Patent Publication Number: US-10780281-B2

Title: Evaluation of ventricle from atrium pacing therapy

Description:
The disclosure herein relates to systems and methods for use in the evaluation of ventricle from atrium (VfA) pacing therapy. 
     SUMMARY 
     The exemplary systems, methods, and interfaces described herein may be configured to assist a user (e.g., a physician) in evaluating a patient and/or evaluating cardiac therapy (e.g., cardiac therapy being performed on a patient during and/or after implantation of cardiac therapy apparatus). The cardiac therapy can be a ventricle from atrium (VfA) cardiac therapy, including single or multiple chamber pacing (e.g., dual or triple chamber pacing), atrioventricular synchronous pacing, asynchronous pacing, triggered pacing, cardiac resynchronization pacing, or tachycardia-related therapy. In one or more embodiments, the systems, methods, and interfaces may be described as being noninvasive. For example, in some embodiments, the systems, methods, and interfaces 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 the patient and/or cardiac therapy. Instead, the systems, methods, and interfaces 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. 
     In at least one embodiment, the exemplary systems and methods can include monitoring electrical activity of a patient to determine electrical heterogeneity information associated with the patient&#39;s cardiac activity. The electrical heterogeneity information can be used to determine whether a paced setting is acceptable for delivering ventricle from atrium (VfA) pacing therapy. In response to the paced setting being unacceptable, additional monitoring and determinations of electrical heterogeneity information can be performed using a variety of paced settings in order to determine which of the paced settings are acceptable. 
     One exemplary system may include an electrode apparatus. The electrode apparatus can include a plurality of external electrodes to monitor electrical activity from tissue of a patient. The exemplary system can further include a computing apparatus. The computing apparatus can include processing circuitry and can be coupled to the electrode apparatus. The computing apparatus can be configured to monitor electrical activity using the plurality of external electrodes. The computing apparatus can be further configured to generate paced (e.g., ventricle from atrium pacing) electrical heterogeneity information based on the monitored electrical activity during delivery of VfA pacing therapy at one or more VfA paced settings. The paced electrical heterogeneity information can be representative of at least one of mechanical cardiac functionality and electrical cardiac functionality. The computing apparatus can be further configured to determine whether one or more of the VfA paced settings for the VfA pacing therapy are acceptable based on the electrical heterogeneity information. 
     In at least one embodiment, an exemplary method can include monitoring electrical activity from tissue of a patient using a plurality of external electrodes. The method can further include generating paced electrical heterogeneity information based on the monitored electrical activity during delivery of VfA pacing therapy at one or more VfA paced settings. The paced electrical heterogeneity information can be representative of at least one of mechanical cardiac functionality and electrical cardiac functionality. The method can further include determining whether the one or more VfA paced settings associated with the pacing therapy are acceptable based on the paced electrical heterogeneity information. 
     In at least one embodiment, an exemplary system can include an electrode apparatus. The electrode apparatus can include a plurality of external electrodes to monitor electrical activity from tissue of a patient. The exemplary system can include computing apparatus. The computing apparatus can include processing circuitry and can be coupled to the electrode apparatus. The computing apparatus can be configured to monitor electrical activity using the plurality of external electrodes during delivery of VfA pacing therapy and to generate electrical heterogeneity information during delivery of VfA pacing therapy. The computing apparatus can be further configured to determine whether a VfA paced setting for the VfA pacing therapy is acceptable based on the electrical heterogeneity information generated from the electrical activity using the VfA paced setting and to adjust the paced setting for the VfA pacing therapy based on whether the VfA pacing therapy is acceptable. 
     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 exemplary system including electrode apparatus, display apparatus, and computing apparatus. 
         FIGS. 2-3  are diagrams of exemplary external electrode apparatus for measuring torso-surface potentials. 
         FIG. 4  is a block diagram of an exemplary method of evaluation of ventricle from atrium pacing therapy. 
         FIG. 5  is a block diagram of another exemplary method of evaluation of ventricle from atrium pacing therapy. 
         FIG. 6  is a block diagram of another exemplary method of evaluation of ventricle from atrium pacing therapy. 
         FIG. 7  is a block diagram of another exemplary method of evaluation of ventricle from atrium pacing therapy. 
         FIG. 8  is a conceptual diagram of an illustrative cardiac therapy system including an intracardiac medical device implanted in a patient&#39;s heart and a separate medical device positioned outside of the patient&#39;s heart. 
         FIG. 9  is an enlarged conceptual diagram of the intracardiac medical device of  FIG. 8  and anatomical structures of the patient&#39;s heart according to one example. 
         FIG. 10  is a perspective view of the intracardiac medical device of  FIGS. 8-9  having a distal fixation and electrode assembly that includes a distal housing-based electrode implemented as a ring electrode. 
         FIG. 11  is a block diagram of illustrative circuitry that may be enclosed within a housing of the intracardiac medical device of  FIGS. 8-10 , for example, to provide the functionality and therapy described herein. 
         FIG. 12  is a perspective view of an exemplary intracardiac medical device according to another example for use with, e.g., the exemplary system of  FIG. 8 . 
         FIG. 13  is a conceptual diagram of a map of a patient&#39;s heart in a standard seventeen ( 17 ) segment view of the left ventricle showing various electrode implantation locations for use with, e.g., the exemplary system and devices of  FIGS. 8-12 . 
     
    
    
     DETAILED DESCRIPTION OF EXEMPLARY 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. 
     Exemplary systems and methods shall be described with reference to  FIGS. 1-13 . 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 methods and systems 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. 
     Cardiac electrical heterogeneity information can be detected or estimated in proximity of a reference location (e.g., which can be a chosen location for implantation of a pacing lead or leadless device for ventricle from atrium pacing cardiac therapy) using unipolar electrocardiogram (ECG) recordings. Such electrical heterogeneity information may be measured and displayed, or conveyed, to an implanter by a system which acquires the ECG signals and generates various metrics of electrical heterogeneity, such as activation times (e.g., depolarization) measured from various ECG locations. 
     Various exemplary systems, methods, and interfaces described herein 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 a patient&#39;s condition and/or ventricle from atrium (VfA) pacing cardiac therapy being performed on, or delivered to, a patient. The VfA pacing cardiac therapy can include pacing a left ventricle of a heart of a patient through an atrium of the heart. A leadless device or pacing lead can be extended (e.g., screwed) through the posterior basal right atrium (a location which can be described as close or in near proximity to the coronary sinus (CS) ostium). The leadless device or pacing lead can be implantable from the triangle of Koch region of the right atrium through the right atrial endocardium and central fibrous body to at least one of deliver cardiac therapy to and 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. In this way, as an example, a leadless pacing device (e.g., including delivering an appropriate fixation mechanism) may be thus able to sense both atrial activity as well as ventricular activity in addition to atrial-ventricular (AV) synchronous pacing. Further, this VfA pacing therapy may be used for left ventricular (LV) resynchronization for heart failure patients with a left bundle branch block (LBBB). In this case, the VfA pacing therapy may enable easier access to left ventricular endocardium without exposing the leadless pacing device or pacing lead to endocardial blood pool. At the same time, the VfA pacing therapy can help engage part of the conduction system of the heart to potentially correct LBBB and more effectively resynchronize the patient&#39;s heart. 
     The present disclosure can include an implantable medical device including a tissue-piercing electrode and optionally a right atrial electrode and/or a right atrial motion detector. The tissue-piercing electrode may be implanted in the basal and/or septal region of the left ventricular myocardium of the patient&#39;s heart from the triangle of Koch region of the right atrium through the right atrial endocardium and central fibrous body. In a leadless implantable medical device, the tissue-piercing electrode may leadlessly extend from a distal end region of a housing of the device, and the right atrial electrode may be leadlessly coupled to the housing (e.g., part of or positioned on the exterior of). The right atrial motion detector may be within the implantable medical device. In a leaded implantable medical device, one or more of the electrodes may be coupled to the housing using an implantable lead. When the device is implanted, the electrodes may be used to sense electrical activity in one or more atria and/or ventricles of a patient&#39;s heart. The motion detector may be used to sense mechanical activity in one or more atria and/or ventricles of the patient&#39;s heart. In particular, the activity of the right atrium and the left ventricle may be monitored and, optionally, the activity of the right ventricle may be monitored. The electrodes may be used to deliver cardiac therapy, such as single- or multi-chamber pacing for atrial fibrillation, atrioventricular synchronous pacing for bradycardia, asynchronous pacing, triggered pacing, cardiac resynchronization pacing for ventricular dyssynchrony, anti-tachycardia pacing, or shock therapy. Shock therapy may be initiated by the implantable medical device. A separate medical device, such as an extravascular ICD, which may also be implanted, may be in operative communication with the implantable medical device and may deliver an electrical shock in response to a trigger, such as a signaling pulse (e.g., triggering, signaling, or distinctive electrical pulse) provided by the device. 
     Reference will now be made to the drawings, which depict one or more aspects described in this disclosure. However, it will be understood that other aspects not depicted in the drawings fall within the scope of this disclosure. Like numbers used in the figures refer to like components, steps, and the like. However, it will be understood that the use of a reference character to refer to an element in a given figure is not intended to limit the element in another figure labeled with the same reference character. In addition, the use of different reference characters to refer to elements in different figures is not intended to indicate that the differently referenced elements cannot be the same or similar. 
     An exemplary system  100  including electrode apparatus  110 , display apparatus  130 , and computing apparatus  140  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  120 . 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. Exemplary electrode apparatus may be described in U.S. Pat. No. 9,320,446 entitled “Bioelectric Sensor Device and Methods” and issued on Apr. 26, 2016, which is incorporated herein by reference in its entirety. Further, exemplary electrode apparatus  110  will be described in more detail in reference to  FIGS. 2-3 . 
     Although not described herein, the exemplary 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 exemplary systems, methods, and interfaces described herein may further use imaging apparatus to provide noninvasive assistance to a user (e.g., a physician) to locate and position a device to deliver VfA cardiac pacing therapy and/or to locate or select a pacing electrode or pacing vector proximate the patient&#39;s heart for Ventricle from atrium pacing therapy in conjunction with the evaluation of Ventricle from atrium pacing therapy. 
     For example, the exemplary systems, methods, and interfaces may provide image guided navigation that may be used to navigate leads including leadless devices, electrodes, leadless electrodes, wireless electrodes, catheters, etc., within the patient&#39;s body while also providing noninvasive cardiac therapy evaluation including determining whether a ventricle from atrium (VfA) paced setting is acceptable or determining whether one or more selected parameters are acceptable, such as selected location information (e.g., location information for the electrodes to target a particular location in the left ventricle). Exemplary systems and methods that use imaging apparatus and/or electrode apparatus may be described in U.S. Patent Publication No. 2014/0371832 filed on Jun. 12, 2013 and entitled “Implantable Electrode Location Selection,” U.S. Patent Publication No. 2014/0371833 filed on Jun. 12, 2013 and entitled “Implantable Electrode Location Selection,” U.S. Patent Publication No. 2014/0323892 filed on Mar. 27, 2014 and entitled “Systems, Methods, and Interfaces for Identifying Effective Electrodes,” U.S. Patent Publication No. 2014/0323882 filed on Mar. 27, 2014 and entitled “Systems, Methods, and Interfaces for Identifying Optical Electrical Vectors,” each of which is incorporated herein by reference in its entirety. 
     Exemplary 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 (MRI), 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. 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 treatment apparatus proximate target locations (e.g., such as locations within the left ventricle, including a selected location within the high posterior basal and/or septal area of the left ventricular cavity) within the heart or other areas of interest. 
     Systems and/or imaging apparatus that may be used in conjunction with the exemplary 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. App. Pub. No. 2011/0112398 to Zarkh et al. published on May 12, 2011, U.S. Pat. App. Pub. No. 2013/0116739 to Brada et al. published on May 9, 2013, 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 display apparatus  130  and the computing apparatus  140  may be configured to display and analyze data such as, e.g., electrical signals (e.g., electrocardiogram data), cardiac information representative of at least one of mechanical cardiac functionality and electrical cardiac functionality, etc. Cardiac information may include, e.g., electrical heterogeneity information or electrical dyssynchrony information, surrogate electrical activation information or data, etc. that is generated using electrical signals gathered, monitored, or collected, using the electrode apparatus  110 . In at least one embodiment, the computing apparatus  140  may be a server, a personal computer, or a tablet computer. The computing apparatus  140  may be configured to receive input from input apparatus  142  and transmit output to the display apparatus  130 . Further, the computing apparatus  140  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 driving a graphical user interface configured to noninvasively assist a user in targeting placement of a pacing device and/or evaluating pacing therapy at that location (e.g., the location of an implantable electrode used for pacing, the location of pacing therapy delivered by a particular pacing vector, 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 . For example, the computing apparatus  140  may be electrically coupled to each of the input apparatus  142  and the display apparatus  130  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  to manipulate, or modify, one or more graphical depictions displayed on the display apparatus  130  and to view and/or select one or more pieces of information related to the cardiac therapy. 
