Patent Publication Number: US-2011066203-A1

Title: Electrode and lead stability indexes and stability maps based on localization system data

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent applications: 
     1) Ser. No. ______, filed concurrently herewith, titled “Electrode and Lead Stability Indexes and Stability Maps Based on Localization System Data” (Attorney Docket AO9P1050); and
 
2) Ser. No. ______, filed concurrently herewith, titled “Electrode and Lead Stability Indexes and Stability Maps Based on Localization System Data” (Attorney Docket A09P1050U501).
 
    
    
     TECHNICAL FIELD 
     Subject matter presented herein relates generally to electrode and lead-based investigation or therapy systems (e.g., cardiac pacing therapies, cardiac stimulation therapies, etc.). Various examples acquire position data using a localization system and, based on the acquired data, calculate stability metrics (e.g., as indexes or maps). 
     BACKGROUND 
     Various surgical procedures rely on placement of electrodes into the body (e.g., electrode devices, electrode-bearing leads or catheters, etc.). For example, a typical implantable cardiac defibrillator (ICD) includes a “can” for placement in a pectoral pocket and an electrode-bearing lead for placement into a chamber of the heart or a vein of the heart. In this example, an electrode of the can and an electrode of the lead can sense cardiac electrical activity indicative of fibrillation and respond (e.g., by control logic in the can) by delivering energy to defibrillate the heart. To ensure proper performance, whether for sensing or for defibrillating, stability of the can and stability of the lead are beneficial. 
     In another example, where a patient is treated by a cardiac resynchronization therapy (CRT) device that relies on biventricular pacing, an electrode-bearing lead may be placed into the right ventricle and another electrode-bearing lead may be placed in a vein of a wall of the left ventricle. As the algorithms for delivery of such therapy become more complex, accurate sensing becomes more important as does an ability to accurately and reproducibly deliver pacing stimuli. In this example, stability of sensing and pacing electrodes becomes quite important. 
     In either example, where an electrode or lead lacks stability or dislodges, depending on the severity, surgery may be required to remedy the issue. Alternatively, if the lack of stability or the dislodgement is tolerated, a device&#39;s ability to delivery therapy in an optimal manner may be compromised (e.g., an electrode configuration for sensing may become unreliable to support an algorithm such as for automatic determination of capture threshold). 
     While many leads include anchoring mechanisms, such mechanisms do not guarantee stability. However, if a lead can be placed in a stable location or a location of known stability, a clinician can predict better possible outcomes and even longevity of an implantable therapy device. As to the latter, data indicates that an unstable electrode is likely to trigger algorithms such as an automatic capture threshold determination algorithm, which, in turn, can consume precious resources (e.g., consider a battery as an implantable device&#39;s limited power supply). 
     While ICD and CRT have been mentioned, electrode and lead stability can be an issue with other investigations or procedures. For example, consider an ablation procedure in a region of the heart that may be accessed via two different catheter paths. If one of the paths proves for more stable placement of an ablation instrument (e.g., electrode, RF, chemical, etc.), the clinician may perform the procedure with less risk and perhaps a better clinical outcome. In another example, consider nerve or tissue stimulation therapies such as those for vagal nerve stimulation or for diaphragm stimulation. These therapies can benefit from known, trackable or otherwise quantifiable stability metrics. In yet another example, consider placement of a sensor in the body that may require stability for suitable signal-to-noise. 
     As described herein, various exemplary techniques can assess stability in acute states and optionally chronic states. As explained, such stability information can be beneficial in aiding a clinician to make decisions regarding an investigation or a therapy. 
     SUMMARY 
     An exemplary method includes selecting an electrode located in a patient; acquiring position information with respect to time for the electrode where the acquiring uses the electrode for repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculating a stability metric for the electrode based on the acquired position information with respect to time; and deciding if the selected electrode, as located in the patient, has a stable location for sensing biological electrical activity, for delivering electrical energy or for sensing biological electrical activity and delivering electrical energy. Various other methods, devices, systems, etc., are also disclosed. 
