead wire  450  extends proximally from the ring electrode  442 , through the wall of the sleeve  478  and the tube  422 . The lead wires  448  and  450  extend through lumen  430  of the tube  422  to the proximal end of the catheter  420  where they can be connected to devices for measuring electric signals in the tissue in contact with the electrodes, for providing pacing signals to the tissue in contact with the electrodes, and to apply ablative energy to the tissues in contact with the electrodes. 
     There is a temperature sensor, such as thermistor  452 , on the distal end of the catheter  420 , for measuring the temperature at the distal end  444  of the end electrode  440 . The thermistor  452  can be secured on an inside surface of the electrode  440  with an adhesive, and allows the temperature of the distal end of the electrode to be measured. Lead wires  454  and  455  extend proximally from the thermistor  452 , through the lumen  430  of the tube  422 , to the proximal end of the catheter  420  to provide temperature information for controlling the temperature of the catheter tip. Thermistor  552  can alternatively be a thermocouple or other temperature sensing device. 
     There is also at least one localization coil  456  in the distal end portion of the catheter  420  for locating the distal end of the catheter. The localization coil  456  is preferably disposed distally of the distal end  428  of the tube  422 , and proximally of the end electrode  440 . The localization coil  456  is enclosed in a jacket  458 , that extends between the distal end  428  of the tube  422 , and the proximal section  446  of the end electrode  440 . The localization coil  456  preferably receives electromagnetic signals from an array of transmitter coils located outside of the patient&#39;s body. Lead wires  460  and  462  extend proximally from the localization coil  456 , through lumen  430  of the tube  422 , to carry signals to the proximal end of the catheter  420 , to be processed to provide three dimensional location and orientation of the coil, and thus the distal end of the catheter  420 . 
     There is a magnetically responsive element  464  in the distal end portion of the catheter  420 . The magnetically responsive element  464  is preferably disposed at least partially, and preferably substantially entirely, inside the hollow end electrode  440 . This reduces the stiffness of the distal end portion of the catheter  420 . The magnetically responsive element  464  may be a body of a permanent magnetic material, such as neodymium-iron-boron (Nd—Fe—B), or a magnetically permeable material, such as iron. There are a plurality of longitudinal grooves  468  in the exterior surface of the magnetically responsive element  464 . As shown in FIGS. 18 and 19, there are preferably six grooves  468  in the magnetically responsive element  464 . The lead wire  448  and the lead wires  464  and  465  extend through one of the grooves  468 . 
     A sleeve  476  surrounds all but the distal-most portion of the catheter  420 , creating an annular space  478 . Irrigating fluid can be passed through the annular space  478 , and then into the openings  480  in the side of the end electrode  440 . The fluid then passes through channels formed between the grooves  468  and the inside wall of the end electrode, where it can flow out the openings  482  in the distal end of the end electrode.