QRS detection and bounding

Abstract

The present disclosure describes a system for cardiac assessment. Electrical activity from tissue of a patient is monitored (410) using a plurality of external electrodes to generate a plurality of electrical signals over time. The plurality of electrical signals is filtered (420) using a first filter having a first frequency range to generate a plurality of first filtered signals. The plurality of electrical signals is filtered (430) using a second filter having a second frequency range different from the first frequency range to generate a plurality of second filtered signals. At least one QRS complex is detected (440) based on the plurality of first filtered signals. A QRS peak of the at least one QRS complex is detected (450) based on the plurality of second filtered signals and the detected at least one QRS complex.

Description

[0001] The disclosure herein relates to systems and methods for detecting and surrounding QRS complexes in cardiac signals monitored by a plurality of external electrodes.

[0002] Implantable medical devices (IMDs), such as implantable pacemakers, cardioverters, defibrillators, or pacemaker-cardioverter-defibrillators, provide therapeutic electrical stimulation to the heart. An IMD can provide pacing to address bradycardia, or provide pacing or electrical shocks to terminate tachyarrhythmias such as tachycardia or fibrillation. In some cases, a medical device can sense intrinsic depolarizations of the heart, detect arrhythmias based on the intrinsic depolarizations (or absence thereof), and control delivery of electrical stimulation to the heart if an arrhythmia is detected based on the intrinsic depolarizations.

[0003] IMDs can also provide cardiac resynchronization therapy (CRT), a form of pacing. CRT involves delivering pacing to the left ventricle or both left and right ventricles. The timing and location of pacing pulses delivered to the ventricles can be selected to improve the coordination and efficiency of ventricular contractions.

[0004] In addition to the implantable medical device itself, a system for implanting a medical device can include a workstation or other equipment. In some cases, this other equipment assists a physician or other technician in placing an intracardiac lead at a particular location on the heart. In some cases, the equipment provides information to the physician about electrical activity of the heart and the location of the intracardiac lead. The equipment can perform similar functions to the medical device, including delivering electrical stimulation to the heart and sensing depolarizations of the heart. In some cases, the equipment can include equipment for obtaining an electrocardiogram (ECG) via electrodes on the surface or skin of the patient. More specifically, the patient can have a plurality of electrodes on an ECG belt or vest that surrounds the torso of the patient. After the belt or vest has been secured to the torso, the physician can perform a series of tests to assess the patient's cardiac response. The assessment process can include detecting a baseline rhythm in which no electrical stimulation is delivered to the cardiac tissue and another rhythm after electrical stimulation is delivered to the cardiac tissue.

[0005] ECG electrodes placed on the surface of the patient's body can be used for various therapeutic purposes (e.g., cardiac resynchronization therapy), including optimizing lead position, pacing parameters, etc. based on one or more metrics derived from signals captured by the ECG electrodes. By way of example, electrical heterogeneity information can come from electrical activation times computed from a plurality of electrodes on the surface of the body.

[0006] Additionally, signals from a plurality of electrodes on the surface of the body can be used to determine one or more specific ECG features, such as QRS onset, peak, QRS offset, etc., of a series of multiple heartbeats. Such ECG features can themselves be used to assess cardiac health and / or therapy, or can be used to extrapolate or compute activation times. SUMMARY

[0007] The example systems and methods described herein can be configured to assist a user (e.g., a physician) in configuring cardiac therapy (e.g., cardiac therapy performed on a patient during and / or after implantation of a cardiac therapy device). The systems and methods can be described as being non-invasive. For example, the systems and methods can not require implantable devices, such as leads, probes, sensors, catheters, etc., to assess and configure cardiac therapy. Instead, the systems and methods can use electrical measurements taken non-invasively using a plurality of external electrodes that, for example, are attached to the skin of a patient around the torso of the patient.

[0008] An example system for cardiac assessment can include an electrode device including a plurality of external electrodes to be disposed proximate to the skin of a patient. A computing device includes processing circuitry. The computing device is operably coupled to the electrode device. The computing device is configured to monitor electrical activity from tissue of the patient using the plurality of external electrodes to generate a plurality of electrical signals over time. The plurality of electrical signals is filtered using a first filter having a first frequency range to generate a plurality of first filtered signals. The plurality of electrical signals is filtered using a second filter having a second frequency range different from the first frequency range to generate a plurality of second filtered signals. At least one QRS complex is detected based on the plurality of first filtered signals. A QRS peak of the at least one QRS complex is detected based on the plurality of second filtered signals and the detected at least one QRS complex.

[0009] An example method for cardiac assessment includes monitoring electrical activity from tissue of a patient using a plurality of external electrodes to generate a plurality of electrical signals. The plurality of electrical signals is filtered using a first filter having a first frequency range to generate a plurality of first filtered signals. The plurality of electrical signals is filtered using a second filter having a second frequency range different from the first frequency range to generate a plurality of second filtered signals. At least one QRS complex is detected based on the plurality of first filtered signals. A QRS peak of the at least one QRS complex is detected based on the plurality of second filtered signals and the detected at least one QRS complex.

[0010] An example system for cardiac assessment can include an electrode device including a plurality of external electrodes to be disposed proximate to a patient's skin. A computing device includes processing circuitry. The computing device is operably coupled to the electrode device. The computing device is configured to monitor electrical activity from tissue of a patient using the plurality of external electrodes to generate a plurality of electrical signals over time. The plurality of electrical signals are filtered using at least one filter to generate a plurality of filtered signals. QRS peaks are detected based on the plurality of filtered signals. A threshold function is determined based on the QRS peaks. The threshold function is configured to provide a sensitivity for detecting at least one subsequent QRS complex. The at least one QRS complex is detected based on the threshold function.

[0011] An example method for cardiac assessment can include monitoring electrical activity from tissue of a patient using a plurality of external electrodes to generate a plurality of electrical signals over time. The plurality of electrical signals are filtered using at least one filter to generate a plurality of filtered signals. QRS peaks are detected based on the plurality of filtered signals. A threshold function is determined based on the QRS peaks. The threshold function is configured to provide a sensitivity for detecting at least one subsequent QRS complex. The at least one QRS complex is detected based on the threshold function.

[0012] An example system for cardiac assessment can include an electrode device including a plurality of external electrodes to be disposed proximate to a patient's skin. A computing device includes processing circuitry. The computing device is operably coupled to the electrode device. The computing device is configured to monitor electrical activity from tissue of a patient using the plurality of external electrodes to generate a plurality of electrical signals over time. The plurality of electrical signals are filtered using a first filter and a second filter to generate a plurality of first filtered signals and a plurality of second filtered signals. The first filter and the second filter have different frequency ranges. QRS peaks are detected based on the plurality of first and second filtered signals. A dispersion signal is generated from the plurality of second filtered signals. The dispersion signal represents a dispersion of the plurality of second filtered signals over time. A first derivative signal is determined based on the dispersion signal. A QRS onset time value and a QRS offset time value corresponding to the at least one QRS complex are determined based on the first derivative signal.

[0013] The above summary is not intended to describe every embodiment or implementation of the present disclosure. A more complete understanding will become apparent and appreciated by referring to the following detailed description and claims in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 FIG. 1 is a diagram of an example system including an electrode device, a display device, and a computing device.

[0015] Figures 2-3FIG. 1 is a diagram of an exemplary external electrode device for measuring torso surface potentials.

[0016] Figure 4 An exemplary method for detecting a QRS complex is shown.

[0017] Figure 5 An exemplary method for detecting a QRS complex and at least one subsequent QRS complex based on a threshold function is shown.

[0018] Figure 6A And Figure 6B A more detailed process for detecting at least one QRS complex according to embodiments described herein is shown.

[0019] Figure 7 An example threshold function according to embodiments described herein is shown.

[0020] Figure 8 An exemplary method for determining onset and offset of a corresponding QRS complex is shown.

[0021] Figure 9 And Figures 10A-10C A more detailed process for determining onset and offset values of at least one QRS complex according to embodiments described herein is shown.

[0022] Figure 11 FIG. 1 is a diagram of an illustrative system including an illustrative implantable medical device (IMD).

[0023] Figure 12A FIG. 1 is a diagram of an illustrative system including an illustrative implantable medical device (IMD). Figure 11 FIG. 1 is a diagram of an illustrative system including an illustrative implantable medical device (IMD).

[0024] Figure 12B FIG. 1 is a diagram of an illustrative system including an illustrative implantable medical device (IMD). Figure 12A FIG. 1 is a diagram of an illustrative system including an illustrative implantable medical device (IMD).

[0025] Figure 13A FIG. 1 is a diagram of an illustrative system including an illustrative implantable medical device (IMD). Figures 11-1 2. A block diagram of an illustrative IMD of the system of, e.g., FIG. 1.

[0026] Figure 13B Another block diagram of illustrative IMD (e.g., implantable pulse generator) circuitry and associated leads employed in the system of, e.g., FIG. 1. Figures 11-1 2. A block diagram of an illustrative IMD of the system of, e.g., FIG. 1. DETAILED DESCRIPTION

[0027] In the following detailed description of illustrative embodiments, reference is made to the accompanying drawings that form a part hereof, and in which are shown, by way of illustration, specific embodiments that can be practiced. It is to be understood that other embodiments can be utilized and structural changes can be made without departing from the scope of the present disclosure presented herein (e.g., still falling within). In the drawings:

[0028] Reference will be made to Figures 1-1 3 illustrative systems and methods are described. It will be apparent to those skilled in the art that elements or processes from one embodiment can be used in conjunction with those of the other embodiments without departing from the scope of the present disclosure as set forth herein. Such modifications to particular embodiments are not to be construed as beyond the scope of the present disclosure. Further, it will be apparent to those skilled in the art that the embodiments described herein can include numerous not necessarily mutually exclusive elements. Still further, it will be apparent to those skilled in the art that the timing of processes and sizes and shapes of various elements can be modified without departing from the scope of the present disclosure, although certain timings, one or more shapes and / or sizes, or element types can be preferred over others.

[0029] A plurality of electrocardiogram (ECG) signals (e.g., torso surface potentials) can be measured or monitored using a plurality of external electrodes positioned around a surface or skin of a patient. The ECG signals can be used to evaluate and configure cardiac therapy, such as, for example, cardiac therapy provided by an implantable medical device that performs cardiac resynchronization therapy (CRT). As described herein, the ECG signals can be acquired or obtained non-invasively, as, for example, implantable electrodes can not be used to measure the ECG signals. Further, the ECG signals can be used to determine cardiac electrical activation times that can be used to generate various metrics (e.g., electrical heterogeneity information) that can be used by a user (e.g., a physician) to optimize one or more settings or parameters of cardiac therapy (e.g., pacing therapy), such as CRT.

[0030] Various illustrative systems, methods, and graphical user interfaces can be configured to non-invasively assist a user (e.g., a physician) in evaluating cardiac health and / or configuration (e.g., optimization) of cardiac therapy using an electrode apparatus including external electrodes, a display device, and a computing device. Figure 1 An illustrative system 100 is depicted that includes an electrode apparatus 110, a computing device 140, and a remote computing device 160.

[0031] The electrode device 110 as illustrated includes a plurality of electrodes that are incorporated into or included within a band that is wrapped around the chest or torso of the patient 14. According to various embodiments, the electrode device includes about 40 electrodes. The electrode device 110 is operably coupled to the computing device 140 (e.g., by one or wired electrical connections, wirelessly, etc.) to provide electrical signals from each of the electrodes to the computing device 140 for analysis, evaluation, etc. An illustrative electrode device can be described in U.S. Patent No. 9,320,446, entitled "Bioelectric Sensor Device and Methods," filed March 27, 2014, and issued March 26, 2016. Further, reference will be made to Figures 2-3 The illustrative electrode device 110 is described in greater detail.

[0032] Although not described herein, the illustrative system 100 can further include an imaging device. The imaging device can be any type of imaging device configured to image or provide an image of at least a portion of a patient in a non-invasive manner. For example, the imaging device can provide an image of a patient without using any components or parts that can be located within the patient, such as contrast solution. It should be appreciated that the illustrative systems, methods, and interfaces described herein can further use the imaging device to provide non-invasive assistance to a user (e.g., a physician) to position or place one or more pacing electrodes near a heart of a patient in connection with configuration of cardiac therapy.

[0033] For example, the illustrative systems and methods can provide image-guided navigation that can be used to navigate a lead including electrodes, leadless electrodes, wireless electrodes, catheters, etc. within a patient while also providing non-invasive cardiac therapy configuration, including determining effective or optimal pre-excitation intervals, such as A-V intervals and V-V intervals, etc. The illustrative systems and methods using an imaging device and / or an electrode device can be described in U.S. Patent No. 9,877,789 to Ghosh et al., U.S. Patent No. 10,251,555 to Ghosh et al., U.S. Patent No. 9,924,884 to Ghosh et al., U.S. Patent No. 10,064,567 to Ghosh et al.