     Another exemplary method includes selecting an electrode located in a patient wherein the electrode comprises a lead-based electrode; acquiring position information with respect to time for the electrode, during both loaded and unloaded conditions of the lead, where the acquiring uses the electrode for repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculating both loaded and unloaded stability metrics for the electrode based on the acquired position information with respect to time; and comparing the unloaded and loaded stability metrics to decide whether the electrode, as located in the patient, comprises a stable location for delivery of therapy. 
     Another exemplary method includes selecting an electrode located in a patient; acquiring position information with respect to time for the electrode, during both acute and chronic states of the electrode, where the acquiring uses the electrode for repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculating an acute state stability metric and a chronic state stability metric for the electrode based on the acquired position information with respect to time; and comparing the acute state stability metric to the chronic state stability metric to decide whether the electrode, as located in the patient in the chronic state, comprises a stable location for delivery of a therapy. The chronic state stability metric of an electrode may be monitored over time to decide whether stability of the electrode has changed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features and advantages of the described implementations can be more readily understood by reference to the following description taken in conjunction with the accompanying drawings. 
         FIG. 1  is a simplified diagram illustrating an exemplary implantable stimulation device in electrical communication with at least three leads implanted into a patient&#39;s heart and at least one other lead for sensing and/or delivering stimulation and/or shock therapy. Other devices with more or fewer leads may also be suitable. 
         FIG. 2  is a functional block diagram of an exemplary implantable stimulation device illustrating basic elements that are configured to provide cardioversion, defibrillation, pacing stimulation and/or other tissue stimulation. The implantable stimulation device is further configured to sense information and administer therapy responsive to such information. 
         FIG. 3  is a block diagram of an exemplary method for selecting one or more configurations, optimizing therapy and/or monitoring conditions based at least in part on one or more stability metrics. 
         FIG. 4  is a block diagram of the exemplary method of  FIG. 3  along with various options. 
         FIG. 5  is an exemplary arrangement of a lead and electrodes for acquiring position information and optionally other information for use in determining one or more stability metrics. 
         FIG. 6  is a plot of position information with respect to time for a series of electrodes of a lead where a shift has occurred as evidenced by relatively distinct groupings of electrode position traces or trajectories in a three-dimensional space. 
         FIG. 7  is a plot of position information with respect to time over multiple cardiac cycles for two electrode locations where in one location the electrode exhibits a relatively stable trajectory and where the other location the electrode exhibits a less stable or unstable trajectory. 
         FIG. 8  is a block diagram of an exemplary method for determining a path length metric and a path area metric and for comparing such metrics for different paths. 
         FIG. 9  is a block diagram of an exemplary method for determining various stability indexes based on position information of an electrode acquired over multiple cardiac cycles. 
         FIG. 10  is a diagram of an exemplary stability metric map and associated plots of stability index versus electrode position or number for electrodes of a right ventricular lead and for electrodes of a left ventricular lead (e.g., a coronary sinus lead). 
         FIG. 11  is a block diagram of an exemplary method for stability analysis of position information acquired during intrinsic activation of the heart and position information acquired during paced activation of the heart. 
         FIG. 12  is a block diagram of an exemplary method for gating acquisition of position information where the gating relies on information sensed using a stable electrode configuration. 
         FIG. 13  is a block diagram of an exemplary method for deciding whether dislodgement occurred for a lead or an electrode. 
         FIG. 14  is a block diagram of an exemplary method for acquiring position information during a chronic state and comparing chronic state information to acute state information or previously acquired (e.g., historic) chronic state information to thereby assess stability of one or more electrodes or leads. 
         FIG. 15  is an exemplary system for acquiring information and analyzing information to assess stability of an electrode, a lead or implanted device. 
     
    
    
     DETAILED DESCRIPTION 
     The following description includes the best mode presently contemplated for practicing the described implementations. This description is not to be taken in a limiting sense, but rather is made merely for the purpose of describing the general principles of the implementations. The scope of the described implementations should be ascertained with reference to the issued claims. In the description that follows, like numerals or reference designators are typically used to reference like parts or elements throughout. 
