Search

EP-4740883-A1 - TISSUE PROXIMITY INDICATOR THRESHOLD FOR CARDIAC ABLATION

EP4740883A1EP 4740883 A1EP4740883 A1EP 4740883A1EP-4740883-A1

Abstract

In one exemplary mode, an apparatus includes a catheter including an electrode to provide an intracardiac electrogram (IEGM) signal and a signal used to sense impedance, an ablation energy generator configured to conduct ablative energy to the electrode of the catheter based on user input, a controller configured to sample the IEGM signal from the electrode before and after a given ablation, and sense impedance between the electrode and tissue, and a processor configured to compare the sensed impedance with a TPI threshold to determine a contact status of the electrode with respect to the tissue, render to a display an indication of the determined contact status, compute a change in the IEGM signal due to the given ablation, and adjust the TPI threshold for subsequent ablations based on the computed change in the IEGM signal due to the given ablation of the tissue with the electrode.

Inventors

  • Gliner, Vadim
  • GOVARI, ASSAF

Assignees

  • Biosense Webster (Israel) Ltd.

Dates

Publication Date
20260513
Application Date
20251110

Claims (10)

  1. An apparatus, comprising: a catheter (14) including an electrode (26) to provide an intracardiac electrogram (IEGM) signal and a signal used to sense impedance; an ablation energy generator (50) configured to conduct ablative energy to the electrode (26) of the catheter (14) based on user input; a controller (30) configured to: sample the IEGM signal from the electrode (26) before and after a given ablation; and sense impedance between the electrode (26) and tissue (80); and a processor (56) configured to: compare the sensed impedance with a tissue proximity indicator (TPI) threshold to determine a contact status of the electrode (26) with respect to the tissue (80); render to a display (27) an indication of the determined contact status; compute a change in the IEGM signal due to the given ablation; and adjust the TPI threshold for subsequent ablations based on the computed change in the IEGM signal due to the given ablation of the tissue (80) with the electrode (26).
  2. The apparatus according to claim 1, wherein the processor (56) is configured to iteratively adjust TPI thresholds based on respective previous TPI thresholds and respective reductions in voltage of the IEGM signal due to ablation at respective ablation sites.
  3. The apparatus according to claim 1 or 2, wherein the processor (56) is configured to: check a stability of movement of the electrode (26) during ablation; and adjust the TPI threshold based on the stability of movement of the electrode (26) being within a given limit.
  4. The apparatus according to any one of claims 1 to 3, wherein the processor (56) is configured to decrease the TPI threshold based on observing at least a given reduction in the IEGM signal due to ablation of the tissue (80) with the electrode (26).
  5. The apparatus according to any one of claims 1 to 4, wherein the processor (56) is configured to increase the TPI threshold based on observing less than a given reduction in the IEGM signal due to ablation of the tissue (80) with the electrode (26).
  6. The apparatus according to any one of claims 1 to 5, wherein the processor (56) is configured to receive user input to determine threshold adjustment factors.
  7. The apparatus according to any one of claims 1 to 6, wherein the processor (56) is configured to: identify minimum and maximum impedances and corresponding minimum and maximum TPI limits; and define an estimated TPI threshold to be between the minimum and maximum TPI limits and based on a function of the minimum and maximum TPI limits.
  8. The apparatus according to any one of claims 1 to 7, wherein the processor (56) is configured to adjust the TPI threshold per electrode (26) of the catheter (14).
  9. The apparatus according to any one of claims 1 to 7, wherein the processor (56) is configured to adjust the TPI threshold such that a same TPI threshold is maintained for multiple electrodes (26) of the catheter (14).
  10. The apparatus according to any one of claims 1 to 9, wherein the processor (56) is configured to compute a new TPI threshold based on a previous TPI threshold less a first factor multiplied by: a reduction in a voltage of the IEGM signal less a second factor.

