Reference electrode dedicated to catheter tissue proximity estimation

Abstract

To estimate the proximity of a catheter to a tissue.SOLUTION: A catheter includes a shaft having a distal end and an expandable distal-end assembly configured for insertion into a cavity of an organ of a patient. The expanded assembly defines an inner volume and includes (i) a proximal base section configured to couple the assembly to the shaft's distal end, (ii) a plurality of functional electrodes that are at least partially external to the inner volume and configured to be placed in contact with wall tissue of the cavity, and (iii) a reference ring electrode located on the proximal base section of the assembly externally to the inner volume, where the reference ring electrode is selectively positioned outside of the inner volume at the base section, and where the reference ring electrode is configured to be coupled with each of the functional electrodes for generating an electric field between each of the functional electrodes and the ring electrode.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure generally relates to invasive medical probes, and more specifically 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. 2023 / 0112251 describes a system including a catheter and a processor. The catheter includes a distal end assembly coupled to the distal end of a shaft for insertion into a cavity of a patient's organ, the distal end assembly including (i) one or more functional electrodes configured to be disposed in contact with the wall tissue of the cavity and (ii) a reference electrode configured to be disposed within the cavity without contacting the wall tissue. The reference electrode is disclosed as an electrode disposed within an internal volume defined by the distal end assembly. By selectively positioning the reference electrode within the internal volume, the reference electrode is spaced apart from the tissue wall. The processor is configured to (i) estimate one or more impedances between one or more of the functional electrodes and the reference electrode and, based on the impedance, determine for at least some of the one or more functional electrodes whether the functional electrode is 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

[0005] Overview A catheter having a plurality of functional electrodes attached to an expandable distal end assembly of the catheter can be used to electroanatomically map and / or ablate the wall tissue of a cavity of a patient's organ, such as a ventricle. In a mapping and / or ablation procedure in the ventricle, a physician can operate the expanded distal end assembly to bring the electrodes into contact with the heart chamber wall and acquire and / or apply electrical signals.

[0006] The quality of the electrical mapping and / or ablation depends on the proximity of the functional electrode to the cavity wall tissue (also referred to as "tissue proximity indication (TPI)" in the present disclosure). 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] The processor can be configured to estimate the proximity using calibrated proximity data that converts between impedance and electrode-tissue proximity. One method of calculating the TPI is (i) to identify the range of the lowest and highest values recorded over time from the monitored imbalance, (ii) to normalize the monitored impedance according to the range, and (iii) to associate the normalized range with the scale of the TPI.

[0008] In another option, the TPI is a binary value, e.g., 0 when there is no contact and 1 when there is contact. One way to calculate the binary TPI is to (i) identify the range of the lowest and highest values recorded over time from the monitored imbalance, (ii) set a threshold according to that range, and (iii) define the corresponding normalized threshold according to the range of the normalized TPI. For example, for a normalized threshold of 0.7, above it, the reported TPI is 1, and below it, it is 0.

[0009] This system measures the impedance between a pair of electrodes, where in this case, one electrode is a reference electrode within the blood pool and the other is a functional electrode. Based on this measurement, the processor executes an algorithm to identify the proximity of the functional electrode to the tissue. The minimum impedance occurs when the functional electrode is sufficiently within the ventricular blood pool, while the maximum impedance occurs when the functional electrode is in full contact, e.g., engaged at the limiting pressure. The impedance readings are continuous between these two limit values.

[0010] In some known methods, the reference electrode is placed within the internal volume of an expandable distal assembly as described above in this specification. The inventors have found that improved sensitivity can be achieved by directing a larger portion of the electric field outwardly over a volume that may include a part of the tissue wall. For this purpose, the inventors propose placing the reference electrode outside the internal volume of the expandable distal assembly at a location where it is separated from any contact with the tissue.

