Local detection of catheter to tissue proximity with enhanced spatial coverage

Abstract

To estimate proximity of catheters to tissue.SOLUTION: A system includes a catheter, a signal generator, an interface, and a processor. The catheter includes an expandable distal-end assembly including (i) a plurality of functional electrodes that are at least partially external to an inner volume of the assembly, the functional electrodes configured to be placed in contact with wall tissue of a cardiac chamber, (ii) a proximal reference electrode located at a proximal end of the assembly externally to the inner volume, and (iii) a distal reference electrode located at a distal edge of the expandable assembly externally to the inner volume. The signal generator is configured to generate the AC signal between the proximal and distal reference electrodes. The interface is configured to sense the resulting electrical AC signal. The processor is configured to, based on the sensed AC signals, determine, for at least one given functional electrode, proximity of the electrode to the wall tissue.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure generally relates to invasive medical probes, and more particularly to estimating the proximity of a catheter to tissue.

Background Art

[0002] Techniques for estimating the proximity of electrodes of a catheter to tissue have been previously proposed in the patent literature. For example, U.S. Patent Application Publication No. 2021 / 0059743 describes a system including an expandable frame and a processor. The expandable frame includes (i) one or more ablation electrodes disposed on the outer surface of the frame and configured to be placed in contact with the wall tissue of a patient's cavity, and (ii) a stem electrode coupled immediately proximal to the balloon and an end electrode coupled immediately distal to the balloon, respectively. The processor is configured to (a) measure one or more first impedances between one or more of the ablation electrodes and the stem electrode, (b) measure one or more second impedances between one or more of the ablation electrodes and the end electrode, and (c) determine, based on the first impedance and the second impedance, whether at least some of the one or more ablation electrodes are in physical contact with the wall tissue.

[0003] A more complete understanding of the present disclosure will be obtained by reading the following detailed description of the embodiments of the present disclosure in conjunction with the drawings.

Brief Description of the Drawings

[0004]

Figure 1

Figure 2

Figure 3

Figure 4

[0005] Overview The wall tissue of a heart cavity can be electroanatomically mapped and / or ablated using a catheter having a plurality of functional electrodes attached to an expandable distal end assembly of the catheter. In a mapping and / or ablation procedure in a heart cavity, a physician operates the expanded distal end assembly to contact the electrodes with the heart cavity wall to acquire and / or apply electrical signals.

[0006] The quality of electrical mapping and / or ablation depends on the proximity of the functional electrodes to the wall tissue of the cavity. The proximity can typically be estimated using a parameter called a tissue proximity indication (TPI). The scale of proximity can use any unit (e.g., an index in the range of 1 to 10), or can give a physical unit of distance.

[0007] For example, TPI can be estimated from the AC impedance readings by measuring the electrical impedance between a functional electrode of unknown proximity to tissue, disposed on an expandable distal assembly, and a reference ring electrode located on the proximal base section of the expandable assembly, where the reference electrode is located outside the internal volume defined by the expandable assembly. An example of such an electrical technique is described in U.S. Patent Application No. 18 / 530,268, filed on December 6, 2023, under the title "Reference Electrode Dedicated to Catheter Tissue Proximity Estimation".

[0008] However, in a large distal assembly, electrical measurements of more distal electrodes can be difficult (e.g., because the impedance to the reference electrode on the base section may not be sensitive enough to tissue proximity).

[0009] Embodiments of the present disclosure described herein expand the effective range of proximity sensing by adding a distal reference electrode effective at the distal end of the assembly, located outside the internal volume defined by the expandable assembly, to the proximal ring electrode. The AC signal generator, during operation, applies an AC signal between the distal and proximal ends to establish an electric field therebetween.

[0010] Due to the increase in electrical impedance by the tissue, as the assembly approaches the wall tissue, the electric field increases around some of the functional electrodes. The reason for the increase is that, as seen in Figure 3, the electric field lines are pushed away from the tissue and become denser in the adjacent blood. Typically, both the distal reference electrode and the proximal reference electrode remain located within the blood pool.

