Lesion arrhythmia source finder using directed graph

Abstract

A system includes a display and a processor. The processor is configured to: (i) receive a cardiac electrophysiological (EP) velocity vector map; (ii) calculating a set of directed graphs from at least some of the velocity vectors; (iii) using the directed graph, identifying a corresponding origin velocity vector on the EP velocity vector map; (iv) defining one or more regions on the EP velocity vector map; (v) determining whether the one or more regions contain a source of focus of arrhythmia based on the origin velocity vector in each of the one or more regions; and (vi) visualizing a region on the EP map identified as containing a lesion source to a user on the display.

Description

Technical Field

[0001] The present disclosure generally relates to cardiac electrophysiology (EP) mapping and, more particularly, to the analysis of cardiac EP maps. Background Art

[0002] Computer-aided analysis of EP maps generated from EP signals acquired from catheters has been previously described in the patent literature. Such EP maps can assist in locating and planning treatment of the positions of arrhythmogenic tissue.

[0003] The present disclosure will be more fully understood from the following detailed description of an example of the present disclosure in conjunction with the accompanying drawings, in which: Brief Description of the Drawings

[0004] Figure 1 is a schematic illustration of a catheter-based electrophysiology (EP) mapping and ablation system according to an example of the present disclosure;

[0005] Figure 2 is a schematic volumetric rendering of a coherent EP activation map of a left atrial anatomy with conduction arrows superimposed thereon, the conduction arrows illustrating the propagation of an EP activation wave;

[0006] Figure 3A and Figure 3B are schematic diagrams of a set of velocity vectors and a set of directed graphs based on the velocity vectors, respectively, according to an example of the present disclosure; and

[0007] Figure 4 is a flowchart schematically illustrating a method for identifying a source of an arrhythmia according to an example of the present disclosure. Detailed Description

[0008] Overview

[0009] Probe-based (e.g., multi-electrode catheter-based) cardiac diagnostic and treatment systems can measure a large number of intracardiac electrophysiology (EP) signals, such as electrograms (EGMs), during invasive procedures. Typically, the analysis of such a large amount of EP information is facilitated by generating one or more EP maps and presenting them to a user (e.g., a doctor or a clinical application specialist).

[0010] Various types of EP maps can be generated for the internal tissue surface of a cardiac chamber (such as the left atrium of the heart). One such map is sometimes referred to as a coherent activation wave propagation map, also referred to hereinafter as a "velocity vector map", in which vectors indicating the EP conduction velocity (speed and direction) are superimposed on the cardiac anatomical surface.

[0011] Velocity vector maps can be used to attempt to detect the source of the lesion causing the arrhythmia by visual inspection of the map. However, in some types of arrhythmias, such as in scar-related atrial tachycardia, the EP behavior has a complex pattern, and the EP velocity vector map shows a visual jumble of multiple velocity vectors, making it difficult for the user to interpret. This poses a challenge for doctors performing invasive catheterization to diagnose and ablate one or more abnormal lesion sources to eliminate the arrhythmia.

[0012] Although computer-aided analysis of the EP conduction properties of a surface embedded in 3D space can further assist the user in the examination, such analysis is very difficult and requires powerful algorithms and computing capabilities. In addition, such analysis may not be complete because, for example, a full analysis of a manifold in 3D space requires more information than the information obtained from the measured EP values.

[0013] Examples of the present disclosure described herein provide a method and algorithm for automatically identifying the source of a lesion causing an arrhythmia. In some examples, the processor uses a directed graph to calculate the relationships between velocity vectors. Based on the calculated relationships, the processor identifies the vector origin of the directed graph. Using the directed graph, the processor determines a subset of the origin vectors of the velocity vectors. The processor then defines one or more regions on the EP velocity vector map and identifies the origin vectors that are spatially close to each other within each given region. The processor applies the divergence theorem to determine whether the identified origin velocity vectors that are so close to each other exhibit indications of the presence of a lesion source in each associated region.