     Overview 
     Various exemplary techniques described herein pertain to stability analysis of electrodes or lead in the body. For example, during an intraoperative procedure, a clinician may maneuver a catheter to various locations in one or more chambers or vessels of the heart and acquire position information sufficient to calculate one or more stability metrics. In various examples, acquisition of position information may occur for a chronic state, for example, sufficient to calculated one or more chronic state stability metrics. 
     Various exemplary methods may be implemented, for example, using a pacing system analyzer (PSA) and a localization system or a specialized localization system. Various examples are described with respect to the ENSITE® NAVX® localization system; noting that other types of localization systems may be used. 
     Various techniques aim to facilitate lead implants, particularly for leads that enter the coronary sinus to reach distal branches thereof. For example, a clinician can view a map of stability metrics and readily decide to locate a lead in a region with appropriate stability, whether for sensing or pacing. A typical intraoperative, acute state process occurs iteratively (i.e., select or move, acquire, calculate; select or move, acquire, calculate; . . . ). In this iterative process, a clinician may note whether a location is of acceptable stability or of unacceptable stability. 
     As described herein, various techniques can calculate stability metrics and generate maps. Various techniques may operate in conjunction with one or more PSA functionalities, for example, to create and display maps that show variations in stability metrics with respect to anatomic features. 
     As described herein, various exemplary techniques can be used to make decisions as to cardiac pacing therapy and optimization of a cardiac pacing therapy (e.g., CRT or other pacing therapies). In a clinical trial, acute resynchronization was shown to be a significant factor in assessing CRT efficacy and long-term outcome 1 . Various methods described herein, build on this clinical finding by formulating specialized techniques and stability metrics associated with locations for pacing and sensing. In turn, a clinician can assess how a particular CRT therapy or configuration thereof may be expected to perform at time of implant or, in some instances, after implant.  1 G B Bleeker, S A Mollema, E R Holman, N Van De Veire, C Ypenburg, E Boersma, E E van der Wall, M J Schalij, J J Bax. “Left Ventricular Resynchronization is Mandatory for Response to Cardiac Resynchronization Therapy: Analysis in Patients with Echocardiographic Evidence of Left Ventricular Dyssynchrony at Baseline”.  Circulation  2007; 116: 1440-1448. 
     An exemplary stimulation device is described followed by various techniques for acquiring and calculating stability metrics. The drawings and detailed description elucidate details of various distinct stability metrics that may be used singly or in combination during an assessment or an optimization process (e.g., acute or chronic). 
     Exemplary Device 
     The techniques described below are intended to be implemented in connection with any device that is configured or configurable to delivery cardiac therapy and/or sense information germane to cardiac therapy. 
       FIG. 1  shows an exemplary stimulation device  100  in electrical communication with a patient&#39;s heart  102  by way of three leads  104 ,  106 ,  108 , suitable for delivering multi-chamber stimulation and shock therapy. The leads  104 ,  106 ,  108  are optionally configurable for delivery of stimulation pulses suitable for stimulation of nerves or other tissue. In addition, the device  100  includes a fourth lead  110  having, in this implementation, three electrodes  144 ,  144 ′,  144 ″ suitable for stimulation and/or sensing of physiologic signals. This lead may be positioned in and/or near a patient&#39;s heart and/or remote from the heart. 
     The right atrial lead  104 , as the name implies, is positioned in and/or passes through a patient&#39;s right atrium. The right atrial lead  104  optionally senses atrial cardiac signals and/or provide right atrial chamber stimulation therapy. As shown in  FIG. 1 , the stimulation device  100  is coupled to an implantable right atrial lead  104  having, for example, an atrial tip electrode  120 , which typically is implanted in the patient&#39;s right atrial appendage. The lead  104 , as shown in  FIG. 1 , also includes an atrial ring electrode  121 . Of course, the lead  104  may have other electrodes as well. For example, the right atrial lead optionally includes a distal bifurcation having electrodes suitable for stimulation and/or sensing. 
