Using statistical features of multiple grouped ECG signals to detect inconsistent signals

Abstract

The present invention is entitled "Detecting inconsistent signals using statistical features of multiple grouped ECG signals." The present invention discloses a system comprising a signal acquisition circuit and a processor. The signal acquisition circuit is configured to receive multiple intracardiac signals acquired by multiple electrodes of an intracardiac probe in a patient's heart. The processor is configured to: extract multiple annotation values ​​from the intracardiac signals; select a group of the intracardiac signals; identify one or more annotation values ​​in the group that statistically deviate by more than a predefined deviation measure; and visualize annotation values ​​other than the statistically deviated annotation values ​​to a user.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This patent application is related to U.S. patent application entitled “Optimizing Mapping of ECG Signals Retrospectively by Detecting Inconsistency” filed on even date herewith and having attorney docket number BIO6197USNP1, the disclosure of which is incorporated herein by reference. Technical Field

[0003] The present invention relates generally to in vivo medical procedures and devices, and particularly to in vivo cardiac electrocardiogram (ECG) sensing. Background Art

[0004] When measuring and annotating internal electrocardiogram (iECG) signals generated by a large number of electrodes, it may be desirable to process these signals (eg, by a computer) in order to reduce embedded noise.

[0005] There are various methods for such iECG signal processing. For example, U.S. Patent Application 2009 / 0089048 describes an automatic method for determining the local activation time (LAT) of four or more multi-channel electrocardiogram signals, the multi-channel electrocardiogram signal including a ventricular channel, a mapping channel, and a plurality of reference channels.

[0006] Another example is Yan et al., “A 13μA Analog Signal Processing IC for Accurate Recognition of Multiple Intra-Cardiac Signals,” IEEE Transactions On Biomedical Circuits And Systems, Vol. 7, December 6, 2013, which describes an analog signal processing IC for low-power cardiac rhythm analysis featuring three identical but independent intra-ECG readout channels, each including an analog QRS feature extractor for low power consumption and rapid diagnosis of the electrocardiogram. Summary of the Invention

[0007] One embodiment of the invention described herein provides a system comprising a signal acquisition circuit and a processor. The signal acquisition circuit is configured to receive a plurality of intracardiac signals acquired by a plurality of electrodes of an intracardiac probe in a patient's heart. The processor is configured to: extract a plurality of annotation values ​​from the intracardiac signals; select a group of the intracardiac signals; identify one or more annotation values ​​in the group that are statistically deviated by more than a predefined deviation measure; and visualize the annotation values ​​other than the statistically deviated annotation values ​​to a user.

[0008] In some embodiments, the processor is configured to define the measure of deviation based on a standard score of the annotation values. In another embodiment, the processor is configured to define the measure of deviation based on one or more percentiles of the annotation values.

[0009] In one embodiment, the processor is configured to calculate a deviation of the annotation value on an intracardiac signal acquired by a selected subset of spatially correlated electrodes located no more than a predefined distance from one another in the heart. In another embodiment, the processor is configured to average the intracardiac signal over a plurality of time-correlated cardiac cycles occurring within a predefined time period when calculating the deviation of the annotation value.

[0010] In the disclosed embodiments, the processor is configured to correct one or more of the annotation values ​​in a given intracardiac signal acquired by a given electrode in the group to compensate for displacement of the given electrode relative to other electrodes in the group. In some embodiments, the annotation values ​​include local activation time (LAT). In an exemplary embodiment, the processor is configured to visualize the annotation values ​​by superimposing the annotation values, except for statistically deviated annotation values, on a model of the heart.

[0011] According to one embodiment of the present invention, a method is further provided, comprising receiving a plurality of intracardiac signals acquired by a plurality of electrodes of an intracardiac probe in a patient's heart, extracting a plurality of annotation values ​​from the intracardiac signals, selecting a group of intracardiac signals, identifying one or more annotation values ​​in the group that are statistically deviated by more than a predefined deviation measure, and visualizing the annotation values ​​other than the statistically deviated annotation values ​​to a user.

