Patent Publication Number: US-11648406-B2

Title: Systems, methods, and interfaces for identifying effective electrodes

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is a continuation application of U.S. patent application Ser. No. 14/227,955, filed Mar. 27, 2014, which claims the benefit of U.S. Provisional Patent Application 61/913,795 entitled “Systems, Methods, and Interfaces for Identifying Effective Electrodes” and filed on Dec. 9, 2013 and U.S. Provisional Patent Application 61/817,483 entitled “Identifying Effective Electrodes” and filed on Apr. 30, 2013, each of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     The disclosure herein relates to systems, methods, and interfaces for identifying effective electrodes used to sense signals from tissue and/or deliver therapy to tissue. The identified electrodes may be used in systems, methods, and interfaces for navigating an implantable electrode to a region of a patient&#39;s heart for cardiac therapy. 
     Electrodes may be used in various systems, devices, and methods for medical treatment of a patient. More specifically, electrodes may be located adjacent, or in contact, with tissue (e.g., skin, cardiac tissue, etc.) of a patient to sense signals from the tissue of the patient and/or deliver therapy to the tissue of the patient. Each of the electrodes may be effective or ineffective for sensing signals from the tissue of the patient and/or delivering therapy to the tissue of the patient for multiple reasons. For example, an electrode may not be effectively coupled to, or in contact with, the tissue of the patient rendering the electrode ineffective for sensing signals form the tissue of the patient and/or delivering therapy to the tissue of the patient. Further, for example, an electrode, or an electrical connection between the electrode and monitoring apparatus, may be damaged or otherwise non-functional rendering the electrode ineffective for sensing signals from the tissue of the patient and/or delivering therapy to the tissue of the patient. 
     Exemplary apparatus that utilize multiple electrodes may include multipolar catheters (e.g., catheters including multiple electrodes, etc.) configured to record activation times/voltage mapping simultaneously at different points along a coronary sinus vein or some other anatomic structure (e.g., used for electrical mapping). Further, exemplary apparatus may include multi-electrode electrocardiogram (ECG) systems for body-surface potential mapping configured to record simultaneous ECG measurements from multiple electrodes. 
     SUMMARY 
     The exemplary systems, apparatus, and methods described herein may be configured to analyze one or more signals from one or more electrodes and evaluate the one or more signals to determine whether the one or more electrodes are effective for sensing signals and/or delivering therapy. 
     An exemplary system for identifying effective electrodes may include electrode apparatus and computing apparatus. The electrode apparatus may include a plurality of electrodes (e.g., surface electrodes positioned in an array) configured to be located proximate tissue of a patient. The computing apparatus may be coupled to the electrode apparatus for sensing electrical activity using the electrode apparatus and may be configured to perform an effectiveness test for each electrode of the plurality of electrodes resulting in an effectiveness value (e.g., a Pearson correlation coefficient) for each electrode. To perform the effectiveness test for each electrode, the computing apparatus may be further configured to monitor a signal from the patient using an electrode, store a portion of the signal over a preset time period (e.g., less than or equal to 250 milliseconds) for each cardiac cycle of at least two cardiac cycles (e.g. storing the portion of the signal based on a recurring fiducial element within a cardiac signal), where each portion corresponds to the same time frame within each cardiac cycle, and compare at least two stored portions of the signal to provide the effectiveness value representative of the effectiveness of the electrode for sensing signals from the tissue of the patient. 
     An exemplary method for identifying effective electrodes in a plurality of electrodes (e.g., surface electrodes positioned in an array) located proximate tissue of a patient may include monitoring a signal from the patient using an electrode, storing a portion of the signal over a preset time period (e.g., less than or equal to 250 milliseconds) for each cardiac cycle of at least two cardiac cycles (e.g. storing the portion of the signal based on a recurring fiducial element within a cardiac signal), where each portion corresponds to the same time frame within each cardiac cycle, and comparing at least two stored portions of the signal to provide an effectiveness value (e.g., a Pearson correlation coefficient) representative of the effectiveness of the electrode for sensing signals from the tissue of the patient. 
     An exemplary system for identifying effective electrodes may include electrode means for monitoring a signal from the patient and computing means for storing a portion of the signal over a preset time period for each cardiac cycle of at least two cardiac cycles. Each portion may correspond to the same time frame within each cardiac cycle. The computing means may be further for comparing at least two stored portions of the signal to provide an effectiveness value representative of the effectiveness of the electrode for sensing signals from the tissue of the patient. 
     An exemplary system for use in cardiac therapy may include electrode apparatus (e.g., a plurality of electrodes configured to be located proximate tissue of a patient), display apparatus including a graphical user interface (e.g., the graphical user interface may be configured to present information for use in assisting a user in at least one of assessing a patient&#39;s cardiac health, evaluating and adjusting cardiac therapy delivered to a patient, and navigating at least one implantable electrode to a region of the patient&#39;s heart (e.g., graphically depict at least a portion of anatomy, such as blood vessel anatomy, of the patient&#39;s heart for use in assisting a user in navigating at least one implantable electrode to a region of the patient&#39;s heart, etc.), and computing apparatus coupled to the electrode apparatus and display apparatus. The computing apparatus may be configured to perform an effectiveness test for each electrode of the plurality of electrodes resulting in an effectiveness value for each electrode. To perform the effectiveness test for each electrode, the computing apparatus may be further configured to monitor a signal from the patient using an electrode and store a portion of the signal over a preset time period for each cardiac cycle of at least two cardiac cycles. Each portion may correspond to the same time frame within each cardiac cycle. The computing apparatus may be further configured to compare at least two stored portions of the signal to provide the effectiveness value representative of the effectiveness of the electrode for sensing signals from the tissue of the patient. The computing apparatus may be further configured to display, on the graphical user interface, information for use in assisting a user in at least one of assessing a patient&#39;s cardiac health, evaluating and adjusting cardiac therapy delivered to a patient, and navigating at least one implantable electrode to a region of the patient&#39;s heart (e.g., at least a portion of anatomy, such as blood vessel anatomy, of the patient&#39;s heart for use in assisting a user in navigating at least one implantable electrode to a region of the patient&#39;s heart, etc.). 
     An exemplary method for use in cardiac therapy may include monitoring a signal from the patient using an electrode and storing a portion of the signal over a preset time period for each cardiac cycle of at least two cardiac cycles, each portion corresponds to the same time frame within each cardiac cycle. The exemplary method may further include comparing at least two stored portions of the signal to provide an effectiveness value representative of the effectiveness of the electrode for sensing signals from the tissue of the patient and displaying, on a graphical user interface, information for use in assisting a user in at least one of assessing a patient&#39;s cardiac health, evaluating and adjusting cardiac therapy delivered to a patient, and navigating at least one implantable electrode to a region of the patient&#39;s heart (e.g., at least a portion of anatomy of the patient&#39;s heart for use in assisting a user in navigating at least one implantable electrode to a region of the patient&#39;s heart, etc.). 
     An exemplary system for use in cardiac therapy may include electrode means for monitoring a signal from the patient and computing means for storing a portion of the signal over a preset time period for each cardiac cycle of at least two cardiac cycles. Each portion may correspond to the same time frame within each cardiac cycle. The computing means may be further for comparing at least two stored portions of the signal to provide an effectiveness value representative of the effectiveness of the electrode for sensing signals from the tissue of the patient. The exemplary system may further include display means for displaying, on a graphical user interface, information for use in assisting a user in at least one of assessing a patient&#39;s cardiac health, evaluating and adjusting cardiac therapy delivered to a patient, and navigating at least one implantable electrode to a region of the patient&#39;s heart (e.g., at least a portion of anatomy, such as blood vessel anatomy, of the patient&#39;s heart for use in assisting a user in navigating at least one implantable electrode to a region of the patient&#39;s heart, etc.). 
     In one or more embodiments, the effectiveness value may include a correlation value, the computing apparatus may be further configured to execute or the method may further include disabling any electrode of the plurality of electrodes having a correlation value less than a selected threshold value (e.g., greater than or equal to 0.7 and less than or equal to about 0.95). In one or more embodiments, the effectiveness value may include a correlation value, the computing apparatus may be further configured to execute or the method may further include enabling any electrode of the plurality of electrodes having a correlation value greater than or equal to a selected threshold value. 
     In one or more embodiments, the computing apparatus may be further configured to execute or the method may further include performing an additional effectiveness test for each electrode of the plurality of electrodes resulting in another correlation value for each electrode if more than a selected percentage of the plurality of electrodes had a correlation value less than a selected threshold value. In one or more embodiments, the computing apparatus may be further configured to execute or the method may further include aligning the at least two portions of the signal prior to the comparison. 
     One exemplary system for identifying effective electrodes may include electrode apparatus and computing apparatus. The electrode apparatus may include a plurality of electrodes (e.g., surface electrodes positioned in an array) configured to be located proximate tissue of a patient. The computing apparatus may be coupled to the electrode apparatus for sensing electrical activity using the electrode apparatus and may be configured to perform an effectiveness test for each electrode of the plurality of electrodes resulting in an effectiveness value (e.g., representing a correlation value between the primary electrode and one neighbor electrode, a Pearson correlation coefficient, etc.) for each electrode. To perform the effectiveness test for each electrode, the computing apparatus may be further configured to monitor a first signal from the patient using a primary electrode and monitor at least one secondary signal from the patient using at least one neighbor electrode. At least one neighbor electrode may be spatially adjacent to the primary electrode (e.g., within 3 centimeters from the primary electrode). The computing apparatus may be further configured to store a portion of the first signal over a time period (e.g., corresponding to ventricular depolarization, less than or equal to 250 milliseconds, etc.), store a portion of each of the at least one secondary signal over the time period, and compare the portion of the first signal to the portion of each of the at least one secondary signal to provide at least one effectiveness value representative of the effectiveness of the electrode for sensing cardiac signals from the tissue of the patient. 
     One exemplary method for identifying effective electrodes (e.g., surface electrodes positioned in an array) may include monitoring a first signal from a patient using a primary electrode and monitoring at least one secondary signal from the patient using at least one neighbor electrode. At least one neighbor electrode may be spatially adjacent to the primary electrode (e.g., within 3 centimeters from the primary electrode). The exemplary method may further include storing a portion of the first signal over a time period (e.g., corresponding to ventricular depolarization, less than or equal to 250 milliseconds, etc.), storing a portion of each of the at least one secondary signal over the time period, and comparing the portion of the first signal to the portion of each of the at least one secondary signal to provide at least one effectiveness value (e.g., representing a correlation value between the primary electrode and one neighbor electrode, a Pearson correlation coefficient, etc.) representative of the effectiveness of the electrode for sensing cardiac signals from the tissue of the patient. 
     An exemplary system for identifying effective electrodes may include electrode means for monitoring a first signal from a patient using a primary electrode and for monitoring at least one secondary signal from the patient using at least one neighbor electrode, where the at least one neighbor electrode is spatially adjacent to the primary electrode, and computing means for storing a portion of the first signal over a time period, for storing a portion of each of the at least one secondary signal over the time period, and for comparing the portion of the first signal to the portion of each of the at least one secondary signal to provide at least one effectiveness value representative of the effectiveness of the electrode for sensing cardiac signals from the tissue of the patient. 