[0011] Embodiments of the present disclosure described herein provide a ring electrode selectively disposed at the base of an expandable assembly proximate to an expandable portion of a distal assembly. The base of the expandable assembly, which is part of the assembly, is the element by which the assembly is coupled to the distal end of the catheter shaft, i.e., the ring reference electrode is distal to the shaft. Since the ring reference electrode is at the base of the expandable assembly, typically it does not contact the tissue wall while the expandable assembly is in the expanded state. In addition, the diameter of the ring reference electrode is about 2 - 5 mm, while the distal end assembly in the expanded state is spherical with a diameter of about 20 - 30 mm. Due to this large difference in diameter, by placing the reference electrode at the base of the distal end assembly, the assembly functions as a spacer that separates the reference electrode from the tissue.

[0012] The path of the potential between such a ring reference electrode and the functional electrodes is susceptible to the influence of tissue proximity because both the plurality of functional electrodes and the reference ring electrode are outside the internal volume defined by the expandable assembly. Thus, the proximity is based on monitoring the increase in impedance over time for each functional electrode.

[0013] In addition, mainly in the case of a basket catheter, as shown in FIG. 2, by coating the inward side of the spline with an insulating coating, the electric field path through the inward side of the functional electrodes can be eliminated and / or reduced.

[0014] In one example, an additional guard ring protrudes further than the reference ring electrode and is configured to function as a spacer that prevents contact between the reference ring and the tissue wall. In this way, the guard ring reduces cases of contact, for example, near the ridges of the anatomical structure of the ventricle.

[0015] In some examples, since the distal end assembly is essentially one piece made from a Nitinol tube, the base section is conductive as the proximal section of the distal end assembly. In these examples, the reference ring electrode is electrically insulated from the Nitinol base.

[0016] Finally, despite the efforts described above, the reference electrode may, in some cases, contact the tissue. This can be identified by comparing the electrical signals from all the functional electrodes. If all of the signals from all of the functional electrodes indicate contact (e.g., all show an increase in impedance simultaneously), it is most likely caused by the reference electrode contacting the tissue since some of the functional electrodes should always be immersed in the blood pool. Thus, in this case, the system discards this reading.

[0017] 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 10 is configured to determine, for example, whether a given functional electrode 26 among a 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 ventricle, prior to performing a diagnosis and / or ablation.

[0018] System 10 includes one or more catheters that are percutaneously inserted by physician 24 through a patient's vasculature and into a ventricle of heart 12 or a vascular structure. Typically, a delivery sheath catheter is inserted into the left atrium or right atrium near a desired location of heart 12. Thereafter, one or more catheters can be inserted into the delivery sheath catheter to reach the 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 figure 45, physician 24 contacts the basket-type expandable distal end assembly 28 (hereinafter also referred to as "expandable distal end assembly 28") attached to the shaft 44 of catheter 14 to the heart wall to sense a target site within heart 12. In the case of ablation, physician 24 similarly moves the distal end of the ablation catheter to the target site for ablation.

[0019] As seen in insertion figure 65, 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. 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, position sensor 29 is a magnetic-based position sensor that includes a magnetic coil for sensing three-dimensional (3D) position. The distal end 46 of shaft 44 may include an amplifier circuit configured to amplify the output from the three EMCs of sensor 29.

[0020] 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. Using the operation with the external position pad 25 (each EMC uses a different frequency), the processor can identify the position of each EMC 29 on the coordinate system of the position tracking system.

[0021] 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.

[0022] 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 positions 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).

[0023] 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.

[0024] 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 each of reference ring electrode 17 and functional electrode 26. The processor measures the corresponding impedance between each functional electrode 26 and reference ring electrode 17 disposed at the base 37 of the distal assembly 28 that is expandable outside the internal volume 77 defined by the spline of the assembly 28. Having an electrical path to the assembly 28 between each functional electrode 26 and reference ring electrode 17 improves the sensitivity of the measurement to tissue proximity. The reference ring electrode 17 is disposed on the base of the assembly 28 at a location that avoids contact with the tissue wall while the distal assembly 28 is in the expanded state, as described in more detail in FIG. 2.

[0025] Recorder 11 displays an electrogram 21 captured by body surface ECG electrodes 18 and an intracardiac electrogram (IEGM) captured by 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.