[0012] The present invention will be more fully understood through the following detailed description of embodiments of the present invention in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 is a schematic illustration of an electroanatomical system for multi-channel measurement of ECG signals within a heart according to an embodiment of the present invention;

[0014] Figure 2A diagram schematically illustrating a plurality of electrodes collecting signals in a plurality of cardiac cycles according to an embodiment of the present invention;

[0015] Figure 3A is a flow chart schematically illustrating a first method for enhancing the reliability of annotation values ​​according to an embodiment of the present invention;

[0016] Figure 3B is a flow chart schematically illustrating a second method for enhancing the reliability of annotation values ​​according to an embodiment of the present invention; and

[0017] Figure 4 The flowchart schematically illustrates an improved method for enhancing the reliability of annotation values ​​according to an embodiment of the present invention. DETAILED DESCRIPTION

[0018] Overview

[0019] Cardiac diagnostic and therapeutic systems based on intracardiac probes (e.g., catheter-based) can measure multiple intracardiac signals, such as electrocardiograms (ECGs), during invasive procedures. Such systems can use electrodes mounted at the distal end of the probe (hereinafter also referred to as "distal electrodes") to acquire multiple intracardiac signals. The measured signals can be used to provide physicians with visual cardiac information, such as 3-D mapping of the patient's intracardiac pathological electrographic sources, and to support corrective medical procedures, such as ablation.

[0020] The measured signal is typically weak, with a low signal-to-noise ratio (SNR). Furthermore, some electrodes may have a poor or nonexistent galvanic connection to the tissue. On the other hand, many electrodes are used, so the data the system receives from them may contain some redundancy.

[0021] Embodiments of the invention disclosed herein provide an intracardiac probe-based electroanatomical measurement and analysis system and method using statistical properties of signals collected by distal electrodes to improve the quality and reliability of the collected data.

[0022] In the description below, we will refer to annotated values ​​of Local Activation Time (LAT). However, the disclosed technology is not limited to LAT; in various embodiments of the present invention, annotated values ​​of various other suitable signal parameters may be used.

[0023] In some embodiments according to the present invention, the processor extracts the annotation value (e.g., LAT) of the signal and then calculates the statistical properties of the LAT values ​​of a set of signals collected by a corresponding set of electrodes (which may include all or some electrodes). In one embodiment, the statistical properties include the average value of the LAT values ​​of the set of signals (e.g., ); in other embodiments, the characteristic also includes the standard deviation of the group (e.g., ). The processor then uses a statistical method to determine, for each signal in the set of signals, whether the signal's annotation value is a valid value or a value that should be ignored.

[0024] In another embodiment, the statistical characteristic includes the quartiles of the set of LAT values. The processor calculates the first quartile Q1 and the third quartile Q3, and then ignores all values ​​below Q1 or above Q3 (the first quartile (Q1) is defined as the middle number between the minimum and median of the data set; the third quartile (Q3) is the middle value between the median and the highest value of the data set). Alternatively, the processor may define a measure of the deviation of the LAT value based on any other suitable percentile (or multiple percentiles) of the LAT value. Further alternatively, any other suitable process of discarding abnormal LAT values ​​may be used.

[0025] The technology disclosed above assumes that in the absence of noise and irregular current connections, the group of electrodes exhibit similar annotation values. Typically, the annotation values ​​collected by electrodes far away from each other can vary significantly. In addition, the signal from each electrode can be periodically annotated with each heartbeat ("cardiac cycle"), and the annotation values ​​derived from cardiac cycles that are far away from each other in time can vary. In one embodiment, the group of signals is correlated. In some embodiments, the tracking system measures the geometric position of the electrodes, and the group includes annotation values ​​derived only from adjacent electrodes ("spatially correlated", i.e., electrodes that are no more than a predefined distance apart). In other embodiments, the group includes annotation values ​​only from adjacent cardiac cycles ("temporally correlated", i.e., all cardiac cycles that occur within a predefined time period); and in one embodiment, the group includes values ​​that are both spatially and temporally correlated (referred to as "correlated values" for short).

