Reducing harm to IEGM in time division multiplexing systems

Abstract

In one embodiment, a medical system includes: a catheter interface including electrode wires configured to be electrically connected to respective electrodes of a catheter; and a signal generation device configured to generate signal pulses, each of the signal pulses having a carrier frequency and having a non-rectangular signal envelope, the signal generation device configured to time-division multiplex the signal pulses between the electrode lines.

Description

Technical Field

[0001] The present disclosure relates to medical systems and, in particular but not exclusively, to signal generation. Background Art

[0002] A wide range of medical procedures involve placing probes, such as catheters, inside a patient. One medical procedure in which these types of probes or catheters have proven very useful is the treatment of cardiac arrhythmias. Cardiac arrhythmias, particularly atrial fibrillation, have been a common and dangerous medical condition, especially in the elderly population.

[0003] The diagnosis and treatment of cardiac arrhythmias involve mapping the electrical properties of cardiac tissue (particularly the endocardium and cardiac volume), and selectively ablating cardiac tissue by applying energy. In such procedures, a catheter is inserted into a heart chamber and optionally around a heart chamber. In most procedures, multiple catheters are inserted into the patient. The catheters can include mapping catheters, ablation catheters, temperature sensing catheters, and image sensing catheters. Some catheters are dedicated to being placed in specific locations of an anatomical structure, such as the coronary sinus, esophagus, atrium, ventricle. The catheters have multiple electrical channels, and some catheters have more channels than others, depending on the number of sensors and electrodes included in each catheter. The number and type of catheters depend on the procedure and the workflow preferred by the physician. Brief Description of the Drawings

[0004] The present disclosure will be understood from the following detailed description in conjunction with the accompanying drawings, in which:

[0005] Figure 1 is a diagrammatic view of a catheter-based electrophysiological mapping and ablation system constructed and operated according to an exemplary mode of the present disclosure;

[0006] Figure 2 is Figure 1 a block diagram of a patient interface unit in the system of

[0007] Figure 3 is including Figure 1 steps in a method of operating a system of

[0008] Figure 4 is for Figure 1 an example signal pulse in the system of Detailed Description

[0009] Overview

[0010] One method of tracking the position of a catheter is based on catheter electrodes that transmit position signals at different unique frequencies. The signals can be detected by body surface patches and processed by a processor, for example, based on the distribution of current or impedance on the body surface patches, to calculate the position of the catheter and / or the electrodes.

[0011] In contemporary catheters, the number of electrodes has increased dramatically. This increase will result in an increase in the number of signals at different unique frequency positions, an increase in the frequency band accommodating all unique frequencies, and an increase in the number of frequency generators generating these signals. To address this issue, time division multiplexing (TDM) can be used to transmit signals such that the same signal frequency can be used for multiple electrodes, while guiding the signals to different electrodes among these electrodes during different time periods. For example, it is transmitted from electrode 1 during time period A and from electrode 2 during time period B, and so on. In this way, the electrodes can be divided into groups that transmit at the same group of frequencies, and at any given time, only one electrode in each group transmits. In this way, the number of different frequencies and frequency generators is reduced. Each TDM signal for each time period is typically a signal pulse with a rectangular envelope.

[0012] The same electrodes that transmit the position signals also detect intracardiac electrograms (IEGMs). Due to the non-linear surface impedance between the metal electrodes and the blood pool, the transmitted TDM signal pulses cause artifacts (such as signal spikes) in the detected IEGM corresponding to the start and end points of the TDM burst. Throughout the TDM signal pulse, a direct current (DC) signal component is also superimposed on the IEGM signal.

[0013] Accordingly, in an exemplary mode of the present disclosure, TDM signal pulses are generated using a non-rectangular signal envelope, thereby reducing or eliminating signal spikes in the detected IEGM. The signal pulses are time division multiplexed between electrode lines to different catheter electrodes.

[0014] The non-rectangular signal envelope can be generated in the following manner: the peak-to-peak amplitude of the envelope gradually increases over time to a maximum peak-to-peak amplitude, and then after a given time period, the envelope gradually decreases over time to zero (or other minimum) peak-to-peak amplitude. The gradual increase in the peak-to-peak amplitude of the envelope can be based on the error function (ERF) or other suitable functions. The gradual decrease in the peak-to-peak amplitude of the envelope can be based on the complementary error function (ERFC) or other suitable functions.

