Automated graphical presentation of electrophysiological parameters

Abstract

The invention is entitled "Automatic graphical presentation of electrophysiological parameters". The invention provides a medical device comprising a probe configured to be inserted into a body of a patient. The probe comprises electrodes configured to contact tissue of a region within the body. The device further comprises a display screen, a position tracking system configured to acquire position coordinates of the electrodes within the body, and a processor. The processor is configured to: acquire electrophysiological signals from the electrodes while causing the electrodes to remain stationary in the region; extract electrophysiological parameters from the signals; compute a measure of consistency of the parameters; and render a three-dimensional (3D) map of the tissue to the display screen, while superimposing on the map a visual indication of the extracted parameters at locations where the measure of consistency satisfies a consistency criterion, in response to the position coordinates, and automatically discarding from the map parameters where the measure of consistency does not satisfy the consistency criterion.

Description

TECHNICAL FIELD

[0001] The present invention relates generally to electrophysiological measurements, and in particular to apparatus and methods for automatic mapping of electrophysiological parameters. BACKGROUND

[0002] Electrophysiological (EP) maps of a patient's tissue are generated by positioning one or more electrodes on a region of the tissue, acquiring EP signals of the region, and then repeating the process for different regions. EP parameters are extracted from the EP signals in each measured region and then displayed on an image of the tissue. SUMMARY

[0003] Embodiments of the invention described below provide improved methods and apparatus for mapping electrophysiological parameters.

[0004] Accordingly, in accordance with embodiments of the invention, there is provided a medical apparatus comprising a probe configured for insertion into a body of a patient, wherein the probe comprises one or more electrodes configured to contact tissue of a region within the body. The apparatus further comprises a display screen, a position tracking system configured to acquire position coordinates of the one or more electrodes within the body, and a processor. The processing unit is configured to: acquire, from the one or more electrodes, respective electrophysiological signals when causing the one or more electrodes to remain stationary at respective positions in the region for at least a preset length of time; extract, from the electrophysiological signals acquired by the one or more electrodes at the respective positions, respective electrophysiological parameters; and compute a respective measure of consistency of the respective electrophysiological parameters extracted from the electrophysiological signals acquired by the electrodes at each of the respective positions for the preset length of time.

[0005] The processing unit is further configured to render a three-dimensional (3D) map of the tissue to the display screen, while superimposing on the map a visual indication of the extracted electrophysiological parameters at the respective positions for which the respective measure of consistency satisfies a predefined consistency criterion, and to automatically discard from the map the electrophysiological parameters for which the respective measure of consistency does not satisfy the predefined consistency criterion.

[0006] In embodiments disclosed herein, the electrophysiological parameters comprise local activation times (LATs) in a heart of the patient, and the measure of consistency is indicative of a variation in the LATs. Additionally or alternatively, the measure of consistency comprises a peak-to-peak variation of the LATs at any given position, and the consistency criterion requires that the peak-to-peak variation of the LATs does not exceed a predefined limit.

[0007] In another embodiment, the electrophysiological parameter comprises an electrophysiological voltage, and the consistency measure is indicative of a variation of the electrophysiological voltage. Additionally or alternatively, the consistency measure comprises 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 does not exceed a predefined limit.

[0008] In another embodiment, the 3D map is rendered in a background color, and the visual indication comprises a further color superimposed on the background color at the respective location to indicate the value of the extracted electrophysiological parameter.

[0009] According to embodiments of the present application, there is also provided a method for electrophysiological mapping. The method comprises, while causing one or more electrodes to remain stationary at respective locations in a region of a patient's body for at least a preset length of time, acquiring respective electrophysiological signals from the one or more electrodes on a probe in contact with tissue of the region, and simultaneously acquiring position coordinates of the one or more electrodes. Extracting respective electrophysiological parameters from the electrophysiological signals acquired by the one or more electrodes at the respective locations, and calculating respective consistency measures of the respective electrophysiological parameters extracted from the electrophysiological signals acquired by the electrodes at each of the respective locations for the preset length of time. The method further comprises displaying a three-dimensional (3D) map of the tissue, while superimposing on the map, in response to the position coordinates, a visual indication of the extracted electrophysiological parameters at respective locations for which the respective consistency measures satisfy a predefined consistency criterion, and automatically discarding from the map the electrophysiological parameters for which the respective consistency measures do not satisfy the predefined consistency criterion.