     Although as depicted the input apparatus  142  is a keyboard, it is to be understood that the input apparatus  142  may include any apparatus capable of providing input to the computing apparatus  140  to perform the functionality, methods, and/or logic described herein. For example, the input apparatus  142  may include a mouse, a trackball, a touchscreen (e.g., capacitive touchscreen, a resistive touchscreen, a multi-touch touchscreen, etc.), etc. Likewise, the display apparatus  130  may include any apparatus capable of displaying information to a user, such as a graphical user interface  132  including cardiac information, textual instructions, graphical depictions of electrical activation information, graphical depictions of anatomy of a human heart, images or graphical depictions of the patient&#39;s heart, graphical depictions of a leadless pacing device being positioned or placed to provide VfA pacing therapy, 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  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  may include programs or routines for computational mathematics, matrix mathematics, dispersion determinations (e.g. standard deviations, variances, ranges, interquartile ranges, mean absolute differences, average absolute deviations, etc.), filtering algorithms, maximum value determinations, minimum value determinations, threshold determinations, moving windowing algorithms, 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 required to implement one or more exemplary methods and/or processes described herein. Data stored and/or used by the computing apparatus  140  may include, for example, electrical signal/waveform data from the electrode apparatus  110 , dispersions signals, windowed dispersions signals, parts or portions of various signals, electrical activation times from the electrode apparatus  110 , 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, cardiac information, etc.), or any other data that may be necessary for carrying out the one and/or more processes or methods described herein. 
     In one or more embodiments, the exemplary 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 exemplary systems, methods, and/or 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 exemplary systems, methods, and/or 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, is operable to perform operations such as the methods, processes, and/or functionality described herein. 
     The computing apparatus  140  may be, for example, any fixed or mobile computer system (e.g., a controller, a microcontroller, a personal computer, minicomputer, tablet computer, etc.) and may be generally described as including processing circuitry. The exact configuration of the computing apparatus  140  is not limiting, and essentially any device capable of providing suitable computing capabilities and control capabilities (e.g., 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 medium such as a disk or tape, etc.) containing digital bits (e.g., encoded in binary, trinary, etc.) that may be readable and/or writeable by computing apparatus  140  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. 
     Electrical activation times of the patient&#39;s heart may be useful to evaluate a patient&#39;s cardiac condition and/or ventricle from atrium (VfA) cardiac therapy being delivered to a patient. Surrogate electrical activation information or data of one or more regions of a patient&#39;s heart may be monitored, or determined, using electrode apparatus  110  as shown in  FIG. 1  and in  FIG. 2-3 . The exemplary electrode apparatus  110  may be configured to measure body-surface potentials of a patient  120  and, more particularly, torso-surface potentials of a patient  120 . As shown in  FIG. 2 , the exemplary electrode apparatus  110  may include a set, or array, of electrodes  112 , a strap  113 , and interface/amplifier circuitry  116 . In at least one embodiment, a portion of the set of electrodes may be used wherein the portion corresponds to a particular location on the patient&#39;s heart. 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  120  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  120 , including the posterior, lateral, posterolateral, anterolateral, and anterior locations of the torso of a patient  120 . 
     Further, the electrodes  112  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 provide the signals to the computing apparatus  140 . Other exemplary systems may use a wireless connection to transmit the signals sensed by electrodes  112  to the interface/amplifier circuitry  116  and, in turn, the computing apparatus  140 , e.g., as channels of data. For example, the interface/amplifier circuitry  116  may be electrically coupled to each of the computing apparatus  140  and the display apparatus  130  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 . In some examples, the strap  113  may include an elastic band, strip of tape, or cloth. In other examples, the electrodes  112  may be placed individually on the torso of a patient  120 . Further, in other examples, electrodes  112  (e.g., arranged in an array) may be part of, or located within, patches, vests, and/or other manners of securing the electrodes  112  to the torso of the patient  120 . 
     The electrodes  112  may be configured to surround the heart of the patient  120  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  120 . 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  spatially distributed around the torso of patient. Other configurations may have more or fewer electrodes  112 . 
     The computing apparatus  140  may record and analyze the electrical activity (e.g., torso-surface potential signals) sensed by electrodes  112  and amplified/conditioned by the interface/amplifier circuitry  116 . The computing apparatus  140  may be configured to analyze the signals from the electrodes  112  to provide as anterior and posterior electrode signals and surrogate cardiac electrical activation times, e.g., representative of actual, or local, electrical activation times of one or more regions of the patient&#39;s heart as will be further described herein. The computing apparatus  140  may be configured to analyze the signals from the electrodes  112  to provide as anterior-septal electrode signals and surrogate cardiac electrical activation times, e.g., representative of actual, or local, electrical activation times of one or more anterior-septal regions of the patient&#39;s heart, as will be further described herein, e.g., for use in evaluation of VfA pacing therapy. Further, the electrical signals measured at the left anterior surface location of a patient&#39;s torso may be representative, or surrogates, of electrical signals of the left anterior left ventricle region of the patient&#39;s heart, electrical signals measured at the left lateral surface location of a patient&#39;s torso may be representative, or surrogates, of electrical signals of the left lateral left ventricle region of the patient&#39;s heart, electrical signals measured at the left posterolateral surface location of a patient&#39;s torso may be representative, or surrogates, of electrical signals of the posterolateral left ventricle region of the patient&#39;s heart, and electrical signals measured at the posterior surface location of a patient&#39;s torso may be representative, or surrogates, of electrical signals of the posterior left ventricle region of the patient&#39;s heart. In one or more embodiments, measurement of activation times can be performed by measuring the period of time between an onset of cardiac depolarization (e.g., onset of QRS complex) and an appropriate fiducial point such as, e.g., a peak value, a minimum value, a minimum slope, a maximum slope, a zero crossing, a threshold crossing, etc. 
     Additionally, the computing apparatus  140  may be configured to provide graphical user interfaces depicting the surrogate electrical activation times obtained using the electrode apparatus  110 . Exemplary systems, methods, and/or interfaces may noninvasively use the electrical information collected using the electrode apparatus  110  to evaluate a patient&#39;s cardiac condition and/or ventricle from atrium pacing therapy being delivered to the patient. 
       FIG. 3  illustrates another exemplary electrode apparatus  110  that includes a plurality of electrodes  112  configured to surround the heart of the patient  120  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  120 . The electrode apparatus  110  may include a vest  114  upon which the plurality of electrodes  112  may be attached, or to which the electrodes  112  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  through a wired connection  118  and be configured to transmit signals from the electrodes  112  to computing apparatus  140 . As illustrated, the electrodes  112  may be distributed over the torso of a patient  120 , including, for example, the anterior, lateral, posterolateral, anterolateral, and posterior surfaces of the torso of the patient  120 . 
     The vest  114  may be formed of fabric with the electrodes  112  attached to the fabric. The vest  114  may be configured to maintain the position and spacing of electrodes  112  on the torso of the patient  120 . Further, the vest  114  may be marked to assist in determining the location of the electrodes  112  on the surface of the torso of the patient  120 . In one or more embodiments, the vest  114  may include 17 or more anterior electrodes positionable proximate the anterior torso of the patient, and 39 or more posterior electrodes positionable proximate the anterior torso of the patient. In some examples, there may be about 25 electrodes  112  to about 256 electrodes  112  distributed around the torso of the patient  120 , though other configurations may have more or less electrodes  112 . 
     As described herein, the electrode apparatus  110  may be configured to measure electrical information (e.g., electrical signals) representing different regions of a patient&#39;s heart. For example, activation times of different regions of a patient&#39;s heart can be approximated from surface electrocardiogram (ECG) activation times measured using surface electrodes in proximity to surface areas corresponding to the different regions of the patient&#39;s heart. In at least one example, activation times of the anterior-septal region of a patient&#39;s heart can be approximated from surface ECG activation times measured using surface electrodes in proximity to surface areas corresponding to the anterior-septal region of the patient&#39;s heart. That is, a portion of the set of electrodes  112 , and not the entire set, can be used to generate activation times corresponding to a particular location of the patient&#39;s heart that the portion of the set of electrodes corresponds to. 
     The exemplary systems, methods, and interfaces may be used to provide noninvasive assistance to a user in the evaluation of a patient&#39;s cardiac health or status, and/or the evaluation of cardiac therapy such as ventricle from atrium (VfA) pacing therapy by use of the electrode apparatus  110  (e.g., cardiac therapy being presently-delivered to a patient during implantation or after implantation). Further, the exemplary systems, methods, and interfaces may be used to assist a user in the configuration of the cardiac therapy, such as VfA pacing therapy, being delivered to a patient. 
     VfA pacing can be described as providing a synchronized homogeneous activation of ventricles of the heart. As an example, patients with atrial-ventricular (AV) block or prolonged AV timings that can lead to heart failure who have otherwise intact (e.g., normal) QRS can benefit from VfA pacing therapy. In addition, as an example, VfA pacing may provide beneficial activation for heart failure patients with intrinsic ventricular conduction disorders. Further, proper placement of VfA pacing can provide optimal activation of the ventricles for such patients. Further, left ventricular (LV) resynchronization for heart failure patients with left bundle branch block (LBBB) may find that VfA pacing enables easier access to left ventricular endocardium without exposing the leadless device or lead to endocardial blood pool. At the same time, in that example, this can help engage part of the conduction system to potentially correct LBBB and effectively resynchronize the patient. 
     An exemplary method  440  of evaluation of VfA pacing is illustrated in  FIG. 4 . The method  440  can include monitoring electrical activity using a plurality of external electrodes  442 , such as electrodes  112  described herein with reference to  FIGS. 1-3 . The electrical activity can be monitored by a plurality of electrodes during VfA pacing therapy or in the absence of VfA pacing therapy. The monitored electrical activity can be used to evaluate VfA pacing therapy to a patient using, e.g., the exemplary system described herein with respect to  FIGS. 1-3 . The electrical activity monitored using the ECG belt described above can be used to evaluate at least one paced setting of the VfA pacing therapy on the heart. As an example, a paced setting can be any one parameter or a combination of parameters including, but not limited to, electrode position, pacing polarity, pacing output, pacing pulsewidth, timing at which VfA pacing is delivered relative to atrial (A) timing, pacing rate, etc. Further, as an example, the location of the leadless device or a pacing lead can include a location in the left ventricle, accessed through the right atrium within, or in close proximity to, the high posterior basal and/or septal (HPBS) area of the left ventricular cavity. Moreover, pacing of, or in close proximity to, the HPBS area can be selective (e.g., involving stimulation of a particular area of the HPBS alone) or non-selective (e.g., combined pacing at the location of the HPBS and other atrial and/or ventricular septum areas). 
     Further, body-surface isochronal maps of ventricular activation can be constructed using the monitored electrical activity during VfA pacing therapy or in the absence of VfA pacing therapy. The monitored electrical activity and/or the map of ventricular activation can be used to generate electrical heterogeneity information. The electrical heterogeneity information can include determining metrics of electrical heterogeneity. The metrics of electrical heterogeneity can include a metric of standard deviation of activation times (SDAT) of electrodes on a left side of a torso of the patient and/or a metric of mean left ventricular activation time (LVAT) of electrodes on the left side of the torso of the patient. A metric of LVAT may be determined from electrodes on both the anterior and posterior surfaces, which are more proximal to the left ventricle. The metrics of electrical heterogeneity information can include a metric of mean right ventricular activation time (RVAT) of electrodes on the right side of the torso of the patient. A metric of RVAT may be determined from electrodes on both the anterior and posterior surfaces which are more proximal to the right ventricle. The metrics of electrical heterogeneity can include a metric of mean total activation time (mTAT) taken from a plurality of electrode signals from both sides of the torso of the patient, or it may include other metrics (e.g., standard deviation, interquartile deviations, a difference between a latest activation time and earliest activation time) reflecting a range or dispersion of activation times on a plurality of electrodes located on the right side of the patient torso or left side of the patient torso, or combining both right and left sides of the patient torso. The metrics of electrical heterogeneity information can include a metric of anterior-septal activation times (ASAT) of electrodes on the torso in close proximity to the anterior-septal portion of the heart. 
     Thus, the method  440  can include generating electrical heterogeneity information during delivery of VfA pacing therapy at one or more VfA paced settings  444 . The electrical heterogeneity information can be generated using metrics of electrical heterogeneity. As an example, the metrics of electrical heterogeneity can include at least one of an SDAT, an LVAT, an RVAT, an mTAT, and an ASAT. In at least one embodiment, only ASAT may be determined and further used by method  440 , and/or ASAT may be more heavily weighted than other values. 
     The method  440  can include determining whether one or more paced settings associated with the VfA pacing therapy are acceptable  446 . A paced setting can include a plurality of pacing parameters. The plurality of pacing parameters can be acceptable if the patient&#39;s cardiac condition improves, if the VfA pacing therapy is effectively capturing a desired portion of the left ventricle (e.g., the high posterior basal and/or septal area), and/or if a metric of electrical heterogeneity improves by a certain threshold compared to a baseline rhythm or therapy. In at least one embodiment, the determination of whether the paced setting is acceptable can be based on at least one metric of electrical heterogeneity generated from electrical activity during VfA pacing (and also, in some embodiments, during native conduction, or in the absence of VfA pacing). The at least one metric can include at least one of an SDAT, an LVAT, an RVAT, an mTAT, an ASAT. 
