Patent Publication Number: US-2021177294-A1

Title: Automated Graphical Presentation of Electrophysiological Parameters

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to electrophysiological measurements, and particularly to apparatus and methods for automated mapping of electrophysiological parameters. 
     BACKGROUND 
     An electrophysiological (EP) map of a tissue of a patient is generated by positioning one or more electrodes on a region of the tissue, acquiring an EP signal of the region, and then repeating the process for a different region. EP parameters are extracted from the EP signals in each region of measurement, and then displayed over an image of the tissue. 
     SUMMARY 
     Embodiments of the present invention that are described hereinbelow provide improved methods and apparatus for mapping of electrophysiological parameters. 
     There is therefore provided, in accordance with an embodiment of the present invention, a medical apparatus, which includes a probe configured for insertion into a body of a patient, wherein the probe includes one or more electrodes configured to contact tissue of a region within the body. The apparatus further includes a display screen, and a position-tracking system configured to acquire position coordinates of the one or more electrodes within the body, and a processor. A processing unit is configured to acquire respective electrophysiological signals from the one or more electrodes while the one or more electrodes are held stationary at respective locations in the region over at least a preset length of time, to extract respective electrophysiological parameters from the electrophysiological signals acquired by the one or more electrodes at the respective locations, and to compute a respective measure of consistency of the respective electrophysiological parameters extracted from the electrophysiological signals acquired by the electrodes over the preset length of time at each of the respective locations. 
     The processing unit is further configured to render to the display screen a three-dimensional (3D) map of the tissue while superimposing on the map, responsively to the position coordinates, a visual indication of the extracted electrophysiological parameters at the respective locations for which the respective measure of consistency satisfied a predefined consistency criterion, and to discard automatically from the map the electrophysiological parameters for which the respective measure of consistency did not satisfy the predefined consistency criterion. 
     In a disclosed embodiment, the electrophysiological parameter includes a local activation time (LAT) in a heart of the patient, and the measure of consistency is indicative of a variation of the LAT. Additionally or alternatively, the measure of consistency includes a peak-to-peak variation of the LAT at any given location, and the consistency criterion requires that the peak-to-peak variation of the LAT not exceed a predefined limit. 
     In another embodiment, the electrophysiological parameter includes an electrophysiological voltage, and the measure of consistency is indicative of a variation of the electrophysiological voltage. Additionally or alternatively, the measure of consistency includes a peak-to-peak variation of the electrophysiological voltage at any given location, and the consistency criterion requires that the peak-to-peak variation of the electrophysiological voltage not exceed a predefined limit. 
     In yet another embodiment, the 3D map is rendered in a background color, and the visual indication includes other colors superimposed on the background color at the respective locations to indicate a value of the extracted electrophysiological parameter. 
     There is also provided, in accordance with an embodiment of the present invention, a method for electrophysiological mapping. The method includes acquiring respective electrophysiological signals from one or more electrodes on a probe in contact with tissue of a region within a body of a patient while the one or more electrodes are held stationary at respective locations in the region over at least a preset length of time and while acquiring position coordinates of the one or more electrodes. Respective electrophysiological parameters are extracted from the electrophysiological signals acquired by the one or more electrodes at the respective locations, and a respective measure of consistency is computed of the respective electrophysiological parameters extracted from the electrophysiological signals acquired by the electrodes over the preset length of time at each of the respective locations. The method further includes displaying a three-dimensional (3D) map of the tissue while superimposing on the map, responsively to the position coordinates, a visual indication of the extracted electrophysiological parameters at the respective locations for which the respective measure of consistency satisfied a predefined consistency criterion, and automatically discarding from the map the electrophysiological parameters for which the respective measure of consistency did not satisfy the predefined consistency criterion. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic pictorial illustration of a medical apparatus for mapping an EP parameter in a heart of a patient, in accordance with an embodiment of the present invention; 
         FIG. 2  is a flowchart that schematically illustrates a method for automated EP mapping, in accordance with an embodiment of the invention; and 
         FIGS. 3A-3C  are schematic illustrations of an electro-anatomical map, comprising a 3D map of a chamber of a heart, with a superimposed visual indication of EP parameters during a measurement and after an automatic removal of inconsistent EP parameters, in accordance with an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Generating an electrophysiological (EP) map of a tissue of a patient involves positioning one or more electrodes on a region of the tissue, acquiring the signal of the region, and then repeating the process for a different region. When small numbers of electrodes are used, this process generates accurate maps of the EP parameters extracted from these signals, since the physician can observe the acquired signals, and only accept “good” signals (as judged by the physician) into the map. A good signal is typically generated only when the electrode is in good contact with the tissue. Using a small number of electrodes has, however, the drawback that the mapping takes a long time. 