     To sense atrial cardiac signals, ventricular cardiac signals and/or to provide chamber pacing therapy, particularly on the left side of a patient&#39;s heart, the stimulation device  100  is coupled to a coronary sinus lead  106  designed for placement in the coronary sinus and/or tributary veins of the coronary sinus. Thus, the coronary sinus lead  106  is optionally suitable for positioning at least one distal electrode adjacent to the left ventricle and/or additional electrode(s) adjacent to the left atrium. In a normal heart, tributary veins of the coronary sinus include, but may not be limited to, the great cardiac vein, the left marginal vein, the left posterior ventricular vein, the middle cardiac vein, and the small cardiac vein. 
     In the example of  FIG. 1 , the coronary sinus lead  106  includes a series of electrodes  123 . In particular, a series of four electrodes are shown positioned in an anterior vein of the heart  102 . Other coronary sinus leads may include a different number of electrodes than the lead  106 . As described herein, an exemplary method selects one or more electrodes (e.g., from electrodes  123  of the lead  106 ) and determines characteristics associated with conduction and/or timing in the heart to aid in ventricular pacing therapy and/or assessment of cardiac condition. As described in more detail below, an illustrative method acquires information using various electrode configurations where an electrode configuration typically includes at least one electrode of a coronary sinus lead or other type of left ventricular lead. Such information may be used to determine a suitable electrode configuration for the lead  106  (e.g., selection of one or more electrodes  123  of the lead  106 ). 
     An exemplary coronary sinus lead  106  can be designed to receive ventricular cardiac signals (and optionally atrial signals) and to deliver left ventricular pacing therapy using, for example, at least one of the electrodes  123  and/or the tip electrode  122 . The lead  106  optionally allows for left atrial pacing therapy, for example, using at least the left atrial ring electrode  124 . The lead  106  optionally allows for shocking therapy, for example, using at least the left atrial coil electrode  126 . For a complete description of a coronary sinus lead, the reader is directed to U.S. Pat. No. 5,466,254, “Coronary Sinus Lead with Atrial Sensing Capability” (Helland), which is incorporated herein by reference. 
     The stimulation device  100  is also shown in electrical communication with the patient&#39;s heart  102  by way of an implantable right ventricular lead  108  having, in this exemplary implementation, a right ventricular tip electrode  128 , a right ventricular ring electrode  130 , a right ventricular (RV) coil electrode  132 , and an SVC coil electrode  134 . Typically, the right ventricular lead  108  is transvenously inserted into the heart  102  to place the right ventricular tip electrode  128  in the right ventricular apex so that the RV coil electrode  132  will be positioned in the right ventricle and the SVC coil electrode  134  will be positioned in the superior vena cava. Accordingly, the right ventricular lead  108  is capable of sensing or receiving cardiac signals, and delivering stimulation in the form of pacing and shock therapy to the right ventricle. An exemplary right ventricular lead may also include at least one electrode capable of stimulating other tissue; such an electrode may be positioned on the lead or a bifurcation or leg of the lead. A right ventricular lead may include a series of electrodes, such as the series  123  of the left ventricular lead  106 . 
       FIG. 2  shows an exemplary, simplified block diagram depicting various components of stimulation device  100 . The stimulation device  100  can be capable of treating both fast and slow arrhythmias with stimulation therapy, including cardioversion, defibrillation, and pacing stimulation. While a particular multi-chamber device is shown, it is to be appreciated and understood that this is done for illustration purposes only. Thus, the techniques, methods, etc., described below can be implemented in connection with any suitably configured or configurable stimulation device. Accordingly, one of skill in the art could readily duplicate, eliminate, or disable the appropriate circuitry in any desired combination to provide a device capable of treating the appropriate chamber(s) or regions of a patient&#39;s heart. 