     Further, the plurality of pacing parameters can be acceptable if a metric of electrical heterogeneity is greater than or less than a particular threshold, and/or if the location of the pacing therapy to excite the left ventricle causes a particular pattern of excitation of the muscle fibers in the heart. In addition, the plurality of pacing parameters can be acceptable if a metric of electrical heterogeneity indicates a correction of a left bundle branch block (LBBB), and/or if a metric of electrical heterogeneity indicates a complete engagement of a Purkinje system, etc. As an example, a metric of electrical heterogeneity of an ASAT less than or equal to a threshold (e.g., a threshold of 30 ms) and an LVAT less than or equal to a threshold (e.g., a threshold of 30 ms) can indicate a correction of an LBBB, and thus, the paced setting is acceptable. As an example, a metric of electrical heterogeneity of an RVAT less than or equal to a threshold (e.g., a threshold of 30 ms), an ASAT less than or equal to a threshold (e.g., a threshold of 30 ms), and an LVAT less than or equal to a threshold (e.g., a threshold of 30 ms) can indicate a complete engagement of the Purkinje system, and thus the paced setting is acceptable. 
     The paced setting can be determined to be acceptable in response to the VfA pacing therapy using the paced setting being optimal, being beneficial, being indicative of complete engagement of patient&#39;s native cardiac conduction system, being indicative of correction of a ventricular conduction disorder (e.g., left bundle branch block), etc. A paced setting can include at least one of a pacing electrode position (including at least one of a depth, an angle, an amount of turn for a screw-based fixation mechanism, etc.), a voltage, a pulse width, an intensity, a pacing polarity, a pacing vector, a pacing waveform, a timing of the pacing delivered relative to an intrinsic or paced atrial event or relative to the intrinsic His bundle potential, and/or a pacing location, etc. A pacing vector can include any two or more pacing electrodes such as, e.g., a tip electrode to a can electrode, a tip electrode to a ring electrode etc., that are used to deliver the VfA pacing therapy, etc. The pacing location can refer to the location of any of the one or more pacing electrodes that are positioned using a lead, a leadless device, and/or any device or apparatus configured to deliver VfA, as will be further described in association with  FIGS. 8-12 . 
     The method  440  can include adjusting a paced setting for VfA pacing therapy  448 . In at least one embodiment, the paced setting can be adjusted in response to the paced setting being unacceptable. In at least one embodiment, the paced setting can be adjusted in response to the paced setting being within an acceptable range but in order to determine whether the paced setting can be at a position within the acceptable range that is more beneficial, more useful, more functional, etc. for the VfA pacing therapy. As an example, when the paced setting is a location that the VfA pacing therapy is administered within a patient, the paced setting (e.g., location, depth of penetration of helical electrode, angle of helical electrode, etc.) can be adjusted until the VfA pacing therapy results in a metric of electrical heterogeneity that is above or below a threshold metric of electrical heterogeneity. That is, the paced setting can be adjusted to assist in placement of a lead, leadless device, and/or other electrical device to administer the VfA pacing therapy. In another embodiment, the paced setting could be adjusted to find the most optimal metric of electrical heterogeneity. 
     For example, pacing of the left ventricle can utilize a pacing electrode that includes anywhere from an approximately 4 millimeter (mm) long helix to an approximately 12 mm long helix, and the exemplary method  440  may be used to gradually titrate navigating the electrode up to a 4 mm depth, or some other particular depth. In at least one example, the pacing electrode includes an 8 mm long helix. More specifically, the pacing electrode may be partially screwed into or through a posterior basal area of the right atrium. Further, the pacing electrode may pass through the right atrium and be screwed into, attached to, or brought into close proximity to a location in the left ventricle. This location of the left ventricle can include a high posterior basal and/or septal area of the left ventricle where the VfA pacing may be performed, electrical activity may be monitored  442  during such VfA pacing, electrical heterogeneity information may be generated  444 , and it may be determined whether the pacing setting, which in this case, may be an electrode location including depth and/or angle, is acceptable  446 . Next, the paced setting, which in this case may be a location including depth and/or angle, may be adjusted  448 . Thus, the pacing electrode may be screwed in, or through, the right atrium to be positioned in close proximity to or deeper within tissue in order to gain access to the left ventricle, and the method  440  may reiterate or be repeated until such desired location is achieved. In other words, the exemplary method  440  may indicate to a doctor to gradually slow down turning of the helix electrode through the right atrium allowing it to gain access to the left ventricle and be in close proximity to a portion of the left ventricle (e.g., the high posterior basal and/or septal area). 
     Further, in one or more embodiments, a determination of whether the paced setting is acceptable can be based on a particular metric of electrical heterogeneity using an ECG belt. For example, when a paced setting is associated with a first metric value of electrical heterogeneity, an indication (e.g., a display, a prompt, etc.) to turn a pacing electrode helix a particular number of turns can be made (e.g., to adjust the depth and/or angle of implant of the pacing electrode helix). In response to the paced setting being associated with a second metric value of electrical heterogeneity, an indication to stop turning the pacing electrode helix can be made. Furthermore, based on a metric of electrical heterogeneity, an indication of how many more turns of the pacing electrode helix can be indicated to assist in determining how much further to go with the pacing electrode helix. These indications can be displayed on a GUI of a monitor to assist in adjusting the paced setting and/or be on any number of display and/or notification devices. 
     In at least one example, the paced setting can be adjusted at intervals that correlate with a change in the metric of electrical heterogeneity until the metric of electrical heterogeneity is at or proximate a particular metric value. For instance, the adjusting of the paced setting can cause the metric of electrical heterogeneity to approach a particular threshold metric of electrical heterogeneity and, as the metric approaches the particular threshold, the rate at which the paced setting is adjusted can be slowed down. Put another way, as the metric of electrical heterogeneity is further from the particular threshold metric, the paced setting can be adjusted more quickly and as the metric of electrical heterogeneity gets closer to the particular threshold metric, the paced setting can be adjusted more slowly until the metric of electrical heterogeneity is at the particular threshold metric. 
     In at least one example, the paced setting (e.g., location including depth and/or angle) can be adjusted until the VfA pacing therapy results in a correction of bundle branch block (BBB) (or, more specifically, left BBB (LBBB). BBB can refer to a condition in which a delay and/or obstruction along a pathway that the electrical activity of the heart of the patient travels in order for the heart to properly beat. The delay and/or blockage may occur on the pathway that sends electrical impulses to the left or right side of the ventricles of the heart. The paced setting can be adjusted until the delay and/or blockage along the pathway is remedied, which can be indicated by a change in the metric of electrical heterogeneity, the metric of electrical heterogeneity being above or below a particular threshold, and/or any number of electrical information that may indicate that the BBB has been corrected. 
     In at least one example, the paced setting can be adjusted until the metric of electrical heterogeneity indicating a delay and/or blockage of BBB reaches a particular threshold metric. The metric of electrical heterogeneity being at the particular threshold metric can indicate the BBB has been corrected. The paced setting can be adjusted at a greater rate while the metric of electrical heterogeneity is further from the particular threshold metric and adjusted at a slower rate as the metric of electrical heterogeneity gets closer to the particular threshold metric. More specifically in response to at least one metric of electrical heterogeneity such as ASAT and LVAT being below a threshold, such as below 30 milliseconds (ms) for each of ASAT and LVAT, an indication of a correction of LBBB can be determined. 
     In at least one embodiment, the electrical heterogeneity information can be generated while delivering VfA pacing cardiac therapy using a selected first paced setting. In response to the selected first paced setting being determined to be an unacceptable paced setting, a selected second paced setting can be used. As an example, the first paced setting can include a first location of an electrode in the left ventricle, by way of going through the right atrium a first distance. In response to the first location not being indicated as an acceptable location evaluated at one or more pacing voltages, polarities, or timings, a second location within the left ventricle, associated with a second distance through the right atrium, can be used for delivering the VfA pacing therapy. 
     Lead placement at a site at, or in close proximity to, a particular location in the left ventricle (e.g., basal and/or septal area of the left ventricular myocardium) can be determined using the method described above. In at least one example, the method can be performed during implant placement. A decision-making process to determine whether to use the tested location (e.g., a first location) or to try for an additional location (e.g., a second location) for better results could be based on an automated system. As an example, parameters can be set to indicate whether the location is acceptable and when those parameters are met, the system automatically accepts the paced settings (e.g., location for VfA pacing using a lead or leadless device). In response to a determination that the VfA pacing therapy is not acceptable (e.g., the VfA paced setting used to deliver the VfA pacing therapy), the VfA paced setting can be changed. In response to changing the paced setting, a determination of whether the changed VfA paced setting for the VfA pacing therapy is acceptable based on the electrical heterogeneity information generated from the electrical activity using the plurality of external electrodes during delivery of VfA pacing therapy using the changed VfA paced setting can be performed. In at least one example, the data from the metrics of electrical heterogeneity can be provided to a clinician and the clinician can make the decision whether to accept the paced setting (e.g., a location for VfA pacing using a lead or leadless device). 
     In at least one embodiment, a metric of electrical heterogeneity used to determine whether a paced setting is acceptable can be used to compare VfA pacing therapy to cardiac resynchronization therapy (CRT). A metric of electrical heterogeneity while performing CRT can be generated. Then, as an example, the metric of electrical heterogeneity for CRT can be compared to the metric of electrical heterogeneity for VfA pacing. 
       FIG. 5  is a detailed block diagram of another exemplary method  550  of evaluating VfA pacing therapy. The method  550  can include monitoring electrical activity using a plurality of external electrodes  552 , such as electrodes  112  described herein with reference to  FIGS. 1-3 . The electrical activity can be monitored by a plurality of electrodes during VfA pacing therapy or in the absence of VfA pacing therapy. The monitored electrical activity can be used to evaluate VfA pacing therapy to a patient using, e.g., the exemplary system described herein with respect to  FIGS. 1-3 . The electrical activity monitored using the ECG belt described above can be used to evaluate at least one paced setting of the VfA pacing therapy on the heart. 
     The method  550  can include generating baseline electrical heterogeneity information (EHI)  554 . The baseline EHI can be generated in the absence of VfA pacing therapy. That is, the baseline EHI can be generated from electrical activity that is monitored in the absence of the VfA pacing therapy. The baseline EHI can include a baseline metric of electrical heterogeneity. A baseline metric can refer to a metric generated during native AV conduction in the absence of VfA pacing therapy to a patient or a metric generated during previous VfA pacing therapy using different settings or parameters or a metric generated during other cardiac pacing (e.g., more conventional cardiac pacing such as right ventricular pacing). The baseline metric can include at least one of an SDAT, an LVAT, an RVAT, an mTAT, and an ASAT. In one embodiment, an ASAT only baseline metric can be used. 
     The method  550  can include generating paced electrical heterogeneity information (EHI) during delivery of VfA pacing therapy  556 . The paced EHI can include a therapy metric of electrical heterogeneity. A therapy metric can refer to a metric generated while delivering VfA pacing therapy to a patient. The therapy metric can include at least one of an SDAT, an LVAT, an RVAT, an mTAT, and an ASAT. 
     The method  550  can include comparing the baseline EHI to the paced EHI  558 . Comparing the baseline EHI to the paced EHI can include comparing a baseline metric of electrical heterogeneity of the baseline EHI to a therapy metric of electrical heterogeneity of the paced EHI. As an example, a baseline SDAT can be compared to a therapy SDAT, a baseline LVAT can be compared to a therapy LVAT, a baseline RVAT can be compared to a therapy RVAT, a baseline mTAT can be compared to a therapy mTAT, and a baseline ASAT can be compared to a therapy ASAT. Further, for example, in at least one embodiment, a relative percentage difference between one or more metrics of EH generated during delivery of VfA pacing therapy and one or more baseline metrics of EH (either in the absence of delivery of VfA pacing therapy or during previous settings of VfA pacing therapy) may be compared to a threshold percentage. In one embodiment, an baseline ASAT metric of EH can be compared to a paced ASAT metric of EH. 
     The method  550  can include determining whether a paced setting for the VfA pacing therapy is acceptable based on the comparison  560 . A selected paced setting can be used to deliver the VfA pacing therapy and electrical heterogeneity information can be generated while using the paced setting. The determination of whether the paced setting is acceptable can be based on the comparison of the baseline EHI to a therapy EHI while using the paced setting. As an example, VfA pacing using the paced setting may be considered acceptable if the relative percentage difference (e.g., reduction) in EH with pacing compared to EH without pacing is less than or equal or greater than or equal to a percentage threshold. More specifically, in at least one embodiment, the one or more metrics of EH may be SDAT, LVAT, RVAT, mTAT, ASAT, or any combination thereof, and the selected percentage threshold may be between about 1% to about 15%. In at least one embodiment, the selected percentage threshold for the absolute relative difference (e.g., reduction) in EH with VfA pacing compared to without VfA pacing is 5%. In one or more other embodiments the selected percentage may be less than or equal to or greater than or equal to 2%, less than or equal to or greater than or equal to 3%, less than or equal to or greater than or equal to 6%, less than or equal to or greater than or equal to 9%, less than or equal to or greater than or equal to 10%, less than or equal to or greater than or equal to 15%, etc. 
