Systems and methods for intracardiac electrogram measurements

Abstract

The subject of the invention is a system and method of intracardiac electrogram measurement. Methods and systems for determining cardiac tissue activation signals are disclosed. The method provides particularly for determining a far-field component of an intracardiac electrogram (IEGM) signal sensed by at least one of a plurality of electrodes of a catheter. The method includes applying a tissue proximity measurement to each respective electrode of a plurality of the catheter electrodes to assess their respective distance from a tissue surface, respectively; dynamically selecting a subset of one or more electrodes of the plurality of electrodes based on the respective distances, the respective distance of the subset of one or more electrodes from the tissue surface being 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, the respective distances of the electrodes of the subset being above the certain threshold.

Description

Technical Field

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

[0002] A wide range of medical procedures involve placing probes, such as catheters, inside a patient. One medical procedure in which these types of probes or catheters have proven very useful is the treatment of cardiac arrhythmias. Cardiac arrhythmias, particularly atrial fibrillation, have been a common and dangerous medical condition, especially in the elderly population.

[0003] The diagnosis and treatment of cardiac arrhythmias involve mapping the electrical properties of cardiac tissue (particularly the endocardium and cardiac volume), and selectively ablating cardiac tissue by applying energy. In such procedures, a catheter is inserted into a cardiac chamber and optionally around the cardiac chamber. In most procedures, multiple catheters are inserted into the patient. The catheters can include mapping catheters, ablation catheters, temperature sensing catheters, and image sensing catheters. Some catheters are dedicated to being placed in specific locations of anatomical structures, such as the coronary sinus, esophagus, atrium, ventricle. The catheters have multiple electrical channels, and some catheters have more channels than others, depending on the number of sensors and electrodes included in each catheter. The number and type of catheters depend on the procedure and the workflow preferred by the doctor. During the procedure, the electrical activity of the heart is monitored / mapped from the catheter electrodes 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 be implemented in practice, embodiments will now be described by way of non-limiting example only with reference to the accompanying drawings, in which:

[0005] Figure 1 is a schematic diagram showing a catheter-based electrophysiological measurement / mapping system 10 according to an embodiment of the present invention;

[0006] Figure 2 is a schematic diagram of a catheter 14 having a planar distal end assembly adapted to measure IEGM signals according to an embodiment of the present invention;

[0007] Figure 3 is a flowchart showing a method 200 for measuring IEGM signals according to an embodiment of the present invention;

[0008] Figure 4 is a block diagram schematically showing the configuration of an IEGM signal measurement system 100 according to an embodiment of the present invention;

[0009] Like reference numerals are used in the drawings to denote like modules / components or components / modules having similar functions of the present invention. Accordingly, unless otherwise specified, the description of a module / component with reference to a particular embodiment of the present invention should be understood to be applicable to all embodiments of the present invention incorporating such module / component. DETAILED DESCRIPTION

[0010] There is a need in the art for a new and creative technique to accurately determine cardiac tissue activation signals.

[0011] Conventional techniques widely used for measuring or mapping the electrical properties of cardiac tissue typically utilize catheters with volumetric distal end assemblies, such as basket or balloon catheters or other catheters having multiple splines around a specific volume at their distal ends. In such catheters, electrodes typically located on the outer / external surface at the distal end (e.g., on the outer surface of the splines of the catheter) are operated to measure intracardiac electrograms (IEGMs) from the tissue regions in contact therewith, and another electrode typically located within the volume enclosed by the volumetric distal end and thus within the cardiac chamber but away from the intracardiac tissue is operated to measure the far-field component of the IEGM. Thus, the far-field component of the IEGM can then be used to suppress the far-field IEGM component in 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 contact electrode), thereby obtaining the near-field IEGM component of the IEGM signal sensed by the contact electrode. The development over time of the near-field components of the IEGM signals sensed by the respective electrodes in contact with the tissue regions indicates the activation signals in the tissue regions in contact with the respective electrodes.

[0012] Intracardiac catheters are typically disposable elements designated for single use in intracardiac procedures. Accordingly, there is a need in the art to reduce the manufacturing cost of such catheters. As will be appreciated from the following description, one method for reducing the manufacturing cost of a catheter for measuring / mapping the electrical properties of cardiac tissue is to use a catheter with a planar distal end assembly. This significantly reduces the manufacturing cost because such a planar distal end assembly can be formed from a flexible printed circuit board (PCB) with electrodes printed thereon.

[0013] However, the challenge in using such catheters with planar distal end assemblies to measure or map the electrical properties of cardiac tissue arises from the fact that there is no specific location on the planar configuration of the distal end for placing an electrode designated for measuring the far-field IEGM signal component. In fact, any electrode on the planar distal end assembly may occasionally contact or not contact the cardiac tissue, or be close to the cardiac tissue during operation, and thus the far-field IEGM signal component cannot be reliably obtained from any specific electrode.

[0014] Accordingly, the present invention provides a new technique for measuring far-field IEGM signal components in a manner suitable for use in a catheter designated for measuring or mapping the electrical properties of cardiac tissue. The present invention can be used, for example, to determine the far-field component of an IEGM signal sensed by a catheter that does not have an electrode (e.g., a dedicated electrode) specifically adapted / dedicated to sensing the far-field component of the IEGM signal (e.g., when sensing "noise" such as near-field IEGM from its surrounding environment is absent or substantially suppressed). A non-limiting example of such a catheter is the catheter with a planar distal end assembly described below, but the present invention is not limited to this particular type of catheter and can be used to determine the far-field component of an IEGM signal sensed by other catheter types that do not have any particular electrode adapted for far-field IEGM sensing. Accordingly, the present invention provides a solution to the above challenges, facilitating the accurate measurement of tissue activation signals through such catheters.

