Patent Publication Number: US-2021177511-A1

Title: Catheter electrode with multiple thermocouples

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 14/289,802, filed on May 29, 2014, priority of which is hereby claimed. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to medical devices, and particularly to methods and systems for temperature sensing in intra-body medical probes. 
     BACKGROUND OF THE INVENTION 
     Various types of medical probes, such as cardiac ablation catheters, comprise means for sensing temperature. For example, U.S. Pat. No. 5,769,847, whose disclosure is incorporated herein by reference, describes a system and associated method that ablate body tissue using multiple emitters of ablating energy. The system and method convey ablating energy individually to each emitter in a sequence of power pulses. The system and method periodically sense temperature at each emitter and compare the sensed temperatures to a desired temperature established for all emitters to generate a signal individually for each emitter based upon the comparison. The system and method individually vary the power pulse to each emitter based upon the signal for that emitter to maintain the temperatures at all emitters essentially at the desired temperature during tissue ablation. 
     U.S. Patent Application Publication 2011/0160716, whose disclosure is incorporated herein by reference, describes a medical probe including an ablation electrode and a first conductor connected to the ablation electrode. The first conductor is configured to convey ablation energy to the ablation electrode. The probe also includes a second conductor which is connected at a junction to the first conductor so as to form a thermocouple at the junction. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention that is described herein provides a medical probe. The probe includes an elongate body for insertion into an organ of a patient, and an electrode that is attached to the elongate body. Multiple thermocouples are disposed at respective different locations of the electrode and electrically coupled to the electrode, and are configured to sense respective temperatures at the locations. 
     In some embodiments, the probe includes a first conductor that is connected in common to the thermocouples, and multiple second conductors that are each connected to a respective one of the thermocouples, such that electrical potentials between the first conductor and the second conductors are indicative of the respective temperatures of the thermocouples. 
     In an example embodiment, the first conductor includes copper, and the second conductors include constantan. In a disclosed embodiment, the electrode includes an ablation electrode, and the first conductor or one of the second conductors is also used for delivering Radio Frequency (RF) current to the electrode. In an embodiment, the probe includes electrical connections that electrically-connect the first conductor to the electrode at the respective locations of the thermocouples. 
     In an embodiment, at least some of the thermocouples are disposed around a perimeter of the electrode. Additionally or alternatively, at least some of the thermocouples are disposed along the electrode, in parallel with a longitudinal axis of the elongate body. 
     In another embodiment, the electrode includes irrigation holes for delivering irrigation fluid, and the multiple thermocouples are distributed among the irrigation holes. In yet another embodiment, the thermocouples are potted into one or more openings using electrically-conducting potting material. In still another embodiment, the electrode forms a circumferential ring around the elongate body of the medical probe. In an alternative embodiment, the electrode, including the thermocouples, is attached to a balloon. 
     There is additionally provided, in accordance with an embodiment of the present invention, an electrode including an electrode body and multiple thermocouples. The electrode body is attached to a medical probe inserted into an organ of a patient. The multiple thermocouples are electrically coupled at respective different locations of the electrode body and electrically coupled to the electrode body, and are configured to sense respective temperatures at the locations. In some embodiments the electrode includes an ablation electrode and the electrode body is metallic. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, pictorial illustration of a system for cardiac electrophysiological (EP) mapping and ablation, in accordance with an embodiment of the present invention; 
         FIG. 2  is a schematic, pictorial illustration of an irrigated tip ablation electrode, in accordance with an embodiment of the present invention; 
         FIG. 3  is a schematic, pictorial illustration of a ring ablation electrode, in accordance with an embodiment of the present invention; and 
         FIGS. 4 and 5  are diagrams showing interconnection of multiple Thermocouples (TCs) in an ablation electrode, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Embodiments of the present invention that are described herein provide improved medical probes for performing cardiac ablation and other minimally-invasive medical procedures. In the disclosed embodiments, a medical probe such as a cardiac catheter comprises an electrode having multiple thermocouples disposed thereon. The thermocouples are configured to sense the temperature at their respective locations, and thus provide a mapping of the temperature across the electrode. 
     Measuring temperature at multiple locations on a given electrode is important, for example, in scenarios in which the temperature gradients across the electrode are large. Such gradients occur, for example, in irrigated tip ablation electrodes. Nevertheless, the disclosed techniques are suitable for use with various other types of probes and electrodes. 
     In some embodiments, the wiring connected to the thermocouples is simplified by sharing one of the thermocouple conductors among multiple thermocouples. In an example embodiment, the thermocouples share a common copper conductor. The second conductor, e.g., a constantan conductor, is separate for each thermocouple. Additionally or alternatively, one of the thermocouple conductors, e.g., a common copper conductor, may also be used for delivering Radio Frequency (RF) current to the electrode. 
     Specific example implementations of irrigated tip and ring electrodes are described herein. Several techniques for mounting the thermocouples, e.g., using welding or potting with electrically-conductive-epoxy, are proposed. 
