High-resolution, high-dynamic-range PFA map

Abstract

This invention provides a system and method for planning and monitoring cardiac ablation using anatomical maps. [Solution] The method involves dividing a three-dimensional (3D) rendering of at least a portion of the heart into voxels having coordinates in the coordinate system of a position mapping system 10. Using the position tracking system, the positions of one or more electrodes of a catheter 14 are measured within the heart 12 during an ablation session that includes multiple ablation instances. Each measurement position is assigned a predetermined number of voxels closest to that position. An ablation score is calculated for each voxel, and the ablation score represents at least the number of ablation instances affecting the voxel.

Description

Technical Field

[0001] The present disclosure generally relates to cardiac ablation, and more specifically to systems and methods for planning and monitoring cardiac ablation using anatomical maps.

Background Art

[0002] Providing an indication of ablation sites on an anatomical map of the inner wall of the ventricle has been previously proposed in the patent literature. For example, U.S. Patent No. 9,757,182 describes a method that includes receiving the positions of a plurality of ablation sites formed on the surface of the heart. Distances are measured between at least some of the ablation sites based on the positions. One or more gaps between ablation sites that meet alarm criteria are identified. The identified gaps are shown to the operator.

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

Brief Description of the Drawings

[0004] [Figure 1] Schematic illustration of a catheter-based electroanatomical (EA) mapping and ablation system according to an example of the present disclosure. [Figure 2] High-resolution, high-dynamic range ablation map of cardiac wall tissue according to an example of the present disclosure. [Figure 3] Schematic diagram of a graphical user interface (GUI) used to filter instances of inappropriate ablation so as not to affect the map of FIG. 2 according to an example of the present disclosure. [Figure 4] Flowchart schematically showing a method for generating a high-resolution, high-dynamic range ablation map according to an example of the present disclosure.

Mode for Carrying Out the Invention

[0005] overview In some cardiac catheter ablation procedures, physicians ablate tissue in specific anatomical areas of the heart, such as the ventricles, to treat arrhythmias. For example, a physician may ablate the entire circumference of the opening of the pulmonary veins (PV) in the left atrium to treat atrial fibrillation (AFib).

[0006] Catheter ablation using pulsed-field ablation (PFA) techniques may require multiple iterations to isolate the entire circumference of the mouth. In each iteration, the ablation catheter must be moved to areas that are still insufficiently ablated or have not been ablated at all.

[0007] To successfully complete the ablation, the physician may be assisted by ablation tags superimposed on a 3D rendering of the target anatomical region of the heart; this combination is hereafter referred to as the “ablation map.” The 3D rendering may be, for example, an anatomical map or an electroanatomical (EA) map (e.g., a local excitation time to arrival (LAT) map). The ablation tags represent the location of the partially or completely ablated surface tissue.

[0008] Using an ablation map, physicians can attempt to identify unablated areas of proarrhythmic cardiac tissue (known as “ablation gaps”), such as ablation gaps in the ablated tissue around the PV orifice.

[0009] However, ablation tags are large icons that indicate the point location where the catheter applied ablation, and they do not accurately reflect the post-ablation tissue condition. In particular, such ablation maps do not accurately represent the actual shape of the ablation gap area.

[0010] The accuracy of ablation maps is further reduced because catheter electrodes randomly change position during ablation, typically due to respiration, heartbeat, or muscle contraction. This random change in ablation location prevents any single ablation tag from providing an accurate discrete representation of the level of ablation at any given tissue location.

[0011] The examples of the disclosure described below provide an algorithm for generating high-resolution and high-dynamic-range ablation maps that overcome the limitations described above. The disclosed ablation maps are generated by superimposing small, densely spread ablation tags onto a 3D rendering of a portion of the heart, such as on an anatomical map. Each tag location is assigned to a map voxel defined by the coordinate system of a position tracking system. The resulting disclosed ablation tags depict high-resolution ablated tissue regions (e.g., with millimeter resolution) represented on the map.