     In at least one embodiment, as an example, the threshold percentage can be 5% for each of SDAT and LVAT. Thus, in this embodiment, if the change (e.g., reduction) in SDAT from baseline conduction to VfA pacing therapy is greater than or equal to 5% and the change (e.g., reduction) in LVAT from baseline conduction to VfA pacing therapy is greater than or equal to 5%, it may be determined that the VfA pacing therapy is acceptable. Conversely, if the change (e.g., relative reduction) in SDAT from baseline conduction to VfA pacing therapy is less than 5% and the change (e.g., relative reduction) in LVAT from baseline conduction to VfA pacing therapy is less than 5%, it may be determined that the VfA pacing therapy is unacceptable. The threshold reduction of metrics of electrical heterogeneity (e.g., reduction of electrical dyssynchrony) from baseline to pacing can indicate an improvement in resynchronization of the patient&#39;s heart. 
     Additionally, although the comparison of EH metrics to thresholds and the comparison of the percentage difference between EH metrics generated during delivery of VfA pacing therapy and EH baseline metrics are described separately, it is to be understood that each process may be used by itself or together to determine whether the Vfa pacing therapy is acceptable (or more specifically, whether one or more parameters of the VfA pacing therapy are acceptable). 
     The method  550  can further include adjusting the paced setting for the VfA pacing therapy  562 . The adjustment of the paced setting can be performed in response to the determination  560  that the paced setting for the VfA pacing therapy is acceptable. In this example, the paced setting could be adjusted to find a paced setting that is more acceptable than the already accepted paced setting. That is, a paced setting may be acceptable due to corresponding therapy EHI being within an acceptable range but adjusting to another paced setting may result in therapy EHI that is closer to a particular portion of the range that is more acceptable. Further, in at least one embodiment, the adjustment of the paced setting can be performed in response to the determination  560  that the paced setting for the VfA pacing therapy is unacceptable. 
     In response to the paced setting being adjusted, the process can repeat, starting with monitoring electrical activity  552 , generating baseline EHI  554 , generating paced EHI  556 , comparing baseline EHI to therapy EHI  558 , and determining whether the paced setting is acceptable  560 . This iterative process can repeat until either a paced setting is determined to be acceptable or the paced setting is within acceptable ranges, etc. As an example, where the paced setting is one of location, the location (including at least one of depth and angle) of an implantable electrode for delivering VfA pacing therapy can be adjusted, and this process repeated, until the therapy EHI associated with a particular location of the implantable electrode is acceptable. 
       FIG. 6  is a block diagram of another exemplary method  446 - 1  of evaluation of ventricle from atrium pacing therapy. The method  446 - 1  can be described as one exemplary embodiment of method step  446  in method  440  described in association with  FIG. 4 . That is, determining whether paced setting(s) for the VfA pacing therapy is acceptable  446  of method  440  can include the steps of method  446 - 1  in  FIG. 6 . The method  446 - 1  can include determining whether an anterior-septal activation time (ASAT) value is equal to or less than an ASAT threshold  664 . An anterior-septal region may be described as referring to a location in front of the interventricular septum, which refers to the curved slanting wall that separates the right and left ventricles of the heart and is composed of a muscular lower part and a thinner more membranous upper part. The ASAT value can be a value generated from electrical activity gathered by external electrodes in close proximity to the anterior-septal region or whose electrical activity corresponds to the anterior-septal region. In at least one example, the ASAT threshold can be 30 ms. The ASAT threshold can be greater than or equal to about 20 ms, greater than or equal to about 30 ms, greater than or equal to about 40 ms, greater than or equal to about 50 ms, greater than or equal to about 60 ms, etc. Also, the ASAT threshold can be less than or equal to about 25 ms, less than or equal to about 35 ms, less than or equal to about 45 ms, less than or equal to about 55 ms, etc. 
     The method  446 - 1  can include determining whether a left ventricular activation time (LVAT) value is below an LVAT threshold  666 . The LVAT value can be a value generated from electrical activity gathered by external electrodes in close proximity to the left ventricular region or whose electrical activity corresponds to the left ventricular region. In at least one example, the LVAT threshold can be 30 ms. The LVAT threshold can be greater than or equal to about 20 ms, greater than or equal to about 30 ms, greater than or equal to about 40 ms, greater than or equal to about 50 ms, greater than or equal to about 60 ms, etc. Also, the LVAT threshold can be less than or equal to about 25 ms, less than or equal to about 35 ms, less than or equal to about 45 ms, less than or equal to about 55 ms, etc. 
     The method  446 - 1  can include determining that the paced setting appears to correct a left bundle branch block (LBBB) in response to the ASAT value and the LVAT value being below their respective thresholds  668 . As an example, the ASAT value can be less than or equal to a threshold of 30 ms and the LVAT value can be less than or equal to a threshold of 30 ms in order to indicate that the LBBB has been corrected. In at least one example, the ASAT threshold can be greater than or equal to 20 ms and the LVAT threshold can be greater than or equal to 20 ms, the ASAT threshold can be greater than or equal to 25 ms and the LVAT threshold can be greater than or equal to 25 ms, the ASAT threshold can be greater than or equal to 20 ms and the LVAT threshold can be greater than or equal to 30 ms, the ASAT threshold can be greater than or equal to 30 ms and the LVAT threshold can be greater than or equal to 20 ms, and so forth for any combination of ASAT and LVAT thresholds. Also, the ASAT threshold can be less than or equal to 20 ms and the LVAT threshold can be less than or equal to 20 ms, the ASAT threshold can be less than or equal to 25 ms and the LVAT threshold can be less than or equal to 25 ms, the ASAT threshold can be less than or equal to 20 ms and the LVAT threshold can be less than or equal to 30 ms, the ASAT threshold can be less than or equal to 30 ms and the LVAT threshold can be less than or equal to 20 ms, and so forth for any combination of ASAT and LVAT thresholds. Thus, if during VfA pacing, the ASAT is less than or equal to a ASAT threshold and the LVAT is less than equal to an LVAT threshold, it may be determined that the VfA pacing therapy is correcting the LBBB. 
       FIG. 7  is a block diagram of another exemplary method  446 - 2  of evaluation of ventricle from atrium pacing therapy. The method  446 - 2  can be described as one exemplary embodiment of method step  446  in method  440  described in association with  FIG. 4 . That is, determining whether paced setting(s) for the VfA pacing therapy is acceptable  446  of method  440  can include the steps of method  446 - 2  in  FIG. 6 . The method  446 - 2  can include determining whether a right ventricular activation time (RVAT) value is equal to or less than an RVAT threshold  771 . The RVAT value can be a value generated from electrical activity gathered by external electrodes in close proximity to the right ventricular region or whose electrical activity corresponds to the right ventricular region. In at least one example, the RVAT threshold can be 30 ms. In at least one example, the RVAT threshold can be 30 ms. The RVAT threshold can be greater than or equal to about 20 ms, greater than or equal to about 30 ms, greater than or equal to about 40 ms, greater than or equal to about 50 ms, greater than or equal to about 60 ms, etc. Also, the RVAT threshold can be less than or equal to about 25 ms, less than or equal to about 35 ms, less than or equal to about 45 ms, less than or equal to about 55 ms, etc. 
     The method  446 - 2  can include determining whether an anterior-septal activation time (ASAT) value is equal to or less than an ASAT threshold  773 . An anterior-septal region can refer to a location in front of the interventricular septum, which refers to the curved slanting wall that separates the right and left ventricles of the heart and is composed of a muscular lower part and a thinner more membranous upper part. The ASAT value can be a value generated from electrical activity gathered by external electrodes in close proximity to the anterior-septal region or whose electrical activity corresponds to the anterior-septal region. In at least one example, the ASAT threshold can be 30 ms. The ASAT threshold can be greater than or equal to about 20 ms, greater than or equal to about 30 ms, greater than or equal to about 40 ms, greater than or equal to about 50 ms, greater than or equal to about 60 ms, etc. Also, the ASAT threshold can be less than or equal to about 25 ms, less than or equal to about 35 ms, less than or equal to about 45 ms, less than or equal to about 55 ms, etc. 
     The method  446 - 2  can include determining whether a left ventricular activation time (LVAT) value is equal to or less than an LVAT threshold  775 . The LVAT value can be a value generated from electrical activity gathered by external electrodes in close proximity to the right ventricular region or whose electrical activity corresponds to the right ventricular region. In at least one example, the LVAT threshold can be 30 ms. The LVAT threshold can be greater than or equal to about 20 ms, greater than or equal to about 30 ms, greater than or equal to about 40 ms, greater than or equal to about 50 ms, greater than or equal to about 60 ms, etc. Also, the LVAT threshold can be less than or equal to about 25 ms, less than or equal to about 35 ms, less than or equal to about 45 ms, less than or equal to about 55 ms, etc. 
     The method  446 - 2  can include determining that the paced setting causes complete engagement of a Purkinje system in response to the RVAT, ASAT, and LVAT values being below their respective thresholds  777 . As an example, the RVAT value can be less than or equal to a threshold of 30 ms, an ASAT value can be less than or equal to a threshold of 30 ms, and an LVAT value can be less than or equal to a threshold of 30 ms in order to indicate that there is complete engagement of the Purkinje system. The Purkinje system can be partially and/or completely engaged through the His bundle, or bundle of His, which refers to a collection of heart muscle cells specialized for electrical conduction. The His bundle can transmit electrical impulses from the atrial-ventricular (AV) node (located between the atria and ventricles) to a point of the apex of the fascicular branches via the bundle branches. The fascicular branches then lead to the Purkinje fibers, which can provide fast electrical conduction to the ventricles, thereby causing the cardiac muscle of the ventricles to contract more efficiently at a paced interval. Traditional cardiac pacing therapies have included electrical stimulation of ventricular muscle which provides an alternative pathway of electrical activation usually bypassing the fast conduction path provided by His bundle and Purkinje fibers, often resulting in slower cell to cell conduction and lower efficiency in cardiac contraction than that potentially achievable through successful stimulation of the His bundle. 
     In at least one example, the RVAT threshold can be less than, equal to, or greater than 20 ms, the ASAT threshold can be less than, equal to, or greater than 20 ms, and the LVAT threshold can be less than, equal to, or greater than 20 ms. In other example, the RVAT threshold can be less than, equal to, or greater than 25 ms, the ASAT threshold can be less than, equal to, or greater than 25 ms, and the LVAT threshold can be less than, equal to, or greater than 25 ms. In other example, the RVAT threshold can be less than, equal to, or greater than 20 ms, the ASAT threshold can be less than, equal to, or greater than 20 ms, and the LVAT threshold can be less than, equal to, or greater than 30 ms. In other example, the RVAT value can be less than, equal to, or greater than 30 ms, the ASAT threshold can be less than, equal to, or greater than 30 ms, and the LVAT threshold can be less than, equal to, or greater than 20 ms. In another example, the RVAT threshold can be 30 ms, the ASAT threshold can be 20 ms, and the LVAT threshold can be 30 ms, and so forth for any combination of RVAT, ASAT, and LVAT thresholds. Thus, if during VfA pacing, the RVAT is less than or equal to an RVAT threshold, the ASAT is less than or equal to an ASAT threshold, and the LVAT is less than equal to an LVAT threshold, it may be determined that there is complete and/or substantially complete engagement of the Purkinje system. 
     The exemplary systems, methods, and graphical user interfaces described herein may be used with respect to the implantation and configuration of an implantable medical device (IMD) and/or one or more leads configured to be located proximate one or more portions of a patient&#39;s heart, e.g., proximate a location in the left ventricle). For example, the exemplary systems, methods, and interfaces may be used in conjunction with an exemplary therapy system  10  described herein with reference to  FIGS. 8-12 . 
     Although the present disclosure describes leadless and leaded implantable medical devices, reference is first made to  FIG. 8  showing a conceptual diagram of a cardiac therapy system  2  including an intracardiac medical device  10  that may be configured for single or dual chamber therapy and implanted in a patient&#39;s heart  8 . In some embodiments, the device  10  may be configured for single chamber pacing and may, for example, switch between single chamber and multiple chamber pacing (e.g., dual or triple chamber pacing). As used herein, “intracardiac” refers to a device configured to be implanted entirely within a patient&#39;s heart, for example, to provide cardiac therapy. The device  10  is shown implanted in the right atrium (RA) of the patient&#39;s heart  8  in a target implant region  4 . The device  10  may include one or more fixation members  20  that anchor a distal end of the device against the atrial endocardium in a target implant region  4 . The target implant region  4  may lie between the Bundle of His  5  and the coronary sinus  3  and may be adjacent the tricuspid valve  6 . The device  10  may be described as a ventricle-from-atrium (VfA) device, which may sense or provide therapy to one or both ventricles (e.g., right ventricle, left ventricle, or both ventricles, depending on the circumstances) while being generally disposed in the right atrium. In particular, the device  10  may include a tissue-piercing electrode that may be implanted in the basal and/or septal region of the left ventricular myocardium of the patient&#39;s heart from the triangle of Koch region of the right atrium through the right atrial endocardium and central fibrous body. 