     Housing  200  for the stimulation device  100  is often referred to as the “can”, “case” or “case electrode”, and may be programmably selected to act as the return electrode for all “unipolar” modes. Housing  200  may further be used as a return electrode alone or in combination with one or more of the coil electrodes  126 ,  132  and  134  for shocking or other purposes. Housing  200  further includes a connector (not shown) having a plurality of terminals  201 ,  202 ,  204 ,  206 ,  208 ,  212 ,  214 ,  216 ,  218 ,  221 ,  223  (shown schematically and, for convenience, the names of the electrodes to which they are connected are shown next to the terminals). 
     To achieve right atrial sensing, pacing and/or other stimulation, the connector includes at least a right atrial tip terminal (A R  TIP)  202  adapted for connection to the atrial tip electrode  120 . A right atrial ring terminal (A R  RING)  201  is also shown, which is adapted for connection to the atrial ring electrode  121 . To achieve left chamber sensing, pacing, shocking, and/or autonomic stimulation, the connector includes at least a left ventricular tip terminal (V L  TIP)  204 , a left atrial ring terminal (A L  RING)  206 , and a left atrial shocking terminal (A L  COIL)  208 , which are adapted for connection to the left ventricular tip electrode  122 , the left atrial ring electrode  124 , and the left atrial coil electrode  126 , respectively. Connection to suitable stimulation electrodes is also possible via these and/or other terminals (e.g., via a stimulation terminal S ELEC  221 ). The terminal S ELEC  221  may optionally be used for sensing. For example, electrodes of the lead  110  may connect to the device  100  at the terminal  221  or optionally at one or more other terminals. 
     A terminal  223  allows for connection of a series of left ventricular electrodes. For example, the series of four electrodes  123  of the lead  106  may connect to the device  100  via the terminal  223 . The terminal  223  and an electrode configuration switch  226  allow for selection of one or more of the series of electrodes and hence electrode configuration. In the example of  FIG. 2 , the terminal  223  includes four branches to the switch  226  where each branch corresponds to one of the four electrodes  123 . 
     To support right chamber sensing, pacing, shocking, and/or autonomic nerve stimulation, the connector further includes a right ventricular tip terminal (V R  TIP)  212 , a right ventricular ring terminal (V R  RING)  214 , a right ventricular shocking terminal (RV COIL)  216 , and a superior vena cava shocking terminal (SVC COIL)  218 , which are adapted for connection to the right ventricular tip electrode  128 , right ventricular ring electrode  130 , the RV coil electrode  132 , and the SVC coil electrode  134 , respectively. 
     At the core of the stimulation device  100  is a programmable microcontroller  220  that controls the various modes of cardiac or other therapy. As is well known in the art, microcontroller  220  typically includes a microprocessor, or equivalent control circuitry, designed specifically for controlling the delivery of stimulation therapy, and may further include RAM or ROM memory, logic and timing circuitry, state machine circuitry, and I/O circuitry. Typically, microcontroller  220  includes the ability to process or monitor input signals (data or information) as controlled by a program code stored in a designated block of memory. The type of microcontroller is not critical to the described implementations. Rather, any suitable microcontroller  220  may be used that is suitable to carry out the functions described herein. The use of microprocessor-based control circuits for performing timing and data analysis functions are well known in the art. As described herein, the microcontroller  220  operates according to control logic, which may be in the form of hardware, software (including firmware) or a combination of hardware and software. With respect to software, control logic instructions may be stored in memory (e.g., memory  260 ) for execution by the microcontroller  220  to implement control logic. 
     Representative types of control circuitry that may be used in connection with the described embodiments can include the microprocessor-based control system of U.S. Pat. No. 4,940,052, the state-machine of U.S. Pat. Nos. 4,712,555 and 4,944,298, all of which are incorporated by reference herein. For a more detailed description of the various timing intervals used within the stimulation device and their inter-relationship, see U.S. Pat. No. 4,788,980, also incorporated herein by reference. 
