Expansion of Electrocardiogram (ECG) Acquisition Capability of a Catheter-Based Heart System

Abstract

The present invention is titled "Expansion of Electrocardiogram (ECG) Acquisition Capability of a Catheter-Based Cardiac System". The present invention discloses a method, including receiving an analog body surface signal from a body surface electrode and a plurality of analog unipolar signals from a plurality of unipolar electrodes of an invasive probe. Designating a first unipolar electrode to serve as a common electrical ground and a common timing reference for the analog unipolar signals and the analog body surface signal. Digitizing the analog unipolar signals to generate digital unipolar signals sampled with respect to a digital ground. Defining an analog bipolar signal between the first unipolar electrode and a second unipolar electrode of the probe and a digital bipolar signal formed by the first unipolar electrode and the second unipolar electrode. During the connection of the first unipolar electrode to the digital ground, estimating a ground offset and a timing offset between the analog bipolar signal and the digital bipolar signal. Applying the ground offset and the timing offset to measure a third unipolar signal sensed by a third unipolar electrode.

Description

[0001] Cross - Reference to Related Applications

[0002] This patent application claims the benefit of U.S. Provisional Patent Application 62 / 863,679, filed on June 19, 2019, the disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention generally relates to the acquisition and processing of electrophysiological signals, and more particularly to the processing of electrocardiogram (ECG) signals acquired using a catheter. Background Art

[0004] Electrocardiogram (ECG) is a well-established cardiac diagnostic technique. Various techniques for measuring ECG signals have been proposed in the patent literature. For example, in some aspects, U.S. Patent 9,398,862 describes a method that includes measuring unipolar signals responsive to electrical activity in a heart chamber at one or more electrodes. In some embodiments, signals are measured at a single catheter location within a ventricle or at several locations over a number of heartbeats. The method further includes determining bipolar physiological information at a plurality of locations on the surface based at least in part on Laplace's equation and based on the measured unipolar signals and the position of one or more electrodes relative to the surface.

[0005] As another example, Chinese Patent Application Publication 2018 / 11333583 describes a method and a measuring device for measuring the ECG pulse wave propagation time. A synchronous acquisition method measures the pulse wave signal, extracts the pulse wave signal and ECG feature points, and calculates the pulse conduction time. Based on the ECG in the pre-systole period, the method obtains the pulse wave propagation time by calculating and subtracting the pre-systole period from the calculated pulse conduction time. The present invention removes the influence of the pre-systole period and improves the measurement accuracy of the pulse wave propagation time. Summary of the Invention

[0006] The present invention discloses a method that includes receiving (i) analog body surface signals from one or more body surface electrodes attached to the exterior of a patient, and (ii) a plurality of analog unipolar signals from a plurality of unipolar electrodes of a probe inserted into an organ of the patient. A first unipolar electrode is designated from the plurality of unipolar electrodes to serve as a common electrical ground and a common timing reference for the analog unipolar signals and the analog body surface signals. The analog unipolar signals are digitized to produce corresponding digital unipolar signals by sampling the analog unipolar signals with respect to digital ground. The following signals are defined: (i) an analog bipolar signal between the first unipolar electrode and a second unipolar electrode of the probe, and (ii) a digital bipolar signal formed by the corresponding digital unipolar signals derived from the first unipolar electrode and the second unipolar electrode. During a period when the first unipolar electrode is connected to digital ground, the ground offset and the timing offset between the analog bipolar signal and the digital bipolar signal are estimated.

[0007] Apply a ground offset and a timing offset to measure a third unipolar signal sensed by a third unipolar electrode of a catheter relative to a body surface signal.

[0008] In some embodiments, the analog unipolar signals and the digital unipolar signals include electrocardiograms.

[0009] In some embodiments, the analog body surface signals include Wilson central terminal (WCT) signals.

[0010] According to another embodiment of the present invention, there is also provided a device including a circuit and a processor. The circuit is configured to: (a) receive analog body surface signals from one or more body surface electrodes attached to the outside of a patient; (b) receive a plurality of analog unipolar signals from a plurality of unipolar electrodes of a probe inserted into an organ of the patient; (c) designate a first unipolar electrode from the plurality of unipolar electrodes to serve as a common electrical ground and a common timing reference for the analog unipolar signals and the analog body surface signals; (d) digitize the analog unipolar signals to generate corresponding digital unipolar signals by sampling the analog unipolar signals relative to a digital ground; and (e) define (i) an analog bipolar signal between the first unipolar electrode and a second unipolar electrode of the probe and (ii) a digital bipolar signal formed by the corresponding digital unipolar signals derived from the first unipolar electrode and the second unipolar electrode. The processor is configured to estimate a ground offset and a timing offset between the analog bipolar signal and the digital bipolar signal during a period when the first unipolar electrode is connected to the digital ground; and apply the ground offset and the timing offset to measure a third unipolar signal sensed by a third unipolar electrode of the probe relative to the body surface signal.