     An exemplary system for use in cardiac therapy may include electrode apparatus (e.g., a plurality of electrodes configured to be located proximate tissue of a patient) and display apparatus including a graphical user interface (e.g., the graphical user interface may be configured to present information for use in assisting a user in at least one of assessing a patient&#39;s cardiac health, evaluating and adjusting cardiac therapy delivered to a patient, and navigating at least one implantable electrode to a region of the patient&#39;s heart (e.g., graphically depict at least a portion of anatomy, such as blood vessel anatomy, of the patient&#39;s heart for use in assisting a user in navigating at least one implantable electrode to a region of the patient&#39;s heart, etc.). The exemplary system may further include computing apparatus coupled to the electrode apparatus and display apparatus. The computing apparatus may be configured to perform an effectiveness test for each electrode of the plurality of electrodes resulting in an effectiveness value for each electrode. To perform the effectiveness test for each electrode, the computing apparatus may be further configured to monitor a first signal from the patient using a primary electrode, monitor at least one secondary signal from the patient using at least one neighbor electrode, where the at least one neighbor electrode is spatially adjacent to the primary electrode, store a portion of the first signal over a time period, and store a portion of each of the at least one secondary signal over the time period. The computing apparatus may be further configured to compare the portion of the first signal to the portion of each of the at least one secondary signal to provide at least one effectiveness value representative of the effectiveness of the electrode for sensing cardiac signals from the tissue of the patient and display, on the graphical user interface, information for use in assisting a user in at least one of assessing a patient&#39;s cardiac health, evaluating and adjusting cardiac therapy delivered to a patient, and navigating at least one implantable electrode to a region of the patient&#39;s heart (e.g., at least a portion of anatomy, such as blood vessel anatomy, of the patient&#39;s heart for use in assisting a user in navigating at least one implantable electrode to a region of the patient&#39;s heart, etc.). 
     An exemplary method for use in cardiac therapy may include monitoring a first signal from a patient using a primary electrode and monitoring at least one secondary signal from the patient using at least one neighbor electrode, where the at least one neighbor electrode is spatially adjacent to the primary electrode. The exemplary method may further include storing a portion of the first signal over a time period, storing a portion of each of the at least one secondary signal over the time period, and comparing the portion of the first signal to the portion of each of the at least one secondary signal to provide at least one effectiveness value representative of the effectiveness of the electrode for sensing cardiac signals from the tissue of the patient. The exemplary method may further include displaying, on a graphical user interface, information for use in assisting a user in at least one of assessing a patient&#39;s cardiac health, evaluating and adjusting cardiac therapy delivered to a patient, and navigating at least one implantable electrode to a region of the patient&#39;s heart (e.g., at least a portion of anatomy, such as blood vessel anatomy, of the patient&#39;s heart for use in assisting a user in navigating at least one implantable electrode to a region of the patient&#39;s heart, etc.). 
     An exemplary system for use in cardiac therapy may include electrode means for monitoring a first signal from a patient using a primary electrode and for monitoring at least one secondary signal from the patient using at least one neighbor electrode, where the at least one neighbor electrode is spatially adjacent to the primary electrode, and computing means for storing a portion of the first signal over a time period, for storing a portion of each of the at least one secondary signal over the time period, and for comparing the portion of the first signal to the portion of each of the at least one secondary signal to provide at least one effectiveness value representative of the effectiveness of the electrode for sensing cardiac signals from the tissue of the patient. The exemplary system may further include display means for displaying, on a graphical user interface, information for use in assisting a user in at least one of assessing a patient&#39;s cardiac health, evaluating and adjusting cardiac therapy delivered to a patient, and navigating at least one implantable electrode to a region of the patient&#39;s heart (e.g., at least a portion of anatomy, such as blood vessel anatomy, of the patient&#39;s heart for use in assisting a user in navigating at least one implantable electrode to a region of the patient&#39;s heart, etc.). 
     In one or more embodiments, the effectiveness value may include a correlation value, and the computing apparatus may be further configured to execute or the method may further include disabling any electrode of the plurality of electrodes having all of their at least one correlation value less than or equal to a selected threshold value (e.g., greater than or equal to 0.7 and less than or equal to about 0.95). 
     In one or more embodiments, the computing apparatus may be further configured to execute or the method may further include performing an additional effectiveness test for each electrode of the plurality of electrodes resulting in at least one additional correlation value for each electrode if more than a selected percentage of the plurality of electrodes had all of their at least one correlation value less than a selected threshold value. 
     In one or more embodiments, the computing apparatus may be further configured to execute or the method may further include generating a graphical map including the plurality of electrodes spatially distributed and the effectiveness values of the plurality of electrodes. 
     One exemplary system for identifying effective electrodes may include electrode apparatus and computing apparatus. The electrode apparatus may include a plurality of electrodes configured to be located proximate tissue of a patient. The computing apparatus may be coupled to the electrode apparatus for sensing electrical activity using the electrode apparatus and may be configured to perform an effectiveness test for each electrode of the plurality of electrodes resulting in an effectiveness value for each electrode. To perform the effectiveness test for each electrode, the computing apparatus may be further configured to monitor a signal from the patient using an electrode, store a portion of the signal over a preset time period, and compare at least one morphological feature of the portion of the signal to at least one physiological indication value to provide the effectiveness value representative of the effectiveness of the electrode for sensing signals from the tissue of the patient. In at least one embodiment, the at least one morphological feature may include at least one of maximum value, minimum value, difference between maximum and minimum value, maximum slope, minimum slope, and difference between maximum slope and minimum slope. 
     In at least one embodiment, the system or method may be configured to compare morphologic similarity of a signal recorded at an electrode within an electrode array with that of its spatially adjacent neighbor electrodes, e.g., using a Pearson correlation coefficient or a waveform match percentage, etc. The largest value of correlation coefficient or waveform match percentage or the “best match” value of these or similar metrics (e.g., value(s), functions, comparisons, differences, averages, slopes, etc.) may be selected and the process may be repeated for each electrode in the array to find the “best match” value for each electrode. Then, electrodes may be selected to be used (e.g., for further analysis) based on whose “best match” value exceeds a certain threshold (e.g., a correlation coefficient greater than or equal to 0.8 and/or a waveform match percentage score greater than 70). In essence, valid cardiac signals from an electrode within a spatial electrode-array may bear a high degree of similarity with signals from at least one of the neighbor electrodes whereas non-physiological signals (e.g., noise) may be uncorrelated with signals monitored by neighbor electrodes (e.g., valid cardiac signals, noise, etc.). 
     One exemplary method relates to time correlation of beats sensed from one electrode and includes picking a timing fiducial element (e.g., a V-s or VP marker, a dominant peak or valley on a given ECG lead, etc.) corresponding to each beat, generating a window over a signal of each beat at each electrode about the fiducial, computing a correlation between the windowed signals at each electrode for beats j and j−1, and finding all electrodes which yield a correlation less than or equal to 0.8. In at least one embodiment, the method includes determining if a number of electrodes with a correlation less than or equal to 0.8 exceeds N/2 (where N is the number of electrodes), and if not, eliminating electrodes with correlation less than or equal to 0.8 and performing analysis with remaining electrodes for beats j and j−1. Further, if the electrodes are within the correlation, then skip beats j and j−1 and move on to the next pair of beats (j, j+1) to repeat analysis and/or adjust electrode positions. The exemplary method may be repeated for each electrode of the N electrodes. 
     One exemplary method may include comparing morphologic similarity of signals recorded at an electrode within an N array (e.g., 6 or 7 electrodes, 2 or more electrodes, etc.) with that of its spatially adjacent neighbors. The morphologic comparison may employ the Pearson correlation coefficient, waveform match percentage, and/or any number of methods. The method further includes selecting the largest value of correlation coefficient or waveform match percentage or the ‘best match’ value of these or similar metrics (e.g., value(s), functions, comparisons, differences, averages, slopes, etc.), repeating for each electrode in the array and finding the ‘best match’ value of that electrode, and selecting signals (e.g., for further analysis) from electrodes in which the ‘best match’ value exceeds a certain threshold (e.g., a correlation coefficient greater than 0.8 or waveform match percentage score greater than 70). 
     One exemplary apparatus for automatically selecting electrodes from a surface electrode-array for CRT implant feedback (e.g., evaluating electrical dyssynchrony of the heart of a patient) may include sensing means for sensing a signal from a first one of surface electrode-array in response to the ventricular pacing stimulus, storing means for storing the first sensed signal, sensing means for sensing a second signal from a second one of surface electrode-array in response to the ventricular pacing stimulus, storing means for storing the second sensed signal, processing means for comparing morphologic features between the first and second signals, determining means for determining similarity of the morphological features between the first and second signals, and means for repeatedly processing each electrode of the surface electrode array. Further, the processing means may be configured for determining greatest similarity of the morphological features between two adjacent electrodes of the surface electrode array. The exemplary apparatus may further include selecting means for selecting two adjacent electrodes that exhibit the greatest similarity of the morphological features following the repeated operations for each electrode of the surface electrode array, wherein the selecting means is performed without processing data related to intraventricular synchrony. 
     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 an exemplary implantable medical device (IMD). 
         FIG.  2 A  is a diagram of the exemplary IMD of  FIG.  1   . 
         FIG.  2 B  is a diagram of an enlarged view of a distal end of the electrical lead disposed in the left ventricle of  FIG.  2 A . 
         FIG.  3 A  is a block diagram of an exemplary IMD, e.g., the IMD of  FIGS.  1 - 2   . 
         FIG.  3 B  is another block diagram of an exemplary IMD (e.g., an implantable pulse generator) circuitry and associated leads employed in the system of  FIGS.  1 - 2    for providing three sensing channels and corresponding pacing channels. 
         FIG.  4    is a diagram of an exemplary system including electrode apparatus, imaging apparatus, display apparatus, and computing apparatus. 
         FIGS.  5 A- 5 B  are conceptual diagrams illustrating exemplary systems for measuring torso-surface potentials. 
         FIG.  6    is a block diagram of an exemplary method of identifying an effective electrode using single signal correlation. 
         FIG.  7    is a block diagram of an exemplary method of identifying one or more effective electrodes using single signal correlation. 
         FIG.  8    is a diagram of an exemplary electrode array. 
         FIG.  9    is a block diagram of an exemplary method of identifying an effective electrode using spatial signal correlation, e.g. using the electrode array of  FIG.  8   . 
         FIG.  10    depicts a graph depicting correlation values for a plurality of electrodes. 
         FIG.  11    depicts three graphs depicting signals for ineffective electrodes. 
         FIG.  12    depicts two graphs depicting signals for effective electrodes. 
         FIG.  13    depicts a graph of a distribution of correlation values for a plurality of electrodes evaluated by, e.g., the exemplary methods of  FIGS.  6 - 7  and  9   . 
         FIG.  14    is a block diagram of an exemplary method of identifying an effective electrode using morphological features. 
         FIG.  15    is an exemplary graphical user interface depicting blood vessel anatomy configured to assist a user in navigating an implantable electrode to a region of a patient&#39;s heart for cardiac therapy. 
         FIG.  16    is an exemplary graphical user interface depicting a human heart including activation times mapped thereon configured to assist a user in navigating an implantable electrode to a region of a patient&#39;s heart for cardiac therapy. 
     
    
    
     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, apparatus, and methods shall be described with reference to  FIGS.  1 - 16   . 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, apparatus, 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. 
     As described herein, various exemplary systems, apparatus, and methods may utilize electrodes configured to sense one or more signals from tissue of a patient and/or deliver therapy to tissue of the patient. For example, electrodes may be included in apparatus such as vests, bands, belts, straps, patches, any wearable garment, t-shirts, bras, hats (e.g., for neural signals), etc. and may be configured to be located externally to the patient in contact with the skin of the patient for, e.g., monitoring cardiac signals (e.g., electrocardiograms) of a patient, mapping a patient&#39;s heart, etc. Further, for example, electrodes may be individually located, or placed, on a patient. Further, for example, electrodes may be included in or on apparatus such as a basket catheter, a sock, etc., and may be configured to be located within internal spaces (e.g., cardiac spaces) of a patient, e.g., for cardiac mapping purposes, etc. Further, for example, electrodes may be included as part of an implantable medical device (IMD) and located on one or more leads configured to be located proximate one or more portions of a patient&#39;s heart. 