[0014] In some examples, the processor generates or receives an EP map of velocity vectors {V}. The processor uses the newly disclosed method to construct a set of directed graphs, where the processor generates a capture volume in space (such as a cone with a predefined radius and solid angle) and aligns the capture volume with each vector head. If the tail of another vector falls within the capture volume (e.g., the cone), the processor generates a directed graph portion from these two vectors. The processor traverses all the vectors and deletes overlapping selectors (e.g., recurring directed graph portions) until a unique complete set of directed graphs is received. Isolated vectors (e.g., vectors that are not associated with any other vector using the disclosed method) are also considered (minimal) directed graphs.

[0015] Each arc in the directed graph has a defined direction, extending from the "tail" vertex to the "head" vertex. The processor analyzes each directed graph to identify the arcs whose tails are the origin of the EP propagation. The origin arcs are the arcs in the directed graph that are only connected to arcs that extend away from the origin arcs. There are no arcs extending towards the origin arcs.

[0016] Then, the processor strips each directed graph from its branches, which leaves only the set of "stripped" directed graphs, all of which are origin arcs. At this stage, the processor only considers the vectors corresponding to the single origin arc found, which are hereinafter referred to as "origin vectors". The processor analyzes each such origin vector to identify the tails of the origin vectors that are in close proximity to each other. In one example, the processor defines a volume (e.g., an ellipsoid) that intersects the EP surface and checks which tails (i.e., origin positions) on the surface can be enclosed within the ellipsoid.

[0017] In some examples, using a predefined criterion (e.g., the minimum number of such vectors at each given volume), the processor fits a vector field function to the vectors (e.g., fitting the velocity vector field approximation function V(r)). In other examples, the processor may consider a discrete set of origin vectors. However, the fitting function V(r) enhances the algorithm's resilience to missing data (e.g., to incomplete mapping).

[0018] By applying the divergence theorem to V(r), the processor determines whether all the origin vectors point away from the lesion source. For example, if the vector derivatives along each of the x-axis, y-axis, and z-axis are greater than 0, then all the origin vectors point away from the lesion source. In this case, the processor designates the surface contained within the volume as containing the lesion source of the arrhythmia. In some examples, the processor may use differential or integral analysis to perform vector calculus analysis.

[0019] In one example, if the processor finds a location to be a lesion point, the processor calculates the average position based on the tails of all the vectors. Finally, the processor graphically indicates the identified cardiac tissue locations on the EP mapping diagram, such as tissue regions for the user to consider for ablation.

[0020] In some examples, the processor considers the entire set of directed graphs. In other examples, the processor considers (e.g., selects) a subset of the most unbalanced directed graphs in favor of open arcs. Considering the vertices of the graph, the number of heads connected to (extending to) that vertex is called the in-degree of that vertex. The number of tails connected to (extending from) the vertex is called its out-degree (also known as the branching factor in a tree). The processor supports graphs with out-degree > in-degree, and for this, a positive integer threshold can be used, which only considers directed graphs that satisfy (out-degree - in-degree) ≥ N, where N = 1, 2,.... In another example, the processor only considers the simplest directed graphs, i.e., directed graphs that only have arcs branching from the origin. An example of such a simple directed graph is a directed graph with two vectors that are not parallel and originate from the same location, where the resulting directed graph has (out-degree - in-degree) = 2 - 0 ≥ 2.

[0021] System Description

[0022] Figure 1 is a schematic illustration of a catheter-based electrophysiology (EP) mapping and ablation system 10 according to an example of the present disclosure.

[0023] System 10 may include a plurality of catheters that are inserted by a physician 24 through a patient's vascular system via the skin into a chamber or vascular structure of the heart 12. In the illustrated example, a delivery sheath catheter is inserted into the left atrium or right atrium near a desired location within the heart 12. Then, a plurality of catheters may be inserted into the delivery sheath catheter to reach that desired location. The plurality of catheters may include a catheter dedicated to sensing intracardiac electrogram (IEGM) signals, a catheter dedicated to ablation, and / or a catheter dedicated to both sensing and ablation. An example EP mapping catheter 14 configured for sensing IEGM is illustrated herein. The physician 24 places the distal end 28 (also referred to hereinafter as “distal end assembly 28”) of the catheter 14 in contact with the heart wall for sensing a target site within the heart 12. For ablation, the physician 24 similarly brings the distal end of the ablation catheter to the target site for ablation.