[0015] Reference Figure 1 , which schematically illustrates a catheter-based electrophysiological mapping system 10. System 10 includes a catheter 14 for sensing cardiac tissue activation signals or, in other words, intracardiac electrogram (IEGM) signals. The catheter 14 can be inserted by a physician 24 through the patient's vascular system via the skin into a chamber or vascular structure of the heart 12. Typically, a delivery sheath catheter is inserted into the left atrium or right atrium near the desired location in the heart 12. Then, one or more catheters can be inserted into the delivery sheath catheter to reach the desired location in the heart 12. An exemplary catheter 14 configured for sensing IEGM is shown herein. The physician 24 can place the distal end assembly 28 of the catheter 14 in contact with the heart wall for sensing a target site in the heart 12.

[0016] 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 cardiac tissue proximal thereto. The catheter 14 can additionally include a position sensor 29 embedded in or near the distal end assembly 28 for tracking 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) position and / or orientation.

[0017] A magnetic-based position sensor 29 can operate in conjunction with a positioning pad 25 that includes a plurality of magnetic coils 32 configured to generate a magnetic field within a predefined working volume. The real-time position of the distal end assembly 28 of the catheter 14 can be tracked based on the magnetic field generated by the positioning pad 25 and sensed by the magnetic-based position sensor 29. The system 10 also optionally includes one or more patches 38 that are positioned for skin contact on the patient 23 to establish a positioning reference for the positioning pad 25. Details of magnetic-based position sensing techniques are described, for example, in U.S. Patents 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, and 6,892,091.

[0018] The recorder 11 records and displays the electrogram 21 captured using the body surface electrocardiogram (ECG) electrodes 18 and the intracardiac electrogram (IEGM) captured using the electrodes 26 of the catheter 14. The recorder 11 can include pacing capabilities for pacing the heart rhythm and / or can be electrically connected to an independent pacemaker.

[0019] In some embodiments, the system 10 can also be adapted to perform tissue ablation. In such embodiments, the system 10 can include an ablation energy generator 50 and a catheter (not specifically shown) dedicated to tissue ablation. To this end, the 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, the doctor 24 can similarly place the distal end of the ablation catheter in contact with the target site to ablate the tissue there. The ablation energy generator 50 is adapted to conduct ablation energy to one or more of the electrodes at the distal end of the ablation catheter. The energy generated by the ablation energy generator 50 can include, but is not limited to, radiofrequency (RF) energy or pulsed field ablation (PFA) energy (including unipolar or bipolar high voltage DC pulses that can be used to achieve irreversible electroporation (IRE)), or combinations thereof. In an embodiment, the catheter 14 can also be configured and operable for tissue ablation and can thus be adapted for IEGM sensing and ablation.

[0020] The Patient Interface Unit (PIU) 30 is an interface configured to establish electrical connectivity 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, electrophysiological devices such as one or more catheters, positioning pads 25, body surface ECG electrodes 18, electrode patches 38, ablation energy generators 50, and recorders 11. Optionally and preferably, the PIU 30 further includes processing capabilities for performing real-time calculations of the position of the catheter and for performing ECG / IEMG signal processing and / or calculations.

[0021] The workstation 55 includes one or more processors and user interface capabilities, the one or more processors having a memory and / or storage device in which appropriate operating software is stored. The workstation 55 may provide a plurality of functions, optionally including: (1) performing three-dimensional (3D) modeling of the endocardial anatomy and rendering a model or anatomical map 20 for display on a display device 27, (2) displaying on the display device 27 the (or other data) compiled from the recorded electrograms 21 in the form of representative visual markers or images superimposed on the rendered anatomical map, (3) displaying the real-time position and orientation of one or more catheters within the heart chambers, and (4) displaying on the display device 27 sites of interest such as where activation signals are measured / mapped or ablation energy has been applied. An article of commerce embodying the elements of the system 10 may be the CARTO TM 3 system, available from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA 92618.

[0022] Reference Figure 2 , schematically shows an example of a catheter 14 for IEGM sensing. In this example, the catheter 14 has a planar distal end 28 suitable 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 in this example the distal end assembly 28 of the catheter has a planar configuration and includes a plurality of electrodes 26 suitable for IEGM sensing. The plurality of electrodes 26 generally includes a first plurality of electrodes and a second plurality of electrodes disposed on opposite surfaces P1 and P2 of the planar configuration of the distal end assembly 28, respectively (only the electrodes 26 from one side of the planar distal end assembly 28 are shown in the figure).

[0023] Shaft 14H includes a reference electrode 22 disposed on shaft 14H near the distal end assembly 28. As described in more detail below, reference electrode 22 facilitates measuring the distance between measurement electrode 26 and the heart tissue, and thus enables evaluation of the far-field component of the IEGM signal sensed thereby in accordance with the techniques of the present invention as described in more detail below. As will be understood by those skilled in the art, in order to measure the cardiac tissue activation signal at the region of interest of the cardiac tissue, the far-field component of the IEGM signal should generally be measured (e.g., by an electrode that is far enough from the cardiac tissue but still within the cardiac blood pool). The far-field component should then be subtracted / suppressed from the IEGM signal measured by each electrode that contacts the cardiac tissue at the region of interest, thereby obtaining the near-field component of the IEGM signal at that region of interest, which over time indicates the cardiac tissue activation signal at the tissue region of interest. However, in some catheters, such as catheter 14 whose distal end assembly 28 is planar, there may not be a specific electrode dedicated to measuring the far-field component of the IEGM signal, and more specifically, there is no specific electrode that preferentially remains away from the cardiac tissue wall such that it can accurately measure the far-field component of the IEGM signal sensed by electrode 26. For example, during operation of the planar distal end assembly 28 of catheter 14, all or some of the electrodes located on one surface (e.g., P1) of the planar distal end assembly 28 may contact the tissue of the cardiac wall, while all or some 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 three-dimensional, such as in a basket or balloon catheter type), there is no specific location on the distal end assembly 28 where an electrode can be placed to verifiably not contact the cardiac tissue. Thus, in this type of catheter, where there is no specific electrode designated for sensing the far-field IEGM, it is necessary to dynamically identify and select, during operation, electrodes among the plurality of electrodes 26 that do not contact the cardiac tissue and are far enough from the cardiac tissue, and use the signals from those selected electrodes to determine the far-field EGM signal. To achieve this, reference electrode 22 is provided on catheter 14 and is adapted / dedicated to performing tissue proximity sensing / measurement based on the impedance between each of electrodes 26 and reference electrode 22, thereby evaluating the distance between one or more of electrodes 26 and the cardiac tissue.

