Patent Description:
Invasive cardiac techniques for mapping electrophysiological (EP) properties of cardiac tissue were previously proposed in the patent literature. For example, <CIT> describes an efficient system for diagnosing arrhythmias and directing catheter therapies that may allow for measuring, classifying, analyzing, and mapping spatial EP patterns within a body. The efficient system may further guide arrhythmia therapy and update maps as treatment is delivered. The efficient system may use a medical device having a high density of sensors with a known spatial configuration for collecting EP data and positioning data. Further, the efficient system may also use an electronic control system for computing and providing the user with a variety of metrics, derivative metrics, high definition (HD) maps, HD composite maps, and general visual aids for association with a geometrical anatomical model shown on a display device.

As another example, <CIT> describes a system for determining EP data, the system comprising an electronic control unit configured to acquire electrophysiology signals from a plurality of electrodes of one or more catheters, select at least one clique of electrodes from the plurality of electrodes to determine a plurality of local E field data points, determine the location and orientation of the plurality of electrodes, process the electrophysiology signals from the at least one clique from a full set of bi-pole sub-cliques to derive the local E field data points associated with the at least one clique of electrodes, derive at least one orientation independent signal from the at least one clique of electrodes from the information content corresponding to weighted parts of electrogram signals, and display or output catheter-orientation-independent EP information to a user or process.

<CIT> describes method and system for mapping an anatomical structure, that include sensing activation signals of intrinsic physiological activity with a plurality of mapping electrodes disposed in or near the anatomical structure, each of the plurality of mapping electrodes having an electrode location. A vector field map which represents a direction of propagation of the activation signals at each electrode location is generated to identify a signature pattern and a location in the vector field map according to at least one vector field template. A target location of the identified signature pattern is identified according to a corresponding electrode location.

Document <CIT> discloses a cardiac mapping system comprising a medical examination device to capture data over time at multiple sample locations over a surface of at least one chamber of a heart. The device includes a display screen and processing circuitry configured to: process the captured data to determine a description of a propagation of activation wavefronts associated with a plurality of activation times over the surface of the at least one chamber of the heart, calculate a plurality of activation wavefront propagation path traces wherein each one activation wavefront propagation path trace of the plurality of activation wavefront propagation path traces describes a point on one activation wavefront of the activation wavefronts being propagated over the surface of the at least one chamber of the heart according to an advancement of the one activation wavefront such that the plurality of activation wavefront propagation path traces describe the propagation of a plurality of different points according to corresponding ones of the activation wavefronts. The processor also prepares a visualization showing the plurality of activation wavefront propagation path traces on a representation of the at least one chamber of the heart; and render the visualization to the display screen.

Document <CIT> discloses a map of cardiac activation wavefronts that can be created from a plurality of mesh nodes, each of which is assigned a conduction velocity vector. Directed edges are defined to interconnect the mesh nodes, and weights are assigned to the directed edges, thereby creating a weighted directed conduction velocity graph. A user can select one or more points within the weighted directed conduction velocity graph (which do not necessarily correspond to nodes), and one or more cardiac activation wavefronts passing through these points can be identified using the weighted directed conduction velocity graph. The cardiac activation wavefronts can then be displayed on a graphical representation of the cardiac geometry.

The invention is defined by appended claim <NUM>.

Intracardiac electrophysiological (EP) mapping is a catheter-based method that is sometimes applied to characterize cardiac EP wave propagation abnormalities, such those that cause an arrhythmia. In a typical catheter-based procedure, a distal end of a catheter, which comprises multiple sensing-electrodes, is inserted into the heart to sense a set of data points comprising measured locations over a wall tissue of a cardiac chamber and a respective set of EP signals, from which the EP mapping system can produce a map, such as an EP map, of the cardiac chamber.

For diagnostics in particular, the propagation direction of the EP wave at a region of the wall tissue may also be needed. The propagation direction of the cardiac wave can be found by creating a particular EP timing diagram map, called local activation time (LAT) map, of regions of the cardiac chamber.

