WEIGHTING PROJECTED ELECTROPHYSIOLOGICAL WAVE VELOCITY WITH SIGMOID CURVE

Abstract

A method includes receiving, for at least a region of an anatomical map of at least a portion of a heart, positions and respective electrophysiological (EP) wave propagation velocity vectors, the vectors having respective magnitudes. The magnitudes are nonlinearly scaled. Scaled vectors having the scaled magnitudes, are presented by being overlaid on the anatomical map.

Claims

1. A method, comprising: receiving, for at least a region of an anatomical map of at least a portion of a heart, positions and respective electrophysiological (EP) wave propagation velocity vectors, the vectors having respective magnitudes; nonlinearly scaling the magnitudes; and presenting scaled vectors, having the scaled magnitudes, overlaid on the anatomical map.

2. The method according to claim 1, wherein nonlinearly scaling the magnitudes comprises: dividing a range of the magnitudes into a low-magnitude region, a high-magnitude region, and an intermediate-magnitude region between the low-magnitude region and the high-magnitude region; and emphasizing magnitude differences within the intermediate-magnitude region, relative to the low-magnitude region and the high-magnitude region.

3. The method according to claim 1, wherein nonlinearly scaling the magnitudes comprises applying a sigmoid function to the magnitudes.

4. The method according to claim 1, wherein presenting the scaled vectors comprises visualizing the scaled vectors as arrows.

5. A system, comprising: an interface, which is configured to receive, for at least a region of an anatomical map of at least a portion of a heart, positions and respective electrophysiological (EP) wave propagation velocity vectors, the vectors having respective magnitudes; and a processor, which is configured to: nonlinearly scale the magnitudes; and present scaled vectors, having the scaled magnitudes, overlaid on the anatomical map.

6. The system according to claim 5, wherein the processor is configured to nonlinearly scale the magnitudes by: dividing a range of the magnitudes into a low-magnitude region, a high-magnitude region, and an intermediate-magnitude region between the low-magnitude region and the high-magnitude region; and emphasizing magnitude differences within the intermediate-magnitude region relative to the low-magnitude region and the high-magnitude region.

7. The system according to claim 5, wherein the processor is configured to nonlinearly scale the magnitudes by applying a sigmoid function to the magnitudes.

8. The system according to claim 5, wherein the processor is configured to present the scaled vectors by visualizing the scaled vectors as arrows.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a schematic, pictorial illustration of a cardiac three-dimensional (3D) navigation and electrophysiological (EP) mapping system, in accordance with an embodiment of the present invention;

[0011] FIG. 2 is a graph of a sigmoid function used by the processor of the mapping system of FIG. 1 to generate the EP map shown in FIG. 1, in accordance with an embodiment of the present invention; and

[0012] FIG. 3 is flow chart that schematically illustrates a method and algorithm for nonlinearly scaling wave propagation presented in an EP map using the sigmoid function of FIG. 2, in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Overview

[0013] In order to characterize cardiac electrophysiological (EP) abnormalities of a patient, a catheter-based EP mapping system may be used for generating an EP map of least part of the heart of the patient, such as an EP map of a cardiac chamber. In a typical catheter-based EP mapping procedure, a distal end of a catheter, which comprises one or more sensing electrodes, is inserted into the heart to sense EP signals. As a physician operating the system moves the distal end inside the heart, the EP mapping system acquires EP signals at various cardiac locations, as well as the respective positions of the distal end. Based on these acquired signals, a processor of the mapping system generates the required EP map.

[0014] Typically, the processor of the EP mapping system presents the measured EP map, for example a map of EP wavefront propagation, overlaid (e.g., projected) on a heart anatomy visualized by, for example, a volume (3D) rendering of at least a portion of the heart. Such an overlaid rendering may be very useful in diagnosing cardiac irregularities. For example, the processor may overlay EP wavefront velocity vectors on an anatomical map, where the magnitude and direction of the vectors give a measure of the cardiac electrical activity. An aggregate of such vectors may indicate a clinical pattern, such as an anomalous conduction path causing an arrhythmia (e.g., a rotor).