     In at least one embodiment, a spatial surface electrode array configured to record cardiac signals for computing indices related to electrical dyssynchrony and ventricular activation (which, e.g., may be useful as feedback for cardiac resynchronization therapy implant) may be used. Further, metrics computed from signals from the electrode arrays may be used to, e.g., estimate the time of delivery of left ventricular pacing for optimal fusion for left ventricular-only fusion pacing (e.g., adaptive cardiac resynchronization therapy), estimate scar-burden, etc. 
     As described herein, various exemplary systems, apparatus, and methods may utilize electrodes configured for any kind of cardiac mapping grid e.g., a sock of electrodes to map electrical activity on the outer surface of the heart, a basket or constellation catheter to map electrical activity within a chamber or the endocardial wall, multipolar leads to map electrical activity of the heart or within a vein in the heart, multi-electrode catheters used for mapping, etc. 
     Electrodes may be effective or ineffective for sensing signals and/or delivering therapy depending on multiple factors such as whether the electrodes are properly located, whether the electrodes are in sufficient contact with tissue, whether the electrodes or the connections to the electrodes are damaged, etc. As such, a practical problem with a multi-electrode array may be that some of the electrodes may not be effective, and thus, may not provide valid signals (e.g., valid cardiac signals, signals having an adequate signal-to-noise ratio, etc.). 
     The exemplary systems, apparatus, and methods described herein may provide a way of automated selection of effective electrodes, or electrodes with valid signals, with little error and/or with minimum operator input. The exemplary systems, apparatus, and methods may provide automated selection of effective electrodes based on similarities, or correlations, of a portion, or window, of a signal for an electrode for a cardiac cycle with another portion of the signal for the electrode for another cardiac cycle. Further, the exemplary systems, apparatus, and methods may provide automated selection of effective electrodes based on similarities, or correlations, of a signal of an electrode with a signal of the spatially adjacent neighbor electrode(s). The automated identification of effective electrodes (e.g., capable of sensing valid cardiac signals) and exclusion of electrodes with noise may provide subsequent analysis with signals from the array that is accurate and provides correct assessment of the electrical dyssynchrony of the heart of a patient that may facilitate patient selection for CRT, facilitate placement of implantable leads (e.g., one or more left ventricular leads) and programming of device parameters for CRT during an implantation procedure, reprogramming of device parameters for CRT during a follow-up visit, etc. For example, a user may make a diagnosis, prescribe CRT, position therapy devices, e.g., leads, or adjust or select treatment parameters based on the indicated electrical dyssynchrony. 
     The exemplary methods and processes described herein may be utilized and implemented by one or more (e.g., two or more, a plurality, etc.) systems, apparatus, and devices that include and/or are coupled to at least one electrode. For example, the exemplary methods and processes may be used by an exemplary therapy system  10  described herein with reference to  FIGS.  1 - 3    and exemplary sensing systems  110 ,  111  including a spatial electrode-array as described herein with reference to  FIGS.  5 A- 5 B . Although only therapy system  10  and sensing systems  110 ,  111  are described and depicted herein, it is to be understood that the exemplary methods and processes may be used by any system including computing apparatus capable of analyzing signals from one or more electrodes. The computing apparatus, for example, may be located in an external computer or programmer, may be located in an IMD, or may be located on a server attached to a network. 
       FIG.  1    is a conceptual diagram illustrating an exemplary therapy system  10  that may be used to deliver pacing therapy to a patient  14 . Patient  14  may, but not necessarily, be a human. The therapy system  10  may include an implantable medical device  16  (IMD), which may be coupled to leads  18 ,  20 ,  22  and/or a programmer  24 . The IMD  16  may be, e.g., an implantable pacemaker, cardioverter, and/or defibrillator, that provides electrical signals to the heart  12  of the patient  14  via electrodes coupled to one or more of the leads  18 ,  20 ,  22 . 
     The leads  18 ,  20 ,  22  extend into the heart  12  of the patient  14  to sense electrical activity of the heart  12  and/or to deliver electrical stimulation to the heart  12 . In the example shown in  FIG.  1   , the right ventricular (RV) lead  18  extends through one or more veins (not shown), the superior vena cava (not shown), and the right atrium  26 , and into the right ventricle  28 . The left ventricular (LV) coronary sinus lead  20  extends through one or more veins, the vena cava, the right atrium  26 , and into the coronary sinus  30  to a region adjacent to the free wall of the left ventricle  32  of the heart  12 . The right atrial (RA) lead  22  extends through one or more veins and the vena cava, and into the right atrium  26  of the heart  12 . 
     The IMD  16  may sense, among other things, electrical signals attendant to the depolarization and repolarization of the heart  12  via electrodes coupled to at least one of the leads  18 ,  20 ,  22 . The IMD  16  may be configured to determine or identify effective electrodes located on the leads  18 ,  20 ,  22  using the exemplary methods and processes described herein. In some examples, the IMD  16  provides pacing therapy (e.g., pacing pulses) to the heart  12  based on the electrical signals sensed within the heart  12 . The IMD  16  may be operable to adjust one or more parameters associated with the pacing therapy such as, e.g., AV delay and other various timings, pulse width, amplitude, voltage, burst length, etc. Further, the IMD  16  may be operable to use various electrode configurations to deliver pacing therapy, which may be unipolar, bipolar, quadripoloar, or further multipolar. For example, a multipolar lead may include several electrodes which can be used for delivering pacing therapy. Hence, a multipolar lead system may provide, or offer, multiple electrical vectors to pace from. A pacing vector may include at least one cathode, which may be at least one electrode located on at least one lead, and at least one anode, which may be at least one electrode located on at least one lead (e.g., the same lead, or a different lead) and/or on the casing, or can, of the IMD. While improvement in cardiac function as a result of the pacing therapy may primarily depend on the cathode, the electrical parameters like impedance, pacing threshold voltage, current drain, longevity, etc. may be more dependent on the pacing vector, which includes both the cathode and the anode. The IMD  16  may also provide defibrillation therapy and/or cardioversion therapy via electrodes located on at least one of the leads  18 ,  20 ,  22 . Further, the IMD  16  may detect arrhythmia of the heart  12 , such as fibrillation of the ventricles  28 ,  32 , and deliver defibrillation therapy to the heart  12  in the form of electrical pulses. In some examples, IMD  16  may be programmed to deliver a progression of therapies, e.g., pulses with increasing energy levels, until a fibrillation of heart  12  is stopped. 
     In some examples, a programmer  24 , which may be a handheld computing device or a computer workstation, may be used by a user, such as a physician, technician, another clinician, and/or patient, to communicate with the IMD  16  (e.g., to program the IMD  16 ). For example, the user may interact with the programmer  24  to retrieve information concerning the effectiveness of one or more electrodes, one or more detected or indicated faults associated within the IMD  16  and/or the pacing therapy delivered therewith. The IMD  16  and the programmer  24  may be configured to work together to determine or identify effective electrodes located on the leads  18 ,  20 ,  22  using the exemplary methods and processes described herein. For instance, computing apparatus located in one or both of the IMD  16  and the programmer  24  may be configured to analyze or evaluate signals from one or more electrodes to determine the effectiveness of the electrodes. The IMD  16  and the programmer  24  may communicate via wireless communication using any techniques known in the art. Examples of communication techniques may include, e.g., low frequency or radiofrequency (RF) telemetry, but other techniques are also contemplated. 
       FIG.  2    is a conceptual diagram illustrating the IMD  16  and the leads  18 ,  20 ,  22  of therapy system  10  of  FIG.  1    in more detail. The leads  18 ,  20 ,  22  may be electrically coupled to a therapy delivery module (e.g., for delivery of pacing therapy), a sensing module (e.g., for sensing one or more signals from one or more electrodes configured to contact tissue of a patient), and/or any other modules of the IMD  16  via a connector block  34 . In some examples, the proximal ends of the leads  18 ,  20 ,  22  may include electrical contacts that electrically couple to respective electrical contacts within the connector block  34  of the IMD  16 . In addition, in some examples, the leads  18 ,  20 ,  22  may be mechanically coupled to the connector block  34  with the aid of set screws, connection pins, or another suitable mechanical coupling mechanism. 
     Each of the leads  18 ,  20 ,  22  includes an elongated insulative lead body, which may carry a number of conductors (e.g., concentric coiled conductors, straight conductors, etc.) separated from one another by insulation (e.g., tubular insulative sheaths). In the illustrated example, bipolar electrodes  40 ,  42  are located proximate to a distal end of the lead  18 . In addition, the bipolar electrodes  44 ,  45 ,  46 ,  47  are located proximate to a distal end of the lead  20  and the bipolar electrodes  48 ,  50  are located proximate to a distal end of the lead  22 . 
     The electrodes  40 ,  44 ,  45 ,  46 ,  47 ,  48  may take the form of ring electrodes, and the electrodes  42 ,  50  may take the form of extendable helix tip electrodes mounted retractably within the insulative electrode heads  52 ,  54 ,  56 , respectively. Each of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50  may be electrically coupled to a respective one of the conductors (e.g., coiled and/or straight) within the lead body of its associated lead  18 ,  20 ,  22 , and thereby coupled to respective ones of the electrical contacts on the proximal end of the leads  18 ,  20 ,  22 . 
     Additionally, electrodes  44 ,  45 ,  46  and  47  may have an electrode surface area of about 5.3 mm 2  to about 5.8 mm 2 . Electrodes  44 ,  45 ,  46 , and  47  may also referred to as LV 1 , LV 2 , LV 3 , and LV 4 , respectively. The LV electrodes (i.e., left ventricle electrode  1  (LV 1 )  44 , left ventricle electrode  2  (LV 2 )  45 , left ventricle electrode  3  (LV 3 )  46 , and left ventricle  4  (LV 4 )  47  etc.) on the lead  20  can be spaced apart at variable distances. For example, electrode  44  may be a distance of, e.g., about 21 millimeters (mm), away from electrode  45 , electrodes  45  and  46  may be spaced a distance of, e.g. about 1.3 mm to about 1.5 mm, away from each other, and electrodes  46  and  47  may be spaced a distance of, e.g. 20 mm to about 21 mm, away from each other. 
     The electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50  may further be used to sense electrical signals (e.g., morphological waveforms within electrograms (EGM)) attendant to the depolarization and repolarization of the heart  12 . The sensed electrical signals may be used to determine whether the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50  are effective (e.g., capable of sensing valid cardiac signals, capable of delivering therapy, in sufficient contact with cardiac tissue, etc.). The electrical signals are conducted to the IMD  16  via the respective leads  18 ,  20 ,  22 . In some examples, the IMD  16  may also deliver pacing pulses via the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50  to cause depolarization of cardiac tissue of the patient&#39;s heart  12 . In some examples, as illustrated in  FIG.  2 A , the IMD  16  includes one or more housing electrodes, such as housing electrode  58 , which may be formed integrally with an outer surface of a housing  60  (e.g., hermetically-sealed housing) of the IMD  16  or otherwise coupled to the housing  60 . Any of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48  and  50  may be used for unipolar sensing or pacing in combination with housing electrode  58 . In other words, any of electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58  may be used in combination to form a sensing vector, e.g., a sensing vector that may be used to evaluate and/or analyze the effectiveness of pacing therapy. It is generally understood by those skilled in the art that other electrodes can also be selected to define, or be used for, pacing and sensing vectors. Further, any of electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 , which are not being used to deliver pacing therapy, may be used to sense electrical activity during pacing therapy. 