[0010] The present application will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 is a schematic illustration of a medical device for mapping EP parameters in a patient's heart according to embodiments of the present application;

[0012] Figure 2 is a flowchart schematically illustrating a method for automatic EP mapping according to embodiments of the present application; and

[0013] Figures 3A to 3C is a schematic illustration of an electroanatomical map comprising a 3D map of a heart chamber with superimposed visual indications of EP parameters after a measurement period and automatic removal of inconsistent EP parameters according to embodiments of the present application. DETAILED DESCRIPTION

[0014] SUMMARY

[0015] Generating an electro-physiologic (EP) map of a patient's tissue involves positioning one or more electrodes on a region of the tissue, acquiring signals for that region, and then repeating the process for different regions. When a small number of electrodes is used, the process generates an accurate map of EP parameters extracted from the signals, as the physician can observe the acquired signals and accept only "good" signals (as judged by the physician) for the map. A good signal is typically generated only when the electrode is in good contact with the tissue. However, using a small number of electrodes has the disadvantage of requiring a long time to map.

[0016] For a catheter with a large number of electrodes, the mapping time is reduced, but the accuracy is reduced, as the physician cannot properly detect all the signals being generated at the same time within the available time. The task of accepting good signals (and rejecting other signals) can be facilitated by presenting the physician with the results of an analysis of the signals, i.e., values of EP parameters across the measured region. (For brevity, "values of EP parameters" will be referred to simply as "EP parameters" in the following description.) The task can be further facilitated by presenting these values in graphical form, such as a map of the values. However, the physician still needs to use his / her subjective judgment to accept or reject the analyzed results, with inherent variability in the acceptance aspect due to subjectivity. Moreover, requiring the physician to judge the quality of these results further consumes his / her time and attention in the mapping procedure, especially in the case of using a large number of electrodes.

[0017] Embodiments of the invention described herein address these problems by providing a medical device that includes a probe, a display screen, a position tracking system, and a processor. The probe, which includes one or more electrodes, is inserted into a patient's body so that the probe contacts tissue in the body. While the probe and its electrodes are held stationary on the tissue for a predetermined length of time, the position tracking system acquires position coordinates of the electrodes, and the processor acquires EP signals from the electrodes. The processor extracts respective EP parameters from the signals, and computes a measure of consistency of the values at each electrode position. The processor renders a three-dimensional (3D) map of the tissue to the display screen, while superimposing on the map a visual indication of the extracted EP parameters at positions where the measure of consistency meets a predefined consistency criterion. The processor automatically discards from the map EP parameters whose respective measure of consistency does not meet the predefined criterion.

[0018] This approach facilitates the rapid and automated determination of points on the tissue where the acquired EP parameters are valid, without having to rely on the physician's subjective and time-consuming subjective assessment.

[0019] In the disclosed embodiments, the processor displays a 3D map of the chamber of the heart in which the EP parameters are being mapped. The 3D map is rendered in a neutral tone or a single color, such as gray. The EP parameters can include, for example, local activation times (LATs) measured in the myocardium or bipolar or unipolar maximum voltage. The LAT is the time interval between a reference time determined, for example, from a body surface ECG or intracardiac electrogram, and the time of a local depolarization event. Other available scalar functions of the physiological parameters can be computed and displayed, then superimposed on the combined display of LATs (as pseudo-color) and propagation velocities (as arrows). One such available scalar function is the voltage range measured at each sampling point (displayed as pseudo-color): abnormally low range is diagnostic of scar tissue, on which the conduction velocity can be displayed as arrows. The LATs can be determined manually (and typically by the system automatically) by marking one or more of: (a) the maximum negative slope of the voltage of the unipolar recording (-dV / dt); (b) the maximum absolute voltage of the bipolar recording, (c) the maximum absolute slope dV / dt of the bipolar recording, or (d) the minimum voltage of the bipolar recording. The system determines automatically) : (a) the maximum negative slope of the voltage of the unipolar recording (-dV / dt); (b) the maximum absolute voltage of the bipolar recording, (c) the maximum absolute slope dV / dt of the bipolar recording, or (d) the minimum voltage of the bipolar recording.