[0015] Various methods can be used for calculating the velocity of the wave velocity in the heart, and the velocity may be displayed as described above. However, a surgeon observing the velocities is not typically interested in value differences of the velocities at their extremities, i.e., when the velocities are very low or very high. Typically, the surgeon is mostly interested in differences in values in an intermediate range of velocities.

[0016] Embodiments of the present invention that are described hereinafter use a non-uniform scaling function (e.g., a nonlinear scaling function) to suppress changes in the low and high velocities and at least retain or emphasize changes in the intermediate range of velocities. In particular, the disclosed technique applies a processor to put a low weighting on the very high values (magnitude of the velocity vector) and on the very low values, because these value ranges are suspected of containing outliers due to errors or noise. High weighting may be applied on the intermediate range, because the intermediate range is expected to be more representative of the actual velocity of the propagation wave.

[0017] To this end, a processor applies a nonlinear scaling function to the magnitudes of the EP wavefront propagation vectors, to redraw the EP wavefront propagation. The scaled vectors are accordingly overlaid on a heart anatomy. A user may look at the original EP map and/or at the nonlinearly scaled map.

[0018] Examples of a nonlinear scaling function that can be used include a sigmoid function, a suitable polynomial function and a piecewise linear function, to name only a few.

[0019] Typically, the processor is programmed in software containing a particular algorithm that enables the processor to conduct each of the processor-related steps and functions outlined above.

[0020] The disclosed visualization technique to nonlinearly scale EP wavefront propagation on 3D cardiac anatomy may improve the diagnostic value of catheter-based EP mapping procedures.

System Description

[0021] FIG. 1 is a schematic, pictorial illustration of a cardiac three-dimensional (3D) navigation and electrophysiological (EP) mapping system 21, in accordance with an embodiment of the present invention. System 21 may be configured to analyze substantially any physiological parameter or combinations of such parameters. In the description herein, by way of example, EP signals analyzed are assumed to be potential-spatiotemporal relationships of intra-cardiac electrograms (EGM) and/or extra-cardiac (body surface) electrocardiograms (ECG). In order to fully characterize such relationships, a processor 28 uses the ECG signals to produce one or more EP maps, such as a local activation time (LAT) map and/or an EP wave vector map 31.

[0022] FIG. 1 shows an investigative procedure wherein system 21 measures actual electrical activity of a heart 23 using a probe 29. Typically, probe 29 comprises a catheter which is inserted into the body of patient 25 during an EP mapping procedure performed by a physician 27 using system 21. A distal end assembly 32 of probe 29 is assumed to have multiple electrodes 22. In the shown embodiment, distal end assembly 32 is multi-arm type (with five arms 20), though the distal end may have any other shape, such as a basket or a loop.

[0023] The measured EP signals are inputted to processor 28 via interface circuits 35, and, as noted above and among other usages, are used to create EP wave velocity map 31, presented on a display 26, of at least part of the wall tissue of heart 23 of a patient 25. In general, display 26, which typically presents a graphic user interface to the physician, provides a visual representation of the EP signals sensed by electrodes 22, and/or an image and/or map 31 of heart 23 while it is being investigated.

[0024] System 21 is controlled by a system processor 28 in communication with a memory 33. In some embodiments, processor 28 uses memory 33 for storing EP wave velocity map 31 of at least part of wall tissue of heart 23 of patient 25. Processor 28 is typically mounted in a console 34.

[0025] As seen in an inset 45, EP wave vector map 31 comprises a plurality of velocity vectors 75 (not all labeled for the sake of simplicity) describing the propagation velocity of activation wavefronts associated with, for example, the activation times. Each vector 75 is visualized as an arrow that is overlaid at a respective position of map and has a respective magnitude and a respective direction. The magnitude of the arrow is indicative of (although not necessarily proportional to, as will be explained below) the magnitude of the EP wave at the respective position. The direction of the arrow is indicative of the direction of the EP wave at the respective position.