     As described in further detail with reference to  FIGS.  3 A- 3 B , the housing  60  may enclose a therapy delivery module that may include a stimulation generator for generating cardiac pacing pulses and defibrillation or cardioversion shocks, as well as a sensing module for monitoring the patient&#39;s heart rhythm. The leads  18 ,  20 ,  22  may also include elongated electrodes  62 ,  64 ,  66 , respectively, which may take the form of a coil. The IMD  16  may deliver defibrillation shocks to the heart  12  via any combination of the elongated electrodes  62 ,  64 ,  66  and the housing electrode  58 . The electrodes  58 ,  62 ,  64 ,  66  may also be used to deliver cardioversion pulses to the heart  12 . Further, the electrodes  62 ,  64 ,  66  may be fabricated from any suitable electrically conductive material, such as, but not limited to, platinum, platinum alloy, and/or other materials known to be usable in implantable defibrillation electrodes. Since electrodes  62 ,  64 ,  66  are not generally configured to deliver pacing therapy, any of electrodes  62 ,  64 ,  66  may be used to sense electrical activity (e.g., for use in determining electrode effectiveness, for use in analyzing pacing therapy effectiveness, etc.) and may be used in combination with any of electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 . In at least one embodiment, the RV elongated electrode  62  may be used to sense electrical activity of a patient&#39;s heart during the delivery of pacing therapy (e.g., in combination with the housing electrode  58  forming a RV elongated coil, or defibrillation electrode-to-housing electrode vector). 
     The configuration of the exemplary therapy system  10  illustrated in  FIGS.  1 - 2    is merely one example. In other examples, the therapy system may include epicardial leads and/or patch electrodes instead of or in addition to the transvenous leads  18 ,  20 ,  22  illustrated in  FIG.  1   . Further, in one or more embodiments, the IMD  16  need not be implanted within the patient  14 . For example, the IMD  16  may deliver various cardiac therapies to the heart  12  via percutaneous leads that extend through the skin of the patient  14  to a variety of positions within or outside of the heart  12 . In one or more embodiments, the system  10  may utilize wireless pacing (e.g., using energy transmission to the intracardiac pacing component(s) via ultrasound, inductive coupling, RF, etc.) and sensing cardiac activation using electrodes on the can/housing and/or on subcutaneous leads. 
     In other examples of therapy systems that provide electrical stimulation therapy to the heart  12 , such therapy systems may include any suitable number of leads coupled to the IMD  16 , and each of the leads may extend to any location within or proximate to the heart  12 . For example, other examples of therapy systems may include three transvenous leads located as illustrated in  FIGS.  1 - 2   . Still further, other therapy systems may include a single lead that extends from the IMD  16  into the right atrium  26  or the right ventricle  28 , or two leads that extend into a respective one of the right atrium  26  and the right ventricle  28 . 
       FIG.  3 A  is a functional block diagram of one exemplary configuration of the IMD  16 . As shown, the IMD  16  may include a control module  81 , a therapy delivery module  84  (e.g., which may include a stimulation generator), a sensing module  86 , and a power source  90 . 
     The control module  81  may include a processor  80 , memory  82 , and a telemetry module  88 . The memory  82  may include computer-readable instructions that, when executed, e.g., by the processor  80 , cause the IMD  16  and/or the control module  81  to perform various functions attributed to the IMD  16  and/or the control module  81  described herein. Further, the memory  82  may include any volatile, non-volatile, magnetic, optical, and/or electrical media, such as a random access memory (RAM), read-only memory (ROM), non-volatile RAM (NVRAM), electrically-erasable programmable ROM (EEPROM), flash memory, and/or any other digital media. An exemplary capture management module may be the left ventricular capture management (LVCM) module described in U.S. Pat. No. 7,684,863 issued Mar. 23, 2010, which is incorporated herein by reference in its entirety. 
     The processor  80  of the control module  81  may include any one or more of a microprocessor, a controller, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), and/or equivalent discrete or integrated logic circuitry. In some examples, the processor  80  may include multiple components, such as any combination of one or more microprocessors, one or more controllers, one or more DSPs, one or more ASICs, and/or one or more FPGAs, as well as other discrete or integrated logic circuitry. The functions attributed to the processor  80  herein may be embodied as software, firmware, hardware, or any combination thereof. 
     The control module  81  may be used to determine the effectiveness of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66  using the exemplary methods and/or processes described herein according to a selected one or more programs, which may be stored in the memory  82 . Further, the control module  81  may control the therapy delivery module  84  to deliver therapy (e.g., electrical stimulation therapy such as pacing) to the heart  12  according to a selected one or more therapy programs, which may be stored in the memory  82 . More specifically, the control module  81  (e.g., the processor  80 ) may control various parameters of the electrical stimulus delivered by the therapy delivery module  84  such as, e.g., AV delays, pacing pulses with the amplitudes, pulse widths, frequency, or electrode polarities, etc., which may be specified by one or more selected therapy programs (e.g., AV delay adjustment programs, pacing therapy programs, pacing recovery programs, capture management programs, etc.). As shown, the therapy delivery module  84  is electrically coupled to electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66 , e.g., via conductors of the respective lead  18 ,  20 ,  22 , or, in the case of housing electrode  58 , via an electrical conductor disposed within housing  60  of IMD  16 . Therapy delivery module  84  may be configured to generate and deliver electrical stimulation therapy such as pacing therapy to the heart  12  using one or more of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66 . 
     For example, therapy delivery module  84  may deliver pacing stimulus (e.g., pacing pulses) via ring electrodes  40 ,  44 ,  45 ,  46 ,  47 ,  48  coupled to leads  18 ,  20 , and  22 , respectively, and/or helical tip electrodes  42 ,  50  of leads  18 ,  20 , and  22 . Further, for example, therapy delivery module  84  may deliver defibrillation shocks to heart  12  via at least two of electrodes  58 ,  62 ,  64 ,  66 . In some examples, therapy delivery module  84  may be configured to deliver pacing, cardioversion, or defibrillation stimulation in the form of electrical pulses. In other examples, therapy delivery module  84  may be configured deliver one or more of these types of stimulation in the form of other signals, such as sine waves, square waves, and/or other substantially continuous time signals. 
     The IMD  16  may further include a switch module  85  and the control module  81  (e.g., the processor  80 ) may use the switch module  85  to select, e.g., via a data/address bus, which of the available electrodes are used to deliver therapy such as pacing pulses for pacing therapy, or which of the available electrodes are used for sensing. The switch module  85  may include a switch array, switch matrix, multiplexer, or any other type of switching device suitable to selectively couple the sensing module  86  and/or the therapy delivery module  84  to one or more selected electrodes. More specifically, the therapy delivery module  84  may include a plurality of pacing output circuits. Each pacing output circuit of the plurality of pacing output circuits may be selectively coupled, e.g., using the switch module  85 , to one or more of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66  (e.g., a pair of electrodes for delivery of therapy to a pacing vector). In other words, each electrode can be selectively coupled to one of the pacing output circuits of the therapy delivery module using the switching module  85 . 
     The sensing module  86  is coupled (e.g., electrically coupled) to sensing apparatus, which may include, among additional sensing apparatus, the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66  to monitor electrical activity of the heart  12 , e.g., electrocardiogram (ECG)/electrogram (EGM) signals, etc. The ECG/EGM signals may be used to identify the effectiveness of each of the electrodes  40 ,  42 ,  44 ,  46 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66  (e.g., by monitoring or measuring the signals for analysis by the control module  81 , the programmer  24 , etc.). Further, the ECG/EGM signals may be used to measure or monitor activation times (e.g., ventricular activations times, etc.), heart rate (HR), heart rate variability (HRV), heart rate turbulence (HRT), deceleration/acceleration capacity, deceleration sequence incidence, T-wave alternans (TWA), P-wave to P-wave intervals (also referred to as the P-P intervals or A-A intervals), R-wave to R-wave intervals (also referred to as the R-R intervals or V-V intervals), P-wave to QRS complex intervals (also referred to as the P-R intervals, A-V intervals, or P-Q intervals), QRS-complex morphology, ST segment (i.e., the segment that connects the QRS complex and the T-wave), T-wave changes, QT intervals, electrical vectors, etc. 
     The switch module  85  may be also be used with the sensing module  86  to select which of the available electrodes are used, or enabled, to, e.g., sense electrical activity of the patient&#39;s heart (e.g., one or more electrical vectors of the patient&#39;s heart using any combination of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66 ). Likewise, the switch module  85  may be also be used with the sensing module  86  to select which of the available electrodes are not to be used (e.g., disabled) to, e.g., sense electrical activity of the patient&#39;s heart (e.g., one or more electrical vectors of the patient&#39;s heart using any combination of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66 ). In some examples, the control module  81  may select the electrodes that function as sensing electrodes via the switch module within the sensing module  86 , e.g., by providing signals via a data/address bus. 
     In some examples, sensing module  86  includes a channel that includes an amplifier with a relatively wider pass band than the R-wave or P-wave amplifiers. Signals from the selected sensing electrodes may be provided to a multiplexer, and thereafter converted to multi-bit digital signals by an analog-to-digital converter for storage in memory  82 , e.g., as an electrogram (EGM). In some examples, the storage of such EGMs in memory  82  may be under the control of a direct memory access circuit. The control module  81  (e.g., using the processor  80 ) may employ digital signal analysis techniques to characterize the digitized signals stored in memory  82  to analyze and/or classify one or more morphological waveforms of the EGM signals to determine which electrodes are effective (e.g., operable for capturing valid signals), determine which electrodes are ineffective (e.g., inoperable for capturing valid signals), determine pacing therapy effectiveness, etc. For example, the processor  80  may be configured to determine, or obtain, one more features of one or more sensed morphological waveforms within one or more electrical vectors of the patient&#39;s heart and store the one or more features within the memory  82  for use in comparing features, values, etc. of the waveforms to determine effectiveness of the electrodes. 
     In some examples, the control module  81  may operate as an interrupt driven device, and may be responsive to interrupts from pacer timing and control module, where the interrupts may correspond to the occurrences of sensed P-waves and R-waves and the generation of cardiac pacing pulses. Any necessary mathematical calculations may be performed by the processor  80  and any updating of the values or intervals controlled by the pacer timing and control module may take place following such interrupts. A portion of memory  82  may be configured as a plurality of recirculating buffers, capable of holding one or more series of measured intervals, which may be analyzed by, e.g., the processor  80  in response to the occurrence of a pace or sense interrupt to determine whether the patient&#39;s heart  12  is presently exhibiting atrial or ventricular tachyarrhythmia. 
     The telemetry module  88  of the control module  81  may include any suitable hardware, firmware, software, or any combination thereof for communicating with another device, such as the programmer  24  as described herein with respect to  FIG.  1   . For example, under the control of the processor  80 , the telemetry module  88  may receive downlink telemetry from and send uplink telemetry to the programmer  24  with the aid of an antenna, which may be internal and/or external. The processor  80  may provide the data to be uplinked to the programmer  24  and the control signals for the telemetry circuit within the telemetry module  88 , e.g., via an address/data bus. In some examples, the telemetry module  88  may provide received data to the processor  80  via a multiplexer. 
     The various components of the IMD  16  are further coupled to a power source  90 , which may include a rechargeable or non-rechargeable battery. A non-rechargeable battery may be selected to last for several years, while a rechargeable battery may be inductively charged from an external device, e.g., on a daily or weekly basis. 