     System Description 
       FIG. 1  is a schematic, pictorial illustration of a system  20  for cardiac electrophysiological (EP) mapping and ablation, in accordance with an embodiment of the present invention. System  20  comprises a probe, such as a catheter  24 , and a control console  34 . In the embodiment described hereinbelow, catheter  24  is used for EP mapping an ablation in a heart  26  of a patient  30 . Alternatively, catheter  24  or other suitable probes may be used, mutatis mutandis, for other therapeutic purposes in the heart. In one embodiment, system  20  is based on the CARTO™ system produced by Biosense-Webster, Inc. (Diamond Bar, Calif.). 
     In the example system of  FIG. 1 , an operator  22 , such as a physician, inserts catheter  24  through the vascular system of patient  30  so that a distal end  28  of the catheter enters a chamber (e.g., a ventricle or atrium) of heart  26 . Catheter  24  is typically connected by a suitable connector at its proximal end to console  34 . 
     In this embodiment, system  20  uses magnetic position sensing to determine position coordinates of distal end  28  of catheter  24  inside heart  26 . For this purpose, a driver circuit  38  in console  34  drives field generators  32  to generate magnetic fields within the body of patient  30 . Typically, field generators  32  comprise coils, which are placed below the patient&#39;s torso at fixed, known positions. These coils generate magnetic fields in a predefined working volume that contains heart  26 . A magnetic field sensor (not shown) within the distal end of catheter  24  generates electrical signals in response to these magnetic fields. 
     A signal processor  40  processes these signals in order to determine the position coordinates of the distal end of catheter  24 , typically including both location and orientation coordinates. This method of position sensing is implemented, for example, in the above-mentioned CARTO system. Alternatively or additionally, system  20  may use other methods of position sensing that are known in the art, such as ultrasonic or electrical impedance-based methods. 
     Processor  40  in console  34  typically comprises a general-purpose computer processor, with suitable front end and interface circuits for receiving signals from catheter  24  and for controlling and receiving inputs from the other components of console  34 . Processor  40  may be programmed in software to carry out the functions that are described herein. The software may be downloaded to processor  40  in electronic form, over a network, for example, or it may be provided, alternatively or additionally, on tangible, non-transitory media, such as optical, magnetic or electronic memory media. Further alternatively or additionally, some or all of the functions of processor  40  may be carried out by dedicated or programmable digital hardware components. 
     Based on the signals received from catheter  24  and other components of system  20 , processor  40  drives a display  42  to present operator  22  with a three-dimensional (3D) map of heart  26 . The map may indicate cardiac electrophysiological activity measured by catheter  24 , as well as providing visual feedback regarding the position of the catheter in the patient&#39;s body and status information and guidance regarding the procedure that is in progress. Operator  22  may control system  20  using various input devices  48  on console  34 . 
     Although  FIG. 1  shows a particular system configuration and application environment, the principles of the present invention may similarly be applied in other therapeutic applications using not only catheters, but also medical probes of other types. 
     Catheter Electrodes with Multiple Thermocouples 
     In some embodiments of the present invention, catheter comprises an electrode having multiple thermocouples disposed thereon. The thermocouples are electrically-coupled to the electrode body. The thermocouples are configured for measuring the temperature at multiple respective locations on the electrode. The measured temperatures are then used by processor  40  in console  34  for controlling the procedure as appropriate. In the embodiments described herein the electrode in question is an ablation electrode. Alternatively, however, the disclosed techniques can be used with various other suitable types of electrodes. 
       FIG. 2  is a schematic, pictorial illustration of an irrigated tip ablation electrode, in accordance with an embodiment of the present invention. The electrode of  FIG. 2  is located at distal end  28  of catheter  24 . The electrode comprises a metallic electrode body  56 , which is brought into contact with a selected spot on the inner heart surface and delivers Radio-Frequency (RF) current to a selected spot. 
     Multiple irrigation holes  52  are formed in electrode body  56 . Irrigation fluid is pumped through holes  52  in order to cool the electrode and surrounding tissue during the ablation procedure. When using an ablation electrode of this sort, considerable temperature gradients may develop across the electrode. Such gradients may be on the order of 10° C., for example. 
     In order to monitor and control the temperature during ablation, the electrode of  FIG. 2  comprises multiple thermocouples (TCs)  50  that are mounted at multiple respective locations of the electrode, typically distributed among the irrigation holes. In  FIG. 2  the TCs are shown on the outside of body  56 , for the sake of clarity. Alternatively, however, the TCs may be coupled to the interior of body  56 , i.e., below the electrode surface, since metallic body  56  is thermally conductive. 
     In various embodiments, any suitable number of TCs  50  may be used, and the TCs may be distributed across body  56  in any suitable way. In an example embodiment, at least some of the TCs are distributed around the perimeter of the electrode. Additionally or alternatively, at least some of the TCs may be distributed along the electrode, in parallel with the longitudinal axis of catheter  24 . 