[0026] 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 may include radiofrequency (RF) energy or pulsed-field ablation (PFA) energy, or a combination thereof, including unipolar or bipolar high voltage DC pulses that may be used to effect irreversible electroporation (IRE), but is not limited thereto.

[0027] 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 positions and execute ECG calculations.

[0028] 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 a three-dimensional (3D) model of the endocardial anatomical structure to 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 superimposed on the rendered anatomical map 20, (iii) display the real-time positions and orientations of a plurality of catheters within the heart chamber, and (iv) display on the display device 27 regions of interest such as the locations where ablation energy has been applied, and may provide a plurality of functions including these. 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.

[0029] Although a basket assembly is depicted in FIG. 1, 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 are disposed on the membrane.

[0030] Estimation of Touch Proximity (TP) of Functional Electrodes of Expandable Assemblies 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.

[0031] 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 22 is electrically insulated from the environment over most of its region by an insulating layer 262.

[0032] When expanded, as shown in FIG. 2, the expandable distal end assembly 281 defines 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.

[0033] The plurality of functional electrodes 226 are at least partially external to the internal volume and are configured to be positioned to contact the wall tissue of the cavity. The reference ring electrode 217 (such as the ring electrode 17 of FIG. 1) is disposed on the proximal base 227 of the expandable distal end assembly 281 and external to the internal volume 277. 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.

[0034] In the embodiment of FIG. 2, the reference ring electrode 217 is a ring attached to the outer periphery of the proximal base section 227. The reference ring electrode 217 can be disposed on an insulating layer (not shown), for example, when the base section 227 is conductive (e.g., when made of nitinol).

[0035] The proximal base section 227 further includes a mechanical guard ring 231 that protrudes outwardly from the proximal base to prevent the reference electrode 227 from contacting the wall tissue, i.e., farther away from the reference electrode 227.

[0036] The processor 56 estimates the proximity of a given electrode 226 to the wall tissue (the wall tissue is not shown) based on the impedance signal between the electrode 226 and the reference electrode 217. The processor may use the impedance value itself or the increase in the impedance value relative to the baseline impedance measured when both electrodes are deep inside the blood pool.

[0037] 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 in contact with the tissue is minimized. The coating 241 can be a certain type of polymer or an additional dielectric layer (e.g., silicon nitride).

[0038] 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 are disposed on the membrane.

[0039] Method for estimating the contact proximity (TP) of electrodes of an expandable assembly Figure 3 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.

[0040] In an electric field generation step 303, a signal generator 35 generates an AC electric field between the outer surface of each of a reference ring electrode 217 and a functional electrode 226.

[0041] Next, in a baseline impedance monitoring step 304, the system 10 monitors the impedance between each of the functional electrodes 226 and the reference ring electrode 217.

[0042] In an impedance range identification step 306, since the basket often contacts the wall tissue of the cavity, the processor identifies the impedance ranges 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. Clinically, at this stage or later, the physician 24 may further attempt to contact at least a subset of the functional electrodes 226 with the tissue, for example, over the entire lateral circumference of the assembly 281, as is done in a pulmonary vein isolation procedure for treating atrial fibrillation.

[0043] Using the monitored impedances and their identified ranges, the processor calculates the TPI for each functional electrode or group of such electrodes in TPI calculation step 308. One way to calculate the TPI is to find the lowest and highest impedance values recorded over time and normalize the impedance measurements for the detected range by associating (e.g., transforming) the normalized range with the scale of the TPI.

[0044] Finally, in TPI reporting step 310, the system 10 reports the TPI for each of the functional electrodes 226 or groups thereof to indicate the contact and / or proximity of these functional electrodes to the ventricular wall tissue.

[0045] The exemplary flowchart shown in FIG. 3 is selected purely for the purpose of clarifying the concept. This embodiment also includes additional steps of the algorithm, such as acquiring an intracardiac electrogram, which 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

[0046] (Example 1) The catheter (14) comprises a shaft (44) and an expandable distal end assembly (28). The shaft has a distal end (44) configured to be inserted into the lumen of an organ (12) of a patient (23). The expandable distal end assembly (28) defines an internal volume (77) upon expansion, and the distal end assembly (28) comprises (i) a proximal base section (37) configured to couple the distal end assembly (28) to the distal end (46) of the shaft (44), (ii) 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 of the lumen, and (iii) a reference ring electrode (17) positioned on the proximal base section (37) of the distal end assembly (28) external to the internal volume (77), selectively disposed external to the internal volume (77) at the base section of the distal end assembly, and configured to be coupled to each of the plurality of functional electrodes (26) to generate an electric field between each of the plurality of functional electrodes (26) and the ring electrode (17).

[0047] (Example 2) The catheter (14) according to Example 1, wherein the reference ring electrode (17) is attached to the outer periphery of the proximal base section (37) and is electrically insulated from the base section (37).

[0048] (Example 3) The catheter (14) according to either Example 1 or 2, wherein the distal end assembly (28) is a basket assembly (281) having an expandable frame including a plurality of splines (22), and the functional electrodes (26) are coupled to the splines (22).

[0049] (Example 4) The catheter (14, 214) according to any one of Examples 1 to 3, comprising a remote field electrode (223) positioned within the internal volume (77, 277).

[0050] (Example 5) The distal end assembly is a balloon assembly having an expandable membrane, and the functional electrode is disposed on the membrane, the catheter (14) according to any one of Examples 1 to 3.

[0051] (Example 6) The catheter (14, 214) according to any one of Examples 1 to 5, further comprising a mechanical guard ring (231) disposed proximal to the reference ring electrodes (17, 217), protruding outwardly from the proximal base section (37, 227) more proximal than the reference ring electrodes, and configured to function as a spacer to prevent contact between the reference ring (17, 217) and the tissue wall.

[0052] (Example 7) The system (10) comprises a catheter (14), a signal generator (35), an interface (30), and a processor (56). The catheter (14) includes a shaft (44) and an expandable distal end assembly (28). The shaft has a distal end (44) configured to be inserted into a cavity of an organ (12) of a patient (23). The expandable distal end assembly (28), when expanded, defines an internal volume (77), and the distal end assembly (28) comprises (i) a proximal base section (37) configured to couple the distal end assembly (28) to the distal end (46) of the shaft (44), (ii) 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 of the cavity, and (iii) a reference ring electrode (17) positioned on the proximal base section (37) of the distal end assembly (28) external to the internal volume (77), selectively disposed external to the internal volume (77) at the base section of the distal end assembly, and configured to be coupled to each of the plurality of functional electrodes (26) to generate an electric field between each of the plurality of functional electrodes (26) and the ring electrode (17). The signal generator (35) is configured to generate an AC signal between the reference ring electrode (17) and each of the functional electrodes (26). The interface (30) is configured to receive electrical readings between the plurality of functional electrodes (26) and the reference ring electrode (17). The processor (56) is configured to (i) estimate a respective impedance between the functional electrode (26) and the reference ring electrode (17) from the electrical readings, and (ii) estimate, based on the impedance, the proximity of the functional electrode (26) to the wall tissue for at least a given functional electrode (26) of the plurality of functional electrodes (26).

[0053] (Example 8) The signal generator (35) is configured to generate an AC signal between each of the reference ring electrodes (17, 217) and each of the functional electrodes (26, 226) by generating an electric field between the outer surface of each of the reference ring electrodes (17, 217) and the functional electrodes (26, 226), in the system (10) described in Example 7.

[0054] (Example 9) The processor (56) is configured to determine that the reference ring electrodes (17, 217) are in physical contact with the wall tissue by determining that all of the measured impedances of a plurality of the functional electrodes (26, 226) are higher than a given threshold, in the system (10) described in either Example 7 or 8.

[0055] (Example 10) The processor (56) is configured to estimate the proximity using calibrated proximity data that converts between impedance and electrode-tissue proximity, in the system (10) described in any one of Examples 7 to 9.