[0024] In this non-limiting example, a reference electrode 22 is disposed on the shaft 14H of the catheter 14 and is adapted to facilitate tissue proximity measurements. Then, the IEGM signals acquired / measured by a subset of electrodes 26 identified as being far enough 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 measurements, in this example, the reference electrode 22 is disposed on the shaft 14H of the catheter in such a way that during intracardiac surgery within the heart with the catheter 14, it contacts body fluid (e.g., blood encountered when the catheter is inserted through the patient's vascular system), while generally remaining away from and not contacting tissue / heart tissue. This arrangement enables the use of the reference electrode 22 for impedance-based tissue proximity measurements, by which the impedance between the reference electrode and each respective electrode of the electrodes 26 can be used to evaluate the distance of the respective electrode from the heart tissue. Preferably, in some embodiments, the reference electrode 22 is configured to have an annular shape (e.g., surrounding the shaft 14H).

[0025] In fact, although the reference electrode 22 is located on the shaft 14H in this case and is arranged such that it generally does not contact the tissue, it may still not be suitable for providing an accurate measurement of the far-field IEGM component. One reason for this may be that the reference electrode is generally relatively large and can thus capture both near-field and far-field components when it is in proximity to the tissue wall. One reason may be that when the reference electrode 22 is placed on the shaft 14H (and is generally relatively large), it is often too close to the tissue (e.g., the tissue of the vascular system through which the catheter can be inserted), and thus may capture both the far-field component of the IEGM signal and its near-field component from the tissue region adjacent to it. Another reason is that in some cases, when the catheter 14 is delivered via a delivery sheath, the reference electrode 22 located on the shaft 14H can remain within the delivery sheath and is thus substantially shielded from sensing the far-field component of the IEGM signal.

[0026] Nevertheless, according to embodiments 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, and thereby facilitate the identification and dynamic selection of a subset of the electrodes 26 that are far enough from the tissue and through which far-field signals can be accurately measured. As 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 / metric) can be performed by measuring the impedance of the respective electrodes 26 whose tissue proximity is to be evaluated (e.g., the impedance between each respective electrode and the reference electrode 22), and determining the tissue proximity of one or more of the electrodes 26 based on their impedance. Examples of tissue proximity measurement / techniques that can be implemented according to the present invention to evaluate the tissue proximity of one or more of the electrodes 26 are disclosed, for example, in U.S. Patent Application Publication No. 2021 / 0177504, which is incorporated herein by reference.

[0027] Optionally, the shaft 14H further includes a position sensor 29, which is typically embedded at or near the distal end assembly 28 of the catheter to enable tracking of the position of the distal end assembly 28 (e.g., along with the electrodes 26 thereon) by the system 100, and thereby enable special mapping of the activation signals sensed by the electrodes 26 or some of them.

[0028] Generally, the catheter 14 is implemented as a disposable catheter. In some embodiments, the planar distal end assembly 28 of the catheter 14 is configured to have a flexible printed circuit board (PCB) and have a first plurality of electrodes and a second plurality of electrodes among the electrodes 26 disposed / manufactured on opposite sides / surfaces P1 and P2 of the flexible PCB. This particularly provides a cost-effective manufacture of the catheter 14, reducing its production cost and thus also reducing the cost of medical procedures (such as epicardial procedures in which the catheter can be utilized).

[0029] Returning to Figure 1 , as described above, electrophysiological devices such as the surface ECG device 38, which includes a plurality of ECG electrode patches externally attached to the patient's body / skin, and other electrophysiological devices such as additional catheters (not specifically shown) connected to the PIU 30, facilitate the electrical communication between these electrophysiological devices and the workstation 55. The PIU 30 can include, for example, a signal processor that is particularly adapted to apply analog-to-digital conversion (sampling) to the signals received from the electrophysiological devices connected thereto, and / or encapsulate these signals in data packets and transmit them to the workstation 55 and / or the recorder 11.

[0030] According to the present invention, system 10 includes an IEGM signal measurement system 100 (a subsystem of system 10) capable of determining at least a far-field component of an IEGM signal sensed by electrodes 26 of a catheter, such as catheter 14, which may not have specific electrodes designated for measuring far-field IEGM signal components. The IEGM signal measurement system 100 may also be adapted to determine a near-field component of an IEGM signal measured by one or more of the electrodes 26 of the catheter and, optionally, thereby determine an activation signal AS in a tissue region proximate the one or more electrodes 26. In various embodiments, the system 100 is implemented as a subsystem of system 10, and the components of the system 100 may be included in or implemented as any one or more of the following: workstation 55, PIU 30, and recorder 11 of system 10 or distributed therebetween (e.g., implemented by one or more processors and / or signal processors of those subsystems).

[0031] Now refer together to Figure 3 and Figure 4 , which illustrate techniques for measuring far-field IEGM components and, optionally, also near-field components and / or tissue activation signals in embodiments according to the present invention. Figure 3 is a flowchart of a method 200 for determining a far-field IEGM component and, optionally, also determining a near-field IEGM component and / or a cardiac tissue activation signal based on the far-field IEGM component. Figure 4 is a block diagram illustrating an embodiment of an IEGM signal measurement system 100 implementing the method 200.