[0012] An instance of electrode ablation affects the entire ablation zone around each voxel to which the measured electrode position is assigned. This ablation zone includes a predetermined number of N nearest voxels (e.g., several dozen nearest voxels), where N is determined from a model or empirically. For example, the number and spatial configuration of assigned voxels mimic or "fill" the shape of the corresponding electrode, which may vary depending on the electrode shape.

[0013] During an ablation session, any voxel within an ablation zone may experience several ablation instances. The number of instances typically ranges from zero to a maximum allowable number, which can reach several dozen. The range of ablation instances (hereinafter also referred to as "applications") defines the range of ablation scores assigned to a voxel. In some cases, a voxel's ablation score defines the total level of ablation accumulated at the voxel location due to various ablation instances. In other cases, the ablation score is based on the proportion of hits per instance to the total number of hits per instance, as defined below.

[0014] A processor executing the disclosed algorithm calculates an ablation score for each affected voxel and graphically encodes (e.g., shading) each ablation tag according to the voxel's ablation score. The resulting ablation map has a high dynamic range (e.g., stepwise) representation of the level of ablation at the tagged voxel locations. This high dynamic range provides, for example, a detailed diagram of the ablation level around the mouth.

[0015] In some examples, the disclosed ablation map is updated on the fly as the ablation session progresses. In other examples, the ablation map also takes into account the results of past ablation sessions by graphically encoding ablation tags according to the ablation instances accumulated across all past ablation sessions.

[0016] In some examples, the disclosed technology provides a graphical user interface (GUI) that allows the user to filter voxel ablation instances if the ablation does not meet one or more conditions in the instance. Thus, voxel ablation instances are not scored if, for example, they are performed with too low a touch proximity index (TPI), with an unacceptable (e.g., too low) electrode contact force, at an outlier tracking electrode location, or over a duration that is too short.

[0017] System Description Figure 1 is a schematic diagram illustrating a catheter-based electroanatomical (EA) mapping and ablation system 10, as illustrated in the present disclosure.

[0018] System 10 includes multiple catheters that are percutaneously inserted by a physician 24 into the lumen or vascular structure of the heart 12 through the patient's vascular system (as shown in insert 45). Typically, a delivery sheath catheter is inserted into a ventricle, such as the left or right atrium, near a desired location in the heart 12. Multiple catheters may then be inserted into the delivery sheath catheter to reach the desired location. The multiple catheters may include a catheter dedicated to pacing, a catheter for sensing intracardiac electrographic signals, a catheter dedicated to ablation, and / or a catheter dedicated to both EA mapping and ablation. An exemplary catheter 14 shown herein is configured to sense bipolar electrographic and pulsed-field ablation (PFA). The physician 24 brings the distal tip 28 of the catheter 14 (hereinafter also referred to as the distal end assembly 28) into contact with the heart wall in order to ablate a target site in the heart 12.

[0019] As shown in inset 65, the catheter 14 is an exemplary catheter including a lasso distal end assembly 28, which optionally includes one, preferably more than one, electrodes 26 distributed along a curved spline 22. The catheter 14 may further include a position sensor 29 embedded in or near the distal end 28 on the shaft 46 of the catheter 14 to track the position and orientation of the distal end 28. Optionally and preferably, the position sensor 29 is a magnetic-based position sensor including three magnetic coils for sensing three-dimensional (3D) position and orientation.

[0020] A magnetic-based position sensor 29 may operate in conjunction with a position pad 25 which 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 tip 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. Details of magnetic-based position sensing technology are described in U.S. Patents 5,5391,199, 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.

[0021] System 10 includes one or more electrode patches 38 positioned for skin contact with the patient 23 to establish a position reference for the position pad 25, as well as impedance-based tracking of the electrodes 26. For impedance-based tracking, a current is directed to the electrodes 26 and sensed by the electrode skin patches 38, thereby allowing the position of each electrode to be triangulated via the electrode patches 38. Details of impedance-based position tracking techniques are described in U.S. Patents 7,536,218, 7,756,576, 7,848,787, 7,869,865, and 8,456,182.