       FIG.  3 B  is another embodiment of a functional block diagram for IMD  16 .  FIG.  3 B  depicts bipolar RA lead  22 , bipolar RV lead  18 , and bipolar LV CS lead  20  without the LA CS pace/sense electrodes and coupled with an implantable pulse generator (IPG) circuit  31  having programmable modes and parameters of a bi-ventricular DDD/R type known in the pacing art. In turn, the sensor signal processing circuit  91  indirectly couples to the timing circuit  83  and via data and control bus to microcomputer circuitry  33 . The IPG circuit  31  is illustrated in a functional block diagram divided generally into a microcomputer circuit  33  and a pacing circuit  21 . The pacing circuit  21  includes the digital controller/timer circuit  83 , the output amplifiers circuit  51 , the sense amplifiers circuit  55 , the RF telemetry transceiver  41 , the activity sensor circuit  35  as well as a number of other circuits and components described below. 
     Crystal oscillator circuit  89  provides the basic timing clock for the pacing circuit  21 , while battery  29  provides power. Power-on-reset circuit  87  responds to initial connection of the circuit to the battery for defining an initial operating condition and similarly, resets the operative state of the device in response to detection of a low battery condition. Reference mode circuit  37  generates stable voltage reference and currents for the analog circuits within the pacing circuit  21 , while analog to digital converter ADC and multiplexer circuit  39  digitizes analog signals and voltage to provide real time telemetry if a cardiac signals from sense amplifiers  55 , for uplink transmission via RF transmitter and receiver circuit  41 . Voltage reference and bias circuit  37 , ADC and multiplexer  39 , power-on-reset circuit  87  and crystal oscillator circuit  89  may correspond to any of those presently used in current marketed implantable cardiac pacemakers. 
     If the IPG is programmed to a rate responsive mode, the signals output by one or more physiologic sensor are employed as a rate control parameter (RCP) to derive a physiologic escape interval. For example, the escape interval is adjusted proportionally to the patient&#39;s activity level developed in the patient activity sensor (PAS) circuit  35  in the depicted, exemplary IPG circuit  31 . The patient activity sensor  27  is coupled to the IPG housing and may take the form of a piezoelectric crystal transducer as is well known in the art and its output signal is processed and used as the RCP. Sensor  27  generates electrical signals in response to sensed physical activity that are processed by activity circuit  35  and provided to digital controller/timer circuit  83 . Activity circuit  35  and associated sensor  27  may correspond to the circuitry disclosed in U.S. Pat. No. 5,052,388 issued Oct. 1, 1991 and U.S. Pat. No. 4,428,378 issued Jan. 31, 1984, each of which is incorporated herein by reference in its entirety. Similarly, the exemplary systems, apparatus, and methods described herein may be practiced in conjunction with alternate types of sensors such as oxygenation sensors, pressure sensors, pH sensors and respiration sensors, all well known for use in providing rate responsive pacing capabilities. Alternately, QT time may be used as the rate indicating parameter, in which case no extra sensor is required. Similarly, the exemplary embodiments described herein may also be practiced in non-rate responsive pacemakers. 
     Data transmission to and from the external programmer is accomplished by way of the telemetry antenna  57  and an associated RF transceiver  41 , which serves both to demodulate received downlink telemetry and to transmit uplink telemetry. Uplink telemetry capabilities will typically include the ability to transmit stored digital information, e.g. operating modes and parameters, EGM histograms, and other events, as well as real time EGMs of atrial and/or ventricular electrical activity and marker channel pulses indicating the occurrence of sensed and paced depolarizations in the atrium and ventricle, as are well known in the pacing art. 
     Microcomputer  33  contains a microprocessor  80  and associated system clock and on-processor RAM and ROM chips  82 A and  82 B, respectively. In addition, microcomputer circuit  33  includes a separate RAM/ROM chip  82 C to provide additional memory capacity. Microprocessor  80  normally operates in a reduced power consumption mode and is interrupt driven. Microprocessor  80  is awakened in response to defined interrupt events, which may include A-TRIG, RV-TRIG, LV-TRIG signals generated by timers in digital timer/controller circuit  83  and A-EVENT, RV-EVENT, and LV-EVENT signals generated by sense amplifiers circuit  55 , among others. The specific values of the intervals and delays timed out by digital controller/timer circuit  83  are controlled by the microcomputer circuit  33  by way of data and control bus from programmed-in parameter values and operating modes. In addition, if programmed to operate as a rate responsive pacemaker, a timed interrupt, e.g., every cycle or every two seconds, may be provided in order to allow the microprocessor to analyze the activity sensor data and update the basic A-A, V-A, or V-V escape interval, as applicable. In addition, the microprocessor  80  may also serve to define variable, operative AV delay intervals and the energy delivered to each ventricle. 
     In one embodiment, microprocessor  80  is a custom microprocessor adapted to fetch and execute instructions stored in RAM/ROM unit  82  in a conventional manner. It is contemplated, however, that other implementations may be suitable to practice the present invention. For example, an off-the-shelf, commercially available microprocessor or microcontroller, or custom application-specific, hardwired logic, or state-machine type circuit may perform the functions of microprocessor  80 . 
     Digital controller/timer circuit  83  operates under the general control of the microcomputer  33  to control timing and other functions within the pacing circuit  320  and includes a set of timing and associated logic circuits of which certain ones pertinent to the present invention are depicted. The depicted timing circuits include URI/LRI timers  83 A, V-V delay timer  83 B, intrinsic interval timers  83 C for timing elapsed V-EVENT to V-EVENT intervals or V-EVENT to A-EVENT intervals or the V-V conduction interval, escape interval timers  83 D for timing A-A, V-A, and/or V-V pacing escape intervals, an AV delay interval timer  83 E for timing the A-LVp delay (or A-RVp delay) from a preceding A-EVENT or A-TRIG, a post-ventricular timer  83 F for timing post-ventricular time periods, and a date/time clock  83 G. 
     The AV delay interval timer  83 E is loaded with an appropriate delay interval for one ventricular chamber (e.g., either an A-RVp delay or an A-LVp delay as determined using known methods) to time-out starting from a preceding A-PACE or A-EVENT. The interval timer  83 E triggers pacing stimulus delivery, and can be based on one or more prior cardiac cycles (or from a data set empirically derived for a given patient). 
     The post-event timer  83 F time out the post-ventricular time period following an RV-EVENT or LV-EVENT or a RV-TRIG or LV-TRIG and post-atrial time periods following an A-EVENT or A-TRIG. The durations of the post-event time periods may also be selected as programmable parameters stored in the microcomputer  33 . The post-ventricular time periods include the PVARP, a post-atrial ventricular blanking period (PAVBP), a ventricular blanking period (VBP), a post-ventricular atrial blanking period (PVARP) and a ventricular refractory period (VRP) although other periods can be suitably defined depending, at least in part, on the operative circuitry employed in the pacing engine. The post-atrial time periods include an atrial refractory period (ARP) during which an A-EVENT is ignored for the purpose of resetting any AV delay, and an atrial blanking period (ABP) during which atrial sensing is disabled. It should be noted that the starting of the post-atrial time periods and the AV delays can be commenced substantially simultaneously with the start or end of each A-EVENT or A-TRIG or, in the latter case, upon the end of the A-PACE which may follow the A-TRIG. Similarly, the starting of the post-ventricular time periods and the V-A escape interval can be commenced substantially simultaneously with the start or end of the V-EVENT or V-TRIG or, in the latter case, upon the end of the V-PACE which may follow the V-TRIG. The microprocessor  80  also optionally calculates AV delays, post-ventricular time periods, and post-atrial time periods that vary with the sensor based escape interval established in response to the RCP(s) and/or with the intrinsic atrial rate. 
     The output amplifiers circuit  51  contains a RA pace pulse generator (and a LA pace pulse generator if LA pacing is provided), a RV pace pulse generator, and a LV pace pulse generator or corresponding to any of those presently employed in commercially marketed cardiac pacemakers providing atrial and ventricular pacing. In order to trigger generation of an RV-PACE or LV-PACE pulse, digital controller/timer circuit  83  generates the RV-TRIG signal at the time-out of the A-RVp delay (in the case of RV pre-excitation) or the LV-TRIG at the time-out of the A-LVp delay (in the case of LV pre-excitation) provided by AV delay interval timer  83 E (or the V-V delay timer  83 B). Similarly, digital controller/timer circuit  83  generates an RA-TRIG signal that triggers output of an RA-PACE pulse (or an LA-TRIG signal that triggers output of an LA-PACE pulse, if provided) at the end of the V-A escape interval timed by escape interval timers  83 D. 
     The output amplifiers circuit  51  includes switching circuits for coupling selected pace electrode pairs from among the lead conductors and the IND_CAN electrode  20  to the RA pace pulse generator (and LA pace pulse generator if provided), RV pace pulse generator and LV pace pulse generator. Pace/sense electrode pair selection and control circuit  53  selects lead conductors and associated pace electrode pairs to be coupled with the atrial and ventricular output amplifiers within output amplifiers circuit  51  for accomplishing RA, LA, RV and LV pacing. 
     The sense amplifiers circuit  55  contains sense amplifiers corresponding to any of those presently employed in contemporary cardiac pacemakers for atrial and ventricular pacing and sensing. High impedance P-wave and R-wave sense amplifiers may be used to amplify a voltage difference signal that is generated across the sense electrode pairs by the passage of cardiac depolarization wavefronts. The high impedance sense amplifiers use high gain to amplify the low amplitude signals and rely on pass band filters, time domain filtering and amplitude threshold comparison to discriminate a P-wave or R-wave from background electrical noise. Digital controller/timer circuit  83  controls sensitivity settings of the atrial and ventricular sense amplifiers  55 . 
     The sense amplifiers are typically uncoupled from the sense electrodes during the blanking periods before, during, and after delivery of a pace pulse to any of the pace electrodes of the pacing system to avoid saturation of the sense amplifiers. The sense amplifiers circuit  55  includes blanking circuits for uncoupling the selected pairs of the lead conductors and the IND-CAN electrode  20  from the inputs of the RA sense amplifier (and LA sense amplifier if provided), RV sense amplifier and LV sense amplifier during the ABP, PVABP and VBP. The sense amplifiers circuit  55  also includes switching circuits for coupling selected sense electrode lead conductors and the IND-CAN electrode  20  to the RA sense amplifier (and LA sense amplifier if provided), RV sense amplifier and LV sense amplifier. Again, sense electrode selection and control circuit  53  selects conductors and associated sense electrode pairs to be coupled with the atrial and ventricular sense amplifiers within the output amplifiers circuit  51  and sense amplifiers circuit  55  for accomplishing RA, LA, RV and LV sensing along desired unipolar and bipolar sensing vectors. 
     Right atrial depolarizations or P-waves in the RA-SENSE signal that are sensed by the RA sense amplifier result in a RA-EVENT signal that is communicated to the digital controller/timer circuit  83 . Similarly, left atrial depolarizations or P-waves in the LA-SENSE signal that are sensed by the LA sense amplifier, if provided, result in a LA-EVENT signal that is communicated to the digital controller/timer circuit  83 . Ventricular depolarizations or R-waves in the RV-SENSE signal are sensed by a ventricular sense amplifier result in an RV-EVENT signal that is communicated to the digital controller/timer circuit  83 . Similarly, ventricular depolarizations or R-waves in the LV-SENSE signal are sensed by a ventricular sense amplifier result in an LV-EVENT signal that is communicated to the digital controller/timer circuit  83 . The RV-EVENT, LV-EVENT, and RA-EVENT, LA-SENSE signals may be refractory or non-refractory, and can inadvertently be triggered by electrical noise signals or aberrantly conducted depolarization waves rather than true R-waves or P-waves. 
     As described herein, various exemplary systems, methods, and interfaces may be configured to use electrode apparatus including external electrodes, imaging apparatus, display apparatus, and computing apparatus to noninvasively assist a user (e.g., a physician) in selecting one or more locations (e.g., implantation site regions) proximate a patient&#39;s heart for one or more implantable electrodes and/or to navigate one or more implantable electrodes to the selected location(s). An exemplary system  100  including electrode apparatus  110 , imaging apparatus  120 , display apparatus  130 , and computing apparatus  140  is depicted in  FIG.  4   . 