[0024] Catheter 14 is an exemplary catheter that includes one (and preferably a plurality) of electrodes 26 optionally disposed above a plurality of splines 22 at the distal end 28 and configured to sense IEGM signals. Catheter 14 may additionally include a positioning sensor 29 embedded in or near the distal end 28 for tracking the position and orientation of the distal end 28. Optionally and preferably, the positioning sensor 29 is a magnetic-based positioning sensor that includes three magnetic coils for sensing three-dimensional (3D) position and orientation.

[0025] The magnetic-based positioning sensor 29 may operate in conjunction with a position pad 25 that includes a plurality of magnetic coils 32 configured to generate a magnetic field within a predefined workspace. The real-time position of the distal end 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 positioning sensor 29. Details of magnetic-based positioning sensing techniques are described in U.S. Pat. Nos. 5,539,199, 5,443,489, 5,558,091, 6,172,499, 6,239,724, 6,332,089, 6,484,118, 6,618,612, 6,690,963, 6,788,967, and 6,892,091.

[0026] System 10 includes one or more electrode patches 38 that are positioned to contact the skin of patient 23 to establish a position reference for impedance-based tracking of position pad 25 and electrodes 26. For impedance-based tracking, current is directed toward electrodes 26 and sensed at the electrode skin patches 38 such that the position of each electrode can be triangulated via the electrode patches 38. Details of impedance-based position tracking techniques are described in U.S. Patent Nos. 7,536,218, 7,756,576, 7,848,787, 7,869,865, and 8,456,182.

[0027] Recorder 11 displays an electrogram 21 captured using body surface ECG electrodes 18 and an intracardiac electrogram (IEGM) captured using electrodes 26 of catheter 14. Recorder 11 may include pacing capabilities for pacing the heart rhythm and / or may be electrically connected to an independent pacemaker.

[0028] System 10 may include an ablation energy generator 50 that is adapted to conduct ablation energy to one or more electrodes at the distal end of a catheter configured for ablation. The energy generated by ablation energy generator 50 may include, but is not limited to, radiofrequency (RF) energy or pulsed field ablation (PFA) energy (including unipolar or bipolar high voltage DC pulses to be used to effect irreversible electroporation (IRE)), or combinations thereof.

[0029] Patient interface unit (PIU) 30 is an interface configured to enable electrical connectivity between a catheter, electrophysiology equipment, a power source, and a workstation 55 for controlling the operation of System 10. The electrophysiology equipment of System 10 may include, for example, multiple catheters, position pad 25, body surface ECG electrodes 18, electrode patches 38, ablation energy generator 50, and recorder 11. Optionally and preferably, PIU 30 additionally includes processing capabilities for performing real-time position calculations of the catheter and for performing ECG calculations.

[0030] Workstation 55 includes a memory 57, a processor unit 56 with a memory or storage device loaded with appropriate operating software, and user interface capabilities. Workstation 55 may provide multiple functions, optionally including: (1) performing three-dimensional (3D) modeling of the endocardial anatomy and rendering a model or POI map 20 for display on display device 27; (2) displaying, on display device 27, an activation sequence (or other data) compiled from the recorded electrogram 21 with representative visual markers or images included on the rendered POI map 20; (3) displaying the real-time position and orientation of multiple catheters within the heart chambers; and (4) displaying sites of interest, such as where ablation energy is applied, on display device 27. A commercial product embodying the elements of System 10 may be CARTOTM The 3 System was purchased from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA 92618.

[0031] Lesion Arrhythmia Source Finder Using Directed Graph

[0032] Figure 2 It is a schematic volumetric rendering of a coherent EP activation mapping diagram 200 of a left atrial anatomical structure overlaid with conduction arrows 220 (also referred to herein as "velocity vectors"), which illustrate the propagation of an EP activation wave.