[0032] In operation 210 of method 200, a catheter, such as catheter 14, is provided having a plurality of electrodes 26 disposed at its distal end assembly 28 in a manner adapted to sense IEGM signals from tissue regions in contact therewith, respectively. The electrodes 26 may be disposed, for example, at the outer surface of the distal end assembly 28 of catheter 14. Optionally, the catheter further includes a reference electrode 22 as described above. Alternatively, in some embodiments, the reference electrode 22 need not be located on the catheter 14 and may be arranged differently to contact body fluid while remaining remote from the body / heart tissue.

[0033] Perform operation 220 of method 200 to determine the far-field component FF of the IEGM signal E sensed by electrode 26 of catheter 14. To achieve this, in operation 220a, tissue proximity measurements are applied to each respective one of the plurality of electrodes 26 to evaluate the respective distance D 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 more of the plurality of electrodes 26 at the distal end assembly 28 of catheter 14, and typically more than one electrode is preferred. In some embodiments, tissue proximity measurements are implemented, for example, by techniques similar to those disclosed in U.S. Patent Application Publication No. 2021 / 0177504.

[0034] For example, the tissue proximity measurements may be implemented by tissue proximity processor / processing unit 110 of system 100. For example, tissue proximity processing unit 110 may be performed by a signal processor associated with the system and connected to the plurality of electrodes 26 and reference electrode 22. The signal processor implementing tissue proximity processing unit 110 may deliver a current including one or more frequency components between each respective one of the plurality of electrodes 26 and reference electrode 22, and measure the respective impedance therebetween (e.g., optionally the measured impedance for each frequency component of the delivered current). Since tissue typically has a significantly different impedance from body fluid / blood, the respective impedance measured in this way between each respective electrode and reference electrode 22 provides an indication of the distance D between the respective electrode and the tissue.

[0035] More specifically, since impedance readings are typically very sensitive to tissue proximity and may vary from patient to patient, in some embodiments, the relationship between the impedance of the electrodes and the respective distance D may be inferred dynamically during the medical procedure. In such embodiments, optionally in operation 220a (e.g., in at least one iteration of the operation), the impedance values from each electrode whose impedance is being measured may be stored by system 100. Then, based on the distribution characteristics of the measured impedance values (e.g., based on the measured maximum impedance and minimum impedance), 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 may be determined in real time during the medical procedure. Thus, based on this relationship or impedance threshold, the distance D of the respective electrodes may be evaluated in 220a based on their measured impedance.

[0036] Thus, as Figure 4 shown by way of non-limiting example, data / signals indicative of the respective distance D of the plurality of electrodes 26 are determined and provided by tissue proximity processing unit 110 in this way.

[0037] However, at the same time, and not necessarily simultaneously with the tissue proximity measurement operation 220a but typically after it, IEGM signal measurement results are obtained from one or more of the plurality of electrodes 26, respectively, in Figure 4 which is labeled as E. The IEGM signal measurement result E can be implemented, for example, by the IEGM signal measurement processor / processing unit 120 of the system 100 as shown in Figure 4 . The IEGM signal E is typically measured for at least some of the electrodes 26, at least some of which may include electrodes 26 whose respective tissue distances D are evaluated to be above a specific distance threshold D TH in operation 220a, and optionally for one or more of the electrodes 26, the near-field IEGM signal components of which will be inferred in the optional operation 240 described below. Alternatively, in some embodiments, the IEGM signal E can be measured for all or a predetermined set of the electrodes 26. The IEGM signal E can be measured for the electrodes according to any suitable technique understood by those skilled in the art. For example, in some specific implementations, the IEGM signal E of the corresponding electrode in the electrodes 26 can be measured by performing monopolar IEGM signal measurement known in the art to monitor / measure the voltage between the corresponding electrode and another electrode (e.g., during a time frame), and the other electrode can be, for example, one or more of the body surface ECG electrodes 18 of the system 10 and / or one or more of the electrode patches 38 described above.

[0038] In some non-limiting embodiments, the tissue proximity processing unit 110 and the IEGM signal measurement processing unit 120 can be implemented by a signal processor, which can be part of the PIU 30 of the system 10 described above. The signal processor, such as the PIU 30, can communicate signals, for example, with the electrodes 26, and optionally with the reference electrode 22 (for tissue proximity processing), and optionally also with another electrode, such as 18, which can be used for monopolar IEGM signal measurement. The signal processor can implement various signal processing capabilities, such as impedance and / or voltage measurement between the electrodes coupled thereto, signal / noise filtering, analog-to-digital conversion, and / or other signal processing understood by those skilled in the art. As will be described in more detail below, the tissue proximity processing unit 110 and the IEGM signal measurement processing unit 120 can be repeatedly executed during successive time frames (e.g., each on the order of 50 milliseconds (ms)) in order to evaluate the tissue proximity D of the plurality of electrodes 26 and the IEGM signal measurement results E of some or all of them as described above for each successive time frame. In the case of implementing analog-to-digital conversion, each such time frame can include, for example, 50 samples, assuming a sampling rate on the order of 1 kHz, for example.

[0039] To determine / evaluate the far-field IEGM component FF sensed (e.g., co-sensed) by electrode 26, operation 220 of method 200 also includes sub-operations 220b and 220c. In operation 220b, a subset of electrodes 26 whose respective tissue distance / proximity D was evaluated as being above a specific distance threshold D in operation 220a is selected (e.g., dynamically selected per time frame) for further processing of their IEGM signals E, and based thereon, the (common) far-field IEGM component FF in the IEGM signal is determined. The minimum distance threshold D for the electrodes above which they are selected TH generally results in the IEGM signals sensed thereby being expected to consist mostly of the far-field component FF and to a lesser extent of the near-field IEGM component NF. For example, the distance threshold D TH can be selected to be at least D TH > 5 mm. TH > 5 millimeters.