[0015] In some exemplary modes, a digital signal pulse representation is retrieved from a memory by a processor (such as a field programmable gate array (FPGA)), and the processor provides the retrieved digital signal pulse representation to a digital-to-analog converter (DAC), which converts the digital signal pulse representation into an analog signal including signal pulses with a non-rectangular envelope.

[0016] The DC signal component superimposed on the IEGM signal can be reduced or eliminated by generating signal pulses such that the maximum current density on the catheter electrode is less than the threshold current density. The threshold current density can be determined by adjusting the amplitude of the signal pulses and examining the IEGM signal until the DC signal component is eliminated or sufficiently reduced. For iridium-platinum electrodes, the estimated threshold current density is about 0.44 mA / mm 2 .

[0017] System Description

[0018] Reference Figure 1 , which is a diagrammatic view of a catheter-based electrophysiological mapping and ablation system 10 constructed and operated in accordance with an exemplary mode of the present disclosure. The system 10 includes a plurality of catheters that are inserted by a physician 24 through the patient's vascular system via the skin into the chambers or vascular structures of the heart 12. Generally, a delivery sheath catheter is inserted into the left atrium or right atrium near the desired location in the heart 12. Then, one or more catheters can be inserted into the delivery sheath catheter to reach the desired location in the heart 12. The plurality of catheters can include catheters dedicated to sensing intracardiac electrogram (IEGM) signals, catheters dedicated to ablation, and / or catheters dedicated to both sensing and ablation. An example catheter 14 configured for sensing IEGM is illustrated herein. The physician 24 can place the distal end 28 of the catheter 14 in contact with the heart wall for sensing a target site in the heart 12. For ablation, the physician 24 can similarly place the distal end of the ablation catheter in contact with the target site for ablating tissue.

[0019] The catheter 14 is an exemplary catheter that includes one (and preferably a plurality) of electrodes 26 optionally disposed above a plurality of splines 22 at the distal end 28 and configured to sense IEGM signals. The catheter 14 can additionally include a position sensor 29 embedded in or near the distal end 28 for tracking the position and orientation of the distal end 28. The position sensor 29 can be a magnetic-based position sensor that includes three magnetic coils for sensing three-dimensional (3D) position and orientation (including roll).

[0020] The magnet-based position sensor 29 can operate in conjunction with the positioning pad 25, which includes a plurality of magnetic coils 32 configured to generate a magnetic field in a predetermined workspace. The real-time position of the distal end 28 of the catheter 14 can be tracked based on the magnetic field generated by the positioning pad 25 and sensed by the magnet-based position sensor 29. Details of magnet-based position sensing techniques are described in U.S. Patent Nos. 5,539,199, 5,443,489, 5,558,091, 6,172,499, 6,239,724, 6,332,089, 6,484,118, 6,618,612, 6,690,963, 6,788,967, and 6,892,091.

[0021] The system 10 includes one or more electrode (body surface) patches 38 positioned to contact the skin of the patient 23 to establish a position reference for impedance-based tracking of the positioning pad 25 and the electrodes 26. For impedance-based tracking, current is directed to the electrodes 26 and sensed at the electrode body surface patches 38 such that the position of each electrode can be triangulated (or otherwise calculated) via the electrode patches 38. Details of impedance-based position tracking techniques are described in U.S. Patent Nos. 7,536,218, 7,756,576, 7,848,787, 7,869,865, and 8,456,182.

[0022] The recorder 11 records and displays the electrogram 21 captured using the body surface ECG electrodes 18 and the intracardiac electrogram (IEGM) captured using the electrodes 26 of the catheter 14. The recorder 11 can include pacing capabilities for pacing the heart rhythm and / or can be electrically connected to an independent pacemaker.

[0023] The system 10 can include an ablation energy generator 50 adapted to conduct ablation energy to one or more electrodes at the distal end of a catheter configured for ablation. The energy generated by the ablation energy generator 50 can include, but is not limited to, radiofrequency (RF) energy or pulsed field ablation (PFA) energy (including unipolar or bipolar high voltage DC pulses that can be used to effect irreversible electroporation (IRE)), or combinations thereof.

[0024] The Patient Interface Unit (PIU) 30 is an interface configured to establish electrical communication between a catheter, other electrophysiology equipment, a power source, and a workstation 55 for controlling the operation of the system 10. The electrophysiology equipment of the system 10 can include, for example, a plurality of catheters, positioning pads 25, body surface ECG electrodes 18, electrode patches 38, an ablation energy generator 50, and a recorder 11. Optionally and preferably, the PIU 30 additionally has processing capabilities for implementing real-time calculation of the position of the catheter and for performing ECG calculations.