     The device  10  may be described as a leadless implantable medical device. As used herein, “leadless” refers to a device being free of a lead extending out of the patient&#39;s heart  8 . In other words, a leadless device may have a lead that does not extend from outside of the patient&#39;s heart to inside of the patient&#39;s heart. Some leadless devices may be introduced through a vein, but once implanted, the device is free of, or may not include, any transvenous lead and may be configured to provide cardiac therapy without using any transvenous lead. A leadless VfA device, in particular, does not use a lead to operably connect to an electrode in the ventricle when a housing of the device is positioned in the atrium. A leadless electrode may be coupled to the housing of the medical device without using a lead between the electrode and the housing. 
     The device  10  may include one or more dart electrode  12  having a straight shaft extending from the distal end region of device  10 , through the atrial myocardium and the central fibrous body, and into the ventricular myocardium  14  or along the ventricular septum, without perforating entirely through the ventricular endocardial or epicardial surfaces. The dart electrode  12  may carry an electrode at the distal end region of the shaft for positioning the electrode within the ventricular myocardium for sensing ventricular signals and delivering ventricular pulses (e.g., to depolarize the left ventricle to initiate a contraction of the left ventricle). In some examples, the electrode at the distal end region of the shaft is a cathode electrode provided for use in a bipolar electrode pair for pacing and sensing. While the implant region  4  is shown in  FIG. 8  to enable one or more electrodes of the one or more dart electrodes  12  to be positioned in the ventricular myocardium, it is recognized that a device having the aspects disclosed herein may be implanted at other locations for multiple chamber pacing (e.g., dual or triple chamber pacing), single chamber pacing with multiple chamber sensing, single chamber pacing and/or sensing, or other clinical therapy and applications as appropriate. 
     The cardiac therapy system  2  may also include a separate medical device  50  (depicted diagrammatically in  FIG. 8 ), which may be positioned outside the patient&#39;s heart  8  (e.g., subcutaneously) and may be operably coupled to the patient&#39;s heart  8  to deliver cardiac therapy thereto. In one example, separate medical device  50  may be an extravascular ICD. In some embodiments, an extravascular ICD may include a defibrillation lead with a defibrillation electrode. A therapy vector may exist between the defibrillation electrode on the defibrillation lead and a housing electrode of the ICD. Further, one or more electrodes of the ICD may also be used for sensing electrical signals related to the patient&#39;s heart  8 . The ICD may be configured to deliver shock therapy including one or more defibrillation or cardioversion shocks. For example, if an arrhythmia is sensed, the ICD may send a pulse via the electrical lead wires to shock the heart and restore its normal rhythm. In some examples, the ICD may deliver shock therapy without placing electrical lead wires within the heart or attaching electrical wires directly to the heart (subcutaneous ICDs). Examples of extravascular, subcutaneous ICDs that may be used with the system  2  described herein may be described in U.S. Pat. No. 9,278,229 (Reinke et al.), issued 8 Mar. 2016, which is incorporated herein by reference in its entirety. 
     In the case of shock therapy, e.g., the defibrillation shocks provided by the defibrillation electrode of the defibrillation lead, separate medical device  50  (e.g., extravascular ICD) may include a control circuit that uses a therapy delivery circuit to generate defibrillation shocks having any of a number of waveform properties, including leading-edge voltage, tilt, delivered energy, pulse phases, and the like. The therapy delivery circuit may, for instance, generate monophasic, biphasic, or multiphasic waveforms. Additionally, the therapy delivery circuit may generate defibrillation waveforms having different amounts of energy. For example, the therapy delivery circuit may generate defibrillation waveforms that deliver a total of between approximately 60-80 Joules (J) of energy for subcutaneous defibrillation. 
     The separate medical device  50  may include a sensing circuit. The sensing circuit may be configured to obtain electrical signals sensed via one or more combinations of electrodes and process the obtained signals. The components of the sensing circuit may be analog components, digital components, or a combination thereof. The sensing circuit may, for example, include one or more sense amplifiers, filters, rectifiers, threshold detectors, analog-to-digital converters (ADCs) or the like. The sensing circuit may convert the sensed signals to digital form and provide the digital signals to the control circuit for processing or analysis. For example, the sensing circuit may amplify signals from sensing electrodes and convert the amplified signals to multi-bit digital signals by an ADC. The sensing circuit may also compare processed signals to a threshold to detect the existence of atrial or ventricular depolarizations (e.g., P- or R-waves) and indicate the existence of the atrial depolarization (e.g., P-waves) or ventricular depolarizations (e.g., R-waves) to the control circuit. 
     The device  10  and the separate medical device  50  may cooperate to provide cardiac therapy to the patient&#39;s heart  8 . For example, the device  10  and the separate medical device  50  may be used to detect tachycardia, monitor tachycardia, and/or provide tachycardia-related therapy. For example, the device  10  may communicate with the separate medical device  50  wirelessly to trigger shock therapy using the separate medical device  50 . As used herein, “wirelessly” refers to an operative coupling or connection without using a metal conductor between the device  10  and the separate medical device  50 . In one example, wireless communication may use a distinctive, signaling, or triggering electrical pulse provided by the device  10  that conducts through the patient&#39;s tissue and is detectable by the separate medical device  50 . In another example, wireless communication may use a communication interface (e.g., an antenna) of the device  10  to provide electromagnetic radiation that propagates through patient&#39;s tissue and is detectable, for example, using a communication interface (e.g., an antenna) of the separate medical device  50 . 
       FIG. 9  is an enlarged conceptual diagram of the intracardiac medical device  10  and anatomical structures of the patient&#39;s heart  8 . The intracardiac device  10  may include a housing  30 . The housing  30  may define a hermetically sealed internal cavity in which internal components of the device  10  reside, such as a sensing circuit, therapy delivery circuit, control circuit, memory, telemetry circuit, other optional sensors, and a power source as generally described in conjunction with  FIG. 11  below. The housing  30  may be formed from an electrically conductive material including titanium or titanium alloy, stainless steel, MP35N (a non-magnetic nickel-cobalt-chromium-molybdenum alloy), platinum alloy or other bio-compatible metal or metal alloy. In other examples, the housing  30  may be formed from a non-conductive material including ceramic, glass, sapphire, silicone, polyurethane, epoxy, acetyl co-polymer plastics, polyether ether ketone (PEEK), a liquid crystal polymer, or other biocompatible polymer. 
     The housing  30  may be described as extending between a distal end region  32  and a proximal end region  34  in a generally cylindrical shape to facilitate catheter delivery. In other embodiments, the housing  30  may be prismatic or any other shape so as to perform the functionality and utility described herein. The housing  30  may include a delivery tool interface member  26 , e.g., at the proximal end  34 , for engaging with a delivery tool during implantation of the device  10 . 
     All or a portion of the housing  30  may function as an electrode during cardiac therapy, for example, in sensing and/or pacing. In the example shown, the housing-based electrode  24  is shown to circumscribe a proximal portion of the housing  30 . When the housing  30  is formed from an electrically conductive material, such as a titanium alloy or other examples listed above, portions of the housing  30  may be electrically insulated by a non-conductive material, such as a coating of parylene, polyurethane, silicone, epoxy, or other biocompatible polymer, leaving one or more discrete areas of conductive material exposed to define the proximal housing-based electrode  24 . When the housing  30  is formed from a non-conductive material, such as a ceramic, glass or polymer material, an electrically-conductive coating or layer, such as a titanium, platinum, stainless steel, or alloys thereof, may be applied to one or more discrete areas of the housing  30  to form the proximal housing-based electrode  24 . In other examples, the proximal housing-based electrode  24  may be a component, such as a ring electrode, that is mounted or assembled onto the housing  30 . The proximal housing-based electrode  24  may be electrically coupled to internal circuitry of the device  10 , e.g., via the electrically-conductive housing  30  or an electrical conductor when the housing  30  is a non-conductive material. 
     In the example shown, the proximal housing-based electrode  24  is located nearer to the housing proximal end region  34  than the housing distal end region  32  and is therefore referred to as a “proximal housing-based electrode”  24 . In other examples, however, the housing-based electrode  24  may be located at other positions along the housing  30 , e.g., relatively more distally than the position shown. 
     At the distal end region  32 , the device  10  may include a distal fixation and electrode assembly  36 , which may include one or more fixation members  20 , in addition to one or more dart electrodes  12  of equal or unequal length. The dart electrode  12  may include a shaft  40  extending distally away from the housing distal end region  32  and may include one or more electrode elements, such as a tip electrode  42  at or near the free, distal end region of the shaft  40 . The tip electrode  42  may have a conical or hemi-spherical distal tip with a relatively narrow tip diameter (e.g., less than about 1 mm) for penetrating into and through tissue layers without using a sharpened tip or needle-like tip having sharpened or beveled edges. 
     The shaft  40  of the dart electrode  12  may be a normally straight member and may be rigid. In other embodiments, the shaft  40  may be described as being relatively stiff but still possessing limited flexibility in lateral directions. Further, the shaft  40  may be non-rigid to allow some lateral flexing with heart motion. However, in a relaxed state, when not subjected to any external forces, the shaft  40  may maintain a straight position as shown to hold the tip electrode  42  spaced apart from the housing distal end region  32  at least by the height  47  of the shaft  40 . The dart electrode  12  may be configured to pierce through one or more tissue layers to position the tip electrode  42  within a desired tissue layer, e.g., the ventricular myocardium. As such, the height  47  of the shaft  40  may correspond to the expected pacing site depth, and the shaft may have a relatively high compressive strength along its longitudinal axis to resist bending in a lateral or radial direction when pressed against the implant region  4 . If a second dart electrode  12  is employed, its length may be unequal to the expected pacing site depth and may be configured to act as an indifferent electrode for delivering of pacing energy to the tissue. A longitudinal axial force may be applied against the tip electrode  42 , e.g., by applying longitudinal pushing force to the proximal end  34  of the housing  30 , to advance the dart electrode  12  into the tissue within target implant region. The shaft  40  may be longitudinally non-compressive. The shaft  40  may be elastically deformable in lateral or radial directions when subjected to lateral or radial forces to allow temporary flexing, e.g., with tissue motion, but may return to its normally straight position when lateral forces diminish. When the shaft  40  is not exposed to any external force, or to only a force along its longitudinal central axis, the shaft  40  may retain a straight, linear position as shown. 
     The one or more fixation members  20  may be described as one or more “tines” having a normally curved position. The tines may be held in a distally extended position within a delivery tool. The distal tips of tines may penetrate the heart tissue to a limited depth before elastically curving back proximally into the normally curved position (shown) upon release from the delivery tool. Further, the fixation members  20  may include one or more aspects described in, for example, U.S. Pat. No. 9,675,579 (Grubac et al.), issued 13 Jun. 2017, and U.S. Pat. No. 9,119,959 (Rys et al.), issued 1 Sep. 2015, each of which is incorporated herein by reference in its entirety. 
     In some examples, the distal fixation and electrode assembly  36  includes a distal housing-based electrode  22 . In the case of using the device  10  as a pacemaker for multiple chamber pacing (e.g., dual or triple chamber pacing) and sensing, the tip electrode  42  may be used as a cathode electrode paired with the proximal housing-based electrode  24  serving as a return anode electrode. Alternatively, the distal housing-based electrode  22  may serve as a return anode electrode paired with tip electrode  42  for sensing ventricular signals and delivering ventricular pacing pulses. In other examples, the distal housing-based electrode  22  may be a cathode electrode for sensing atrial signals and delivering pacing pulses to the atrial myocardium in the target implant region  4 . When the distal housing-based electrode  22  serves as an atrial cathode electrode, the proximal housing-based electrode  24  may serve as the return anode paired with the tip electrode  42  for ventricular pacing and sensing and as the return anode paired with the distal housing-based electrode  22  for atrial pacing and sensing. 
     As shown in this illustration, the target implant region  4  in some pacing applications is along the atrial endocardium  18 , generally inferior to the AV node  15  and the His bundle  5 . The dart electrode  42  may define the height  47  of the shaft  40  for penetrating through the atrial endocardium  18  in the target implant region  4 , through the central fibrous body  16 , and into the ventricular myocardium  14  without perforating through the ventricular endocardial surface  17 . When the height  47  of the dart electrode  12  is fully advanced into the target implant region  4 , the tip electrode  42  may rest within the ventricular myocardium  14 , and the distal housing-based electrode  22  may be positioned in intimate contact with or close proximity to the atrial endocardium  18 . The dart electrode  12  may have a total combined height  47  of tip electrode  42  and shaft  40  from about 3 mm to about 8 mm in various examples. The diameter of the shaft  40  may be less than about 2 mm, and may be about 1 mm or less, or even about 0.6 mm or less. 
     The device  10  may include a motion detector  11  within the housing  30 . The motion detector  11  may be used to monitor mechanical activity, such as atrial mechanical activity (e.g., an atrial contraction) and/or ventricular mechanical activity (e.g., a ventricular contraction). In some embodiments, the motion detector  11  may be used to detect right atrial mechanical activity. A non-limiting example of a motion detector  11  includes an accelerometer. In some embodiments, the mechanical activity detected by the motion detector  11  may be used to supplement or replace electrical activity detected by one or more of the electrodes of the device  10 . For example, the motion detector  11  may be used in addition to, or as an alternative to, the proximal housing-based electrode  24 . 
     The motion detector  11  may also be used for rate response detection or to provide a rate-responsive IMD. Various techniques related to rate response may be described in U.S. Pat. No. 5,154,170 (Bennett et al.), issued Oct. 13, 1992, entitled “Optimization for rate responsive cardiac pacemaker,” and U.S. Pat. No. 5,562,711 (Yerich et al.), issued Oct. 8, 1996, entitled “Method and apparatus for rate-responsive cardiac pacing,” each of which is incorporated herein by reference in its entirety. 
       FIG. 10  is a three-dimensional perspective view of the device  10  capable of cardiac therapy. As shown, the distal fixation and electrode assembly  36  includes the distal housing-based electrode  22  implemented as a ring electrode. The distal housing-based electrode  22  may be positioned in intimate contact with or operative proximity to atrial tissue when fixation member tines  20   a ,  20   b  and  20   c  of the fixation members  20 , engage with the atrial tissue. The tines  20   a ,  20   b  and  20   c , which may be elastically deformable, may be extended distally during delivery of device  10  to the implant site. For example, the tines  20   a ,  20   b , and  20   c  may pierce the atrial endocardial surface as the device  10  is advanced out of the delivery tool and flex back into their normally curved position (as shown) when no longer constrained within the delivery tool. As the tines  20   a ,  20   b  and  20   c  curve back into their normal position, the fixation member  20  may pull the distal fixation member and electrode assembly  36  toward the atrial endocardial surface. As the distal fixation member and electrode assembly  36  is pulled toward the atrial endocardium, the tip electrode  42  may be advanced through the atrial myocardium and the central fibrous body and into the ventricular myocardium. The distal housing-based electrode  22  may then be positioned against the atrial endocardial surface. 
     The distal housing-based electrode  22  may include a ring formed of an electrically conductive material, such as titanium, platinum, iridium, or alloys thereof. The distal housing-based electrode  22  may be a single, continuous ring electrode. In other examples, portions of the ring may be coated with an electrically insulating coating, e.g., parylene, polyurethane, silicone, epoxy, or other insulating coating, to reduce the electrically conductive surface area of the ring electrode. For instance, one or more sectors of the ring may be coated to separate two or more electrically conductive exposed surface areas of the distal housing-based electrode  22 . Reducing the electrically conductive surface area of the distal housing-based electrode  22 , e.g., by covering portions of the electrically conductive ring with an insulating coating, may increase the electrical impedance of the distal housing-based  22 , and thereby, reduce the current delivered during a pacing pulse that captures the myocardium, e.g., the atrial myocardial tissue. A lower current drain may conserve the power source, e.g., one or more rechargeable or non-rechargeable batteries, of the device  10 . 
     As described above, the distal housing-based electrode  22  may be configured as an atrial cathode electrode for delivering pacing pulses to the atrial tissue at the implant site in combination with the proximal housing-based electrode  24  as the return anode. The electrodes  22  and  24  may be used to sense atrial P-waves for use in controlling atrial pacing pulses (delivered in the absence of a sensed P-wave) and for controlling atrial-synchronized ventricular pacing pulses delivered using the tip electrode  42  as a cathode and the proximal housing-based electrode  24  as the return anode. In other examples, the distal housing-based electrode  22  may be used as a return anode in conjunction with the cathode tip electrode  42  for ventricular pacing and sensing. 
       FIG. 11  is a block diagram of circuitry that may be enclosed within the housing  30  ( FIG. 10 ) to provide the functions of cardiac therapy using the device  10  according to one example. The separate medical device  50  ( FIG. 8 ) may include some or all the same components, which may be configured in a similar manner. The electronic circuitry enclosed within housing  30  may include software, firmware, and hardware that cooperatively monitor atrial and ventricular electrical cardiac signals, determine when a cardiac therapy is necessary, and/or deliver electrical pulses to the patient&#39;s heart according to programmed therapy mode and pulse control parameters. The electronic circuitry may include a control circuit  80  (e.g., including processing circuitry), a memory  82 , a therapy delivery circuit  84 , a sensing circuit  86 , and/or a telemetry circuit  88 . In some examples, the device  10  includes one or more sensors  90  for producing a signal that is correlated to a physiological function, state, or condition of the patient, such as a patient activity sensor, for use in determining a need for pacing therapy and/or controlling a pacing rate. 
     The power source  98  may provide power to the circuitry of the device  10  including each of the components  80 ,  82 ,  84 ,  86 ,  88 , and  90  as needed. The power source  98  may include one or more energy storage devices, such as one or more rechargeable or non-rechargeable batteries. The connections between the power source  98  and each of the components  80 ,  82 ,  84 ,  86 ,  88 , and  90  are to be understood from the general block diagram illustrated but are not shown for the sake of clarity. For example, the power source  98  may be coupled to one or more charging circuits included in the therapy delivery circuit  84  for providing the power needed to charge holding capacitors included in the therapy delivery circuit  84  that are discharged at appropriate times under the control of the control circuit  80  for delivering pacing pulses, e.g., according to a dual chamber pacing mode such as DDI(R). The power source  98  may also be coupled to components of the sensing circuit  86 , such as sense amplifiers, analog-to-digital converters, switching circuitry, etc., sensors  90 , the telemetry circuit  88 , and the memory  82  to provide power to the various circuits. 
     The functional blocks shown represent functionality included in the device  10  and may include any discrete and/or integrated electronic circuit components that implement analog, and/or digital circuits capable of producing the functions attributed to the medical device  10  herein. The various components may include processing circuitry, such as an application specific integrated circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group), and memory that execute one or more software or firmware programs, a combinational logic circuit, state machine, or other suitable components or combinations of components that provide the described functionality. The particular form of software, hardware, and/or firmware employed to implement the functionality disclosed herein will be determined primarily by the particular system architecture employed in the medical device and by the particular detection and therapy delivery methodologies employed by the medical device. Providing software, hardware, and/or firmware to accomplish the described functionality in the context of any modern cardiac medical device system, given the disclosure herein, is within the abilities of one of skill in the art. 
     The memory  82  may include any volatile, non-volatile, magnetic, or electrical non-transitory computer readable storage media, such as random-access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, or any other memory device. Furthermore, the memory  82  may include a non-transitory computer readable media storing instructions that, when executed by one or more processing circuits, cause the control circuit  80  and/or other processing circuitry to perform a single, dual, or triple chamber pacing (e.g., single or multiple chamber pacing) function or other sensing and therapy delivery functions attributed to the device  10 . The non-transitory computer-readable media storing the instructions may include any of the media listed above. 
     The control circuit  80  may communicate, e.g., via a data bus, with the therapy delivery circuit  84  and the sensing circuit  86  for sensing cardiac electrical signals and controlling delivery of cardiac electrical stimulation therapies in response to sensed cardiac events, e.g., P-waves and R-waves, or the absence thereof. The tip electrode  42 , the distal housing-based electrode  22 , and the proximal housing-based electrode  24  may be electrically coupled to the therapy delivery circuit  84  for delivering electrical stimulation pulses to the patient&#39;s heart and to the sensing circuit  86  and for sensing cardiac electrical signals. 
     The sensing circuit  86  may include an atrial (A) sensing channel  87  and a ventricular (V) sensing channel  89 . The distal housing-based electrode  22  and the proximal housing-based electrode  24  may be coupled to the atrial sensing channel  87  for sensing atrial signals, e.g., P-waves attendant to the depolarization of the atrial myocardium. In examples that include two or more selectable distal housing-based electrodes, the sensing circuit  86  may include switching circuitry for selectively coupling one or more of the available distal housing-based electrodes to cardiac event detection circuitry included in the atrial sensing channel  87 . Switching circuitry may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple components of the sensing circuit  86  to selected electrodes. The tip electrode  42  and the proximal housing-based electrode  24  may be coupled to the ventricular sensing channel  89  for sensing ventricular signals, e.g., R-waves attendant to the depolarization of the ventricular myocardium. 
     Each of the atrial sensing channel  87  and the ventricular sensing channel  89  may include cardiac event detection circuitry for detecting P-waves and R-waves, respectively, from the cardiac electrical signals received by the respective sensing channels. The cardiac event detection circuitry included in each of the channels  87  and  89  may be configured to amplify, filter, digitize, and rectify the cardiac electrical signal received from the selected electrodes to improve the signal quality for detecting cardiac electrical events. The cardiac event detection circuitry within each channel  87  and  89  may include one or more sense amplifiers, filters, rectifiers, threshold detectors, comparators, analog-to-digital converters (ADCs), timers, or other analog or digital components. A cardiac event sensing threshold, e.g., a P-wave sensing threshold and an R-wave sensing threshold, may be automatically adjusted by each respective sensing channel  87  and  89  under the control of the control circuit  80 , e.g., based on timing intervals and sensing threshold values determined by the control circuit  80 , stored in the memory  82 , and/or controlled by hardware, firmware, and/or software of the control circuit  80  and/or the sensing circuit  86 . 
     Upon detecting a cardiac electrical event based on a sensing threshold crossing, the sensing circuit  86  may produce a sensed event signal that is passed to the control circuit  80 . For example, the atrial sensing channel  87  may produce a P-wave sensed event signal in response to a P-wave sensing threshold crossing. The ventricular sensing channel  89  may produce an R-wave sensed event signal in response to an R-wave sensing threshold crossing. The sensed event signals may be used by the control circuit  80  for setting pacing escape interval timers that control the basic time intervals used for scheduling cardiac pacing pulses. A sensed event signal may trigger or inhibit a pacing pulse depending on the particular programmed pacing mode. For example, a P-wave sensed event signal received from the atrial sensing channel  87  may cause the control circuit  80  to inhibit a scheduled atrial pacing pulse and schedule a ventricular pacing pulse at a programmed atrioventricular (AV) pacing interval. If an R-wave is sensed before the AV pacing interval expires, the ventricular pacing pulse may be inhibited. If the AV pacing interval expires before the control circuit  80  receives an R-wave sensed event signal from the ventricular sensing channel  89 , the control circuit  80  may use the therapy delivery circuit  84  to deliver the scheduled ventricular pacing pulse synchronized to the sensed P-wave. 
     In some examples, the device  10  may be configured to deliver a variety of pacing therapies including bradycardia pacing, cardiac resynchronization therapy, post-shock pacing, and/or tachycardia-related therapy, such as ATP, among others. For example, the device  10  may be configured to detect non-sinus tachycardia and deliver ATP. The control circuit  80  may determine cardiac event time intervals, e.g., PP intervals between consecutive P-wave sensed event signals received from the atrial sensing channel  87 , RR intervals between consecutive R-wave sensed event signals received from the ventricular sensing channel  89 , and P-R and/or R-P intervals received between P-wave sensed event signals and R-wave sensed event signals. These intervals may be compared to tachycardia detection intervals for detecting non-sinus tachycardia. Tachycardia may be detected in a given heart chamber based on a threshold number of tachycardia detection intervals being detected. 
     The therapy delivery circuit  84  may include atrial pacing circuit  83  and ventricular pacing circuit  85 . Each pacing circuit  83  and  85  may include charging circuitry, one or more charge storage devices such as one or more low voltage holding capacitors, an output capacitor, and/or switching circuitry that controls when the holding capacitor(s) are charged and discharged across the output capacitor to deliver a pacing pulse to the pacing electrode vector coupled to respective pacing circuits  83  or  85 . The tip electrode  42  and the proximal housing-based electrode  24  may be coupled to the ventricular pacing circuit  85  as a bipolar cathode and anode pair for delivering ventricular pacing pulses, e.g., upon expiration of an AV or VV pacing interval set by the control circuit  80  for providing atrial-synchronized ventricular pacing and a basic lower ventricular pacing rate. 
     The atrial pacing circuit  83  may be coupled to the distal housing-based electrode  22  and the proximal housing-based electrode  24  to deliver atrial pacing pulses. The control circuit  80  may set atrial pacing intervals according to a programmed lower pacing rate or a temporary lower rate set according to a rate-responsive sensor indicated pacing rate. Atrial pacing circuit may be controlled to deliver an atrial pacing pulse if the atrial pacing interval expires before a P-wave sensed event signal is received from the atrial sensing channel  87 . The control circuit  80  starts an AV pacing interval in response to a delivered atrial pacing pulse to provide synchronized multiple chamber pacing (e.g., dual or triple chamber pacing). 
     Charging of a holding capacitor of the atrial or ventricular pacing circuit  83  or  85  to a programmed pacing voltage amplitude and discharging of the capacitor for a programmed pacing pulse width may be performed by the therapy delivery circuit  84  according to control signals received from the control circuit  80 . For example, a pace timing circuit included in the control circuit  80  may include programmable digital counters set by a microprocessor of the control circuit  80  for controlling the basic pacing time intervals associated with various single chamber or multiple chamber pacing (e.g., dual or triple chamber pacing) modes or anti-tachycardia pacing sequences. The microprocessor of the control circuit  80  may also set the amplitude, pulse width, polarity, or other characteristics of the cardiac pacing pulses, which may be based on programmed values stored in the memory  82 . 
     The device  10  may include other sensors  90  for sensing signals from the patient for use in determining a need for and/or controlling electrical stimulation therapies delivered by the therapy delivery circuit  84 . In some examples, a sensor indicative of a need for increased cardiac output may include a patient activity sensor, such as an accelerometer. An increase in the metabolic demand of the patient due to increased activity as indicated by the patient activity sensor may be determined by the control circuit  80  for use in determining a sensor-indicated pacing rate. 
     Control parameters utilized by the control circuit  80  for sensing cardiac events and controlling pacing therapy delivery may be programmed into the memory  82  via the telemetry circuit  88 , which may also be described as a communication interface. The telemetry circuit  88  includes a transceiver and antenna for communicating with an external device such as a programmer or home monitor, using radio frequency communication or other communication protocols. The control circuit  80  may use the telemetry circuit  88  to receive downlink telemetry from and send uplink telemetry to the external device. In some cases, the telemetry circuit  88  may be used to transmit and receive communication signals to/from another medical device implanted in the patient. 
       FIG. 12  is a three-dimensional perspective view of another leadless intracardiac medical device  710  that may be configured for single or multiple chamber cardiac therapy (e.g., dual or triple chamber cardiac therapy) according to another example. The device  710  may include a housing  730  having an outer sidewall  735 , shown as a cylindrical outer sidewall, extending from a housing distal end region  732  to a housing proximal end region  734 . The housing  730  may enclose electronic circuitry configured to perform single or multiple chamber cardiac therapy, including atrial and ventricular cardiac electrical signal sensing and pacing the atrial and ventricular chambers. Delivery tool interface member  726  is shown on the housing proximal end region  734 . 
     A distal fixation and electrode assembly  736  may be coupled to the housing distal end region  732 . The distal fixation and electrode assembly  736  may include an electrically insulative distal member  772  coupled to the housing distal end region  732 . The tissue piercing electrode  712  extends away from the housing distal end region  732 , and multiple non-tissue piercing electrodes  722  may be coupled directly to the insulative distal member  772 . The tissue piercing electrode  712  extends in a longitudinal direction away from the housing distal end region  732  and may be coaxial with the longitudinal center axis  731  of the housing  730 . 
     The tissue piercing distal electrode  712  may include an electrically insulated shaft  740  and a tip electrode  742 . In some examples, the tissue piercing distal electrode  712  is an active fixation member including a helical shaft  740  and a distal cathode tip electrode  742 . The helical shaft  740  may extend from a shaft distal end region  743  to a shaft proximal end region  741 , which may be directly coupled to the insulative distal member  772 . The helical shaft  740  may be coated with an electrically insulating material, e.g., parylene or other examples listed herein, to avoid sensing or stimulation of cardiac tissue along the shaft length. The tip electrode  742  is at the shaft distal end region  743  and may serve as a cathode electrode for delivering ventricular pacing pulses and sensing ventricular electrical signals using the proximal housing-based electrode  724  as a return anode when the tip electrode  742  is advanced into ventricular tissue. The proximal housing-based electrode  724  may be a ring electrode circumscribing the housing  730  and may be defined by an uninsulated portion of the longitudinal sidewall  735 . Other portions of the housing  730  not serving as an electrode may be coated with an electrically insulating material as described above in conjunction with  FIG. 9 . 
     Using two or more tissue-piercing electrodes (e.g., of any type) penetrating into the LV myocardium may be used for more localized pacing capture and may mitigate ventricular pacing spikes affecting capturing atrial tissue. In some embodiments, multiple tissue-piercing electrodes may include two or more of a dart-type electrode (e.g., electrode  12  of  FIGS. 8-9 ), a helical-type electrode (e.g., electrode  712 ) Non-limiting examples of multiple tissue-piercing electrodes include two dart electrodes, a helix electrode with a dart electrode extending therethrough (e.g., through the center), or dual intertwined helixes. Multiple tissue-piercing electrodes may also be used for bipolar or multi-polar pacing. 
     In some embodiments, one or more tissue-piercing electrodes (e.g., of any type) that penetrate into the LV myocardium may be a multi-polar tissue-piercing electrode. A multi-polar tissue-piercing electrode may include one or more electrically active and electrically separate elements, which may enable bipolar or multi-polar pacing from one or more tissue-piercing electrodes. 
     Multiple non-tissue piercing electrodes  722  may be provided along a periphery of the insulative distal member  772 , peripheral to the tissue piercing electrode  712 . The insulative distal member  772  may define a distal-facing surface  738  of the device  710  and a circumferential surface  739  that circumscribes the device  710  adjacent to the housing longitudinal sidewall  735 . Non-tissue piercing electrodes  722  may be formed of an electrically conductive material, such as titanium, platinum, iridium, or alloys thereof. In the illustrated embodiment, six non-tissue piercing electrodes  722  are spaced apart radially at equal distances along the outer periphery of insulative distal member  772 , however, two or more non-tissue piercing electrodes  722  may be provided. 
     Non-tissue piercing electrodes  722  may be discrete components each retained within a respective recess  774  in the insulative member  772  sized and shaped to mate with the non-tissue piercing electrode  722 . In other examples, the non-tissue piercing electrodes  722  may each be an uninsulated, exposed portion of a unitary member mounted within or on the insulative distal member  772 . Intervening portions of the unitary member not functioning as an electrode may be insulated by the insulative distal member  772  or, if exposed to the surrounding environment, may be coated with an electrically insulating coating, e.g., parylene, polyurethane, silicone, epoxy, or other insulating coating. 
     When the tissue piercing electrode  712  is advanced into cardiac tissue, at least one non-tissue piercing electrode  722  may be positioned against, in intimate contact with, or in operative proximity to, a cardiac tissue surface for delivering pulses and/or sensing cardiac electrical signals produced by the patient&#39;s heart. For example, non-tissue piercing electrodes  722  may be positioned in contact with right atrial endocardial tissue for pacing and sensing in the atrium when the tissue piercing electrode  712  is advanced into the atrial tissue and through the central fibrous body until the distal tip electrode  742  is positioned in direct contact with ventricular tissue, e.g., ventricular myocardium and/or a portion of the ventricular conduction system. 
     Non-tissue piercing electrodes  722  may be coupled to the therapy delivery circuit  84  and the sensing circuit  86  (see  FIG. 11 ) enclosed by the housing  730  to function collectively as a cathode electrode for delivering atrial pacing pulses and for sensing atrial electrical signals, e.g., P-waves, in combination with the proximal housing-based electrode  724  as a return anode. Switching circuitry included in the sensing circuit  86  may be activated under the control of the control circuit  80  to couple one or more of the non-tissue piercing electrodes to the atrial sensing channel  87 . Distal, non-tissue piercing electrodes  722  may be electrically isolated from each other so that each individual one of the electrodes  722  may be individually selected by switching circuitry included in the therapy delivery circuit  84  to serve alone or in a combination of two or more of the electrodes  722  as an atrial cathode electrode. Switching circuitry included in the therapy delivery circuit  84  may be activated under the control of the control circuit  80  to couple one or more of the non-tissue piercing electrodes  722  to the atrial pacing circuit  83 . Two or more of the non-tissue piercing electrodes  722  may be selected at a time to operate as a multi-point atrial cathode electrode. 
     Certain non-tissue piercing electrodes  722  selected for atrial pacing and/or atrial sensing may be selected based on atrial capture threshold tests, electrode impedance, P-wave signal strength in the cardiac electrical signal, or other factors. For example, a single one or any combination of two or more individual non-tissue piercing electrodes  722  functioning as a cathode electrode that provides an optimal combination of a low pacing capture threshold amplitude and relatively high electrode impedance may be selected to achieve reliable atrial pacing using minimal current drain from the power source  98 . 
     In some instances, the distal-facing surface  738  may uniformly contact the atrial endocardial surface when the tissue piercing electrode  712  anchors the housing  730  at the implant site. In that case, all the electrodes  722  may be selected together to form the atrial cathode. Alternatively, every other one of the electrodes  722  may be selected together to form a multi-point atrial cathode having a higher electrical impedance that is still uniformly distributed along the distal-facing surface  738 . Alternatively, a subset of one or more electrodes  722  along one side of the insulative distal member  772  may be selected to provide pacing at a desired site that achieves the lowest pacing capture threshold due to the relative location of the electrodes  722  to the atrial tissue being paced. 
     In other instances, the distal-facing surface  738  may be oriented at an angle relative to the adjacent endocardial surface depending on the positioning and orientation at which the tissue piercing electrode  712  enters the cardiac tissue. In this situation, one or more of the non-tissue piercing electrodes  722  may be positioned in closer contact with the adjacent endocardial tissue than other non-tissue piercing electrodes  722 , which may be angled away from the endocardial surface. By providing multiple non-tissue piercing electrodes along the periphery of the insulative distal member  772 , the angle of the tissue piercing electrode  712  and the housing distal end region  732  relative to the cardiac surface, e.g., the right atrial endocardial surface, may not be required to be substantially parallel. Anatomical and positional differences may cause the distal-facing surface  738  to be angled or oblique to the endocardial surface, however, multiple non-tissue piercing electrodes  722  distributed along the periphery of the insulative distal member  772  increase the likelihood of good contact between one or more electrodes  722  and the adjacent cardiac tissue to promote acceptable pacing thresholds and reliable cardiac event sensing using at least a subset of multiple electrodes  722 . Contact or fixation circumferentially along the entire periphery of the insulative distal member  772  may not be required. 
     The non-tissue piercing electrodes  722  are shown to each include a first portion  722   a  extending along the distal-facing surface  738  and a second portion  722   b  extending along the circumferential surface  739 . The first portion  722   a  and the second portion  722   b  may be continuous exposed surfaces such that the active electrode surface wraps around a peripheral edge  776  of the insulative distal member  772  that joins the distal facing surface  738  and the circumferential surface  739 . The non-tissue piercing electrodes  722  may include one or more of the electrodes  772  along the distal-facing surface  738 , one or more electrodes along the circumferential surface  739 , one or more electrodes each extending along both of the distal-facing surface  738  and the circumferential surface  739 , or any combination thereof. The exposed surface of each of the non-tissue piercing electrodes  722  may be flush with respective distal-facing surfaces  738  and/or circumferential surfaces. In other examples, each of the non-tissue piercing electrodes  722  may have a raised surface that protrudes from the insulative distal member  772 . Any raised surface of the electrodes  722 , however, may define a smooth or rounded, non-tissue piercing surface. 
     The distal fixation and electrode assembly  736  may seal the distal end region of the housing  730  and may provide a foundation on which the electrodes  722  are mounted. The electrodes  722  may be referred to as housing-based electrodes. The electrodes  722  may not be not carried by a shaft or other extension that extends the active electrode portion away from the housing  730 , like the distal tip electrode  742  residing at the distal tip of the helical shaft  740  extending away from the housing  730 . Other examples of non-tissue piercing electrodes presented herein that are coupled to a distal-facing surface and/or a circumferential surface of an insulative distal member include the distal housing-based ring electrode  22  ( FIG. 10 ), the distal housing-based ring electrode extending circumferentially around the assembly  36  ( FIG. 10 ), button electrodes, other housing-based electrodes, and other circumferential ring electrodes. Any non-tissue piercing electrodes directly coupled to a distal insulative member, peripherally to a central tissue-piercing electrode, may be provided to function individually, collectively, or in any combination as a cathode electrode for delivering pacing pulses to adjacent cardiac tissue. When a ring electrode, such as the distal ring electrode  22  and/or a circumferential ring electrode, is provided, portions of the ring electrode may be electrically insulated by a coating to provide multiple distributed non-tissue piercing electrodes along the distal-facing surface and/or the circumferential surface of the insulative distal member. 