[0011] A circuit is used to measure the resulting AC signal at each of the functional electrodes to detect the increased impedance. When an electric field is applied using a current source of a certain magnitude, the functional electrodes function like independent voltage sensors. The voltage increases with the impedance. When a voltage source is used, the functional electrodes function like independent current sensors. The current decreases with the impedance.

[0012] The change in the resulting AC voltage and / or current signal is sensed between the functional electrode and another given electrode such as a proximal reference ring electrode and / or a distal reference electrode and / or a remote field electrode located within the internal volume and / or another functional electrode on the spline.

[0013] In some embodiments, such as the embodiment of the basket assembly of FIG. 2, the distal reference electrode is created by electrically connecting to a distal structure that connects the spline of the assembly at the distal end. In other embodiments, the distal electrode is disposed (e.g., on a membrane).

[0014] The change in impedance as a function of the proximity of the functional electrode to the tissue to detect the proximity of the catheter to the tissue expands the spatial effective range, as shown in FIG. 3.

[0015] Description of the System FIG. 1 is a schematic depiction of a catheter-based electroanatomical (EA) mapping and ablation system 10 according to an embodiment of the present disclosure. The system 20 is configured to determine, for example, whether a given functional electrode 26 among the plurality of functional electrodes 26 of the basket catheter 14 is in sufficient contact with (or in proximity to) the tissue or is immersed in the blood pool 33 of the cardiac chamber before performing a diagnosis and / or ablation.

[0016] System 10 includes one or more catheters that are percutaneously inserted by a physician 24 into a cardiac chamber or vascular structure of a patient through the patient's vasculature. Typically, a delivery sheath catheter is inserted into the left atrium or right atrium near a desired location of the heart 12. Thereafter, one or more catheters can be inserted into the delivery sheath catheter to reach a desired location. The one or more catheters may include a catheter dedicated to sensing intracardiac electrogram (IEGM) signals, a catheter dedicated to ablation, and / or a catheter dedicated to both sensing and ablation. An exemplary basket catheter 14 configured to sense IEGM is shown herein. As seen in insertion view 45, the physician 24 contacts the heart wall with a basket-type expandable distal end assembly 28 (hereinafter also referred to as "expandable distal end assembly 28") attached to the shaft 44 of the catheter 14 to sense a target site within the heart 12. In the case of ablation, the physician 24 similarly moves the distal end of the ablation catheter to the target site for ablation.

[0017] As seen in insertion view 65, the catheter 14 is an exemplary catheter that optionally includes one, preferably a plurality of functional electrodes 26 configured to detect IEGM signals distributed across a plurality of splines 22 in the expandable distal end assembly 28. The catheter 14 additionally includes a proximal position sensor 29 (e.g., TAS29 with three EMCs) embedded in the distal end 46 of the shaft 44 near the expandable distal end assembly 28 to track the position of the distal end of the expandable distal end assembly 28. Optionally and preferably, the position sensor 29 is a magnetic-based position sensor that includes a magnetic coil for sensing a three-dimensional (3D) position. The distal end 46 of the shaft 44 may include an amplifier circuit configured to amplify the output from the three EMCs of the sensor 29.

[0018] The magnetic position sensor 29 operates with an external position pad 25 that includes a plurality of magnetic coils 32 configured to generate a magnetic field within a given working volume. The processor can use the operation with the external position pad 25 (at different frequencies for each EMC) to determine the position of the EMC 29 on the coordinate system of the position tracking system.

[0019] Details of magnetic - based position sensing techniques are described in U.S. Pat. Nos. 5,539,199; 5,443,489; 5,558,091; 6,172,499; 6,239,724; 6,332,089; 6,484,118; 6,618,612; 6,690,963; 6,788,967; 6,892,091.

[0020] The system 10 includes one or more electrode patches 38 disposed for skin contact with the patient 23 to establish a position reference for the position pad 25 and impedance - based tracking of the functional electrodes 26. For impedance - based tracking, a current is directed to the electrodes 26 and detected at the electrode - skin patches 38, whereby the location of each electrode can be triangulated via the electrode patches 38. The real - time orientation of the expandable distal - end assembly 28 of the catheter 14 can be calculated from the position of the tracked electrodes 26. This relative orientation is revealed by the angle formed between the distal end 46 and the longitudinal axis 42 of the expandable assembly 28 (extending to the distal edge 16 of the assembly).