[0025] The workstation 55 includes a memory, a processor unit having a memory or storage device with appropriate operating software stored therein, and user interface capabilities. The workstation 55 can provide multiple functions, optionally including: (1) performing three-dimensional (3D) modeling of the endocardial anatomy and rendering a model or anatomic map 20 for display on a display device 27; (2) displaying an activation sequence (or other data) compiled from the recorded electrograms 21 with representative visual markers or images superimposed on the rendered anatomic map 20 on the display device 27; (3) displaying the real-time position and orientation of a plurality of catheters within the heart chambers; and (4) displaying sites of interest (such as where ablation energy has been applied) on the display device 27. An article embodying the elements of the system 10 may be commercially available under the trade name CARTO TM 3 system is purchased from Biosense Webster, Inc., 31A Technology Drive, Irvine, CA 92618.

[0026] Now refer to Figure 2 , which is Figure 1 a block diagram of the patient interface unit 30 in the system 10 of. The PIU 30 includes a signal generation device 40, a position tracking system 42, a signal processing device 44, and a catheter interface 46. The catheter interface 46 includes an electrode wire 58 configured to be electrically connected to the corresponding electrodes 26 of the catheter 14 via one or more suitable connectors.

[0027] The signal generation device 40 includes a memory 48, a processing circuit 52 (such as an FPGA or a suitable application-specific integrated circuit (ASIC) or a microprocessor programmed with suitable software), a digital-to-analog converter 54, and a switching circuit 56. The signal generation device 40 is configured to generate signal pulses that are time-division multiplexed via the electrode wire 58 of the catheter interface 46 to the electrodes 26 of the catheter 14, as described in more detail below with reference to Figure 3 more detailed description.

[0028] Figure 2 shows the catheter 14, which is configured to be inserted into a living subject (e.g., patient 23, for simplicity, in Figure 2into a body part (e.g., heart 12) depicted as a box). The electrode 26 of the catheter 14 is configured to emit a position signal in response to a time-division multiplexed signal pulse generated by the signal generation device 40.

[0029] As referenced Figure 1 as described, the electrode patch 38 (or body surface electrode) is configured to be applied to the body surface (e.g., chest and / or back) of a living subject (e.g., patient 23) and to detect the position signal emitted by the electrode 26 of the catheter 14. The position tracking system 42 is configured to calculate the position of the catheter 14 (and / or the electrode 26 of the catheter 14) in response to the detected position signal, e.g., in response to the distribution of current and / or impedance on the electrode patch 38. The position tracking system 42 identifies the electrode 26 of one of the position signals transmitted based on the transmission frequency of the detected position signal and the time period during which the position signal is detected according to the time schedule of the TDM used in the system 10.

[0030] The signal processing device 44 is configured to: receive electroanatomical signals from the electrode 26 and from the body surface ECG electrode 18 via the electrode wire 58, and process the received electroanatomical signals (e.g., by filtering the signals and / or calculating annotation times).

[0031] Now refer to Figure 3 which is a flowchart 60 of the steps in the method of operation of the system 10 including Figure 1 . The signal generation device 40 is configured to generate signal pulses (block 62). Each signal pulse in the signal pulses has a carrier frequency and has a non-rectangular signal envelope, as referenced Figure 4 described in more detail. The carrier frequency can have any suitable value, e.g., in the range of 50 kHz to 250 kHz or in the range of 100 kHz to 110 kHz. The signal generation device 40 is configured to time-division multiplex the signal pulses between the electrode wires 58 using, e.g., the switching circuit 56, which switches the output of the digital-to-analog converter 54 to different electrode wires 58 according to a time-division multiplexing schedule. For example, during time period A, the output of the digital-to-analog converter 54 is connected to the electrode wire X, and during time period B, the output of the digital-to-analog converter 54 is connected to the electrode wire Y, and in each time period, the digital-to-analog converter 54 generates the entire signal pulse.

[0032] Now refer to Figure 4 which is an example signal pulse 80 in the system 10 for Figure 1 . The signal pulse 80 includes a non-rectangular signal envelope 82 and a carrier frequency 84.