[0026] In some embodiments, after calculating the statistical properties of the set of relevant LAT values, the processor omits LAT values ​​from the set that are statistically deviant (e.g., significantly different from the mean of the set of values) (the remaining set of LAT values ​​will be referred to as the set of valid LAT values). Thus, LAT values ​​corresponding to electrodes with poor connections or electrodes experiencing extreme noise can be eliminated from the set of valid LAT values.

[0027] In an embodiment, to determine whether a LAT value deviates statistically from the mean LAT of a group of signals, the processor measures the deviation of the annotated LAT value from the mean of the group of LAT values. In one embodiment, the measure of deviation is the standard score of the value (defined as the difference between the value and the mean divided by the standard deviation), which is compared to preset limits. For example, values ​​that are more than 3.5 standard deviations above the mean (standard score = 3.5) or more than 1.5 standard deviations below the mean (standard score = -1.5) can be considered statistically deviated and therefore omitted. In another embodiment, the processor omits values ​​below the first quartile or above the third quartile.

[0028] In some embodiments of the present invention, the processor can mitigate variations in LAT values ​​for spatially related electrodes due to differences in time delays in propagation of cardiac signals within the heart. According to an embodiment, the processor can correct the LAT annotation acquired by a given electrode by compensating for the displacement of the given electrode relative to other electrodes to eliminate differences in propagation delays.

[0029] In summary, according to embodiments of the present invention, the quality and reliability of a set of annotation values ​​for spatially and / or temporally correlated intracardiac signals can be improved by calculating statistical properties of the set of annotation values, comparing the annotation values ​​to a mean value of the set, and omitting values ​​that are far from the mean value from the set of valid values. In some embodiments, the set of annotation values ​​can first be modified to correct for signal propagation delays before the statistical properties are calculated.

[0030] System Description

[0031] Figure 1 is a schematic illustration of an electroanatomical system 21 for multi-channel measurement of ECG signals in a heart, according to an embodiment of the present invention. In some embodiments, system 21 is used for electroanatomical mapping of the heart.

[0032] Figure 1 A physician 22 is depicted using an electroanatomical catheter 23 to perform electroanatomical mapping of a heart 24 of a patient 25. The catheter 23 includes at its distal end one or more arms 26, which may be mechanically flexible, with one or more distal electrodes 27 coupled to each of the one or more arms. It should be understood that although Figure 1 A catheter with five arms is depicted, but other types of catheters may be used in accordance with alternative embodiments of the present invention. The electrodes are coupled to a processor 34 through an interface 32 .

[0033] During an electroanatomical mapping procedure, a tracking system is used to track the intracardiac position of the distal electrodes 27 so that each of the acquired electrophysiological signals can be associated with a known intracardiac position. One example of a tracking system is the Active Current Location (ACL) system described in U.S. Patent 8,456,182. In the ACL system, a processor estimates the respective position of the distal electrodes based on impedance measured between each of the distal electrodes 27 and a plurality of surface electrodes 28 coupled to the skin of the patient 25. (For ease of illustration, Figure 1 Only one surface electrode is shown.) The processor can then associate any electrophysiological signals received from distal electrode 27 with the location where the signal was acquired.

[0034] In some embodiments, multiple distal electrodes 27 acquire intracardiac ECG signals from tissue of a chamber of heart 24. The processor includes signal acquisition circuitry 36 coupled to receive the intracardiac signals from interface 32, memory 38 to store data and / or instructions, and a processing unit 42 (e.g., a CPU or other processor).

[0035] The signal acquisition circuit 36 ​​digitizes the intracardiac signals to generate a plurality of digital signals, and then transmits the digitized signals to a processing unit 42 included in the processor 28 .

[0036] Among other tasks, the processing unit 42 is configured to extract annotation parameters from the signals, calculate statistical properties, such as the average value of the annotation parameters for multiple groups of adjacent signals that may be similar (in this context, adjacent signals refer to signals from electrodes that are close to each other ("spatially correlated"), and / or annotation values ​​extracted from cardiac cycles that are close to each other in time ("temporally correlated")).

[0037] The processing unit is further configured to discard (i.e., omit) from the set potentially invalid annotation values ​​(such as annotations from electrodes with poor current connections or subject to strong temporal noise) after calculating the statistical properties. The remaining annotation values ​​will hereinafter be referred to as "valid annotation values."