[0034] The illustrative imaging device can be configured to capture x-ray images and / or any other alternative imaging modalities. For example, the imaging device can be configured to capture images or image data using isocentric fluoroscopy, bi-plane fluoroscopy, ultrasound, computed tomography (CT), multi-slice computed tomography (MSCT), magnetic resonance imaging (MRI), high intensity focused ultrasound (HIFU), optical coherence tomography (OCT), intravascular ultrasound (IVUS), two-dimensional (2D) ultrasound, three-dimensional (3D) ultrasound, four-dimensional (4D) ultrasound, intraoperative CT, intraoperative MRI, etc. Further, it should be appreciated that the imaging device can be configured to capture a plurality of successive images (e.g., continuously) to provide video frame data. In other words, a plurality of images taken over time using the imaging device can provide video frame, or motion picture, data. An exemplary system employing ultrasound can be found in U.S. Patent Application Publication No. 2017 / 0303840 to Stadler et al., entitled NONINVASIVE ASSESSMENT OF CARDIAC RESYNCHRONIZATION THERAPY, which is incorporated herein by reference in its entirety. Additionally, these images can also be acquired and displayed in two, three, or four dimensions. In more advanced forms, four-dimensional surface rendering of the heart or other regions of the body can also be achieved by incorporating cardiac data or other soft tissue data from mapping charts or preoperative image data captured from MRI, CT, or echocardiographic modalities. Image data sets from hybrid modalities, such as positron emission tomography (PET) combined with CT or single photon emission computed tomography (SPECT) combined with CT can also provide functional image data overlaid on anatomical data, for example, for navigating an implantable device to a target location within the heart or other region of interest.

[0035] Systems and / or imaging devices that can be used in conjunction with the illustrative systems and methods described herein are described in U.S. Patent Application Publication No. 2005 / 0008210 to Evron et al., published January 13, 2005, U.S. Patent No. 2006 / 0074285 to Zarkh et al., published April 6, 2006, U.S. Patent No. 8,731,642 to Zarkh et al., published May 20, 2014, U.S. Patent No. 8,861,830 to Brada et al., published October 14, 2014, U.S. Patent No. 6,980,675 to Evron et al., published December 27, 2005, U.S. Patent No. 7,286,866 to Okerlund et al., published October 23, 2007, U.S. Patent No. 7,308,297 to Reddy et al., published December 11, 2011, U.S. Patent No. 7,308,299 to Burrell et al., published December 11, 2011, U.S. Patent No. 7,321,677 to Evron et al., published January 22, 2008, U.S. Patent No. 7,346,381 to Okerlund et al., published March 18, 2008, U.S. Patent No. 7,454,248 to Burrell et al., published November 18, 2008, U.S. Patent No. 7,499,743 to Vass et al., published March 3, 2009, U.S. Patent No. 7,565,190 to Okerlund et al., published July 21, 2009, U.S. Patent No. 7,587,074 to Zarkh et al., published September 8, 2009, U.S. Patent No. 7,599,730 to Hunter et al., published October 6, 2009, U.S. Patent No. 7,613,500 to Vass et al., published November 3, 2009, U.S. Patent No. 7,742,629 to Zarkh et al., published June 22, 2010, U.S. Patent No. 7,747,047 to Okerlund et al., published June 29, 2010, U.S. Patent No. 7,778,685 to Evron et al., published August 17, 2010, U.S. Patent No. 7,778,686 to Vass et al., published August 17, 2010, U.S. Patent No. 7,813,785 to Okerlund et al., published October 12, 2010, U.S. Patent No. 7,996,063 to Vass et al., published August 9, 2011, U.S. Patent No. 8,060,185 to Hunter et al., published November 15, 2011, and U.S. Patent No. 8,401,616 to Verard et al., published March 19, 2013.

[0036] Computing device 140 and remote computing device 160 can each include a display device 130, 170, respectively, that can be configured to display and analyze data, such as, for example, electrical signals (e.g., electrocardiogram data), electrical activation times, electrical heterogeneity information, and the like. For example, a plurality of electrical signals collected or monitored by electrode device 110 can be analyzed or evaluated by computing device 140 and remote computing device 160 to determine or detect QRS complexes therein, such that, for example, the QRS complexes can be further evaluated and analyzed for various metrics, activation time maps, and the like. Further, each QRS complex can be surrounded— a time period around the QRS complex or a start and end of the QRS complex can be determined. Further, for example, one cardiac cycle or beat of a plurality of cardiac cycles or beats represented by the electrical signals collected or monitored by electrode device 110 can be analyzed and evaluated for one or more metrics, including activation times and electrical heterogeneity information, which can be related to therapeutic properties of one or more parameters related to cardiac therapy, such as, for example, pacing parameters, lead position, and the like. More specifically, for example, a QRS complex of a single cardiac cycle can be evaluated for one or more metrics, such as, for example, QRS onset, QRS offset, QRS peak, electrical heterogeneity information (EHI), electrical activation times referenced to earliest activation time, left ventricular or thoracic standard deviation of electrical activation times (LVED), standard deviation of activation times (SDAT), mean left ventricular or thoracic surrogate electrical activation time (LVAT), QRS duration (e.g., interval between QRS onset to QRS offset), difference between mean left surrogate activation time and mean right surrogate activation time, relative or absolute QRS morphology, difference between higher percentile and lower percentile of activation times (higher percentile can be 90%, 80%, 75%, 70%, and the like, and lower percentile can be 10%, 15%, 20%, 25%, and 30%, and the like), central tendency (e.g., median or mode), dispersion (e.g., mean deviation, standard deviation, variance, interquartile deviation, range), and the like. Further, each of the one or more metrics can be location specific. For example, some metrics can be computed from signals recorded or monitored from electrodes positioned around a selected region of the patient, such as, for example, the left side of the patient, the right side of the patient, and the like.

[0037] In at least one embodiment, an activation map can be created by first interpolating the 2x20 matrix of activation times using a reverse distance weighted interpolation step, and then using a two-dimensional bicubic interpolation method. More specifically, the earliest (smallest) activation time across all active electrodes can be determined, and this earliest (smallest) activation time subtracted from each activation time. On all electrodes, if the electrode is marked as active, the activation time is used directly in the bicubic interpolation step. If the electrode is marked as inactive, all active electrodes are found to be in the same band plane (anterior or posterior), and the contribution of each active electrode pair to the interpolation is its activation time value weighted by the inverse of the square of the distance from the inactive electrode. For example,

[0038]

[0039] where

[0040]

[0041] Further, within the 2x10 array of activation times on each band plane, for each 2x2 set of adjacent points forming a‘unit square’, a system of 16 equations can be solved to find the 16 coefficients of a two-dimensional polynomial function that can be used to find interpolated values at any fractional part within the unit square. This process can be repeated for all possible sets of adjacent 2x2 points.

[0042] In at least one embodiment, one or both of computing device 140 and remote computing arrangement 160 can be a server, a personal computer, a tablet, a mobile device, and a cellular telephone. Computing device 140 can be configured to receive input from input device 142 (e.g., a keyboard) and transmit output to display device 130, and remote computing arrangement 160 can be configured to receive input from input device 162 (e.g., a touchscreen) and transmit output to display device 170. One or both of computing device 140 and remote computing arrangement 160 can include a data storage arrangement that can allow access to processing programs or routines and / or one or more other types of data, such as for example, for analyzing a plurality of electrical signals captured by electrode device 110, for determining or detecting QRS complexes and time periods related thereto, for determining QRS onset, QRS offset, median, mode, mean, peak or maximum, nadir or minimum, for determining electrical activation times, for driving a graphical user interface configured to non-invasively assist a user in configuring one or more pacing parameters or settings, such as for example, pacing rate, ventricular pacing rate, A-V interval, V-V interval, pacing pulse width, pacing vector, multipoint pacing vector (e.g., left ventricular vector quad lead), pacing voltage, pacing configuration (e.g., biventricular pacing, right ventricular only pacing, left ventricular only pacing, etc.), as well as arrhythmia detection and therapy, rate adaptation settings and performance, and the like.

[0043] Computing device 140 can be operatively coupled to input device 142 and display device 130 to, for example, transmit data to and from each of input device 142 and display device 130, and remote computing arrangement 160 can be operatively coupled to input device 162 and display device 170 to, for example, transmit data to and from each of input device 162 and display device 170. For example, computing device 140 and remote computing arrangement 160 can be electrically coupled to input devices 142, 162 and display devices 130, 170 using, for example, analog electrical connections, digital electrical connections, wireless connections, bus-based connections, network-based connections, internet-based connections, and the like. As further described herein, a user can provide input to input devices 142, 162 in order to view and / or select one or more pieces of configuration information related to a cardiac therapy delivered by a cardiac therapy device, such as for example, an implantable medical device.

[0044] Although the input devices 142 as depicted are a keyboard and the input devices 162 are a touch screen, it should be understood that the input devices 142, 162 can include any device capable of providing input to the computing device 140 and the computing apparatus 160 to perform the functions, methods, and / or logic described herein. For example, the input devices 142, 162 can include a keyboard, a mouse, a trackball, a touch screen (e.g., a capacitive touch screen, a resistive touch screen, a multi-touch touch screen, etc.), etc. Likewise, the display devices 130, 170 can include any device capable of displaying information to a user, such as the graphical user interfaces 132, 172 including: electrode status information, electrically activated graphical maps, a plurality of signals of an external electrode over one or more heartbeats, QRS complexes, various cardiac therapy regimen selection areas, various cardiac therapy regimen rankings, various pacing parameters, electrical heterogeneity information (EHI), textual instructions, graphical depictions of the anatomy of a human heart, images or graphical depictions of a patient’s heart, graphical depictions of the location of one or more electrodes, graphical depictions of a human torso, images or graphical depictions of a patient’s torso, graphical depictions or actual images of implanted electrodes and / or leads, etc. Further, the display devices 130, 170 can include liquid crystal displays, organic light-emitting diode screens, touch screens, cathode ray tube displays, etc.

[0045] The processing programs or routines stored and / or executed by the computing device 140 and the remote computing apparatus 160 can include programs or routines for computational mathematics, matrix mathematics, decomposition algorithms, compression algorithms (e.g., data compression algorithms), calibration algorithms, image construction algorithms, signal processing algorithms (e.g., various filtering algorithms, Fourier transforms, fast Fourier transforms, etc.), standardization algorithms, comparison algorithms, vector mathematics, or any other processing used to implement one or more illustrative methods and / or processes described herein. The data stored and / or used by the computing device 140 and the remote computing apparatus 160 can include, for example, electrical signal / waveform data (e.g., a plurality of QRS complexes) from the electrode device 110, electrical activation times from the electrode device 110, heart sound / signal / waveform data from an acoustic sensor, graphics (e.g., graphical elements, icons, buttons, windows, dialog boxes, drop-down menus, graphical fields, graphical regions, 3D graphics, etc.), graphical user interfaces, results of one or more processing programs or routines employed in accordance with the present disclosure (e.g., electrical signals, electrical heterogeneity information, etc.), or any other data used to perform one and / or more processes or methods described herein.

[0046] In one or more embodiments, the illustrative systems, methods, and interfaces can be implemented using one or more computer programs executing on programmable computers such as computers that include, for example, processing capabilities, data storage (e.g., volatile or non-volatile memory and / or storage elements), input devices, and output devices. Program code and / or logic described herein can be applied to input data to perform the functions described herein and generate desired output information. The output information can be applied as input to one or more other devices and / or methods as described herein or as would be applied in a known fashion.

[0047] Any of the one or more programs can be provided using any programmable language such as a high level procedural and / or object oriented programming language that is suitable for communicating with a computer system. Any such programs may, for example, be stored on any suitable device (e.g., storage media) that is readable by a general or special purpose programming device (e.g., a computer) for configuring and operating the computer when the appropriate device reads the instructions to perform the procedures described herein. In other words, at least in one embodiment, the illustrative systems, methods, and interfaces can be implemented using a computer readable storage medium configured with computer programs to configure a computer to operate in a specific and predefined manner. Further, in at least one embodiment, the illustrative systems, methods, and / or interfaces can be described as being implemented by logic (e.g., object code) encoded in one or more non-transitory media that includes code for execution and, when executed by a processor or processing circuit, the code is operable to perform operations such as the methods, procedures, and / or functions as described herein.