[0021] Details of impedance - based position tracking techniques are described in U.S. Pat. Nos. 7,536,218; 7,756,576; 7,848,787; 7,869,865; and 8,456,182.

[0022] Catheter 14 is configured to acquire an electrical signal indicative of the proximity of any given functional electrode 26 to the wall tissue of the heart 12. For this purpose, signal generator 35 is configured to generate an AC signal between a distal reference electrode 37 and a proximal reference ring electrode 17, both of which are located outside the internal volume 77 defined by the spline of assembly 28.

[0023] Signal generator 35 can be a voltage source and / or a current source or a combination of both. The readout circuitry in PIU 30 is configured to monitor (e.g., sense) the resulting AC signals respectively between each of the functional electrodes 26 and a reference electrode, such as distal reference electrode 37 and / or proximal reference electrode 17, etc. The sensed AC signals are used to estimate the proximity of each functional electrode 26 to the tissue, as will be described later with respect to FIG. 3.

[0024] Recorder 11 displays the potential map 21 captured by the body surface ECG electrodes 18 and the intracardiac electrogram (IEGM) captured by the functional electrodes 26 of catheter 14. Recorder 11 may include pacing capabilities for pacing the rhythm of the heart and / or may be electrically connected to an independent pacer.

[0025] System 10 may include an ablation energy generator 50 adapted to deliver ablation energy to a subset of the plurality of electrodes 26 in the distal assembly 28 of catheter 14 configured for ablation. The energy generated by ablation energy generator 50 can include high frequency (RF) energy or pulsed field ablation (PFA) energy, or a combination thereof, including unipolar or bipolar high voltage DC pulses that can be used to effect irreversible electroporation (IRE), but is not limited thereto.

[0026] The patient interface unit (PIU) 30 is configured to establish electrical communication between a catheter, an electrophysiology device, a power source, and a workstation 55 that controls the operation of the system 10. The electrophysiology devices of the system 10 may include, for example, a plurality of catheters, a position pad 25, body surface ECG electrodes 18, electrode patches 38, an ablation energy generator 50, and a recorder 11. Optionally and preferably, the PIU 30 additionally includes the processing capabilities to perform real-time calculations of catheter position and execute ECG calculations.

[0027] The workstation 55 includes a memory 57, a processor unit 56 having a memory or storage device in which appropriate operating software is loaded, and user interface functions. The workstation 55 may optionally (i) render to model the endocardial anatomical structure in three-dimension (3D) and display a model or anatomical map 20 on a display device 27, (ii) display on the display device 27 a representative visual display or image of an activation sequence (or other data) compiled from the recorded potential map 21 overlaid on the rendered anatomical map 20, (iii) display the real-time position and orientation of a plurality of catheters within the heart chamber, and (iv) display on the display device 27 a site of interest such as the location where ablation energy has been applied, and may provide a plurality of functions including. One commercially available product embodying the elements of the system 10 is available as the CARTO (trademark) 3 system available from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA, 92618.

[0028] Although a basket assembly is described in FIG. 1, the disclosed technique can be applied, with necessary modifications, to an expandable balloon assembly having an expandable membrane, in which case the functional electrodes are disposed on the membrane.

[0029] Estimation of Touch Proximity (TP) of Functional Electrodes of an Expandable Assembly Figure 2 is a schematic depiction of a basket catheter assembly 281 configured for electrical measurement of the proximity of functional electrode 226 to the wall tissue of a cavity, according to an embodiment of the present disclosure. The basket assembly 281 can be used to practice the basket assembly 28 of FIG. 1 above. As shown, the assembly 281 is part of a catheter 214 that further includes a shaft 244 having a distal end 246. The distal end assembly 228 includes a proximal base 227 configured to couple the assembly to the distal end 246 of the shaft 244.

[0030] The basket assembly 281 is realized as an expandable frame that includes a plurality of splines 222, in which case the functional electrodes 226 are coupled to the splines. Each of the splines 222 is electrically insulated from the environment over most of its area by an insulating layer 262.