However, determining a propagation vector of an EP wave in the cardiac chamber is a time-consuming process for any given region. Typically, LATs for a number of locations around the region need to be calculated, and then the vector derived from the LATs and the positions of the locations. Embodiments of the present invention that are described hereinafter provide efficient systems configured to acquire EP data and automatically calculate such a propagation vector in real time for a region in a cardiac chamber.

Among other features, the disclosed systems may use, in a particular way, various types of multi-electrode catheters, such as a basket catheter or a multi-arm catheter (e.g., PentaRay™ or OctaRay™, made by Biosense-Webster). The multi-electrode catheter is brought into contact with tissue (e.g., pressed against tissue) at a region of the cardiac chamber so that its "pole" (e.g., a distal tip where the spines of the basket connect, or from where the multiple arms originate) is on the chosen cardiac tissue region, and electrodes on the spines/arms are in contact with wall tissue at a tissue region of the cardiac chamber to acquire EP signals.

In an embodiment, to calculate a propagation vector, a processor first divides (e.g., arbitrarily divides) the cardiac tissue region where the electrode locations are into two sections, using a virtual plane containing the axis of the catheter. Then, using EP signals acquired from each electrode, the processor calculates the LAT values at the electrode locations (i.e., respective tissue locations) in each section to find a first section of the two sections having the smaller average LAT values, and a second section of the two sections having higher average value.

Then, the processor determines a first representative location in the first section, and a second representative location in the second section. The processor calculates between the first and second representative locations a propagation vector indicative of propagation of an EP wave that has generated the EP signals, and presents the propagation vector to a user.

In one embodiment, for the section with the lower average LAT value, the processor finds the location with the minimum LAT value therein. For the section with the higher average LAT value, the processor finds the location with the maximum LAT value therein. From the known displacements (distance and direction) between the two locations, and the respective known time difference in LAT values, the processor calculates a propagation (e.g., velocity) vector (speed and direction) of the EP wave. The processor may then draw an arrow, corresponding to the vector, on a map of the cardiac chamber. The length of the arrow, its color or a graphical pattern (e.g., gradient or hatched patterns) may be set to correspond to the speed.

In another embodiment, rather than calculate the velocity vector from the minimum of the LAT values at the section with the lower average LAT value to the maximum of the LAT values at the section with the higher average LAT value, the processor calculates a vector between a center-of-mass wall tissue location of the lower average LAT value and a center-of-mass wall tissue location of the higher average LAT value. To this end, the processor performs a center-of-mass calculation in the first section of a first wall tissue location of the lower average LAT value and a center-of-mass calculation in the second section of a second wall tissue location of the higher average LAT value. Then the processor calculates a center-of-mass propagation vector between the first and second center-of-mass locations of an EP wave that presumably generated the EP signals, and presents the center-of-mass propagation vector to a user. The center-of-mass calculations typically include calculating a weighted average of each center-of-mass location using two or more LAT values of each section as weights.

In some clinical cases, such as in a reentry type of arrhythmia, while the catheter is in an approximately fixed position, the velocity vector oscillates in direction (backwards and forwards). This occurs typically if the catheter is at a junction, where the wave actually alternates in direction, for example, due to the wave encountering aberrant unidirectional propagation-blocking tissue. In this case the processor calculates an additional vector, and the two vectors may be displayed on the screen as two arrows distinguished by a different brightness/thickness/length/color according to their relative magnitude.

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 systems for efficient derivation and clear presentation of propagation direction(s) of an EP wave may improve catheter-based arrhythmia diagnostics and treatment procedures.

<FIG> is a schematic, pictorial illustration of an electrophysiological (EP) mapping system <NUM> comprising different possible multi-electrode catheters, in accordance with embodiments 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 analyzed signals are assumed to be intra-cardiac electrogram potential-time relationships. In order to fully characterize such relationships, the signals at various locations need to be referenced in time to each other, such as is done during LAT map generation. The time referencing is accomplished by measuring relative to a reference time (e.g., an instance in time), such as the beginning of each QRS complex of an ECG reference signal (i.e., the beginning of every heartbeat). The method for generating an LAT map is described in<CIT>, cited above.