[0020] During the measurement, the processor extracts the EP parameters of several heartbeats (e.g., 3 to 7) and keeps updating the 3D map of each heartbeat by superimposing on the map an indication of the EP parameters. The indication can be, for example, a color code in which the lowest values of the EP parameters are represented by blue, the highest values by red, and the intermediate values by colors of the visible spectrum between blue and red. The 3D map can be updated after each heartbeat based on the last measured EP parameters or a cumulative average of the EP parameters. Alternatively, the 3D map can be updated only after the EP parameters during several heartbeats have been measured, then only with points passing a consistency criterion, as described below.

[0021] The processor also computes a measure of consistency of the EP parameters during several heartbeats, reflecting the variation of the extracted values during the heartbeats. The criterion applied to the measure of consistency can require, for example, that the variation be no more than a certain threshold, e.g., a voltage threshold. When the variation at a given measurement point on the tissue exceeds the threshold, the EP parameter measured at that point is rejected, and the corresponding region on the 3D map is displayed with the neutral background color.

[0022] System Description

[0023] Figure 1 is a schematic view of a medical device 20 for mapping EP parameters in a heart 26 of a patient 28, according to an embodiment of the application.

[0024] The physician 30 navigates a basket catheter 40, shown in detail in inset 45, into a target location in the heart 26 of the patient 28 by manipulating the shaft 22 using a manipulator 32 proximate the proximal end of the catheter and / or from the flexing of the sheath 23. In the embodiment seen in inset 25, the physician 30 uses the catheter 40 to perform an electroanatomical mapping of a heart chamber. EP signals are acquired from tissue by using electrodes 48 on the basket catheter 40 that contact the tissue, as further detailed below.

[0025] The catheter 40 is inserted into the sheath 23 in a collapsed configuration, and only after the catheter exits the sheath 23 does the catheter expand to its intended functional shape, as shown in inset 45. By containing the catheter 40 in a collapsed configuration, the sheath 23 also serves to minimize trauma to blood vessels on its way to the target location.

[0026] The basket catheter 40 incorporates a magnetic sensor 50A at the distal edge of the shaft 22 (i.e., at the proximal edge of the basket catheter 40) (see inset 45). Typically, although not necessarily, the sensor 50A is a three-axis sensor (TAS) comprising three microcoils oriented in different directions. In the illustrated embodiment, a second magnetic sensor 50B is incorporated in the distal edge of the basket catheter. The sensor 50B can be, for example, a single-axis sensor (SAS) or a three-axis sensor (TAS). Alternatively, the catheter 40 can include other kinds of magnetic sensors at these locations or other locations.

[0027] The catheter 40 also includes a plurality of expandable spines 55, which can be mechanically flexible, with a plurality of electrodes 48 (e.g., 120 electrodes in total) coupled with each expandable spine. The electrodes 48 are configured to contact tissue of the patient 28 to sense EP signals. The magnetic sensor 50A and the magnetic sensor 50B, as well as the electrodes 48, are connected through wires that pass through the shaft 22 to various processing circuits in the console 24.

[0028] Alternatively, the apparatus 20 can include other types of catheters, as well as other types of electrode arrays, such as inflatable balloon catheters with electrodes 48 on the outer surface.

[0029] The medical device 20 includes a magnetic sensing subsystem for determining the position and orientation of the basket catheter 40, and thus the electrodes 48. The 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 the console 24. The magnetic field generated by the coils 42 induces electrical signals in the sensors 50A and 50B indicative of the position and / or orientation of the sensors. The signals from the sensors 50A and 50B are transmitted back to the tracking module 43, which converts the signals to corresponding digital inputs to the processor 41. The processor 41 uses these inputs to calculate the position and orientation of the basket catheter 40, and thus the respective positions of each of the electrodes 48.

[0030] Methods for position and / or orientation sensing using external magnetic fields and magnetic sensors, such as the sensors 50A and 50B, are implemented in various medical applications, for example in the CARTO® system available from Biosense Webster, Inc. (Irvine, California). Such methods are described in detail in U.S. Patents 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612, and 6,332,089, PCT Patent Publication WO 96 / 05768, and U.S. Patent Application Publications 2002 / 0065455 Al, 2003 / 0120150 Al, and 2004 / 0068178 Al, the disclosures of which are incorporated herein by reference in their entireties.