[0056] (Example 11) The method is to insert the expandable distal end assembly (28) of the catheter (14) into the cavity of the organ (12) of the patient (23), where the distal end assembly (28) defines an internal volume (77) upon expansion, and the assembly includes (i) a proximal base section (37) configured to couple the distal end assembly to the distal end (46) of the catheter shaft (44), (ii) a plurality of functional electrodes (26) configured to be at least partially outside the internal volume (77) and in contact with the wall tissue of the cavity, and (iii) A reference ring electrode (17) disposed on a proximal base section (37) of a distal end assembly (28) outside the internal volume (77), selectively disposed outside the internal volume at the base section of the distal end assembly, and configured to be coupled to each of the plurality of functional electrodes (26) to generate an electric field between each of the plurality of functional electrodes and the ring electrode (17). An AC signal is generated between the reference ring electrode (17) and each of the functional electrodes (26). An electrical reading resulting from between the plurality of functional electrodes (26) and the reference ring electrode (17) is received. Each impedance is estimated from the electrical reading between the functional electrode (26) and the reference ring electrode (17). Based on this impedance, for at least a given functional electrode (26) of the plurality of functional electrodes, the proximity of the functional electrode to the wall tissue is estimated.

[0057] The embodiments described herein mainly address cardiac diagnostic applications, but the methods and systems described herein can also be used for other medical applications.

[0058] It will be understood that the embodiments described above are given by way of example only and that the present disclosure is not limited to what is particularly shown and described hereinabove. Rather, the scope of the present disclosure includes both combinations and sub - combinations of the various 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.

[0059] 〔Embodiments〕 (1) A catheter, comprising a shaft having a distal end configured to be inserted into a cavity of a patient's organ, an expandable distal end assembly that defines an internal volume upon expansion, a proximal base section configured to couple the distal end assembly to the distal end of the shaft, 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 cavity, and A reference ring electrode disposed on the proximal base section of the distal end assembly external to the internal volume, selectively disposed external to the internal volume at the base section of the distal end assembly, and configured to be coupled to each of the plurality of functional electrodes to generate an electric field between each of the plurality of functional electrodes and the ring electrode, the reference ring electrode An expandable distal end assembly including A catheter comprising. (2) The catheter according to embodiment 1, wherein the reference ring electrode is attached to the outer periphery of the proximal base section and is electrically insulated from the base section. (3) The catheter according to embodiment 1, wherein the distal end assembly is a basket assembly having an expandable frame including a plurality of splines, and the functional electrodes are coupled to the splines. (4) The catheter according to embodiment 1, including a remote field electrode disposed within the internal volume. (5) The catheter according to embodiment 1, wherein the distal end assembly is a balloon assembly having an expandable membrane, and the functional electrodes are disposed on the membrane.

[0060] (6) The catheter according to embodiment 1, further comprising a mechanical guard ring disposed proximal to the reference ring electrode, protruding further outward from the proximal base section than the reference ring electrode, and configured to function as a spacer to prevent contact between the reference ring and the tissue wall. (7) A system, A catheter, A shaft having a distal end configured to be inserted into a cavity of a patient's organ, An expandable distal end assembly that defines an internal volume upon expansion, A proximal base section configured to couple the distal end assembly to the distal end of the shaft, 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 cavity, and A reference ring electrode disposed on the proximal base section of the distal end assembly external to the internal volume, selectively disposed external to the internal volume at the base section of the distal end assembly, and configured to be coupled to each of the plurality of functional electrodes to generate an electric field between each of the plurality of functional electrodes and the ring electrode, a reference ring electrode An expandable distal end assembly including A catheter including A signal generator configured to generate an AC signal between the reference ring electrode and each of the functional electrodes, An interface configured to receive electrical readings between the plurality of functional electrodes and the reference ring electrode, A processor, Estimating respective impedances between the functional electrodes and the reference ring electrode from the electrical readings, Based on the impedance, estimating the proximity of the functional electrode to the wall tissue for at least a given functional electrode among the plurality of functional electrodes A processor configured as such, A system comprising. (8) The system according to embodiment 7, wherein the signal generator is configured to generate the AC signal between the reference ring electrode and each of the functional electrodes by generating an electric field between the outer surface of the reference ring electrode and each of the functional electrodes. (9) The system according to embodiment 7, wherein the processor is configured to determine that the reference ring electrode is in physical contact with the wall tissue by determining that all of the measured impedances among the plurality of functional electrodes are higher than a given threshold. (10) The system of embodiment 7, wherein the processor is configured to estimate the proximity using calibrated proximity data that converts between impedance and electrode-tissue proximity.

