System and method of intracardiac-electrogram measurement

Abstract

To measure cardiac tissue activation signals.SOLUTION: A method and system to determine cardiac tissue activation signals are disclosed. The method determines a far-field component of an Intracardiac Electrogram (IEGM) signal sensed by at least one electrode of a plurality of electrodes of a catheter. The method includes: applying tissue proximity measurement to each electrode of a multitude of the catheter's electrodes to assess respective distances thereof respectively from a tissue surface; dynamically selecting, based on the respective distances, a subset of one or more electrodes of the multitude whose respective distances from the tissue surface are above a certain threshold; and determining a far-field component of the IEGM signal by averaging IEGM signal measurements from the electrodes of the subset whose respective distances are above the certain threshold.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention is in the field of signal processing of physiological signals, and particularly relates to the measurement of cardiac tissue activation signals, such as intracardiac-electrograms (IEGMs) used for electrocardiogram monitoring or mapping during medical treatment.

Background Art

[0002] A wide range of medical treatments involve placing probes, such as catheters, inside a patient's body. One medical treatment in which these types of probes or catheters have proven extremely useful is in the treatment of cardiac arrhythmias. Cardiac arrhythmias and atrial fibrillation remain particularly persistent as dangerous medical conditions, especially in the elderly population.

[0003] Diagnosis and treatment of cardiac arrhythmias include mapping the electrical properties of cardiac tissue, particularly the endocardium and cardiac volume, and selectively ablating cardiac tissue by applying energy. Catheters are inserted into the heart cavity during such procedures and optionally around the heart cavity. In most procedures, multiple catheters are inserted into the patient. Catheters can include mapping catheters, ablation catheters, temperature sensing catheters, and image sensing catheters. Some catheters are dedicated to placement in specific parts of the anatomical structure, such as the coronary sinus, esophagus, atria, and ventricles. Catheters have multiple electrical channels, and some have more channels than other electrical channels depending on the number of sensors and electrodes included in each catheter. The number and type of catheters vary depending on the procedure and the workflow preferred by the physician. During the procedure, the electrical activity of the heart is monitored / mapped from the electrodes of the catheter and optionally from body surface electrodes attached to the patient's skin.

Brief Description of the Drawings

[0004] To better understand the subject matter disclosed herein and to illustrate how the subject matter can actually be carried out, embodiments will be described herein by way of merely non-limiting examples with reference to the accompanying drawings.

Figure 1

Figure 2

Figure 3

Figure 4

[0005] In the drawings, like reference numerals are used to indicate like modules / elements of the present invention, or elements / modules having like functions. Thus, unless otherwise specified, the description of a module / element with respect to a particular embodiment of the present invention should be understood to apply to all embodiments of the present invention in which such module / element is incorporated.

DETAILED DESCRIPTION OF THE INVENTION

[0006] In the art, there is a need for novel and inventive techniques for accurately determining cardiac tissue activation signals.

[0007] Conventional techniques widely used to measure or map the electrical properties of cardiac tissue often utilize catheters with a distal end assembly of a certain volume, such as basket or balloon catheters, or alternatively, other catheters having a plurality of splines at the distal end that surround a particular volume. In such catheters, typically, electrodes located on the outer / external surface of the distal end (e.g., on the external surface of the catheter splines) are operated to measure an intracardiac electrogram (IEGM) from the tissue region in contact therewith, and typically, another electrode located remotely from the intracardiac tissue, within the volume surrounded by the distal end of the volume, and thus within the cardiac chamber, is operated to measure the far-field component of the IEGM. Thus, the far-field component of the IEGM is used to suppress the far-field IEGM component within the IEGM signal obtained from the electrode in contact with the tissue (e.g., by subtracting the far-field IEGM component from the IEGM signal obtained from the contacting electrode), thereby obtaining the near-field IEGM component of the IEGM signal sensed by the contacting electrode. The occurrence of the near-field component of the IEGM signal sensed by each electrode in contact with the tissue region over time indicates the activation signal in the tissue region in contact with each electrode.

[0008] Intracardiac catheters are typically disposable elements designed for single use in intracardiac surgery. Thus, there is a need in the art to reduce the manufacturing cost of such catheters. As will be understood from the following description, one approach to reducing the manufacturing cost of catheters for measuring / mapping the electrical properties of cardiac tissue is to use a catheter having a planar distal end assembly. This can significantly reduce the manufacturing cost because such a planar distal end assembly can be formed by a flexible printed circuit board (PCB) having electrodes printed thereon.

[0009] However, when using such a catheter having a planar distal end assembly for measuring or mapping the electrical properties of cardiac tissue, the problem lies in the fact that there is no specific location for placing electrodes designed to measure the far-field IEGM signal component in the planar configuration of the distal end. In fact, any of the electrodes on the planar distal end assembly may or may not intermittently contact the cardiac tissue during operation and may be proximal to the cardiac tissue. Thus, the far-field IEGM signal component cannot be reliably obtained from any specific electrode.

[0010] Accordingly, the present invention provides a novel technique for measuring the far-field IEGM signal component in a manner suitable for use with a catheter designed for measuring or mapping the electrical properties of cardiac tissue. The present invention may be used, for example, to determine the far-field component of an IEGM signal sensed by a catheter that does not have electrodes specifically adapted / dedicated to sensing the far-field comment of the IEGM signal (e.g., dedicated electrodes) (e.g., without sensing "noise" such as near-field IEGM from its surroundings or with substantially suppressed). Non-limiting examples of such catheters are the catheters described hereinafter in this specification having a planar distal end assembly, but the present invention is not limited to this specific type of catheter and may be used to determine the far-field component of an IEGM signal sensed by any other catheter type that does not have any specific electrodes suitable for far-field IEGM sensing. Accordingly, the present invention provides a solution to the above problem and facilitates accurate measurement of tissue activation signals by such catheters.

[0011] Refer to FIG. 1 which schematically illustrates a catheter-based electrophysiological mapping system 10. The system 10 includes a catheter 14 for sensing cardiac tissue activation signals, or in other words, intracardiac electrogram (IEGM) signals. The catheter 14 may be percutaneously inserted by a physician 24 into a cardiac chamber or vascular structure of the heart 12 through the patient's vasculature. Typically, a delivery sheath catheter is inserted into the left atrium or right atrium near the desired location of the heart 12. Thereafter, one or more catheters may be inserted into the delivery sheath catheter to reach the desired location within the heart 12. An exemplary catheter 14 configured to sense IEGM is illustrated herein. The physician 24 can place the distal end assembly 28 of the catheter 14 in contact with the heart wall to sense a target site in the heart 12.