       FIG. 2  also shows an atrial pulse generator  222  and a ventricular pulse generator  224  that generate pacing stimulation pulses for delivery by the right atrial lead  104 , the coronary sinus lead  106 , and/or the right ventricular lead  108  via an electrode configuration switch  226 . It is understood that in order to provide stimulation therapy in each of the four chambers of the heart (or to autonomic nerves) the atrial and ventricular pulse generators,  222  and  224 , may include dedicated, independent pulse generators, multiplexed pulse generators, or shared pulse generators. The pulse generators  222  and  224  are controlled by the microcontroller  220  via appropriate control signals  228  and  230 , respectively, to trigger or inhibit the stimulation pulses. 
     Microcontroller  220  further includes timing control circuitry  232  to control the timing of the stimulation pulses (e.g., pacing rate, atrio-ventricular (AV) delay, interatrial conduction (AA) delay, or interventricular conduction (VV) delay, etc.) as well as to keep track of the timing of refractory periods, blanking intervals, noise detection windows, evoked response windows, alert intervals, marker channel timing, etc., which is well known in the art. 
     Microcontroller  220  further includes an arrhythmia detector  234 . The detector  234  can be utilized by the stimulation device  100  for determining desirable times to administer various therapies. The detector  234  may be implemented in hardware as part of the microcontroller  220 , or as software/firmware instructions programmed into the device and executed on the microcontroller  220  during certain modes of operation. 
     Microcontroller  220  further includes a morphology discrimination module  236 , a capture detection module  237  and an auto sensing module  238 . These modules are optionally used to implement various exemplary recognition algorithms and/or methods presented below. The aforementioned components may be implemented in hardware as part of the microcontroller  220 , or as software/firmware instructions programmed into the device and executed on the microcontroller  220  during certain modes of operation. The capture detection module  237 , as described herein, may aid in acquisition, analysis, etc., of information relating to IEGMs and, in particular, act to distinguish capture versus non-capture versus fusion. 
     The microcontroller  220  further includes an optional position detection module  239 . The module  239  may be used for purposes of acquiring position information, for example, in conjunction with a device (internal or external) that may use body surface patches or other electrodes (internal or external). The microcontroller  220  may initiate one or more algorithms of the module  239  in response to a signal detected by various circuitry or information received via the telemetry circuit  264 . Instructions of the module  239  may cause the device  100  to measure potentials using one or more electrode configurations where the potentials correspond to a potential field generated by current delivered to the body using, for example, surface patch electrodes. Such a module may help monitor position and cardiac mechanics in relationship to cardiac electrical activity and may help to optimize cardiac resynchronization therapy. The module  239  may operate in conjunction with various other modules and/or circuits of the device  100  (e.g., the impedance measuring circuit  278 , the switch  226 , the A/D  252 , etc.). 
     The electronic configuration switch  226  includes a plurality of switches for connecting the desired electrodes to the appropriate I/O circuits, thereby providing complete electrode programmability. Accordingly, switch  226 , in response to a control signal  242  from the microcontroller  220 , determines the polarity of the stimulation pulses (e.g., unipolar, bipolar, etc.) by selectively closing the appropriate combination of switches (not shown) as is known in the art. 
     Atrial sensing circuits  244  and ventricular sensing circuits  246  may also be selectively coupled to the right atrial lead  104 , coronary sinus lead  106 , and the right ventricular lead  108 , through the switch  226  for detecting the presence of cardiac activity in each of the four chambers of the heart. Accordingly, the atrial and ventricular sensing circuits,  244  and  246 , may include dedicated sense amplifiers, multiplexed amplifiers, or shared amplifiers. Switch  226  determines the “sensing polarity” of the cardiac signal by selectively closing the appropriate switches, as is also known in the art. In this way, the clinician may program the sensing polarity independent of the stimulation polarity. The sensing circuits (e.g.,  244  and  246 ) are optionally capable of obtaining information indicative of tissue capture. 