[0040] In operation 220c, the far-field component FF of the IEGM signal (e.g., for the respective time frame) is determined by averaging the IEGM signal measurements E from the respective electrodes 26 of the subset selected in 220b (or otherwise aggregating via a different aggregation scheme), the electrodes of this subset having a respective distance D from the tissue surface that is above the minimum distance threshold D TH . The aggregation / averaging of the signals from multiple electrodes provides for suppressing / averaging out noise components (e.g., near-field signal remnants that, although having a relative distance from the tissue, can still be weakly sensed by the electrodes of the subset), thereby reliably obtaining a substantially "noise-free" far-field component FF.

[0041] For some time frames, operation 220b may not result in any selected electrodes. For example, in the case where reference electrode 22 happens to contact the tissue in its vicinity during a time frame, the distance measurements D obtained for all / any of the electrodes 26 in operation 220a can provide values below the threshold D for all electrodes 26 TH . Thus, in operation 220c, in the case where the number of electrodes identified as having a sufficient distance from the tissue is below a specific predetermined minimum number of electrodes (e.g., the minimum number is at least one and typically more than one), the previous value of the far-field IEGM signal FF measured for the previous time frame can be used in consecutive 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 reference electrode 22 and also because the duration of the time frame is typically less than the characteristic time interval for the variation of the far-field component FF of the IEGM signal.

[0042] For example, in operation 220a, the impedance of all or multiple electrodes 26 on both sides of the planar distal end assembly 28 can be measured with reference to electrode 22. If all the impedances measured in 220a indicate that the corresponding electrodes are in contact with the tissue wall (e.g., relatively high impedance), then in this case, in operation 220b, the system 100 can conclude that the reason for the high impedance is that the reference electrode 22 is in contact with the cavity / tissue wall (since it is generally impossible for multiple electrodes on both sides of the planar distal end assembly 28 to be in contact with the tissue wall simultaneously), and no electrode will be dynamically selected to be away from the tissue. Therefore, in this case, in operation 220c, the previous value of the far-field IEGM signal FF will be provided as the representative of the far-field IEGM signal FF for the current time frame as well.

[0043] Referring to Figure 4 the system 100 shown in, the dynamic selection 220b of a subset of electrodes that are at a sufficient distance D from the tissue (e.g., above a threshold D TH ) can be performed by the signal selector tool 130 of the system 100. The aggregation / averaging 220c of the signals from the subset selected by the signal selector tool 130 can be performed by the signal aggregator tool 140 of the system 100. As will be understood by those skilled in the art, the signal selector tool 130 and / or the signal aggregator tool 140 can be implemented by a signal processing unit (e.g., as part of the PIU 30 of the system 10) and / or by a computerized system / processor (such as Figure 1 the workstation 55 or the recorder 11 shown in). The signal selector tool 130 can include a selector S (e.g., implemented as a signal switch, and / or implemented through a digital / computerized selection process or by other means understood by those skilled in the art). Therefore, the signal aggregator tool 140 can also be implemented through analog, digital, or computerized summing / averaging or other forms of aggregation.

[0044] According to the above, in operation 220, the far-field FF component of the IEGM signal can be determined based on the IEGM signal E measured by the electrodes 26, while generally eliminating the need for dedicated electrodes arranged in the catheter 14 for sensing the intracardiac far-field IEGM component FF.

[0045] As indicated above, operation 220 may be performed to evaluate the far-field FF component of the IEGM signal for each respective time frame (successive / consecutive time frames) at which the IEGM signal E is measured by electrode 26. Thus, as shown in optional operation 230 of method 200, operation 220 may be repeated for a plurality of successive or consecutive time frames in order to update the value of the far-field IEGM component FF for a plurality of time frames during the desired duration of the medical procedure for which the IEGM signal is to be monitored. As described above, for time frames in which the field IEGM component FF cannot be evaluated (e.g., in the case where the reference electrode 22 contacts tissue), (e.g., typically rare time frames), the far-field IEGM component FF evaluated for the corresponding previous time frame may be used. To this end, system 100 may include a buffer (data or signal buffer not specifically shown) that stores the value of the last updated field IEGM component FF in the previous time frame so that this value can be used in such cases).

[0046] Optionally, method 200 further includes operation 240 for evaluating the near-field component NF of the IEGM signal sensed by one or more specific electrodes of interest SE (typically certain electrodes 26 in contact with cardiac tissue) among electrodes 26. The set of specific electrodes for which the near-field component NF is to be determined may be automatically selected by system 10 in various specific implementations (e.g., based on the cardiac electrical activity mapped or measured thereby, possibly based on the region of tissue of interest to be mapped / measured and the position of catheter 14 as determined by position sensor 29), and / or may be selected by doctor 24 operating system 10 in some specific implementations.

[0047] Operation 240 optionally includes sub-operation 240a in which the IEGM signal E measured by one or more specific electrodes of interest SE is obtained (at Figure 3 and Figure 4In a non-limiting example of (showing at least one electrode). In sub-operation 240b, the far-field component FF as determined by operation 220 above is also obtained. The far-field component FF is used to process the IEGM signal E of each of one or more electrodes of interest SE, for determining / evaluating the corresponding near-field component NF of the IEGM signal E sensed thereby, respectively. Generally speaking, the near-field NF component of each electrode of interest SE is determined by suppressing the far-field component FF obtained by operation 220 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 electrode of interest SE consists of both the near-field NF component and the far-field component FF, the near-field NF component is sensed by the electrode from the tissue in its vicinity, while the far-field component FF is generally sensed jointly by the electrodes 26. In this regard, as those skilled in the art of signal operation / processing will understand, the subtraction / suppression can be performed with appropriate weighting of the FF signal according to the amplitude, where the FF signal can be included in the IEGM signal of the corresponding electrode of interest SE (for example, the appropriate weighting can be determined, for example, based on the correlation between the FF component and the corresponding IEGM signal).