     The electrode apparatus  110  as shown includes a plurality of electrodes incorporated, or included within a band wrapped around the chest, or torso, of a patient  14 . The electrode apparatus  110  is operatively coupled to the computing apparatus  140  (e.g., through one or more wired electrical connections, wirelessly, etc.) to provide electrical signals from each of the electrodes to the computing apparatus  140  for analysis. Exemplary electrode apparatus may be described in U.S. Provisional Patent Application 61/913,759 entitled “Bioelectric Sensor Device and Methods” and filed on Dec. 9, 2013 and U.S. patent application Ser. No. 14/227,719 entitled “Bioelectric Sensor Device and Methods” and filed on Mar. 27, 2014, now U.S. Pat. No. 9,320,446, each of which is incorporated herein by reference in its entirety. Further, exemplary electrode apparatus  110  will be described in more detail in reference to  FIGS.  5 A- 5 B . 
     The imaging apparatus  120  may be any type of imaging apparatus configured to image, or provide images of, at least a portion of the patient in a non-invasive manner. For example, the imaging apparatus  120  may not use any components or parts that may be located within the patient to provide images of at least a portion of the patient except non-invasive tools such as contrast solution. It is to be understood that the exemplary systems, methods, and interfaces described herein may noninvasively assist a user (e.g., a physician) in selecting a location proximate a patient&#39;s heart for an implantable electrode, and after the exemplary systems, methods, and interfaces have provided noninvasive assistance, the exemplary systems, methods, and interfaces may then provide assistance to implant, or navigate, an implantable electrode into the patient, e.g., proximate the patient&#39;s heart. 
     For example, after the exemplary systems, methods, and interfaces have provided noninvasive assistance, the exemplary systems, methods, and interfaces may then provide image guided navigation that may be used to navigate leads including electrodes, leadless electrodes, wireless electrodes, catheters, etc., within the patient&#39;s body. Further, although the exemplary systems, methods, and interfaces are described herein with reference to a patient&#39;s heart, it is to be understood that the exemplary systems, methods, and interfaces may be applicable to any other portion of the patient&#39;s body. 
     The imaging apparatus  120  may be configured to capture, or take, x-ray images (e.g., two dimensional x-ray images, three dimensional x-ray images, etc.) of the patient  14 . The imaging apparatus  120  may be operatively coupled (e.g., through one or more wired electrical connections, wirelessly, etc.) to the computing apparatus  140  such that the images captured by the imaging apparatus  120  may be transmitted to the computing apparatus  140 . Further, the computing apparatus  140  may be configured to control the imaging apparatus  120  to, e.g., configure the imaging apparatus  120  to capture images, change one or more settings of the imaging apparatus  120 , etc. 
     It will be recognized that while the imaging apparatus  120  as shown in  FIG.  4    may be configured to capture x-ray images, any other alternative imaging modality may also be used by the exemplary systems, methods, and interfaces described herein. For example, the imaging apparatus  120  may be configured to capture images, or image data, using isocentric fluoroscopy, bi-plane fluoroscopy, ultrasound, computed tomography (CT), multi-slice computed tomography (MSCT), magnetic resonance imaging (MM), high frequency ultrasound (HIFU), optical coherence tomography (OCT), intra-vascular ultrasound (IVUS), two dimensional (2D) ultrasound, three dimensional (3D) ultrasound, four dimensional (4D) ultrasound, intraoperative CT, intraoperative MRI, etc. Further, it is to be understood that the imaging apparatus  120  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  120  may provide 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 an atlas 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 to be used to confidently reach target locations within the heart or other areas of interest. 
     The display apparatus  130  and the computing apparatus  140  may be configured to display and analyze data such as, e.g., surrogate electrical activation data, image data, mechanical motion data, etc. gathered, or collected, using the electrode apparatus  110  and the imaging apparatus  120  to noninvasively assist a user in location selection of an implantable electrode. 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 location selection of an implantable electrode, 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  to view and/or select one or more target or candidate locations of a portion of a patient&#39;s heart as further described herein. 
     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 graphical depictions of anatomy of a patient&#39;s heart, images of a patient&#39;s heart, graphical depictions of locations of one or more electrodes, graphical depictions of one or more target or candidate locations, alphanumeric representations of one or more values, graphical depictions or actual images of implanted electrodes and/or leads, etc. For example, 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 graphical user interfaces  132  displayed by the display apparatus  130  may include, or display, one or more regions used to display graphical depictions, to display images, to allow selection of one or more regions or areas of such graphical depictions and images, etc. As used herein, a “region” of a graphical user interface  132  may be defined as a portion of the graphical user interface  132  within which information may be displayed or functionality may be performed. Regions may exist within other regions, which may be displayed separately or simultaneously. For example, smaller regions may be located within larger regions, regions may be located side-by-side, etc. Additionally, as used herein, an “area” of a graphical user interface  132  may be defined as a portion of the graphical user interface  132  located with a region that is smaller than the region it is located within. Exemplary systems and interfaces may be described in U.S. Provisional Patent Application 61/913,743 entitled “Noninvasive Cardiac Therapy Evaluation” and filed on Dec. 9, 2013 and U.S. patent application Ser. No. 14/228,009 entitled “Noninvasive Cardiac Therapy Evaluation” and filed Mar. 27, 2014, now U.S. Pat. No. 9,986,928, each of which is incorporated herein by reference in its entirety. 
     The processing programs or routines stored and/or executed by the computing apparatus  140  may include programs or routines for computational mathematics, matrix mathematics, decomposition algorithms, compression algorithms (e.g., data compression algorithms), calibration algorithms, image construction algorithms, signal processing algorithms (e.g., 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, image data from the imaging apparatus  120 , electrical signal data 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, 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, mini computer, tablet computer, etc.). The exact configuration of the computing apparatus  130  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 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. 
       FIGS.  5 A- 5 B  are conceptual diagrams illustrating exemplary electrode systems and apparatus for measuring body-surface potentials and, more particularly, torso-surface potentials. As shown in  FIG.  5 A , the exemplary electrode system  110  includes a set or array of electrodes  102 , a strap  104 , interface/amplifier circuitry  103 , and computing apparatus  140  such as described herein with reference to  FIG.  4   . The electrodes  102  are attached, or coupled, to the strap  104  that is configured to be wrapped around the torso of patient such that the electrodes  102  surround the patient&#39;s heart. As further illustrated, the electrodes  102  may be positioned around the circumference of patient, including the posterior, lateral, and anterior surfaces of the torso of patient. In other examples, electrodes  102  may be positioned on any one or more of the posterior, lateral, and anterior surfaces of the torso. Further, the electrodes  102  may be electrically connected to interface/amplifier circuitry  103  via wired connection  108 . The interface/amplifier circuitry  103  may be configured to amplify the signals from the electrodes  102  and provide the signals to the computing apparatus  140 . Other exemplary systems may use a wireless connection to transmit the signals sensed by electrodes  102  to the interface/amplifier circuitry  103  and, in turn, the computing apparatus  140 , e.g., as channels of data. 
     Although in the example of  FIG.  5 A , the system  110  includes a strap  104 , 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  102 . In other examples, the electrodes  102  may be placed individually on the torso of a patient. Further, in other examples, electrodes  102  (e.g., arranged in an array) may be part of, or located within, patches, vests, and/or other means of securing the electrodes  102  to the torso of the patient. 
     The electrodes  102  may be configured to surround the heart of the patient 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 patient. Each of the electrodes  102  may be used in a unipolar configuration to sense the torso-surface potentials that reflect the cardiac signals. The interface/amplifier circuitry  103  may also be coupled to a return or indifferent electrode (not shown) which may be used in combination with each of electrodes  102  for unipolar sensing. In some examples, there may be about 12 to about 50 electrodes  102  spatially distributed around the torso of patient. Other configurations may have more or fewer electrodes  102 . 
     The computing apparatus  140  may record and analyze the torso-surface potential signals sensed by electrodes  102  and amplified/conditioned by the interface/amplifier circuitry  103 . For example, the sensing and computing apparatus described in U.S. Pat. App. Pub. No. 2012/0283587 A1 published Nov. 8, 2012 and U.S. Pat. App. Pub. No. 2012/0284003 A1 published Nov. 8, 2012, each of which is incorporated herein by reference in its entirety, may be used to record and analyze torso-surface potential signals. The computing apparatus  140  may be configured to analyze the signals from the electrodes  102  to determine whether each electrode of the electrodes  102  is effective (e.g., operable for monitoring or sensing signals from the tissue, or skin, of the patient). 
       FIG.  5 B  illustrates another exemplary electrode system  111  that includes a plurality of electrodes  112  configured to surround the heart of the patient 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 patient. The electrode system  111  may include a vest  114  upon which the plurality of electrodes is attached, or to which they are coupled. In at least one embodiment, the plurality, or array, of electrodes  112  may be used to evaluate electrical dyssynchrony in the heart of the patient. Similar to the system  110 , the system  111  may include interface/amplifier circuitry  113  electrically coupled to each of the electrodes  112  through a wired connection  118  and configured to transmit signals from the electrodes  112  to a computing apparatus  140 . As illustrated, the electrodes  112  may be distributed over the torso of patient, including, for example, the anterior, lateral, and posterior surfaces of the torso of patient. 
     The vest  114  may be formed of fabric, or any other material, with the electrodes  112  attached to thereto. The vest  114  may be configured to maintain the position and spacing of electrodes  112  on the torso of the patient. 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. The vest  114  may also be one piece or in multiple pieces to allow simple placement on the anterior and posterior of the patient using anatomical landmarks such as the spine and sternum of the patient. Further, the vest  114  may also be, or be used in conjunction with, a belt or patch(es) including electrodes  112 . In some examples, there may be about 25 to about 256 electrodes  112  distributed around the torso of the patient, though other configurations may have more or fewer electrodes  112 . 
     The exemplary systems, apparatus, and/or methods described herein are configured to identify effective electrodes, and the systems including electrodes, computing apparatus, and display apparatus described herein with reference to  FIGS.  1 - 5    may utilize the exemplary systems, apparatus, and/or methods. More specifically, the exemplary systems, apparatus, and/or methods may be used to determine which electrodes in the systems of  FIGS.  1 - 5    may be effective (or ineffective) for sensing signals from tissue of the patient and/or pacing tissue of the patient. After it is determined which electrodes are effective, the electrodes may be used to assist a user (e.g., a physician) in determining effective pacing vectors, navigating or locating one or more electrodes (e.g., implantable electrodes, electrodes on leads, leadless/wireless electrodes, etc.) to one or more regions of a patient&#39;s heart for therapy, to monitor and display information with respect to the cardiac health of the patient (e.g., before, during, and after implantation of cardiac therapy device), etc. 
     When the band  104  of the surface electrode array system  110  of  FIG.  5 A  or the vest  114  of the surface electrode array system  111  of  FIG.  5 B  is located, or placed, on a patient, some of the electrodes  102 ,  112  may not be in sufficient contact (e.g., not proper contact, not full or complete contact, partial contact, etc.) with the skin of the patient, and thus, may not provide a valid signal (e.g., cardiac signal) from the patient. As such, the exemplary systems, apparatus, and/or methods may be used with the systems  110 ,  111  of  FIGS.  5 A- 5 B  to determine which electrodes  102 ,  112  are effective for sensing valid electrical activity (e.g., not noise) from the skin of the patient. 