       FIG. 3  is a schematic, pictorial illustration of a ring ablation electrode, in accordance with an alternative embodiment of the present invention. In the present example, the ablation electrode is mounted along a section of catheter  24 , not necessarily at the very end of the distal tip. In an example embodiment, the distal tip of the catheter is annular or lasso-shaped, and one or more such ablation electrodes are mounted along the ring- or lasso-shaped distal tip. 
     In this example, too, the electrode comprises a metallic electrode body  60 , and multiple TCs  50  mounted at suitable locations of the electrode. The TCs may be mounted on the exterior or on the interior of body  60 . Any suitable number of TCs  50  may be used, and the TCs may be distributed across body  56  in any suitable way (e.g., around the electrode perimeter and/or along the electrode body). 
     The electrode configurations of  FIGS. 2 and 3  are chosen purely for the sake of conceptual clarity. In alternative embodiments, any other suitable electrode configuration, and any other suitable configuration of TCs on the electrode, can be used. 
     Thermocouple Mounting and Interconnection Schemes 
     In various embodiments, thermocouples (TCs)  50  may comprise any suitable type of TC. The description that follows refers mainly to Type T, copper-constantan (Cu—Co) TCs, but any other suitable TC type can be used in alternative embodiments. 
     In the present example, each TC  50  is formed at the junction of a copper (cu) conductor and a constantan (co) conductor. The electrical potential developing at this junction is indicative of the junction temperature. Processor  40  typically senses the temperature of a given TC by sensing the electrical potential of the TC junction. 
     In some embodiments, one of the conductors is shared by two or more of TCs  50  (possibly by all the TCs). In an example embodiment, all the TCs share a common copper conductor, while the constantan conductors are separate for each TC. In this configuration, for N TCs, the number of conductors that need to be routed through catheter  24  to console  34  is only N+1 (instead of  2 N). This technique simplifies the catheter wiring, enables reduction in catheter diameter, and/or frees internal volume in the catheter for other purposes. 
       FIG. 4  is a diagram showing interconnection of TCs  50  in an ablation electrode, in accordance with an embodiment of the present invention. In the present example, a copper conductor  64  is connected in series to TCs  50 , i.e., is common to multiple TCs. Multiple constantan conductors  68  are connected to TCs  50 , respectively, i.e., a separate constantan conductor  68  per TC. 
     Conductors  64  and  68  may run through catheter  24  to console  34 , or they may run through a partial length of the catheter, e.g., as far as the catheter handle. At the far side of the conductors, suitable circuitry senses the electrical potential between copper conductor  64  and each constantan conductor  68 . These electrical potentials are indicative of the temperatures of the respective TCs. 
     In some embodiments, a common conductor (e.g., copper conductor) is shared by all TCs  50  of the electrode. In alternative embodiments, the TCs are divided into groups, and the TCs in each group share a common conductor. Other suitable interconnection schemes can also be used. 
       FIG. 5  is a cross-section diagram showing interconnection of TCs  50  in an ablation electrode, in accordance with an embodiment of the present invention. In this example, conductor  64  is a 40-gauge copper conductor that is common to multiple TCs  50 . Conductors  68  are 48-gauge constantan conductors, one per each TC  50 . 
     In the present example, copper conductor  64  is also electrically connected to electrode body  60 , and is used for delivering RF current from a generator in console  34  to electrode body  60 . Electrical connection between copper conductor  64  and electrode body  60  is provided by one or more connections  72 . As can be seen in the figure, connections  72  are collocated with TCs  50 . In other words, copper conductor  64  is electrically-connected to electrode body  60  at the locations of the thermocouples. Typically, the gauge of conductor  64  is chosen to withstand the RF current level of the ablation signal. 
     The examples of  FIGS. 4 and 5  refer to the ring electrode of  FIG. 3 . Alternatively, however, the disclosed interconnection schemes can be used in the irrigated tip electrode of  FIG. 2 , as well as in any other suitable electrode. 
     TCs  50  are typically attached to the electrode body using some thermally-conductive means, so that the temperature sensed by the TCs will reflect the actual electrode temperature. Any suitable attachment means can be used, such as welding, bonding or potting. In an example embodiment, TCs  50  are fitted in one or more holes formed in the electrode body, and held in place using a suitable potting material. The potting material may comprise, for example, electrically-conductive epoxy. 
     In some embodiments, the electrode, including the multiple thermocouples, is attached to a balloon that is inserted into the patient body. In these embodiments, the electrode may comprise, for example, a flexible circuit or flat thin metal stripe that is bonded to an inflatable balloon. The thermocouples may be attached to the front or back of the electrode surface. When the balloon is inflated, at least part of the electrode, and the corresponding thermocouples, make contact with target tissue. 
     Although the embodiments described herein mainly address cardiac catheters and ablation electrodes, the methods and systems described herein can also be used in various other systems and applications that can benefit from multiple temperature measurements across an electrode. 
     It will thus be appreciated that the embodiments described above are cited by way of example, and 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 thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.