[0022] Recorder 11 displays the cardiac signal 21 (e.g., an electrogram obtained at each tracked cardiac tissue location) acquired using the body surface ECG electrodes 18 and the intracardiac electrogram acquired using the electrodes 26 of the catheter 14. Recorder 11 may include pacing capabilities for pacing the rhythm of the heart and / or may be electrically connected to an independent pacer.

[0023] System 10 may include an ablation energy generator 50 adapted to deliver ablation energy to one or more electrodes at the distal tip of a catheter configured for ablation. The energy generated by ablation energy generator 50 may include radiofrequency (RF) energy or pulse field (PF) energy, or a combination thereof, including monopolar or bipolar and monophasic or biphasic high voltage DC pulses used to effect irreversible electroporation (IRE), but is not limited thereto.

[0024] The patient interface unit (PIU) 30 is an interface configured to establish electrical communication between the catheter, the electrophysiological device, the power supply, and the workstation 55 to control the operation of the system 10 and to receive EA signals from the catheter. The electrophysiological devices of the system 10 may include, for example, a plurality of catheters, the position pads 25, the body surface ECG electrodes 18, the electrode patches 38, the ablation energy generator 50, and the recorder 11. Optionally and preferably, the PIU 30 additionally includes processing capabilities for performing real-time calculations of catheter position and executing ECG calculations.

[0025] The workstation 55 includes a memory 57, a processor 56 unit having a memory or storage device loaded with appropriate operating software, and a user interface function. The workstation 55 may optionally (i) render to model the endocardial anatomical structure in three dimensions (3D) and display a model or anatomical map 20 on the display device 27, (ii) display on the display device 27 a representative visual display or image of an activation sequence (or other data) compiled from the recorded heart signals 21 overlaid on the rendered anatomical map 20, (iii) display the real-time position and orientation of a plurality of catheters within the ventricle, and (iv) display on the display device 27 a site of interest such as a location where ablation energy has been applied, and may provide a plurality of functions including these. One commercially available product embodying the elements of the system 10 is available as the CARTO (trademark) 3 system available from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA, 92618.

[0026] During an ablation session, the processor 56 tracks the position of the catheter electrodes at a high refresh rate of 100 Hz. The results can be hundreds of ablation tags that the processor 56 assigns to different ablated positions. In the disclosed example, the processor 56 executes an algorithm to generate an ablation map (such as the map 200 of FIG. 2) that includes a graphical encoding (e.g., coloring) of the ablation tags according to the existing level of ablation at the voxel positions represented by the ablation tags.

[0027] In some examples, the processor 56 typically comprises a general-purpose computer programmed with software to perform the functions described herein. The software may be downloaded to the computer in electronic form, for example, via a network, or alternatively or additionally, provided and / or stored on a non-temporary tangible medium such as magnetic memory, optical memory, or electronic memory.

[0028] This configuration of System 10 is provided as an example to illustrate a specific problem addressed by the examples of the present disclosure and to demonstrate the application of these examples in improving the performance of such systems. However, the examples of the present disclosure are by no means limited to this particular type of exemplary system, and the principles described herein can be similarly applied to other types of medical systems. For example, other multi-electrode catheter types such as basket catheters may be used.

[0029] High-resolution, high-dynamic-range PFA map Figure 2 shows a high-resolution, high-dynamic-range ablation map 200 of cardiac wall tissue according to an example of the present disclosure. The map 200 was created by overlaying graphically encoded ablation tags (204, 206, 208) on an anatomical map 202, according to an ablation score 205 that counts the ablation instance for each voxel in the ablation session.

[0030] One example of an ablation score is based on the number of PF applications per voxel. Another possible score can be based on the PF index. In PFA, the percentage of hits in any voxel is a useful criterion. For example, assume the percentage of voxel hits associated with electrode positions (every 16 ms) during a PF application (approximately 300 ms). In this example, the maximum number of hits is 18 [=300 / 16], and the hit rate is defined as the ratio of actual hits to maximum hits. This ratio is used to define a percentage threshold for determining whether to count this voxel in the current application.