Description

FIELD OF THE DISCLOSURE The present disclosure relates to relates to ablation with therapeutic intracardiac catheters, and in particular, but not exclusively to, tissue proximity indication during cardiac ablation. BACKGROUND A wide range of medical procedures involve placing probes, such as catheters, within a patient's body. One medical procedure in which these types of probes or catheters have proved extremely useful is in the treatment of cardiac arrhythmias. Cardiac arrhythmias and atrial fibrillation in particular, persist as common and dangerous medical ailments, especially in the aging population. Diagnosis and treatment of cardiac arrhythmias include mapping the electrical properties of heart tissue, especially the endocardium and the heart volume, and selectively ablating cardiac tissue by application of energy. Catheters are inserted into the heart chamber and optionally around the heart chamber during such procedures. In most procedures, multiple catheters are inserted into the patient. Catheters may include mapping, ablation, temperature sensing and image sensing catheters. Some catheters are dedicated for placement in specific parts of the anatomy, e.g., coronary sinus, esophagus, atrium, ventricle. The catheters have multiple electrical channels, some more than others depending on the number of sensors and electrodes included in each catheter. The number and type of catheters depends on the procedure and on the physician preferred workflow. A typical ablation procedure involves the insertion of a catheter having a one or more electrodes at its distal end into a heart chamber. RF (radio frequency) current (or pulsed-field ablation (PFA) energy) is applied through the tip electrode(s) of the ablating catheter, and current flows through the media that surrounds it, i.e., blood and tissue, between the tip electrode(s) and an indifferent electrode. The distribution of current depends on the amount of electrode surface in contact with the tissue as compared to blood, which has a higher conductivity than the tissue. Heating of the tissue occurs due to its electrical resistance. The tissue is heated sufficiently to cause cellular destruction in the cardiac tissue resulting in formation of a lesion within the cardiac tissue which is electrically non-conductive. Therefore, when placing an ablation or other catheter within the body, particularly near the endocardial tissue, it is desirable to have the ablation electrode(s) of the catheter be in direct contact with the tissue. Electrode-tissue contact may be measured based on the impedance between an electrode on a distal end of the catheter and a return electrode. BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure will be understood from the following detailed description, taken in conjunction with the drawings in which: Fig. 1 is a simplified illustration of a catheter-based electrophysiology mapping and ablation system constructed and operative in accordance with an example of the present disclosure;Fig. 2 is a more detailed isometric view of an expandable distal end assembly of a catheter for use with the system of Fig. 1;Fig. 3 is a simplified qualitative illustration showing impedance measured by an electrode in a body cavity as a function of proximity of the electrode from the cavity wall tissue for use in the system of Fig. 1; andFigs. 4A and 4B is a flowchart including steps in a method to adjust a tissue proximity indicator threshold for use in the system of Fig. 1. DESCRIPTION OF EXAMPLES OVERVIEW As previously mentioned, contact between an electrode and tissue may be measured based on impedance between the electrode and the tissue. The quality of contact between the electrode and the tissue may be expressed as a tissue proximity indicator (TPI). The TPI threshold for a particular patient may be used to determine whether the electrode is in sufficient contact with tissue in order to provide a successful ablation, for example. What is generally important from the physician standpoint to consider an electrode being in sufficient contact with tissue, is if the cardiac signal at the ablation site is sufficiently attenuated by the ablation. If the cardiac signal at the tissue is sufficiently attenuated by the ablation, after the fact, the electrode was in sufficient contact with the tissue during the ablation. A TPI threshold may be selected and defines whether a given impedance value indicates sufficient contact for sufficiently attenuating the cardiac signal. For example, if a sensed impedance is greater than the threshold TPI, then the sensed impedance indicates that the electrode is in sufficient contact with the tissue to successfully ablate the tissue, whereas if the sensed impedance is not greater than the TPI threshold, then the sensed impedance indicates that the electrode is not in sufficient contact with the tissue. Therefore, it is important that the TPI threshold is selected carefully so that it indicates the quality of contact n