[0033] The signal generation device 40 is configured to generate a non-rectangular signal envelope 82, wherein the peak-to-peak amplitude of the envelope 82 gradually increases 86 over time (t) to a maximum peak-to-peak amplitude (P), and then after a given time period, the envelope 82 gradually decreases 88 over time (t) to a zero peak-to-peak amplitude (or a given peak-to-peak amplitude). The terms "gradually increases" and "gradually decreases" as used in the specification and claims are defined as the increase or decrease that occurs over time for the non-rectangular signal envelope 82. In other words, when the non-rectangular signal envelope 82 reaches a plateau, the non-rectangular signal envelope 82 increases from a zero peak value to a maximum peak value P over time, and then decreases to a zero peak value over time. The non-rectangular signal envelope 82 can have any suitable width W f For example, the non-rectangular signal envelope 82 can have a width in the range of 10 milliseconds to 100 milliseconds or in the range of 40 milliseconds to 50 milliseconds. The width W of the gradual increase 86 i and the width W of the gradual decrease 88 r can have any suitable width. For example, W i and / or W r can have a width in the range of 50 microseconds to 500 microseconds or in the range of 150 microseconds to 250 microseconds.

[0034] The gradual increase 86 in the peak-to-peak amplitude of the envelope 82 can be based on the error function (ERF) or any suitable function or shape. The gradual decrease 88 of the envelope 82 can be based on the complementary error function (ERFC) or any suitable function or shape.

[0035] The ERF function is defined as:

[0036]

[0037] And ERFC = 1 - ERF.

[0038] erf(x) can be calculated using any suitable value of x. For example, x can be a vector of numbers between 0 and 3.5, with an increment of 0.01 (i.e., x = [0, 0.01, 0.02, 0.03,... 3.5]).

[0039] Referring again to Figure 3 . The memory 48 is configured to store a digital signal pulse representation, for example, Figure 4Point - by - point representation of the signal pulse 80. The processing circuit 52 is configured to retrieve the digital signal pulse representation from the memory 48 (block 66) and provide the digital signal pulse representation to the digital - to - analog converter 54 (block 68), which is configured to convert the digital signal pulse representation into an analog signal including one of the signal pulses 80 (block 70). The steps of blocks 68 and 70 are repeated to generate a series of signal pulses 80 for output to the catheter 14. The output section of the digital - to - analog converter 54 is connected to the switching circuit 56, which is controlled to connect the output section of the digital - to - analog converter 54 to a selected one of the electrode lines 58 during any TDM time period according to the above - mentioned TDM schedule. The switching circuit 56 can be controlled by the processing circuit 52 or any suitable processor. The processing circuit 52 also times the generation of the signal pulses 80 according to the TDM schedule such that the entire signal pulse 80 is transmitted by the corresponding electrode 26 during each TDM time period in the TDM time period.

[0040] In some exemplary modes, the signal - generating device 40 is configured to generate signal pulses 80 having a maximum peak - to - peak amplitude P such that the maximum current density on the electrode 26 due to the signal pulse 80 is less than a given current density. For example, for an iridium - platinum electrode, the current density can be set to less than 0.44 mA / mm 2 .

[0041] In implementation, some or all of the functions of the processing circuit 52 can be combined in a single physical component or, alternatively, implemented using multiple physical components. These physical components can include hard - wired or programmable devices, or a combination of both. In some examples, at least some of the functions of the processing circuit 52 can be implemented by a programmable processor under the control of suitable software. The software can be downloaded electronically to the device (e.g., via a network). Alternatively or in addition, the software can be stored in a tangible non - transitory computer - readable storage medium, such as optical, magnetic, or electronic memory.

[0042] As used herein, the term “about” or “approximately” with respect to any numerical value or range indicates a suitable dimensional tolerance that allows a collection of parts or components to achieve its intended purpose as described herein. More specifically, “about” or “approximately” can refer to a range of values ±20% of the recited value. For example, “about 90%” can refer to a range of values from 72% to 108%.

[0043] Embodiment

[0044] Example 1: A medical system, comprising: a catheter interface, the catheter interface including electrode wires configured to be electrically connected to respective electrodes of a catheter; and a signal generation device configured to generate signal pulses, each of the signal pulses having a carrier frequency and having a non-rectangular signal envelope, the signal generation device being configured to time-division multiplex the signal pulses between the electrode wires.

[0045] Example 2: The system according to Example 1, further comprising: the catheter configured to be inserted into a body part of a living subject, the electrodes being configured to emit position signals in response to the time-division multiplexed signal pulses; body surface electrodes configured to be applied to the body surface of the living subject and to detect the position signals; and a position tracking system configured to calculate the position of the catheter in response to the detected position signals.

[0046] Example 3: The system according to Example 1, further comprising a signal processing device configured to: receive electroanatomical signals from the electrodes via the electrode wires; and process the received electroanatomical signals.