     The non-tissue piercing electrodes  722  and other examples listed above are expected to provide more reliable and effective atrial pacing and sensing than a tissue piercing electrode provided along the distal fixation and electrode assembly  736 . The atrial chamber walls are relatively thin compared to ventricular chamber walls. A tissue piercing atrial cathode electrode may extend too deep within the atrial tissue leading to inadvertent sustained or intermittent capture of ventricular tissue. A tissue piercing atrial cathode electrode may lead to interference with sensing atrial signals due to ventricular signals having a larger signal strength in the cardiac electrical signal received via tissue-piercing atrial cathode electrodes that are in closer physical proximity to the ventricular tissue. The tissue piercing electrode  712  may be securely anchored into ventricular tissue for stabilizing the implant position of the device  710  and providing reasonable certainty that the tip electrode  742  is sensing and pacing in ventricular tissue while the non-tissue piercing electrodes  722  are reliably pacing and sensing in the atrium. When the device  710  is implanted in the target implant region  4 , e.g., as shown in  FIG. 8  the ventricular septum, the tip electrode  742  may reach left ventricular tissue for pacing of the left ventricle while the non-tissue piercing electrodes  722  provide pacing and sensing in the right atrium. The tissue piercing electrode  712  may be in the range of about 4 to about 8 mm in length from the distal-facing surface  738  to reach left ventricular tissue. In some instances, the device  710  may achieve four-chamber pacing by delivering atrial pacing pulses from the atrial pacing circuit  83  via the non-tissue piercing electrodes  722  in the target implant region  4  to achieve bi-atrial (right and left atrial) capture and by delivering ventricular pacing pulses from the ventricular pacing circuit  85  via the tip electrode  742  advanced into ventricular tissue from the target implant region  4  to achieve biventricular (right and left ventricular) capture. 
       FIG. 13  is a two-dimensional (2D) ventricular map  300  of a patient&#39;s heart (e.g., a top-down view) showing the left ventricle  320  in a standard 17 segment view and the right ventricle  322 . The map  300  includes a plurality of areas  326  corresponding to different regions of a human heart. As illustrated, the areas  326  are numerically labeled  1 - 17  (which, e.g., correspond to a standard 17 segment model of a human heart, correspond to 17 segments of the left ventricle of a human heart, etc.). Areas  326  of the map  300  may include basal anterior area  1 , basal anteroseptal area  2 , basal inferoseptal area  3 , basal inferior area  4 , basal inferolateral area  5 , basal anterolateral area  6 , mid-anterior area  7 , mid-anteroseptal area  8 , mid-inferoseptal area  9 , mid-inferior area  10 , mid-inferolateral area  11 , mid-anterolateral area  12 , apical anterior area  13 , apical septal area  14 , apical inferior area  15 , apical lateral area  16 , and apex area  17 . The inferoseptal and anteroseptal areas of the right ventricle  322  are also illustrated, as well as the right bunch branch (RBB) and left bundle branch (LBB). 
     In some embodiments, any of the tissue-piercing electrodes of the present disclosure may be implanted through the right atrial endocardium. In particular, the tissue-piercing electrode may be implanted from the triangle of Koch region of the right atrium. 
     Once implanted, the tissue-piercing electrode may be positioned in the target implant region  4  ( FIG. 8 ), such as the basal and/or septal region of the left ventricular myocardium. With reference to map  300 , the basal region includes one or more of the basal anterior area  1 , basal anteroseptal area  2 , basal inferoseptal area  3 , basal inferior area  4 , mid-anterior area  7 , mid-anteroseptal area  8 , mid-inferoseptal area  9 , and mid-inferior area  10 . With reference to map  300 , the septal region includes one or more of the basal anteroseptal area  2 , basal anteroseptal area  3 , mid-anteroseptal area  8 , mid-inferoseptal area  9 , and apical septal area  14 . 
     In some embodiments, the tissue-piercing electrode may be positioned in the basal and/or septal area of the left ventricular myocardium when implanted. The basal and/or septal region may include one or more of the basal anteroseptal area  2 , basal inferoseptal area  3 , mid-anteroseptal area  8 , and mid-inferoseptal area  9 . 
     In some embodiments, the tissue-piercing electrode may be positioned in the basal and/or septal region of the left ventricular myocardium when implanted. The high inferior/posterior basal and/or septal region of the left ventricular myocardium may include a portion of at least one of the basal inferoseptal area  3  and mid-inferoseptal area  9 . For example, the high inferior/posterior basal and/or septal region may include region  324  illustrated generally as a dashed-line boundary. As shown, the dashed line boundary represents an approximation of about where the high inferior/posterior basal and/or septal region and may take somewhat different shape or size depending on the particular application. 
     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 one or more processors to support one or more aspects of the functionality described in this disclosure. 
     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. 
     ILLUSTRATIVE EMBODIMENTS 
     Embodiment 1 
     A system comprising: 
     electrode apparatus comprising a plurality of external electrodes to monitor electrical activity from tissue of a patient; and 
     computing apparatus comprising processing circuitry and coupled to the electrode apparatus and configured to:
         monitor electrical activity using the plurality of external electrodes;   generate paced electrical heterogeneity information (EHI) based on the monitored electrical activity during delivery of ventricle from atrium (VfA) pacing therapy at one or more VfA paced settings, wherein the paced EHI is representative of at least one of mechanical cardiac functionality and electrical cardiac functionality; and   determine whether the one or more VfA paced settings for the VfA pacing therapy are acceptable based on the paced EHI.       

     Embodiment 2 
     The system of embodiment 1, wherein the one or more VfA paced settings comprise at least one of a voltage, a pulse width, timing of a V-pacing relative to intrinsic or paced atrial timing, and pacing rate. 
     Embodiment 3 
     The system of any one of embodiments 1 to 2, wherein the one or more VfA paced settings comprises a location of at least one implantable electrode wherein the location comprises at least one of depth and angle. 
     Embodiment 4 
     The system of any one of embodiments 1 to 3, wherein the one or more VfA paced settings comprises at least one of a pacing polarity, a pacing vector, and a number of pacing electrodes used. 
     Embodiment 5 
     The system of any one of embodiments 1 to 4, wherein the system further comprises a VfA pacing therapy apparatus, wherein the VfA pacing therapy apparatus comprises 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 the VfA pacing therapy to the left ventricle in the basal and/or septal region of the left ventricular myocardium of the patient&#39;s heart. 
     Embodiment 6 
     The system of any one of embodiments 1 to 5, wherein the VfA paced settings comprises a location of the at least one implantable electrode proximate the high posterior basal and/or septal area of the left ventricle of the patient. 
     Embodiment 7 
     The system of any one of embodiments 1 to 6, wherein the plurality of external electrodes comprises surface electrodes positioned in an array configured to be located proximate skin of a torso of the patient. 
     Embodiment 8 
     The system of any one of embodiments 1 to 7, wherein the paced EHI comprises a metric of electrical heterogeneity, 
     wherein the determining whether the one or more VfA paced settings for the VfA pacing therapy are acceptable comprises determining that the one or more VfA paced settings are acceptable if the metric of electrical heterogeneity is less than or equal to a threshold. 
     Embodiment 9 
     The system of any one of embodiments 1 to 8, wherein the determining whether the one or more VfA paced settings for the VfA pacing therapy are acceptable comprises: 
     generating baseline EHI from the monitored electrical activity without delivery of the VfA pacing therapy; 
     comparing the baseline EHI to the paced EHI; and 
     determining that the one or more VfA paced settings are acceptable based on the comparison of the baseline EHI to the paced EHI. 
     Embodiment 10 
     The system of any one of embodiments 1 to 9, wherein the electrical heterogeneity information comprises at least one metric of electrical heterogeneity, wherein the at least one metric of electrical heterogeneity comprises anterior-septal activation times (ASAT), wherein ASAT comprises activation times monitored from external electrodes of the plurality of external electrodes that correspond to the anterior-septal region of the heart of the patient. 
     Embodiment 11 
     The system of any one of embodiments 1 to 10, wherein the electrical heterogeneity information comprises at least one metric of electrical heterogeneity, wherein the at least one metric of electrical heterogeneity comprises at least one of anterior-septal activation times (ASAT), a standard deviation of activation times (SDAT), a composite left ventricular activation time (LVAT), and a composite right ventricular activation time (RVAT). 
     Embodiment 12 
     The system of any one of embodiments 1 to 11, wherein the computing apparatus is further configured to adjust the one or more VfA paced settings for the VfA pacing therapy based on whether the VfA pacing therapy is acceptable; and 
     wherein the adjusted one or more VfA paced settings is determined to be acceptable in response to the VfA pacing therapy correcting a bundle branch block (BBB). 
     Embodiment 13 
     The system of any one of embodiments 1 to 12, wherein the computing apparatus is further configured to adjust the one or more VfA paced settings for the VfA pacing therapy based on whether the VfA pacing therapy is acceptable; and 
     wherein the adjusted one or more VfA paced settings is determined to be acceptable in response to the VfA pacing therapy completely engaging a Purkinje system of the heart of the patient. 
     Embodiment 14 
     A method comprising: 
     monitoring electrical activity from tissue of a patient using a plurality of external electrodes; 
     generating paced electrical heterogeneity information (EHI) based on the monitored electrical activity during delivery of ventricle from atrium (VfA) pacing therapy at one or more VfA paced settings, wherein the paced EHI is representative of at least one of mechanical cardiac functionality and electrical cardiac functionality; and 
     determining whether the one or more VfA paced settings for the VfA pacing therapy are acceptable based on the paced EHI. 
     Embodiment 15 
     The method of embodiment 14, wherein the one or more VfA paced settings comprise at least one of a voltage, a pulse width, timing of a V-pacing relative to intrinsic or paced atrial timing, and pacing rate. 
     Embodiment 16 
     The method of any one of embodiments 14 to 15, wherein the one or more VfA paced settings comprises a location of at least one implantable electrode wherein the location comprises at least one of depth and angle. 
     Embodiment 17 
     The method of any one of embodiments 14 to 16, wherein the one or more VfA paced settings comprises at least one of a pacing polarity, a pacing vector, and a number of pacing electrodes used. 
     Embodiment 18 
     The method of any one of embodiments 14 to 17, wherein the delivery of the VfA pacing therapy is performed by a VfA therapy apparatus, wherein the VfA pacing therapy apparatus comprises 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 the VfA pacing therapy to the left ventricle in the basal and/or septal region of the left ventricular myocardium of the patient. 
     Embodiment 19 
     The method of embodiment 18, wherein the VfA paced settings comprises a location of the at least one implantable electrode proximate the high posterior basal and/or septal area of the left ventricle of the patient. 
     Embodiment 20 
     The method of any one of embodiments 14 to 19, wherein the plurality of external electrodes comprises surface electrodes positioned in an array configured to be located proximate skin of a torso of the patient. 
     Embodiment 21 
     The method of any one of embodiments 14 to 20, wherein the paced EHI comprises a metric of electrical heterogeneity, wherein the determining whether the one or more VfA paced settings for the VfA pacing therapy are acceptable comprises determining that the one or more VfA paced settings are acceptable if the metric of electrical heterogeneity is less than or equal to a threshold. 
     Embodiment 22 
     The method of any one of embodiments 14 to 21, wherein the determining whether the one or more VfA paced settings for the VfA pacing therapy are acceptable comprises: 
     generating baseline EHI from the monitored electrical activity without delivery of the VfA pacing therapy; 
     comparing the baseline EHI to the paced EHI; and 
     determining that the one or more VfA paced settings are acceptable based on the comparison of the baseline EHI to the paced EHI. 
     Embodiment 23 
     The method of any one of embodiments 14 to 22, wherein the electrical heterogeneity information comprises at least one metric of electrical heterogeneity, wherein the at least one metric of electrical heterogeneity comprises anterior-septal activation times (ASAT), wherein ASAT comprises activation times monitored from external electrodes of the plurality of external electrodes that correspond to the anterior-septal region of the heart of the patient. 
     Embodiment 24 
     The method of any one of embodiments 14 to 23, wherein the electrical heterogeneity information comprises at least one metric of electrical heterogeneity, wherein the at least one metric of electrical heterogeneity comprises at least one of anterior-septal activation times (ASAT), a standard deviation of activation times (SDAT), a composite left ventricular activation time (LVAT), and a composite right ventricular activation time (RVAT). 
     Embodiment 25 
     The method of any one of embodiments 14 to 24, further comprising adjusting the one or more VfA paced settings for the VfA pacing therapy based on whether the VfA pacing therapy is acceptable; and 
     wherein the adjusted one or more VfA paced settings is determined to be acceptable in response to the VfA pacing therapy correcting a bundle branch block (BBB). 
     Embodiment 26 
     The method of any one of embodiments 14 to 26, wherein the computing apparatus is further configured to adjust the one or more VfA paced settings for the VfA pacing therapy based on whether the VfA pacing therapy is acceptable; and 
     wherein the adjusted one or more VfA paced settings is determined to be acceptable in response to the VfA pacing therapy completely engaging a Purkinje system of the heart of the patient. 
     Embodiment 27 
     A system comprising: 
     electrode apparatus comprising a plurality of external electrodes to monitor electrical activity from tissue of a patient; and 
     computing apparatus comprising processing circuitry and coupled to the electrode apparatus and configured to:
         monitor electrical activity using the plurality of external electrodes during delivery of ventricle from atrium (VfA) pacing therapy;   generate electrical heterogeneity information (EHI) during delivery of VfA pacing therapy;   determine whether a VfA paced setting for the VfA pacing therapy is acceptable based on the EHI generated from the electrical activity using the VfA paced setting; and   adjust the paced setting for the VfA pacing therapy based on whether the VfA pacing therapy is acceptable.