As noted above, system <NUM> comprises a multi-electrode catheter, which can be, among numerous possible options, a basket catheter <NUM> or a multi-arm catheter <NUM> (e.g., a PentaRay™ catheter), both of which are shown in inset <NUM>. The description hereinafter collectively calls the above catheter options, "catheter <NUM>/<NUM>," which means the embodiments described hereinafter hold for either of these multi-electrode catheter types. Each catheter tip <NUM>, <NUM> extends along longitudinal axis L-L.

Multi-electrode catheter <NUM>/<NUM> is inserted by a physician <NUM> through the patient's vascular system into a chamber or vascular structure of a heart <NUM>. Physician <NUM> brings the catheter's distal tip <NUM>/<NUM> into contact with (e.g., presses the tip distally against) wall tissue <NUM> of a cardiac chamber <NUM>, at an EP mapping target tissue site. The catheter typically comprises a handle <NUM> which has suitable controls to enable physician <NUM> to steer, position and orient the distal end of the catheter as desired for EP mapping.

The multi-electrode catheter <NUM>/<NUM> is coupled to a console <NUM>, which enables physician <NUM> to observe and regulate the functions of the catheter. To aid physician <NUM>, the distal portion of the catheter may contain various sensors, such as contact force sensors (not shown) and a magnetic sensor <NUM>/<NUM> that provides position, direction, and orientation signals to a processor <NUM>, located in a console <NUM>. Processor <NUM> may fulfill several processing functions as described below. In particular, electrical signals can be conveyed to and from heart <NUM> from electrodes <NUM>/<NUM> located at or near the distal tip <NUM> of catheter <NUM>/<NUM> via cable <NUM> to console <NUM>. Pacing signals and other control signals may be conveyed from console <NUM> through cable <NUM> and electrodes <NUM>/<NUM> to heart <NUM>.

Console <NUM> includes a monitor <NUM> driven by processor <NUM>. Signal processing circuits in an electrical interface <NUM> typically receive, amplify, filter, and digitize signals from catheter <NUM>/<NUM>, including signals generated by the above-noted sensors and the plurality of sensing electrodes <NUM>. The digitized signals are received and used by console <NUM> and the positioning system to compute the position and orientation of catheter <NUM>/<NUM> and to analyze the EP signals from electrodes <NUM>/<NUM> as described in further detail below.

During the disclosed procedure, the respective locations of electrodes <NUM>/<NUM> are tracked. The tracking may be performed, for example, using the CARTO® <NUM> system, produced by Biosense-Webster. Such a system measures impedances between electrodes <NUM>/<NUM> and a plurality of external electrodes <NUM> that are coupled to the body of the patient. For example, three external electrodes <NUM> may be coupled to the patient's chest, and another three external electrodes may be coupled to the patient's back. (For ease of illustration, only chest electrodes are shown in <FIG>. Wire connections <NUM> link the console <NUM> with body surface electrodes <NUM> and other components of a positioning subsystem to measure location and orientation coordinates of catheter <NUM>/<NUM>. The method of tracking electrode <NUM> positions based on electrical signals, named Active Current Location (ACL), is implemented in various medical applications, as, for example, the aforementioned CARTO®<NUM> system. Details of an ACL subsystem and process are provided in <CIT>, which is assigned to the assignee of the present patent application.

In some embodiments, system <NUM> comprises, in addition to, or instead of, the ACL tracking subsystem, a magnetic position tracking subsystem that determines the position and orientation of magnetic sensor <NUM>, at a distal end of catheter <NUM>/<NUM>, by generating magnetic fields in a predefined working volume, and sensing these fields at the catheter using field generating coils <NUM>. As electrodes <NUM>/<NUM> have known locations on arms <NUM>/<NUM>, and known relationships to one another, once catheter <NUM>/<NUM> is tracked magnetically in the heart, the location of each of electrodes <NUM>/<NUM> in the heart becomes known. A suitable magnetic position tracking subsystem is described in <CIT> and <CIT>.