[0031] Alternatively or additionally, the device 20 can use other position sensing methods to find the positions of the electrodes 48. For example, the processor 41 can map the positions of the electrodes 48 by measuring the impedance between the electrodes 48 and body surface electrodes 49 placed on the chest of the patient 28 and connected to the console 24 by the lead 39.

[0032] The processor 41 additionally receives electrophysiological signals via the electrical interface 44, and uses the information contained in these signals, together with the coordinates provided by the magnetic sensors 50A and 50B, to construct an electroanatomical map 31 of the chamber of the heart 26 in which the catheter 40 is located. During and / or after the procedure, the processor 41 can render the electroanatomical map 31 to the display screen 27.

[0033] ​The processor 41 is generally programmed in software to perform the functions described herein. The software can be downloaded to the computer in electronic form, over a network, for example, or it alternatively or additionally can be supplied and / or stored on non-transitory tangible media, such as magnetic, optical or electronic memory. In particular, the processor 41 runs a special purpose algorithm that enables the processor to perform the steps disclosed in the present application, as described below.

[0034] Figure 1 The exemplary illustrations shown are chosen purely for conceptual clarity. For simplicity and clarity, only elements relevant to the technology disclosed in the present application are shown. Figure 1 The medical device 20 typically comprises additional modules and elements that are not directly relevant to the technology disclosed in the present application and are therefore omitted from the drawings for the sake of clarity. Figure 1 The corresponding description is intentionally omitted. The elements of the medical device 20 and the method described herein can further be applied, for example, to control ablation of tissue of the heart 26.

[0035] Figure 2 is a flowchart 200 schematically illustrating an automated process for EP mapping according to an embodiment of the present application. In this method, only EP parameter values that meet certain consistency criteria are incorporated into the map. The embodiment shown in the flowchart 200 refers to an example of EP signal acquisition from a chamber of the heart 26 (cf. Fig. 1). In alternative embodiments, EP parameter values can be acquired using other kinds of mapping devices, not only from the heart, but also from other organs and tissues, as will be apparent to the skilled reader after reading this specification. Figure 1 ) In alternative embodiments, EP parameter values can be acquired using other kinds of mapping devices, not only from the heart, but also from other organs and tissues, as will be apparent to the skilled reader after reading this specification.

[0036] The process shown in the flowchart 200 starts with a start step 202. In a map generation step 204, a uniform grey (or other suitable background color) 3D map of the ventricle is generated by the processor 41 and rendered onto the display screen 27. The 3D map is generated, for example, from an image of the heart 26 previously stored in the processor, or based on position measurements taken by the catheter. Alternatively, the 3D map can be generated while displaying the EP parameters. In an acquisition step 206, the processor 41 receives signals from the electrodes 48 in contact with the myocardial tissue in a portion of the chamber of the heart 26 from a preset number of consecutive heartbeats. Typically, the signals are acquired over a sequence of 3 to 7 heartbeats, but alternatively, a larger number of heartbeats can be sampled. In a tracking step, the processor 41 receives signals from the tracking module 43 and calculates the respective position coordinates of the electrodes 48.

[0037] In a computing and displaying step 208, the processor 41 extracts the EP parameter for each heartbeat from the signals received in the acquisition step 206. Based on the position coordinates received in the tracking step 207, the processor displays the parameter by applying a corresponding color code to the appropriate region of the 3D map generated in step 204. The color coding can comprise, for example, displaying the lowest value of the EP parameter in blue, the highest value in red, and the intermediate values between the lowest and highest values in the same order as the order of colors in the visible spectrum. However, other color coding schemes such as known in the art can alternatively be used, as well as shades or symbols. The EP parameter can be displayed in this step as the result of the last measurement or as a cumulative average. Alternatively, the color coding can be superimposed on the 3D map after the EP parameter has been measured for several heartbeats, then only containing the points passing through a consistency criterion, as applied in the following steps.

[0038] In a consistency evaluation step 210, the processor 41 evaluates a consistency measure of the EP parameter between two heartbeats against a predefined consistency criterion. For the sake of brevity, the EP parameters whose consistency measure meets the consistency criterion are also referred to as "consistent EP parameters" in the following description, while those not meeting the consistency criterion are referred to as "inconsistent EP parameters". The consistency measure as well as the consistency criterion are defined in the present embodiment according to the peak-to-peak inter-beat variation of the EP parameter.

[0039] In a first decision step 212, based on the result of the consistency evaluation step 210, the processor 41 decides whether the EP parameter decision meets the consistency criterion. For example, when the EP parameter computed in step 208 is the local activation time (LAT), the consistency criterion can take a range of ±10 ms, i.e. if the LAT measured for each of 3 to 7 heartbeats differ from each other within 20 ms, they are considered to meet the consistency criterion. As another example, when the EP parameter is the bipolar or unipolar maximum voltage in the signal sensed by the electrode 48, the consistency criterion can take a range of 20 mV, so that the measured maximum voltages within this range are considered to meet the consistency criterion. Alternatively, a larger or smaller range of the parameter can be considered as the consistency criterion.

[0040] Alternatively, other kinds of consistency criterion can be applied. For example, the processor 41 can compute the mean value of the EP parameter under consideration and the variance of the parameters of the sequence of heartbeats, and can define the consistency criterion according to a maximum acceptable variance.

[0041] When the processor 41 finds in step 212 that the EP parameter has met the consistency criterion, the processor automatically incorporates the color-coded segment in the 3D map in an incorporating step 214. Alternatively, when the consistency criterion is not met, in a removing step 216, the processor returns the region of the map under consideration to the background color.

[0042] In a second decision step 218, the physician 30 decides whether EP signals need to be sampled from additional areas of the ventricle. If the answer is affirmative, the physician moves the basket catheter 40 to another area and starts measuring EP signals from this area from the acquisition step 206. Alternatively, when an EP value is rejected in the first decision step 212, the physician 30 can decide to resample the signal from this area. When no more EP signals need to be sampled, the process ends in an end step 222.

[0043] Figure 3A 、 Figure 3B and Figure 3C is a schematic of an electroanatomical map 31 of a 3D map 300 of a chamber of a heart 26 according to an embodiment of the present application, with a visual indication of superimposed EP parameters during the measurement and after automatic removal of inconsistent EP parameters. The map 300 is initially colored in gray on the display screen 27 and the color is updated in each stage of the measurement using the basket catheter 40 according to the method of Figure 2 as detailed below.

[0044] In Figure 3A , a colored overlay 302 is superimposed on the 3D map 300 as a visual indication of the EP parameters resulting from the computing and displaying step 208. In Figure 3A , the colored overlay 302 can have consistent and inconsistent values. The basket catheter 40 is positioned over a zone 304, but the gray indication of the zone has not yet measured EP parameters in this zone.

[0045] Figure 3B shows the 3D map 300 with a colored overlay 306 now superimposed on the zone 304 of Figure 3A , indicating the values of the measured EP parameters.

[0046] Figure 3C shows the 3D map 300 with only the consistent EP parameters superimposed as a colored overlay 308. The inconsistent values of the measured EP parameters have now been removed from the zone 310 in the removing step 216 Figure 2 . This zone is thus displayed in gray of the map 300. The physician 30 will thus only see the colored overlay 308 representing the consistent EP parameters. The rejection of the inconsistent EP parameters has been done automatically by the processor 41 without any involvement of the physician 30.

[0047] Although EP parameters are measured from the heart 26 in the disclosed embodiments, in alternative embodiments, the method of automatically accepting or rejecting EP parameters can be applied to other tissues of the patient 28 body. Further, in alternative embodiments, more than one type of EP parameter can be measured and displayed simultaneously.

[0048] It is to be understood that the above-mentioned embodiments are cited by way of example, and that the present application is not limited to the above- specifically shown and described. Rather, the scope of the present application includes combinations and sub-combinations of the various features recited above, as well as variations and modifications thereof, which will occur to those skilled in the art upon reading the above description and which are not disclosed in the prior art.