     For catheters with large numbers of electrodes, the mapping time is reduced, but the accuracy is decreased, since the physician is incapable of properly inspecting all the simultaneously generated signals within the available time. The task of accepting good signals (and rejecting others) may be facilitated by presenting to the physician the analyzed results of the signals, i.e., the values of an EP parameter across the measured region. (For the sake of brevity, “value of an EP parameter” will in the following description be referred to simply as “EP parameter.”) The task may be further facilitated by presenting these values in a graphical form, such as a map of the values. However, the physician is still required to use his/her subjective judgement in accepting or rejecting the analyzed results, with an inherent variability in the acceptance due to subjectivity. Moreover, requiring the physician to judge the quality of these results will further tax his/her time and attention during the mapping procedure, especially if a large number of electrodes is used. 
     The embodiments of the present invention that are described herein address these problems by providing a medical apparatus comprising a probe, a display screen, a position-tracking system, and a processor. The probe, which comprises one or more electrodes, is inserted into a body of a patient so that it contacts tissue within the body. While the probe and its electrodes are held stationary on the tissue over a preset length of time, the position-tracking system acquires the position coordinates of the electrodes, and the processor acquires EP signals from the electrodes. The processor extracts the respective EP parameters from the signals, and computes a measure of consistency of the values at each electrode location. The processor renders to the display screen a three-dimensional (3D) map of the tissue while superimposing on the map a visual indication of the extracted EP parameters at the locations for which the measure of consistency satisfied a predefined consistency criterion. The processor automatically discards from the map the EP parameters for which the respective measure of consistency did not satisfy the predefined criterion. 
     This approach facilitates rapid automated decisions as to the points on the tissue where the acquired EP parameters are valid, without having to rely on a subjective and time-consuming assessment by the physician. 
     In a disclosed embodiment, the processor displays a 3D map of a chamber of the heart in which EP parameter is being mapped. The 3D map is presented in a neutral color tone or monotone color, such as gray. The EP parameter may comprise, for example, a local activation time (LAT) measured in the myocardium or a bipolar or unipolar maximum voltage. LAT is the time interval between a reference time determined, for example, from the body surface ECG or intracardiac electrogram, and the time of the local depolarization event. Other useful scalar functions of the physiological parameters, may be calculated and displayed, superposed on a combined display of LAT (as pseudocolor) and propagation velocity (as arrows). One such useful scalar function is the range of voltages measured at each sampled point (displayed as a pseudocolor): an abnormally low range is diagnostic of scar tissue, upon which the conduction velocity may be displayed as arrows. LAT can be determined manually (and usually automatically by the CARTO® system) by marking one or more of (a) the maximum negative slope of the voltage of the unipolar recording (−dV/dt); (b) maximum absolute voltage of the bipolar recording, (c) the maximum absolute slope dV/dt of the bipolar recording or (d) minimum voltage of the bipolar recording. 