[0033] The conduction arrows 220 are the aforementioned velocity EP vectors, all vectors having a fixed length, and each vector having the direction of a corresponding slowness vector at its location in shape, which provides additional visualization of EP activity. Generally speaking, the conduction arrows have different lengths, which represent, in addition to direction, the magnitude of slowness.

[0034] In Figure 2 it, the ellipsoid 202 intersects the anatomical surface to define a curved surface region (e.g., region) 205 with a boundary 207 on the EP mapping surface. It can be seen that within the region 205, some of the conduction arrows 220 appear to share a common origin. However, since this visual perception may be misleading, a quantitative analysis such as that disclosed below is required to verify whether there is a source of arrhythmia within the region 205 (e.g., at the location 204). This analysis can actually find the corresponding set of origin vectors that are included in the set of conduction arrows 220 and are the result of the source.

[0035] To this end, after identifying the region 205 as potentially including a source using a directed graph, as described in FIG. 3, the processor can estimate whether the sign of one of the divergence theorem integrals below is positive in order to determine whether there is indeed a source therein:

[0036]

[0037] The left integral is the surface integral over the region 205, and the right integral is the line integral over the boundary l207 of the region 205. V S is a 2D vector function approximation of the velocity origin vector, which is defined on a surface (i.e., a 2D manifold) 295.

[0038] Additionally, the disclosed technique estimates the location of the exact position 204 within the internal region 205 that is the source (e.g., by finding the average position).

[0039] Alternatively, the processor may estimate whether the sign of one of the divergence theorem integrals below is positive to determine whether there is a source:

[0040]

[0041] The left integral is a volume integral over the ellipsoid 202, and the right integral is a surface integral over the surface S of the ellipsoid 202. V is an approximation of the vector function of the velocity origin vector, which is defined over the volume of the ellipsoid 202.

[0042] Figure 3A and Figure 3B are schematic diagrams of a set 300 of velocity vectors 310 according to an example of the present disclosure and a set of directed graphs 301, 311, 321, 331, and 341 based on the set of velocity vectors 300. The set of velocity vectors 300 is taken from a continuous part (e.g., a region) of the EP mapping surface including the velocity vector mapping 200. There are correct mathematical methods to transform (e.g., project) vectors between a surface (such as in the mapping 200) and a 2D curve graph (such as in Figure 3A or a 3D curve graph (not shown), and the latter is used in a natural way to represent vectors located on a variable surface in 3D.

[0043] Figure 3A shows a set 300 of velocity vectors 310 covering a part of the anatomical surface. For clarity of display, the simplified graph is 2D, but in fact the vectors are 3D.

[0044] The processor 28 has numbered the vectors so as to index the vectors for placement in the directed graph. By numbering the vectors (e.g., giving an index), the processor ensures that all vectors are considered in the process of generating a unique set of directed graphs from these vectors.

[0045] The processor 28 may number the vectors based on, for example, the local activation time (LAT) values at the corresponding tail positions, so as to be ready to place the vectors in the directed graph. The same LAT value (up to a given tolerance) at two vector positions that are close enough (e.g., within a few mm tolerance) indicates that the two vectors can be considered to share a common tail.

[0046] As described later in Figure 3B using the directed graph, the processor identifies the vectors 391, 392, 393, 394, 395, and 396 as origin vectors.

[0047] To generate a directed graph from the vectors 310, the processor uses a newly disclosed method, where each processor generates a cone (shown as angular segment 350 in 2D) with a predefined radius 360 and a given solid angle (shown as angle 370 in 2D) and assigns the cone to each vector head (e.g., aligned with the vector head). If the tail of another vector falls within the cone, the processor generates a directed graph portion from these two vectors. The processor traverses all the vectors and removes overlapping selectors (e.g., reoccurring directed graph portions) until a unique complete set of directed graphs is received. Isolated vectors (e.g., vectors not associated with any other vector using the disclosed method) are also considered (minimal) directed graphs.

[0048] Figure 3B Directed graphs 301, 311, 321, 331, and 341 based on some of the velocity vectors 310 in the set 300 are schematically shown. As shown, each of these directed graphs consists of an arc 302 and a vertex 303 and has a unique origin vertex 304. The open end 306 of the arc counts the out-degree of each directed graph. For example, directed graph 321 has an in-degree = 1 and an out-degree = 2.

[0049] The processor strips each directed graph from its branches, which leaves only the "stripped" set of directed graphs, all of which are origin arcs.

[0050] At this stage, the processor only considers the origin vectors corresponding to the found origin arcs. For example, the origin positions 304 of the arcs 381, 382, 383, 384, 385, and 386 of the directed graph correspond to the origin vectors 391, 392, 393, 394, 395, and 396, respectively. Some of these origin vectors fall within the Figure 2 region 205 defined by the processor and are thus considered to be in close proximity to each other.

[0051] The processor now tests whether the origin vectors in region 205 indicate an arrhythmogenic lesion source using the above calculus analysis.

[0052] In some examples, using a predefined criterion (e.g., the minimum number of such vectors at each given volume), the processor fits a vector field function to the vectors (e.g., fits the velocity vector field approximation function V(r)) and applies the divergence theorem to V(r). In other examples, the processor may consider a discrete set of origin vectors and calculate a discrete version of the divergence.

[0053] If the answer is yes (i.e., positive divergence), the processor calculates the average of the positions 304 and indicates this position on the EP mapping diagram (e.g., the position projected from the space of the directed graph onto the anatomical surface) as the arrhythmogenic lesion source.

[0054] Figure 4 is a flowchart schematically illustrating a method for identifying a source of arrhythmia according to an example of the present disclosure. According to the presented example, the process performed by the algorithm begins with the processor 28 receiving (e.g., uploading) an EP mapping diagram including velocity vectors (such as Figure 2 the EP mapping diagram 200) at the velocity vector mapping upload step 402.

[0055] Next, at the directed graph construction step 404, based on the velocity vectors, the processor constructs a set of directed graphs. Figure 3A and Figure 3B shows an example of this step.

[0056] At the directed graph assignment step 406, the processor selects those simple directed graphs that have an origin and have the most open arcs (e.g., have the maximum out-degree value). In another example, the processor selects a subset of the directed graphs that also have an origin, and this subset of directed graphs may also include more complex graphs (e.g., multi-vertex graphs) and is the most unbalanced in favor of open arcs.

[0057] At the directed graph stripping step 407, the processor strips the branches from the directed graph and only retains the origin arcs of the graph.

[0058] In the step 408 of grouping the directed graphs, the processor 28 finds the corresponding origin vectors and the tail positions of the groups that are spatially close to each other (such as within a surface area (e.g., area 205)).

[0059] At the vector field function fitting step 410, the processor fits the velocity vector field approximation function V(r) to the origin vectors within the region (e.g., in the manifold region 205).

[0060] Using the divergence theorem, the processor calculates at the lesion source determination step 412 whether all the origin vectors point away from the lesion source. For example, if the vector derivatives along each of the x-axis, y-axis, and z-axis are all greater than 0, then all the origin vectors point away from the lesion source.

[0061] If the answer in the check step 414 is "no", the process returns to step 408 to search for the lesion source in another region of the velocity vector mapping diagram.

[0062] If the answer in the check step 414 is "yes", the processor indicates at the arrhythmogenic region indication step 416 that the examined region on the EP mapping diagram includes the source of the arrhythmia.

[0063] In a subsequent optional indication step 418 at the arrhythmogenic location, the processor calculates an average position based on the tail positions of all the vectors. Finally, the processor graphically indicates on the EP mapping the identified cardiac tissue location, such as a tissue area for the user to consider for ablation.

[0064] Finally, at an arrhythmogenic location display step 20, the processor displays on the EP mapping the position found in step 418.

[0065] Examples

[0066] Example 1

[0067] A system (10) includes a display (27) and a processor (56). The processor is configured to: (i) receive a cardiac electrophysiology (EP) velocity vector (220) mapping (200); (ii) calculate a set of directed graphs (301, 311, 321, 331, 341) from at least some of the velocity vectors (220); (iii) use the directed graphs (301, 311, 321, 331, 341) to identify corresponding origin velocity vectors (391, 392, 393, 394, 395, 396) on the EP velocity vector mapping (200); (iv) define one or more regions (205) on the EP velocity vector mapping; (v) determine whether the one or more regions (205) contain an arrhythmogenic focus (204) based on the origin velocity vectors in each of the one or more regions; and (vi) visualize on the display (27) for the user the regions (205) on the EP mapping (200) identified as containing the focus (204).

[0068] Example 2

[0069] The system according to embodiment 1, wherein the processor (56) is further configured to estimate the position (204) of the focus within the region (205) and visualize the position (204) on the EP mapping (200).

[0070] Example 3

[0071] The system according to any one of embodiments 1 and 2, wherein the processor (56) is configured to calculate the set of directed graphs (301, 311, 321, 331, 341) by arranging the velocity vectors (220) according to the spatial and temporal proximity between the velocity vectors.

[0072] Example 4

[0073] The system according to any one of embodiments 1 to 3, wherein the first velocity vector and the second velocity vector (220) are considered to be spatially and temporally close if (i) the tail positions of the first velocity vector and the second velocity vector share the same local activation time (LAT) until a threshold tolerance is reached, and (ii) the tail positions are separated by no more than a threshold distance.

[0074] Example 5

[0075] The system according to any one of embodiments 1 to 4, wherein the processor (56) is configured to identify the region (205) by determining three or more origin vectors that are within a predefined spatial proximity to each other.

[0076] Example 6

[0077] The system according to any one of embodiments 1 to 5, wherein the processor (56) is configured to determine whether the region (205) contains the lesion source (204) by fitting a vector function to the velocity origin vectors in the region and performing vector calculus operations on the fitted vector function.

[0078] Example 7

[0079] The system according to any one of embodiments 1 to 6, wherein the processor (56) is configured to determine whether the region (205) contains the lesion source (204) by estimating whether the sign of the divergence of the fitted vector function in the region is positive.

[0080] Example 8

[0081] The system according to any one of embodiments 1 to 7, wherein the processor (56) is configured to calculate a set of directed graphs (301, 311, 321, 331, 341) from at least some of the velocity vectors (220) by performing the following steps, the steps including: (i) assigning a cone (250) having a predefined radius (260) and a given solid angle (270) to the head of each velocity vector (220); and (ii) generating a directed graph (301, 311, 321, 331, 341) portion from the two vectors if the tail of another vector (220) falls within the cone.

[0082] Example 9

[0083] The system according to any one of embodiments 1 to 8, wherein the processor (56) is configured to use the directed graph to identify corresponding origin velocity vectors (391, 392, 393, 394, 395, 396) by identifying origin arcs (381, 382, 383, 384, 385, 386) and matching origin vectors with each origin arc.

[0084] Example 10

[0085] A method includes receiving a cardiac electrophysiology (EP) velocity vector (220) mapping (200). Calculating a set of directed graphs (301, 311, 321, 331, 341) from at least some of the velocity vectors (220). Using the directed graphs (301, 311, 321, 331, 341), identifying corresponding origin velocity vectors (391, 392, 393, 394, 395, 396) on the EP velocity vector mapping (200). Determining whether the one or more regions (205) contain a source of arrhythmia (204) based on the origin velocity vectors in each of the one or more regions. Visualizing, on the display (27), to a user the regions (205) on the EP mapping (200) identified as containing the source of arrhythmia (204).

[0086] It should be understood that the above embodiments are cited by way of example, and the present disclosure is not limited to what is specifically shown and described above. Instead, the scope of the present disclosure includes combinations and sub - combinations of the various features described above, as well as their variations and modifications, which will occur to those skilled in the art upon reading the above description and which are not disclosed in the prior art. Documents incorporated by reference into this patent application are considered an inseparable part of this application, unless any terms defined in these incorporated documents conflict with the definitions explicitly or implicitly given in this specification, in which case only the definitions in this specification should be considered.

Claims

1. A system, comprising: a display; and a processor configured to: receive a cardiac electrophysiology (EP) velocity vector map; calculate a set of directed graphs from at least some of the velocity vectors; use the directed graphs to identify corresponding origin velocity vectors on the EP velocity vector map; define one or more regions on the EP velocity vector map; determine whether the one or more regions contain a lesion source of arrhythmia based on the origin velocity vectors in each of the one or more regions; and visually present to a user on the display the regions on the EP map identified as containing the lesion source.

2. The system according to claim 1, wherein The processor is further configured to estimate the location of the lesion source within the region and visually present the location on the EP map.

3. The system according to claim 1, wherein, The processor is configured to calculate the set of directed graphs by arranging the corresponding velocity vectors according to the spatial and temporal proximity between the velocity vectors.

4. The system according to claim 3, wherein, The first velocity vector and the second velocity vector are considered to be spatially and temporally proximal if (i) the tail positions of the first velocity vector and the second velocity vector share the same local activation time (LAT) up to a threshold tolerance, and (ii) the tail positions are separated by no more than a threshold distance.

5. The system according to claim 1, wherein The processor is configured to identify the region by determining three or more origin vectors within a predefined spatial proximity to each other.

6. The system according to claim 1, wherein, The processor is configured to determine whether the region contains the lesion source by fitting a vector function to the velocity origin vectors in the region and performing vector calculus operations on the fitted vector function.

7. The system according to claim 6, wherein, The processor is configured to determine whether the region contains the lesion source by estimating whether the sign of the divergence of the fitted vector function in the region is positive.

8. The system according to claim 1, wherein, The processor is configured to calculate the set of directed graphs from at least some of the velocity vectors by performing steps including: assigning a cone with a predefined radius and a given solid angle to each velocity vector head; and generating a directed graph portion from the two vectors if the tail of another vector falls within the cone.

9. The system according to claim 1, wherein The processor is configured to use the directed graphs to identify the corresponding origin velocity vectors by identifying origin arcs and matching origin vectors to each origin arc.

10. A method, comprising: receiving a cardiac electrophysiology (EP) velocity vector map; calculating a set of directed graphs from at least some of the velocity vectors; using the directed graphs to identify corresponding origin velocity vectors on the EP velocity vector map; defining one or more regions on the EP velocity vector map; determining whether the one or more regions contain a lesion source of arrhythmia based on the origin velocity vectors in each of the one or more regions; and visually presenting to a user on the display the regions on the EP map identified as containing the lesion source.

11. The method according to claim 10, and including estimating the location of the lesion source within the region and visually presenting the location on the EP map.

12. The method according to claim 10, wherein, Calculating the set of directed graphs includes arranging corresponding velocity vectors based on the spatial and temporal proximity between the velocity vectors.

13. The method according to claim 12, wherein, The first velocity vector and the second velocity vector are considered to be spatially and temporally proximate if (i) the tail positions of the first velocity vector and the second velocity vector share the same local activation time (LAT) up to a threshold tolerance, and (ii) the tail positions are separated by no more than a threshold distance.

14. The method according to claim 12, wherein, Identifying the region includes determining three or more origin vectors that are within a predefined spatial proximity to each other.

15. The method according to claim 12, wherein, Determining whether the region contains the lesion source includes fitting a vector function to the velocity origin vectors in the region and performing vector calculus operations on the fitted vector function.

16. The method according to claim 15, wherein, Determining whether the region contains the lesion source includes estimating whether the sign of the divergence of the fitted vector function in the region is positive.

17. The method according to claim 10, wherein Calculating the set of directed graphs from at least some of the velocity vectors includes performing steps that include: Assigning a cone with a predefined radius and a given solid angle to each velocity vector head; and Generating a directed graph portion from the two vectors if the tail of another vector falls within the cone.

18. The method according to claim 10, wherein Using the directed graph to identify the corresponding origin velocity vectors includes identifying origin arcs and matching origin vectors to each origin arc.

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