[0047] Example 4: The system according to Example 1, wherein the signal generation device is configured to generate the non-rectangular signal envelope, wherein the peak-to-peak amplitude of the envelope gradually increases over time to a maximum peak-to-peak amplitude.

[0048] Example 5: The system according to Example 1, wherein the signal generation device is configured to generate the non-rectangular signal envelope, wherein the peak-to-peak amplitude of the envelope gradually increases over time to a maximum peak-to-peak amplitude, and then after a given time period, the envelope gradually decreases over time to a zero peak-to-peak amplitude.

[0049] Example 6: The system according to Example 5, wherein the gradual increase in the peak-to-peak amplitude of the envelope is based on the error function (ERF).

[0050] Example 7: The system according to Example 6, wherein the gradual decrease in the envelope is based on the complementary error function (ERFC).

[0051] Example 8: The system according to Example 1 further includes a memory configured to store digital signal pulse representations. The signal generation device includes a processing circuit and a digital-to-analog converter. The processing circuit is configured to retrieve the digital signal pulse representations from the memory and provide the digital signal pulse representations to the digital-to-analog converter. The digital-to-analog converter is configured to convert the digital signal pulse representations into an analog signal including one of the signal pulses.

[0052] Example 9: The system according to Example 1, wherein the signal generation device is configured to generate the signal pulses having a maximum peak-to-peak amplitude such that the maximum current density on the electrodes is less than a given current density.

[0053] Example 10: A medical system includes: a catheter interface including electrode wires configured to be electrically connected to respective electrodes of a catheter; and a signal generation device configured to generate signal pulses and time-division multiplex the signal pulses between the electrode wires. The signal generation device is configured to generate the signal pulses having a maximum peak-to-peak amplitude such that the maximum current density on the electrodes is less than a given current density.

[0054] Example 11: A computer-implemented method includes: generating signal pulses, each of the signal pulses having a carrier frequency and a non-rectangular signal envelope; and time-division multiplexing the signal pulses between electrode wires configured to be electrically connected to respective electrodes of a catheter.

[0055] Example 12: The method according to Example 11 further includes: the electrodes emitting position signals in response to the time-division multiplexed signal pulses; body surface electrodes applied to a body surface of a live subject detecting the position signals; and calculating a position of the catheter in response to the detected position signals.

[0056] Example 13: The method according to Example 11 further includes: receiving electroanatomical signals from the electrodes via the electrode wires; and processing the received electroanatomical signals.

[0057] Example 14: The method according to Example 11 further includes: generating the non-rectangular signal envelope, wherein a peak-to-peak amplitude of the envelope gradually increases over time to a maximum peak-to-peak amplitude.

[0058] Example 15: The method according to Example 11 further includes: generating the non-rectangular signal envelope, wherein a peak-to-peak amplitude of the envelope gradually increases over time to a maximum peak-to-peak amplitude and then, after a given time period, the envelope gradually decreases over time to a zero peak-to-peak amplitude.

[0059] Example 16: The method according to Example 15, wherein the gradual increase in the peak-to-peak amplitude of the envelope is based on an error function (ERF).

[0060] Example 17: The method according to Example 16, wherein the gradual decrease of the envelope is based on a complementary error function (ERFC).

[0061] Example 18: The method according to Example 11, further comprising: storing a digital signal pulse representation; retrieving the stored digital signal pulse representation; and converting the digital signal pulse representation into an analog signal including one of the signal pulses.

[0062] Example 19: The method according to Example 11, wherein the generating comprises: generating the signal pulse having the maximum peak-to-peak amplitude such that the maximum current density on the electrode is less than a given current density.

[0063] Example 20: A computer-implemented method comprising: generating signal pulses; and time-division multiplexing the signal pulses between electrode lines configured to be electrically connected to respective electrodes of a catheter, wherein the generating comprises: generating the signal pulse having the maximum peak-to-peak amplitude such that the maximum current density on the electrode is less than a given current density.

[0064] For clarity, various features of the present disclosure described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, for brevity, various features of the present disclosure described in the context of a single embodiment may also be provided separately or in any suitable sub-combination.

[0065] The above embodiments are cited by way of example, and the present disclosure is not limited to what is specifically shown and described above. Instead, the scope of the present disclosure includes combinations and sub-combinations of the various features described above, as well as their variations and modifications, 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 system, comprising: A catheter interface, the catheter interface including electrode wires configured to be electrically connected to respective electrodes of a catheter; And A signal generation device configured to generate signal pulses, each of the signal pulses having a carrier frequency and having a non-rectangular signal envelope, the signal generation device being configured to time-division multiplex the signal pulses between the electrode wires.