[0031] Ablation map 200 represents a portion of the left atrium, including PV orifice 210. Ablation tags (204, 206, 208) are superimposed on the voxel locations of map 200 to depict the tissue region of orifice 210 at high resolution (e.g., millimeter resolution) as represented by the ablated anatomical map. Each tag location is set at the center of each voxel, defined by mapping system coordinates.

[0032] The high-resolution, high-dynamic-range ablation map 200 provides a clear view of the ablation progress by graphically encoding the ablation tags. As shown, the high-density ablation tags (204, 206, 208) indicate the ablation results, with ablation tag 208 having a darker hue and indicating the fully ablated outer periphery of the mouth 210. Ablation tag 206, having an intermediate hue, is common in adjacent parts of the circumference, indicating that this area is partially ablated. Ablation tag 204, with a lighter hue, indicates the less ablated area around the mouth.

[0033] The ablation map 200 is available to the user during the ablation session. The processor can update the ablation map 200 as the isolation of the PV orifice 210 by PFA progresses using the electrode 26 of the distal end assembly 28 of the catheter 14.

[0034] Figure 3 is a schematic diagram of a graphical user interface (GUI) 111 used in an example of this disclosure to filter out instances of inappropriate ablation that do not affect map 200 in Figure 2. By using GUI 111, the ablation score 205 can be increased in each affected voxel only by considering effective ablation application according to the user's preference.

[0035] In the disclosed GUI, checkbox 333 on GUI 111 allows the user to select which ablation instances are filtered and excluded, such as ablation instances at locations where touch proximity or touch force was insufficient, or where the electrode position was found to be an outlier. Meeting time is a mandatory criterion included in the algorithm.

[0036] Figure 3 is provided as an example. Additional or alternative filtration criteria may be considered.

[0037] A method for generating high-resolution, high-dynamic-range ablation maps. Figure 4 is a schematic flowchart illustrating a method for generating a high-resolution, high-dynamic-range ablation map 200 according to an example of the present disclosure. According to the example presented, the algorithm performs a process in which the processor 56 receives an EA map of at least a portion of the ventricle in an EA map receiving step 402.

[0038] In voxel definition step 404, the processor divides the EA map region for ablation (e.g., the PV mouth region) into predetermined voxels. A typical voxel size is 1 mm. 3 That is the case.

[0039] In the position tracking step 406, the electrode positions of the catheter are tracked. This tracking is performed only during pulsed-field ablation (PFA) application. The processor calculates a new position after a predetermined time, for example, every tens of milliseconds (in particular, e.g., 16 milliseconds), which may correspond to tracking several or more positions of each electrode during a single application. In the case of a multi-electrode catheter 14, the processor tracks the positions of multiple electrodes simultaneously.

[0040] In the voxel assignment step 408, each tracked electrode position is assigned the N voxels closest to the electrode position (for example, N=19 in a cubic grid). N may vary depending on the grid used. For example, a tetrahedral grid or a hexagonal pyramidal grid may be used.

[0041] In the ablation application process 410, the processor performing the PFA application (e.g., an instance) instructs the generator to continuously deliver PF energy for a period of typically 300–400 ms. A PF session involves the PF generator performing a predetermined sequence of PFA applications, typically 12–24 applications (e.g., instances), with a 1-second interval between applications. To avoid tracking the supply of energy to electrodes with insufficient tissue contact (e.g., in the blood), the system can gate the ablation when the TPI exceeds a predetermined threshold.

[0042] In the duration check step 412, the processor checks whether the duration of a PF instance in any of the N voxels around a given electrode position exceeds a threshold duration (e.g., exceeds 25 milliseconds). Another threshold criterion may be the minimum percentage of hits in a voxel during a single application.