Based on the EP signals from electrodes <NUM>/<NUM> having tracked locations, electrical activation maps may be prepared, according to the methods disclosed in <CIT>, and <CIT>, and <CIT>.

Processor <NUM> uses software stored in a memory <NUM> to operate system <NUM>. The software 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 as disclosed herein, including in <FIG>, that enables processor <NUM> to perform the disclosed steps, as further described below.

The example illustration shown in <FIG> is chosen purely for the sake of conceptual clarity. Other types of EP sensing geometries, such as of a balloon catheter comprising electrode segments, described in <CIT>, may also be employed.

System <NUM> typically comprises additional modules and elements that are not directly related to the disclosed techniques, and thus are intentionally omitted from <FIG> and from the corresponding description. The elements of system <NUM> described herein may be further applied, for example, to control an ablation of tissue of heart <NUM>.

<FIG> are schematic distal views of electrodes <NUM>/<NUM> of one of the catheters of <FIG> in contact with tissue and measuring electrophysiological (EP) signals, in accordance with embodiments of the present invention. The figures further show tissue <NUM> and a distal portion <NUM> of the spines or arms <NUM>/<NUM> of catheter <NUM>/<NUM> that are pressed against tissue <NUM>, as viewed at a distal direction from a location proximally to the spines or arms on the axis L-L of the catheter. The spines or arms <NUM>/<NUM> are coupled together at distal tip <NUM>/<NUM> of the catheter.

In some embodiments, processor <NUM> divides the spines/arms into two sections, using a virtual plane <NUM> containing the axis L-L of the catheter. Processor <NUM> may select the sections, i.e., select plane <NUM>, arbitrarily or in accordance with a certain selection criterion. For example, the virtual plane <NUM> is configured to intersect with the central longitudinal axis L-L of the catheter and may not intersect with any of the spine or arm of catheter <NUM> or <NUM>. Then, using EP signals acquired from each electrode <NUM>/<NUM>, the processor calculates the LAT values at the electrode locations in each section. Processor <NUM> then finds which of the two sections (S1 or S2) is characterized by lower average LAT values (e.g., has the lower average LAT value out of the two sections), and which is characterized by higher average LAT values (e.g., has the higher average value out of the two sections).

In the embodiment shown in <FIG>, virtual plane <NUM> separates the spines or arms into two sections, a first section S1 with the lower average LAT value and another or second section S2 with a higher average LAT value. The first section S1 is determined by the processor to find the minimum LAT value, and its location is determined to be at point <NUM> (which may be the location of a sensing electrode on the spine or arm of a catheter <NUM> or <NUM>). For the other or second section S2 with the higher average LAT value, the processor finds the maximum LAT value, and its location <NUM> (which may be the location of a sensing electrode on the spine or arm of a catheter <NUM> or <NUM>). Locations <NUM> and <NUM> are referred to herein as "representative locations" because each of them represents its entire respective section by a single data point.

From the known displacements (distance and direction) between the two representative locations, and the known times (the difference in LAT values), the processor calculates a velocity vector (speed and direction) of an EP wave <NUM> that generated the signals as it propagates in tissue under the catheter. The processor may then draw an arrow <NUM>, corresponding to the vector, on a map of the cardiac chamber and provide this in display screen <NUM>. The length of arrow <NUM>, and/or its color, may be set to correspond to the speed.

In the embodiment shown in <FIG>, rather than calculating the velocity vector from the minimum of the LAT values at the section with the lower average LAT value to the maximum of the LAT values at the section with the higher average LAT value, the vector is calculated between the centers-of-mass locations of the lower average and higher average LAT values, using the following equation to find the center of mass locations: <MAT>.

In <FIG>, by way of example, i=<NUM>,<NUM> for each center of mass location. That is, center-of-mass wall tissue location <NUM> is calculated from Eq. <NUM> using LAT values and respective locations <NUM> and <NUM>, and center-of-mass wall tissue location <NUM> is calculated using LAT values and respective locations <NUM> and <NUM>. The processor may then draw an arrow <NUM> corresponding to the vector between locations <NUM> and <NUM>. Thus, in the example of <FIG>, the centers-of-mass of the two sections (locations <NUM> and <NUM>) serve as the representative locations. In alternative embodiments, processor <NUM> may choose the representative locations in the two sections in any other suitable way.