[0048] To implement the optional operation 240, as Figure 4 shown, the system 100 may include, for example, an optional electrode selector 150 (which may be adapted to provide the IEGM signal measured by one or more specific electrodes of interest SE) and a signal suppression tool / filter 160 (which may be adapted to receive the far-field IEGM component FF and the IEGM signal measured by each corresponding electrode of interest SE, and is adapted to suppress the former / subtract the former from the latter, so as to generate the near-field component NF of the IEGM signal component of the corresponding electrode of interest SE). As those skilled in the art will understand, the electrode selector 150 and / or the signal suppression tool / filter 160 can be implemented, for example, by analog or digital means (such as as part of a signal processor (such as through the PIU 30)) or by a computerized system as Figure 1 shown (such as through the workstation 55).

[0049] Generally speaking, operation 240 can be performed in each corresponding time frame of interest, at which the near-field component NF of a specific electrode of interest SE will be evaluated. For this purpose, as will be understood from the above description, operation 240 can be performed synchronously with operation 220, such that the far-field component FF obtained for the corresponding time frame is suppressed from the IEGM signal E obtained from each electrode of interest SE for the corresponding / same time frame, thereby generating the near-field signal NF sensed by the electrode SE during that time frame.

[0050] Optionally, method 200 may further include operation 250, by which operation 240 is repeated for a plurality of time frames to determine / record the tissue activation signal AS sensed by each of the electrodes of interest SE from the tissue in its vicinity. The tissue activation signal AS is used herein to specify the aggregation / cumulation of the near-field signal NF components measured by each respective measured electrode of interest SE in each of a plurality of time frames during the duration of one of the plurality of time frames. Operation 250 may be performed, for example, by Figure 4 the recorder 170 of the system 100 shown in, which may be, for example, part of the recorder 11 of the system 10 that records the tissue activation signal of the electrode of interest SE.

[0051] To this end, the above-described system 100 and method 200 illustrate specific implementations of the technology of the present invention to evaluate 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 suitable electrodes dedicated to sensing the intracardiac far-field IEGM signal FF. For clarity, the system 100 is shown in Figure 4 with separate designations for a plurality of components that perform different functions / operations of method 100. However, as will be understood by those skilled in the art, the system 100 may generally be implemented with different sets of components and may be implemented, for example, by a general-purpose signal processor and / or a general-purpose computerized system having software and / or hardware suitable for performing the operations of the above-described method 200. Additionally, as described above, the systems and methods implementing the present invention may be 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 frames, and further thereby optionally determine the tissue activation signal based on the near-field components evaluated for a plurality of time frames.

[0052] Embodiment

[0053] Example 1. A method 220 for determining a cardiac tissue activation signal, the method comprising:

[0054] I. Providing a catheter 14, the catheter including a plurality of electrodes 26 disposed at its distal end assembly 28;

[0055] II. Determining 220 the far-field component FF of the intracardiac electrogram (IEGM) signal E sensed by at least one of the plurality of electrodes 26 by performing the following steps:

[0056] (a) Applying a tissue proximity measurement 220a to each respective one of the plurality of electrodes 26 to evaluate the respective distance D of the plurality of electrodes from the tissue surface;

[0057] (b) Dynamically select a subset of one or more of the plurality of electrodes 26 at 220b based on the respective distance D, the subset of one or more electrodes having a respective distance from the tissue surface that is above a specific threshold; and

[0058] (c) Determine the far - field component FF by averaging the IEGM signal measurement results E from the respective electrodes of the subset, the respective electrodes of the subset having a respective distance D from the tissue surface that is above the specific threshold.

[0059] Example 2. The method 200 according to Example 1 further includes:

[0060] III. Evaluate 240 the near - field component NF of the IEGM signal sensed by the at least one electrode by subtracting the far - field component from the IEGM signal measurement results obtained from the at least one electrode.

[0061] Example 3. The method 200 according to Example 2 further includes repeating operations II and III (230, 250) to determine the development of the near - field component NF of the EGM signal E over time, and thereby obtain the cardiac tissue activation signal of the tissue near the at least one electrode.

[0062] Example 4. In the method 200 according to Example 1, applying the tissue proximity measurement (220a) to the respective electrode includes applying an excitation current through the respective electrode and measuring the impedance of the electrode, and thereby evaluating the tissue proximity D based on the impedance.

[0063] Example 5. In the method 200 according to Example 4, the impedance is measured between the respective electrode and a reference electrode 22, the reference electrode being arranged near the end of the shaft 14H of the catheter 14 that is proximal to the distal end assembly 28 such that it generally remains spaced from the tissue during the operation of the catheter 14.

[0064] Example 6. In the method 200 according to Example 1, the far - field component FF of the IEGM signal E is repeatedly updated (230) by repeating operation II (220).

[0065] Example 7. In the method 200 according to Example 6, 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 having a respective distance D from the tissue surface that is identified by the dynamic selection (220b) as being above a specific threshold D TH is below a specific predetermined minimum number of electrodes. For example, the predetermined minimum number of electrodes having a distance D above the specific threshold D TH is such that below this number, the far - field component FF is not updated and its previous value remains for the one or more electrodes.