[0031] When expanded, as shown in FIG. 2, the expandable distal end assembly 281 forms an internal volume 277. At the base of the internal volume 277 of the assembly, the remote field electrode 223 is used to remove the remote field signal from the IEGM signal acquired by the electrode 226.

[0032] The plurality of functional electrodes 226 are configured to be at least partially outside the internal volume and positioned to contact the wall tissue of the cavity. The proximal reference ring electrode 217 (such as the ring electrode 17 of FIG. 1) is disposed outside the internal volume 277 and on the proximal base 227 of the expandable distal end assembly 281. The position of the ring-shaped electrode 217 on the base 227 is set to avoid contact with the tissue wall while the distal end assembly 281 is in the expanded state.

[0033] The distal reference ring electrode 237 (such as the ring electrode 37 in FIG. 1) is disposed at the distal end of the expandable distal assembly 281 outside the internal volume 277. The distal reference electrode 237 is realized by the non-electrically insulated distal portion 257 of the nitinol assembly 281. The distal reference electrode 237 is configured to be disposed within the cavity while preventing contact with the wall tissue by being positioned thereon about the distal edge. The distal electrode 237 is electrically realized (e.g., functions as an electrode) by electrically wiring the spline 222 to a circuit for applying an AC signal. The other pole of such a circuit is the proximal reference electrode 217.

[0034] The proximal base section 227 further includes a mechanical guard ring 231 that protrudes from the proximal base beyond the reference electrode 227 to prevent the reference electrode 227 from contacting the wall tissue.

[0035] The processor 56 applies an AC signal between the reference electrodes 237 and 217. The processor estimates the proximity of a given electrode 226 to the wall tissue (the wall tissue is not shown) based on the resulting monitored AC signal between the electrode 226 and the reference electrodes 237 and 217. The processor may use the monitored AC signal (e.g., voltage or current), or the change in the monitored AC signal relative to a baseline AC signal obtained when all electrodes are deep within the blood pool, as detailed in FIG. 3.

[0036] A further improvement in measurement accuracy can be achieved by applying an internal electrical insulation coating 241 to the electrode 226 such that the electrode portion in the blood contacting the tissue is minimized. The coating 241 can be of a polymer type or another dielectric layer (e.g., silicon nitride).

[0037] Although a basket assembly is described in FIG. 2, the disclosed technique can be applied, with the necessary modifications, to an expandable balloon assembly having an expandable membrane, in which case the functional electrodes and the distal reference electrode are disposed on the membrane.

[0038] Estimation of Touch Proximity (TP) of Distal Functional Electrodes of an Expandable Assembly FIG. 3 is a schematic depiction of the basket assembly 281 of FIG. 2, according to an embodiment of the present disclosure, in which some of the functional electrodes 226 are positioned deep within the blood pool 33 and others are positioned proximate to the wall 81 of the tissue 131.

[0039] During operation, the AC signal generator 35 applies an AC signal between the distal reference electrode 237 and the proximal reference electrode 217 to establish electric field lines (366, 368) therebetween.

[0040] As seen in the figure, as the assembly 281 approaches the wall tissue 131, due to the increase in electrical impedance by the tissue 88, the electric field line 368 becomes denser around some of the functional electrodes 226. The reason for the increase is that the electric field line 368 is pushed away from the tissue 88 and becomes denser in the adjacent blood. Typically, both the distal reference electrode and the proximal reference electrode remain positioned within the blood pool.

[0041] A circuit (e.g., within the PIU 30) is used to measure the resulting AC signal at each of the functional electrodes 226 to detect the increased impedance. When an electric field is applied using a current source of a certain magnitude, the functional electrodes 226 function like independent voltage sensors. The voltage increases with the impedance. When a voltage source is used, the functional electrodes 226 function like independent current sensors. The current decreases with the increase in impedance.

[0042] The actual proximity of each functional electrode or subset (e.g., group) of electrodes can be presented to the user in the GUI in the form of a TPI scale.