[0043] If the answer is No, the processor discards the instance in the ablation instance discard step 414, taking into consideration the ablation score of that voxel.

[0044] For voxels that have been ablated for a duration exceeding a threshold, the processor increments the ablation score 205 by 1 in the ablation score count step 416. In the session check step 418, the processor checks whether the session has ended. If it has not ended, the processor repeats steps 410 to 416.

[0045] When the ablation session is completed, in the ablation score storage step 420, the processor stores the aggregated (e.g., accumulated) ablation score for each voxel in that session.

[0046] In the ablation tag generation process 422, the processor 56 assigns an ablation tag to each of the scored voxels. The tags are graphically encoded (e.g., color-coded) according to the cumulative ablation score of each voxel. If an ablation score already exists for a voxel due to a previous ablation, the processor selects the highest score for the voxel from all scores and graphically encodes (color-codes) the ablation tag.

[0047] Finally, in the ablation map generation step 424, the processor overlays graphically encoded (color-coded) ablation tags onto the EP map in order to generate an ablation map such as map 200.

[0048] After generating the ablation map, the processor 56 can either present it to the user on the display device 27 or store it in memory 57.

[0049] By analyzing graphically encoded (e.g., color-coded) high-resolution voxel ablation tags using the generated ablation map, it may be easier (for example, for the user) to identify non-ablated or low-ablated areas of ablated tissue, i.e., "ablation gaps." For example, the user can identify areas with brighter colors as locations where additional ablation may be needed and direct future ablations to those areas.

[0050] A flowchart in Figure 4 is provided as an example. In other examples, the process may include different steps, such as including more voxel filtering steps instead of letting the user choose whether to activate such as GUI 111 in Figure 3. The processor may receive any other 3D rendering of the ventricle. [Examples]

[0051] (Example 1) The method involves dividing a three-dimensional (3D) rendering (202) of at least a portion of the heart into voxels having coordinates in the coordinate system of a position mapping system (10). Using the position tracking system, the position of one or more electrodes (26) of a catheter is measured within the heart during an ablation session that includes multiple ablation instances. Each measurement location is assigned a predetermined number of voxels closest to that location. Each ablation score (205) is calculated for each voxel, and the ablation score represents at least the number of ablation instances affecting the voxel. Each ablation tag (204, 206, 208) is assigned to each voxel, and the ablation tags are graphically encoded according to the voxel's ablation score (205). The graphically encoded ablation tags (204, 206, 208) are overlaid on the 3D rendering (202) to generate an ablation map (200). The ablation map (200) is presented to the user.

[0052] (Example 2) The method according to Example 1, wherein calculating the ablation score (205) includes including the ablation instance in the voxel's ablation score (205) only if the duration of ablation in the ablation instance exceeds a predetermined threshold.

[0053] (Example 3) The method according to Example 1, wherein calculating the ablation score (205) includes including an ablation instance in the voxel's ablation score (205) only if the hit rate in the ablation instance exceeds a predetermined threshold.

[0054] (Example 4) The method according to any one of Examples 1 to 3, wherein assigning a predetermined number of voxels closest to a position includes assigning the closest voxels as defined by one of a cubic grid, a tetrahedron grid, and a hexagonal pyramidal grid.

[0055] (Example 5) The method according to any one of Examples 1 to 4, wherein graphically encoding the ablation tags (204, 206, 208) includes coloring the ablation tags (204, 206, 208) with a shade of color representing the ablation score (205).

[0056] (Example 6) The method according to any one of Examples 1 to 5, comprising providing a graphical user interface (GUI) (111) configured to allow a user to exclude ablation instances from the calculation of an ablation score (205) based on at least one of insufficient electrode contact force and a very low touch proximity index (TPI).

[0057] (Example 7) The method according to claim 1, wherein the catheter is a multi-electrode catheter (14).

[0058] (Example 8) The method according to claim 1, wherein part of the heart is a ventricle.