     During the measurement, the processor extracts the EP parameters over several (for example 3-7) heartbeats, and keeps updating the 3D map for each heartbeat, by superimposing onto the map an indication of the EP parameters. This indication may be, for example, a color code, wherein the lowest value of the EP parameter is denoted by blue, the highest by red, and the intermediate values by the colors of the visible spectrum between blue and red. The 3D map may be updated after each heartbeat based on the last measured EP parameters or on a cumulative average of the EP parameters. Alternatively, the 3D map may be updated only after the EP parameters have been measured over the several heartbeats, and then only with the points that pass the criterion for consistency, as described below. 
     The processor also computes a measure of consistency for the EP parameter over these several heartbeats, reflecting the variation of the extracted values over the heartbeats. The criterion applied to the measure of consistency may require, for example, that the variation be no greater than a certain threshold, for example a voltage threshold. When the variation exceeds this threshold at a given measurement point on the tissue, the measured EP parameter at this point is rejected, and the corresponding area on the 3D map is displayed in its neutral background color. 
     System Description 
       FIG. 1  is a schematic pictorial illustration of a medical apparatus  20  for mapping an EP parameter in a heart  26  of a patient  28 , in accordance with an embodiment of the present invention. 
     A physician  30  navigates a basket catheter  40 , seen in detail in an inset  45 , to a target location in heart  26  of patient  28 , by manipulating a shaft  22 , using a manipulator  32  near the proximal end of the catheter, and/or deflection from a sheath  23 . In the embodiment seen in an inset  25 , physician  30  uses catheter  40  to perform electro-anatomical mapping of a cardiac chamber. EP signals are acquired from tissue by using electrodes  48  on basket catheter  40  touching the tissue, as further detailed below. 
     Catheter  40  is inserted in a collapsed configuration, through sheath  23 , and only after the catheter exits sheath  23  does the catheter expand to its intended functional shape, as shown in inset  45 . By containing catheter  40  in a collapsed configuration, sheath  23  also serves to minimize vascular trauma on its way to the target location. 
     Basket catheter  40  incorporates a magnetic sensor  50 A, seen in inset  45 , at the distal edge of shaft  22  (i.e., at the proximal edge of basket catheter  40 ). Typically, although not necessarily, sensor  50 A is a Triple-Axis Sensor (TAS), comprising three miniature coils oriented in different directions. In the pictured embodiment, a second magnetic sensor  50 B is incorporated in a distal edge of the basket catheter. Sensor  50 B may be a Single-Axis Sensor (SAS) or a Triple-Axis Sensor (TAS), for example. Alternatively, catheter  40  may comprise other sorts of magnetic sensors, at these or other locations. 
     Catheter  40  further comprises multiple expandable spines  55 , which may be mechanically flexible, to each of which are coupled multiple electrodes  48  for a total of, for example, 120 electrodes. Electrodes  48  are configured to touch the tissue of patient  28  for sensing EP signals. Magnetic sensors  50 A and  50 B and electrodes  48  are connected by wires running through shaft  22  to various processing circuits in a console  24 . 
     Alternatively, apparatus  20  may comprise other types of catheters, with other sorts of electrode arrays, such as an inflatable balloon catheter with electrodes  48  on its outer surface. 
     Medical apparatus  20  comprises a magnetic-sensing sub-system for determining the position and orientation of basket catheter  40 , and thereby the positions of electrodes  48 . Patient  28  is placed in a magnetic field generated by a pad containing magnetic field generator coils  42 , which are driven by a tracking module  43  in console  24 . The magnetic fields generated by coils  42  give rise to electrical signals in sensors  50 A and  50 B, which are indicative of the position and/or orientation of the sensors. The signals form sensors  50 A and  50 B are transmitted back to tracking module  43 , which converts the signals to corresponding digital inputs to a processor  41 . Processor  41  uses these inputs to calculate the position and orientation of basket catheter  40  and thus to find the respective location of each of electrodes  48 . 