[0043] Method for Estimating Touch Proximity (TP) of Distal Functional Electrodes of an Expandable Assembly Figure 4 is a flowchart schematically showing a method and an algorithm for estimating the proximity of a functional electrode to the wall tissue of a cavity according to an embodiment of the present invention. According to this embodiment, the algorithm executes a process that starts by identifying, in a basket baseline positioning step 302, that an extended basket assembly 281 is within a blood pool 33 in the heart cavity of the heart 12. This identification can be performed using fluoroscopy or contact force sensing to verify that there is no mechanical interaction between the basket assembly 281 and the ventricular wall tissue at least in some time portions.

[0044] Next, in an AC signal (i.e., voltage or current) application step 304, the system 10 applies an AC signal between the reference electrodes 237 and 217.

[0045] Then, in a step 306 of monitoring the resulting AC signal, the system 10 monitors the resulting AC signal between each of the functional electrodes 226 and a reference electrode, such as the distal reference electrode 237 and / or the proximal reference electrode 217 and / or the remote field electrode 223, etc.

[0046] In a resulting AC signal range identification step 308, since the basket often contacts the wall tissue of the cavity, the processor identifies the range of the AC signal for contact and non-contact with respect to the monitored cumulative value. This range can be specified from the integrated output from all the functional electrodes 226.

[0047] Using the monitored AC signals and their identified ranges, the processor calculates the TPI for each functional electrode or for a group of such electrodes in a TPI calculation step 310.

[0048] Finally, in a TPI reporting step 312, the system 10 reports the TPI for each of the functional electrodes 226 or a group thereof to indicate the contact and / or proximity of these functional electrodes to the heart cavity wall tissue.

[0049] The exemplary flowchart shown in FIG. 4 is selected purely for the purpose of clarifying concepts. This embodiment also includes additional steps of algorithms such as obtaining an intracardiac electrocardiogram, but these are intentionally omitted from the disclosure herein to provide a more simplified flowchart. In addition, other steps such as temperature measurement and application of perfusion are also omitted for clarity of presentation.

Example

[0050] (Example 1) System (10) includes a catheter (14), a signal generator (35), an interface (30), and a processor (56). The catheter includes a shaft (44) having a distal end (46) configured for insertion into a patient's (23) heart cavity, and an expandable distal end assembly (28) that defines an internal volume (77) upon expansion, the expandable distal end assembly including: (i) a plurality of functional electrodes (26) at least partially external to the internal volume (77) and configured to be disposed in contact with the wall tissue (131) of the heart cavity; (ii) a proximal reference electrode (17) external to the internal volume (77) and located at the proximal end of the expandable distal end assembly (28); and (iii) a distal reference electrode (37) external to the internal volume (77) and located at the distal end (16) of the expandable distal end assembly (28). The proximal reference ring electrode (17) and the distal reference electrode (37) are configured to be coupled to each other and each: (i) generate an AC signal between the reference electrodes (17, 37); and (ii) sense the resulting AC signal at each of the plurality of functional electrodes (26) and at a given electrode (17, 37, 223). The signal generator (35) is configured to generate an AC signal between the distal reference electrode (37) and the proximal reference ring electrode (17). The interface (30) is configured to sense the resulting AC signal between each of the plurality of functional electrodes (26) and a given electrode (17, 37, 223). The processor (56) is configured to determine, based on the sensed AC signal, the proximity of a given functional electrode (26) of at least one of the plurality of functional electrodes to the wall tissue (131) of the heart cavity.

[0051] (Example 2) A given electrode (26) is one of a proximal reference ring electrode (17, 217), a distal reference electrode (37, 237), a remote field electrode (223) located within the internal volume (77, 277), and another functional electrode (26) on a spline, of the system (10) described in Example 1.

[0052] (Example 3) The signal generator (35) is configured to generate an AC signal by generating an AC voltage of a constant magnitude, and the interface (30) is configured to sense the resulting AC signal by sensing the resulting AC current, for the system (10) according to any one of Examples 1 and 2.

[0053] (Example 4) The signal generator (35) is configured to generate an AC signal by generating an AC current of a constant magnitude, and the interface (30) is configured to sense the resulting AC signal by sensing the resulting AC voltage, for the system (10) according to any one of Examples 1 and 2.