[0048] Computing device 140 and remote computing device 160 can be, for example, any fixed or mobile computer system (e.g., controller, microcontroller, personal computer, microcomputer, tablet computer, etc.). The exact configuration of computing device 140 and remote computing device 160 is not limiting, and any device capable of providing suitable computing and control capabilities (e.g., signal analysis, mathematical functions such as median, mode, average, maximum value determination, minimum value determination, slope determination, minimum slope determination, maximum slope determination, graphics processing, etc.) can be used. As described herein, digital files can be any medium (e.g., volatile or non-volatile memory, CD-ROM, punched card, magnetically recordable magnetic tape, etc.) containing digital bits (e.g., encoded in binary or ternary) that can be read and / or written by computing device 140 and remote computing device 160 as described herein. Moreover, as described herein, a user-readable format file can be any representation of data (e.g., ASCII text, binary numbers, hexadecimal numbers, decimal numbers, graphics, etc.) that can be presented on any medium (e.g., paper, monitor, etc.) that is readable and / or understandable to the user.

[0049] In view of the foregoing, it will be apparent that the functions described in one or more embodiments according to this disclosure can be implemented in any manner as known to those skilled in the art. Thus, the computer language, computer system, or any other software / hardware intended for implementing the processes described herein should not be limited to the scope of the systems, processes, or programs described herein (e.g., the functions provided by such systems, processes, or programs).

[0050] The illustrative electrode device 110 can be configured to measure the surface potential of the patient 14's body and, more specifically, the surface potential of the patient 14's torso. For example... Figure 2 As shown, the illustrative electrode device 110 may include an assembly or array of external electrodes 112, a strip 113, and an interface / amplifier circuitry 116. The electrodes 112 may be attached to or coupled to the strip 113, and the strip 113 may be configured to wrap around the torso of the patient 14 such that the electrodes 112 surround the patient's heart. As further shown, the electrodes 112 may be positioned around the circumference of the patient 14, including posterior, lateral, posterolateral, anterolateral, and anterior positions of the patient 14's torso.

[0051] The illustrative electrode device 110 can be further configured to measure or monitor at least one or both sounds from the patient 14. For example... Figure 2As shown, the illustrative electrode apparatus 110 can include a set or array of acoustic sensors 120 attached or coupled to the strap 113. The strap 113 can be configured to wrap around the torso of the patient 14 such that the acoustic sensors 120 surround the heart of the patient. As further shown, the acoustic sensors 120 can be positioned around the circumference of the patient 14, including posterior, lateral, posterolateral, anterolateral, and anterior locations of the torso of the patient 14.

[0052] Further, the electrodes 112 and the acoustic sensors 120 can be electrically connected to the interface / amplifier circuit 116 via wired connections 118. The interface / amplifier circuit 116 can be configured to amplify signals from the electrodes 112 and the acoustic sensors 120 and provide the signals to one or both of the computing device 140 and the remote computing apparatus 160. Other illustrative systems can use wireless connections (e.g., as data channels) to transmit signals sensed by the electrodes 112 and the acoustic sensors 120 to the interface / amplifier circuit 116, and in turn, to one or both of the computing device 140 and the remote computing apparatus 160. In one or more embodiments, the interface / amplifier circuit 116 can be electrically coupled to the computing device 140 using, for example, analog electrical connections, digital electrical connections, wireless connections, bus-based connections, network-based connections, Internet-based connections, etc.

[0053] Although in the illustrative embodiment shown in FIG. 1, the electrodes 112 and the acoustic sensors 120 are electrically connected to the interface / amplifier circuit 116 via wired connections 118, other illustrative systems can use wireless connections (e.g., as data channels) to transmit signals sensed by the electrodes 112 and the acoustic sensors 120 to the interface / amplifier circuit 116, and in turn, to one or both of the computing device 140 and the remote computing apparatus 160. Figure 2In the example of FIG. 1, the electrode apparatus 110 includes a strap 113, but in other examples, any of a variety of mechanisms (e.g., tape or adhesive) can be employed to assist in spacing and placement of the electrodes 112 and acoustic sensors 120. In some examples, the strap 113 can include an elastic band, a strip of tape, or cloth. Further, in some examples, the strap 113 can be part of or integrated with an article of clothing (e.g., a t-shirt). In other examples, the electrodes 112 and acoustic sensors 120 can be placed individually on the torso of the patient 14. Further, in other examples, one or both of the electrodes 112 (e.g., in an array arrangement) and acoustic sensors 120 (e.g., also in an array arrangement) can be part of or within a patch, a vest, and / or other means of securing the electrodes 112 and acoustic sensors 120 to the torso of the patient 14. Still further, in other examples, one or both of the electrodes 112 and acoustic sensors 120 can be part of or within two material portions or two patches. One of the two patches can be on the front side of the torso of the patient 14 (so as to, for example, monitor electrical signals representative of the front side of the heart of the patient, measure surrogate cardiac electrical activation times representative of the front side of the heart of the patient, monitor or measure sounds of the front side of the patient, etc.) and the other patch can be on the back side of the torso of the patient 14 (so as to, for example, monitor electrical signals representative of the back side of the heart of the patient, measure surrogate cardiac electrical activation times representative of the back side of the heart of the patient, monitor or measure sounds of the back side of the patient, etc.). And still further, in other examples, one or both of the electrodes 112 and acoustic sensors 120 can be arranged in top and bottom rows that extend from the front side of the patient 14 through the left side of the patient 14 to the back side of the patient 14. Still further, in other examples, one or both of the electrodes 112 and acoustic sensors 120 can be arranged in a curve around the axillary region, and the density of electrodes / sensors on the right chest can be lower than the density of the other remaining regions.

[0054] The electrodes 112 can be configured to surround the heart of the patient 14 and record or monitor electrical signals associated with depolarization and repolarization of the heart after the signals have propagated through the torso of the patient 14. Each of the electrodes 112 can be used in a unipolar configuration to sense torso surface potentials that reflect cardiac signals. The interface / amplifier circuit 116 can also be coupled to a return or indifferent electrode (not shown) that can be used in combination with each of the electrodes 112 for unipolar sensing.

[0055] In some examples, the electrode apparatus 110 can include about 12 to about 50 electrodes 112 and about 12 to about 50 acoustic sensors 120 distributed spatially around the torso of the patient. Other configurations can have more or fewer electrodes 112 and more or fewer acoustic sensors 120. It should be appreciated that the electrodes 112 and acoustic sensors 120 can not be arranged or distributed in an array that extends all around or completely around the patient 14. Rather, the electrodes 112 and acoustic sensors 120 can be arranged in an array that extends only around a portion of the patient 14 or partially around the patient. For example, the electrodes 112 and acoustic sensors 120 can be distributed on the front side, back side, and left side of the patient, with fewer or no electrodes and acoustic sensors near the right side, including the back and front regions of the right side of the patient.

[0056] The computing device 140 can record and analyze torso surface potential signals sensed by the electrodes 112 and sound signals sensed by the acoustic sensors 120, which are amplified / conditioned by the interface / amplifier circuit 116. The computing device 140 can be configured to analyze the electrical signals from the electrodes 112 to detect or determine QRS complexes, QRS onset and offset, and time periods related thereto, and to provide electrocardiogram (ECG) signals, information, or data from the heart of the patient, as will be further described herein. The computing device 140 can be configured to analyze the electrical signals from the acoustic sensors 120 to provide sound signals, information, or data from the patient’s body and / or a device implanted therein, such as a left ventricular assist device.

[0057] Additionally, the computing device 140 and the remote computing device 160 can be configured to provide graphical user interfaces 132, 172 that depict various information related to the electrode apparatus 110 and data collected or sensed using the electrode apparatus 110. For example, the graphical user interfaces 132, 172 can depict ECGs including QRS complexes obtained using the electrode apparatus 110 and sound data including sound waves obtained using the acoustic sensors 120, and other information related thereto. The illustrative systems and methods can use the electrical information collected using the electrode apparatus 110 and the sound information collected using the acoustic sensors 120 to assess the cardiac health of the patient and to assess and configure cardiac therapy delivered to the patient non-invasively.

[0058] Further, the electrode apparatus 110 can further include reference and / or drive electrodes positioned around the lower torso of the patient 14, for example, that can be further used by the system 100. For example, the electrode apparatus 110 can include three reference electrodes and can combine the signals from the three reference electrodes to provide a reference signal. Further, the electrode apparatus 110 can use three tail-end reference electrodes (e.g., instead of the standard reference used in the Wilson Central Terminal) to obtain a "true" unipolar signal with less noise by averaging the three tail-end positioned reference signals.

[0059] Figure 3 Another illustrative electrode apparatus 110 is shown that includes a plurality of electrodes 112 configured to surround the heart of the patient 14 and record or monitor electrical signals associated with depolarization and repolarization of the heart after signals have propagated through the torso of the patient 14 and a plurality of acoustic sensors 120 configured to surround the heart of the patient 14 and record or monitor sound signals associated with the heart after signals have propagated through the torso of the patient 14. The electrode apparatus 110 can include a vest 114 to which the plurality of electrodes 112 and the plurality of acoustic sensors 120 can be attached or to which the electrodes 112 and acoustic sensors 120 can be coupled. In at least one embodiment, the plurality of electrodes 112 or array of electrodes can be used to collect electrical information, such as surrogate electrical activation times. Similar to the electrode apparatus 110 of Figure 2 the electrode apparatus 110, Figure 3 The electrode apparatus 110 can include an interface / amplifier circuit 116 electrically coupled to each of the electrodes 112 and acoustic sensors 120 by a wired connection 118 and configured to transmit signals from the electrodes 112 and acoustic sensors 120 to the computing device 140. As shown, the electrodes 112 and acoustic sensors 120 can be distributed on the torso of the patient 14, including, for example, posterior, lateral, posterolateral, anterolateral, and anterior locations of the torso of the patient 14.

[0060] The vest 114 can be formed of a fabric to which the electrodes 112 and acoustic sensors 120 are attached. The vest 114 can be configured to maintain the positioning and spacing of the electrodes 112 and acoustic sensors 120 on the torso of the patient 14. Further, the vest 114 can be marked to assist in determining the location of the electrodes 112 and acoustic sensors 120 on the surface of the torso of the patient 14. In some examples, there can be about 25 to about 256 electrodes 112 and about 25 to about 256 acoustic sensors 120 distributed around the torso of the patient 14, although other configurations can have more or fewer electrodes 112 and more or fewer acoustic sensors 120.

[0061] Illustrative systems, methods, and interfaces can be used to provide noninvasive assistance to a user in the assessment of a patient's cardiac health (e.g., prior to or during the delivery of cardiac therapy) and / or the assessment and configuration of cardiac therapy currently being delivered to the patient (e.g., by an implantable medical device delivering pacing therapy, by an LVAD, etc.). Further, it should be appreciated that the computing device 140 and the remote computing device 160 can be operatively coupled to one another in a variety of different ways in order to conduct or perform the functions described herein. For example, in the depicted embodiment, the computing device 140 can be operatively wirelessly coupled to the remote computing device 160, as depicted by the wireless signal lines emanating therebetween. Additionally, as opposed to a wireless connection, one or more of the computing device 140 and the remote computing device 160 can be operatively coupled by one or wired electrical connections.

[0062] According to embodiments described herein, the illustrative system 100, which can be referred to as an ECG belt system, can be used with cardiac therapy systems and devices (e.g., CRT pacing devices) to calculate various metrics related to a patient's cardiac health (e.g., standard deviation of activation times (SDAT)) across one or more cardiac cycles (or heartbeats) and specifically based on activation times or other data collected during each QRS event of a cardiac cycle (heartbeat). According to various embodiments, the illustrative system 100 can be used to calculate or generate electrical heterogeneity information, such as, for example, SDAT of a cardiac cycle during CRT delivery (e.g., SDAT for a cardiac cycle in which CRT pacing is delivered). For example, the illustrative system 100 can be used to calculate electrical heterogeneity information for a cardiac cycle during biventricular and / or left ventricular pacing. Further, the embodiments described herein can be used to assess a patient's cardiac health and / or non-CRT pacing. If the electrical heterogeneity information is inaccurate, the output of the illustrative system 100 can be misleading, which can potentially impact lead placement (e.g., implantable leads are not placed in an optimal location) and / or optimal device programming. For example, if the SDAT is inaccurate, the SDAT can be artificially low, which can cause a clinician to not reposition a currently positioned lead, rather than repositioning the lead for a better response.

[0063] An illustrative process for determining SDAT can first calculate the mean or signal of the active channels as follows:

[0064]

[0065] The squared standard deviation can then be determined as follows (for i = 1 to the number of active channels):

[0066]

[0067] SDAT can then be calculated as follows:

[0068]

[0069] An illustrative procedure for determining LVAT can be described as the mean of the activation times of the designated left ventricular channels, where each left ventricular activation time is referenced to the earliest activation time of all valid channels, and can be expressed as follows:

[0070]

[0071] To determine electrical heterogeneity information, each QRS event or complex with multiple cardiac cycles can be detected. Inaccurate detection of QRS events or complexes can result in detection of false activation times, leading to inaccurate electrical heterogeneity information. According to various embodiments, a QRS event onset or start and / or a QRS event offset or end is determined to give bounds on where to measure (e.g., to determine a fiducial point within each of the plurality of cardiac signals). Embodiments herein describe procedures for detecting QRS complexes and setting their bounds.

[0072] Figure 4 An exemplary method 400 for detecting QRS complexes according to embodiments described herein is shown in FIG. 4. Electrical activity from tissue of a patient is monitored 410 using a plurality of external electrodes to generate a plurality of electrical signals over time. The plurality of electrodes can be external surface electrodes configured in a belt or vest, similar to that described herein with respect to Figures 1-3 Each of the electrodes can be positioned or disposed about the torso of the patient so as to monitor electrical activity from a plurality of different locations about the torso of the patient (e.g., to acquire a torso potential). Each of the different locations in which the electrodes are located can correspond to electrical activation of a different portion or region of cardiac tissue of the heart of the patient.

[0073] The plurality of electrical signals is filtered 420 using a first filter having a first frequency range to generate a plurality of first filtered signals. According to various configurations, the first filter is a bandpass filter configured to filter out signals outside of a range of about 0.05 Hz to about 150 Hz. In some cases, the first filter is a bandpass filter configured to filter out signals outside of a range of about 10 Hz to about 32 Hz.

[0074] The plurality of electrical signals is filtered 430 using a second filter having a second frequency range different from the first frequency range to generate a plurality of second filtered signals. According to various configurations, the second filter is a bandpass filter configured to filter out signals outside of a range of about 0.05 Hz to about 150 Hz. In some cases, the first filter is a bandpass filter configured to filter out signals outside of a range of about 0.5 Hz to about 20 Hz.

[0075] It can be described that the first and second filters provide zero-phase digital filtering (Bessel filtering) by processing input data in the forward and time-reversed directions. This results in the following characteristics: zero-phase distortion; a filter transfer function that is equal to the squared magnitude of the original IIR filter derived from the Bessel filter with a bilinear transformation; and a filter order that is twice the order of the filter coefficients of the designed infinite impulse response (IIR) filter. Further, zero-phase filtering can be accomplished by the following steps: filtering data in the forward direction; time-reversing the data; filtering the data in the time-reversed direction; and time-reversing the output of the previous steps to obtain the original time correspondence of the data.

[0076] Illustrative IIR filters and coefficients are as follows:

[0077]

[0078] Coefficients for an illustrative 20 Hz low pass IIR filter can be as follows: a0 = 1.000, a1 = -1.790211747962553, a2 = 0.804402717060237, a3 = 0, a4 = 0, b0 = 0.003547742274421, b1 = 0.007095484548842, b2 = 0.003547742274420, b3 = 0, b4 = 0.

[0079] Coefficients for an illustrative 10 Hz - 32 Hz bandpass IIR filter can be as follows: a0 = 1, a1 = -3.74704252837753, a2 = 5.28457739282789, a3 = -3.32507118261580, a4 = 0.787677403869584, b0 = 0.00422287948064259, b1 = -1.33226762955019e-15, b2 = -0.00844575896128053, b3 = -3.10862446895044e-15, b4 = 0.00422287948064337.

[0080] Coefficients for an illustrative 0.5 Hz - 20 Hz bandpass IIR filter can be as follows: a0 = 1, a1 = -3.79453631373899, a2 = 5.39795683527122, a3 = -3.41222897663138, a4 = 0.808808595500041, b0 = 0.00338079909581213, b1 = 0, b2 = -0.00676159819162336, b3 = 1.33226762955019e-15, b4 = 0.00338079909581224.

[0081] The at least one QRS complex is detected 440 based on the plurality of first filtered signals. According to various configurations, detecting the at least one QRS complex includes generating a first dispersion signal (e.g., a standard deviation) based on the plurality of first filtered signals. The QRS complex is detected based on the dispersion signal. For example, the QRS complex can be detected by determining a peak of the first dispersion signal.

[0082] The at least one QRS peak is detected 450 based on the plurality of second filtered signals and the detected at least one QRS complex. According to various configurations, detecting the at least one QRS peak includes generating a second dispersion signal based on the plurality of second filtered signals. The second dispersion signal can represent a dispersion of the plurality of second filtered signals over time. The QRS peak is detected 450 based on the second dispersion signal.

[0083] The dispersion signal described herein can represent a dispersion of the plurality of cardiac signals over time. The dispersion signal can be a standard deviation of the plurality of cardiac signals over time. In other embodiments, the dispersion signal can be a variance, a coefficient of variance, a range, a mean absolute deviation, a measure of central tendency (e.g., like a mean), a interquartile deviation of amplitude, a median absolute deviation obtained with respect to a measure of central tendency like a mean, a median, a mode, and / or another statistical measure of the plurality of cardiac signals over time.

[0084] A predetermined length of a blanking window can be initialized based on the first dispersion signal. The blanking window can be used to determine the QRS peak by determining a maximum amplitude within the blanking window. According to various configurations, the predetermined length of the blanking window is in a range of about 100 ms to about 600 ms. In some cases, the predetermined length of the blanking window is about 200 ms. The predetermined length can be set in the factory and / or can be adjusted in the field. According to various implementations, the length of the blanking window is set based on at least one previously detected QRS complex.

[0085] In one or more embodiments, a threshold function is calculated based on a QRS peak. The threshold function can be used to detect at least one subsequent QRS complex, as will be described in greater detail herein. According to various implementations, the threshold function can be used to detect the subsequent QRS complex by providing a sensitivity to detection of the at least one subsequent QRS complex. The threshold function can be an attenuation threshold signal based on one or both of the peaks of the first and second dispersion signals. For example, an attenuation parameter can be calculated using one or both of the peaks of the first and second dispersion signals. The process can start with each new QRS complex detected, such that a different threshold function is calculated for each QRS complex. According to various embodiments, the threshold function can be based on parameters of more than one previously detected QRS complex.

[0086] Figure 5 An exemplary method 500 for detecting QRS complexes and at least one subsequent QRS complex based on a threshold function is shown in FIG. 5. Electrical activity from tissue of a patient is monitored 510 using a plurality of external electrodes to generate a plurality of electrical signals over time. The plurality of electrical signals is filtered 520 using at least one filter to generate a plurality of filtered signals. According to various implementations, one or both of the bandpass filters 420, 430 described are used to filter the plurality of electrical signals. QRS peaks are detected 530 based on the plurality of filtered signals, and a threshold function can be determined 540 based on the QRS peaks. At least one subsequent QRS complex can be detected 550 based on (e.g., using) the threshold function. Figure 4 An exemplary method 500 for detecting QRS complexes and at least one subsequent QRS complex based on a threshold function is shown in FIG. 5. Electrical activity from tissue of a patient is monitored 510 using a plurality of external electrodes to generate a plurality of electrical signals over time. The plurality of electrical signals is filtered 520 using at least one filter to generate a plurality of filtered signals. According to various implementations, one or both of the bandpass filters 420, 430 described are used to filter the plurality of electrical signals. QRS peaks are detected 530 based on the plurality of filtered signals, and a threshold function can be determined 540 based on the QRS peaks. At least one subsequent QRS complex can be detected 550 based on (e.g., using) the threshold function.

[0087] Figure 6A and Figure 6B A more detailed process for detecting at least one QRS complex according to embodiments described herein is shown. A plurality of electrical signals or ECG signals are received 610. According to various implementations, the ECG signals are received from external electrode devices (e.g., ECG belts) as described herein. Initially, the ECG signals can be detrended 615 to remove any trends (e.g., mean value changes) of the ECG signals over time, such as an increase or decrease in the mean value over time. For example, it can be described that an algorithm based on linear regression of data is used to detrend each ECG signal to remove baseline drift. The algorithm can calculate a least squares regression line through all the points within a 5000 sample record, and then subtract that line from the original signal.

[0088] In at least one embodiment, the least squares regression line of data can be defined as follows:

[0089]

[0090] The definition uses the following equation:

[0091] and

[0092] Then, the predicted value can be subtracted from the raw data at each time point to obtain new detrended values:

[0093]

[0094] Further, the system can determine 620 whether all electrodes are valid, which can involve determining, for example, whether any electrodes are returning outlier data that can indicate that the electrode is not receiving accurate data. Illustrative systems and methods for determining whether an electrode and / or ECG signal is valid can be described in U.S. Patent No. 9,924,884, issued March 27, 2018, and U.S. Patent No. 10,064,567, issued September 4, 2018.

[0095] In at least one embodiment, determining ECG signals to include in the calculation is done using an ECG signal filtered according to a 20 Hz low pass filter and portions of the signal defined by a start and an offset as described herein by the following steps. The Pearson correlation coefficient of each electrode compared to its two neighboring electrodes can be calculated. A signal can be declared invalid if at least one of the following is true: peak-to-peak > 6 mV; peak-to-peak < (0.2 * median peak-to-peak); peak-to-peak <= 0.12 mV; correlation of two neighboring electrodes <= 0.6 (not applicable to electrodes 1 and 40, which are located at either end); the absolute value of the ratio of the minimum amplitude relative to the baseline and the maximum amplitude relative to the baseline is greater than 1, where the baseline is the signal amplitude located at the start and the minimum amplitude is the signal amplitude located at the offset; and the absolute value of the ratio of the maximum amplitude relative to the baseline and the minimum amplitude relative to the baseline is greater than 1, where the baseline is the signal amplitude located at the start and the maximum amplitude is the signal amplitude located at the offset; lead-off according to the amplifier between the start and offset of a selected beat. Any signal that is not declared invalid can be determined to be valid.

[0096] The ECG signal is filtered 630 using a first filter to create a first filtered signal. The first filter can be the same as the filter described in connection with Figure 4The described filter is the same. A first dispersion signal is determined based on the first filtered signal 632. A peak of the first dispersion signal is determined 634. According to various configurations, a minimum percentage of the peak and a predetermined value can be used to determine the location of the first QRS complex. For example, a minimum of about 35% of the peak and a value of about 0.075 can be used to determine the location of the first QRS complex. In some cases, it can be determined whether 35% of the peak is less than a base threshold (e.g., 0.025). If it is determined that the minimum is less than the base threshold, the base threshold can be used to detect the time of the first QRS complex. The time of the first QRS complex can be used to initialize 640 a blanking window for determining the first QRS peak.

[0097] The ECG signal is filtered 635 with a second filter to create a second filtered signal. The second filter can be the same as the first filter described in connection with Figure 4 The described filter is the same. A first dispersion signal is determined based on the first filtered signal 632. A peak of the first dispersion signal is determined 634. According to various configurations, a minimum percentage of the peak and a predetermined value can be used to determine the location of the first QRS complex. For example, a minimum of about 35% of the peak and a value of about 0.075 can be used to determine the location of the first QRS complex. In some cases, it can be determined whether 35% of the peak is less than a base threshold (e.g., 0.025). If it is determined that the minimum is less than the base threshold, the base threshold can be used to detect the time of the first QRS complex. The time of the first QRS complex can be used to initialize 640 a blanking window for determining the first QRS peak.

[0098] The system can continue to monitor 650 the ECG signal for at least one subsequent QRS complex. The monitoring can be initiated or occur after a predetermined amount of time has elapsed after the detected first QRS complex and / or after a predetermined amount of time after the first QRS peak. For example, the system can begin monitoring for at least one subsequent QRS complex in a range of about 100 ms to about 600 ms after the detected first QRS peak. In some cases, the system begins monitoring for at least one subsequent QRS complex about 200 ms after the detected first QRS peak.

[0099] A threshold function can be calculated 655 based on the first detected QRS complex. The threshold function provides a sensitivity for detecting one or more subsequent QRS complexes. Additional details regarding illustrative threshold function calculations or determinations are further described herein. Figure 7 The threshold function can be calculated 655 based on the first detected QRS complex. The threshold function provides a sensitivity for detecting one or more subsequent QRS complexes. Additional details regarding illustrative threshold function calculations or determinations are further described herein.

[0100] It is determined 670 whether the time elapsed from the first QRS peak to the total monitoring time is less than a predetermined value. The predetermined value can be in a range from about 4000 ms to about 5000 ms. In some cases, the predetermined value is about 4750 ms. In some embodiments, the predetermined interval can be set based on the total monitoring time (e.g., total monitoring time - 250 milliseconds). If the total monitoring time is 10 s (10000 ms), the value of the predetermined interval can be about 9750 ms. If it is determined 670 that the elapsed time is less than the predetermined value, the system can begin monitoring for another QRS complex. If it is determined 670 that the elapsed time is greater than the predetermined value, the system can continue discarding 675 any detected QRS complexes that do not meet the selection criteria and the process end 680. The selection criteria can include that all detected QRS complexes are greater than a predetermined length. For example, the predetermined length can be in a range from about 250 ms to about 600 ms. In some cases, the predetermined length is about 400 ms. According to various embodiments, the selection criteria can include that a QRS complex is detected within a predetermined time limit. The predetermined time limit can be in a range from about 4000 ms to about 5000 ms. In some cases, the predetermined time limit is about 4750 ms.

[0101] Figure 7 An example threshold function according to embodiments described herein is shown. Here, the maximum amplitude of the first filtered signal is used to detect the first QRS complex. According to various embodiments, the maximum amplitude of the first filtered signal is used to determine the start 710 of the blanking window (A0) at time tl. The maximum amplitude within the blanking window 720 is determined to be the QRS peak. After a predetermined amount of time 725 after the start 710 of the blanking window, the system can continue monitoring for a subsequent QRS complex at time t2.

[0102] A threshold function 740 can then be calculated based on the detected QRS peak. The threshold function can be configured to provide sensitivity for detecting subsequent QRS complexes. According to various embodiments described herein, the threshold function 740 can be configured to decrease at time t2 until at least one subsequent QRS complex is detected and / or a base threshold 780 is reached. According to various embodiments, the base threshold is a base percentage of the QRS peak. For example, the base threshold can be in a range from about 0.5% to about 5% of the QRS peak. In some cases, the base threshold is about 3%.

[0103] According to various implementations, the threshold function 740 is configured to decrease from a first threshold percentage (Al) at time t2 to a second threshold percentage (A2) at time t3. At least a portion of this decrease can be a substantially linear decrease or a non-linear decrease. The threshold function can be configured to decrease from Al at time t2 (e.g., a predetermined amount of time after the start of the blanking window) to A2 at t3. Al can be in a range of about 50% to about 80% of the QRS peak 730. In some cases, Al is about 60% of the QRS peak 730. A2 can be in a range of about 10% to about 50% of the QRS peak 730. In some cases, A2 is about 30% of the QRS peak.

[0104] The threshold function 730 can be configured to remain constant between t3 and t4. According to various configurations, ti is about 0 ms, t2 is about 200 ms, t3 is about 1200 ms, t4 is about 1700 ms, and / or t5 is about 2200 ms. In some cases, the threshold function 740 is configured to decrease to a third threshold percentage (A3) of the QRS peak at t4. A3 can be in a range of about 5% to about 20% of the QRS peak 730. In some cases, A3 is about 15% of the QRS peak. The threshold function can then be configured to decrease linearly or non-linearly to a base threshold percentage between t4 and t5. If a subsequent QRS complex 790 is detected, a new blanking window 792 and a new threshold function 795 are established.

[0105] Figure 8 An exemplary method 800 for determining a start and an offset of a corresponding QRS complex is shown in FIG. 8. Electrical activity from tissue of a patient is monitored 810 using a plurality of external electrodes to generate a plurality of electrical signals over time. The plurality of electrical signals is filtered 820 using a first filter and a second filter to generate a plurality of first filtered signals and a plurality of second filtered signals, the first and second filters having different frequency ranges. A QRS peak is detected 830 based on the plurality of first filtered signals and the plurality of second filtered signals, as described herein with respect to Figure 4 to FIG. 6.

[0106] A dispersion signal can be generated 840 from the plurality of second filtered signals, and then a first derivative signal can be determined 850 based on the dispersion signal. At least one of a QRS start time and a QRS offset time corresponding to the QRS complex can be determined 860 based on the first derivative signal.

[0107] According to various implementations, the onset time and the offset time can be used to calculate an activation time of at least one QRS complex of each of the plurality of cardiac signals. Specifically, a fiducial point (e.g., a maximum negative slope) within a QRS duration between a QRS onset time value and a QRS offset time value can be determined, which can be used to determine the activation time. At least one measure of electrical heterogeneity can be determined based on the activation times of the plurality of cardiac signals for each QRS complex.

[0108] Figure 9 and Figures 10A-10C A more detailed process 900 for determining onset and offset values for at least one QRS complex is shown in accordance with implementations described herein. The timing of one or more QRS peaks is received 910. In other words, the time at which each of the QRS peaks occurs can have been determined, for example, using substantially the same process described in connection with Figures 4-7 or can be determined using one or more different processes, and then received 910.

[0109] Additionally, an ECG signal can be received 920. For example, the ECG signal can be received from an ECG strip, and then filtered 930 as shown in the example of Figure 10A According to various configurations, the ECG signal is filtered using one or more bandpass filters configured to remove or "filter out" signals outside of a predetermined range. For example, the bandpass filter can be configured to remove or "filter out" signals outside of a range of about 0.5 Hz to about 20 Hz.

[0110] A dispersion signal of the filtered signal is determined 940 as shown in Figure 10B The dispersion signal is then smoothed 950. For example, the dispersion signal can be smoothed to reduce outliers due to noise. According to various implementations, the dispersion signal can be smoothed using a 25-point equal-weighted smoother.

[0111] A first derivative signal of the smoothed signal is generated as shown in Figure 10C A first window is set 970 to a predetermined amount of time before the QRS peak, and a second window is set 980 to a predetermined amount of time after the QRS peak. The amount of time before the QRS peak and the amount of time after the QRS peak can be substantially the same. For example, the predetermined amount of time before the QRS peak and the predetermined amount of time after the QRS peak can be in a range of about 100 ms to about 150 ms. In some cases, the predetermined amount of time before the QRS peak and the predetermined amount of time after the QRS peak is about 120 ms. In one or more implementations, the predetermined amount of time before the QRS peak and the predetermined amount of time after the QRS peak are different. The predetermined amounts before and after the QRS peak can be set in the factory and / or can be adjusted in the field.

[0112] A positive peak 1010 and a negative peak 1020 of the derivative signal are determined. A second window is set 974 a predetermined amount of time before the positive peak 1010 and set 984 a predetermined amount of time after the negative peak 1020. The predetermined amount of time before the positive peak and the predetermined amount of time after the negative peak can be substantially the same. For example, the predetermined amount of time before the positive peak and the predetermined amount of time after the negative peak can be in a range of about 100 ms to about 150 ms. In some cases, the predetermined amount of time before the positive peak and the predetermined amount of time after the negative peak is about 120 ms. In some configurations, the predetermined amount of time before the positive peak and the predetermined amount of time after the negative peak are different from each other. The predetermined amount of time before the positive peak and the predetermined amount of time after the negative peak can be set in the factory and / or can be adjusted in the field.

[0113] The QRS onset 978 is determined by finding 976 a last point in the second window that is less than a first predetermined percentage of the QRS peak. The first predetermined percentage can be in a range of about 10% to about 30% of the QRS peak. In some cases, the first predetermined percentage is about 20%.

[0114] The QRS offset 988 is determined by finding 986 a first time in the second window that is greater (i.e., more positive) than a second predetermined percentage of the QRS peak. The second predetermined percentage can be in a range of about 10% to about 30% of the QRS peak. In some cases, the second predetermined percentage is about 20%. It should be appreciated that the first predetermined percentage and the second predetermined percentage can be set in the factory and / or can be reprogrammed in the field. The first predetermined percentage and the second predetermined percentage can be based on a QRS history of a patient and / or multiple patients.

[0115] Illustrative cardiac therapy systems and devices can be further described herein with reference to Figures 11-1 3, which can utilize the illustrative systems, interfaces, methods, and processes described herein with reference to Figures 11-1 3 can utilize the illustrative systems, interfaces, methods, and processes described herein with reference to Figures 1-1 0.

[0116] Figure 11 To illustrate a conceptual diagram of the illustrative therapy system 10, the therapy system can be used to deliver pacing therapy to a patient 14. The patient 14 can, but need not be, a human. The therapy system 10 can include an implantable medical device 16 (IMD) that can be coupled to leads 18, 20, 22. The IMD 16 can be, for example, an implantable pacemaker, cardioverter, and / or defibrillator that delivers or provides electrical signals (e.g., pacing, etc.) to a heart 12 of the patient 14 via electrodes coupled to one or more of the leads 18, 20, 22 and / or senses electrical signals from the heart of the patient.

[0117] The leads 18, 20, 22 extend into the heart 12 of the patient 14 to sense electrical activity of the heart 12 and / or to deliver electrical stimulation to the heart 12. In Figure 11 In the illustrated example, the right ventricular (RV) lead 18 extends through one or more veins (not shown), the superior vena cava (not shown), and the right atrium 26, and into the right ventricle 28. The left ventricular (LV) coronary sinus lead 20 extends through one or more veins, the vena cava, the right atrium 26, and into the coronary sinus 30 to a region adjacent to a free wall of the left ventricle 32 of the heart 12. The right atrial (RA) lead 22 extends through one or more veins and the vena cava, and into the right atrium 26 of the heart 12.

[0118] The IMD 16 can sense electrical signals attendant to the depolarization and repolarization of the heart 12 via electrodes coupled to at least one of the leads 18, 20, 22. In some examples, the IMD 16 provides pacing therapy (e.g., pacing pulses) to the heart 12 based on the electrical signals sensed within the heart 12. The IMD 16 can be operable to adjust one or more parameters associated with the pacing therapy, such as, for example, A-V delay and other various timing, pulse width, amplitude, voltage, burst length, etc. Further, the IMD 16 can be operable to deliver pacing therapy using various electrode configurations, which can be unipolar, bipolar, quadripolar, or otherwise multipolar. For example, a multipolar lead can include several electrodes that can be used to deliver pacing therapy. Thus, a multipolar lead system can provide or offer multiple electrical vectors to pace from. A pacing vector can include at least one cathode, which can be at least one electrode located on at least one lead, and at least one anode, which can be at least one electrode located on at least one lead (e.g., the same lead or a different lead) and / or on a housing or can of the IMD. While improvement in cardiac function as a result of pacing therapy can primarily depend on the cathode, electrical parameters like impedance, pacing threshold voltage, current drain, longevity, etc. can be more dependent on the pacing vector, which includes both the cathode and the anode. The IMD 16 can also provide defibrillation therapy and / or cardioversion therapy via electrodes located on at least one of the leads 18, 20, 22. Further, the IMD 16 can detect arrhythmias of the heart 12, such as fibrillation of the ventricles 28, 32, and defibrillate the heart 12 with electrical pulses. In some examples, the IMD 16 can be programmed to deliver a progression of therapies, e.g., pulses with increasing energy levels, until a fibrillation of the heart 12 is stopped.

[0119] Figures 12A-B To explain in more detail Figure 11conceptual diagram of IMD 16 and leads 18, 20, 22 of therapy system 10. Leads 18, 20, 22 can be electrically coupled to therapy delivery modules (e.g., for delivering pacing therapy), sensing modules (e.g., for sensing one or more signals from one or more electrodes), and / or any other modules of IMD 16 via connector block 34. In some examples, the proximal ends of leads 18, 20, 22 can include electrical contacts that electrically couple to respective electrical contacts within connector block 34 of IMD 16. Additionally, in some examples, leads 18, 20, 22 can be mechanically coupled to connector block 34 by way of set screws, connecting pins, or another suitable mechanical coupling mechanism.

[0120] Each of leads 18, 20, 22 includes an elongated insulated lead body that can carry a plurality of conductors (e.g., concentric coil conductors, straight conductors, etc.) separated from one another by insulation (e.g., a tubular insulating jacket). In the illustrated example, bipolar electrodes 40, 42 are located near the distal end of lead 18. Additionally, bipolar electrodes 44, 45, 46, 47 are located near the distal end of lead 20, and bipolar electrodes 48, 50 are located near the distal end of lead 22.

[0121] Electrodes 40, 44, 45, 46, 47, 48 can take the form of ring electrodes, and electrodes 42, 50 can take the form of extendable helical tip electrodes that are retractably mounted within insulated electrode heads 52, 54, 56, respectively. Each of electrodes 40, 42, 44, 45, 46, 47, 48, 50 can be electrically coupled to a respective one of the conductors (e.g., coil conductors and / or straight conductors) within the lead body of its associated lead 18, 20, 22, and thereby to a respective one of the electrical contacts on the proximal end of lead 18, 20, 22.

[0122] Additionally, the electrode surface area of electrodes 44, 45, 46, and 47 can be about 5.3 mm 2 to about 5.8 mm 2 . Electrodes 44, 45, 46, and 47 can also be referred to as LV1, LV2, LV3, and LV4, respectively. The LV electrodes (i.e., left ventricular electrode 1 (LV1) 44, left ventricular electrode 2 (LV2) 45, left ventricular electrode 3 (LV3) 46, and left ventricular 4 (LV4) 47, etc.) on lead 20 can be spaced apart at variable distances. For example, electrode 44 can be a distance of, for example, about 21 millimeters (mm) from electrode 45, electrodes 45 and 46 can be spaced apart from one another by a distance of, for example, about 1.3 mm to about 1.5 mm, and electrodes 46 and 47 can be spaced apart from one another by a distance of, for example, 20 mm to about 21 mm.

[0123] The electrodes 40, 42, 44, 45, 46, 47, 48, 50 can further be used to sense electrical signals (e.g., morphological waveforms within an electrogram (EGM)) that accompany depolarization and repolarization of the heart 12. The electrical signals are conducted to the IMD 16 by the respective leads 18, 20, 22. In some examples, the IMD 16 can also deliver pacing pulses via the electrodes 40, 42, 44, 45, 46, 47, 48, 50 to cause depolarization of cardiac tissue of the patient’s heart 12. In examples where the IMD 16 is configured to deliver pacing therapy, the electrodes 40, 42, 44, 45, 46, 47, 48, 50 can be used to sense electrical activity of the heart 12 during delivery of the pacing therapy. Figure 12A In some examples as illustrated, the IMD 16 includes one or more housing electrodes, such as the housing electrode 58, which can be integrally formed with or otherwise coupled to an outer surface of a housing 60 (e.g., a hermetically sealed housing) of the IMD 16. Any of the electrodes 40, 42, 44, 45, 46, 47, 48, 50 can be combined with the housing electrode 58 for unipolar sensing or pacing. It is generally understood by those skilled in the art that other electrodes can also be selected to define pacing and sensing vectors or for pacing and sensing vectors. Further, any of the electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58 can be used to sense electrical activity during pacing therapy when not being used to deliver pacing therapy.

[0124] As referenced above, the electrodes 40, 42, 44, 45, 46, 47, 48, 50 can be used to sense electrical activity of the heart 12 during delivery of pacing therapy. In some examples, the electrodes 40, 42, 44, 45, 46, 47, 48, 50 can be used to sense electrical activity of the heart 12 during delivery of pacing therapy in combination with the housing electrode 58. In some examples, the electrodes 40, 42, 44, 45, 46, 47, 48, 50 can be used to sense electrical activity of the heart 12 during delivery of pacing therapy in combination with the housing electrode 58 and the defibrillation electrodes 62, 64, 66. Figure 12A As described in further detail, the housing 60 can encase a therapy delivery module, which can include a stimulation generator for generating cardiac pacing pulses and defibrillation or cardioversion shocks, and a sensing module for monitoring electrical signals of the patient’s heart (e.g., the patient’s heart rhythm). The leads 18, 20, 22 can also include elongated electrodes 62, 64, 66, respectively, which can take the form of coils. The IMD 16 can deliver defibrillation shocks to the heart 12 via any combination of the elongated electrodes 62, 64, 66 and the housing electrode 58. The electrodes 58, 62, 64, 66 can also be used to deliver cardiac cardioversion pulses to the heart 12. Further, the electrodes 62, 64, 66 can be made of any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloys, and / or other materials known for use in implantable defibrillation electrodes. As the electrodes 62, 64, 66 are generally not configured for pacing therapy, any of the electrodes 62, 64, 66 can be used to sense electrical activity and can be used in combination with any of the electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58. In at least one embodiment, the RV elongated electrode 62 can be used to sense electrical activity of the patient’s heart during delivery of pacing therapy (e.g., in combination with the housing electrode 58 or a defibrillation electrode-to-housing electrode vector).

[0125] Figures 11-13The illustrated configuration of the therapy system 10 is just one example. In other examples, the therapy system can include epicardial leads and / or patch electrodes in place of Figure 11 The illustrated transvenous leads 18, 20, 22, or as an alternative to Figure 11 The illustrated transvenous leads 18, 20, 22 are shown in addition to. In other examples, the therapy system 10 can be absent of transvenous leads (e.g., leadless / wireless pacing systems) or present of leads implanted (e.g., transvenously or using methods) into the left chamber of the heart (e.g., as Figure 11 The illustrated, implanted in / around the septal region of the heart as an addition to or alternative to transvenous leads placed into the right chamber of the heart. Further, in one or more embodiments, the IMD 16 need not be implanted within the patient 14. For example, the IMD 16 can deliver various cardiac therapies to the heart 12 via a percutaneous lead that extends through the skin of the patient 14 to a location within or outside of the heart 12. In one or more embodiments, the system 10 can utilize wireless pacing (e.g., using energy transfer via ultrasound, inductive coupling, RF, etc. to a pacing component(s) within the heart) and sensed cardiac activation using electrodes on the housing / case and / or subcutaneous leads.

[0126] In other examples of therapy systems that provide electrical stimulation therapy to the heart 12, such therapy systems can include any suitable number of leads coupled to the IMD 16, and each of the leads can extend to any location within or proximate to the heart 12. For example, as Figures 11-1 3The illustrated, other examples of therapy systems can include three transvenous leads positioned. Still further, other therapy systems can include a single lead extending from the IMD 16 into the right atrium 26 or right ventricle 28 or two leads extending into respective ones of the right atrium 26 and right ventricle 28.

[0127] Figure 13A is a functional block diagram of one illustrative configuration of the IMD 16. As shown, the IMD 16 can include a control module 81, a therapy delivery module 84 (e.g., which can include a stimulation generator), a sensing module 86, and a power source 90.

[0128] The control module or device 81 can include a processor 80, a memory 82, and a telemetry module or device 88. The memory 82 can include computer-readable instructions that, when executed by, for example, the processor 80, cause the IMD 16 and / or the control module 81 to perform various functions attributed to the IMD 16 and / or the control module 81 described herein. Further, the memory 82 can include any volatile, nonvolatile, magnetic, optical, and / or electrical media, such as a random access memory (RAM), read-only memory (ROM), nonvolatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, and / or any other digital media. An exemplary capture management module can be a left ventricular capture management (LVCM) module, as described in U.S. Patent No. 7,684,863, entitled "LV THRESHOLD MEASUREMENT AND CAPTURE MANAGEMENT," issued March 23, 2010.

[0129] The processor 80 of the control module 81 can include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), and / or equivalent discrete or integrated logic circuitry. In some examples, the processor 80 can include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, and / or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functionality attributed to the processor 80 herein can be embodied in software, firmware, hardware, or any combination thereof.

[0130] The control module 81 can control the therapy delivery module 84 to deliver therapy (e.g., electrical stimulation therapy such as pacing) to the heart 12 in accordance with one or more selected therapy programs that can be stored in the memory 82. More specifically, the control module 81 (e.g., the processor 80) can control various parameters of electrical stimulation delivered by the therapy delivery module 84 (such as, for example, A-V delays, V-V delays, pacing pulses having amplitudes, pulse widths, frequencies, or electrode polarities, etc.) that can be specified by one or more selected therapy programs (e.g., A-V and / or V-V delay adjustment programs, pacing therapy programs, pacing resumption programs, capture management programs, etc.). As shown, the therapy delivery module 84 is electrically coupled to the electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66, e.g., via conductors of the respective leads 18, 20, 22 or, in the case of the housing electrode 58, via electrical conductors disposed within the housing 60 of the IMD 16. The therapy delivery module 84 can be configured to generate and deliver electrical stimulation therapy, such as pacing therapy, to the heart 12 using one or more of the electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66.

[0131] For example, the therapy delivery module 84 can deliver pacing stimulation (e.g., pacing pulses) via the ring electrodes 40, 44, 45, 46, 47, 48 coupled to the leads 18, 20, 22 and / or the helix tip electrodes 42, 50 of the leads 18, 22. Further, for example, the therapy delivery module 84 can deliver defibrillation shocks to the heart 12 via at least two of the electrodes 58, 62, 64, 66. In some examples, the therapy delivery module 84 can be configured to deliver pacing, cardioversion, or defibrillation stimulation in the form of electrical pulses. In other examples, the therapy delivery module 84 can be configured to deliver one or more of these types of stimulation in the form of other signals such as sinusoidal, square-wave, and / or other substantially continuous time signals.

[0132] IMD 16 can further include a switch module 85, and control module 81 (e.g., processor 80) can use switch module 85 to select, e.g., via a data / address bus, which of the available electrodes to use to deliver therapy, such as pacing pulses for pacing therapy, or which of the available electrodes to use for sensing. Switch module 85 can include an array of switches, a matrix of switches, multiplexers, or any other type of switching device suitable to selectively couple sensing module 86 and / or therapy delivery module 84 to one or more selected electrodes. More specifically, therapy delivery module 84 can include a plurality of pacing output circuits. Each of the plurality of pacing output circuits can be selectively coupled to one or more of electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66, e.g., using switch module 85 (e.g., a pair of electrodes for delivering therapy to a bipolar or multipolar pacing vector). In other words, each electrode can be selectively coupled to one of the pacing output circuits of therapy delivery module using switch module 85.

[0133] Sensing module 86 is coupled (e.g., electrically coupled) to sensing devices, which in additional sensing devices can include electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66 to monitor electrical activity of heart 12, e.g., electrocardiogram (ECG) / electrogram (EGM) signals, etc. The ECG / EGM signals can be used to measure or monitor activation times (e.g., ventricular activation times, etc.), heart rate (HR), heart rate variability (HRV), heart rate turbulence (HRT), deceleration / acceleration capacity, deceleration sequence morbidity, T-wave alternans (TWA), P-wave to P-wave intervals (also referred to as P-P intervals or A-A intervals), R-wave to R-wave intervals (also referred to as R-R intervals or V-V intervals), P-wave to QRS complex intervals (also referred to as P-R intervals, A-V intervals, or P-Q intervals), QRS complex morphology, ST segment (i.e., the segment connecting the QRS complex and the T wave), T wave changes, QT interval, electrical vector, etc.

[0134] The switch module 85 can also be used with the sensing module 86 to select which of the available electrodes to use or to enable to, for example, sense electrical activity of the patient's heart (e.g., one or more electrical vectors of the patient's heart using any combination of electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66). Likewise, the switch module 85 can also be used with the sensing module 86 to select which of the available electrodes not to use (e.g., to disable) to, for example, sense electrical activity of the patient's heart (e.g., one or more electrical vectors of the patient's heart using any combination of electrodes 40, 42, 44, 45, 46, 47, 48, 50, 58, 62, 64, 66), etc. In some examples, the control module 81 can select electrodes to act as sensing electrodes via the switch module within the sensing module 86, for example, by providing signals over a data / address bus.

[0135] In some examples, the sensing module 86 includes a channel that includes an amplifier having a relatively wider passband than an R-wave or P-wave amplifier. The signal from the selected sensing electrode can be provided to a multiplexer and thereafter converted to a multi-bit digital signal by an analog-to-digital converter for storage in the memory 82, for example, as an electrogram (EGM). In some examples, storage of such EGMs in the memory 82 can be under the control of a direct memory access circuit.

[0136] In some examples, the control module 81 can operate as an interrupt driven device and can respond to interrupts from the pacemaker timing and control module, where the interrupts can correspond to the occurrence of sensed P-waves and R-waves and the generation of cardiac pacing pulses. Any necessary mathematical calculations can be performed by the processor 80 and any updating of values or intervals controlled by the pacemaker timing and control module can occur following such interrupts. A portion of the memory 82 can be configured as a plurality of recirculating buffers capable of holding one or more series of measured intervals that can be analyzed by, for example, the processor 80 in response to the occurrence of pacing or sensing interrupts to determine whether the patient's heart 12 is currently exhibiting atrial or ventricular tachyarrhythmia.

[0137] The telemetry module 88 of the control module 81 can include any suitable hardware, firmware, software, or any combination thereof for communicating with another device, such as a programmer. For example, under the control of the processor 80, the telemetry module 88 can receive downlink telemetry from and send uplink telemetry to a programmer with the aid of an antenna, which can be internal and / or external. The processor 80 can provide, e.g., data to be uplinked to the programmer and control signals for the telemetry circuit within the telemetry module 88, e.g., via an address / data bus. In some examples, the telemetry module 88 can provide received data to the processor 80 via a multiplexer.

[0138] The various components of the IMD 16 are further coupled to a power source 90, which can include a rechargeable or non-rechargeable battery. The non-rechargeable battery can be selected to last for several years, while a rechargeable battery can be inductively charged from an external device, e.g., on a daily or weekly basis.

[0139] Figure 13B is another embodiment of a functional block diagram of an IMD 16 depicting bipolar RA lead 22, bipolar RV lead 18, and bipolar LV CS lead 20 without LA CS pacing / sensing electrodes and coupled to an implantable pulse generator (IPG) circuit 31 having programmable modes known in the pacing art and parameters of the biventricular DDD / R type. In turn, sensor signal processing circuit 91 is coupled indirectly to timing circuit 43 and via a data and control bus to microcomputer circuit 33. The IPG circuit 31 is shown in a functional block diagram that is generally divided into microcomputer circuit 33 and pacing circuit 21. Pacing circuit 21 includes digital controller / timer circuit 43, output amplifier circuit 51, sense amplifier circuit 55, RF telemetry transceiver 41, activity sensor circuit 35, and many other circuits and components described below.