[0059] (Example 9) A display device (27), (i) dividing a three-dimensional (3D) rendering (202) of at least a portion of the heart into voxels having coordinates in the coordinate system of a position mapping system (10), (ii) using a position tracking system to measure the position of one or more electrodes (26) of a catheter in the heart during an ablation session including multiple ablation instances, (iii) assigning a predetermined number of voxels closest to each measured position, and (iv) for each voxel, each ablation representing at least a number of ablation instances affecting that voxel A system comprising a processor (56) configured to perform the following: (v) calculate a score (205); (v) assign each ablation tag (204, 206, 208) to each voxel and graphically encode the ablation tags according to the ablation score (205) of the voxels; (vi) generate an ablation map (200) by overlaying the graphically encoded ablation tags (204, 206, 208) onto a 3D rendering (202); and (vii) present the ablation map (200) to the user on a display device (27).

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

[0061] The embodiments described above are illustrative examples, and it should be understood that this disclosure is not limited to those specifically illustrated and described above. Rather, the scope of this disclosure includes both combinations and partial combinations of the various features described above, as well as variations and modifications thereof not disclosed in the prior art, which may be conceived by those skilled in the art by reading the foregoing.

[0062] [Implementation Method] (1) Divide the three-dimensional (3D) rendering of at least a portion of the heart into voxels having coordinates in the coordinate system of the position mapping system, Using a position tracking system, the position of one or more electrodes of the catheter in the heart is measured during an ablation session that includes multiple ablation instances, Assigning a predetermined number of voxels closest to each measured position, The ablation score for each voxel is calculated, wherein the ablation score represents at least the number of ablation instances affecting the voxel. Assigning an ablation tag to each voxel, and graphically encoding the ablation tag according to the ablation score of the voxel, The graphically encoded ablation tags are superimposed onto the 3D rendering to generate an ablation map, A method comprising presenting the ablation map to the user. (2) The method according to Embodiment 1, wherein calculating the ablation score includes including the ablation instance in the ablation score of a voxel only if the duration of ablation in the ablation instance exceeds a predetermined threshold. (3) The method according to Embodiment 1, wherein calculating the ablation score includes including the ablation instance in the ablation score of a voxel only if the hit rate in the ablation instance exceeds a predetermined threshold. (4) The method according to Embodiment 1, wherein assigning the nearest predetermined number of voxels to the position includes assigning the nearest voxels as defined by a cubic grid, a tetrahedron grid, and a hexagonal pyramidal grid. (5) The method according to Embodiment 1, wherein graphically encoding the ablation tag includes coloring the ablation tag with a shade of color representing the ablation score.

[0063] (6) The method according to Embodiment 1, comprising providing a graphical user interface (GUI) configured to enable the user to exclude ablation instances from the calculation of the ablation score based on at least one of insufficient electrode contact force and a very low touch proximity index (TPI). (7) The method according to embodiment 1, wherein the catheter is a multi-electrode catheter. (8) The method according to Embodiment 1, wherein the part of the heart is a ventricle. (9) A system, Display devices and, It is a processor, The 3D rendering of at least a portion of the heart is divided into voxels having coordinates in the coordinate system of a position mapping system, Using a position tracking system, the position of one or more electrodes of the catheter in the heart is measured during an ablation session that includes multiple ablation instances, Assigning a predetermined number of voxels closest to each measured position, The ablation score for each voxel is calculated, wherein the ablation score represents at least the number of ablation instances affecting the voxel. Assigning an ablation tag to each voxel, and graphically encoding the ablation tag according to the ablation score of the voxel, The graphically encoded ablation tags are superimposed onto the 3D rendering to generate an ablation map, A system comprising a processor configured to present the ablation map to a user on the display device. (10) The system according to Embodiment 9, wherein the processor is configured to calculate the ablation score by including the ablation instance in the ablation score of a voxel only if the duration of ablation in the ablation instance exceeds a predetermined threshold.