[0011] In conjunction with the accompanying drawings, the present invention will be more fully understood through the following detailed description of embodiments of the present invention, wherein: Description of the Drawings

[0012] Figure 1 Is a schematic diagram of a catheter-based electrophysiological sensing system according to an embodiment of the present invention;

[0013] Figures 2A - 2C Is for an embodiment of the present invention to enable Figure 1 Of the system to measure unipolar signals from a catheter and a circuit diagram; and

[0014] Figure 3 Is schematically shown according to an embodiment of the present invention using Figure 1 Of the system to measure a method flow diagram of a plurality of electrode signals from a catheter. Detailed Description

[0015] Overview

[0016] Conventional catheter-based cardiac systems are sometimes configured to measure a limited number of signals, e.g., up to a few dozen electrocardiogram (ECG) channels. However, modern diagnostic catheters can have more electrodes located within a subject's organ (e.g., the heart), e.g., 256 electrodes. To accommodate the additional channels of modern diagnostic catheters, signals from such catheters (e.g., 256-channel basket catheters) can be transmitted via a digital communication link to a conventional catheter-based system for processing all channels.

[0017] To transmit analog signals from a catheter via a digital link, an analog-to-digital converter (ADC) module (referred to herein as an "ADC dongle" or simply a "dongle") is inserted between the diagnostic catheter and the conventional catheter-based system.

[0018] Some clinical applications require acquisition of catheter signals as unipolar signals referenced to a Wilson Central Terminal (WCT) ground coupled to the conventional system, which is formed by three body surface electrodes attached to the patient's skin. The WCT ground is obtained by averaging the voltages of three external active limb electrodes measured with respect to a return ground electrode, which is further described in "True Unipolar ECG Machine for Wilson Central Terminal Measurements" by Gaetano D. Gargiulo (The MARCS Institute, University of Western Sydney, Kingswood, NSW2747, Australia) published in May 2015 and "Wilson’s Central Terminal, the keystone to electrogram recording - What, where and why?" by John Silberbauer (EP Fellow, San Raffaele Hospital, Milan) published on April 23, 2013, both of which are incorporated by reference in the appendix.

[0019] When the conventional system processor uses the digitized signal from any one of the 256 ECG channels of an internally positioned catheter to derive and analyze a unipolar signal referenced to the WCT ground, two problems arise.

[0020] The first problem is that the electrical ground of the ADC dongle (relative to which the unipolar signal is digitized) and the ground of the conventional catheter-based system (e.g., the WCT ground) are different. Thus, the digitized unipolar amplitude input from the catheter will have an incorrect amplitude on the conventional catheter-based system.

[0021] A second problem is that the timing of the digital signal (e.g., signal phase) is not related to the timing of the WCT ground of the original catheter-based system. Asynchronous signals (digital catheter signals relative to analog ground signals) thus cannot be related to each other (even if there is no problem with ground amplitude).

[0022] The embodiments of the present invention described below provide devices and methods to overcome the lack of a common ground and the lack of signal synchronization between the original system and modern diagnostic catheters coupled via a digital link. The disclosed techniques allow, for example, accurate measurement of multiple unipolar ECG signals using the original system.

[0023] In some embodiments, the disclosed device is provided to overcome the lack of a common ground and the lack of signal synchronization described above. The device includes an interface circuit of the original system, which is configured to receive analog body surface signals (e.g., WCT ground signals) from one or more body surface electrodes attached to the outside of the patient.