[0054] (Example 5) The proximal reference ring electrodes (17, 217) are located on the proximal base (227) section of the expandable distal end assembly (28, 281) outside the internal volume (77, 277), for the system (10) according to any one of Examples 1 to 4.

[0055] (Example 6) The distal end assembly (28, 281) is a basket having an expandable frame including a plurality of splines (22, 222) electrically insulated from the surrounding environment, and the functional electrodes (26, 226) are coupled to the splines (22, 222), for the system (10) according to any one of Examples 1 to 5.

[0056] (Example 7) The distal reference electrodes (37, 237) are formed from the distal ends of the splines (22, 222) that are (i) electrically exposed to the surrounding environment and (ii) electrically connected to each other (257), for the system (10) according to any one of Examples 1 to 6.

[0057] (Example 8) The distal assembly is a balloon assembly having an expandable membrane, and the functional electrodes are disposed on the membrane, the system (10) described in Example 1.

[0058] (Example 9) The distal reference electrode is disposed on the distal end of the membrane, the system (10) described in Example 8.

[0059] (Example 10) The method is to insert a catheter (14) comprising a shaft (44, 244) having a distal end (46, 246) into a patient's heart cavity, the catheter further comprising an expandable distal assembly (28, 281) that defines an internal volume (77, 277) upon expansion, the distal assembly comprising: (i) a plurality of functional electrodes (26) that are at least partially external to the internal volume and are configured to be disposed in contact with the wall tissue (131) of the heart cavity; (ii) a proximal reference electrode (17, 217) that is external to the internal volume and is located at the proximal end of the expandable distal assembly (28, 281); and (iii) a distal reference electrode (37, 237) that is external to the internal volume and is located at the distal edge (16) of the expandable distal assembly, the proximal reference ring electrode and the distal reference electrode being coupled to each other and each being for: (i) generating an AC signal between the reference electrodes; and (ii) sensing the resulting AC signal on each of the plurality of functional electrodes and a given electrode (217, 237, 223). The AC signal is generated between the distal reference electrode (37, 237) and the proximal reference ring electrode (17, 217). Each resulting AC signal is sensed between each of the plurality of functional electrodes (26, 226) and the given electrode. Based on the sensed AC signal, for at least one given functional electrode (26, 226) of the plurality of functional electrodes, the proximity of the functional electrode to the wall tissue (131) of the heart cavity is determined.

[0060] The embodiments described herein primarily address cardiac diagnostic applications, but the methods and systems described herein can also be used for other medical applications.

[0061] It should be understood that the embodiments described above are merely examples, and the present disclosure is not limited to those specifically illustrated and described herein. Rather, the scope of the present disclosure includes both the various combinations and sub - combinations of the features described above, as well as those variations and modifications thereof that would occur to those skilled in the art upon reading the foregoing description and that are not disclosed in the prior art.

[0062] 〔Embodiment〕 (1) A system comprising a catheter comprising a shaft having a distal end configured for insertion into a patient's heart cavity, an expandable distal - end assembly that defines an internal volume upon expansion, a plurality of functional electrodes that are at least partially external to the internal volume and are configured to be disposed in contact with the wall tissue of the heart cavity, a proximal reference electrode located external to the internal volume and at the proximal end of the expandable distal - end assembly, a distal reference electrode located external to the internal volume and at the distal edge of the expandable distal - end assembly wherein the proximal reference ring electrode and the distal reference electrode are coupled to each other and are each (i) for generating an AC signal between the reference electrodes and (ii) for sensing the resulting AC signal on each of the plurality of functional electrodes and on a given electrode, an expandable distal - end assembly, a catheter comprising a signal generator configured to generate the AC signal between the distal reference electrode and the proximal reference ring electrode, an interface configured to sense the resulting AC signal between each of the plurality of functional electrodes and the given electrode, a processor configured to determine, based on the sensed AC signal, the proximity of at least one given functional electrode of the plurality of functional electrodes to the wall tissue of the heart cavity, a system comprising. (2) The given electrode is one of the proximal reference ring electrode, the distal reference electrode, the long-distance field electrode located within the internal volume, and another functional electrode on the spline, in the system according to Embodiment 1. (3) The signal generator is configured to generate the AC signal by generating an AC voltage of a certain magnitude, and the interface is configured to sense the resulting AC signal by sensing the resulting AC current, in the system according to Embodiment 1. (4) The signal generator is configured to generate the AC signal by generating an AC current of a certain magnitude, and the interface is configured to sense the resulting AC signal by sensing the resulting AC voltage, in the system according to Embodiment 1. (5) The proximal reference ring electrode is located outside the internal volume and on the proximal base section of the expandable distal end assembly, in the system according to Embodiment 1.