[0066] Example 8. Method 200 according to Example 7, wherein applying the tissue proximity measurement to the respective electrode (220a) includes measuring the impedance between the respective electrode and a reference electrode 22 disposed on the catheter 14 such that it generally remains spaced apart from the tissue; and wherein in repetitions (230) where the number of electrodes is below a specific predetermined minimum number, the reference electrode 22 is considered to be in contact with the tissue, and thus the update of the far-field component of the EGM signal in those repetitions is skipped.

[0067] Example 9. Method 200 according to 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 plurality of EGM electrodes and a second plurality of EGM electrodes disposed on opposite surfaces P1 and P2 of the distal end assembly 28, respectively.

[0068] Example 10. Method 200 according to Example 1, which is adapted to enable the evaluation of the far-field component FF of the EGM signal E while the catheter 14 does not have dedicated electrodes for sensing the far-field component FF disposed in its distal end assembly 28.

[0069] Example 11. Method 200 according to Example 9, wherein the distal end assembly of the catheter 14 includes a flexible printed circuit board (PCB), and the first plurality of electrodes and the second plurality of electrodes are located on opposite sides of the PCB.

[0070] Example 12. A system 100 for determining cardiac tissue activation signals, the system 100 being connectable to a catheter 14 having a plurality of electrodes 26 disposed at its distal end assembly 28;

[0071] wherein the system 100 includes one or more processors connectable for signal communication with the plurality of electrodes 26; and

[0072] wherein the one or more processors are adapted to determine (220) the far

[0073] field component FF of the intracardiac electrogram (IEGM) signal E sensed by at least one of the plurality of electrodes 26 by performing the following steps:

[0074] (a) Applying (220a) a tissue proximity measurement to each respective electrode of the plurality of electrodes 26 to evaluate the respective distance D of the plurality of electrodes from the tissue surface;

[0075] (b) Dynamically selecting (220b) a subset of one or more of the plurality of electrodes, the subset of one or more electrodes having a respective distance D from the tissue surface higher than a specific threshold D TH ; and

[0076] (c) Obtain IEGM signal measurements E from the respective electrodes of the subset, where the respective distance D of the respective electrodes of the subset from the tissue surface is higher than a specific threshold D TH ; and

[0077] (d) Determine (220c) the far - field component FF as the average of the IEGM signal measurements E obtained from the respective electrodes of the subset, where the respective distance D of the respective electrodes of the subset from the tissue surface is higher than the specific threshold D TH .

[0078] 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 IEGM signal measurements obtained from at least one electrode

[0079] Example 14. The system 100 according to Example 13, wherein one or more processors are adapted to determine the cardiac tissue activation signal AS in the tissue near the at least one electrode by repeatedly (230, 250) determining (230, 250) the far - field component FF and the near - field component NF and thereby determining the development of the near - field component NF of the IEGM signal over time, where this development indicates the cardiac tissue activation signal AS

[0080] Example 15. The system 100 according to Example 12, wherein one or more processors are adapted to apply the tissue proximity measurement (220a) to the respective electrodes by: delivering an excitation current through the respective electrode and measuring the impedance of the electrode to thereby evaluate tissue proximity based on the impedance

[0081] Example 16. The system 100 according to Example 15, wherein the delivery of the excitation current is carried out between the respective electrode and a reference electrode 22, the reference electrode being arranged near the end of the shaft 14H proximal to the distal end assembly 28 of the catheter 14 such that it generally remains spaced apart from the tissue

[0082] Example 17. The system 100 according to Example 12, wherein the one or more processors are adapted to repeatedly update (230) the far - field component of the IEGM signal by repeating the method operations 220a to 220c; and wherein the update of the far - field component of the IEGM signal is skipped during the repetitions of the following: where the number of electrodes having a respective distance D from the tissue surface higher than a specific threshold D TH identified by the dynamic selection operation 220b is lower than a specific predetermined minimum number of electrodes (the minimum number can be one or in some cases more than one to facilitate an improved measurement / evaluation of the far - field component by averaging the signals of several electrodes).

[0083] Example 18. A 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; wherein the distal end assembly 28 has a planar configuration and includes a plurality of electrodes 26 and a reference electrode 22, the plurality of electrodes including a first plurality of electrodes and a second plurality of electrodes disposed on opposite surfaces P1 and P2 of the planar configuration of the distal end assembly 28, respectively, and the reference electrode is disposed on the shaft 14H near the distal end assembly 28 so that corresponding tissue proximity measurements can be made for one or more corresponding electrodes of the plurality of electrodes by measuring the impedance between the reference electrode 22 and the corresponding electrode 26.

[0084] Example 19. The catheter 14 according to Example 18, wherein at least one of the following cases exists:

[0085] - The distal end assembly 28 includes a flexible printed circuit board (PCB), wherein the first plurality of electrodes and the second plurality of electrodes are located on opposite sides of the PCB;

[0086] - The reference electrode 22 is positioned on the shaft such that during intracardiac surgery with the catheter within the heart, the reference electrode 28 is generally away from the tissue of the heart while being in contact with blood, thereby facilitating tissue proximity measurements based on the impedance; and

[0087] - The reference electrode has an annular shape.

[0088] Example 20. The catheter 14 according to Example 18, which is configured as a disposable catheter.

Claims

1. A method for determining a cardiac tissue activation signal, the method comprising: I. Providing a catheter comprising a plurality of electrodes disposed at a distal end assembly thereof; II. determining a far-field component of an intracardiac electrogram (IEGM) signal sensed by at least one electrode of said plurality of said electrodes by performing the following steps: (a) applying a tissue proximity measurement to each respective electrode of a plurality of said electrodes to assess a respective distance of said plurality of electrodes from a tissue surface; (b) dynamically selecting, based on the corresponding distances, a subset of one or more electrodes of the plurality of electrodes whose corresponding distances from the tissue surface are above a certain threshold; and (c) determining said far-field component by averaging IEGM signal measurements from said respective electrodes of said subset whose respective distances from said tissue surface are above said certain threshold.