[0026] In particular, as seen in inset 45, EP wave vector map 31 comprises a plurality of velocity vectors 75 that utilize the aforementioned non-uniform scaling function (e.g., sigmoid function) to emphasize magnitude differences in a selected range of vector magnitudes that is of interest. Non-uniform scaling described in greater detail in FIG. 2. Extreme ends of the range of velocity vector magnitudes, i.e., very small and very large vectors, as defined below, undergo weaker scaling to downplay differences that are irrelevant to a viewer of EP wave vector map 31.

[0027] In the context of this disclosure, the term “anatomical map” refers to a map that models the 3D shape of at least a portion of the heart, and may have one or more parameters overlaid thereon. An EP map is one special case of an anatomical map, with which one or more electrophysiological parameters are overlaid. An LAT map or an EP wave map is an example of an EP map, and thus also regarded as a type of anatomical map.

[0028] To produce a map such as map 31, processor 28 typically tracks the location of distal end 32 of probe 29 within heart 23 of patient 25. The processor may use any method for location tracking probes known in the art. For example, processor 28 may track probe distal end assembly 32 by measuring impedances between electrode 22 and external patch electrodes 24 attached to patient's 25 skin (only one patch electrode is shown for clarity). The Carto3® system, produced by Biosense-Webster (Irvine, Calif.) uses such impedance measurements for location tracking.

[0029] The software run by processor 28 may be downloaded to processor 28 in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. In particular, processor 28 runs a dedicated algorithm that enables processor 28 to perform the disclosed steps, as described below.

Weighting Projected EP Wave Velocity with Sigmoid Curve

[0030] FIG. 2 is a graph of a sigmoid function 200 used by the processor of mapping system 21 of FIG. 1 to generate EP map 31 shown in FIG. 1, in accordance with an embodiment of the present invention.

[0031] The graph has a horizontal axis representing the calculated wave velocity magnitudes before scaling, and a vertical axis representing the wave velocity magnitudes after scaling (the magnitudes of vectors 75 that are displayed to the user). The range of magnitudes before scaling is divided into three regions: A for low velocities, B for intermediate velocities, and C for high velocities. Applying sigmoid curve 200 to the calculated magnitudes yields small changes in the displayed values in region A and region C, (i.e., weak scaling). However, in region B, which corresponds to intermediate velocity values, changes in magnitude are emphasized (i.e., undergo strong scaling) in the displayed value.

[0032] FIG. 2 is brought by way of example. While FIG. 2 shows a sigmoid function, any other suitable nonlinear function may be used, such as a polynomial or piecewise linear function.

[0033] FIG. 3 is flow chart that schematically illustrates a method and algorithm for nonlinearly scaling wave propagation presented in EP map 31 using the sigmoid function 200 of FIG. 2, in accordance with an embodiment of the present invention.

[0034] The algorithm, according to the presented embodiment, carries out a process that begins with processor 28 receiving a set of EP propagation velocity vectors having a range of magnitudes, at an EP mapping data receiving step 302.

[0035] Next, at nonlinear scaling step 304, processor 28 applies a nonlinear scaling function (e.g., a sigmoid function) over the range to the vectors, to nonlinearly scale the vectors as described in FIG. 2.

[0036] Next, processor 28 overlays the nonlinearly scaled EP velocity vectors on an anatomical rendering of a heart to obtain an EP map such as EP map 31 of FIG. 1, at a scaled EP map generation step 306. In an embodiment, processor 40 further makes sails 60 semi-transparent, at a sail visualization step 76. Processor 28 presents the resulting visualization (nonlinearly scaled EP wave velocities) to physician 27 on display 26.

[0037] The example flow chart shown in FIG. 3 is chosen purely for the sake of conceptual clarity. The present embodiment also comprises additional steps of the algorithm. Examples include additional visualizations, such as conduction arrows between and under sails 60. Such additional steps have been omitted from the disclosure herein purposely on order to provide a more simplified flow chart.

[0038] It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered.