Patent Publication Number: US-11642533-B2

Title: Systems and methods for evaluating cardiac therapy

Description:
The present application claims the benefit of U.S. Provisional Application No. 62/930,393, filed Nov. 4, 2019, which is incorporated herein by reference in its entirety. 
    
    
     The disclosure herein relates to systems and methods for use in evaluating cardiac therapy using external electrode apparatus and configuring such cardiac therapy. 
     Implantable medical devices (IMDs), such as implantable pacemakers, cardioverters, defibrillators, or pacemaker-cardioverter-defibrillators, provide therapeutic electrical stimulation to the heart. IMDs may provide pacing to address bradycardia, or pacing or shocks in order to terminate tachyarrhythmia, such as tachycardia or fibrillation. In some cases, the medical device may sense intrinsic depolarizations of the heart, detect arrhythmia based on the intrinsic depolarizations (or absence thereof), and control delivery of electrical stimulation to the heart based on the intrinsic depolarizations. 
     IMDs may also provide cardiac resynchronization therapy (CRT), which is a form of pacing. CRT involves the delivery of pacing to the left ventricle, or both the left and right ventricles, as well as the atria. The timing and location of the delivery of pacing pulses to the ventricle(s) may be selected to improve the coordination and efficiency of ventricular contraction. 
     Systems for implanting medical devices may include workstations or other equipment in addition to the implantable medical device itself. In some cases, these other pieces of equipment assist the physician or other technician with placing the intracardiac leads at particular locations on or in the heart. In some cases, the equipment provides information to the physician about the electrical activity of the heart and the location of the intracardiac lead. 
     Systems and devices, e.g., that perform CRT, may offer a lot of different pacing parameters or programming options, which include different pacing electrodes and vectors (e.g., quadripolar leads), different pacing configurations (e.g., biventricular, left ventricle only), different pacing timings (e.g., AV timing, VV timing for biventricular pacing), etc. External electrode apparatus can measure the efficacy of resynchronization for a given parameter set and may help tailor cardiac therapy device programming to maximize the degree of resynchronization. However, there are likely hundreds of permutations of pacing parameters, and hence, an efficient way to arrive at the optimal pacing parameter set in a given patient may be important for increasing the clinical efficiency. 
     SUMMARY 
     The illustrative systems and methods described herein may be configured to assist a user (e.g., a physician) in evaluating and configuring cardiac therapy (e.g., cardiac therapy being performed on a patient during and/or after implantation of cardiac therapy apparatus). In one or more embodiments, the systems and methods may be described as being noninvasive. For example, in some embodiments, the systems and methods may not need, or include, implantable devices such as leads, probes, sensors, catheters, implantable electrodes, etc. to monitor, or acquire, a plurality of cardiac signals from tissue of the patient for use in evaluating and configuring the cardiac therapy being delivered to the patient. Instead, the systems and methods may use electrical measurements taken noninvasively using, e.g., a plurality of external electrodes attached to the skin of a patient about the patient&#39;s torso. 
     The illustrative systems and methods may include the use of an external electrode apparatus, or ECG belt, that is applied to the torso of a patient to determine optimal synchrony during biventricular and left ventricular pacing. The illustrative systems and methods may be described as providing an efficient search for optimal parameters for electrocardiogram (ECG) belt guided programming of pacing therapy. Efficient parameter search for cardiac resynchronization therapy (CRT) optimization based on ECG belt may be important for clinical efficiency and adoption. 
     In one or more embodiments, the efficient search for optimal parameters may start with limiting the set of parameters based on patient&#39;s intrinsic physiology and other device measurements related to pace capture thresholds or phrenic nerve stimulation (PNS) thresholds for pacing options/electrodes available. For example, the paced AV timing (e.g., the time period between intrinsic or paced atrial depolarization or contraction and a ventricular pace) may be tested between 40% and 80% of patient&#39;s intrinsic AV timing (e.g., the time period between intrinsic or paced atrial depolarization or contraction and an intrinsic ventricular depolarization or contraction). If the patient has an AV block, the AV timing may be set to a nominal value (e.g., the AV timing may not be based on the patient&#39;s intrinsic AV timing). Similarly, pacing electrodes, or specifically pacing electrodes being used as cathodes, may be excluded based on consideration of capture thresholds and phrenic nerve stimulation (PNS) thresholds. Additionally, pacing electrodes, or specifically pacing electrodes being used as cathodes, may be excluded manually by a user (e.g., a physician) or may be excluded based on population studies of similar patients. 
     In one or more embodiments, the testing may proceed in a stage-wise fashion with biventricular pacing and left ventricular-only pacing being evaluated across the available pacing electrodes at an AV timing that is either set to a nominal value or set to a percentile of the patient&#39;s intrinsic AV timing (e.g., 70% of an intrinsic AV timing previously measured) that is optimal for most patients based on population studies. The electrode or pacing vector with the best resynchronization may be included for further testing for finding optimal AV timing and VV timing (e.g., the period of time between an intrinsic or paced left ventricular depolarization and a right ventricular pace). For example, initially, a limited set of AV delays may be tested at, e.g., 70%, 50%, and 80% of the patient&#39;s intrinsic AV timing. If one of the AV timings provides more efficient resynchronization than others (e.g., exceeded by a certain threshold), then more AV timings may be tested around the one AV timing to arrive at an optimal AV timing. If all three AV timings of the limited set show similar degrees of resynchronization, then the 70% AV timing may be selected (e.g., picked as optimal). 
     In another embodiment, the evaluation or testing of AV timing for cardiac pacing therapy may start with an AV timing of 40% of the patient&#39;s intrinsic AV timing and the paced AV timing may be changed in steps, which can be adapted based on the changes in degree of resynchronization achieved between successive paced AV timings (e.g., bigger steps if changes in degrees of resynchronization are not greater than a pre-specified threshold). In one or more embodiments, a similar strategy can be adapted for VV timing as well as various other pacing settings. In another embodiment, if the current pacing parameter set yields a degree of resynchronization that exceeds a threshold derived from previous population studies indicating more likelihood of better outcomes, no further testing may be performed, and the current pacing parameter set may be selected. 
     One illustrative system for use in cardiac therapy evaluation may include electrode apparatus comprising a plurality of external electrodes to monitor electrical activity from tissue of a patient and a computing apparatus comprising processing circuitry and operably coupled to the electrode apparatus. The computing apparatus may be configured to monitor electrical activity using the plurality of external electrodes, generate electrical heterogeneity information (EHI) based on the monitored electrical activity, and initiate delivery of pacing therapy using a plurality of different pacing vectors. Each different pacing vector may use a combination of pacing electrodes different from the remaining different pacing vectors. The computing apparatus may be further configured to select one or more of the plurality of different pacing vectors based on the generated EHI from the electrical activity monitored during the delivery of pacing therapy using a plurality of different pacing vectors, initiate delivery of pacing therapy using the one or more selected different pacing vectors and a plurality of different settings of a pacing parameter, and identify one or more of the plurality of different settings of the pacing parameter based on the generated EHI from the electrical activity monitored during delivery of pacing therapy using the one or more selected different pacing vectors and the plurality of different settings of the pacing parameters. 
     One illustrative method for use in cardiac therapy evaluation may include monitoring electrical activity using a plurality of external electrodes from tissue of a patient, generating electrical heterogeneity information (EHI) based on the monitored electrical activity, and initiating delivery of pacing therapy using a plurality of different pacing vectors. Each different pacing vector may use a combination of pacing electrodes different from the remaining different pacing vectors. The illustrative method may further include selecting one or more of the plurality of different pacing vectors based on the generated EHI from the electrical activity monitored during the delivery of pacing therapy using a plurality of different pacing vectors, initiating delivery of pacing therapy using the one or more selected different pacing vectors and a plurality of different settings of a pacing parameter, and identifying one or more of the plurality of different settings of the pacing parameter based on the generated EHI from the electrical activity monitored during delivery of pacing therapy using the one or more selected different pacing vectors and the plurality of different settings of the pacing parameters. 
     One illustrative system for use in cardiac therapy evaluation may include electrode apparatus comprising a plurality of external electrodes to monitor electrical activity from tissue of a patient and a computing apparatus comprising processing circuitry and operably coupled to the electrode apparatus. The computing apparatus may be configured to monitor electrical activity using the plurality of external electrodes, generate electrical heterogeneity information (EHI) based on the monitored electrical activity, and initiate delivery of pacing therapy using a first parameter at a plurality of different first settings. The computing apparatus may be further configured to select one or more of the plurality of different first settings for the first parameter based on the generated EHI from the electrical activity monitored during the delivery of pacing therapy using the plurality of different first settings, initiate delivery of pacing therapy using the one or more selected different first settings and a second parameter at a plurality of different second settings, and identify one or more of the plurality of different second setting values based on the generated EHI from the electrical activity monitored during delivery of pacing therapy using the one or more selected different first settings and the plurality of different second settings. 
     The above summary is not intended to describe each embodiment or every implementation of the present disclosure. A more complete understanding will become apparent and appreciated by referring to the following detailed description and claims taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a diagram of an illustrative system including electrode apparatus, display apparatus, and computing apparatus. 
         FIGS.  2 - 3    are diagrams of illustrative external electrode apparatus for measuring torso-surface potentials. 
         FIG.  4    is a block diagram of an illustrative method of evaluation and configuration of cardiac therapy. 
         FIG.  5 A  is a block diagram of an illustrative method of efficient evaluation of a cardiac therapy parameter. 
         FIG.  5 B  depicts an example of a range of AV timings being efficiently evaluated according to the method of  FIG.  5 A . 
         FIG.  6 A  is a block diagram of another illustrative method of efficient evaluation of a cardiac therapy parameter. 
         FIG.  6 B  depicts an example of a range of AV timings being efficiently evaluating according to the method of  FIG.  6 A . 
         FIG.  7    is a diagram of an illustrative system including an illustrative implantable medical device (IMD). 
         FIG.  8 A  is a diagram of the illustrative IMD of  FIG.  7   . 
         FIG.  8 B  is a diagram of an enlarged view of a distal end of the electrical lead disposed in the left ventricle of  FIG.  8 A . 
         FIG.  9 A  is a block diagram of an illustrative IMD, e.g., of the systems of  FIGS.  7 - 8   . 
         FIG.  9 B  is another block diagram of an illustrative IMD (e.g., an implantable pulse generator) circuitry and associated leads employed in the systems of  FIGS.  7 - 8   ). 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     In the following detailed description of illustrative embodiments, reference is made to the accompanying figures of the drawing which form a part hereof, and in which are shown, by way of illustration, specific embodiments which may be practiced. It is to be understood that other embodiments may be utilized and structural changes may be made without departing from (e.g., still falling within) the scope of the disclosure presented hereby. 
     Illustrative systems and methods shall be described with reference to  FIGS.  1 - 9   . 
     It will be apparent to one skilled in the art that elements or processes from one embodiment may be used in combination with elements or processes of the other embodiments, and that the possible embodiments of such systems, methods, and devices using combinations of features set forth herein is not limited to the specific embodiments shown in the Figures and/or described herein. Further, it will be recognized that the embodiments described herein may include many elements that are not necessarily shown to scale. Still further, it will be recognized that timing of the processes and the size and shape of various elements herein may be modified but still fall within the scope of the present disclosure, although certain timings, one or more shapes and/or sizes, or types of elements, may be advantageous over others. 
     A plurality of electrocardiogram (ECG) signals (e.g., torso-surface potentials) may be measured, or monitored, using a plurality of external electrodes positioned about the surface, or skin, of a patient. The ECG signals may be used to evaluate and configure cardiac therapy such as, e.g., cardiac therapy provide by an implantable medical device performing cardiac resynchronization therapy (CRT). As described herein, the ECG signals may be gathered or obtained noninvasively since, e.g., implantable electrodes may not be used to measure the ECG signals. Further, the ECG signals may be used to determine cardiac electrical activation times, which may be used to generate various metrics (e.g., electrical heterogeneity information) that may be used by a user (e.g., physician) to optimize one or more settings, or parameters, of cardiac therapy (e.g., pacing therapy) such as CRT. 
     Various illustrative systems, methods, and graphical user interfaces may be configured to use electrode apparatus including external electrodes, display apparatus, and computing apparatus to noninvasively assist a user (e.g., a physician) in the evaluation of cardiac health and/or the configuration (e.g., optimization) of cardiac therapy. An illustrative system  100  including electrode apparatus  110 , computing apparatus  140 , and a remote computing device  160  is depicted in  FIG.  1   . 
     The electrode apparatus  110  as shown includes a plurality of electrodes incorporated, or included, within a band wrapped around the chest, or torso, of a patient  14 . The electrode apparatus  110  is operatively coupled to the computing apparatus  140  (e.g., through one or wired electrical connections, wirelessly, etc.) to provide electrical signals from each of the electrodes to the computing apparatus  140  for analysis, evaluation, etc. Illustrative electrode apparatus may be described in U.S. Pat. No. 9,320,446 entitled “Bioelectric Sensor Device and Methods” filed Mar. 27, 2014 and issued on Mar. 26, 2016, which is incorporated herein by reference in its entirety. Further, illustrative electrode apparatus  110  will be described in more detail in reference to  FIGS.  2 - 3   . 
     Although not described herein, the illustrative system  100  may further include imaging apparatus. The imaging apparatus may be any type of imaging apparatus configured to image, or provide images of, at least a portion of the patient in a noninvasive manner. For example, the imaging apparatus may not use any components or parts that may be located within the patient to provide images of the patient except noninvasive tools such as contrast solution. It is to be understood that the illustrative systems, methods, and interfaces described herein may further use imaging apparatus to provide noninvasive assistance to a user (e.g., a physician) to locate, or place, one or more pacing electrodes proximate the patient&#39;s heart in conjunction with the configuration of cardiac therapy. 
     For example, the illustrative systems and methods may provide image guided navigation that may be used to navigate leads including electrodes, leadless electrodes, wireless electrodes, catheters, etc., within the patient&#39;s body while also providing noninvasive cardiac therapy configuration including determining an effective, or optimal, pre-excitation intervals such as A-V and V-V intervals, etc. Illustrative systems and methods that use imaging apparatus and/or electrode apparatus may be described in U.S. Pat. App. Pub. No. 2014/0371832 to Ghosh published on Dec. 18, 2014, U.S. Pat. App. Pub. No. 2014/0371833 to Ghosh et al. published on Dec. 18, 2014, U.S. Pat. App. Pub. No. 2014/0323892 to Ghosh et al. published on Oct. 30, 2014, U.S. Pat. App. Pub. No. 2014/0323882 to Ghosh et al. published on Oct. 20, 2014, each of which is incorporated herein by reference in its entirety. 
     Illustrative imaging apparatus may be configured to capture x-ray images and/or any other alternative imaging modality. For example, the imaging apparatus may 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 (MM), high frequency ultrasound (HIFU), optical coherence tomography (OCT), intra-vascular ultrasound (IVUS), two dimensional (2D) ultrasound, three dimensional (3D) ultrasound, four dimensional (4D) ultrasound, intraoperative CT, intraoperative MRI, etc. Further, it is to be understood that the imaging apparatus may be configured to capture a plurality of consecutive images (e.g., continuously) to provide video frame data. In other words, a plurality of images taken over time using the imaging apparatus may provide video frame, or motion picture, data. An exemplary system that employs ultrasound can be found in U.S. patent application Ser. No. 15/643,172 entitled NONINVASIVE ASSESSMENT OF CARDIAC RESYNCHRONIZATION THERAPY to Stadler et al., incorporated by reference in its entirety. Additionally, the images may also be obtained 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 may also be achieved by incorporating heart data or other soft tissue data from a map or from pre-operative image data captured by MRI, CT, or echocardiography modalities. Image datasets from hybrid modalities, such as positron emission tomography (PET) combined with CT, or single photon emission computer tomography (SPECT) combined with CT, could also provide functional image data superimposed onto anatomical data, e.g., to be used to navigate implantable apparatus to target locations within the heart or other areas of interest. 
     Systems and/or imaging apparatus that may be used in conjunction with the illustrative systems and method described herein are described in U.S. Pat. App. Pub. No. 2005/0008210 to Evron et al. published on Jan. 13, 2005, U.S. Pat. App. Pub. No. 2006/0074285 to Zarkh et al. published on Apr. 6, 2006, U.S. Pat. No. 8,731,642 to Zarkh et al. issued on May 20, 2014, U.S. Pat. No. 8,861,830 to Brada et al. issued on Oct. 14, 2014, U.S. Pat. No. 6,980,675 to Evron et al. issued on Dec. 27, 2005, U.S. Pat. No. 7,286,866 to Okerlund et al. issued on Oct. 23, 2007, U.S. Pat. No. 7,308,297 to Reddy et al. issued on Dec. 11, 2011, U.S. Pat. No. 7,308,299 to Burrell et al. issued on Dec. 11, 2011, U.S. Pat. No. 7,321,677 to Evron et al. issued on Jan. 22, 2008, U.S. Pat. No. 7,346,381 to Okerlund et al. issued on Mar. 18, 2008, U.S. Pat. No. 7,454,248 to Burrell et al. issued on Nov. 18, 2008, U.S. Pat. No. 7,499,743 to Vass et al. issued on Mar. 3, 2009, U.S. Pat. No. 7,565,190 to Okerlund et al. issued on Jul. 21, 2009, U.S. Pat. No. 7,587,074 to Zarkh et al. issued on Sep. 8, 2009, U.S. Pat. No. 7,599,730 to Hunter et al. issued on Oct. 6, 2009, U.S. Pat. No. 7,613,500 to Vass et al. issued on Nov. 3, 2009, U.S. Pat. No. 7,742,629 to Zarkh et al. issued on Jun. 22, 2010, U.S. Pat. No. 7,747,047 to Okerlund et al. issued on Jun. 29, 2010, U.S. Pat. No. 7,778,685 to Evron et al. issued on Aug. 17, 2010, U.S. Pat. No. 7,778,686 to Vass et al. issued on Aug. 17, 2010, U.S. Pat. No. 7,813,785 to Okerlund et al. issued on Oct. 12, 2010, U.S. Pat. No. 7,996,063 to Vass et al. issued on Aug. 9, 2011, U.S. Pat. No. 8,060,185 to Hunter et al. issued on Nov. 15, 2011, and U.S. Pat. No. 8,401,616 to Verard et al. issued on Mar. 19, 2013, each of which is incorporated herein by reference in its entirety. 
     The computing apparatus  140  and the remote computing device  160  may each include display apparatus  130 ,  170 , respectively, that may be configured to display and analyze data such as, e.g., electrical signals (e.g., electrocardiogram data), electrical activation times, electrical heterogeneity information, etc. For example, one cardiac cycle, or one heartbeat, of a plurality of cardiac cycles, or heartbeats, represented by the electrical signals collected or monitored by the electrode apparatus  110  may be analyzed and evaluated for one or more metrics including activation times and electrical heterogeneity information that may be pertinent to the therapeutic nature of one or more parameters related to cardiac therapy such as, e.g., pacing parameters, lead location, etc. More specifically, for example, the QRS complex of a single cardiac cycle may be evaluated for one or more metrics such as, e.g., 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), average left ventricular or thoracic surrogate electrical activation times (LVAT), QRS duration (e.g., interval between QRS onset to QRS offset), difference between average left surrogate and average right surrogate activation times, relative or absolute QRS morphology, difference between a higher percentile and a lower percentile of activation times (higher percentile may be 90%, 80%, 75%, 70%, etc. and lower percentile may be 10%, 15%, 20%, 25% and 30%, etc.), other statistical measures of central tendency (e.g., median or mode), dispersion (e.g., mean deviation, standard deviation, variance, interquartile deviations, range), etc. Further, each of the one or more metrics may be location specific. For example, some metrics may be computed from signals recorded, or monitored, from electrodes positioned about a selected area of the patient such as, e.g., the left side of the patient, the right side of the patient, etc. 
     In at least one embodiment, one or both of the computing apparatus  140  and the remote computing device  160  may be a server, a personal computer, a tablet computer, a mobile device, and a cellular telephone. The computing apparatus  140  may be configured to receive input from input apparatus  142  (e.g., a keyboard) and transmit output to the display apparatus  130 , and the remote computing device  160  may be configured to receive input from input apparatus  162  (e.g., a touchscreen) and transmit output to the display apparatus  170 . One or both of the computing apparatus  140  and the remote computing device  160  may include data storage that may allow for access to processing programs or routines and/or one or more other types of data, e.g., for analyzing a plurality of electrical signals captured by the electrode apparatus  110 , for determining QRS onsets, QRS offsets, medians, modes, averages, peaks or maximum values, valleys or minimum values, for determining electrical activation times, for driving a graphical user interface configured to noninvasively assist a user in configuring one or more pacing parameters, or settings, such as, e.g., 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 ventricle only pacing, left ventricle only pacing, etc.), and arrhythmia detection and treatment, rate adaptive settings and performance, etc. 
     The computing apparatus  140  may be operatively coupled to the input apparatus  142  and the display apparatus  130  to, e.g., transmit data to and from each of the input apparatus  142  and the display apparatus  130 , and the remote computing device  160  may be operatively coupled to the input apparatus  162  and the display apparatus  170  to, e.g., transmit data to and from each of the input apparatus  162  and the display apparatus  170 . For example, the computing apparatus  140  and the remote computing device  160  may be electrically coupled to the input apparatus  142 ,  162  and the display apparatus  130 ,  170  using, e.g., analog electrical connections, digital electrical connections, wireless connections, bus-based connections, network-based connections, internet-based connections, etc. As described further herein, a user may provide input to the input apparatus  142 ,  162  to view and/or select one or more pieces of configuration information related to the cardiac therapy delivered by cardiac therapy apparatus such as, e.g., an implantable medical device. 
     Although as depicted the input apparatus  142  is a keyboard and the input apparatus  162  is a touchscreen, it is to be understood that the input apparatus  142 ,  162  may include any apparatus capable of providing input to the computing apparatus  140  and the computing device  160  to perform the functionality, methods, and/or logic described herein. For example, the input apparatus  142 ,  162  may include a keyboard, a mouse, a trackball, a touchscreen (e.g., capacitive touchscreen, a resistive touchscreen, a multi-touch touchscreen, etc.), etc. Likewise, the display apparatus  130 ,  170  may include any apparatus capable of displaying information to a user, such as a graphical user interface  132 ,  172  including electrode status information, graphical maps of electrical activation, a plurality of signals for the external electrodes over one or more heartbeats, QRS complexes, various cardiac therapy scenario selection regions, various rankings of cardiac therapy scenarios, various pacing parameters, electrical heterogeneity information (EHI), textual instructions, graphical depictions of anatomy of a human heart, images or graphical depictions of the patient&#39;s heart, graphical depictions of locations of one or more electrodes, graphical depictions of a human torso, images or graphical depictions of the patient&#39;s torso, graphical depictions or actual images of implanted electrodes and/or leads, etc. Further, the display apparatus  130 ,  170  may include a liquid crystal display, an organic light-emitting diode screen, a touchscreen, a cathode ray tube display, etc. 
     The processing programs or routines stored and/or executed by the computing apparatus  140  and the remote computing device  160  may 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. Data stored and/or used by the computing apparatus  140  and the remote computing device  160  may include, for example, electrical signal/waveform data from the electrode apparatus  110  (e.g., a plurality of QRS complexes), electrical activation times from the electrode apparatus  110 , cardiac sound/signal/waveform data from acoustic sensors, graphics (e.g., graphical elements, icons, buttons, windows, dialogs, pull-down menus, graphic areas, graphic regions, 3D graphics, etc.), graphical user interfaces, results from one or more processing programs or routines employed according to the disclosure herein (e.g., electrical signals, electrical heterogeneity information, etc.), or any other data that may be used for carrying out the one and/or more processes or methods described herein. 
     In one or more embodiments, the illustrative systems, methods, and interfaces may be implemented using one or more computer programs executed 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 may be applied to input data to perform functionality described herein and generate desired output information. The output information may 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. 
     The one or more programs used to implement the systems, methods, and/or interfaces described herein may be provided using any programmable language, e.g., a high-level procedural and/or object orientated 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., a storage media, that is readable by a general or special purpose program running on a computer system (e.g., including processing apparatus) for configuring and operating the computer system when the suitable device is read for performing the procedures described herein. In other words, at least in one embodiment, the illustrative systems, methods, and interfaces may be implemented using a computer readable storage medium, configured with a computer program, where the storage medium so configured causes the computer to operate in a specific and predefined manner to perform functions described herein. Further, in at least one embodiment, the illustrative systems, methods, and interfaces may 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 circuitry, is operable to perform operations such as the methods, processes, and/or functionality described herein. 
     The computing apparatus  140  and the remote computing device  160  may be, for example, any fixed or mobile computer system (e.g., a controller, a microcontroller, a personal computer, minicomputer, tablet computer, etc.). The exact configurations of the computing apparatus  140  and the remote computing device  160  are not limiting, and essentially any device capable of providing suitable computing capabilities and control capabilities (e.g., signal analysis, mathematical functions such as medians, modes, averages, maximum value determination, minimum value determination, slope determination, minimum slope determination, maximum slope determination, graphics processing, etc.) may be used. As described herein, a digital file may be any medium (e.g., volatile or non-volatile memory, a CD-ROM, a punch card, magnetic recordable tape, etc.) containing digital bits (e.g., encoded in binary, trinary, etc.) that may be readable and/or writeable by the computing apparatus  140  and the remote computing device  160  described herein. Also, as described herein, a file in user-readable format may be any representation of data (e.g., ASCII text, binary numbers, hexadecimal numbers, decimal numbers, graphically, etc.) presentable on any medium (e.g., paper, a display, etc.) readable and/or understandable by a user. 
     In view of the above, it will be readily apparent that the functionality as described in one or more embodiments according to the present disclosure may be implemented in any manner as would be known to one skilled in the art. As such, the computer language, the computer system, or any other software/hardware which is to be used to implement the processes described herein shall not be limiting on the scope of the systems, processes, or programs (e.g., the functionality provided by such systems, processes, or programs) described herein. 
     The illustrative electrode apparatus  110  may be configured to measure body-surface potentials of a patient  14  and, more particularly, torso-surface potentials of a patient  14 . As shown in  FIG.  2   , the illustrative electrode apparatus  110  may include a set, or array, of external electrodes  112 , a strap  113 , and interface/amplifier circuitry  116 . The electrodes  112  may be attached, or coupled, to the strap  113  and the strap  113  may be configured to be wrapped around the torso of a patient  14  such that the electrodes  112  surround the patient&#39;s heart. As further illustrated, the electrodes  112  may be positioned around the circumference of a patient  14 , including the posterior, lateral, posterolateral, anterolateral, and anterior locations of the torso of a patient  14 . 
     The illustrative electrode apparatus  110  may be further configured to measure, or monitor, sounds from at least one or both the patient  14 . As shown in  FIG.  2   , the illustrative electrode apparatus  110  may include a set, or array, of acoustic sensors  120  attached, or coupled, to the strap  113 . The strap  113  may be configured to be wrapped around the torso of a patient  14  such that the acoustic sensors  120  surround the patient&#39;s heart. As further illustrated, the acoustic sensors  120  may be positioned around the circumference of a patient  14 , including the posterior, lateral, posterolateral, anterolateral, and anterior locations of the torso of a patient  14 . 
     Further, the electrodes  112  and the acoustic sensors  120  may be electrically connected to interface/amplifier circuitry  116  via wired connection  118 . The interface/amplifier circuitry  116  may be configured to amplify the signals from the electrodes  112  and the acoustic sensors  120  and provide the signals to one or both of the computing apparatus  140  and the remote computing device  160 . Other illustrative systems may use a wireless connection to transmit the signals sensed by electrodes  112  and the acoustic sensors  120  to the interface/amplifier circuitry  116  and, in turn, to one or both of the computing apparatus  140  and the remote computing device  160 , e.g., as channels of data. In one or more embodiments, the interface/amplifier circuitry  116  may be electrically coupled to the computing apparatus  140  using, e.g., analog electrical connections, digital electrical connections, wireless connections, bus-based connections, network-based connections, internet-based connections, etc. 
     Although in the example of  FIG.  2    the electrode apparatus  110  includes a strap  113 , in other examples any of a variety of mechanisms, e.g., tape or adhesives, may be employed to aid in the spacing and placement of electrodes  112  and the acoustic sensors  120 . In some examples, the strap  113  may include an elastic band, strip of tape, or cloth. Further, in some examples, the strap  113  may be part of, or integrated with, a piece of clothing such as, e.g., a t-shirt. In other examples, the electrodes  112  and the acoustic sensors  120  may be placed individually on the torso of a patient  14 . Further, in other examples, one or both of the electrodes  112  (e.g., arranged in an array) and the acoustic sensors  120  (e.g., also arranged in an array) may be part of, or located within, patches, vests, and/or other manners of securing the electrodes  112  and the acoustic sensors  120  to the torso of the patient  14 . Still further, in other examples, one or both of the electrodes  112  and the acoustic sensors  120  may be part of, or located within, two sections of material or two patches. One of the two patches may be located on the anterior side of the torso of the patient  14  (to, e.g., monitor electrical signals representative of the anterior side of the patient&#39;s heart, measure surrogate cardiac electrical activation times representative of the anterior side of the patient&#39;s heart, monitor or measure sounds of the anterior side of the patient, etc.) and the other patch may be located on the posterior side of the torso of the patient  14  (to, e.g., monitor electrical signals representative of the posterior side of the patient&#39;s heart, measure surrogate cardiac electrical activation times representative of the posterior side of the patient&#39;s heart, monitor or measure sounds of the posterior side of the patient, etc.). And still further, in other examples, one or both of the electrodes  112  and the acoustic sensors  120  may be arranged in a top row and bottom row that extend from the anterior side of the patient  14  across the left side of the patient  14  to the posterior side of the patient  14 . Yet still further, in other examples, one or both of the electrodes  112  and the acoustic sensors  120  may be arranged in a curve around the armpit area and may have an electrode/sensor-density that less dense on the right thorax that the other remaining areas. 
     The electrodes  112  may be configured to surround the heart of the patient  14  and record, or monitor, the electrical signals associated with the depolarization and repolarization of the heart after the signals have propagated through the torso of a patient  14 . Each of the electrodes  112  may be used in a unipolar configuration to sense the torso-surface potentials that reflect the cardiac signals. The interface/amplifier circuitry  116  may also be coupled to a return or indifferent electrode (not shown) that may be used in combination with each electrode  112  for unipolar sensing. 
     In some examples, there may be about 12 to about 50 electrodes  112  and about 12 to about 50 acoustic sensors  120  spatially distributed around the torso of a patient. Other configurations may have more or fewer electrodes  112  and more or fewer acoustic sensors  120 . It is to be understood that the electrodes  112  and acoustic sensors  120  may not be arranged or distributed in an array extending all the way around or completely around the patient  14 . Instead, the electrodes  112  and acoustic sensors  120  may be arranged in an array that extends only part of the way or partially around the patient  14 . For example, the electrodes  112  and acoustic sensors  120  may be distributed on the anterior, posterior, and left sides of the patient with less or no electrodes and acoustic sensors proximate the right side (including posterior and anterior regions of the right side of the patient). 
     The computing apparatus  140  may record and analyze the torso-surface potential signals sensed by electrodes  112  and the sound signals sensed by the acoustic sensors  120 , which are amplified/conditioned by the interface/amplifier circuitry  116 . The computing apparatus  140  may be configured to analyze the electrical signals from the electrodes  112  to provide electrocardiogram (ECG) signals, information, or data from the patient&#39;s heart as will be further described herein. The computing apparatus  140  may be configured to analyze the electrical signals from the acoustic sensors  120  to provide sound signals, information, or data from the patient&#39;s body and/or devices implanted therein (such as a left ventricular assist device). 
     Additionally, the computing apparatus  140  and the remote computing device  160  may be configured to provide graphical user interfaces  132 ,  172  depicting various information related to the electrode apparatus  110  and the data gathered, or sensed, using the electrode apparatus  110 . For example, the graphical user interfaces  132 ,  172  may depict ECGs including QRS complexes obtained using the electrode apparatus  110  and sound data including sound waves obtained using the acoustic sensors  120  as well as other information related thereto. Illustrative systems and methods may noninvasively use the electrical information collected using the electrode apparatus  110  and the sound information collected using the acoustic sensors  120  to evaluate a patient&#39;s cardiac health and to evaluate and configure cardiac therapy being delivered to the patient. 
     Further, the electrode apparatus  110  may further include reference electrodes and/or drive electrodes to be, e.g. positioned about the lower torso of the patient  14 , that may be further used by the system  100 . For example, the electrode apparatus  110  may include three reference electrodes, and the signals from the three reference electrodes may be combined to provide a reference signal. Further, the electrode apparatus  110  may use of three caudal reference electrodes (e.g., instead of standard references used in a Wilson Central Terminal) to get a “true” unipolar signal with less noise from averaging three caudally located reference signals. 
       FIG.  3    illustrates another illustrative electrode apparatus  110  that includes a plurality of electrodes  112  configured to surround the heart of the patient  14  and record, or monitor, the electrical signals associated with the depolarization and repolarization of the heart after the 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, the sound signals associated with the heart after the signals have propagated through the torso of the patient  14 . The electrode apparatus  110  may include a vest  114  upon which the plurality of electrodes  112  and the plurality of acoustic sensors  120  may be attached, or to which the electrodes  112  and the acoustic sensors  120  may be coupled. In at least one embodiment, the plurality, or array, of electrodes  112  may be used to collect electrical information such as, e.g., surrogate electrical activation times. Similar to the electrode apparatus  110  of  FIG.  2   , the electrode apparatus  110  of  FIG.  3    may include interface/amplifier circuitry  116  electrically coupled to each of the electrodes  112  and the acoustic sensors  120  through a wired connection  118  and be configured to transmit signals from the electrodes  112  and the acoustic sensors  120  to computing apparatus  140 . As illustrated, the electrodes  112  and the acoustic sensors  120  may be distributed over the torso of a patient  14 , including, for example, the posterior, lateral, posterolateral, anterolateral, and anterior locations of the torso of a patient  14 . 
     The vest  114  may be formed of fabric with the electrodes  112  and the acoustic sensors  120  attached to the fabric. The vest  114  may be configured to maintain the position and spacing of electrodes  112  and the acoustic sensors  120  on the torso of the patient  14 . Further, the vest  114  may be marked to assist in determining the location of the electrodes  112  and the acoustic sensors  120  on the surface of the torso of the patient  14 . In some examples, there may 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 , though other configurations may have more or fewer electrodes  112  and more or fewer acoustic sensors  120 . 
     The illustrative systems and methods may be used to provide noninvasive assistance to a user in the evaluation of a patient&#39;s cardiac health and/or evaluation and configuration of cardiac therapy being presently delivered to the patient (e.g., by an implantable medical device, by a LVAD, etc.). For example, the illustrative systems and methods may be used to assist a user in the configuration and/or adjustment of one or more cardiac therapy settings such as, e.g., selection of pacing electrodes, selection of pacing vectors, optimization of the A-V interval, or delay, of pacing therapy (e.g., left ventricular-only, or left univentricular, pacing therapy) and the A-V interval, or delay, and the V-V interval, or delay, of pacing therapy (e.g., biventricular pacing therapy). 
     Further, it is to be understood that the computing apparatus  140  and the remote computing device  160  may be operatively coupled to each other in a plurality of different ways so as to perform, or execute, the functionality described herein. For example, in the embodiment depicted, the computing device  140  may be wireless operably coupled to the remote computing device  160  as depicted by the wireless signal lines emanating therebetween. Additionally, as opposed to wireless connections, one or more of the computing apparatus  140  and the remoting computing device  160  may be operably coupled through one or wired electrical connections. 
     An illustrative method  200  of evaluation and configuration of cardiac therapy is depicted in  FIG.  4   . The illustrative method  200  may be generally described to be used in the efficient, noninvasive evaluation and configuration (e.g., optimization) of cardiac therapy. The illustrative method  200  may be described as being noninvasive because the method does not use invasive apparatus to perform the evaluation of the cardiac therapy. The cardiac therapy being delivered, however, may be described as being invasive such as, e.g., one or more pacing electrodes may be implanted proximate a patient&#39;s heart. Thus, the illustrative method  200  may be used to evaluate and configure such invasive cardiac therapy. 
     The illustrative method  200  may be generally described as efficiently determining pacing settings or values for a plurality of pacing parameters for cardiac pacing therapy such as, e.g., left ventricular-only pacing therapy, biventricular pacing therapy, etc. The method  200  may utilize various techniques and processes to make such determination, or selection, of pacing settings or values efficient. 
     It is to be understood that pacing therapy may have a plurality of different pacing parameters such as e.g., AV timing, VV timing, selection of pacing electrodes or pacing vector (e.g., multisite pacing), selection of multiple pacing electrodes or multipoint pacing vectors, pacing pulse widths, pacing pulse amplitudes (e.g., voltage), ventricular pacing rates, pacing configurations (e.g., biventricular pacing, right ventricle only pacing, left ventricle only pacing, etc.), rate adaptive pacing settings, etc. Each of these different pacing parameters may include a plurality of different settings or values. Some of the different pacing parameters may extend across an entire range of values. 
     For example, one pacing parameter that will be described frequently herein may be a pacing vector, which is the identity of the one or more pacing electrodes used to deliver pacing to the patient&#39;s heart. A plurality of pacing vectors may exist depending on the number of pacing electrodes positioned proximate the patient&#39;s heart to delivering cardiac pacing therapy thereto. The plurality of pacing vectors may include every different combination using one or more of the pacing electrodes positioned in or about the patient&#39;s heart. For instance, if there are four pacing electrodes configured to pace the patient&#39;s heart, sixteen different pacing vectors may be derived from the four pacing electrodes. In other words, sixteen different combinations of pacing electrodes may be used to pace the patient&#39;s heart when there are four pacing electrodes. The pacing vector may be described in terms of the identities, or names, of the electrodes being used to deliver pacing therapy. 
     Further, for example, one pacing parameter that will also be described frequently herein may be a paced AV timing, which is the time period between intrinsic or paced depolarization of the atria and the delivery of a ventricular pace. The paced AV timing may be described in terms of a time value. For instance, the paced AV timing may be between about 40 ms and about 300 ms. The paced AV timing may be described in terms of a percentage of the patient&#39;s intrinsic AV timing. For instance, the paced AV timing may be between about 30% and about 90% of the patient&#39;s intrinsic AV timing. Other timings such as VV timing may be similarity described but with different values. 
     The illustrative method  200  may be configured to efficiently evaluate, or test, each of the plurality of different pacing parameters such as pacing vector, AV timing, and others. Generally, the illustrative method  200  may be described as testing, or evaluating, a first pacing parameter while isolating the remaining pacing parameters (e.g., fixing the remaining pacing parameters such that the values or settings thereof do not change during the testing of the first pacing parameter), and once a value or setting for the first pacing parameter has been selected (e.g., optimized), then a second pacing parameter may be evaluated while the first pacing parameter is isolated (e.g., the first pacing parameter may be fixed, or remain unchanged, at the selected setting or value). 
     The illustrative method  200  may include monitoring, or measuring, electrical activity using a plurality of external electrodes  202 . The plurality of external electrodes may be similar to the external electrodes provided by the electrode apparatus  110  as described herein with respect to  FIGS.  1 - 3   . For example, the plurality of external electrodes may be part, or incorporated into, a vest or band that is located about a patient&#39;s torso. More specifically, the plurality of electrodes may be described as being surface electrodes positioned in an array configured to be located proximate the skin of the torso of a patient. The electrical activity monitored that is prior to the delivery of cardiac therapy may be referred to as “baseline” electrical activity because no therapy is delivered to the patient such that the patient&#39;s heart is in its natural, or intrinsic, rhythm. 
     Although monitoring electrical activity  202  is the first process noted in the method  200 , it is be understood that monitoring electrical activity  202  can occur, or take place, anytime within the method  200  but primarily during the delivery of pacing therapy to evaluate, or test, various different pacing parameters as will be described further herein. 
     Before beginning the evaluation of the plurality of different pacing parameters, some settings or values of such different pacing parameters may already be determined to be undesirable or unnecessary for use in delivery cardiac pacing therapy. For example, some pacing vectors, and electrodes thereof, may be known to stimulate the patient&#39;s phrenic nerve (e.g., based on previous clinic data) or to have a high likelihood to stimulate the patient&#39;s phrenic nerve (e.g., based on population studies and/or other metrics). Further, for example, some pacing vectors, and electrodes thereof, may be known to have high capture thresholds (e.g., based on previous clinic data) or to have high likelihoods of having high capture thresholds (e.g., based on population studies and/or other metrics). In one or more embodiments, capture threshold is the amplitude and pulse width of the electrical pace delivered by a pacing electrode or more than one pacing electrode in a multipoint, or multisite, pacing vector that is needed to capture the myocardial tissue electrically and depolarize myocardial tissue effectively. If a pacing vector has a high capture threshold, then the battery life of the cardiac therapy device may be shortened and less desirable. Thus, pacing vectors having high capture thresholds are less desirable. 
     The illustrative method  200  may include removing settings or values  204  that may not be desirable or may not be necessary. For example, any pacing electrodes, or specifically pacing electrodes being used as cathodes, for use in providing the plurality of different pacing vectors that stimulate or may likely stimulate the patient&#39;s phrenic nerve may be disqualified, or removed, from the plurality of different pacing vectors to be evaluated or tested. Further, for example, pacing electrodes (e.g., for use in providing the plurality of different pacing vectors) that exceed a selected capture threshold may be disqualified, or removed, from the plurality of different pacing vectors to be evaluated or tested. The selected capture threshold may be between about 4 volts (V) and about 6 V. In at least one embodiment, the selected capture threshold is 5 V. Further, for example, various settings or values may be removed, or excluded, manually by a user (e.g., physician using a graphical user interface). 
     For instance, if four different pacing electrodes may be used to deliver cardiac pacing therapy, which provides sixteen different, or unique, pacing vectors, and one of the four pacing electrodes when functioning as a cathode is known or determined to stimulate the phrenic nerve or has too high of a pacing threshold, then such electrode may be removed as a potential cathode to deliver pacing therapy thereby limiting the amount of different pacing vectors to twelve different, or unique, pacing vectors. 
     Additionally, for example, the range of values of one or more pacing parameters may be limited thereby removing values  204 . For instance, the AV timing may be limited to between about 40% and about 80% of the patient&#39;s intrinsic AV timing as opposed to, e.g., testing a larger percentage range or a larger range of time values without using the patient&#39;s intrinsic value as a baseline value. Additionally, if the patient has AV block, the AV timing may be initially set to a selected nominal value as opposed to testing or evaluating a range of values. In this way, less time values for the AV timing parameter may be tested thereby increasing the efficiency of configuring the AV timing for a patient&#39;s cardiac therapy. Furthermore, if the patient has atrial fibrillation and/or atrial tachycardia, then AV timing may not be tested (as, e.g., delivery of pacing therapy based on AV timing would not be helpful in such situations). In at least one embodiment, a user (e.g., physician) may determine that the patient is undergoing atrial fibrillation and/or atrial tachycardia and may manually remove AV timing from the pool of settings available. In another embodiment, AV timing may be automatically removed from the pool of settings available in response to the patient undergoing atrial fibrillation and/or atrial tachycardia (e.g., AF/AT detected by the system, AF/AT input by a user, etc.). 
     In other words, the efficient search for optimal parameters described herein may start with limiting the set of values or settings of certain parameters based on patient&#39;s intrinsic physiology and other device measurements related to pace capture thresholds or phrenic nerve stimulation (PNS) thresholds for pacing options/electrodes available. 
     During, or simultaneous with, the monitoring, or collecting, of electrical activity  202 , the illustrative method  200  may further include delivering cardiac pacing therapy  206 . In at least one embodiment, each of the electrodes may be coupled to one or more leads implanted in, or proximate to, the patient&#39;s heart. Further, in at least one embodiment, the cardiac therapy  206  may be delivered by a leadless electrode. Illustrative cardiac therapy using an implantable electrode and lead may be further described herein with reference to  FIGS.  6 - 8   . Although the systems and devices of  FIGS.  6 - 8    include three leads, it is to be understood that the illustrative systems and methods described herein may be used with any type of cardiac pacing systems including no leads, less than three leads, and more than three leads. As described herein, although the cardiac therapy delivery may be described as being invasive, the illustrative methods and systems may be described as being noninvasive because the illustrative methods and systems may only initiate the delivery of and configure the cardiac therapy, and the illustrative methods and systems may further use electrical signals that are monitored, or taken, from the patient noninvasively. Further, illustrative cardiac therapy may utilize an leaded or leadless implantable cardiac device that includes a tissue-piercing electrode implantable from the triangle of Koch region of the right atrium through the right atrial endocardium and central fibrous body to deliver cardiac therapy to or sense electrical activity of the left ventricle in the basal and/or septal region of the left ventricular myocardium of a patient&#39;s heart as described in U.S. Provisional Patent Application Ser. No. 62/647,414 entitled “VfA CARDIAC THERAPY” and filed on Mar. 23, 2018, and U.S. Provisional Patent Application Ser. No. 62/725,763 entitled “ADAPTIVE VfA CARDIAC THERAPY” and filed on Aug. 31, 2018, each of which is incorporated by reference herein in their entireties. 
     The cardiac pacing therapy may be delivered using a particular, unique configuration of the plurality of different cardiac pacing parameters. For example, the cardiac pacing therapy may be left ventricular-only pacing at an AV timing of 55% of the patient&#39;s intrinsic AV timing, using a pacing vector of a single pacing electrode (LV 1 ), at a pacing amplitude of 3.5 volts, and with a pulse width of 0.8 milliseconds (ms). For that particular, unique configuration of cardiac pacing parameters, the monitored electrical activity may be used to generate electrical heterogeneity information (EHI)  208 . The EHI may be described as information, or data, representative of at least one of mechanical cardiac functionality and electrical cardiac functionality. The EHI and other cardiac therapy information may be described in U.S. Provisional Patent Application No. 61/834,133 entitled “METRICS OF ELECTRICAL DYSSYNCHRONY AND ELECTRICAL ACTIVATION PATTERNS FROM SURFACE ECG ELECTRODES” and filed on Jun. 12, 2013, which is hereby incorporated by reference it its entirety. 
     Electrical heterogeneity information (e.g., data) may be defined as information indicative of at least one of mechanical synchrony or dyssynchrony of the heart and/or electrical synchrony or dyssynchrony of the heart. In other words, electrical heterogeneity information may represent a surrogate of actual mechanical and/or electrical functionality of a patient&#39;s heart. In at least one embodiment, relative changes in electrical heterogeneity information (e.g., from baseline heterogeneity information to therapy heterogeneity information, from a first set of heterogeneity information to a second set of therapy heterogeneity information, etc.) may be used to determine a surrogate value representative of the changes in hemodynamic response (e.g., acute changes in LV pressure gradients). The left ventricular pressure may be typically monitored invasively with a pressure sensor located in the left ventricular of a patient&#39;s heart. As such, the use of electrical heterogeneity information to determine a surrogate value representative of the left ventricular pressure may avoid invasive monitoring using a left ventricular pressure sensor. 
     In at least one embodiment, the electrical heterogeneity information may include a standard deviation of ventricular activation times measured using some or all of the external electrodes, e.g., of the electrode apparatus  110 . Further, local, or regional, electrical heterogeneity information may include standard deviations and/or averages of activation times measured using electrodes located in certain anatomic areas of the torso. For example, external electrodes on the left side of the torso of a patient may be used to compute local, or regional, left electrical heterogeneity information. 
     The electrical heterogeneity information may be generated using one or more various systems and/or methods. For example, electrical heterogeneity information may be generated using an array, or a plurality, of surface electrodes and/or imaging systems as described in U.S. Pat. App. Pub. No. 2012/0283587 A1 published Nov. 8, 2012 and entitled “ASSESSING INRA-CARDIAC ACTIVATION PATTERNS AND ELECTRICAL DYSSYNCHRONY,” U.S. Pat. App. Pub. No. 2012/0284003 A1 published Nov. 8, 2012 and entitled “ASSESSING INTRA-CARDIAC ACTIVATION PATTERNS”, and U.S. Pat. No. 8,180,428 B2 issued May 15, 2012 and entitled “METHODS AND SYSTEMS FOR USE IN SELECTING CARDIAC PACING SITES,” each of which is incorporated herein by reference in its entirety. 
     Electrical heterogeneity information may include one or more metrics or indices. 
     For example, one of the metrics, or indices, of electrical heterogeneity may be a standard deviation of activation times (SDAT) measured using some or all of the electrodes on the surface of the torso of a patient. In some examples, the SDAT may be calculated using the estimated cardiac activation times over the surface of a model heart. 
     Another metric, or index, of electrical heterogeneity may be a left standard deviation of surrogate electrical activation times (LVED) monitored by external electrodes located proximate the left side of a patient. Further, another metric, or index, of electrical heterogeneity may include an average of surrogate electrical activation times (LVAT) monitored by external electrodes located proximate the left side of a patient. The LVED and LVAT may be determined (e.g., calculated, computed, etc.) from electrical activity measured only by electrodes proximate the left side of the patient, which may be referred to as “left” electrodes. The left electrodes may be defined as any surface electrodes located proximate the left ventricle, which includes region to left of the patient&#39;s sternum and spine. In one embodiment, the left electrodes may include all anterior electrodes on the left of the sternum and all posterior electrodes to the left of the spine. In another embodiment, the left electrodes may include all anterior electrodes on the left of the sternum and all posterior electrodes. In yet another embodiment, the left electrodes may be designated based on the contour of the left and right sides of the heart as determined using imaging apparatus (e.g., x-ray, fluoroscopy, etc.). 
     Another illustrative metric, or index, of dyssynchrony may be a range of activation times (RAT) that may be computed as the difference between the maximum and the minimum torso-surface or cardiac activation times, e.g., overall, or for a region. The RAT reflects the span of activation times while the SDAT gives an estimate of the dispersion of the activation times from a mean. The SDAT also provides an estimate of the heterogeneity of the activation times, because if activation times are spatially heterogeneous, the individual activation times will be further away from the mean activation time, indicating that one or more regions of heart have been delayed in activation. In some examples, the RAT may be calculated using the estimated cardiac activation times over the surface of a model heart. 
     Another illustrative metric, or index, of electrical heterogeneity information may include estimates of a percentage of surface electrodes located within a particular region of interest for the torso or heart whose associated activation times are greater than a certain percentile, such as, for example the 70th percentile, of measured QRS complex duration or the determined activation times for surface electrodes. The region of interest may, e.g., be a posterior, left anterior, and/or left-ventricular region. The illustrative metric, or index, may be referred to as a percentage of late activation (PLAT). The PLAT may be described as providing an estimate of percentage of the region of interest, e.g., posterior and left-anterior area associated with the left ventricular area of heart, which activates late. A large value for PLAT may imply delayed activation of a substantial portion of the region, e.g., the left ventricle, and the potential benefit of electrical resynchronization through CRT by pre-exciting the late region, e.g., of left ventricle. In other examples, the PLAT may be determined for other subsets of electrodes in other regions, such as a right anterior region to evaluate delayed activation in the right ventricle. Furthermore, in some examples, the PLAT may be calculated using the estimated cardiac activation times over the surface of a model heart for either the whole heart or for a particular region, e.g., left or right ventricle, of the heart. 
     In one or more embodiments, the electrical heterogeneity information may include indicators of favorable changes in global cardiac electrical activation such as, e.g., described in Sweeney et al., “Analysis of Ventricular Activation Using Surface Electrocardiography to Predict Left Ventricular Reverse Volumetric Remodeling During Cardiac Resynchronization Therapy,” Circulation, 2010 Feb. 9, 121(5): 626-34 and/or Van Deursen, et al., “Vectorcardiography as a Tool for Easy Optimization of Cardiac Resynchronization Therapy in Canine LBBB Hearts,” Circulation Arrhythmia and Electrophysiology, 2012 Jun. 1, 5(3): 544-52, each of which is incorporated herein by reference in its entirety. Heterogeneity information may also include measurements of improved cardiac mechanical function measured by imaging or other systems to track motion of implanted leads within the heart as, e.g., described in Ryu et al., “Simultaneous Electrical and Mechanical Mapping Using 3D Cardiac Mapping System: Novel Approach for Optimal Cardiac Resynchronization Therapy,” Journal of Cardiovascular Electrophysiology, 2010 Feb. 21(2): 219-22, Sperzel et al., “Intraoperative Characterization of Interventricular Mechanical Dyssynchrony Using Electroanatomic Mapping System—A Feasibility Study,” Journal of Interventional Cardiac Electrophysiology, 2012 November, 35(2): 189-96, and/or U.S. Pat. App. Pub. No. 2009/0099619 A1 entitled “METHOD FOR OPTIMIZAING CRT THERAPY” and published on Apr. 16, 2009, each of which is incorporated herein by reference in its entirety. 
     Additionally, although not depicted in the block diagram of  FIG.  4   , the electrical heterogeneity information may be generated  208  for electrical activity monitored without, or before the delivery of, cardiac therapy, which may be referred to as baseline electrical heterogeneity information. 
     Once the electrical heterogeneity information (EHI)  208  has been generated for the present, unique cardiac pacing configuration, the illustrative method  200  may adjust a first parameter of the plurality of different cardiac pacing parameters  210 . The remaining pacing parameters other than the first parameter of the present, unique cardiac pacing configuration may remain unchanged. In this way, no other parameters other than the first parameter being adjusted or changed should affect the cardiac therapy outcome, and thus, the first parameter may be isolated for analysis. 
     After the first parameter has been adjusted, the method  200  may return to delivering pacing therapy  206  with the first parameter being adjusted and generating EHI  208  based on the electrical activity monitored during the delivery of such pacing therapy. The method  200  may continue looping until the first parameter has been completely and/or successfully evaluated or tested. 
     For example, the first parameter may have a range of values or settings at which it may be tested or evaluated, and if cardiac therapy has been delivered at each of the range or values or settings while electrical activity has been monitored and EHI generated, then it may be determined that the first parameter has been completed evaluated or tested. It is to be understood that although any numerical range of parameter values may mathematically have an infinite number of values therebetween, each parameter may have a minimum step, or adjustment, value by which it may be adjusted that limits the amount of iterations within a particular range. 
     Further for example, if, while cardiac therapy is being delivered at each of the range or values or settings, the EHI generated from the monitored electrical activity indicates that the cardiac therapy is effective for the patient, then it may be determined that the first parameter has been successfully evaluated or tested. In this circumstance, the method  200  may stop at this point as the current configuration was determined to be effective. The effectiveness of the current configuration may be compared to a threshold value, which may be based on patient population studies. More specifically, the EHI may be SDAT, and if the SDAT is less than or equal to a selected SDAT threshold such as, e.g., 30 ms, then the current cardiac therapy pacing configuration may be determined to be effective, and the cardiac therapy evaluation and testing may cease. In other words, if the current parameter set yields a degree of resynchronization that exceeds a threshold derived from previous population studies indicating more likelihood of better outcomes, no further testing may be completed. 
     The illustrative method  200 , however, may not evaluate, or test, the first parameter at every possible value or setting. Instead, the method  200  may utilize one or more processes, e.g., depending on the parameter being evaluated or tested, to increase efficiency. An illustrative method  250  of efficient evaluation of a cardiac therapy parameter is depicted in  FIG.  5 A . The method  250  may include delivering the cardiac pacing therapy at a subset of settings  252 . The subset of settings, or values, may be less, likely substantially less, than entire range of possible settings or values. In one or more embodiments, the subset of settings, or values, may be spread equidistantly about the range of possible settings, or values, if, e.g., the parameter as a chronological, numerical range of possible settings or values. In one or more embodiments, the subset of settings, or values, may be based on patient metrics and population studies of similar patients. In other words, the subset of settings, or values, that are initially tested may be have been effective or optimal when used on other patients that are similar to the current patient. Further, it may be described that different settings be automatically proposed to a user (e.g., physician) based on data selected from a pool of patients that have similar characteristics to the patient and/or data already known about the patient. Thus, the process  252  may first evaluate a few different settings, or values, of a parameter as opposed to evaluating every possible setting, or value, of the parameter. 
     The method  250  may then select the best one or more settings, or values, from the subset based on the effectiveness of the settings or values. In one or more embodiments, the best one or more settings or values may be the most effective one or more settings or values (e.g., most effective at increasing cardiac resynchronization of the patient&#39;s heart). For example, electrical activity may be monitored using external electrode apparatus, an EHI may be generated based on the monitored electrical activity, and the best one or more settings, values, of the subset may be selected. In one example, a single setting of the subset (e.g., the best setting) may be selected. In other examples, more the one setting of the subset may be selected if, e.g., the more one setting exceed a selected threshold value indicative of effective cardiac therapy. 
     Then, to further fine tune the parameter, the method  250  may deliver pacing therapy at a range of settings, or values, proximate the selected best setting(s)  258 . In other words, settings that are close to, or similar to, the selected best settings(s) may be used to deliver cardiac pacing therapy. The method  250  may then identify a setting from the range of settings proximate the selected best settings(s)  258  based on the effectiveness of the settings (e.g., similar to as before using EHI to determine the effectiveness of the cardiac therapy being delivered). 
     An example of a range of AV timings being efficiently evaluated according to the method of  FIG.  5 A  is depicted in  FIG.  5 B . In the first range  260  of paced AV timing percentage of a patient&#39;s intrinsic AV timing, three different paced AV timing percentages are using to delivery cardiac therapy and evaluated, namely, 50%, 70%, and 80%. Each of the three different paced AV timing percentages are the subset of the settings of the paced AV timing. The effectiveness of each of the three different paced AV timing percentages may be monitored and evaluated similar to as described herein with respect to method  200  of  FIG.  4   . One or more of the three different paced AV timing percentages may be determined to be best or most effective. As shown, a single paced AV timing percentage is determined to the best or most effective as indicated by the dashed-line circle  264  encircling the paced AV timing percentage 50%. 
     Next, a range  262  of settings proximate the paced AV timing percentage 50% may be evaluated. As shown, the range of settings proximate the paced AV timing percentage 50% extends 15% to either side of the paced AV timing percentage 50% on the range  262  (i.e., from 35% to 65%). Further, every 5% from the paced AV timing percentage 50% to the 15% decrease or increase is tested. In other words, a 5% step or adjustment is utilized. Although this embodiment utilizes a 5% step or adjustment, it is to be understood that steps, or adjustments, greater than or less than 5% may be utilized. Further, in one or more embodiments, the step or adjustment size may be based on patient metrics and population studies of similar patients. In other words, a step or adjustment size may be used that has been effective or optimal when used to evaluate pacing therapy with other patients that are similar to the current patient. 
     One or more of the different paced AV timing percentages of the range  262  of settings may be determined to be best or most effective. As shown, the single paced AV timing percentage of 55% is determined to the best or most effective as indicated by the dashed-line circle  266 . Thus, less than the entire range of settings, or values, for the pacing AV timing may be evaluated using the processes shown in  FIGS.  5 A- 5 B  in an efficient manner while resulting an effective setting, or value, for paced AV timing. 
     Another illustrative method  270  of efficient evaluation of a cardiac therapy parameter is depicted in  FIG.  6 A . The method  270  may include delivering the cardiac pacing therapy  272  while varying a pacing parameter. The setting, or value, of the pacing parameter may be increased by a selected increment to, e.g., traverse a range of different settings or values  274 . For each setting or value, the effectiveness of the setting or value may be monitored and evaluated similar to as described herein with respect to method  200  of  FIG.  4   . If the setting or value is determined to less effective than the last setting or value evaluated, then the method  270  may increase the selected increment  276 , and conversely, if the setting or value is determined to more effective than the last setting evaluated, then the method  270  may decrease the selected increment  278 . In other words, if the previous setting or value for the pacing parameter provided better results than the current setting or value, then the process “speeds up” the evaluation of the remaining settings or values by increasing the increment or step, and if the current setting or value for the pacing parameter provided better results than the previous setting or value, then the process “slows down” the evaluation of the remaining settings or values by decreasing the increment or step. In one or more embodiments, a user (e.g., a physician) may be to select whether or not the method  270  may be performed for one or more parameters. For instance, a user may desire that every setting or value be evaluated, or tested, for one or more parameters (e.g., a standard process), and thus, the user instruct the system to not evaluate, or test, such parameters in the efficient manner described by method  270 . Instead, such parameters may be tested in a standard, incremental manner. Additionally, in one or more embodiments, the selected increment  278  may be adjusted based on pooled patient population data and/or previously known data about the patient. 
     An example of a range of AV timings being efficiently evaluated according to the method of  FIG.  6 A  is depicted in  FIG.  6 B . In this example, the paced AV timing percentage range  280  extends between 100% and 25% of the patient&#39;s intrinsic AV timing, and the testing, or evaluation, thereof starts at 100%. The current increment, or step,  282  is indicated below the range  280 . In this example, the increment  282  starts at, or is initially set to, 5% of the patient&#39;s intrinsic AV timing. In other embodiments, it is to be understood that the increment may be less than 5%. When the paced AV timing percentage 95% is evaluated and determined to be less effective than the paced AV timing percentage 100%, the increment may be increased by 5% to 10%. As such, the next paced AV timing percentage evaluated is the paced AV timing percentage 85% (i.e., 95% minus the increased increment of 10%). As shown, the paced AV timing percentage 85% is determined to be less effective than the last paced AV timing percentage 95%, and thus, the increment is increased by 5% to 15%. 
     The next paced AV timing percentage evaluated is the paced AV timing percentage 70% (i.e., 85% minus the increased increment of 15%), which is determined to be more effective than the last paced AV timing percentage 85%, and thus, the increment is decreased by 5% to 10%. Likewise, the next paced AV timing percentage 60% is determined to be more effective than the last paced AV timing percentage 70%, and thus, the increment is decreased by 5% to 5%. The next paced AV timing percentage evaluated is the paced AV timing percentage 55%, which is determined to be similarly effective than the last paced AV timing percentage 60%, and thus, the increment is neither decreased nor increased. 
     In this example, a threshold value may be used to determine whether effectiveness of a setting is more effective, less effective, or similar to the previously value. The threshold value may be a percentage difference of a metric of effectiveness from the previous setting to the current setting such as, e.g., 5%. For example, the threshold value may be between about 2% and about 25%. Further, the threshold value may be greater than or equal to 2%, greater than or equal to 4%, greater than or equal to 6%, greater than or equal to 10%, etc. and/or less than or equal to 25%, less than or equal to about 20%, less than or equal to about 17%, less than or equal to about 15%, etc. In one illustrative embodiment, if SDAT has improved by 5% from the previous setting, then it may be determined that the current setting is more effective than the previous setting, and conversely, if SDAT has worsened by 5% from the previous setting, then it may be determined that the setting is less effective than the previous setting. If SDAT has not worsened or improved by 5% from the previous setting, then it may be determined that the setting is similarly effective to the previous setting. 
     The next paced AV timing percentage 50% is determined to be less effective than the last paced AV timing percentage 55%, and thus, the increment is increased by 5% to 10%. Further, the next paced AV timing percentage 40% is determined to be less effective than the last paced AV timing percentage 50%, and thus, the increment is decreased by 5% to 15%. In other words, the changing of AV delay may be completed in steps or increments, which can be adapted based on the changes in degree of resynchronization achieved between successive AVs (e.g., bigger steps if changes in degrees of resynchronization is not greater than a pre-specified threshold). 
     The single paced AV timing percentage of 55% may be determined to the best or most effective as indicated by the dashed-line circle  284 . Thus, less than the entire range of settings, or values, for the pacing AV timing may be evaluated using the processes shown in  FIGS.  6 A- 6 B  in an efficient manner while resulting an effective paced AV timing. 
     Additionally, although the illustrative methods  250 ,  270  described herein with respect to  FIGS.  5 - 6    show the evaluation and adjustment of AV timing, it is to be understood that the first parameter evaluated and adjusted according to method  200  may include any one pacing parameter such as, e.g., AV timing, VV timing, selection of pacing electrodes or pacing vector, selection of multiple pacing electrodes or multipoint pacing vectors, pacing pulse widths, pacing pulse amplitudes (e.g., voltage), ventricular pacing rates, pacing configurations (e.g., biventricular pacing, right ventricle only pacing, left ventricle only pacing, etc.), rate adaptive pacing settings, etc. 
     In one illustrative embodiment, the first parameter evaluated and adjusted by the method  200  may be pacing vector. Thus, the method  200  may initiate delivery of pacing therapy using a plurality of different pacing vectors, where each different pacing vector uses a combination of pacing electrodes different from the remaining different pacing vectors, and then select one or more of the plurality of different pacing vectors, e.g., based on generated EHI from the electrical activity monitored during the delivery of pacing therapy using the plurality of different pacing vectors. 
     After the first parameter has been evaluated and adjusted, the setting, or value, for the first parameter may be identified and fixed  212 . More specifically, for example, the setting or value for the first parameter may be displayed on a graphical user interface such as the graphical user interfaces  132 ,  172  shown herein with respect to  FIG.  1   . In this way, a clinician (e.g., physician) may be apprised of the most effective setting or value for the first parameter as determined by the method  200 . 
     Additionally, for example, the setting or value for the first parameter may be fixed or remain constant for the remainder of the method  200  so as to, e.g., isolate the first parameter from the evaluation and adjustment of other parameters. In one illustrative example, the first parameter may be pacing vector, and thus, the most effective, or best, pacing vector may be identified and fixed  212  such that the remainder of method  200  can focus on evaluation and adjustment of other pacing parameters (e.g., without different pacing vectors affecting the process). 
     After the first parameter may be identified and fixed  212 , the method  200  may adjust a second parameter  214 , generate EHI  216  from the electrical activity monitored by external electrodes during delivering of cardiac therapy at the first fixed pacing parameter and the adjusted second pacing parameter, and continue looping until the most effective, or best, setting or value for the second pacing parameter is determined. After the second parameter has been evaluated and adjusted, the setting, or value, for the second parameter may be identified  218 . Similar to as before with the first parameter, for example, the setting or value for the second parameter may be displayed on a graphical user interface such as the graphical user interfaces  132 ,  172  shown herein with respect to  FIG.  1   . In this way, a clinician (e.g., physician) may be apprised of the most effective setting or value for the second parameter as determined by the method  200 . 
     In one illustrative embodiment, the first parameter evaluated and adjusted by the method  200  may be AV timing. Thus, the method  200  may initiate delivery of pacing therapy using the fixed first pacing parameter and a plurality of different AV timings, and then select one or more of the plurality of different AV timings, e.g., based on generated EHI from the electrical activity monitored during the delivery of pacing therapy using the fixed first pacing parameter and the plurality of different AV timings. 
     Similar to as already described herein with respect to the first parameter, the illustrative method  200  may not evaluate, or test, the second parameter at every possible value or setting. Instead, the method  200  may utilize one or more processes, e.g., depending on the parameter being evaluated or tested, to increase efficiency such as the illustrative methods  250 ,  270  described herein with respect to  FIGS.  5 - 6   . 
     Additionally, at any time during the evaluation and adjustment of pacing parameters using method  200 , if cardiac pacing therapy being delivered is determined be substantially effective, the method  200  may halt and simply identify the current pacing settings or values for the plurality of different pacing parameters. For example, a selected threshold may be utilized to determine whether the current cardiac pacing settings or values are effective enough to halt the method  200 . In one instance, the generated EHI may be compared to a selected threshold. More specifically, if SDAT for a particular pacing configuration is less than or equal to 20 ms and a reduction in the SDAT from the patient&#39;s intrinsic or baseline rhythm (i.e., prior to or without pacing therapy) is greater than 10%, then the method  200  may halt and simply identify the current pacing settings or values for the plurality of different pacing parameters. 
     Thus, it may be described that the initiation of delivery of pacing therapy may be halted if generated EHI is greater than a selected threshold and the pacing settings or values (e.g., such as the paced vector, etc.) using during the monitoring of the electrical activity that resulted in the EHI being halted may be identified. In this way, if the method  200  finds a substantially effective pacing configuration, the method  200  can stop without spending any more time searching other pacing configurations. 
     Illustrative cardiac therapy systems and devices may be further described herein with reference to  FIGS.  7 - 9    that may utilizes the illustrative systems, interfaces, methods, and processes described herein with respect to  FIGS.  1 - 5   . 
       FIG.  7    is a conceptual diagram illustrating an illustrative therapy system  10  that may be used to deliver pacing therapy to a patient  14 . Patient  14  may, but not necessarily, be a human. The therapy system  10  may include an implantable medical device  16  (IMD), which may be coupled to leads  18 ,  20 ,  22 . The IMD  16  may be, e.g., an implantable pacemaker, cardioverter, and/or defibrillator, that delivers, or provides, electrical signals (e.g., paces, etc.) to and/or senses electrical signals from the heart  12  of the patient  14  via electrodes coupled to one or more of the leads  18 ,  20 ,  22 . 
     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 the example shown in  FIG.  7   , 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 the 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 . 
     The IMD  16  may sense, among other things, 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  may be operable to adjust one or more parameters associated with the pacing therapy such as, e.g., A-V delay and other various timings, pulse wide, amplitude, voltage, burst length, etc. Further, the IMD  16  may be operable to use various electrode configurations to deliver pacing therapy, which may be unipolar, bipolar, quadripoloar, or further multipolar. For example, a multipolar lead may include several electrodes that can be used for delivering pacing therapy. Hence, a multipolar lead system may provide, or offer, multiple electrical vectors to pace from. A pacing vector may include at least one cathode, which may be at least one electrode located on at least one lead, and at least one anode, which may be at least one electrode located on at least one lead (e.g., the same lead, or a different lead) and/or on the casing, or can, of the IMD. While improvement in cardiac function as a result of the pacing therapy may primarily depend on the cathode, the electrical parameters like impedance, pacing threshold voltage, current drain, longevity, etc. may be more dependent on the pacing vector, which includes both the cathode and the anode. The IMD  16  may 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  may detect arrhythmia of the heart  12 , such as fibrillation of the ventricles  28 ,  32 , and deliver defibrillation therapy to the heart  12  in the form of electrical pulses. In some examples, IMD  16  may be programmed to deliver a progression of therapies, e.g., pulses with increasing energy levels, until a fibrillation of heart  12  is stopped. 
       FIGS.  8 A- 8 B  are conceptual diagrams illustrating the IMD  16  and the leads  18 ,  20 ,  22  of therapy system  10  of  FIG.  7    in more detail. The leads  18 ,  20 ,  22  may be electrically coupled to a therapy delivery module (e.g., for delivery of pacing therapy), a sensing module (e.g., for sensing one or more signals from one or more electrodes), and/or any other modules of the IMD  16  via a connector block  34 . In some examples, the proximal ends of the leads  18 ,  20 ,  22  may include electrical contacts that electrically couple to respective electrical contacts within the connector block  34  of the IMD  16 . In addition, in some examples, the leads  18 ,  20 ,  22  may be mechanically coupled to the connector block  34  with the aid of set screws, connection pins, or another suitable mechanical coupling mechanism. 
     Each of the leads  18 ,  20 ,  22  includes an elongated insulative lead body, which may carry a number of conductors (e.g., concentric coiled conductors, straight conductors, etc.) separated from one another by insulation (e.g., tubular insulative sheaths). In the illustrated example, bipolar electrodes  40 ,  42  are located proximate to a distal end of the lead  18 . In addition, bipolar electrodes  44 ,  45 ,  46 ,  47  are located proximate to a distal end of the lead  20  and bipolar electrodes  48 ,  50  are located proximate to a distal end of the lead  22 . 
     The electrodes  40 ,  44 ,  45 ,  46 ,  47 ,  48  may take the form of ring electrodes, and the electrodes  42 ,  50  may take the form of extendable helix tip electrodes mounted retractably within the insulative electrode heads  52 ,  54 ,  56 , respectively. Each of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50  may be electrically coupled to a respective one of the conductors (e.g., coiled and/or straight) within the lead body of its associated lead  18 ,  20 ,  22 , and thereby coupled to a respective one of the electrical contacts on the proximal end of the leads  18 ,  20 ,  22 . 
     Additionally, electrodes  44 ,  45 ,  46  and  47  may have an electrode surface area of about 5.3 mm 2  to about 5.8 mm 2 . Electrodes  44 ,  45 ,  46 , and  47  may also be referred to as LV 1 , LV 2 , LV 3 , and LV 4 , respectively. The LV electrodes (i.e., left ventricle electrode  1  (LV 1 )  44 , left ventricle electrode  2  (LV 2 )  45 , left ventricle electrode  3  (LV 3 )  46 , and left ventricle  4  (LV 4 )  47  etc.) on the lead  20  can be spaced apart at variable distances. For example, electrode  44  may be a distance of, e.g., about 21 millimeters (mm), away from electrode  45 , electrodes  45  and  46  may be spaced a distance of, e.g. about 1.3 mm to about 1.5 mm, away from each other, and electrodes  46  and  47  may be spaced a distance of, e.g. 20 mm to about 21 mm, away from each other. 
     The electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50  may further be used to sense electrical signals (e.g., morphological waveforms within electrograms (EGM)) attendant to the depolarization and repolarization of the heart  12 . The electrical signals are conducted to the IMD  16  via the respective leads  18 ,  20 ,  22 . In some examples, the IMD  16  may also deliver pacing pulses via the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50  to cause depolarization of cardiac tissue of the patient&#39;s heart  12 . In some examples, as illustrated in  FIG.  8 A , the IMD  16  includes one or more housing electrodes, such as housing electrode  58 , which may be formed integrally with an outer surface of a housing  60  (e.g., hermetically-sealed housing) of the IMD  16  or otherwise coupled to the housing  60 . Any of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50  may be used for unipolar sensing or pacing in combination with the housing electrode  58 . It is generally understood by those skilled in the art that other electrodes can also be selected to define, or be used for, pacing and sensing vectors. Further, any of electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 , when not being used to deliver pacing therapy, may be used to sense electrical activity during pacing therapy. 
     As described in further detail with reference to  FIG.  8 A , the housing  60  may enclose a therapy delivery module that may include a stimulation generator for generating cardiac pacing pulses and defibrillation or cardioversion shocks, as well as a sensing module for monitoring the electrical signals of the patient&#39;s heart (e.g., the patient&#39;s heart rhythm). The leads  18 ,  20 ,  22  may also include elongated electrodes  62 ,  64 ,  66 , respectively, which may take the form of a coil. The IMD  16  may 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  may also be used to deliver cardioversion pulses to the heart  12 . Further, the electrodes  62 ,  64 ,  66  may be fabricated from any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloy, and/or other materials known to be usable in implantable defibrillation electrodes. Since electrodes  62 ,  64 ,  66  are not generally configured to deliver pacing therapy, any of electrodes  62 ,  64 ,  66  may be used to sense electrical activity and may be used in combination with any of electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 . In at least one embodiment, the RV elongated electrode  62  may be used to sense electrical activity of a patient&#39;s heart during the delivery of pacing therapy (e.g., in combination with the housing electrode  58 , or defibrillation electrode-to-housing electrode vector). 
     The configuration of the illustrative therapy system  10  illustrated in  FIGS.  7 - 9    is merely one example. In other examples, the therapy system may include epicardial leads and/or patch electrodes instead of or in addition to the transvenous leads  18 ,  20 ,  22  illustrated in  FIG.  7   . Additionally, in other examples, the therapy system  10  may be implanted in/around the cardiac space without transvenous leads (e.g., leadless/wireless pacing systems) or with leads implanted (e.g., implanted transvenously or using approaches) into the left chambers of the heart (in addition to or replacing the transvenous leads placed into the right chambers of the heart as illustrated in  FIG.  7   ). Further, in one or more embodiments, the IMD  16  need not be implanted within the patient  14 . For example, the IMD  16  may deliver various cardiac therapies to the heart  12  via percutaneous leads that extend through the skin of the patient  14  to a variety of positions within or outside of the heart  12 . In one or more embodiments, the system  10  may utilize wireless pacing (e.g., using energy transmission to the intracardiac pacing component(s) via ultrasound, inductive coupling, RF, etc.) and sensing cardiac activation using electrodes on the can/housing and/or on subcutaneous leads. 
     In other examples of therapy systems that provide electrical stimulation therapy to the heart  12 , such therapy systems may include any suitable number of leads coupled to the IMD  16 , and each of the leads may extend to any location within or proximate to the heart  12 . For example, other examples of therapy systems may include three transvenous leads located as illustrated in  FIGS.  7 - 9   . Still further, other therapy systems may include a single lead that extends from the IMD  16  into the right atrium  26  or the right ventricle  28 , or two leads that extend into a respective one of the right atrium  26  and the right ventricle  28 . 
       FIG.  9 A  is a functional block diagram of one illustrative configuration of the IMD  16 . As shown, the IMD  16  may include a control module  81 , a therapy delivery module  84  (e.g., which may include a stimulation generator), a sensing module  86 , and a power source  90 . 
     The control module, or apparatus,  81  may include a processor  80 , memory  82 , and a telemetry module, or apparatus,  88 . The memory  82  may include computer-readable instructions that, when executed, e.g., by 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  may include any volatile, non-volatile, magnetic, optical, and/or electrical media, such as a random-access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAIVI), electrically-erasable programmable ROM (EEPROM), flash memory, and/or any other digital media. An illustrative capture management module may be the left ventricular capture management (LVCM) module described in U.S. Pat. No. 7,684,863 entitled “LV THRESHOLD MEASUREMENT AND CAPTURE MANAGEMENT” and issued Mar. 23, 2010, which is incorporated herein by reference in its entirety. 
     The processor  80  of the control module  81  may 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  may 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 functions attributed to the processor  80  herein may be embodied as software, firmware, hardware, or any combination thereof. 
     The control module  81  may control the therapy delivery module  84  to deliver therapy (e.g., electrical stimulation therapy such as pacing) to the heart  12  according to a selected one or more therapy programs, which may be stored in the memory  82 . More, specifically, the control module  81  (e.g., the processor  80 ) may control various parameters of the electrical stimulus delivered by the therapy delivery module  84  such as, e.g., A-V delays, V-V delays, pacing pulses with the amplitudes, pulse widths, frequency, or electrode polarities, etc., which may be specified by one or more selected therapy programs (e.g., A-V and/or V-V delay adjustment programs, pacing therapy programs, pacing recovery programs, capture management programs, etc.). As shown, the therapy delivery module  84  is electrically coupled to electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66 , e.g., via conductors of the respective lead  18 ,  20 ,  22 , or, in the case of housing electrode  58 , via an electrical conductor disposed within housing  60  of IMD  16 . Therapy delivery module  84  may 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 . 
     For example, therapy delivery module  84  may deliver pacing stimulus (e.g., pacing pulses) via ring electrodes  40 ,  44 ,  45 ,  46 ,  47 ,  48  coupled to leads  18 ,  20 ,  22  and/or helical tip electrodes  42 ,  50  of leads  18 ,  22 . Further, for example, therapy delivery module  84  may deliver defibrillation shocks to heart  12  via at least two of electrodes  58 ,  62 ,  64 ,  66 . In some examples, therapy delivery module  84  may be configured to deliver pacing, cardioversion, or defibrillation stimulation in the form of electrical pulses. In other examples, therapy delivery module  84  may be configured deliver one or more of these types of stimulation in the form of other signals, such as sine waves, square waves, and/or other substantially continuous time signals. 
     The IMD  16  may further include a switch module  85  and the control module  81  (e.g., the processor  80 ) may use the switch module  85  to select, e.g., via a data/address bus, which of the available electrodes are used to deliver therapy such as pacing pulses for pacing therapy, or which of the available electrodes are used for sensing. The switch module  85  may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple the sensing module  86  and/or the therapy delivery module  84  to one or more selected electrodes. More specifically, the therapy delivery module  84  may include a plurality of pacing output circuits. Each pacing output circuit of the plurality of pacing output circuits may be selectively coupled, e.g., using the switch module  85 , to one or more of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66  (e.g., a pair of electrodes for delivery of 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 the therapy delivery module using the switching module  85 . 
     The sensing module  86  is coupled (e.g., electrically coupled) to sensing apparatus, which may include, among additional sensing apparatus, the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66  to monitor electrical activity of the heart  12 , e.g., electrocardiogram (ECG)/electrogram (EGM) signals, etc. The ECG/EGM signals may be used to measure or monitor activation times (e.g., ventricular activations times, etc.), heart rate (HR), heart rate variability (HRV), heart rate turbulence (HRT), deceleration/acceleration capacity, deceleration sequence incidence, T-wave alternans (TWA), P-wave to P-wave intervals (also referred to as the P-P intervals or A-A intervals), R-wave to R-wave intervals (also referred to as the R-R intervals or V-V intervals), P-wave to QRS complex intervals (also referred to as the P-R intervals, A-V intervals, or P-Q intervals), QRS-complex morphology, ST segment (i.e., the segment that connects the QRS complex and the T-wave), T-wave changes, QT intervals, electrical vectors, etc. 
     The switch module  85  may also be used with the sensing module  86  to select which of the available electrodes are used, or enabled, to, e.g., sense electrical activity of the patient&#39;s heart (e.g., one or more electrical vectors of the patient&#39;s heart using any combination of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66 ). Likewise, the switch module  85  may also be used with the sensing module  86  to select which of the available electrodes are not to be used (e.g., disabled) to, e.g., sense electrical activity of the patient&#39;s heart (e.g., one or more electrical vectors of the patient&#39;s heart using any combination of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66 ), etc. In some examples, the control module  81  may select the electrodes that function as sensing electrodes via the switch module within the sensing module  86 , e.g., by providing signals via a data/address bus. 
     In some examples, sensing module  86  includes a channel that includes an amplifier with a relatively wider pass band than the R-wave or P-wave amplifiers. Signals from the selected sensing electrodes may be provided to a multiplexer, and thereafter converted to multi-bit digital signals by an analog-to-digital converter for storage in memory  82 , e.g., as an electrogram (EGM). In some examples, the storage of such EGMs in memory  82  may be under the control of a direct memory access circuit. 
     In some examples, the control module  81  may operate as an interrupt-driven device and may be responsive to interrupts from pacer timing and control module, where the interrupts may correspond to the occurrences of sensed P-waves and R-waves and the generation of cardiac pacing pulses. Any necessary mathematical calculations may be performed by the processor  80  and any updating of the values or intervals controlled by the pacer timing and control module may take place following such interrupts. A portion of memory  82  may be configured as a plurality of recirculating buffers, capable of holding one or more series of measured intervals, which may be analyzed by, e.g., the processor  80  in response to the occurrence of a pace or sense interrupt to determine whether the patient&#39;s heart  12  is presently exhibiting atrial or ventricular tachyarrhythmia. 
     The telemetry module  88  of the control module  81  may 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  may receive downlink telemetry from and send uplink telemetry to a programmer with the aid of an antenna, which may be internal and/or external. The processor  80  may provide the data to be uplinked to a programmer and the 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  may provide received data to the processor  80  via a multiplexer. 
     The various components of the IMD  16  are further coupled to a power source  90 , which may include a rechargeable or non-rechargeable battery. A non-rechargeable battery may be selected to last for several years, while a rechargeable battery may be inductively charged from an external device, e.g., on a daily or weekly basis. 
       FIG.  9 B  is another embodiment of a functional block diagram for IMD  16  that depicts bipolar RA lead  22 , bipolar RV lead  18 , and bipolar LV CS lead  20  without the LA CS pace/sense electrodes and coupled with an implantable pulse generator (IPG) circuit  31  having programmable modes and parameters of a bi-ventricular DDD/R type known in the pacing art. In turn, the sensor signal processing circuit  91  indirectly couples to the timing circuit  43  and via data and control bus to microcomputer circuitry  33 . The IPG circuit  31  is illustrated in a functional block diagram divided generally into a microcomputer circuit  33  and a pacing circuit  21 . The pacing circuit  21  includes the digital controller/timer circuit  43 , the output amplifiers circuit  51 , the sense amplifiers circuit  55 , the RF telemetry transceiver  41 , the activity sensor circuit  35  as well as a number of other circuits and components described below. 
     Crystal oscillator circuit  89  provides the basic timing clock for the pacing circuit  21  while battery  29  provides power. Power-on-reset circuit  87  responds to initial connection of the circuit to the battery for defining an initial operating condition and similarly, resets the operative state of the device in response to detection of a low battery condition. Reference mode circuit  37  generates stable voltage reference and currents for the analog circuits within the pacing circuit  21 . Analog-to-digital converter (ADC) and multiplexer circuit  39  digitize analog signals and voltage to provide, e.g., real time telemetry of cardiac signals from sense amplifiers  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  may correspond to any of those used in illustrative implantable cardiac pacemakers. 
     If the IPG is programmed to a rate responsive mode, the signals output by one or more physiologic sensors are employed as a rate control parameter (RCP) to derive a physiologic escape interval. For example, the escape interval is adjusted proportionally to the patient&#39;s activity level developed in the patient activity sensor (PAS) circuit  35  in the depicted, illustrative IPG circuit  31 . The patient activity sensor  27  is coupled to the IPG housing and may take the form of a piezoelectric crystal transducer. The output signal of the patient activity sensor  27  may be processed and used as an RCP. Sensor  27  generates electrical signals in response to sensed physical activity that are processed by activity circuit  35  and provided to digital controller/timer circuit  43 . Activity circuit  35  and associated sensor  27  may correspond to the circuitry disclosed in U.S. Pat. No. 5,052,388 entitled “METHOD AND APPARATUS FOR IMPLEMENTING ACTIVITY SENSING IN A PULSE GENERATOR” and issued on Oct. 1, 1991 and U.S. Pat. No. 4,428,378 entitled “RATE ADAPTIVE PACER” and issued on Jan. 31, 1984, each of which is incorporated herein by reference in its entirety. Similarly, the illustrative systems, apparatus, and methods described herein may be practiced in conjunction with alternate types of sensors such as oxygenation sensors, pressure sensors, pH sensors, and respiration sensors, for use in providing rate responsive pacing capabilities. Alternately, QT time may be used as a rate indicating parameter, in which case no extra sensor is required. Similarly, the illustrative embodiments described herein may also be practiced in non-rate responsive pacemakers. 
     Data transmission to and from the external programmer is accomplished by way of the telemetry antenna  57  and an associated RF transceiver  41 , which serves both to demodulate received downlink telemetry and to transmit uplink telemetry. Uplink telemetry capabilities may include the ability to transmit stored digital information, e.g., operating modes and parameters, EGM histograms, and other events, as well as 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 ventricle. 
     Microcomputer  33  contains a microprocessor  80  and associated system clock and on-processor RAM and ROM chips  82 A and  82 B, respectively. In addition, microcomputer circuit  33  includes a separate RAM/ROM chip  82 C to provide additional memory capacity. Microprocessor  80  normally operates in a reduced power consumption mode and is interrupt driven. Microprocessor  80  is awakened in response to defined interrupt events, which may include A-TRIG, RV-TRIG, LV-TRIG signals generated by timers in digital timer/controller circuit  43  and A-EVENT, RV-EVENT, and LV-EVENT signals generated by sense amplifiers circuit  55 , among others. The specific values of the intervals and delays timed out by digital controller/timer circuit  43  are controlled by the microcomputer circuit  33  by way of data and control bus from programmed-in parameter values and operating modes. In addition, if programmed to operate as a rate responsive pacemaker, a timed interrupt, e.g., every cycle or every two seconds, may be provided in order to allow the microprocessor to analyze the activity sensor data and update the basic A-A, V-A, or V-V escape interval, as applicable. In addition, the microprocessor  80  may also serve to define variable, operative A-V delay intervals, V-V delay intervals, and the energy delivered to each ventricle and/or atrium. 
     In one embodiment, microprocessor  80  is a custom microprocessor adapted to fetch and execute instructions stored in RAM/ROM unit  82  in a conventional manner. It is contemplated, however, that other implementations may be suitable to practice the present disclosure. For example, an off-the-shelf, commercially available microprocessor or microcontroller, or custom application-specific, hardwired logic, or state-machine type circuit may perform the functions of microprocessor  80 . 
     Digital controller/timer circuit  43  operates under the general control of the microcomputer  33  to control timing and other functions within the pacing circuit  21  and includes a set of timing and associated logic circuits of which certain ones pertinent to the present disclosure are depicted. The depicted timing circuits include URI/LRI timers  83 A, V-V delay timer  83 B, intrinsic interval timers  83 C for timing elapsed V-EVENT to V-EVENT intervals or V-EVENT to A-EVENT intervals or the V-V conduction interval, escape interval timers  83 D for timing A-A, V-A, and/or V-V pacing escape intervals, an A-V delay interval timer  83 E for timing the A-LVp delay (or A-RVp delay) from a preceding A-EVENT or A-TRIG, a post-ventricular timer  83 F for timing post-ventricular time periods, and a date/time clock  83 G. 
     The A-V delay interval timer  83 E is loaded with an appropriate delay interval for one ventricular chamber (e.g., either an A-RVp delay or an A-LVp) to time-out starting from a preceding A-PACE or A-EVENT. The interval timer  83 E triggers pacing stimulus delivery and can be based on one or more prior cardiac cycles (or from a data set empirically derived for a given patient). 
     The post-event timer  83 F times out the post-ventricular time period following an RV-EVENT or LV-EVENT or a RV-TRIG or LV-TRIG and post-atrial time periods following an A-EVENT or A-TRIG. The durations of the post-event time periods may also be selected as programmable parameters stored in the microcomputer  33 . The post-ventricular time periods include the 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 periods can be suitably defined depending, at least in part, on the operative 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 starting of the post-atrial time periods and the A-V delays can be commenced substantially simultaneously with the start or end of each A-EVENT or A-TRIG or, in the latter case, upon the end of the A-PACE which may follow the A-TRIG. Similarly, the starting of the post-ventricular time periods and the V-A escape interval can be commenced substantially simultaneously with the start or end of the V-EVENT or V-TRIG or, in the latter case, upon the end of the V-PACE which may follow the V-TRIG. The microprocessor  80  also optionally calculates A-V delays, V-V delays, post-ventricular time periods, and post-atrial time periods that vary with the sensor-based escape interval established in response to the RCP(s) and/or with the intrinsic atrial and/or ventricular rate. 
     The output amplifiers circuit  51  contains a RA pace pulse generator (and a LA pace pulse generator if LA pacing is provided), a RV pace pulse generator, a LV pace pulse generator, and/or any other pulse generator configured to provide atrial and ventricular pacing. In order to trigger generation of an RV-PACE or LV-PACE pulse, digital controller/timer circuit  43  generates the RV-TRIG signal at the time-out of the A-RVp delay (in the case of RV pre-excitation) or the LV-TRIG at the time-out of the A-LVp delay (in the case of LV pre-excitation) provided by A-V delay interval timer  83 E (or the V-V delay timer  83 B). Similarly, digital controller/timer circuit  43  generates an RA-TRIG signal that triggers output of an RA-PACE pulse (or an LA-TRIG signal that triggers output of an LA-PACE pulse, if provided) at the end of the V-A escape interval timed by escape interval timers  83 D. 
     The output amplifiers circuit  51  includes switching circuits for coupling selected pace electrode pairs from among the lead conductors and the IND-CAN electrode  21  to the RA pace pulse generator (and LA pace pulse generator if provided), RV pace pulse generator and LV pace pulse generator. Pace/sense electrode pair selection and control circuit  53  selects lead conductors and associated pace electrode pairs to be coupled with the atrial and ventricular output amplifiers within output amplifiers circuit  51  for accomplishing RA, LA, RV and LV pacing. 
     The sense amplifiers circuit  55  contains sense amplifiers for atrial and ventricular pacing and sensing. High impedance P-wave and R-wave sense amplifiers may be used to amplify a voltage difference signal that is generated across the sense electrode pairs by the passage of cardiac depolarization wavefronts. The high impedance sense amplifiers use high gain to amplify the low amplitude signals and rely on pass band filters, time domain filtering and amplitude threshold comparison to discriminate a P-wave or R-wave from background electrical noise. Digital controller/timer circuit  43  controls sensitivity settings of the atrial and ventricular sense amplifiers  55 . 
     The sense amplifiers may be uncoupled from the sense electrodes during the blanking periods before, during, and after delivery of a pace pulse to any of the pace electrodes of the pacing system to avoid saturation of the sense amplifiers. The sense amplifiers circuit  55  includes blanking circuits for uncoupling the selected pairs of the lead conductors and the IND-CAN electrode  21  from the inputs of the RA sense amplifier (and LA sense amplifier if provided), RV sense amplifier and LV sense amplifier during the ABP, PVABP and VBP. The sense amplifiers circuit  55  also includes switching circuits for coupling selected sense electrode lead conductors and the IND-CAN electrode  21  to the RA sense amplifier (and LA sense amplifier if provided), RV sense amplifier and LV sense amplifier. Again, sense electrode selection and control circuit  53  selects conductors and associated sense electrode pairs to be coupled with the atrial and ventricular sense amplifiers within the output amplifiers circuit  51  and sense amplifiers circuit  55  for accomplishing RA, LA, RV, and LV sensing along desired unipolar and bipolar sensing vectors. 
     Right atrial depolarizations or P-waves in the RA-SENSE signal that are sensed by the RA sense amplifier result in a RA-EVENT signal that is communicated to the digital controller/timer circuit  43 . Similarly, left atrial depolarizations or P-waves in the LA-SENSE signal that are sensed by the LA sense amplifier, if provided, result in a LA-EVENT signal that is communicated to the digital controller/timer circuit  43 . Ventricular depolarizations or R-waves in the RV-SENSE signal are sensed by a ventricular sense amplifier result in an RV-EVENT signal that is communicated to the digital controller/timer circuit  43 . Similarly, ventricular depolarizations or R-waves in the LV-SENSE signal are sensed by a ventricular sense amplifier result 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 may be refractory or non-refractory and can inadvertently be triggered by electrical noise signals or aberrantly conducted depolarization waves rather than true R-waves or P-waves. 
     The techniques described in this disclosure, including those attributed to the IMD  16 , the computing apparatus  140 , and/or various constituent components, may be implemented, at least in part, in hardware, software, firmware, or any combination thereof. For example, various aspects of the techniques may 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 devices, or other devices. The term “module,” “processor,” or “processing circuitry” may generally refer to any of the foregoing logic circuitry, alone or in combination with other logic circuitry, or any other equivalent circuitry. 
     Such hardware, software, and/or firmware may 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 may 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 may be performed by separate hardware or software components or integrated within common or separate hardware or software components. 
     When implemented in software, the functionality ascribed to the systems, devices and techniques described in this disclosure may 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, or the like. The instructions may be executed by processing circuitry and/or one or more processors to support one or more aspects of the functionality described in this disclosure. 
     Illustrative Embodiments 
     Embodiment 1. A system for use in cardiac therapy evaluation comprising:
         electrode apparatus comprising a plurality of external electrodes to monitor electrical activity from tissue of a patient; and   a computing apparatus comprising processing circuitry and operably coupled to the electrode apparatus, the computing apparatus configured to:   monitor electrical activity using the plurality of external electrodes,   generate electrical heterogeneity information (EHI) based on the monitored electrical activity,   initiate delivery of pacing therapy using a plurality of different pacing vectors, wherein each different pacing vector uses a combination of pacing electrodes different from the remaining different pacing vectors,   select one or more of the plurality of different pacing vectors based on the generated EHI from the electrical activity monitored during the delivery of pacing therapy using a plurality of different pacing vectors,   initiate delivery of pacing therapy using the one or more selected different pacing vectors and a plurality of different settings of a pacing parameter, and   identify one or more of the plurality of different settings of the pacing parameter based on the generated EHI from the electrical activity monitored during delivery of pacing therapy using the one or more selected different pacing vectors and the plurality of different settings of the pacing parameters.       

     Embodiment 2. A method for use in cardiac therapy evaluation comprising:
         monitoring electrical activity using a plurality of external electrodes from tissue of a patient;   generating electrical heterogeneity information (EHI) based on the monitored electrical activity;   initiating delivery of pacing therapy using a plurality of different pacing vectors, wherein each different pacing vector uses a combination of pacing electrodes different from the remaining different pacing vectors;   selecting one or more of the plurality of different pacing vectors based on the generated EHI from the electrical activity monitored during the delivery of pacing therapy using a plurality of different pacing vectors;   initiating delivery of pacing therapy using the one or more selected different pacing vectors and a plurality of different settings of a pacing parameter; and   identifying one or more of the plurality of different settings of the pacing parameter based on the generated EHI from the electrical activity monitored during delivery of pacing therapy using the one or more selected different pacing vectors and the plurality of different settings of the pacing parameters.       

     Embodiment 3: The system or method of any one of embodiments 1-2, wherein the EHI comprises a standard deviation of electrical activation times monitored by the plurality of external electrodes. 
     Embodiment 4: The system or method of any one of embodiments 1-3, wherein the plurality of different paced settings comprises a plurality of different A-V and/or V-V timings. 
     Embodiment 5: The system or method of embodiment 4, wherein the plurality of different A-V timings are between 40% of the patient&#39;s intrinsic A-V delay and 80% of the patient&#39;s intrinsic A-V delay. 
     Embodiment 6: The system or method of any one of embodiments 1-5, wherein the pacing parameter comprises one of A-V timing and V-V timing, wherein initiating delivery of pacing therapy using the one or more selected different pacing vectors and a plurality of different settings of the pacing parameter and identifying one or more of the plurality of different settings of the pacing parameter based on the generated EHI from the electrical activity monitored during delivery of pacing therapy using the one or more selected different pacing vectors and a plurality of different settings of the pacing parameter comprises:
         initiating the delivery of pacing therapy using the one or more selected pacing vectors and a subset of a plurality of different time values for the pacing parameter;   selecting a time value of the subset of the plurality of different time values for the pacing parameter based on the generated EHI from the electrical activity monitored during delivery of pacing therapy using the one or more selected different pacing vectors and the subset of the plurality of different time values for the pacing parameter;   initiating the delivery of pacing therapy using the one or more selected pacing vectors and a proximal set of different time values for the pacing parameter within a selected range of the selected time value; and   identifying one or more of the proximal set of different time values for the pacing parameter based on the generated EHI from the electrical activity monitored during delivery of pacing therapy using the one or more selected different pacing vectors and the proximal set of different time values for the pacing parameter within a selected range of the selected time value.       

     Embodiment 7: The system or method of any one of embodiments 1-6, wherein the pacing parameter comprises one of A-V timing and V-V timing, wherein initiating delivery of pacing therapy using the one or more selected different pacing vectors and a plurality of different settings of the pacing parameter comprises:
         initiating the delivery of pacing therapy using the one or more selected pacing vectors and a time value for the pacing parameter;   increasing the time value by a selected increment;   increasing the selected increment if the monitored electrical activity indicates that the time value is less effective than previously monitored; and   decreasing the selected increment if the monitored electrical activity indicates that time value is more effective than previously monitored.       

     Embodiment 8: The system or method of any one of embodiments 1-7, wherein the computing apparatus is further configured to execute or the method further comprises:
         disqualify any pacing electrodes for use in providing the plurality of different pacing vectors that stimulates the phrenic nerve.       

     Embodiment 9: The system or method of any one of embodiments 1-8, wherein the computing apparatus is further configured to execute or the method further comprises:
         disqualify any pacing electrodes for use in providing the plurality of different pacing vectors that exceeds a selected capture threshold.       

     Embodiment 10: The system or method of any one of embodiments 1-9, wherein delivery of pacing therapy using a plurality of different pacing vectors comprises delivery of pacing therapy using a selected A-V timing if the patient has an atrioventricular block. 
     Embodiment 11: The system or method of any one of embodiments 1-10, wherein selecting one or more of the plurality of different pacing vectors based on the generated EHI from the electrical activity monitored during the delivery of pacing therapy using a plurality of different pacing vectors comprises selecting a single different pacing vector. 
     Embodiment 12: The system or method of any one of embodiments 1-11, wherein the computing apparatus is further configured to execute or the method further comprises:
         halting initiation of delivery of pacing therapy if generated EHI is greater than a selected threshold; and   identifying the paced vector and paced settings using during the monitoring of the electrical activity that resulted in the EHI being halted.       

     Embodiment 13: The system or method of any one of embodiments 1-12, wherein the computing apparatus is further configured to execute or the method further comprises removing A-V timing from the plurality of difference paced settings in response to an indication of atrial fibrillation or atrial tachycardia. 
     Embodiment 14: A system for use in cardiac therapy evaluation comprising:
         electrode apparatus comprising a plurality of external electrodes to monitor electrical activity from tissue of a patient; and   a computing apparatus comprising processing circuitry and operably coupled to the electrode apparatus, the computing apparatus configured to:   monitor electrical activity using the plurality of external electrodes,   generate electrical heterogeneity information (EHI) based on the monitored electrical activity,   initiate delivery of pacing therapy using a first parameter at a plurality of different first settings,   select one or more of the plurality of different first settings for the first parameter based on the generated EHI from the electrical activity monitored during the delivery of pacing therapy using the plurality of different first settings,   initiate delivery of pacing therapy using the one or more selected different first settings and a second parameter at a plurality of different second settings, and   identify one or more of the plurality of different second setting values based on the generated EHI from the electrical activity monitored during delivery of pacing therapy using the one or more selected different first settings and the plurality of different second settings.       

     This disclosure has been provided with reference to illustrative embodiments and is not meant to be construed in a limiting sense. As described previously, one skilled in the art will recognize that other various illustrative applications may use the techniques as described herein to take advantage of the beneficial characteristics of the apparatus and methods described herein. Various modifications of the illustrative embodiments, as well as additional embodiments of the disclosure, will be apparent upon reference to this description.