     Methods of position and/or orientation sensing using external magnetic fields and magnetic sensors, such as sensors  50 A and  50 B, are implemented in various medical applications, for example, in the CARTO® system, available from Biosense Webster, Inc. (Irvine, Calif.). Such methods are described in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. Patent Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1, whose disclosures are all incorporated herein by reference. 
     Alternatively or additionally, apparatus  20  may use other methods of position sensing to find the locations of electrodes  48 . For example, processor  41  may map the locations of electrodes  48  by measuring impedances between electrodes  48  and body-surface electrodes  49 , which are placed on the chest of patient  28  and connected to console  24  by leads  39 . 
     Processor  41  additionally receives electrophysiological signals via electrical interface  44 , and uses the information contained in these signals together with the coordinates provided by magnetic sensors  50 A and  50 B to construct an electro-anatomical map  31  of the chamber of heart  26  in which catheter  40  is located. During and/or following the procedure, processor  41  may render electro-anatomical map  31  to a display screen  27 . 
     Processor  41  is typically programmed in software to carry out the functions described herein. The software may be downloaded to the computer 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  41  runs a dedicated algorithm that enables the processor to perform the disclosed steps, as described below. 
     The example illustration shown in  FIG. 1  is chosen purely for the sake of conceptual clarity.  FIG. 1  shows only elements related to the disclosed techniques for the sake of simplicity and clarity. Medical apparatus  20  typically comprises additional modules and elements that are not directly related to the disclosed techniques, and thus are intentionally omitted from  FIG. 1  and from the corresponding description. The elements of medical apparatus  20  and the methods described herein may be further applied, for example, to control an ablation of tissue of heart  26 . 
       FIG. 2  is a flowchart  200  that schematically illustrates an automated process for EP mapping, in accordance with an embodiment of the invention. In this method, only EP parameters satisfying a certain consistency criterion are incorporated in the map. The embodiment shown in flowchart  200  refers to an example of acquiring EP signals from a chamber of heart  26  (with reference to  FIG. 1 ). In alternative embodiments, the values of EP parameters may be acquired using other sorts of mapping apparatus, not only from the heart, but also from other organs and tissue, as will be apparent to those skilled in the art after reading the present description. 
     The process illustrated by flowchart  200  begins in a start step  202 . In a map generation step  204 , a uniformly gray (or other suitable background color) 3D map of the heart chamber is generated by processor  41  and rendered onto display screen  27 . The 3D map is generated, for example, from an image of heart  26  previously stored in the processor, or based on position measurements taken by a catheter. Alternatively, the 3D map may be generated concurrently with displaying the EP parameters. In an acquisition step  206 , processor  41  receives signals from electrodes  48 , which are in contact with myocardial tissue in a part of a chamber of heart  26 , over a preset number of consecutive heartbeats. Typically, the signals are acquired over a sequence of 3-7 heartbeats, but larger numbers of heartbeats may alternatively be sampled. In a tracking step, processor  41  receives signals from tracking module  43 , and computes the respective location coordinates of electrodes  48 . 
     In a computation and display step  208 , processor  41  extracts the EP parameters separately for each heartbeat from the signals received in acquisition step  206 . The processor displays the parameters by applying a corresponding color code to the appropriate region of the 3D map generated in step  204 , based on the position coordinates received in tracking step  207 . The color-coding may comprise, for example, showing the lowest values of the EP parameter as a blue color, the highest values as a red color, and intermediate values between the lowest and highest values in the same order as colors in a visible spectrum. However, other color-coding schemes, as well as shading or symbols, such as are known in the art, may alternatively be used. The EP parameters may be displayed at this step either as the last measured results or as a cumulative average. Alternatively, the color coding may be superimposed on the 3D map after the EP parameters have been measured over the several heartbeats, and then only with the points that pass the criterion for consistency, as applied in the following steps. 