2. The method according to claim 1, further comprising: I. Estimating a near-field component of the IEGM signal sensed by the at least one electrode by subtracting the far-field component from a (concurrent) IEGM signal measurement obtained from the at least one electrode.

3. The method according to claim 2 includes repeating operations II and III to determine the development of the near-field component of the EGM signal over time, and thereby obtaining a cardiac tissue activation signal of the tissue near the at least one electrode.

4. The method of claim 1 , wherein applying the tissue proximity measurement to the respective electrodes in (a) comprises applying an excitation current through the respective electrodes and measuring impedance of the electrodes, and thereby assessing the tissue proximity based on the impedance.

5. A method according to claim 4, wherein the impedance is measured between the corresponding electrode and a reference electrode, and the reference electrode is arranged near the end of the shaft of the catheter near the distal end assembly so that it is generally maintained spaced apart from the tissue during operation of the catheter.

6. The method of claim 1, wherein the far-field component of the IEGM signal is repeatedly updated by repeating operation II.

7. A method according to claim 6, wherein the updating of the far-field component of the IEGM signal is skipped in the repetition of operation II, wherein the number of electrodes identified by the dynamic selection (b) as having the corresponding distance from the tissue surface above the certain threshold is lower than a certain predetermined minimum number of electrodes.

8. A method according to claim 7, wherein in (a) applying the tissue proximity measurement to the corresponding electrode includes measuring the impedance between the corresponding electrode and a reference electrode, the reference electrode being arranged to generally remain spaced apart from the tissue; and wherein in repetitions in which the number of said electrodes is less than a certain predetermined minimum number, the reference electrode is assessed to be in contact with the tissue, thereby skipping the update of the far-field component of the EGM signal in those repetitions.

9. The method according to claim 1, wherein the distal end assembly of the catheter has a planar structure, and the plurality of EGM electrodes include a first plurality of the EGM electrodes and a second plurality of the EGM electrodes respectively arranged on opposite surfaces at the distal end assembly of the catheter.

10. The method of claim 1, adapted to enable said evaluation of said far-field component of said EGM signal while said catheter does not have dedicated electrodes disposed in its distal tip assembly for sensing said far-field component.

11. The method of claim 9, wherein the distal tip assembly of the catheter comprises a flexible printed circuit board (PCB), wherein the first and second pluralities of electrodes are at opposite sides of the PCB.

12. A system for determining activation signals of cardiac tissue, The system is connectable to a catheter having a plurality of electrodes disposed at a distal end assembly thereof; wherein the system comprises one or more processors connectable for signal communication with the plurality of electrodes; and wherein the one or more processors are adapted to determine a far-field component of an intracardiac electrogram (IEGM) signal sensed by at least one electrode of the plurality of said electrodes by performing the following steps: (a) applying a tissue proximity measurement to each respective electrode of a plurality of said electrodes to assess a respective distance of said plurality of electrodes from a tissue surface; (b) dynamically selecting, based on the corresponding distances, a subset of one or more electrodes of the plurality of electrodes whose corresponding distances from the tissue surface are above a certain threshold; and (c) obtaining IEGM signal measurements from the respective electrodes of the subset whose respective distances from the tissue surface are above 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 distances from the tissue surface are above the certain threshold.

13. The system of claim 12, wherein the one or more processors are adapted to further evaluate a near-field component of the IEGM signal sensed by at least one of the electrodes by subtracting the far-field component from an IEGM signal measurement obtained from the at least one electrode.

14. A system according to claim 13, wherein the one or more processors are suitable for determining a cardiac tissue activation signal in tissue near the at least one electrode 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 over time, whereby the development indicates the cardiac tissue activation signal.

15. A system according to claim 12, wherein the one or more processors are suitable for applying the tissue proximity measurement to the corresponding electrode in (a) by the following steps: delivering an excitation current through the corresponding electrode and measuring the impedance of the electrode to thereby assess the tissue proximity based on the impedance.

16. A system according to claim 15, wherein the delivery of the excitation current impedance is performed between the corresponding electrode and a reference electrode, and the reference electrode is arranged near the end of the shaft of the distal tip assembly of the catheter so that it is generally maintained spaced apart from the tissue.

17. A system according to claim 12, wherein the one or more processors are suitable for repeatedly updating the far-field component of the IEGM signal by repeating operations (a) to (d); and wherein the update of the far-field component of the IEGM signal is skipped in the repetition of operations (a) to (d), wherein the number of the electrodes identified by the dynamic selection (b) as having the corresponding distance from the tissue surface above the certain threshold is lower than a predetermined minimum number of electrodes.

18. A catheter for intracardiac electrogram (IEGM) mapping, the catheter comprising an axis and a distal end assembly connected to one end of the axis, wherein the distal end assembly of the catheter has a planar structure and comprises a plurality of electrodes and a reference electrode, the plurality of electrodes comprising a first plurality of electrodes and a second plurality of electrodes respectively arranged on opposite surfaces of the planar structure of the distal end assembly, the reference electrode being arranged on the axis near the distal end assembly so as to enable corresponding tissue proximity measurements to be performed for one or more corresponding electrodes among the plurality of electrodes by measuring the impedance between the reference electrode and the corresponding electrode.

19. The catheter of claim 18, wherein there is at least one of the following: The distal tip assembly includes a flexible printed circuit board (PCB), wherein the first plurality of electrodes and the second plurality of electrodes are at opposite sides of the PCB; The reference electrode is positioned on the shaft such that during intracardiac procedures with the catheter in the heart, the reference electrode is generally away from tissue of the heart while in contact with blood to facilitate the impedance-based measurement of the tissue proximity; and The reference electrode has a ring shape.

20. The catheter of claim 18, configured as a disposable catheter.

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