[0140] Crystal oscillator circuit 89 provides a basic timing clock to pacing circuit 21 when battery 29 provides power. Power-on reset circuit 87 responds to initial connection of the circuit to the battery for defining initial operating conditions and similarly resets the operating state of the device in response to detecting a low battery condition. Reference mode circuit 37 generates stable voltage references and currents for analog circuits within pacing circuit 21. Analog-to-digital converter (ADC) and multiplexer circuit 39 digitizes analog signals and voltages to provide, e.g., real-time telemetry of cardiac signals from sense amplifier 55 for uplink transmission via RF transmitter and receiver circuit 41. Voltage reference and bias circuit 37, ADC and multiplexer 39, power-on reset circuit 87, and crystal oscillator circuit 89 can correspond to any of those used in illustrative implantable cardiac pacemakers.

[0141] If the IPG is programmed in rate responsive mode, the signal output by one or more physiological sensors is used as a rate control parameter (RCP) to derive a physiologic escape interval. For example, the escape interval is adjusted in proportion to a patient activity level generated in a patient activity sensor (PAS) circuit 35 in the illustrative IPG circuit 31 depicted. The patient activity sensor 27 is coupled to the IPG housing and can take the form of a piezoelectric crystal transducer. The output signal of the patient activity sensor 27 can be processed and used as an RCP. The sensor 27 generates an electrical signal in response to sensed body activity, which is processed by the activity circuit 35 and provided to the digital controller / timer circuit 43. The activity circuit 35 and associated sensor 27 can correspond to the circuitry disclosed in U.S. Patent Nos. 5,052,388, entitled “METHOD AND APPARATUS FOR IMPLEMENTING ACTIVITY SENSING IN A PULSE GENERATOR” and issued October 1, 1991, and 4,428,378, entitled “RATE ADAPTIVE PACER” and issued January 31, 1984. Similarly, the illustrative systems, devices, and methods described herein can be practiced in conjunction with alternative types of sensors, such as oxygenation sensors, pressure sensors, pH sensors, and respiration sensors, for providing rate responsive pacing capabilities. Alternatively, the QT time can be used as a rate indicating parameter, in which case no additional sensors are needed. Similarly, the illustrative embodiments described herein can also be practiced in non-rate responsive pacemakers.

[0142] Data transfer to and from an external programmer is accomplished through the telemetry antenna 57 and associated RF transceiver 41, which is used to both demodulate received downlink telemetry and to transmit uplink telemetry. Uplink telemetry capabilities can include the ability to transmit stored digital information, e.g., operating mode and parameters, EGM histograms and other events, and real-time EGMs of atrial and / or ventricular electrical activity and marker channel pulses indicating the occurrence of sensed and paced depolarizations in the atrium and ventricles.

[0143] Microcomputer 33 contains a microprocessor 80 and associated system clock and on-processor RAM chip 82A and ROM chip 82B. In addition, microcomputer circuit 33 includes a separate RAM / ROM chip 82C to provide additional memory capacity. Microprocessor 80 is normally operated in a reduced power consumption mode and is interrupt driven. Microprocessor 80 is awakened in response to defined interrupt events which can include A-TRIG, RV-TRIG, LV-TRIG signals generated by timers in digital timer / controller circuit 43, as well as A-EVENT, RV-EVENT and LV-EVENT signals generated by sense amplifier circuit 55, among others. The specific values of intervals and delays timed by digital controller / timer circuit 43 are controlled by microcomputer circuit 33 through data and control buses from programmed parameter values and operating modes. In addition, if programmed to operate as a rate responsive pacemaker, timing interrupts can be provided, e.g., every cycle or every two seconds, to allow the microprocessor to analyze activity sensor data and update the underlying A-A, V-A or V-V escape interval, if applicable. In addition, microprocessor 80 can also be used to define variable, programmable A-V delay intervals, V-V delay intervals and energy delivered to each ventricle and / or atrium.

[0144] In one embodiment, microprocessor 80 is a custom microprocessor adapted to fetch and execute instructions stored in RAM / ROM units 82 in a conventional manner. However, other implementations can be suitable to practice the present disclosure. For example, an off-the-shelf, commercially available microprocessor or microcontroller or custom, hard-wired logic or state machine type circuit can perform the functions of microprocessor 80.

[0145] Digital controller / timer circuit 43 operates under the general control of microcomputer 33 to control timing and other functions within pacing circuit 21 and includes a set of timing and associated logic circuits, some of which are depicted in relation to the present disclosure. The depicted timing circuits include URI / LRI timers 83A, V-V delay timers 83B, intrinsic interval timers 83C for timing elapsed V-EVENT to V-EVENT intervals or V-EVENT to A-EVENT intervals or V-V conduction intervals, escape interval timers 83D for timing A-A, V-A and / or V-V pacing escape intervals, A-V delay interval timers 83E for timing A-LVp delays (or A-RVp delays) from a prior A-EVENT or A-TRIG, post-ventricular timers 83F for timing post-ventricular time periods, and date / time clock 83G.

[0146] An A-V delay interval timer 83E is loaded with the appropriate delay interval for one ventricular chamber (e.g., A-RVp delay or A-LVp) to time out from a previous A-PACE or A-EVENT. The interval timer 83E triggers the delivery of a pace stimulus and can be based on one or more previous cardiac cycles (or based on a data set empirically derived for a given patient).

[0147] An event post timer 83F times out a post-ventricular time period following an RV-EVENT or LV-EVENT or RV-TRIG or LV-TRIG and a post-atrial time period following an A-EVENT or A-TRIG. The duration of the event post time periods can also be selected as programmable parameters stored in the microcomputer 33. The post-ventricular time periods include a PVARP, a post-atrial ventricular blanking period (PAVBP), a ventricular blanking period (VBP), a post-ventricular atrial blanking period (PVARP), and a ventricular refractory period (VRP), although other time periods can be defined as appropriate depending at least in part on the operational circuitry employed in the pacing engine. The post-atrial time periods include an atrial refractory period (ARP) during which an A-EVENT is ignored for the purpose of resetting any A-V delay, and an atrial blanking period (ABP) during which atrial sensing is disabled. It should be noted that the start of the post-atrial time periods and the A-V delay can begin substantially contemporaneously with the start or end of each A-EVENT or A-TRIG, or in the latter case, at the end of an A-PACE that can follow an A-TRIG. Similarly, the start of the post-ventricular time periods and the V-A escape interval can begin substantially contemporaneously with the start or end of a V-EVENT or V-TRIG, or in the latter case, at the end of a V-PACE that can follow a V-TRIG. The microprocessor 80 also optionally extrapolates the A-V delay, the V-V delay, the post-ventricular time periods, and the post-atrial time periods, which vary in response to one or more sensor-based escape intervals established in response to an RCP and / or an intrinsic atrial and / or ventricular rate.

[0148] The output amplifier circuit 51 contains the RA pacing pulse generator (and the LA pacing pulse generator, if LA pacing is provided), the RV pacing pulse generator, the LV pacing pulse generator, and / or any other pulse generators configured to provide atrial and ventricular pacing. To trigger the generation of an RV-PACE or LV-PACE pulse, the digital controller / timer circuit 43 generates an RV-TRIG signal when the A-RVp delay (in the case of RV pre-excitation) provided by the A-V delay interval timer 83E (or the V-V delay timer 83B) times out or an LV-TRIG when the A-LVp delay (in the case of LV pre-excitation) times out. Similarly, the digital controller / timer circuit 43 generates an RA-TRIG signal that triggers the output of an RA-PACE pulse (or an LA-TRIG signal that triggers the output of an LA-pacing pulse, if provided) at the end of the V-A escape interval timed by the escape interval timer 83D.

[0149] The output amplifier circuit 51 includes a switching circuit for coupling selected pairs of pacing electrodes among the lead conductors and the IND-CAN electrode 20 to the RA pacing pulse generator (and the LA pacing pulse generator, if provided), the RV pacing pulse generator, and the LV pacing pulse generator. The pacing / sense electrode pair selection and control circuit 53 selects the lead conductors and associated pairs of pacing electrodes to couple to the atrial and ventricular output amplifiers within the output amplifier circuit 51 for implementing RA, LA, RV, and LV pacing.

[0150] The sense amplifier circuit 55 contains sense amplifiers for atrial and ventricular pacing and sensing. High impedance P-wave and R-wave sense amplifiers can be used to amplify the voltage difference signal generated across a sense electrode pair due to the passage of a cardiac depolarization wavefront. High impedance sense amplifiers use high gain to amplify low amplitude signals and rely on passband filtering, time domain filtering, and amplitude threshold comparisons to distinguish P-waves or R-waves from background electrical noise. The digital controller / timer circuit 43 controls the sensitivity settings of the atrial and ventricular sense amplifiers 55.

[0151] The sense amplifiers can be decoupled from the sensing electrodes during a blanking period before, during, and after the delivery of a pacing pulse into any of the pacing electrodes of the pacing system to avoid saturation of the sense amplifiers. The sense amplifier circuit 55 includes blanking circuitry for decoupling selected pairs of lead conductors and the IND-CAN electrode 20 from the inputs of the RA sense amplifier (and LA sense amplifier, if provided), the RV sense amplifier, and the LV sense amplifier during ABP, PVABP, and VBP. The sense amplifier circuit 55 also includes switching circuitry for coupling selected sensing electrode lead conductors and the IND-CAN electrode 20 to the RA sense amplifier (and LA sense amplifier, if provided), the RV sense amplifier, and the LV sense amplifier. Again, the sense electrode selection and control circuit 53 selects the conductors and associated pairs of sensing electrodes to be coupled to the output amplifier circuit 51 and the atrial and ventricular sense amplifiers within the sense amplifier circuit 55 for RA, LA, RV, and LV sensing along the desired unipolar and bipolar sensing vectors.

[0152] A right atrial depolarization or P-wave in the RA-SENSE signal sensed by the RA sense amplifier results in a RA-EVENT signal that is communicated to the digital controller / timer circuit 43. Similarly, a left atrial depolarization or P-wave in the LA-SENSE signal sensed by the LA sense amplifier (if provided) results in a LA-EVENT signal that is communicated to the digital controller / timer circuit 43. A ventricular depolarization or R-wave in the RV-SENSE signal sensed by the ventricular sense amplifier results in an RV-EVENT signal that is communicated to the digital controller / timer circuit 43. Similarly, a ventricular depolarization or R-wave in the LV-SENSE signal sensed by the ventricular sense amplifier results in an LV-EVENT signal that is communicated to the digital controller / timer circuit 43. The RV-EVENT, LV-EVENT, and RA-EVENT, LA-SENSE signals can be either in a refractory or a sensing portion, and can be inadvertently triggered by electrical noise signals or aberrantly conducted depolarization waves rather than by true R-waves or P-waves.

[0153] The techniques described in this disclosure, including those attributed to IMD 16, computing device 140, and / or various constituent components, can be implemented, at least in part, in hardware, software, firmware or any combination thereof. For example, various aspects of the techniques can be implemented within one or more processors, including one or more microprocessors, DSPs, ASICs, FPGAs, or any other equivalent integrated or discrete logic circuitry, as well as any combinations of such components, embodied in programmers, such as physician or patient programmers, stimulators, image processing apparatuses, or other devices. The terms "module," "processor," or "processing circuitry" can generally refer to any of the

[0154] Such hardware, software, and / or firmware can be implemented within the same device or within separate devices to support the various operations and functions described in this disclosure. In addition, any of the described units, modules or components can be implemented together or separately as discrete but interoperable logic devices. Depiction of different features as modules or units is intended to highlight different functional aspects and does not necessarily imply that such modules or units must be realized by separate hardware or software components. Rather, functionality associated with one or more modules or units can be performed by separate hardware or software components, or integrated within common or separate hardware or software components.

[0155] When implemented in software, the functionality ascribed to the systems, devices and techniques described in this disclosure can be embodied as instructions on a computer-readable medium such as RAM, ROM, NVRAM, EEPROM, FLASH memory, magnetic data storage media, optical data storage media, and the like. The instructions can be executed by processing circuitry and / or one or more processors to support one or more aspects of the functionality described in this disclosure.

[0156] Exemplary Embodiments

[0157] Embodiment 1. A system for cardiac assessment, the system comprising:

[0158] an electrode device comprising a plurality of external electrodes to be disposed proximate to a patient's skin; and

[0159] a computing device comprising processing circuitry, the computing device operably coupled to the electrode device and configured to:

[0160] monitor electrical activity from tissue of the patient using the plurality of external electrodes to generate a plurality of electrical signals over time;

[0161] filtering the plurality of electrical signals using a first filter having a first frequency range to generate a plurality of first filtered signals;

[0162] filtering the plurality of electrical signals using a second filter having a second frequency range different from the first frequency range to generate a plurality of second filtered signals;

[0163] detecting at least one QRS complex based on the plurality of first filtered signals; and

[0164] detecting a QRS peak of the at least one QRS complex based on the plurality of second filtered signals and the detected at least one QRS complex.

[0165] Embodiment 2. The system of embodiment 1, wherein the first filter is a bandpass filter configured to filter out frequencies outside a range of about 10 Hz to about 32 Hz.