[0024] The disclosed device further includes additional (e.g., external or independent) circuitry, which includes an ADC module, wherein the additional circuitry is configured to: receive multiple analog unipolar signals from multiple unipolar electrodes of a probe inserted into an organ of the patient; designate a first unipolar electrode from the multiple unipolar electrodes to serve as a common electrical ground and a common timing reference for the analog unipolar signals and the analog body surface signals; digitize the analog unipolar signals to generate corresponding digital unipolar signals by sampling the analog unipolar signals relative to a digital ground; and define (i) an analog bipolar signal between the first unipolar electrode and a second unipolar electrode of the probe and (ii) a digital bipolar signal formed by the corresponding digital unipolar signals derived from the first unipolar electrode and the second unipolar electrode.

[0025] The disclosed device further includes a processor of the original system, which is configured to estimate the ground offset and timing offset between the analog bipolar signal and the digital bipolar signal during the connection of the first unipolar electrode to the digital ground; and apply the ground offset and timing offset to measure a third unipolar signal sensed by a third unipolar electrode of the probe (e.g., catheter) relative to the body surface signal.

[0026] In other words, the disclosed technique sacrifices one of the electrodes of the probe and uses that electrode to serve as a common ground and a common timing reference between the digital signal and the original analog signal.

[0027] To estimate the timing offset, the processor command interface circuit of the original system applies a high-pass filter (i.e., “drift”) to both the analog bipolar signal input and the digital bipolar signal. These two bipolar signals are then transmitted to the cross-correlator circuit of the original system, which cross-correlates the two bipolar signals. In one embodiment, the processor uses the cross-correlated bipolar signals to synchronize the clocks of the original system and the dongle signal to eliminate the timing offset between the analog bipolar signal and the digital bipolar signal.

[0028] To apply the ground offset to measure the third monopolar signal, after applying the timing offset, the processor of the original system calculates the corresponding monopolar signal acquired by the third electrode of the probe. The processor can calculate the monopolar voltage by calculating the value of V x -V WCT (where X = 1, 2, …, 256) for any third catheter electrode X (i.e., for the digitized signal from any catheter electrode transmitted via the digital link), as described below.

[0029] Typically, the processor is programmed with software that includes a specific algorithm that enables the processor to perform each of the processor-related steps and functions listed above.

[0030] The disclosed technique provides a simple and effective device that enables an original system to accurately measure multiple monopolar signals acquired by multiple electrodes of a modern catheter. Thus, the disclosed technique can increase the availability of diagnostic services based on modern catheters.

[0031] System Description

[0032] Figure 1 Schematic illustration of a catheter-based electrophysiological sensing system 20 according to an embodiment of the present invention. The system 20 can be, for example, a 3 system manufactured by Biosense-Webster (Irvine, California). As shown, the system 20 includes a catheter 21 having a shaft 22 that is navigated by a physician 30 into the heart 26 of a patient 28. In the illustrated example, the physician 30 inserts the shaft 22 through a sheath 23 while manipulating the shaft 22 using a manipulator 32 near the proximal end of the catheter.

[0033] In the embodiments described herein, the catheter 21 can be used for any suitable diagnostic purpose, such as electrophysiological mapping of the heart 26. An ECG recorder 35 can receive various types of ECG signals sensed by the system 20 during the procedure.

[0034] As shown in Illustration 25, the distal end of the shaft 22 of the catheter 21 is equipped with a multi-electrode basket catheter 40. Illustration 45 shows the arrangement of a plurality of sensing electrodes 48 (i.e., 256 or more channels) of the basket catheter 40. The proximal end of the catheter 21 is connected to the console 24 through an ADC dongle 50. The ADC dongle 50 accommodates the additional channels from the plurality of electrodes 48 by digitizing all the catheter channels and transmitting the digitized signals to the digital link 51 of the console 24.

[0035] The console 24 includes a processor 41 (usually a general-purpose computer), which has a suitable front-end and interface circuit 38 for receiving ECG signals and non-ECG signals (such as position signals) from the sensing electrodes 48 of the catheter 21. The electrodes 48 can include 256 or more sensing electrodes, and each of the electrodes 48 will be indexed as "electrode 48#1, #2, #3...#n" arranged inside or near the heart. For this purpose, the processor 41 is connected to the sensing electrodes 48 via wires extending within the shaft 22. The interface circuit 38 is also configured to receive ECG signals and non-ECG signals from the body surface electrodes 49. Generally, the electrodes 49 are attached to the skin around the chest and legs of the patient 28. The processor 41 is connected to the electrodes 49 via wires extending through the cable 39 to receive signals from the electrodes 49.