2. The system according to claim 1, further comprising: The catheter configured to be inserted into a body part of a living subject, the electrodes being configured to emit position signals in response to the time-division multiplexed signal pulses; Body surface electrodes configured to be applied to the body surface of the living subject and to detect the position signals; And A position tracking system configured to calculate the position of the catheter in response to the detected position signals.

3. The system according to claim 1, further comprising a signal processing device configured to: Receive electroanatomical signals from the electrodes via the electrode wires; and Process the received electroanatomical signals.

4. The system according to claim 1, wherein The signal generation device is configured to generate the non-rectangular signal envelope, wherein the peak-to-peak amplitude of the envelope gradually increases over time to a maximum peak-to-peak amplitude.

5. The system according to claim 1, wherein, The signal generation device is configured to generate the non-rectangular signal envelope, wherein the peak-to-peak amplitude of the envelope gradually increases over time to a maximum peak-to-peak amplitude and then, after a given time period, the envelope gradually decreases over time to a zero peak-to-peak amplitude.

6. The system according to claim 5, wherein, The gradual increase in the peak-to-peak amplitude of the envelope is based on the error function (ERF).

7. The system according to claim 6, wherein, The gradual decrease in the envelope is based on the complementary error function (ERFC).

8. The system according to claim 1, further comprising a memory configured to store digital signal pulse representations, wherein, The signal generation device includes a processing circuit and a digital-to-analog converter, the processing circuit being configured to retrieve the digital signal pulse representation from the memory and provide the digital signal pulse representation to the digital-to-analog converter, the digital-to-analog converter being configured to convert the digital signal pulse representation into an analog signal including one of the signal pulses.

9. The system according to claim 1, wherein The signal generation device is configured to generate the signal pulses having a maximum peak-to-peak amplitude such that the maximum current density on the electrodes is less than a given current density.

10. A medical system, comprising: A catheter interface, the catheter interface including electrode wires configured to be electrically connected to respective electrodes of a catheter; And A signal generation device configured to generate signal pulses and time-division multiplex the signal pulses between the electrode wires, wherein the signal generation device is configured to generate the signal pulses having a maximum peak-to-peak amplitude such that the maximum current density on the electrodes is less than a given current density.

11. A computer-implemented method, comprising: Generating signal pulses, each of the signal pulses having a carrier frequency and having a non-rectangular signal envelope; And Time-division multiplexing the signal pulses between electrode lines configured to be electrically connected to respective electrodes of a catheter.

12. The method of claim 11, further comprising: The electrodes emitting position signals in response to the time-division multiplexed signal pulses; Body surface electrodes applied to a body surface of a live subject detecting the position signals; And Calculating a position of the catheter in response to the detected position signals.

13. The method of claim 11, further comprising: Receiving electroanatomical signals from the electrodes via the electrode lines; And Processing the received electroanatomical signals.

14. The method according to claim 11, further comprising: Generating the non-rectangular signal envelope, wherein a peak-to-peak amplitude of the envelope gradually increases over time to a maximum peak-to-peak amplitude.

15. The method according to claim 11 further comprises: Generating the non-rectangular signal envelope, wherein the peak-to-peak amplitude of the envelope gradually increases over time to a maximum peak-to-peak amplitude and then, after a given time period, the envelope gradually decreases over time to a zero peak-to-peak amplitude.

16. The method according to claim 15, wherein, The gradual increase in the peak-to-peak amplitude of the envelope is based on an error function (ERF).

17. The method according to claim 16, wherein, The gradual decrease in the envelope is based on a complementary error function (ERFC).

18. The method of claim 11, further comprising: Storing a digital signal pulse representation; Retrieving the stored digital signal pulse representation; And Converting the digital signal pulse representation to an analog signal including one of the signal pulses.

19. The method according to claim 11, wherein, The generating includes: generating the signal pulse having the maximum peak-to-peak amplitude such that a maximum current density on the electrode is less than a given current density.

20. A computer-implemented method, comprising: Generating signal pulses; And Time-division multiplexing the signal pulses between the electrode lines configured to be electrically connected to respective electrodes of a catheter, wherein the generating includes: generating the signal pulse having the maximum peak-to-peak amplitude such that a maximum current density on the electrode is less than a given current density.

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