Patent Description:
Electrophysiological (EP) cardiac mapping may use visualizations methods previously proposed in the patent literature, to ease an interpretation of an EP map. 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. Generally, the display is updated immediately following each local depolarization and persisting or gradually fading out until the next local depolarization. Finally, some or all isochrones may be displayed as curved lines on the cardiac surface, for instance at specific intervals since the start of depolarization. This reduces visual clutter and allows a more interpretable superposition of conduction velocity arrows.

As another example, <CIT> describes a method that includes accessing cardiac information acquired via a catheter located at various positions in a venous network of a heart of a patient. The cardiac information comprises position information, electrical information and mechanical information. The method maps local electrical activation times to anatomic positions to generate an electrical activation time map. The method maps local mechanical activation times to anatomic positions to generate a mechanical activation time map. The method further generates an electromechanical delay map by subtracting local electrical activation times from corresponding local mechanical activation times, and renders at least the electromechanical delay map to a display.

"<NPL>) describes a method of electrogram visualization conveying both timing and morphology as well as location of each point within the chamber being studied. Data were used from six patients who had undergone electrophysiological study with the Carto electroanatomic mapping system. Software was written to construct a three-dimensional surface from the imported electrogram locations. Electrograms were time gated and displayed as dynamic bars that extend out from this surface, changing in length and color according to the local electrogram voltage-time relationship to create a ripple map of cardiac activation.

"<NPL>) describes ripple mapping as a method of 3D intracardiac electrogram visualisation that allows activation of the myocardium to be tracked visually without prior assignment of local activation times and without interpolation into unmapped regions.

An embodiment of the present invention provides a method including receiving an anatomical map of at least a portion of a heart. Positions and respective electrocardiogram (ECG) signal amplitudes measured at the positions are received for at least a region of the anatomical map. The ECG signal amplitudes are interpolated to derive a surface representation of the ECG signal amplitudes over the region. The surface representation of the ECG signal amplitudes is presented overlaid on the anatomical map. The anatomical map presents Local Activation Times (LAT).

In some embodiments, presenting the surface representation includes visualizing respective values of the surface representation as topographical heights above the anatomical map.

In some embodiments, presenting the surface representation includes presenting a semi-transparent surface that retains the anatomical map visible.

In an embodiment, interpolating the ECG signal amplitudes includes forming a shape including the interpolated and measured ECG amplitude values.

There is additionally provided, in accordance with an embodiment of the present invention, a system including a memory and a processor. The memory is configured to store an anatomical map of at least a portion of a heart, and to store, for at least a region of the anatomical map, positions and respective electrocardiogram (ECG) signal amplitudes measured at the positions. The processor is configured to interpolate the ECG signal amplitudes to derive a surface representation of the ECG signal amplitudes over the region, and present the surface representation of the ECG signal amplitudes overlaid on the anatomical map. The anatomical map presents Local Activation Times (LAT).

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 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.

In some cases, the processor of the EP mapping system presents the measured EP map overlaid on a heart anatomy visualized by, for example, a volume (3D) rendering of at least a portion of the heart. Such an EP overlaid rendering may be very useful in diagnosing cardiac irregularities. For example, ECG "spikes" overlaid on an anatomical map may be used, where the height of the spikes gives a measure of the ECG signal amplitude at the spike position. The spike representation may indicate an anomalous conduction path causing an arrhythmia.

However, this kind of visualization often tends to be too coarse and/or hides other features of diagnostic value. Moreover, such spikes only give a value of the signal at the given position, not in any intermediate positions, causing discontinuities in visualization, and furthermore the spikes may hide map details beneath or behind the spikes.

Embodiments of the present invention that are described hereinafter use a processor to interpolate between measured values of the ECG signal at points near a selected location, and represent these interpolated values as topographical heights above the 3D rendering. The topographical heights are connected graphically to give a 3D surface referred to as a "sail," having a continuous ripple, instead of a collection of spikes. In an embodiment, the "sails" are made semi-transparent in order not to hide details.

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 overlay interpolated ECG ripples, that may be semi-transparent, 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) signal analysis 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, the signals analyzed are assumed to be intra-cardiac and/or extra-cardiac (body surface) electrocardiogram (ECG) potential-time relationships. In order to fully characterize such relationships, a processor <NUM> uses the ECG signals to produce an EP map, such as a local activation time (LAT) map. A method for generating an LAT map is described in<CIT>.

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, in which one or more electrophysiological parameters are overlaid. A LAT map is an example of an EP map, and thus also regarded as a type of anatomical map.

<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 a mapping procedure performed by a physician <NUM> using system <NUM>. A distal end <NUM> of probe <NUM> is assumed to have electrodes <NUM>. During the procedure patient <NUM> is assumed to be attached to a grounding electrode <NUM>. In addition, electrodes <NUM> are assumed to be attached to the skin of patient <NUM>, in the region of heart <NUM>. In an embodiment, probe <NUM> acquires local intra-cardiac ECG as the probe moves over a portion of the heart chamber. At these instances, probe <NUM> location is recorded as well. The measured signals are used, as noted above and among other usages, to create an LAT map of at least part of the wall tissue of heart <NUM> of a patient <NUM>.