[0061] (11) A method comprising: inserting an expandable distal end assembly of a catheter into a cavity of a patient's organ, the distal end assembly defining an internal volume upon expansion, the assembly comprising: a proximal base section configured to couple the distal end assembly to a distal end of a shaft of the catheter; 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 cavity; and a reference ring electrode disposed on the proximal base section of the distal end assembly external to the internal volume, selectively disposed external to the internal volume at the base section of the distal end assembly, and configured to be coupled to each of the plurality of functional electrodes to generate an electric field between each of the plurality of functional electrodes and the ring electrode; comprising; generating an AC signal between the reference ring electrode and each of the functional electrodes; receiving resulting electrical readings between the plurality of functional electrodes and the reference ring electrode; estimating a respective impedance between the functional electrode and the reference ring electrode from the electrical readings; estimating, based on the impedance, a proximity of the functional electrode to the wall tissue for at least a given functional electrode of the plurality of functional electrodes; comprising a method. (12) The method of embodiment 11, wherein generating the AC signal between the reference ring electrode and each of the functional electrodes comprises generating an electric field between an outer surface of each of the reference ring electrode and the functional electrodes. (13) The method according to embodiment 11, wherein determining that the reference ring electrode is in physical contact with the wall tissue includes determining that all of the measured impedances among the plurality of functional electrodes are higher than a given threshold value. (14) The method according to embodiment 11, wherein estimating the proximity includes using calibrated proximity data that converts between impedance and electrode-tissue proximity. (15) The method according to embodiment 11, wherein the reference ring electrode is attached to the outer periphery of the proximal base section, and the reference ring electrode is electrically insulated from the base section.

[0062] (16) The method according to embodiment 11, wherein the distal end assembly is a basket assembly having an expandable frame including a plurality of splines, and the functional electrodes are coupled to the splines. (17) The method according to embodiment 11, wherein the distal end assembly is a balloon assembly having an expandable membrane, and the functional electrodes are disposed on the membrane. (18) The method according to embodiment 11, including using a mechanical guard ring disposed on the proximal side of the reference ring electrode and protruding further outward from the proximal base section than the reference ring electrode to prevent contact between the reference ring and the tissue wall.

Claims

1. A catheter comprising: a shaft having a distal end configured for insertion into a cavity of a patient; An expandable distal end assembly that defines an interior volume when expanded, comprising: a proximal base section configured to couple the distal tip assembly to a distal end of the shaft; 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 cavity; and a reference ring electrode disposed on the proximal base section of the distal tip assembly outside the internal volume, the reference ring electrode being selectively disposed outside the internal volume at the base section of the distal tip assembly and configured to be coupled with each of the plurality of functional electrodes to generate an electric field between each of the plurality of functional electrodes and the ring electrode. an expandable distal end assembly including: A catheter comprising:

2. The catheter of claim 1 , wherein the reference ring electrode is attached to an outer periphery of the proximal base section and is electrically insulated from the base section.

3. The catheter of claim 1 , wherein the distal end assembly is a basket assembly having an expandable frame including a plurality of splines, the functional electrodes being coupled to the splines.

4. The catheter of claim 1 , comprising a far-field electrode disposed within the interior volume.

5. The catheter of claim 1 , wherein the distal end assembly is a balloon assembly having an expandable membrane, and the functional electrodes are disposed on the membrane.