[0166] Embodiment 3. The system of any one of embodiments 1-2, wherein the second filter is a bandpass filter configured to filter out frequencies outside a range of about 0.5 Hz to about 20 Hz.

[0167] Embodiment 4. The system of any one of embodiments 1-3, wherein detecting the at least one QRS complex comprises:

[0168] generating a dispersion signal based on the plurality of first filtered signals, wherein the dispersion signal represents a dispersion of the plurality of second filtered signals over time; and

[0169] detecting the at least one QRS complex based on the dispersion signal.

[0170] Embodiment 5. The system of any one of embodiments 1-4, wherein detecting the QRS peak comprises:

[0171] determining a standard deviation of the plurality of second filtered signals;

[0172] initializing a blanking window of a predetermined length based on the standard deviation; and

[0173] detecting a peak amplitude of the plurality of second filtered signals within the blanking window.

[0174] Embodiment 6. The system of any one of embodiments 1-5, wherein the computing device is further configured to:

[0175] determine a threshold function based on the QRS peak, the threshold function configured to provide a sensitivity for detecting at least one subsequent QRS complex; and

[0176] detecting the at least one subsequent QRS complex based on the threshold function.

[0177] Embodiment 7. The system of any one of embodiments 1-6, wherein the computing device is further configured to determine a QRS onset time value and a QRS offset time value corresponding to the at least one QRS complex.

[0178] Embodiment 8. The system of embodiment 7, wherein determining the QRS onset time value and the QRS offset time value comprises:

[0179] generating a dispersion signal from the plurality of second filtered signals, wherein the dispersion signal represents a dispersion of the plurality of second filtered signals over time,

[0180] determining a first derivative signal based on the dispersion signal;

[0181] determining a first window of the first derivative signal within a first time period preceding a positive peak of the first derivative signal;

[0182] determining a second window of the first derivative signal within a second time period following a negative peak of the first derivative signal;

[0183] determining the onset time value by determining a last point within the first window that is less than a first threshold value; and

[0184] determining the offset time value by determining a first point within the second window that is greater than a second threshold value.

[0185] Embodiment 9. The system of embodiment 7, wherein the computing device is further configured to determine a plurality of activation times of the at least one QRS complex based on a plurality of cardiac signals within a QRS duration between the QRS onset time value and the QRS offset time value.

[0186] Embodiment 10. The system of embodiment 9, wherein the computing device is further configured to determine at least one measure of electrical heterogeneity based on the plurality of activation times.

[0187] Embodiment 11. The system of any one of embodiments 1-10, wherein the electrical activity represents depolarization of cardiac tissue propagating through a torso of the patient.

[0188] Embodiment 12. The system of any one of embodiments 1-11, wherein the plurality of external electrodes comprises a plurality of surface electrodes positioned proximate to a skin of the torso of the patient.

[0189] Embodiment 13. A method for cardiac assessment, the method comprising:

[0190] monitoring electrical activity from tissue of a patient using a plurality of external electrodes to generate a plurality of electrical signals over time;

[0191] filtering the plurality of electrical signals using a first filter having a first frequency range to generate a plurality of first filtered signals;

[0192] filtering the plurality of electrical signals using a second filter having a second frequency range different from the first frequency range to generate a plurality of second filtered signals;

[0193] detecting at least one QRS complex based on the plurality of first filtered signals; and

[0194] detecting a QRS peak based on the plurality of second filtered signals and the detected at least one QRS complex.

[0195] Embodiment 14. The method of Embodiment 13, further comprising:

[0196] determining a threshold function based on the QRS peak; and

[0197] detecting at least one subsequent QRS complex based on the threshold function.

[0198] Embodiment 15. The method of any one of Embodiments 13-14, further comprising determining a QRS onset time value and a QRS offset time value corresponding to the at least one QRS complex.

[0199] Embodiment 16. The method of any one of Embodiments 13-15, wherein determining a QRS onset time value and a QRS offset time value comprises:

[0200] generating a dispersion signal from the plurality of second filtered signals, wherein the dispersion signal represents a dispersion of the plurality of second filtered signals over time,

[0201] determining a first derivative signal based on the dispersion signal;

[0202] determining a first window of the first derivative signal within a first time period preceding a positive peak value of the first derivative signal;

[0203] determining a second window of the first derivative signal within a second time period following a negative peak value of the first derivative signal;

[0204] determining the onset time value by determining a last point within the first window that is less than a first threshold value; and

[0205] determining the offset time value by determining a first point within the second window that is greater than a second threshold value.

[0206] Embodiment 17. A system for cardiac assessment, the system comprising:

[0207] an electrode device comprising a plurality of external electrodes to be disposed proximate to a patient’s skin; and

[0208] a computing device comprising processing circuitry, the computing device operably coupled to the electrode device and configured to:

[0209] monitor electrical activity from tissue of the patient using the plurality of external electrodes to generate a plurality of electrical signals over time;

[0210] filter the plurality of electrical signals using at least one filter to generate a plurality of filtered signals;

[0211] detect a QRS peak based on the plurality of filtered signals;

[0212] determine a threshold function based on the QRS peak, the threshold function configured to provide a sensitivity for detecting at least one subsequent QRS complex; and

[0213] detect the at least one subsequent QRS complex based on the threshold function.

[0214] Embodiment 18. The method of embodiment 17, wherein the threshold function is configured to decrease from the at least one QRS complex until the at least one subsequent QRS complex is detected or a base threshold is reached.

[0215] Embodiment 19. The system of embodiment 18, wherein the base threshold is a base percentage of the QRS peak.

[0216] Embodiment 20. The system of any one of embodiments 17-19, wherein at least a portion of the threshold function has a linear decrease.

[0217] Embodiment 21. The system of any one of embodiments 17-20, wherein the threshold function is configured to linearly decrease from a first threshold to a second threshold, wherein the first threshold is a first percentage of the QRS peak and the second threshold is a second percentage of the QRS peak.

[0218] Embodiment 22. The system of embodiment 21, wherein the first percentage is about 60% and the second percentage is about 30%.

[0219] Embodiment 23. The system of embodiment 22, wherein the threshold function is configured to remain constant between a time at which the second threshold is reached and a time until a predetermined amount of time after the detected QRS complex.

[0220] Embodiment 24. The system of embodiment 23, wherein the threshold function is configured to decrease to a third threshold that is a third percentage of the QRS peak at the predetermined amount of time.

[0221] Embodiment 25. The system of embodiment 24, wherein the third percentage is about 15%.

[0222] Embodiment 26. The system of embodiment 24, wherein the threshold function is configured to decrease linearly from the third threshold to a base threshold.

[0223] Embodiment 27. The system of embodiment 26, wherein the base percentage is about 3%.

[0224] Embodiment 28. A method for cardiac assessment, the method comprising:

[0225] monitoring electrical activity from tissue of a patient using a plurality of external electrodes to generate a plurality of electrical signals over time;

[0226] filtering the plurality of electrical signals using at least one filter to generate a plurality of filtered signals;

[0227] detecting a QRS peak based on the plurality of filtered signals.

[0228] determining a threshold function based on the QRS peak, the threshold function configured to provide a sensitivity for detecting at least one subsequent QRS complex; and

[0229] detecting the at least one subsequent QRS complex based on the threshold function.

[0230] Embodiment 29. The method of embodiment 28, wherein the threshold function is configured to decrease from the at least one QRS complex until the at least one subsequent QRS complex is detected or a base threshold is reached.

[0231] Embodiment 30. The system of embodiment 29, wherein the base threshold is a base percentage of the QRS peak.

[0232] Embodiment 31. A system for cardiac assessment, the system comprising:

[0233] an electrode device comprising a plurality of external electrodes to be disposed proximate to a skin of a patient; and

[0234] a computing device comprising processing circuitry, the computing device operably coupled to the electrode device and configured to:

[0235] monitor electrical activity from tissue of a patient using a plurality of external electrodes to generate a plurality of electrical signals over time;

[0236] filter the plurality of electrical signals using a first filter and a second filter to generate a plurality of first filtered signals and a plurality of second filtered signals, the first filter and the second filter having different frequency ranges;

[0237] detect a QRS peak based on the plurality of first and second filtered signals.

[0238] generate a dispersion signal from the plurality of second filtered signals, wherein the dispersion signal represents a dispersion of the plurality of second filtered signals over time,

[0239] determine a first derivative signal based on the dispersion signal;

[0240] determine a QRS onset time value and a QRS offset time value corresponding to the at least one QRS complex based on the first derivative signal.

[0241] Implementation 32. The system of implementation 31, wherein determining the QRS onset time value and the QRS offset time value comprises:

[0242] determining a first window of the first derivative signal within a first time period preceding a positive peak of the first derivative signal;

[0243] determining a second window of the first derivative signal within a second time period following a negative peak of the first derivative signal;

[0244] determining the onset time value by determining a last point within the first window that is less than a first threshold value; and

[0245] determining the offset time value by determining a first point within the second window that is greater than a second threshold value.

[0246] Implementation 33. The system of any of implementations 31-32, wherein the computing device is further configured to determine an activation time of the at least one QRS complex within each of the plurality of cardiac signals within a QRS duration between the QRS onset time value and the QRS offset time value.

[0247] Implementation 34. The system of implementation 33, wherein the computing device is further configured to determine at least one measure of electrical heterogeneity based on the activation times of each of the at least one QRS complex within each of the plurality of cardiac signals.

[0248] The present disclosure is provided with reference to illustrative embodiments and is not meant to be interpreted as limiting. As previously described, those skilled in the art will recognize that other various illustrative applications can utilize the advantageous properties of the devices and methods described herein using the techniques as described herein. Various modifications to the illustrative embodiments and additional embodiments of the present disclosure will be apparent to those skilled in the art.

Claims

1. A system for cardiac assessment, the system comprising: an electrode apparatus comprising a plurality of external electrodes to be disposed proximate to a patient's skin; and a computing apparatus comprising processing circuitry, the computing apparatus operably coupled to the electrode apparatus and configured to: monitor electrical activity from tissue of a patient using the plurality of external electrodes to generate a plurality of electrical signals over time; filter the plurality of electrical signals using a first filter having a first frequency range to generate a plurality of first filtered signals; filter the plurality of electrical signals using a second filter having a second frequency range different from the first frequency range to generate a plurality of second filtered signals; detect at least one QRS complex based on the plurality of first filtered signals; detect a QRS peak of the at least one QRS complex based on the plurality of second filtered signals and the detected at least one QRS complex; generate a dispersion signal from the plurality of second filtered signals, wherein the dispersion signal represents a dispersion of the plurality of second filtered signals over time; determine a first derivative signal based on the dispersion signal; and determine a QRS onset time value and a QRS offset time value corresponding to the at least one QRS complex based on the first derivative signal.

2. The system of claim 1, wherein the first filter is a bandpass filter configured to filter out frequencies outside a range of 10 Hz to 32 Hz.

3. The system of any one of claims 1-2, wherein the second filter is a bandpass filter configured to filter out frequencies outside a range of 0.5 Hz to 20 Hz.

4. The system of any one of claims 1-2, wherein detecting the at least one QRS complex comprises: generating a first dispersion signal based on the plurality of first filtered signals, wherein the first dispersion signal represents a dispersion of the plurality of first filtered signals over time; and detecting the at least one QRS complex based on the first dispersion signal.

5. The system of any one of claims 1-2, wherein detecting the QRS peak comprises: determining a standard deviation of the plurality of second filtered signals; initializing a blanking window of a predetermined length based on the standard deviation; and detecting a peak amplitude of the plurality of second filtered signals within the blanking window.

6. The system of any one of claims 1-2, wherein the computing apparatus is further configured to: determine a threshold function based on the QRS peak, the threshold function configured to provide a sensitivity for detecting at least one subsequent QRS complex; and detect the at least one subsequent QRS complex based on the threshold function.

7. The system of claim 1, wherein determining the QRS onset time value and the QRS offset time value comprises: determining a first window of the first derivative signal within a first time period preceding a positive peak of the first derivative signal; ​ ​ ​ determining a second window of the first derivative signal within a second time period following a negative peak of the first derivative signal; determining the onset time value by determining a last point within the first window that is less than a first threshold value; and determining the offset time value by determining a first point within the second window that is greater than a second threshold value.

8. The system of claim 1, wherein the computing device is further configured to determine a plurality of activation times of the at least one QRS complex based on a plurality of cardiac signals within a QRS duration between the QRS onset time value and the QRS offset time value.

9. The system of claim 8, wherein the computing device is further configured to determine at least one measure of electrical heterogeneity based on the plurality of activation times.

10. The system of claim 1, wherein the electrical activity represents depolarization of cardiac tissue propagating through a torso of the patient.

11. The system of claim 1, wherein the plurality of external electrodes comprises a plurality of surface electrodes positioned proximate to the skin of the torso of the patient.

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