[0038] The processing unit 42 visualizes the valid annotation values ​​to the user, i.e., the annotation values ​​excluding the omitted statistically deviant annotation values. In some embodiments, the processing unit 42 visualizes the valid annotation values, for example, by superimposing the valid annotation values ​​on an electroanatomical map 50 of the heart and displaying the map to the physician 22 on a screen 52. Alternatively, the processing unit 42 may visualize the valid annotation values ​​(after omitting the invalid annotation values) in any other suitable manner.

[0039] Figure 1The exemplary illustrations shown are chosen solely for conceptual clarity. In alternative embodiments of the present invention, for example, a voltage gradient may be applied between pairs of surface electrodes 28 and the resulting potentials may be measured using distal electrodes 27 (i.e., using a CMOS sensor manufactured by Biosense-Webster of Irvine, California). 4 technology) to perform position measurement. Therefore, the embodiments of the present invention are applicable to any position sensing method.

[0040] Other types of catheters may be used equivalently, such as Catheter (produced by Biosense-Webster), or basket catheter. A contact sensor can be mounted on the distal end of electroanatomical catheter 23. Other types of electrodes (such as electrodes used for ablation) can be used on distal electrode 27 in a similar manner to collect intracardiac electrophysiological signals.

[0041] Figure 1 Components relevant to embodiments of the present invention are primarily shown. Other system elements, such as external ECG recording electrodes and their connections, are omitted. Various ECG recording system elements, as well as elements for filtering, digitizing, protecting the circuit, etc., are omitted.

[0042] In an alternative embodiment, a readout application specific integrated circuit (ASIC) is used to measure the ECG signal within the heart. The various components used to route the signal acquisition circuit 36 ​​can be implemented in hardware, for example, using one or more discrete components such as a field programmable gate array (FPGA) or an ASIC. In some embodiments, some components of the signal acquisition circuit 36 ​​and / or the processing unit 42 can be implemented in software, or by using a combination of software and hardware components.

[0043] The processing unit 42 typically includes a general-purpose processor having software programmed to perform the functions described herein. For example, the software may be downloaded in electronic form over a network, or alternatively or in addition, the software may be provided and / or stored on non-transitory tangible media such as magnetic, optical, or electronic memory.

[0044] Related Annotation Values

[0045] Relevant annotation values ​​are derived from spatially related electrodes (e.g., electrodes that are geometrically close to each other, i.e., no more than a predefined distance from each other) and / or temporally related signals (e.g., values ​​extracted from cardiac cycles that are close to each other, i.e., occur within no more than a predefined time period). More specifically, relevant annotation values ​​are annotation values ​​for which the combined distance, including the geometric distance between electrodes and the temporal distance between cardiac cycles, is below some predefined threshold.

[0046] Figure 2 2 is a diagram schematically illustrating signal acquisition by multiple electrodes over multiple cardiac cycles. The horizontal axis 202 shows the cardiac cycle (each vertical line is one cardiac cycle), and the vertical axis 204 shows the distance of the electrode from a reference point (only one spatial dimension is shown; it should be understood that two or three dimensions may be used in practice, but are not shown for clarity). Figure 2 In the exemplary embodiment shown, electrodes are present in all horizontal lines, and LAT annotation values ​​are registered for all intersections of horizontal and vertical lines (each intersection will be referred to as a LAT point hereinafter).

[0047] Curve 206 is an iso-LAT line showing the location of the indicated LAT values, and the electrode may measure values ​​interpolated from adjacent iso-LAT curves at corresponding cardiac cycles. For example, the expected registration value for LAT point 208 (which is located vertically between iso-LAT line 714 and iso-LAT line 716) is 715, while the expected registration value for LAT point 210 is 708.5.

[0048] It can be seen that adjacent vertical lines and adjacent horizontal lines have similar LAT values. Circles 212 represent a group of related LAT values ​​214 that are close to each other in terms of geometric (vertical) distance and temporal (horizontal) distance.