     In a consistency evaluation step  210 , processor  41  evaluates a measure of consistency of the EP parameters from heartbeat to heartbeat against a predefined consistency criterion. For the sake of brevity, EP parameters for which the measure of consistency satisfies the consistency criterion are also termed “consistent EP parameters” in the description that follows, whereas those parameters that do not satisfy the consistency criterion are termed “inconsistent EP parameters.” The measure of consistency, as well as the consistency criterion, are defined in the present embodiment in terms of the peak heartbeat-to-heartbeat variation of the EP parameters. 
     In a first decision step  212 , based on the outcome of consistency evaluation step  210 , processor  41  decides whether the EP parameter decides satisfies the consistency criterion. For example, when the EP parameter computed in step  208  is the local activation time (LAT), the consistency criterion can be taken as a range of ±10 ms, i.e., if the LATs measured for each heartbeat over 3-7 heartbeats are within 20 ms of each other, they are considered to satisfy the consistency criterion. An another example, when the EP parameter is a bipolar or unipolar maximum voltage in the signals sensed by electrodes  48 , the consistency criterion can be taken as a range of 20 mV, so that measured maximum voltages within this range are considered to satisfy the consistency criterion. Alternatively, larger or smaller ranges of the parameters can be taken as the consistency criterion. 
     Further alternatively, other sorts of consistency criteria can be applied. For example, processor  41  may compute the mean value of the EP parameter in question and the variance of the parameter over the sequence of heartbeats, and may define the consistency criterion in terms of the maximal acceptable variance. 
     When processor  41  finds that the EP parameter has satisfied the consistency criterion at step  212 , it automatically incorporates the color-coded section in the 3D map, in an incorporation step  214 . Alternatively, when the consistency criterion is not satisfied, the processor returns the area of the map in question to the background color, in a removal step  216 . 
     In a second decision step  218 , physician  30  decides whether EP signals need to be sampled from an additional region of the heart chamber. If the answer is affirmative, the physician moves basket catheter  40  to another region, and the EP signals from that region are measured, starting with acquisition step  206 . Alternatively, when the EP values were rejected in first decision step  212 , physician  30  may decide to re-sample the signals from that region. When no more EP signals need to be sampled, the process ends in an end step  222 . 
       FIGS. 3A, 3B and 3C  are schematic illustrations of electro-anatomical map  31 , comprising a 3D map  300  of a chamber of heart  26 , with a superimposed visual indication of the EP parameters during a measurement and after an automatic removal of inconsistent EP parameters, in accordance with an embodiment of the invention. Map  300  is initially colored in gray on display screen  27 , and the color is updated in accordance with the method of  FIG. 2  in various stages of the measurement using basket catheter  40 , as is detailed below. 
     In  FIG. 3A , a colored overlay  302  is superimposed on 3D map  300  as a visual indication of the EP parameters resulting from computation and display step  208 . In  FIG. 3A , colored overlay  302  may comprise both consistent and inconsistent values. Basket catheter  40  is positioned over an area  304 , but the gray color of the area indicates that no EP parameters have yet been measured in this area. 
       FIG. 3B  shows 3D map  300  with a colored overlay  306  now superimposed on area  304  of  FIG. 3A , indicating the values of the measured EP parameters. 
       FIG. 3C  shows 3D map  300  with only consistent EP parameters superimposed on it as a colored overlay  308 . Inconsistent values of the measured EP parameters have now been removed in removal step  216  ( FIG. 2 ) from an area  310 , so that this area is displayed in the gray color of map  300 . Thus, physician  30  will see only colored overlay  308  representing consistent EP parameters. The rejection of inconsistent EP parameters has been done automatically by processor  41 , without any involvement by physician  30 . 
     Although in the disclosed embodiment the EP parameters were measured from heart  26 , in alternative embodiments the described method of automated acceptance or rejection of EP parameters may be applied other tissue of the body of patient  28 . Moreover, in alternative embodiments more than one type of EP parameter may be measured and displayed simultaneously. 
     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 subcombinations 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.