     Further, for example, when the leads  18 ,  20 ,  22  of the system  10  of  FIGS.  1 - 3    are located, or implanted, in a patient&#39;s heart, some of the electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66  may not be in sufficient contact (e.g., not proper contact, not full or complete contact, partial contact, etc.) with the cardiac tissue of the patient, which may not provide sufficient sensing of cardiac signals and/or pacing functionality. As such, the exemplary systems, apparatus, and/or methods may be used with the system  10  of  FIGS.  1 - 3    to determine which electrodes  40 ,  42 ,  44 ,  45 ,  46 ,  47 ,  48 ,  50 ,  58 ,  62 ,  64 ,  66  are effective for sensing valid electrical activity (e.g., not noise) from the cardiac tissue of the patient and/or delivering effective electrical therapy to the cardiac tissue of the patient. 
     An exemplary method  144  for identifying effective electrodes in a plurality of electrodes is depicted in  FIG.  6   . The exemplary method  144  may be described as using single signal analysis because, for each electrode, only the signal from that electrode is used to determine whether the electrode is effective. Although the exemplary method  144  is described herein with respect to determining the effectiveness of a single electrode, it is to be understood that the method  144  could be repeated (e.g., performed sequentially one electrode at a time) or performed simultaneously for a plurality of electrodes such that each electrode of a plurality of electrodes may be evaluated and determined to be either effective or ineffective. 
     Before executing method  144 , an electrode may be located proximate tissue of a patient configured to sense a signal from the patient. For example, an electrode  102  of the system  110  may be located proximate the torso of a patient and configured to monitor a signal from the skin of the torso of the patient. To determine whether the electrode is effective, the exemplary method  144  may monitor a signal from the electrode  145 . 
     The exemplary method  144  may then store a portion of the signal from the electrode for each cardiac cycle of at least two cardiac cycles  146 . For example, a portion from a first cardiac cycle may be stored and a portion from a second cardiac cycle (e.g., subsequent the first cardiac cycle) may be stored. A portion of the signal may be described as being a “window” or “snapshot” of the signal taken over a preset time period. For example, the preset time period of the portion of the signal may be between about 80 milliseconds (ms) to about 400 ms, such as, e.g., about 80 ms, about 100 ms, about 150 ms, about 200 ms, about 250 ms, about 300 ms, about 350 ms, about 400 ms, etc. The time period may be described as being “preset” because, e.g., the time period may be set by a user. 
     Each portion of the signal may correspond to the same time frame within each cardiac cycle. In other words, each portion may occur during the same part or region of the cardiac cycle. To identify or select the portion of the signal that corresponds to the same time frame within each cardiac cycle, the exemplary method  144  may use one or more recurring fiducial elements, markers, or values within the signal or any other cardiac parameter. In other words, to store a portion of the signal for each cardiac cycle  146 , the exemplary method  144  may store a portion of the signal based on a recurring fiducial element within a cardiac signal or parameter. 
     The recurring fiducial element may include one or more of a ventricular event (e.g., a ventricular pace, a ventricular sense, etc.), an atrial event (e.g., an atrial pace, an atrial sense, etc.), a maximum value (e.g., a peak of a QRS complex, a peak of a P-wave, etc.), a minimum value, a maximum slope value (e.g., a maximum slope of an R-wave, etc.), an amplitude or slope of atrial or ventricular depolarization signal, a crossing of a predefined threshold, etc. The timing of recurring fiducial element, or time when the recurring fiducial occurs, may be used to base the portion of the signal upon. For example, the start of fiducial element may start the time frame or window to store a portion of the signal. 
     For example, the exemplary method  144  may store a 250 ms portion of the signal starting from a ventricular pace (i.e., the selected fiducial element). As such, a first portion may be recorded, or stored, from the start of a ventricular pace for 250 ms during a first a cardiac cycle, and a second portion may be recorded, or stored, from the start of a ventricular pace for 250 ms during a second cardiac cycle that is subsequent to the first cardiac cycle. 
     After at least two portions have been stored  146 , the exemplary method  144  may compare the at least two stored portions of the signal to provide an effectiveness value  147  or other effectiveness information representative of such comparison. The effectiveness value may be representative of the effectiveness of the electrode for using in sensing signals from the tissue of the patient and/or delivering electrical therapy to the tissue of the patient. 
     The effectiveness value may be a correlation value or coefficient (e.g., a Pearson correlation coefficient). Although not shown, the exemplary method  144  may then enable (e.g., use) the electrode if is determined to be effective and/or may disable (e.g., not use or utilize) the electrode if is determined to be ineffective. To determine whether an electrode is effective based on an effectiveness value, the effectiveness value may be compared to a threshold value. If the electrode has an effectiveness value greater than or equal to the threshold value, then the electrode may be enabled. If the electrode has an effectiveness value below the threshold value, then the electrode may be disabled. 
     In an embodiment where the effectiveness value is a Pearson correlation coefficient, the threshold value may be between about 0.5 and 0.98 such as, e.g., 0.8. For example, the threshold value may be greater than or equal to about 0.5, greater than or equal to about 0.6, greater than or equal to about 0.7, greater than or equal to about 0.75, greater than or equal to about 0.8, etc. and/or may be less than or equal to about 0.8, less than or equal to about 0.85, less than or equal to about 0.9, less than or equal to about 0.95, less than or equal to about 0.98, etc. 
     In an embodiment where the effectiveness value is a waveform match percentage, the threshold value may be between about 50% and 100% such as, e.g., 70%. Waveform match percentages may be generated and/or calculated using various techniques and/or process, e.g., as described in U.S. Pat. No. 6,393,316 B1 entitled “METHOD AND APPARATUS FOR DETECTION AND TREATMENT OF CARDIAC ARRHYTHMIAS” issued May 21, 2002, which is incorporated herein by reference in its entirety. For example, the threshold value may be greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, greater than or equal to about 75%, greater than or equal to about 80%, etc. and/or may be less than or equal to about 100%, less than or equal to about 95%, less than or equal to about 90%, less than or equal to about 85%, less than or equal to about 88%, etc. 
     Prior to the comparison, the portions of the cardiac signal may be aligned to compensate for noise-related jitter of the fiducial element with each portion. For example, the portions may be aligned based on timing of at least one of the following features of the signal, or fiducial element: maximum slope, minimum slope, maximum value, minimum value within each window etc. In at least one embodiment, alignment may be performed based on timing of the maximum value, the minimum value, and/or the greater of the magnitudes of the maximum value and the minimum value. 
     In at least one embodiment, an exemplary graphical user interface may graphically depict a plurality of electrodes correlating to a plurality of actual, physical electrodes in a contact with the patient. The graphical user interface may identify which electrodes are determined to be effective and which electrodes are determined to be ineffective. A user may use the graphical user interface to enable or disable each of the electrodes. In other words, a user may be allowed to turn “off” or turn “on” each electrode via a user interface/program that controls the amplifiers and A/D converters. 
     Further, a vest or belt of electrodes may not fit correctly (e.g., too large, too small, etc.) about a patient such that one or more of the electrodes may not make contact with the patient so as to provide an effective electrical signal. A user (e.g., a physician) may recognize which electrodes may not be effective and use a graphical user interface to disable the electrodes recognized to be ineffective. 
     Another exemplary method  156  for identifying effective electrodes of a plurality of electrodes is depicted in  FIG.  7   . The method  156  may include selecting a recurring timing fiducial element  149  to base the windowing (e.g., framing, cropping, etc.) portions of the signal for each cardiac cycle. As described herein, the recurring timing fiducial element may be one or more morphological features of a cardiac signal such as, e.g., a maximum value of the signal, etc. The method  156  may then window a portion of the signal of at least two heart beats, or cardiac cycles  150 . For example, if the fiducial element is a maximum value and the preset time period is 200 ms, the exemplary method  156  may window 200 ms portions of the signal about the maximum value for each cardiac cycle  150 . The window may be selected such that the recurring time fiducial element is centered within the window (time frame), starts the window, ends the window, etc. In other words, the recurring timing fiducial element may start the capture window, stop the capture window, or be located halfway through the capture window. 
     After at least two windowed signals have been stored or captured  150 , a correlation may be computed between the two windowed portions  151  resulting in an effectiveness value. As described herein, in at least one embodiment, a Pearson correlation coefficient may be calculated as the effectiveness value, or in another embodiment, a waveform match percentage may be calculated as the effectiveness value. Based on the effectiveness value, the method  156  may identify if the electrode is effective  152 , e.g., using a threshold value, etc. 
     The method  156  may determine the effectiveness of more than one electrode simultaneously since the signal of each electrode is compared to itself and is not determined based on other signals. In other words, the method  156  may be described as being configured to identify an effective electrode using single signal correlation. For example, if an exemplary system includes eight electrodes, the signal of each of the eight electrodes may be windowed about a fiducial element for at least two cardiac cycles  150  and a correlation may be computed between the at least two windowed signals  151  for each electrode resulting in an effectiveness value for each electrode. The effectiveness value may be used to identify which of the 8 electrodes are effective. 
     Exemplary systems may require a selected number or percentage of effective electrodes, e.g., of those electrodes available in the array. For example, the method  156  may further include a check to confirm that a selected number of electrodes are effective  153 . If such a selected number of electrodes out of the provided electrodes are determined to be effective  153 , then the method  156  may proceed to enabling the effective electrodes  154  and indicating that the system has been initialized, is ready for sensing procedures, etc. To determine if enough electrodes out of the provided electrodes are effective, the method  156  may compare the number of effective electrodes to a threshold value. For example, in a system that includes 50 electrodes, the threshold may be 40 electrodes. Thus, if the 40 or more electrodes are determined to be effective, then the method  156  may proceed to enabling the 40 effective electrodes and disabling the 10 ineffective electrodes. 
     If it is determined that not enough electrodes are effective  153 , the method  156  may optionally re-adjust the electrode positioning  155 . For example, a system or device may suggest to a user to re-adjust the electrode positioning. In the case of a vest including a plurality of electrodes, a user may adjust the vest such that more electrodes make better contact with the skin of the user. Further, the method  156  may restart the identification procedure for each of the electrodes if it is determined that not enough electrodes are effective  153  (as signified by the return arrow to windowing the signal of each beat about a fiducial element  150 ). 
     Signals, such as, e.g., cardiac signals, collected, or monitored from an electrode in a spatial sensor-array may be correlative (e.g., highly correlative) with signals monitored by neighbor electrodes in the spatial sensor-array (e.g., electrodes located in relatively close proximity to one another) if the signals are physiological. Likewise, a lack of, or low, correlation between signals monitored may indicate “bad” or non-physiologic signals. In other words, low correlation may indicate the one or more electrodes are ineffective (e.g., ineffective for sensing, ineffective for delivering therapy, etc.). One or more exemplary automated methods, or algorithms, are described herein that may use correlation coefficients between signals collected by multiple electrodes to determine “bad” or ineffective electrodes (or to determine “good” or effective electrodes). 
     For example, an exemplary array of electrodes  160  is depicted in  FIG.  8   . In at least one embodiment, the array of electrodes  160  may be configured to be located adjacent the torso of a patient. As shown, the array  160  includes a plurality of rows  162  of electrodes. Each row  162  may be described as being spaced apart from another. In other words, each row  162  is spatially oriented which respect to each other. Further, each electrode within each row  162  is spaced apart from one another. In at least one embodiment, the spacing between rows and/or electrodes within each row may be uniform. In at least one embodiment, the space between electrodes may be about 0.5 centimeters (cm) to about 5 cm, such as, e.g., 1 cm, 2 cm, 3 cm, etc. In at least one embodiment, the space between electrodes may be as small as 1 millimeter (mm) (e.g., for intracardiac mapping). In at least one embodiment, the space between electrodes may be about 0.1 mm to about 5 mm, such as, e.g., 0.2 mm, 0.5 mm, 1 mm, 1.5 mm, 2.0 mm, 3.0 mm, etc. 
     Further, for purposes of description of the exemplary methods and/or processes, the electrodes may be described in terms of primary electrodes and proximate neighbor electrodes. The primary electrode is the electrode that is being evaluated for effectiveness using the exemplary methods and/or processes while the proximate neighbor electrodes are the one or more electrodes that may be used to evaluate the effectiveness of the primary electrode. 
     As shown in the array  160 , primary electrode  164  has two proximate neighbor electrodes  166 . Although in this example, the primary electrode  164  has two proximate neighbor electrodes  166 , in other embodiments, the primary electrode may have only one proximate neighbor electrode or more than two proximate neighbor electrodes. Although the neighbor electrodes  166  are located in the same row as the primary electrode  164  as depicted, in other embodiments, neighbor electrodes  166  may be located in rows adjacent to the row containing the primary electrode  164 . 
     In at least one embodiment, the correlation of a depolarization signal at each electrode may be evaluated with two adjacent neighbor electrodes (e.g., vertical neighbors or electrodes along the same line). For example, a correlation may be computed, or generated, between the depolarization signal monitored by a primary electrode and the depolarization signal monitored at each of two adjacent neighbor electrodes resulting in two correlation values (e.g., each correlation value corresponding to a pair of electrodes that includes the primary electrode). The greater of the two correlation values may be assigned to the primary electrode and used to determine whether the primary electrode is effective or ineffective. The method or algorithm may be represented as follows: Greater (corrcoef(signal(j),signal(j+1)), corrcoef (signal(j), signal(j−1)). Primary electrodes located at an extremity, or end, of a vertical line of electrodes will only have one vertical neighbor electrode, and thus, a single correlation value may be generated, or computed, for that primary electrode. 
     An exemplary method of identifying an effective electrode using spatial signal correlation, e.g., using the electrode array of  FIG.  8   , is depicted in  FIG.  9   . The method  170  includes monitoring a first signal from a patient using a primary electrode  172  and monitoring one or more secondary signals from the patient using one or more neighbor electrodes  174 . The neighbor electrode may be located spatially adjacent the primary electrode (e.g., within 3 cm of the primary electrode). For example, each neighbor electrode may be located within a pre-selected, or certain, proximity to the primary electrode. 
     A portion of the first signal may be stored to be used in the comparative analysis  176  and a portion of each of the one or more secondary signals  178  may be stored to also be used in the comparative analysis. To provide useful data, the portions of the first signal and the one or more secondary signals may be chosen to include data other than an ambient signal (e.g., flat line signal, etc.) and/or noise. For example, the portions of the first signal and the one or more secondary signals may correspond to a fiducial element (e.g., a particular event) within a cardiac waveform (e.g., per cardiac cycle) such as, e.g., ventricular depolarization, atrial depolarization, ventricular repolarization, atrial repolarization, etc. 
     Further, each of the portions of the first signal and the secondary signals may be window or cropped for a selected, or preset, period of time such as, e.g., 250 milliseconds. The period of time may be about 100 milliseconds (ms) to about 400 ms, such as, e.g., about 100 ms, about 150 ms, about 200 ms, about 250 ms, about 300 ms, about 400 ms, etc. Further, each portion of the first signal and the secondary signals may occur (and thus, be recorded) at the same time. For example, the portion of the first signal may be recorded at the exact same time the portion of the secondary signals is recorded. In other words, the portions of the first signal and the secondary signals may be stored over the same time period. 
     To determine the effectiveness of the primary electrode, the portion of the first signal may be compared to the portion of each of the secondary signals to provide an effectiveness value for each comparison  180 . For example, if two adjacent neighbor electrodes providing two secondary signals are utilized, a first comparison may occur between the portion of the first signal and the portion of the first secondary signal to provide a first effectiveness value, and a second comparison may occur between the portion of the first signal and the portion of the second secondary signal to provide a second effectiveness value. Each of effectiveness values for each primary electrode may represent a correlation value between the primary electrode and the neighbor electrode. Similar to the methods  130 ,  140  described herein with reference to  FIGS.  5 - 6   , the effectiveness values may be correlation coefficients (e.g., Pearson correlation coefficients), waveform match percentages, etc. 
     The exemplary method  170  may then determine whether the primary electrode is effective by comparing the effectiveness values to a threshold value  182  similar to the threshold values described herein with respect to the methods  130 ,  140  of  FIGS.  5 - 6   . In this embodiment, each primary electrode may have multiple effectiveness values since the signal of the primary electrode may be compared to a secondary signal from more than one secondary electrode. If multiple effectiveness values are generated, various statistical processes may be used to provide a single value. For example, the greatest effectiveness value may be used. Further, for example, an average of the effectiveness values may be used. Still further, effectiveness values that are outliers may be excluded while the remaining effectiveness values may be used. 
     In at least one embodiment, if one of the effectiveness values is greater than a threshold value, then the method  170  may determine that the primary electrode is effective  182 . In other words, a single strong correlation between the primary electrode and an adjacent neighbor electrode may indicate that the primary electrode is effective. 
     Conversely, in at least one embodiment, if all of the effectiveness values are less than a threshold value, then the method  170  may determine that the primary electrode is ineffective  182 . In other words, no strong correlation between the primary electrode and an adjacent neighbor electrode may indicate that the primary electrode is ineffective. 
     The method  170  may be repeated for each electrode of an electrode array or IMD until each electrode is determined to be effective or ineffective. Further, the method  170  may be performed sequentially with one electrode at a time or in parallel by recording the signal from each electrode of a plurality of electrodes at the same time. 
     Although not shown, the exemplary systems and apparatus described herein may provide a display to depict, or show, information with respect to the effectiveness of the electrodes. For example, a graphical representation of an array of electrodes may be depicted on the display and information with respect to the effectiveness of each of the electrodes may be depicted proximate each of the electrodes. In at least one embodiment, a graphical map may be generated that includes a plurality of electrodes spatially distributed and an effectiveness values for each of the plurality of electrodes depicted proximate the electrodes. A user may use the graphical map to determine areas of the array that may not be located, or fitted, properly to the user to create sufficient contact between the electrodes and the tissue of the patient. 
     Further, similar to the method  156  of  FIG.  7   , an additional effectiveness test for each electrode may be performed or repeated if more than a selected percentage of the plurality of electrodes were identified as being ineffective. For example, if 50% of the electrodes had all of their at least one correlation value less than a selected threshold value, then the method  170  may repeat or retest the array of electrodes. Prior to retesting, a user may re-adjust the array of electrodes to, e.g., provide better contact between the electrodes and the tissue of the patient. 
     A graph  190  depicting effectiveness values for a plurality of electrodes is shown in  FIG.  10   . The ineffective electrodes  192  are identifiable on the graph  190  as having effectiveness values less than the threshold value  194 , which, as shown, is 0.8. 
     Cardiac signals measured, or monitored, from ineffective electrodes are depicted in  FIG.  11    and cardiac signals measured, or monitored, from effective electrodes are depicted in  FIG.  12   . As shown, the signals from the ineffective signals appear to not correlate to any pattern or sequence and further appear to depict random noise. The signal from the effective electrodes appears to correlate to a pattern (e.g., a valley) and appear to depict a portion of a valid cardiac signal. 
     A distribution of correlation values for a plurality of electrodes evaluated by, e.g., the exemplary methods of  FIGS.  6 - 7  and  9   , is depicted in  FIG.  13   . As shown in this example, a vast majority of the electrodes had correlation values between 0.9 and 1. 
     An exemplary method  200  of identifying an active or effective electrode using morphological features is depicted in  FIG.  14   . In at least one embodiment, the method  200  may be used prior to the exemplary method  170  described herein with reference to  FIG.  9    to, e.g., prevent signals from spatially adjacent electrodes to be compared, or correlated, when one or more of the spatially adjacent electrodes read, or sense, only a flat line or noise. In at least one embodiment, the method  200  may be performed on its own to provide an effectiveness value for an active or effective electrode. 
     The method  200  includes monitoring a signal using an electrode  202  and analyzing at least one morphological feature of the signal to determine if the electrode is active (or effective)  204 . For example, whether an electrode is active or effective may be determined by at least one of the signal maximum value, minimum value, difference between maximum and minimum value, maximum slope, minimum slope, difference between maximum slope and minimum slope, etc. The morphological feature may be compared to a threshold value (e.g., greater than or equal to a predefined value, less than or equal to another predefined value, etc.). 
     For example, features of the signal from one electrode within a depolarization cycle (e.g., amplitude, slope, etc.) may be used to judge if the value corresponding to those features is within physiologic limits. More specifically, e.g., ECG signal depolarization amplitude value should be within certain physiologic limits such as, e.g., greater than or equal to 0.1 mV and less than or equal to 10 mV. The ECG signal depolarization peak-to-peak amplitude value may be evaluated by comparing the value to the physiological limits to determine if the electrode is active (which, e.g., may be useful if multiple spatially adjacent electrodes are all recording a flat line). Physiologic limits on signal depolarization amplitude for electrode arrays in contact with cardiac tissue may be much larger, e.g., greater than or equal to 1 mV and less than or equal to 50 mV. 
     These values or data for various electrodes may be mapped (e.g., mapped to a grid for visualization, mapped to a database for analysis, etc.) and/or compared to identify one or more active and/or effective electrodes. 
     An exemplary graphical user interface  132  including blood vessel anatomy  134  of a patient&#39;s heart is shown in  FIG.  15    that may be used by a user to navigate an implantable electrode to a region of the patient&#39;s heart. The blood vessel anatomy as well as other data such as mechanical motion information, etc. of the heart may be captured using the imaging apparatus  120  described herein, which may be configured to image at least a portion of blood vessel anatomy of the patient&#39;s heart and provide image data used by the computing apparatus  140  to provide mechanical motion information or data. The data or information depicted on the blood vessel anatomy of the patient&#39;s heart in  FIG.  15    may be further monitored, or gathered, using the electrode apparatus  110  described herein. 
     A user may view and/or use the graphical user interface  132  of  FIG.  15    to determine, or identify, one or more candidate site regions of the displayed portion or region of the patient&#39;s heart for implantation of implantable electrodes. For example, a user may view mechanical motion information, e.g., grey-scaling or color-coding applied to the blood vessel anatomy in  FIG.  15   , and identify a candidate site region of the patient&#39;s heart based on the mechanical motion information. For example, a user may identify one or more regions having, e.g., mechanical motion times greater than a threshold, having the longest mechanical motion time, etc. 
     Another exemplary graphical user interface  132  including a graphical depiction of a patient&#39;s heart  12  is shown in  FIG.  16    that may be used by a user to navigate an implantable electrode to a region of the patient&#39;s heart. More specifically, a posterior side of a human heart  12  is depicted in the graphical user interface  132  of  FIG.  16    with surrogate electrical activation times  136  color-coded, or gray-scaled, across the surface of the heart  12 . As used herein, surrogate electrical activation data (e.g., surrogate electrical activation times, surrogate electrical activation time maps, etc.) may be defined as data representative of actual, or local, electrical activation data of one or more regions of the patient&#39;s heart. For example, 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. 
     As shown, the posterolateral left ventricle region shows late activation (e.g., about 150 milliseconds). In other embodiments, both a posterior and anterior side of a human heart may be graphically depicted and overlaid with electrical activation information. The data or information depicted on the patient&#39;s heart  12  in  FIG.  16    may be further monitored, or gathered, using the electrode apparatus  110  described herein. 
     The techniques described in this disclosure, including those attributed to the IMD  16 , the programmer  24 , 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.