[0049] Figure 2 The exemplary diagrams shown are simplified and are shown solely for the sake of conceptual clarity.In alternative embodiments, for example, the distance between electrodes is non-uniform and the set of correlated signals may not be circular.

[0050] Figure 3A 3 is a flow chart 300 schematically illustrating a first method for enhancing the reliability of annotation values ​​according to an embodiment of the present invention. The process is executed by the processing unit 42 ( Figure 1 The process starts with step 302 of recording signals, where the processing unit records the ECG signals monitored by the electrodes 27 and acquired by the acquisition circuit 36 ​​( Figure 1 ). Next, at step 304 of extracting annotation values, the processing unit calculates annotation values ​​for each electrode and each cardiac cycle.

[0051] The processor then proceeds to a obtain electrode positions step 306 , where the positions of the electrodes are acquired (eg, using ACL techniques) and the spatial position of each electrode is registered, followed by a select group step 308 .

[0052] In step 308, the processing unit selects a set of related annotation values. As described above, the set includes annotation values ​​that are likely similar based on spatially and / or temporally correlated signals.

[0053] Next, the processing unit calculates the mean and standard deviation of all annotation values ​​for the group in a calculate mean and SD step 310. In the context of the present invention, any suitable type of mean may be used, such as an arithmetic mean, a geometric mean, a median, a root mean square (RMS) value, a centroid, or any other mean.

[0054] The processing unit then repeats and sequentially performs steps 312, 314, and either 316 or 318 for each annotation value in the set. In the calculate standard score step 312, the processing unit calculates a standard score for the annotation value (e.g., by dividing the difference between the annotation value and the mean by the standard deviation). In the compare standard score step 314, the processing unit compares the standard score calculated in step 312 with a preset limit. In the discard value step 316, which is performed if the standard score exceeds the preset limit, the processing unit discards the statistically deviant annotation value; and in the add value step 318, which is performed if the standard score is within the preset limit, the processing unit adds the annotation value to the set of valid annotation values.

[0055] For all annotation values ​​for the group, the processor repeats the sequence of steps 312, 314, and 316 or 318. The flow chart may then repeat for other relevant electrode groups (starting from step 308).

[0056] When the process ends, the set of valid annotation values ​​replaces the original set with better reliability because extreme values ​​(e.g. from electrodes with bad galvanic connections) are omitted.

[0057] Figure 3B is a flow chart 350 schematically illustrating a second method for enhancing the reliability of annotation values ​​according to an embodiment of the present invention. Figure 3B The method shown is the same as Figure 3A The methods shown differ only in the statistical properties and the choice of omitted values. Figure 3A In addition to steps 310 and 314 which are different from those of steps 360 and 364 described below, Figure 3A Steps 302 to 318 are shown as follows: Figure 3B Steps 352 to 368 are the same.

[0058] In step 362 of calculating quartiles, the processing unit 42 ( Figure 1 ) Calculate the first quartile (Q1) and the third quartile (Q3) of the group of LAT values ​​(Q1 is defined as the middle number between the minimum and median values ​​of the group of LAT values; Q3 is the middle value between the median and the highest value of the group of LAT values).

[0059] In the step of comparing annotation values ​​364, the processing unit compares the LAT value of the annotation with Q1 and Q3. If the value is less than Q1 or higher than Q3, the processing unit proceeds to step 366 of discarding the annotation value, whereas if the value is between Q1 and Q3, the processing unit proceeds to step 368 of adding the value.

[0060] Figure 3A 、 Figure 3B The exemplary flow chart shown is chosen solely for conceptual clarity. In alternative embodiments, for example, annotation values ​​can be extracted at the time of signal acquisition (rather than after the signals are recorded). In one embodiment, the selection of the signals for the group can be performed by the physician; in other embodiments, the processing unit will select the group based on the region and / or time range indicated by the physician.

[0061] In some embodiments, step 318 ( Figure 3B 368) - In step 316 (366), the processing unit will discard extreme values ​​from the group, and when the process is complete, only good values ​​will remain. In other embodiments, all annotation values ​​are initially marked as invalid, and step 316 (366) is not required.