System <NUM> is controlled by a system processor <NUM>, comprising a processing unit <NUM> communicating with a memory <NUM>. In some embodiments, a memory <NUM>, which is included in system processor <NUM>, stores an LAT and/or ECG map <NUM> of at least part of wall tissue of heart <NUM> of patient <NUM>. Processor <NUM> is typically mounted in a console <NUM>, which comprises operating controls <NUM>, typically including a pointing device <NUM> such as a mouse or trackball, that physician <NUM> uses to interact with the processor.

Processor <NUM> (specifically processing unit <NUM>) runs software, comprising a probe tracker module <NUM>, an ECG module <NUM>, and an ECG amplitude visualization module <NUM>, used for visualizing ECG amplitudes over a 3D rendering of a portion of heart <NUM> anatomy (i.e., in the form of "sails"), as described above and described in further detail below. ECG module <NUM> is coupled to receive actual electrical signals from electrodes <NUM> and electrodes <NUM>. The module is configured to analyze the actual signals and may present the results of the analysis in a standard ECG format, typically a graphical representation moving with time, on display <NUM>.

Probe tracker module <NUM> typically tracks the location of distal end <NUM> of probe <NUM> within the heart of patient <NUM>. The tracker module may use any method for location tracking probes known in the art. For example, module <NUM> may operate a magnetic-field-based location tracking sub-system. (For simplicity, components of such a sub-system are not shown in <FIG>. ) Using tracker module <NUM>, processor <NUM> is able to measure locations of distal end <NUM>. In addition, using both tracker module <NUM> and ECG module <NUM>, the processor is able to measure locations of the distal end, as well as LATs of the actual electrical signals detected at these particular locations.

Alternatively or additionally, tracker module <NUM> may track probe <NUM> by measuring impedances between electrode <NUM>, electrodes <NUM>, and electrodes <NUM>, as well as the impedances to other electrodes which may be located on the probe. (In this case electrodes <NUM> and/or electrodes <NUM> may provide both ECG and location tracking signals. ) The Carto3® system, produced by Biosense-Webster (Irvine, California), uses both magnetic field location tracking and impedance measurements for location tracking.

Results of the operations and visualizations performed by processor <NUM> are presented to physician <NUM> on a display <NUM>, which typically presents a graphic user interface to the physician, a visual representation of the ECG signals sensed by electrodes <NUM>, and/or an image or map of heart <NUM> while it is being investigated. In an embodiment, EP activation analysis module <NUM> presents to the physician a LAT map overlaid with the interpolated ECG amplitude "sails.

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 volume rendering showing ripple-mapping visualization of ECG amplitudes overlaid on a cardiac chamber <NUM> anatomy, in accordance with an embodiment of the present invention. In <FIG>, ECG measured values, i.e., spikes <NUM>, are overlaid on a grey-scale anatomical map, where the height of spikes <NUM> gives a measure of the ECG signal amplitude at the spike positions. As seen, the disclosed visualization method not only gives the value of the ECG spikes at the given position, but also at any intermediate positions, which forms sail <NUM> shapes of the local ECG amplitudes.

As noted above, to visualize ECG signals as disclosed, processor <NUM> interpolates values of ECG signals <NUM> at points near a selected location, and connects the topographical height values above the 3D rendering so as to produce the disclosed continuous ripple visualization. In an embodiment (not shown in <FIG>), processor <NUM> generates semi-transparent sails <NUM> in order not to hide details behind them (i.e., to show details of underlying map).

The example ripple-mapping visualization shown in <FIG> is chosen purely for the sake of conceptual clarity. Various additional visualization tools may apply, such a presenting numbers, a magnifying glass effect to view sails <NUM> in detail, and others.

<FIG> is flow chart that schematically illustrates a method for ripple-mapping visualization of ECG amplitudes shown in <FIG>, in accordance with an embodiment of the present invention. The algorithm, according to the presented embodiment, carries out a process that begins with processor <NUM> assigning measured ECG amplitudes <NUM> to respective locations over an anatomical map of a cardiac chamber (i.e., overlaid on the electro-anatomically - such as LAT - mapped surface of chamber <NUM>), at an ECG amplitude assigning step <NUM>.

Next, at interpolation step <NUM>, processor <NUM> interpolates over values of ECG at points near each location. Next, at each location, processor <NUM> connects measured and interpolated ECG amplitudes to create sails <NUM>, at an interconnecting ECG amplitudes 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 (LAT map with overlaid interpolated ECG amplitudes) 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 method, comprising:
receiving an anatomical map of at least a portion of a heart;
receiving, for at least a region of the anatomical map, positions and respective electrocardiogram (ECG) signal amplitudes measured at the positions;
interpolating the ECG signal amplitudes, to derive a surface representation of the ECG signal amplitudes over the region; and
presenting the surface representation of the ECG signal amplitudes overlaid on the anatomical map, wherein the anatomical map presents local activation times (LATs).