[0063] (6) The distal end assembly is a basket having an expandable frame including a plurality of splines electrically insulated from the surrounding environment, and the functional electrode is coupled to the spline, in the system according to Embodiment 1. (7) The distal reference electrode is formed from the distal ends of the splines that are (i) electrically exposed to the surrounding environment and (ii) electrically connected to each other, in the system according to Embodiment 6. (8) The distal end assembly is a balloon assembly having an expandable membrane, and the functional electrode is disposed on the membrane, in the system according to Embodiment 1. (9) The distal reference electrode is disposed on the distal end of the membrane, in the system according to Embodiment 8. (10) A method, Inserting a catheter having a shaft with a distal end into a patient's heart cavity, the catheter further comprising an expandable distal end assembly that defines an internal volume upon expansion, the distal end assembly including: (i) a plurality of functional electrodes at least partially external to the internal volume and configured to be disposed in contact with the wall tissue of the heart cavity; (ii) a proximal reference electrode external to the internal volume and located at the proximal end of the expandable distal end assembly; and (iii) a distal reference electrode external to the internal volume and located at the distal edge of the expandable distal end assembly, the proximal reference ring electrode and the distal reference electrode being coupled to each other and each being (i) for generating an AC signal between the reference electrodes and (ii) for sensing the resulting AC signal on each of the plurality of functional electrodes and on a given electrode, and Generating the AC signal between the distal reference electrode and the proximal reference ring electrode; Sensing the resulting electrical AC signal between each of the plurality of functional electrodes and the given electrode; Based on the sensed AC signal, determining, for at least one given functional electrode of the plurality of functional electrodes, the proximity of the functional electrode to the wall tissue of the heart cavity; A method comprising.

[0064] (11) The method according to embodiment 10, wherein the given electrode is one of the proximal reference ring electrode, the distal reference electrode, a remote field electrode located within the internal volume, and another functional electrode on the spline. (12) The method according to embodiment 10, wherein generating the AC signal includes generating an AC voltage of a constant magnitude, and sensing the resulting AC signal includes sensing the resulting AC current. (13) The method according to embodiment 10, wherein generating the AC signal includes generating an AC current of a constant magnitude, and sensing the resulting AC signal includes sensing the resulting AC voltage. (14) The method according to embodiment 10, wherein the proximal reference ring electrode is located on a proximal base section of the expandable distal end assembly outside the internal volume. (15) The method according to embodiment 10, wherein the distal end assembly is a basket having an expandable frame including a plurality of splines electrically insulated from the surrounding environment, and the functional electrode is coupled to the splines.

[0065] (16) The method according to embodiment 15, wherein the distal reference electrode is formed from distal ends of the splines that are (i) electrically exposed to the surrounding environment and (ii) electrically connected to each other. (17) The method according to embodiment 10, wherein the distal end assembly is a balloon assembly having an expandable membrane, and the functional electrode is disposed on the membrane. (18) The method according to embodiment 17, wherein the distal reference electrode is disposed on a distal end of the membrane.

Claims

1. 1. A system comprising: A catheter comprising: a shaft having a distal end configured for insertion into a chamber of a patient's heart; An expandable distal end assembly that defines an interior volume when expanded, comprising: a plurality of functional electrodes at least partially exterior to the interior volume and configured to be placed in contact with wall tissue of the heart chamber; a proximal reference electrode located outside the interior volume and at a proximal end of the expandable distal tip assembly; a distal reference electrode located outside the interior volume and at a distal edge of the expandable distal tip assembly. Including, the proximal reference ring electrode and the distal reference electrode are coupled to each other and are respectively for (i) generating an AC signal between the reference electrodes and (ii) sensing the resulting AC signal on each of the plurality of functional electrodes and on a given electrode; an expandable distal end assembly; a catheter comprising: a signal generator configured to generate the AC signal between the distal reference electrode and the proximal reference ring electrode; an interface configured to sense the resulting AC signal between each of the plurality of functional electrodes and the given electrode; a processor configured to determine, for at least one given functional electrode of the plurality of functional electrodes based on the sensed AC signal, a proximity of the functional electrode to wall tissue of the heart chamber; A system including:

2. The system of claim 1 , wherein the given electrode is one of the proximal reference ring electrode, the distal reference electrode, a far field electrode located within the interior volume, and another functional electrode on a spline.

3. 2. The system of claim 1, wherein the signal generator is configured to generate the AC signal by generating an AC voltage of a fixed magnitude, and the interface is configured to sense the respective resulting AC signal by sensing a resulting AC current.

4. 2. The system of claim 1, wherein the signal generator is configured to generate the AC signal by generating an AC current of a constant magnitude, and the interface is configured to sense the respective resulting AC signal by sensing a resulting AC voltage.

5. The system of claim 1 , wherein the proximal reference ring electrode is located outside the interior volume on a proximal base section of the expandable distal tip assembly.

6. The system of claim 1 , wherein the distal end assembly is a basket having an expandable frame including a plurality of splines electrically isolated from the surrounding environment, the functional electrodes being coupled to the splines.

7. 7. The system of claim 6, wherein the distal reference electrode is formed from distal ends of the splines that are (i) electrically exposed to the surrounding environment and (ii) electrically connected to each other.

8. The system of claim 1 , wherein the distal end assembly is a balloon assembly having an expandable membrane, and the functional electrode is disposed on the membrane.

9. The system of claim 8 , wherein the distal reference electrode is disposed on a distal end of the membrane.

10. 1. A method comprising: inserting a catheter including a shaft having a distal end into a patient's heart chamber, the catheter further comprising an expandable distal end assembly defining an interior volume when expanded, the distal end assembly including: (i) a plurality of functional electrodes at least partially outside the interior volume and configured to be placed in contact with wall tissue of the heart chamber; (ii) a proximal reference electrode located outside the interior volume at a proximal end of the expandable distal end assembly; and (iii) a distal reference electrode located outside the interior volume at a distal edge of the expandable distal end assembly, the proximal reference ring electrode and the distal reference electrode being coupled to one another and respectively for (i) generating an AC signal between the reference electrodes and (ii) sensing the resulting AC signal on each of the plurality of functional electrodes and on a given electrode; generating the AC signal between the distal reference electrode and the proximal reference ring electrode; sensing the resulting electrical AC signal between each of the plurality of functional electrodes and the given electrode; determining, for at least one given functional electrode of the plurality of functional electrodes based on the sensed AC signal, a proximity of the functional electrode to wall tissue of the heart chamber; The method includes:

11. The method of claim 10 , wherein the given electrode is one of the proximal reference ring electrode, the distal reference electrode, a far field electrode located within the interior volume, and another functional electrode on a spline.

12. 11. The method of claim 10, wherein generating the AC signal comprises generating an AC voltage of a constant magnitude, and sensing the respective resulting AC signal comprises sensing a resulting AC current.

13. 11. The method of claim 10, wherein generating the AC signal comprises generating an AC current of a constant magnitude, and sensing the respective resulting AC signal comprises sensing a resulting AC voltage.

14. The method of claim 10 , wherein the proximal reference ring electrode is located outside the interior volume on a proximal base section of the expandable distal tip assembly.

15. The method of claim 10 , wherein the distal end assembly is a basket having an expandable frame including a plurality of splines electrically isolated from the surrounding environment, the functional electrodes being coupled to the splines.

16. 16. The method of claim 15, wherein the distal reference electrode is formed from distal ends of the splines that are (i) electrically exposed to the surrounding environment and (ii) electrically connected to each other.

17. The method of claim 10 , wherein the distal end assembly is a balloon assembly having an expandable membrane, and the functional electrode is disposed on the membrane.

18. The method of claim 17 , wherein the distal reference electrode is disposed on a distal end of the membrane.

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