[0062] In some embodiments, other statistical properties than those described above are used; for example, in one embodiment, octaves may be used instead of quartiles, and the processing unit may omit values ​​below the first octave or above the last octave. Further alternatively, any other suitable percentile may be used.

[0063] In alternative embodiments, any other suitable statistical method may be used to detect and omit extreme values.

[0064] Propagation delay compensation

[0065] In some embodiments, the above technique can be improved by correcting the extracted LAT values ​​for expected variations in values ​​due to different spatial locations of the electrodes before calculating the statistical properties. For example, it can be assumed that the waves passing through the heart travel at a given speed (e.g., 1 m / s). By using the known locations of the electrodes that acquired the signal, the theoretical differences in LAT can be applied when calculating the average.

[0066] Figure 4 4 is a flow chart 400 schematically illustrating an improved method for enhancing the reliability of annotation values ​​according to an embodiment of the present invention. The process is executed by the processing unit 42 ( Figure 1). The process starts with step 402 of recording a signal, followed by step 404 of calculating an annotation value, step 406 of obtaining electrode positions, and step 408 of selecting a group, which may be the same as steps 302, 304, 306, and 308 ( FIG. 3 ), respectively.

[0067] Next, the processing unit proceeds to step 410 of correcting the LAT values, wherein for each LAT value of the group, the processing unit calculates and applies an estimated correction based on the spatial position of the electrodes and the assumed wave travel speed. After step 410, the process returns to FIG. 3 at step 310 of calculating the mean and SD.

[0068] Therefore, estimates of the bias caused by propagation delay can be removed from the group, further enhancing the reliability of the annotation signal.

[0069] Figure 4 The exemplary flow chart shown in is selected solely for conceptual clarity. In alternative embodiments, for example, correction for expected signal delay can be incorporated into the steps of calculating the mean and SD. In other embodiments, correction is performed before selecting the group (and therefore, the group can include a larger number of relevant LAT values).

[0070] It should be understood that the above embodiments are cited by way of example, and 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 subcombinations of the various features described 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. The documents incorporated by reference into this patent application are considered to be an integral part of this application, except that if any term defined in these incorporated documents conflicts with a definition explicitly or implicitly given in this specification, only the definition in this specification should be considered.

Claims

1. An electroanatomical system comprising: a signal acquisition circuit configured to receive a plurality of intracardiac signals acquired by a plurality of electrodes of an intracardiac probe in a patient's heart; as well as A processor configured to: extracting a plurality of annotation values ​​from the intracardiac signal; selecting a group of intracardiac signals from the intracardiac signals; correcting one or more of the annotation values ​​of a given intracardiac signal acquired by a given electrode in a set of electrodes acquiring the set of intracardiac signals to compensate for a displacement of the given electrode relative to other electrodes in the set of electrodes; identifying one or more annotation values ​​among the set of corrected annotation values ​​for the intracardiac signal that are statistically deviated by more than a predefined deviation measure; and Annotation values ​​of the corrected annotation values ​​excluding the statistically deviated annotation value are visualized to a user. 2 . The electroanatomical system of claim 1 , wherein the processor is configured to define the measure of the deviation according to a standard score of the annotation value. 3 . The electroanatomical system of claim 1 , wherein the processor is configured to define the measure of the deviation in terms of one or more percentiles of the annotation values.

4. The electroanatomical system of claim 1 , wherein the processor is configured to calculate deviations in corrected annotation values ​​on intracardiac signals acquired by a subset selected from among spatially correlated electrodes in the heart that are no more than a predefined distance apart from each other.

5. The electroanatomical system according to claim 1, wherein: The processor is configured to average the corrected annotation values ​​of the intracardiac signal over a plurality of time-related cardiac cycles occurring within a predefined time period when calculating the deviation of the corrected annotation values.

6. The electroanatomical system of claim 1, wherein the annotation value comprises a local activation time (LAT).

7. The electroanatomical system of claim 1, wherein the processor is configured to visualize the corrected annotation values ​​by superimposing annotation values ​​of the corrected annotation values ​​other than the statistically deviated annotation values ​​on a model of the heart.

Images