6. 10. The catheter of claim 1, further comprising a mechanical guard ring disposed proximally of the reference ring electrode, protruding outward from the proximal base section further than the reference ring electrode and configured to act as a spacer to prevent contact between the reference ring and a tissue wall.

7. 1. A system comprising: A catheter comprising: a shaft having a distal end configured for insertion into a cavity of a patient; An expandable distal end assembly that defines an interior volume when expanded, comprising: a proximal base section configured to couple the distal tip assembly to a distal end of the shaft; 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 cavity; and a reference ring electrode disposed on the proximal base section of the distal tip assembly outside the internal volume, the reference ring electrode being selectively disposed outside the internal volume at the base section of the distal tip assembly and configured to be coupled with each of the plurality of functional electrodes to generate an electric field between each of the plurality of functional electrodes and the ring electrode. an expandable distal end assembly including: a catheter comprising: a signal generator configured to generate an AC signal between the reference ring electrode and each of the functional electrodes; an interface configured to receive electrical readings between the functional electrodes and a reference ring electrode; 1. A processor comprising: estimating from the electrical readings respective impedances between the functional electrode and the reference ring electrode; and estimating, for at least a given functional electrode of the plurality of functional electrodes, a proximity of the functional electrode to the wall tissue based on the impedance. a processor configured to A system comprising:

8. 8. The system of claim 7, wherein the signal generator is configured to generate the AC signal between the reference ring electrode and each of the functional electrodes by generating an electric field between the reference ring electrode and an outer surface of each of the functional electrodes.

9. 8. The system of claim 7, wherein the processor is configured to determine that the reference ring electrode is in physical contact with the wall tissue by determining that all of the measured impedances of the plurality of functional electrodes are above a given threshold.

10. The system of claim 7, wherein the processor is configured to estimate the proximity using calibrated proximity data that converts between impedance and electrode-tissue proximity.

11. 1. A method comprising: Inserting an expandable distal end assembly of a catheter into a cavity of an organ of a patient, the distal end assembly defining an interior volume when expanded, the assembly comprising: a proximal base section configured to couple the distal tip assembly to a distal end of the catheter shaft; 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 cavity; and a reference ring electrode disposed on the proximal base section of the distal tip assembly outside the internal volume, the reference ring electrode being selectively disposed outside the internal volume at the base section of the distal tip assembly and configured to be coupled with each of the plurality of functional electrodes to generate an electric field between each of the plurality of functional electrodes and the ring electrode. and generating an AC signal between the reference ring electrode and each of the functional electrodes; receiving resultant electrical readings between a plurality of said functional electrodes and said reference ring electrode; estimating from the electrical readings respective impedances between the functional electrode and the reference ring electrode; estimating, for at least a given functional electrode of the plurality of functional electrodes based on the impedance, a proximity of the functional electrode to the wall tissue; The method includes:

12. The method of claim 11 , wherein generating the AC signal between the reference ring electrode and each of the functional electrodes comprises generating an electric field between the reference ring electrode and an outer surface of each of the functional electrodes.

13. 12. The method of claim 11, wherein determining that the reference ring electrode is in physical contact with the wall tissue comprises determining that all of the measured impedances of the plurality of functional electrodes are above a given threshold.

14. The method of claim 11, wherein estimating the proximity includes using calibrated proximity data to convert between impedance and electrode-tissue proximity.

15. The method of claim 11 , wherein the reference ring electrode is attached to an outer periphery of the proximal base section, the reference ring electrode being electrically insulated from the base section.

16. The method of claim 11 , wherein the distal end assembly is a basket assembly having an expandable frame including a plurality of splines, and the functional electrodes are coupled to the splines.

17. The method of claim 11 , wherein the distal end assembly is a balloon assembly having an expandable membrane, and the functional electrode is disposed on the membrane.

18. 12. The method of claim 11, comprising preventing contact between the reference ring and a tissue wall using a mechanical guard ring positioned proximal to the reference ring electrode and projecting outward from the proximal base section further than the reference ring electrode.

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