Claims

1. A medical device comprising: a probe configured for insertion into a body of a patient and comprising one or more electrodes configured to contact tissue of a region within the body; a display screen; a position tracking system configured to acquire position coordinates of the one or more electrodes within the body; and a processor configured to: acquire, from the one or more electrodes, respective electrophysiological signals when the one or more electrodes are caused to remain stationary at respective positions in the region for at least a preset length of time; extract, from the electrophysiological signals acquired by the one or more electrodes at the respective positions, respective electrophysiological parameters; compute respective measures of consistency of the respective electrophysiological parameters extracted from the electrophysiological signals acquired by the electrodes at each of the respective positions over the preset length of time; and render a three-dimensional (3D) map of the tissue to the display screen while superimposing on the map, in response to the position coordinates, visual indications of the extracted electrophysiological parameters at the respective positions for which the respective measures of consistency satisfy a predefined consistency criterion, and automatically discarding from the map the electrophysiological parameters for which the respective measures of consistency do not satisfy the predefined consistency criterion.

2. The medical device of claim 1, wherein the electrophysiological parameters comprise local activation times (LATs) in a heart of the patient, and the measure of consistency indicates a variation of the LATs.

3. The medical device of claim 2, wherein the measure of consistency comprises a peak-to-peak variation of the LATs at any given position, and the consistency criterion requires that the peak-to-peak variation of the LATs does not exceed a predefined limit.

4. The medical device of claim 1, wherein the electrophysiological parameters comprise electrophysiological voltages, and the measure of consistency indicates a variation of the electrophysiological voltages.

5. The medical device of claim 4, wherein the measure of consistency comprises a peak-to-peak variation of the electrophysiological voltages at any given position, and the consistency criterion requires that the peak-to-peak variation of the electrophysiological voltages does not exceed a predefined limit.

6. The medical device of claim 1, wherein the three-dimensional (3D) map is rendered in a background color, and the visual indications comprise other colors superimposed on the background color at the respective positions to indicate values of the extracted electrophysiological parameters.

7. A method for electrophysiological mapping, the method comprising: acquiring, from one or more electrodes on a probe in contact with tissue of a region within a body of a patient, respective electrophysiological signals when the one or more electrodes are caused to remain stationary at respective positions in the region for at least a preset length of time, and simultaneously acquiring position coordinates of the one or more electrodes; extracting, from the electrophysiological signals acquired by the one or more electrodes at the respective positions, respective electrophysiological parameters; computing respective measures of consistency of the respective electrophysiological parameters extracted from the electrophysiological signals acquired by the one or more electrodes at the respective positions over the preset length of time; and rendering a three-dimensional (3D) map of the tissue to a display screen while superimposing on the map, in response to the position coordinates, visual indications of the extracted electrophysiological parameters at the respective positions for which the respective measures of consistency satisfy a predefined consistency criterion, and automatically discarding from the map the electrophysiological parameters for which the respective measures of consistency do not satisfy the predefined consistency criterion. computing a respective measure of consistency of the respective electrophysiological parameters extracted from the electrophysiological signals acquired by the electrodes at each of the respective positions in the pre-set length of time; and displaying a three-dimensional (3D) map of the tissue, while superimposing on the map a visual indication of the extracted electrophysiological parameters at the respective positions for which the respective measure of consistency satisfies a pre-defined consistency criterion, and automatically discarding from the map the electrophysiological parameters for which the respective measure of consistency does not satisfy the pre-defined consistency criterion.

8. The method of claim 7, wherein extracting electrophysiological parameters comprises extracting local activation times (LATs) in the patient's heart, and computing the measure of consistency comprises computing a measure indicative of variations in the LATs.

9. The method of claim 8, wherein computing the measure comprises computing a peak-to-peak variation of the LATs at any given position, and wherein the consistency criterion requires that the peak-to-peak variation of the LATs does not exceed a pre-defined limit.

10. The method of claim 7, wherein extracting electrophysiological parameters comprises extracting electrophysiological voltages in the patient's heart, and computing the respective measure of consistency comprises computing a measure indicative of variations in the electrophysiological voltages.

11. The method of claim 10, wherein computing the measure comprises computing a peak-to-peak variation of the electrophysiological voltages at any given position, and wherein the consistency criterion requires that the peak-to-peak variation of the electrophysiological voltages does not exceed a pre-defined limit.

12. The method of claim 7, wherein displaying the three-dimensional (3D) map comprises rendering the three-dimensional (3D) map in a background color, and superimposing the visual indication comprises superimposing an additional color on the background color at the respective positions, thereby indicating respective values of the extracted electrophysiological parameters.

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