[0036] Four of the body surface electrodes 49 are named according to the standard ECG protocol: MA (right arm), LA (left arm), ML (right leg), and LL (left leg). The Wilson central terminal (WCT) can be formed by three of the four named body surface electrodes 49, and the resulting ECG signal V WCT is received by the interface circuit 38.

[0037] To overcome the lack of synchronization between the signals collected by the catheter electrodes 48 and the body surface electrodes 49 described above, the system 20 has two of the catheter electrodes, which are additionally connected to the interface circuit 38 via a first split cable 52. In this way, the original system directly receives the analog bipolar signal. In addition, the above two catheter electrodes provide a digital bipolar signal with respect to the digital ground formed by the second split cable 54, which electrically grounds one of the electrodes to the ground of the dongle 50. The wires 52 and 54 enable the processor 41 of the original system 20 to synchronize the two bipolar signals, and then be able to accurately derive and present the catheter unipolar ECG signals from the electrodes 48 on the original system 20, as described below.

[0038] Processor 41 is typically programmed in software to perform the functions described herein. For example, the software may be downloaded electronically to the processor via a network, or alternatively or in addition, the software may be provided and / or stored on a non-transitory tangible medium such as magnetic, optical, or electronic memory. Specifically, processor 41 runs a dedicated algorithm as disclosed herein, which is included in Figure 3 and enables processor 41 to perform the disclosed steps, as further described below.

[0039] Expansion of ECG Acquisition Capability of a Catheter - Based Heart System

[0040] Figures 2A - 2C Device 100 for enabling a Figure 1 system according to an embodiment of the present invention to measure a unipolar signal from catheter 21, and a circuit diagram thereof.

[0041] As Figure 2A shown, interface circuit 38 receives electrical signals from body surface electrodes 49 via cable 39. Electrodes 49 are typically attached to the patient's skin around the chest and legs of patient 28. Four of the electrodes 49 are shown: MA (right arm), LA (left arm), ML (right leg), LL (left leg). The Wilson central terminal (WCT) is formed by three of these four shown body surface electrodes 49, and the resulting ECG signal V WCT is received by interface circuit 38, as Figure 2B shown.

[0042] As Figure 2B further shown, electrodes 48#1 and #2 are wired via cable 52 into input sockets of interface circuit 38, which directly receive the analog bipolar signal V 12 . Note that any other two of the 256 or more electrodes of catheter 21 may be used for electrodes 48, and using electrodes #1 and #2 does not lose generality. All 256 or more electrodes of electrodes 48 (including electrodes #1 and #2 as well) are connected to interface circuit 38 via a dongle 50 inserted into a socket of digital link 51. As shown, electrode #1 is grounded to the ground of ADC dongle 50 via cable 54 within dongle 50.

[0043] Processor 41 receives an input set of signals via ADC dongle 50 and via digital link 51 in interface circuit 38, the input set of signals including a set of measured and digitized bipolar signals (V x -V 1 ), X = 2, …, n, where n is 256 or greater. Processor 41 also directly receives the measured ground offset signal (V 1 -V WCT), the processor can now compare this measured ground offset signal with the synchronized digitized bipolar signal (V x -V 1 ) are added to derive the unipolar signal. The processor 41 derives the remaining 255 unipolar signals V by calculating the following summation: x -V WCT (ie, relative to V WCT ) in each:

[0044] Formula 1 V x -V WCT =(V x -V 1 )+(V 1 -V WCT ),X=2,…,n

[0045] like Figure 2C As shown, Figure 2A The schematic arrangement shown (for Figure 1 of 3 system) can be implemented with a body surface sensor "BS" connected to a patient interface unit (PIU). The PIU is also connected to a dongle 50 with a diagnostic catheter 48. In this prototype, both the circuit 38 and the processor 41 are combined into the PIU.

[0046] Figure 3 To schematically illustrate the use of an embodiment according to the present invention Figure 1 Flow chart of a method for measuring multiple electrode signals from a catheter by a system. The algorithm according to the present embodiment performs the following process, which begins at a first wiring step 70, where the catheter 21 electrode 48#1 (i.e., the first electrode) and the 48 electrode 48#2 (e.g., 256 electrodes taken from the catheter 21) are directly wired to the interface circuit 38 of the system 20, and then the signals from both are digitized. At a second wiring step 72, the electrode 48#1 is grounded to the ground of the ADC dongle 50.

[0047] At ground offset extraction step 73, the analog potential of electrode 48#1 is measured by interface circuit 38 and compared with the WCT potential to derive the ground offset V 1 -V WCT .