[0012] The catheter 14 is an exemplary catheter that includes a plurality of electrodes 26 at its distal end portion 28 for sensing IEGM signals from the adjacent cardiac tissue. The catheter 14 may additionally include a position sensor 29 embedded within or in the vicinity of the distal end assembly 28 to track the position and orientation of the distal end assembly 28. Optionally, and preferably, the position sensor 29 is a magnetic-based position sensor that includes three magnetic coils for sensing three-dimensional (3D) location and / or orientation.

[0013] The magnetic-based position sensor 29 may operate in conjunction with the position pad 25, which includes a plurality of magnetic coils 32 configured to generate a magnetic field within a predetermined working volume. The real-time position of the distal end assembly 28 of the catheter 14 may be tracked based on the magnetic field generated by the position pad 25 and sensed by the magnetic-based position sensor 29. The system 10 may also optionally include one or more patches 38 positioned for skin contact on the patient 23 to establish a location reference for the location pad 25. Details of magnetic-based position sensing techniques are described, for example, in U.S. Patent 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.

[0014] The recorder 11 records and displays the electrocardiogram 21 captured by the body surface electrocardiogram (ECG) electrodes 18 and the intracardiac electrogram (IEGM) captured by the electrodes 26 of the catheter 14. The recorder 11 may include pacing capabilities for pacing the rhythm of the heart and / or may be electrically connected to an independent pacemaker.

[0015] In some embodiments, system 10 may be further adapted to perform tissue ablation. In such embodiments, system 10 may include an ablation energy generator 50 and a catheter dedicated to tissue ablation (not specifically shown). For this purpose, system 10 can include one or more catheters including a catheter dedicated to IEGM sensing and / or a catheter dedicated to ablation and / or a catheter dedicated to both IEGM and ablation. For ablation, physician 24 can similarly place the distal end of the ablation catheter in contact with the target site for ablation of the tissue. Ablation energy generator 50 is adapted to transmit ablation energy to one or more of the electrodes at the distal end of the ablation catheter. 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 such that they can be used to effect irreversible electroporation (IRE), but are not limited thereto. In an embodiment, catheter 14 may also be configured and operable for tissue ablation and thus may be adapted for both IEGM sensing and ablation.

[0016] The Patient Interface Unit (PIU) 30 is an interface configured to establish electrical communication between medical devices such as catheters and / or other electrophysiological devices, and a workstation 55 for controlling the operation of the system 10. The medical devices of the system 10 may include, for example, one or more catheters, position pads 25, body surface ECG electrodes 18, electrode patches 38, ablation energy generators 50, and recorders 11, etc. electrophysiological devices. Optionally, and preferably, the PIU 30 additionally includes processing capabilities for performing real-time calculations of catheter positions and for performing ECG / IEMG signal processing and / or calculations.

[0017] The workstation 55 includes one or more processors having a memory and / or storage device in which appropriate operating software is stored, and user interface functions. The workstation 55 optionally includes (1) modeling the endocardial anatomical structure in three dimensions (3D) and rendering it to display a model or anatomical map 20 on a display device 27, and (2) compiling (or other data) from the recorded potential map 21 and displaying it on the display device 27 in a representative visual display or image overlaid on the rendered anatomical map, and (3) displaying the real-time location and orientation of one or more catheters within the heart chamber, and (4) displaying on the display device 27 a target site such as a location where an activation signal was measured / mapped or a location where ablation energy was applied. It 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, commercially available from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA, 92618.

[0018] Referring to FIG. 2, an example of a catheter 14 for IEGM sensing is schematically illustrated. In this embodiment, the catheter 14 has a planar distal end 28 adapted for intracardiac electrogram (IEGM) sensing / mapping. More specifically, the catheter includes a shaft 14H and a distal end assembly 28 connected to one end of the shaft 14H, whereby the distal end assembly 28 of the catheter in this example has a planar configuration and includes a plurality of electrodes 26 suitable for IEGM sensing. The plurality of electrodes 26 generally includes a first and a second plurality of electrodes respectively disposed on opposing surfaces P1 and P2 of the planar configuration of the distal end assembly 28 (only the electrodes 26 from one side of the planar distal end assembly 28 are shown in the figure).

[0019] Shaft 14H includes a reference electrode 22 disposed on shaft 14H near distal end assembly 28. As will be described in more detail below, reference electrode 22 facilitates measurement of the distance between electrode 26 and the heart tissue, thereby enabling evaluation of the far-field component of the IEGM signal sensed thereby in accordance with the techniques of the present invention described in more detail below. As will be understood by those skilled in the art, the far-field component of the IEGM signal generally should be measured to measure the cardiac tissue activation signal in the region of interest of the cardiac tissue (e.g., by an electrode that is sufficiently far from the cardiac tissue but within the cardiac blood pool). The far-field component is then subtracted / suppressed from the IEGM signal measured by each electrode that contacts the cardiac tissue in the region of interest to obtain the near-field component of the IEGM signal in the region of interest, which over time indicates the cardiac tissue activation signal in the tissue region of interest. However, in some catheters, such as catheter 14 where distal end assembly 28 is planar, there may not be a dedicated specific electrode for measuring the far-field component of the IEGM signal. More specifically, there is no specific electrode that is pre-maintained away from the tissue wall of the heart so that the far-field component of the IEGM signal sensed by electrode 26 can be accurately measured. For example, during operation using the planar distal end assembly 28 of catheter 14, all or part of the electrodes located on one surface (e.g., P1) of the planar distal end assembly 28 may touch the tissue of the heart wall, while all or part of the electrodes 26 located on the opposite surface (e.g., P2) may not contact the cardiac tissue. Since the distal end assembly 28 in this catheter example 14 is planar (i.e., not volumetric, such as of the basket or balloon catheter type), there is no specific location on distal end assembly 28 where electrodes can be placed to ensure non-contact with the cardiac tissue.Thus, in such types of catheters that do not have specific electrodes designed to sense far-field IEGM, during operation, among the plurality of electrodes 26, there is a need to dynamically identify and select electrodes that do not contact the heart tissue and are sufficiently far away from it, and use the signals from those selected electrodes to determine the far-field EGM signal. To achieve this, the reference electrode 22 is provided on the catheter 14 and is adapted / specialized for performing tissue proximity sensing / measurement based on the impedance between each of the electrodes 26 and the reference electrode 22, thereby evaluating the distance of one or more of the electrodes 26 from the heart tissue.