The illustrations in <FIG> are conceptual and brought by way of example. Actual catheter structure may vary. For example, the number of spines or arms may be larger than shown.

<FIG> is a schematic distal view of electrodes <NUM>/<NUM> of one of the catheters of <FIG> in contact with tissue and measuring electrophysiological (EP) signals, in accordance with another embodiment of the present invention. The catheter <NUM>/<NUM> layout is the same as in <FIG>, but with the catheter placed at a different tissue location where EP wave reentry occurs.

As noted above, in case of a reentry type of arrhythmia, the velocity vector at the region may oscillate in direction (backwards and forwards). This occurs typically if the catheter is at a junction where EP wave <NUM> is actually alternating in direction, for example, due to the wave encountering an aberrant unidirectional propagation blocking tissue <NUM>. In this case, the two EP wave vectors (one of incident EP wave <NUM> and the other of reentry EP wave <NUM>) may be displayed on the screen as two respective arrows, <NUM> and <NUM>, each with a different brightness/thickness/length/color according to their relative magnitudes. In <FIG> the vectors are calculated using the center-of-mass calculation method of <FIG>. One respective vector points from center-of-mass location <NUM> to center-of-mass location <NUM>, and the other from center-of-mass location <NUM> to center-of-mass location <NUM>.

<FIG> is a flow chart that schematically illustrates an algorithm for estimating and presenting a propagation vector of an electrophysiological (EP) wave <NUM>, which may be used in an embodiment of the present invention. The algorithm, according to the presented embodiment, carries out a process that begins with physician <NUM> pressing catheter <NUM>/<NUM> against cardiac tissue region to bring part of electrodes <NUM>/<NUM> to contact with tissue, at a catheter placement step <NUM>.

Then, system <NUM> measures electrode locations over wall tissue <NUM> of cardiac chamber <NUM> and a respective set of EP signals at the locations, generated by an EP wave <NUM>, at a measurement step <NUM>.

Next, processor <NUM> arbitrarily divides the region into two sections, at a region division step <NUM>.

Next, processor <NUM> calculates an LAT value at each electrode location, at an LAT calculation step <NUM>.

Next, at average LAT calculation step <NUM>, processor <NUM> calculates the average LAT value per each section. Typically, one section has a lower average LAT value than the other.

Next, at average LAT location calculation step <NUM>, processor <NUM> calculates center-of-mass locations of the lower and higher average LAT values, using the method described in <FIG>.

Using the center-of-mass locations, processor <NUM> calculates the center-of-mass EP wave propagation vector of EP wave <NUM>, at a vector calculation step <NUM>.

Finally, at a propagation-vector presentation step <NUM>, processor <NUM> overlays (e.g., draws) an arrow, corresponding to the vector, on a map of the cardiac chamber as shown on display <NUM> in <FIG>. The length of the arrow <NUM> or <NUM>, and/or its color, may be set to correspond to the speed.

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, such as operating other sensors mounted on the catheter, such as contact force sensors, which 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>) configured to receive (i) multiple electrophysiological (EP) signals acquired by multiple electrodes (<NUM>/<NUM>) of a multi-electrode catheter (<NUM>/<NUM>) that are in contact with tissue (<NUM>, <NUM>) in a region of a cardiac chamber, and (ii) respective tissue locations at which the electrodes acquired the EP signals; and
a processor (<NUM>), which is configured to:
divide the region into two sections;
using the EP signals acquired by the electrodes, calculate local activation time (LAT) values for the respective tissue locations, and find a first section of the two sections having a smaller average LAT value, and a second section of the two sections having a higher average value;
determine a first representative location in the first section, and a second representative location in the second section;
calculate between the first and second representative locations a propagation vector indicative of propagation of an EP wave that has generated the EP signals;
wherein the processor is further configured to, in case a reentering EP wave is detected, calculate an additional propagation vector for the reentering EP wave; and
present the propagation vectors to a user.