[0048] In parallel, at a bipolar signal measurement step 76 , the interface circuit 38 measures an analog bipolar signal and a digital bipolar signal digitized from the same source of the analog bipolar signal.

[0049] At a clock synchronization step 76 , the interface circuit 38 synchronizes the clocks of the system 20 and the ADC dongle 50 using the measured analog bipolar signal and the digital bipolar signal.

[0050] At sampling step 78, the catheter signals from each electrode are digitized and sampled relative to electrode 48#1 by ADC dongle 50.

[0051] Finally, at the unipolar signal calculation step 80, for the third digitized signal from any electrode 48 different from electrodes 48#1 and #2, the processor 41 calculates the corresponding unipolar signal relative to the WCT ground using Equation 1.

[0052] The exemplary configurations shown in the figures are chosen only for clarity of concept. In alternative embodiments, the techniques disclosed in the present invention may use other suitable configurations, including other wiring schemes, different independent interfaces, and other types of catheters other than basket catheters.

[0053] It should be understood that the above embodiments are cited by way of example and that the present invention is not limited to what is specifically shown and described above. On the contrary, the scope of the present invention includes combinations and sub - combinations of the various features described above, as well as their variations and modifications that would occur to those skilled in the art upon reading the above description and that are not disclosed in the prior art. Documents incorporated by reference into this patent application are considered an integral part of this application, except that if any terms defined in these incorporated documents conflict with the definitions expressly or implicitly given in this specification, only the definitions in this specification shall be considered.

Claims

1. A method, comprising: receiving (i) an analog body surface signal from one or more body surface electrodes attached to the exterior of a patient, and (ii) a plurality of analog monopolar signals from a plurality of monopolar electrodes of a probe inserted into an organ of the patient; designating a first monopolar electrode from the plurality of monopolar electrodes to serve as a common electrical ground and a common timing reference for the analog monopolar signals and the analog body surface signal; digitizing the analog monopolar signals to produce corresponding digital monopolar signals by sampling the analog monopolar signals with respect to the common electrical ground; defining (i) an analog bipolar signal between the first monopolar electrode and a second monopolar electrode of the probe and (ii) a digital bipolar signal formed by corresponding digital monopolar signals derived from the first monopolar electrode and the second monopolar electrode; estimating a ground offset and a timing offset between the analog bipolar signal and the digital bipolar signal while the first monopolar electrode is connected to the common electrical ground; and applying the ground offset and the timing offset to measure a third monopolar signal sensed by a third monopolar electrode of the probe relative to the body surface signal.

2. The method according to claim 1, wherein the analog monopolar signals and the digital monopolar signals comprise electrocardiograms.

3. The method according to claim 1, wherein the analog body surface signal comprises a Wilson central terminal (WCT) signal.

4. An apparatus, comprising: a circuit including an interface circuit configured to: receive an analog body surface signal from one or more body surface electrodes attached to the exterior of a patient; receive a plurality of analog monopolar signals from a plurality of monopolar electrodes of a probe inserted into an organ of the patient; the circuit being configured to: designate a first monopolar electrode from the plurality of monopolar electrodes to serve as a common electrical ground and a common timing reference for the analog monopolar signals and the analog body surface signal; digitize the analog monopolar signals to produce corresponding digital monopolar signals by sampling the analog monopolar signals with respect to the common electrical ground; and define (i) an analog bipolar signal between the first monopolar electrode and a second monopolar electrode of the probe and (ii) a digital bipolar signal formed by corresponding digital monopolar signals derived from the first monopolar electrode and the second monopolar electrode; and a processor configured to: estimate a ground offset and a timing offset between the analog bipolar signal and the digital bipolar signal while the first monopolar electrode is connected to the common electrical ground; and apply the ground offset and the timing offset to measure a third monopolar signal sensed by a third monopolar electrode of the probe relative to the body surface signal.

5. The apparatus according to claim 4, wherein the interface circuit and the processor are included in an existing catheter-based system.

6. The apparatus according to claim 4, wherein the analog monopolar signals and the digital monopolar signals comprise electrocardiograms.

7. The apparatus according to claim 4, wherein the analog body surface signal comprises a Wilson central terminal (WCT) signal.

8. The apparatus according to claim 4, wherein the interface circuit includes a multi-channel digital link configured to receive digitized signals from the probe.

Images