Patent Description:
Visualization methods of a cardiac electrophysiological (EP) map, to ease an interpretation of the EP map, were previously proposed in the patent literature. For example, <CIT> describes a method for determining EP properties of cardiac tissue in order classify an arrhythmia. An eccentricity parameter reflecting the uniformity of a local conduction velocity, and divergence and curl-like sums or closed path integral parameters associated with the local velocity vectors are provided, and a rhythm classification responsive to catheter movement is displayed, thereby facilitating identification of types and causes of arrhythmia disorders. In an embodiment, conduction velocity vector maps are coupled with local activation time (LAT) maps.

As another example, <CIT> describes a method of diagnosing an abnormal condition in a biological structure, such as the heart, including the steps of measuring a physiological response in at least three sampled points on a surface of the biological structure, calculating a vector function related to the response, displaying a representation of the vector function, and inferring the abnormal condition from the representation. The method is deemed therein as useful for diagnosing cardiac arrhythmias, in which case the physiological response is a voltage, from which is inferred a local activation time and the vector function is a gradient of the local activation time, specifically, a conduction velocity.

<CIT> discloses a method of diagnosing an abnormal condition in a biological structure, such as the heart, including the steps of measuring a physiological response at at least three sampled points on a surface of the biological structure, calculating a vector function related to the response, displaying a representation of the vector function, and inferring the abnormal condition from the representation. The method is particularly useful for diagnosing cardiac arrhythmias, in which case the physiological response is a voltage, from which is inferred a local activation time and the vector function is a gradient of the local activation time, specifically, a conduction velocity.

There is provided, in accordance with the present invention, a system including an interface and a processor. The interface 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. The processor is configured to nonlinearly scale the magnitudes, and to present scaled vectors, having the scaled magnitudes, overlaid on the anatomical map. 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 by emphasizing magnitude differences within the intermediate-magnitude region relative to the low-magnitude region and the high-magnitude region.

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. This step is not part of the claimed invention. Based on these acquired signals, a processor of the mapping system generates the required EP map.

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).

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.

The present invention uses a non-uniform scaling function in form of a nonlinear scaling function. In embodiments of the present invention described hereinafter, the non-linear scaling function is used to suppress changes in the low and high velocities and at least retain or emphasize changes in the intermediate range of velocities. 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. In some embodiments of the present invention, high weighting is applied on the intermediate range, because the intermediate range is expected to be more representative of the actual velocity of the propagation wave.

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.

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.

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.

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.

<FIG> is a schematic, pictorial illustration of a cardiac three-dimensional (3D) navigation and electrophysiological (EP) mapping system <NUM>, in accordance with an embodiment of the present invention. System <NUM> 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 <NUM> 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 <NUM>.

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

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

System <NUM> is controlled by a system processor <NUM> in communication with a memory <NUM>. In some embodiments, processor <NUM> uses memory <NUM> for storing EP wave velocity map <NUM> of at least part of wall tissue of heart <NUM> of patient <NUM>. Processor <NUM> is typically mounted in a console <NUM>.

As seen in an inset <NUM>, EP wave vector map <NUM> comprises a plurality of velocity vectors <NUM> (not all labeled for the sake of simplicity) describing the propagation velocity of activation wavefronts associated with, for example, the activation times. Each vector <NUM> 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.

In particular, as seen in inset <NUM>, EP wave vector map <NUM> comprises a plurality of velocity vectors <NUM> 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>. 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 <NUM>.

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.

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

The software run by processor <NUM> may be downloaded to processor <NUM> 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 <NUM> runs a dedicated algorithm that enables processor <NUM> to perform the disclosed steps, as described below.

<FIG> is a graph of a sigmoid function <NUM> used by the processor of mapping system <NUM> of <FIG> to generate EP map <NUM> shown in <FIG>, in accordance with an embodiment of the present invention.

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 <NUM> 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 <NUM> 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.

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

<FIG> is flow chart that schematically illustrates a method and algorithm for nonlinearly scaling wave propagation presented in EP map <NUM> using the sigmoid function <NUM> of <FIG>, in accordance with an embodiment of the present invention. The method is not part of the claimed invention.

The algorithm, according to the presented example, carries out a process that begins with processor <NUM> receiving a set of EP propagation velocity vectors having a range of magnitudes, at an EP mapping data receiving step <NUM>.

Next, at nonlinear scaling step <NUM>, processor <NUM> 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>.

Next, processor <NUM> overlays the nonlinearly scaled EP velocity vectors on an anatomical rendering of a heart to obtain an EP map such as EP map <NUM> of <FIG>, at a scaled EP map generation step <NUM>. In an embodiment, processor <NUM> further makes sails <NUM> semi-transparent, at a sail visualization step <NUM>. Processor <NUM> presents the resulting visualization (nonlinearly scaled EP wave velocities) to physician <NUM> on display <NUM>.

The example flow chart shown in <FIG> 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 <NUM>. Such additional steps have been omitted from the disclosure herein purposely on order to provide a more simplified flow chart.

Claim 1:
A system (<NUM>), comprising:
an interface (<NUM>), which is configured to receive, for at least a region of an anatomical map of at least a portion of a heart (<NUM>), positions and respective electrophysiological (EP) wave propagation velocity vectors (<NUM>), the vectors having respective magnitudes; and
a processor (<NUM>), which is configured to:
scale the magnitudes; and
present scaled vectors, having the scaled magnitudes, overlaid on the anatomical map (<NUM>); and
characterized in that 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.