[0020] In this non-limiting example, the reference electrode 22 is disposed on the shaft 14H of the catheter 14 and is adapted to facilitate tissue proximity measurement. Then, the IEGM signals acquired / measured by a subset of the electrodes 26 identified as being sufficiently far from the tissue are used to determine / evaluate the far-field components of the IEGM signals sensed by one or more of the electrodes 26 in contact with the tissue. To facilitate tissue proximity measurement, the reference electrode 22 in this example is typically maintained away from the tissue / heart tissue and is disposed on the shaft 14H of the catheter in such a manner that it contacts the body fluid (e.g., blood when the catheter is inserted through the patient's vasculature) during the in-heart operation of the catheter 14 within the heart without contacting the tissue / heart tissue. This arrangement enables the use of the reference electrode 22 for impedance-based tissue proximity measurement, thereby allowing the distance of each electrode from the heart tissue to be evaluated using the impedance between the reference electrode and each respective electrode of the plurality of electrodes 26. Preferably, in some embodiments, the reference electrode 22 is configured to have a ring-like shape (e.g., surrounding the shaft 14H).

[0021] In fact, in this case, the reference electrode 22 on the shaft 14H is typically arranged so as not to contact the tissue, yet it may not be suitable for providing an accurate measurement of the far-field IEGM component. One reason for this is that the reference electrode is typically relatively large and thus may be able to capture both the near-field component and the far-field component when brought close to the tissue wall. One reason for this is that since the reference electrode 22 is installed on the shaft 14H (and is typically relatively large), it is generally too close to the tissue (for example, the tissue of the vascular system into which the catheter can be inserted and thus not suitable for accurate sensing of the far-field signal), and thus may be able to capture both the far-field component of the IEGM signal and its near-field component from the tissue region proximal thereto. Another reason is that in some cases where the catheter 14 is delivered via a delivery sheath, the reference electrode 22 located on the shaft 14H may remain within the delivery sheath and thereby be substantially masked from sensing the far-field component of the IEGM signal.

[0022] Nevertheless, according to an embodiment of the present invention, the reference electrode 22 can be used to evaluate the distance of one or more of the electrodes 26 from the heart tissue, thereby facilitating the identification and dynamic selection of a subset of the electrodes 26 that are sufficiently far from the tissue and can accurately measure the far-field signal. As will be described in more detail below, the distance measurement of the electrodes 26, also referred to herein as tissue proximity measurement and / or tissue proximity index, also evaluates the tissue proximity (e.g., the impedance between each respective electrode and the reference electrode 22) and can be performed by measuring the impedance of each respective electrode 26 to determine the tissue proximity of one or more of the electrodes 26 based on those impedances. Examples of tissue proximity measurement / techniques that can be implemented in accordance with the present invention to evaluate the tissue proximity of one or more of the electrodes 26 are disclosed in U.S. Patent Application Publication No. 2021 / 0177504, which is incorporated herein by reference.

[0023] Optionally, the shaft 14H also includes a position sensor 29, which is typically embedded in or near the distal end assembly 28 of the catheter, enabling the system 100 to track the position of the distal end assembly 28 (and the electrodes 26 thereon), thereby enabling a special mapping of the activation signals sensed by the electrodes 26 or some of them.

[0024] Typically, the catheter 14 is implemented as a disposable catheter. In some embodiments, the planar distal end assembly 28 of the catheter 14 is configured using a flexible printed circuit board (PCB) and a first and a second plurality of electrodes 26 mounted / fabricated on both sides / surfaces P1 and P2 of the flexible PCB. This particularly enables a cost-effective fabrication of the catheter 14, reduces its manufacturing cost, and thus also reduces the cost of medical procedures such as epicardial procedures where it can be utilized.

[0025] Returning to FIG. 1, as described above, electrophysiological devices such as a surface ECG device 38 including a plurality of ECG patches attached to the outside of the patient's body / skin, and other electrophysiological devices such as additional catheters (not particularly shown) connected to the PIU 30, where the PIU 30 facilitates electrical communication between these electrophysiological devices and the workstation 55. The PIU 30 may include, for example, among other things, a signal processor adapted to apply analog-to-digital conversion (sampling) to signals received from the electrophysiological devices connected thereto and / or to packetize these signals into data packets and communicate them to the workstation 55 and / or the recorder 11.

[0026] According to the present invention, the system 10 includes an IEGM signal measurement system 100 (a subsystem of the system 10) that can at least determine the far-field component of the IEGM signal sensed by the electrodes of a catheter, such as the electrodes 26 of the catheter 14, and this may not have specific electrodes designed to measure the far-field IEGM signal component. The IEGM signal measurement system 100 determines the near-field component of the IEGM signal measured by one or more of the electrodes 26 of the catheter, and optionally may be further adapted thereby to determine the activation signal AS in the tissue region proximal to one or more of the electrodes 26. In various implementations, the system 100 is implemented as a subsystem of the system 10, and the components of the system 100 can be included in, implemented in, or distributed among any one or more of the workstation 55, PIU 30, and recorder 11 of the system 10 (e.g., can be implemented by one or more processors and / or signal processors of those subsystems).

[0027] Next, refer together to FIGS. 3 and 4, which illustrate techniques for measuring the far-field IEGM component and optionally the near-field component and / or tissue activation signal according to embodiments of the present invention. FIG. 3 is a flowchart of a method 200 for determining the far-field IEGM component and optionally based on the far-field IEGM component, further the near-field IEGM component, and / or the cardiac tissue activation signal. FIG. 4 is a block diagram illustrating an embodiment of the IEGM signal measurement system 100 for implementing the method 200.

[0028] In operation 210 of method 200, a catheter, such as catheter 14 having a plurality of electrodes 26 disposed in distal assembly 28, is provided in a manner suitable for sensing IEGM signals from the tissue regions with which they are in contact. Electrodes 26 can be disposed, for example, on the outer surface of distal assembly 28 of assembly catheter 14. Optionally, the catheter also includes a reference electrode 22 as described above. Alternatively, in some embodiments, the reference electrode 22 need not necessarily be present on catheter 14 and may be disposed in a different manner such that it contacts body fluid while being maintained at a distance from the body / heart tissue.

[0029] Operation 220 of method 200 is performed to determine the far-field component FF of IEGM signal E sensed by electrodes 26 of catheter 14. To achieve this, in operation 220a, a tissue proximity measurement is applied to each respective one of the plurality of electrodes 26 to evaluate the respective distance D of each of the plurality of electrodes from the surface of the tissue (e.g., heart tissue). In this case, the plurality of electrodes for which tissue proximity is evaluated may include one or two or more of the plurality of electrodes 26 in distal assembly 28 of catheter 14, typically preferably two or more electrodes. In some embodiments, the tissue proximity measurement is performed by a technique similar to that disclosed in, for example, U.S. Patent Application Publication No. 2021 / 0177504.

[0030] For example, tissue proximity measurement can be performed by the tissue proximity processor / processing 110 of system 100. For example, the tissue proximity processing 110 may be performed by a signal processor associated with the system and connected to a number of electrodes 26 and a reference electrode 22. The signal processor performing the tissue proximity processing 110 delivers a current including one or more frequency components between each of the electrodes among the number of electrodes 26 and the reference electrode 22, and can measure the respective impedance therebetween (e.g., optionally, the measured impedance for each frequency component in the delivered current). Since tissue typically has an impedance significantly different from body fluid / blood, between each of the electrodes of the reference electrode 22, each of the thus measured impedances provides an indicator D of the distance between the respective electrode and the tissue.

[0031] More specifically, impedance readings are generally very sensitive to tissue proximity and can vary from patient to patient. Thus, in some embodiments, the relationship between the impedance of the electrodes and their respective distances D can be dynamically inferred during a medical procedure. In such embodiments, optionally, in operation 220a (e.g., in at least one iteration of this operation), the impedance values from each electrode for which the impedance is being measured can be stored by system 100. Then, based on the characteristics of the distribution of the measured impedance values (e.g., based on the measured maximum and minimum impedances), the relationship between the measured impedance of the electrodes and their distance D from the tissue, and / or an impedance threshold indicating whether the electrodes are in contact with the tissue can be determined in real time during the medical procedure. Accordingly, based on this relationship or impedance threshold, the distance D of each electrode can be evaluated in 220a from their measured impedance.

[0032] Thus, as illustrated in the non-limiting example of FIG. 4, a non-limiting example of data / signals indicating the respective distances D of a number of electrodes 26 is thus determined and provided by the electrode tissue proximity processing 110.

[0033] In parallel, but not necessarily simultaneously with, and typically subsequent to, the tissue proximity measurement operation 220a, the IEGM signal measurement values, referred to as E in FIG. 4, are obtained from one or more than one of the plurality of electrodes 26, respectively. The IEGM signal measurement value E may be performed, for example, by the IEGM signal measurement processor / processing 120 of the system 100 as illustrated in FIG. 4. The IEGM signal E typically has a specific distance threshold D for each tissue distance D in operation 220a TH is evaluated to exceed at least some of the electrodes 26 that may include the electrodes 26, and optionally, for one or more of the electrodes 26 whose near-field IEGM signal components are inferred in the optional operation 240 described below. Alternatively, in some embodiments, the IEGM signal E may be measured for all or a predetermined set of the electrodes 26. The IEGM signal E may be measured for the electrodes according to any suitable technique, as will be understood by those skilled in the art. For example, in some embodiments, the IEGM signal E of each electrode of the electrodes 26 performs monopolar IEGM signal measurements known in the art to measure each electrode and, for example, one or more of the one or two or more body surface ECG electrodes 18 and / or electrode patches 38 of the system 10 described above. The voltage between another electrode that may be present is monitored / measured (e.g., within a time frame).

[0034] In some non-limiting embodiments, the tissue proximity processing 110 and the IEGM signal measurement processing 120 may be performed by a signal processor that may be part of the PIU 30 of the system 10 described above. The signal processor, e.g., the PIU 30, may signal communicate with, for example, the electrodes 26, and optionally, the reference electrode 22 (used for tissue proximity processing), and optionally, another electrode, e.g., 18, that may be used for monopolar IEGM signal measurement. The signal processor may perform various signal processing capabilities, such as impedance and / or voltage measurements between the electrodes coupled thereto, signal / noise filtering, analog-to-digital conversion, and / or other signal processing as understood by those skilled in the art. As will be described in more detail below, the tissue proximity processing 110 and the IEGM signal measurement processing 120 may be repeatedly executed between successive time frames (e.g., each being on the order of, for example, 50 milliseconds (ms)), thereby, for each successive time frame, evaluating the tissue proximity D for a number of electrodes 26 and the IEGM signal measurement values E for some or all of them as described above. Assuming that an analog-to-digital conversion is performed and, for example, a sampling rate of on the order of 1 kHz is applied, each such time frame may include, for example, 50 samples.

[0035] To determine / evaluate the far-field IEGM component FF sensed (e.g., commonly) by the electrodes 26, operation 220 of method 200 further includes sub-operations 220b and 220c. In operation 220b, a subset of the electrodes 26 that are evaluated as having a respective tissue distance / proximity D greater than a certain distance threshold D TH in operation 220a is selected (e.g., dynamically selected for each time frame) for further processing of their IEGM signals E, and based thereon, the (common) far-field IEGM component FF in the IEGM signals is determined. The minimum distance threshold D above which an electrode is selected THis generally such that the IEGM signal sensed thereby is expected to consist mostly of the far-field component FF and to a lesser extent of the near-field IEGM component NF. For example, a distance threshold D TH is at least D TH > 5 millimeters may be selected.

[0036] In operation 220c, the far-field component FF of the IEGM signal is determined (e.g., for each time frame) by averaging the IEGM signal measurements E from each of the electrodes 26 of the subset selected in 220b where each distance D from the tissue surface exceeds the minimum distance threshold D TH . Aggregation / averaging of the signals from multiple electrodes provides for suppressing / averaging out noise components (e.g., near-field signal remnants that may still be weakly sensed by the subset of electrodes regardless of their relative distance from the tissue), thereby ensuring that the far-field component FF that is substantially "clean" from noise is obtained.

[0037] For some time frames, operation 220b may not result in selected electrodes. For example, if the reference electrode 22 contacts the tissue in its vicinity during the time frame, the distance measurements D obtained in operation 220a for all / any of the electrodes 26 are below the threshold D THA value less than this may be provided. Thus, in operation 220c, if the number of electrodes identified as having a sufficient tissue distance is below a certain predetermined minimum number of electrodes (e.g., the minimum number is at least one and typically two or more), the previous value of the far - field IEGM signal FF measured for the preceding time frame may be used in successive time frames. This generally does not introduce significant artifacts into the measured far - field IEGM signal FF because these cases are typically rare due to the position / configuration of the reference electrode 22, and the time frame is typically of a duration shorter than the characteristic time interval for changes in the far - field component FF of the IEGM signal.

[0038] For example, in operation 220a, the impedance of all or a plurality of electrodes 26 from both sides of the planar distal - end assembly 28 may be measured with respect to the reference electrode 22. If all the impedances being measured in 220a indicate that each electrode is in contact with the tissue wall (e.g., if they are relatively high impedances), in this case, in operation 220b, the system 100 may assert that the cause of the high impedance is that the reference electrode 22 is in contact with the cavity / tissue wall (since it is typically impossible for a plurality of electrodes on both sides of the planar distal - end assembly 28 to be in contact with the tissue wall simultaneously), and electrodes that are away from the tissue are not dynamically selected. Thus, in this case, in operation 220c, the previous value of the far - field IEGM signal FF is provided as representative of the far - field IEGM signal FF for the current time frame.

[0039] Referring to the system 100 illustrated in FIG. 4, the distance D from the tissue is sufficient (e.g., a threshold D THThe dynamic selection 220b of a subset of electrodes (above a threshold) may be performed by the signal selector utility 130 of the system 100. The aggregation / averaging 220c of signals from the subset selected by the signal selector utility 130 can be executed by the signal aggregation utility 140 of the system 100. As will be understood by those skilled in the art, the signal selector utility 130 and / or the signal aggregation utility 140 may be implemented by signal processing (e.g., as part of the PIU 30 of the system 10) and / or by a computerized system / processor such as the workstation 55 or the recorder 11 illustrated in FIG. 1. The signal selector utility 130 may include a selector S (implemented, for example, as a signal switch and / or by a digital / computerized selection process or by other means as understood by those skilled in the art). Accordingly, the signal aggregation utility 140 may also be implemented by analog, digital, or computerized addition / averaging, or other forms of aggregation.

[0040] In view of the above, in operation 220, the far-field FF component of the IEGM signal may be determined based on the IEGM signal E measured by the electrode 26, while generally obviating the need to have dedicated electrodes disposed within the catheter 14 to sense the intracardiac far-field IEGM component FF.

[0041] As described above, operation 220 may be performed to evaluate and determine the far-field FF component of the IEGM signal for each time frame (successive / consecutive time frames) in which the IEGM signal E is measured by electrode 26. Thus, as illustrated in optional operation 230 of method 200, operation 220 may be repeated for a plurality of successive / consecutive time frames to update the values of the far-field IEGM component FF over a desired duration of a medical procedure during which the IEGM signal is to be monitored. As described above, for time frames (which are generally rare) in which the electric-field IEGM component FF cannot be evaluated (e.g., when reference electrode 22 contacts tissue), the far-field IEGM component FF evaluated for the respective preceding time frame may be used. For this purpose, system 100 may include a buffer (a data or signal buffer not specifically shown) that holds the value of the last updated electric-field IEGM component FF in the preceding time frame and enables this value to be used in such cases.

[0042] Optionally, method 200 further includes operation 240 for evaluating the near-field component NF of the IEGM signal sensed by one or more specific target electrodes SE of electrode 26 (typically the electrodes 26 in contact with heart tissue). The specific set of electrodes for which the near-field component NF is determined may be automatically selected by system 10 in various implementations, (e.g., according to the cardiac electrical activity mapped or measured thereby, and in some cases based on the position of catheter 14 that can be determined by the tissue region and position sensor 29 to be mapped / measured), and / or in some implementations, may be selected by physician 24 operating system 10.

[0043] Operation 240 optionally includes sub - operation 240a, in which an IEGM signal E measured by one or more target electrodes SE is obtained (at least one electrode is illustrated in the non - limiting examples of FIGS. 3 and 4). In sub - operation 240b, a far - field component FF as determined by operation 220 above is also acquired. The far - field component FF is used to process the IEGM signal of each of the one or more target electrodes SE to determine / evaluate the near - field component NF of the IEGM signal E sensed thereby. Generally, the near - field NF component of each target electrode SE is determined by suppressing or subtracting the far - field component FF obtained by operation 220 from the IEGM signal E measured by the electrode SE. This is because the IEGM signal E measured by each target electrode SE is composed of both a near - field NF component sensed by the electrode from the surrounding tissue and a far - field component FF typically commonly sensed by electrode 26. In this regard, as understood by those skilled in signal operation / processing, the subtraction / suppression may be performed using appropriate weighting of the FF signal according to the amplitude, in which case the amplitude may be included in the IEGM signal of each target electrode SE (for example, the appropriate weight may be determined based on the correlation between the FF component and each IEGM signal).

[0044] To perform the optional operation 240, the system 100 illustrated in FIG. 4 can include, for example, an optional electrode selector 150 adapted to provide an IEGM signal measured by a particular one or more target electrodes SE, and a signal suppression utility / filter 160 adapted to receive the far-field IEGM component FF and the IEGM signal measured by each respective target electrode SE, and to suppress / subtract the former from the latter to obtain the near-field component NF of the IEGM signal component of each respective target electrode SE. As will be understood by those skilled in the art, the selector 150 and / or the electrode signal suppression utility / filter 160 may be implemented, for example, by analog or digital means (e.g., by the PIU 30) as part of the signal processor illustrated in FIG. 1, or by a computerized system (e.g., by the workstation 55).

[0045] Generally, the operation 240 may be performed for each respective time frame in which the near-field component NF of a particular target electrode SE is evaluated. For this purpose, as will be understood from the above description, the operation 240 is such that the far-field component FF obtained for each time frame is suppressed from the IEGM signal E taken from each target electrode SE for the corresponding / same time frame, thereby resulting in the near-field signal NF sensed by that electrode SE during that time frame, and may be performed in synchronization with the operation 220.

[0046] Optionally, method 200 may also further include operation 250, by which operation 240 is repeated over a plurality of time frames to determine / record the tissue activation signal AS sensed by each target electrode SE from the neighboring tissue. This tissue activation signal AS is used herein to indicate the aggregation / accumulation of the near-field signal NF components measured by each respective measured target electrode SE in each time frame over the duration of one of the plurality of time frames. Operation 250 may be performed, for example, by recorder 170 of system 100 illustrated in FIG. 4, which may be part of recorder 11 of system 10 for recording the tissue activation signal of the target electrode SE.

[0047] For this purpose, the above-described system 100 and method 200 illustrate an embodiment of the technique of the present invention for evaluating the far-field signal component FF of the IEGM signal E sensed by a plurality of electrodes 26 on the distal end assembly of a catheter, such as catheter 14, which may not have a dedicated suitable electrode for sensing the intracardiac far-field IEGM signal FF. For clarity, system 100 is illustrated in FIG. 4 with separate designations of its plurality of components that perform different functions / operations of method 100. However, as will be understood by those skilled in the art, system 100 may generally be implemented using a different set of components, for example, by a general-purpose signal processor and / or a general-purpose computerized system having software and / or hardware adapted to perform the operations of method 200 described above. Additionally, as described above, the systems and methods for implementing the present invention are adapted to determine the far-field component of the IEGM signal measured in one or more time frames, and optionally thereby also determine the near-field component of the IEGM signal for the time frame, and further optionally thereby determine a tissue activation signal based on the near-field components evaluated for a plurality of time frames.

Example

[0048] Example 1. A method 220 for determining a cardiac tissue activation signal, comprising: I. Providing a catheter 14 including a plurality of electrodes 26 disposed at a distal end assembly 28 of the catheter 14; II. Determining a far-field component of an intracardiac electrogram (IEGM) signal sensed by at least one of the plurality of electrodes 26 by: (a) Applying a tissue proximity measurement to each respective electrode of the plurality of electrodes 26 to evaluate a respective distance D of each of the plurality of electrodes from the tissue surface 220a; (b) Dynamically selecting a subset of one or more of the plurality of electrodes 26 whose respective distances from the tissue surface exceed a certain threshold based on each respective distance D 220b; (c) Determining the far-field component FF by averaging IEGM signal measurements E from each electrode in the subset whose respective distances from the tissue surface exceed a certain threshold 220;

[0049] Example 2. The method 200 according to Example 1, further comprising: evaluating a near-field component of the IEGM signal sensed by at least one electrode by subtracting a far-field component NF from (simultaneous) IEGM signal measurements obtained from at least one electrode 240.

[0050] Example 3. The method 200 according to Example 2, further comprising: repeating operations II and III (230, 250) to determine the temporal evolution of the near-field component NF of the EGM signal E, thereby obtaining a cardiac tissue activation signal of tissue near at least one electrode.

[0051] Example 4. The method 200 according to Example 1, wherein applying a tissue proximity measurement to each electrode (220a) includes applying an excitation current through each electrode and measuring the impedance of the electrode, thereby evaluating the tissue proximity D based on the impedance.

[0052] Example 5. Method 200 described in Example 4, wherein the impedance is measured between a reference electrode 22 disposed near the end of the shaft 14H of the catheter 14 proximal to the distal end assembly 28 such that the electrodes remain typically separated from the tissue during operation of the catheter 14.

[0053] Example 6. Method 200 described in Example 1, wherein the far-field component FF of the IEGM signal E is repeatedly updated by repeating operation II (220).

[0054] Example 7. The update of the far-field component FF of the IEGM signal E is skipped in the repetition (230) of operation II where the number of electrodes identified by dynamically selecting those having respective distances D from the tissue surface greater than a certain threshold D TH is less than a certain predetermined minimum number of electrodes. For example, a predetermined minimum number of electrodes having a distance D greater than a certain threshold D, below which number the far-field component FF is not updated and remains at its previous value, is one or more electrodes. TH Example 8. Applying a tissue proximity measurement to each electrode (220a) includes measuring the impedance between each electrode and a reference electrode 22 disposed on the catheter 14 typically remaining separated from the tissue, and in the repetition (230) where the number of electrodes is less than a certain predetermined minimum number, the reference electrode 22 is evaluated as being in contact with the tissue, and thus the update of the far-field component of the EGM signal in those repetitions is skipped. Method 200 described in Example 7.

[0055] Example 9. Method 200 described in Example 1, wherein the distal end assembly 28 of the catheter 14 has a planar configuration and the plurality of EGM electrodes 26 include a first and a second plurality of EGM electrodes respectively disposed on the opposing surfaces P1 and P2 of the distal end assembly 28 of the catheter.

[0056] Example 10. Method 200 described in Example 1, wherein the distal end assembly 28 of the catheter 14 has a planar configuration and the plurality of EGM electrodes 26 include a first and a second plurality of EGM electrodes respectively disposed on the opposing surfaces P1 and P2 of the distal end assembly 28 of the catheter.

[0057] Example 10. The method 200 according to Example 1, wherein the catheter 14 is adapted to enable evaluation of the far - field component FF of the EGM signal E without having dedicated electrodes disposed within the distal - end assembly 28 of the catheter 14 for sensing the far - field component FF.

[0058] Example 11. The method 200 according to Example 9, wherein the distal - end assembly of the catheter 14 comprises a flexible printed circuit board (PCB), and a plurality of first and second electrodes are on both sides of the PCB.

[0059] Example 12. A system 100 for determining a cardiac tissue activation signal, the system 100 being connectable to a catheter 14, the catheter 14 having a plurality of electrodes 26 disposed in its distal - end assembly 28, the system 100 comprising one or more processors connectable for signal communication with the plurality of electrodes 26, the one or more processors being configured to determine the far - field component FF of the intracardiac electrogram (IEGM) signal E sensed by at least one of the plurality of electrodes 26 by (a) applying a tissue proximity measurement to each respective electrode of the plurality of electrodes to evaluate the respective distance D of each of the plurality of electrodes from the tissue surface (220a); (b) dynamically selecting a subset of one or more electrodes of the plurality of electrodes whose respective distance from the tissue surface exceeds a certain threshold D TH based on each respective distance D (220b); (c) obtaining IEGM signal measurements E from each electrode of the subset whose respective distance D from the tissue surface exceeds a certain threshold D TH ; and (d) determining the far - field component FF as the average of the IEGM signal measurements E obtained from each electrode of the subset whose respective distance D from the tissue surface exceeds a certain threshold D TH (220c) (220).

[0060] Example 13. The system 100 according to Example 12, wherein one or more processors are adapted to further evaluate the near-field component NF of the IEGM signal E sensed by at least one of the electrodes 26 by subtracting the far-field component FF from the measured value of the IEGM signal obtained from at least one electrode.

[0061] Example 14. The system 100 according to Example 13, wherein one or more processors are adapted to repeatedly (230, 250) determine (230, 250) the far-field component FF and the near-field component NF, thereby determining the development of the near-field component NF of the IEGM signal over time, and thereby determining the cardiac tissue activation signal AS in the tissue near at least one electrode, whereby the development indicates the cardiac tissue activation signal AS.

[0062] Example 15. The system 100 according to Example 12, wherein one or more processors are adapted to apply a tissue proximity measurement (220a) to each electrode by delivering an excitation current through each electrode and measuring the impedance of the electrode, thereby evaluating the tissue proximity based on the impedance.

[0063] Example 16. The system 100 according to Example 15, wherein the delivery of the excitation current impedance is performed between the reference electrode 22 disposed near the end of the proximal shaft 14H relative to the distal end assembly 28 of the catheter 14 such that each electrode typically remains isolated from the tissue.

[0064] Example 17. One or more processors are adapted to repeatedly update 230 the far-field component of the IEGM signal by repeating operations 220a to 220c of the method, and the update (230) of the far-field component of the IEGM signal is a certain threshold D THSkipped in these repetitions where the number of electrodes identified by the operation 220b of dynamically selecting those having respective distances D from the tissue surface exceeding a predetermined minimum number (the minimum number may be one, or in some cases multiple, to facilitate measurement / evaluation of the far-field component by averaging the signals of several electrodes), the system 100 described in Example 12.

[0065] Example 18. Catheter 14 for intracardiac electrogram (IEGM) mapping. The catheter 14 includes a shaft 14H and a distal end assembly 28 connected to one end of the shaft 14H. The distal end assembly 28 has a planar configuration and includes a plurality of electrodes 26 including first and second pluralities of electrodes respectively disposed on opposing surfaces P1 and P2 of the planar configuration of the distal end assembly 28, and a reference electrode 22. The reference electrode 22 is disposed on the shaft 14H in the vicinity of the distal end assembly 28 so as to enable implementation of respective tissue proximity measurements for each one or two or more of the plurality of electrodes by measuring the impedance between the reference electrode 22 and each electrode 26, the catheter 14.

[0066] Example 19. - The distal end assembly 28 comprises a flexible printed circuit board (PCB), and the first and second pluralities of electrodes are on both sides of the PCB, - The reference electrode 22 is positioned on the shaft such that during intracardiac operation of the catheter within the heart, the reference electrode 28 is typically spaced from the heart tissue and in contact with blood, thereby facilitating impedance-based tissue proximity measurements, and - The reference electrode has at least one of a ring-shaped configuration, the catheter 14 described in Example 18.

[0067] Example 20. The catheter 14 described in Example 18, configured as a disposable catheter.

[0068] 〔Embodiment〕 (1) A method for determining a cardiac tissue activation signal, comprising: I. Providing a catheter, wherein the catheter includes a plurality of electrodes disposed at its distal end assembly; II. Determining a far-field component of an intracardiac electrogram (IEGM) signal sensed by at least one of the plurality of electrodes by: (a) Applying a tissue proximity measurement to each of the plurality of electrodes to evaluate the respective distance of each of the plurality of electrodes from the tissue surface; (b) Dynamically selecting a subset of one or more of the plurality of electrodes whose respective distance from the tissue surface exceeds a certain threshold based on the respective distances; (c) Determining the far-field component by averaging the IEGM signal measurement values from the respective electrodes of the subset whose respective distance from the tissue surface exceeds the certain threshold. (2) The method according to embodiment 1, further comprising evaluating a near-field component of the IEGM signal sensed by the at least one electrode by subtracting the far-field component from the (simultaneous) IEGM signal measurement values obtained from the at least one electrode. (3) The method according to embodiment 2, comprising repeating operations II and III to determine the development of the near-field component of the EGM signal over time, thereby obtaining a cardiac tissue activation signal of the tissue near the at least one electrode. (4) The method according to embodiment 1, wherein applying the tissue proximity measurement to each of the respective electrodes in (a) includes applying an excitation current through each of the respective electrodes and measuring the impedance of the electrode, thereby evaluating the tissue proximity based on the impedance. (5) The method of embodiment 4, wherein the impedance is measured between the respective electrodes and a reference electrode disposed near an end of the catheter shaft proximal to the distal end assembly such that the impedance remains typically separated from the tissue during operation of the catheter.

[0069] (6) The method of embodiment 1, wherein the long distance field component of the IEGM signal is repeatedly updated by repeating operation II. (7) The method of embodiment 6, wherein the update of the long distance field component of the IEGM signal is skipped in a repetition of operation II in which the number of electrodes identified by dynamically selecting those having the respective distances from the tissue surface exceeding a certain threshold is less than a certain predetermined minimum number of electrodes. (8) Applying the tissue proximity measurement to the respective electrodes in (a) includes measuring an impedance between the respective electrodes and a reference electrode typically arranged so as to remain separated from the tissue, and in a repetition where the number of the electrodes is less than the certain predetermined minimum number, the reference electrode is evaluated as being in contact with the tissue, and thus the update of the long distance field component of the EGM signal in those repetitions is skipped. The method of embodiment 7. (9) The method of embodiment 1, wherein the distal end assembly of the catheter has a planar configuration and includes a first and a second plurality of the EGM electrodes respectively disposed on opposing surfaces of the distal end assembly of the catheter. (10) The method of embodiment 1, wherein the catheter is adapted to enable the evaluation of the long distance field component of the EGM signal without having a dedicated electrode disposed within the distal end assembly of the catheter for sensing the long distance field component.

[0070] (11) The method of embodiment 9, wherein the distal end assembly of the catheter comprises a flexible printed circuit board (PCB), and the first and the second plurality of electrodes are on both sides of the PCB. (12) A system for determining a cardiac tissue activation signal, the system being connectable to a catheter, the catheter having a plurality of electrodes disposed at its distal end assembly, the system comprising one or more processors connectable for signal communication with the plurality of electrodes, the one or more processors being adapted to determine a far - field component of an intracardiac electrogram (IEGM) signal sensed by at least one of the plurality of electrodes by (a) applying a tissue proximity measurement to each respective electrode of the plurality of electrodes to evaluate the respective distance of each of the plurality of electrodes from the tissue surface, (b) dynamically selecting a subset of one or more of the plurality of electrodes whose respective distance from the tissue surface exceeds a certain threshold based on the respective distances, (c) obtaining IEGM signal measurements from the respective electrodes of the subset whose respective distance from the tissue surface exceeds the certain threshold, (d) determining the far - field component as an average of the IEGM signal measurements obtained from the respective electrodes of the subset whose respective distance from the tissue surface exceeds the certain threshold. A system so adapted. (13) The system according to embodiment 12, wherein the one or more processors are further adapted to evaluate a near - field component of the IEGM signal sensed by at least one of the electrodes by subtracting the far - field component from the IEGM signal measurement obtained from the at least one electrode. (14) The one or more processors are adapted to determine the near-field component of the IEGM signal over time by repeatedly determining the far-field component and the near-field component and thereby determining the development of the near-field component of the IEGM signal, thereby determining a cardiac tissue activation signal in tissue near the at least one electrode, such that the development indicates the cardiac tissue activation signal, the system of embodiment 13. (15) The one or more processors are adapted to apply the tissue proximity measurement to each of the electrodes in (a) by delivering an excitation current through each of the electrodes and measuring an impedance of the electrode and thereby evaluating the tissue proximity based on the impedance, the system of embodiment 12.

[0071] (16) Delivery of the excitation current impedance is performed between each of the electrodes and a reference electrode disposed near an end of a shaft proximal to the distal end assembly of the catheter such that the electrodes typically remain separated from the tissue, the system of embodiment 15. (17) The one or more processors are adapted to repeatedly update the far-field component of the IEGM signal by repeating operations (a)-(d), and the update of the far-field component of the IEGM signal is skipped in a repetition of operations (a)-(d) in which the number of electrodes identified by dynamically selecting those having respective distances from the tissue surface that exceed a certain threshold is less than a certain predetermined minimum number of electrodes, the system of embodiment 12. A catheter for intracardiac electrogram (IEGM) mapping, comprising a shaft and a distal end assembly connected to one end of the shaft, wherein the distal end assembly of the catheter has a planar configuration and includes a plurality of electrodes including first and second pluralities of electrodes respectively disposed on opposite surfaces of the planar configuration of the distal end assembly, and a reference electrode, wherein the reference electrode is disposed on the shaft in the vicinity of the distal end assembly so as to enable implementation of respective tissue proximity measurements for each one or two or more of the plurality of electrodes by measuring an impedance between the reference electrode and the respective electrode. (19) The distal end assembly comprises a flexible printed circuit board (PCB), and the first and second pluralities of electrodes are on both sides of the PCB. The reference electrode is positioned on the shaft such that during intracardiac operation of the catheter within the heart, the reference electrode is typically spaced from the tissue of the heart and in contact with blood, thereby facilitating the tissue proximity measurement based on the impedance. The catheter according to embodiment 18, wherein at least one of the reference electrodes has an annular shape. (20) The catheter according to embodiment 18, configured as a disposable catheter.

Claims

Claim 1 A system for determining a cardiac tissue activation signal, wherein the system is connectable to a catheter, the catheter having a plurality of electrodes disposed at its distal end assembly, the system comprising one or more processors connectable for signal communication with the plurality of electrodes, wherein the one or more processors determine a far-field component of an intracardiac electrogram (IEGM) signal sensed by at least one of the plurality of electrodes by (a) applying tissue proximity measurements to each respective electrode of the plurality of electrodes to evaluate the respective distance of each of the plurality of electrodes from the tissue surface, (b) dynamically selecting a subset of one or more of the plurality of electrodes whose respective distance from the tissue surface exceeds a certain threshold based on the respective distances, (c) obtaining IEGM signal measurements from the respective electrodes of the subset whose respective distance from the tissue surface exceeds the certain threshold, and (d) determining the far-field component as an average of the IEGM signal measurements obtained from the respective electrodes of the subset whose respective distance from the tissue surface exceeds the certain threshold. A system adapted to determine by performing the above. Claim 2 The system according to claim 1, wherein the one or more processors are further adapted to evaluate a near-field component of the IEGM signal sensed by at least one of the electrodes by subtracting the far-field component from the IEGM signal measurements obtained from the at least one electrode. Claim 3 The system according to claim 2, wherein the one or more processors are adapted to repeatedly determine the far-field component and the near-field component, thereby determining the development of the near-field component of the IEGM signal over time, and thereby determining a cardiac tissue activation signal in tissue near the at least one electrode, whereby the development indicates the cardiac tissue activation signal. Claim 4 The system of claim 1, wherein the one or more processors are adapted to apply the tissue proximity measurement to each of the electrodes in (a) by delivering an excitation current through each of the electrodes and measuring the impedance of the electrode, thereby evaluating the tissue proximity based on the impedance.

5. The system of claim 4, wherein the delivery of the excitation current impedance is performed between each of the electrodes and a reference electrode disposed near an end of the shaft proximal to the distal end assembly of the catheter such that the reference electrode typically remains separated from the tissue.

6. The one or more processors are adapted to repeatedly update the far-field component of the IEGM signal by repeating operations (a) to (d), and the update of the far-field component of the IEGM signal is skipped in the repetition of operations (a) to (d) when the number of electrodes identified by dynamically selecting those having respective distances from the tissue surface exceeding a certain threshold (b) is less than a certain predetermined minimum number of electrodes.

7. A catheter for intracardiac electrogram (IEGM) mapping, comprising a shaft and a distal end assembly connected to one end of the shaft, wherein the distal end assembly of the catheter has a planar configuration and includes a plurality of electrodes including first and second pluralities of electrodes respectively disposed on opposing surfaces of the planar configuration of the distal end assembly and a reference electrode, and the reference electrode is disposed on the shaft near the distal end assembly so as to enable the implementation of respective tissue proximity measurements for each of one or more of the plurality of electrodes by measuring the impedance between the reference electrode and each of the electrodes.

8. The distal end assembly comprises a flexible printed circuit board (PCB), and the first and second pluralities of electrodes are on both sides of the PCB. The reference electrode is positioned on the shaft such that, during intracardiac operation of the catheter within the heart, the reference electrode is typically spaced from the tissue of the heart and in contact with blood, thereby facilitating the tissue proximity measurement based on the impedance, and the reference electrode has at least one of a ring-like shape, the catheter according to claim 7.

9. The catheter according to claim 7, configured as a disposable catheter.

10. A method for determining a cardiac tissue activation signal, comprising: I. providing a catheter, the catheter including a plurality of electrodes disposed at its distal end assembly; II. a far-field component of an intracardiac electrogram (IEGM) signal sensed by at least one of the plurality of electrodes, (a) applying a tissue proximity measurement to each respective electrode of the plurality of electrodes to evaluate the respective distances of the plurality of electrodes from the tissue surface; (b) dynamically selecting a subset of one or more of the plurality of electrodes whose respective distances from the tissue surface exceed a certain threshold based on the respective distances; (c) determining the far-field component by averaging the IEGM signal measurements from the respective electrodes of the subset whose respective distances from the tissue surface exceed the certain threshold.

11. I. The method according to claim 10, further comprising evaluating a near-field component of the IEGM signal sensed by the at least one electrode by subtracting the far-field component from the (simultaneous) IEGM signal measurements obtained from the at least one electrode.

12. The method according to claim 11, comprising repeating operations II and III to determine the development of the near-field component of the EGM signal over time, thereby obtaining a cardiac tissue activation signal of the tissue near the at least one electrode.

13. The method of claim 10, wherein applying the tissue proximity measurement to each of the electrodes in (a) includes applying an excitation current through each of the electrodes and measuring the impedance of the electrode, thereby evaluating the tissue proximity based on the impedance.

14. The method of claim 13, wherein the impedance is measured between each of the electrodes and a reference electrode disposed near an end of the catheter shaft proximal to the distal end assembly such that the reference electrode typically remains separated from the tissue during operation of the catheter.

15. The method of claim 10, wherein the long distance field component of the IEGM signal is repeatedly updated by repeating operation II.

16. The method of claim 15, wherein the update of the long distance field component of the IEGM signal is skipped in a repetition of operation II in which the number of electrodes identified by dynamically selecting those having respective distances from the tissue surface greater than a certain threshold is less than a certain predetermined minimum number of electrodes.

17. The method of claim 16, wherein applying the tissue proximity measurement to each of the electrodes in (a) includes measuring the impedance between each of the electrodes and a reference electrode typically arranged to remain separated from the tissue, and in repetitions where the number of electrodes is less than the certain predetermined minimum number, the reference electrode is evaluated as being in contact with the tissue, and thus the update of the long distance field component of the EGM signal in those repetitions is skipped.

18. The method of claim 10, wherein the distal end assembly of the catheter has a planar configuration and includes first and second pluralities of the EGM electrodes respectively disposed on opposing surfaces of the distal end assembly of the catheter.

19. The method of claim 10, wherein the catheter is adapted to enable the evaluation of the long distance field component of the EGM signal without having a dedicated electrode disposed within the distal end assembly of the catheter for sensing the long distance field component.

20. The method according to claim 18, wherein the distal end assembly of the catheter comprises a flexible printed circuit board (PCB), and the plurality of first and second electrodes are on both sides of the PCB.

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