[0064] (11) The system according to Embodiment 9, wherein the processor is configured to calculate the ablation score by including the ablation instance in the ablation score of a voxel only if the hit rate in the ablation instance exceeds a predetermined threshold. (12) The system according to Embodiment 9, wherein the processor is configured to assign the nearest number of voxels closest to the position by assigning the nearest voxels as defined by a cubic grid, a tetrahedron grid, and a hexagonal pyramidal grid. (13) The system according to embodiment 9, wherein the processor is configured to graphically encode the ablation tag by coloring the ablation tag with a shade of color representing the ablation score. (14) The system according to Embodiment 9, wherein the processor is further configured to provide a graphical user interface (GUI) that enables the user to exclude ablation instances from the calculation of the ablation score based on at least one of insufficient electrode contact force and a very low touch proximity index (TPI). (15) The system according to embodiment 9, wherein the catheter is a multi-electrode catheter.

[0065] (16) The system according to embodiment 9, wherein the portion of the heart is a ventricle.

Claims

1. It is a system, Display devices and, It is a processor, The three-dimensional (3D) rendering of at least a portion of the heart is divided into voxels having coordinates in the coordinate system of a position mapping system, Using a position tracking system, the position of one or more electrodes of the catheter in the heart is measured during an ablation session that includes multiple ablation instances, Assigning a predetermined number of voxels closest to each measured position, The ablation score for each voxel is calculated, wherein the ablation score represents at least the number of ablation instances affecting the voxel. Assigning an ablation tag to each voxel, and graphically encoding the ablation tag according to the ablation score of the voxel, The graphically encoded ablation tags are superimposed onto the 3D rendering to generate an ablation map. A system comprising a processor configured to present the ablation map to a user on the display device.

2. The system according to claim 1, wherein the processor is further configured to calculate the ablation score by including an ablation instance in the ablation score of a voxel only if the duration of ablation in the instance exceeds a predetermined threshold, or if the hit rate in the instance exceeds a predetermined threshold.

3. The system according to claim 1, wherein the processor is configured to assign the nearest predetermined number of voxels closest to the position by assigning the nearest voxel as defined by one of a cubic grid, a tetrahedron grid, and a hexagonal pyramidal grid.

4. The system according to claim 1, wherein the processor is configured to graphically encode the ablation tag by coloring the ablation tag with a shade of color representing the ablation score.

5. The system according to claim 1, wherein the processor is further configured to provide a graphical user interface (GUI) configured to enable the user to exclude ablation instances from the calculation of the ablation score based on at least one of insufficient electrode contact force and a very low touch proximity index (TPI).

6. The three-dimensional (3D) rendering of at least a portion of the heart is divided into voxels having coordinates in the coordinate system of a position mapping system, Using a position tracking system, the position of one or more electrodes of the catheter in the heart is measured during an ablation session that includes multiple ablation instances, Assigning a predetermined number of voxels closest to each measured position, The ablation score for each voxel is calculated, wherein the ablation score represents at least the number of ablation instances affecting the voxel. Assigning an ablation tag to each voxel, and graphically encoding the ablation tag according to the ablation score of the voxel, The graphically encoded ablation tags are superimposed onto the 3D rendering to generate an ablation map. A method comprising presenting the ablation map to the user.

7. The method according to claim 6, wherein calculating the ablation score includes including the ablation instance in the ablation score of a voxel only if the duration of ablation in the ablation instance exceeds a predetermined threshold, or if the hit rate in the ablation instance exceeds a predetermined threshold.

8. The method according to claim 6, wherein assigning the nearest predetermined number of voxels to the position includes assigning the nearest voxels as defined by one of a cubic grid, a tetrahedron grid, or a hexagonal pyramidal grid.

9. The method according to claim 6, wherein graphically encoding the ablation tag includes coloring the ablation tag with a shade of color representing the ablation score.

10. The method according to claim 6, comprising providing a graphical user interface (GUI) configured to enable the user to exclude ablation instances from the calculation of the ablation score based on at least one of insufficient electrode contact force and a very low touch proximity index (TPI).

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