     Each sensing circuit  244  and  246  preferably employs one or more low power, precision amplifiers with programmable gain and/or automatic gain control, bandpass filtering, and a threshold detection circuit, as known in the art, to selectively sense the cardiac signal of interest. The automatic gain control enables the device  100  to deal effectively with the difficult problem of sensing the low amplitude signal characteristics of atrial or ventricular fibrillation. 
     The outputs of the atrial and ventricular sensing circuits  244  and  246  are connected to the microcontroller  220 , which, in turn, is able to trigger or inhibit the atrial and ventricular pulse generators  222  and  224 , respectively, in a demand fashion in response to the absence or presence of cardiac activity in the appropriate chambers of the heart. Furthermore, as described herein, the microcontroller  220  is also capable of analyzing information output from the sensing circuits  244  and  246  and/or the data acquisition system  252  to determine or detect whether and to what degree tissue capture has occurred and to program a pulse, or pulses, in response to such determinations. The sensing circuits  244  and  246 , in turn, receive control signals over signal lines  248  and  250  from the microcontroller  220  for purposes of controlling the gain, threshold, polarization charge removal circuitry (not shown), and the timing of any blocking circuitry (not shown) coupled to the inputs of the sensing circuits,  244  and  246 , as is known in the art. 
     For arrhythmia detection, the device  100  may utilize the atrial and ventricular sensing circuits,  244  and  246 , to sense cardiac signals to determine whether a rhythm is physiologic or pathologic. Of course, other sensing circuits may be available depending on need and/or desire. In reference to arrhythmias, as used herein, “sensing” is reserved for the noting of an electrical signal or obtaining data (information), and “detection” is the processing (analysis) of these sensed signals and noting the presence of an arrhythmia or of a precursor or other factor that may indicate a risk of or likelihood of an imminent onset of an arrhythmia. 
     The exemplary detector module  234 , optionally uses timing intervals between sensed events (e.g., P-waves, R-waves, and depolarization signals associated with fibrillation which are sometimes referred to as “F-waves”) and to perform one or more comparisons to a predefined rate zone limit (i.e., bradycardia, normal, low rate VT, high rate VT, and fibrillation rate zones) and/or various other characteristics (e.g., sudden onset, stability, physiologic sensors, and morphology, etc.) in order to determine the type of remedial therapy (e.g., anti-arrhythmia, etc.) that is desired or needed (e.g., bradycardia pacing, anti-tachycardia pacing, cardioversion shocks or defibrillation shocks, collectively referred to as “tiered therapy”). Similar rules can be applied to the atrial channel to determine if there is an atrial tachyarrhythmia or atrial fibrillation with appropriate classification and intervention. 
     Cardiac signals are also applied to inputs of an analog-to-digital (A/D) data acquisition system  252 . Additional configurations are shown in  FIG. 11  and described further below. The data acquisition system  252  is configured to acquire intracardiac electrogram (IEGM) signals or other action potential signals, convert the raw analog data into a digital signal, and store the digital signals for later processing and/or telemetric transmission to an external device  254 . The data acquisition system  252  is coupled to the right atrial lead  104 , the coronary sinus lead  106 , the right ventricular lead  108  and/or the nerve stimulation lead through the switch  226  to sample cardiac signals across any pair of desired electrodes. A control signal  256  from the microcontroller  220  may instruct the A/D  252  to operate in a particular mode (e.g., resolution, amplification, etc.). 
     Various exemplary mechanisms for signal acquisition are described herein that optionally include use of one or more analog-to-digital converter. Various exemplary mechanisms allow for adjustment of one or more parameter associated with signal acquisition. 
     The microcontroller  220  is further coupled to a memory  260  by a suitable data/address bus  262 , where the programmable operating parameters used by the microcontroller  220  are stored and modified, as required, in order to customize the operation of the stimulation device  100  to suit the needs of a particular patient. Such operating parameters define, for example, pacing pulse amplitude, pulse duration, electrode polarity, rate, sensitivity, automatic features, arrhythmia detection criteria, and the amplitude, waveshape, number of pulses, and vector of each shocking pulse to be delivered to the patient&#39;s heart  102  within each respective tier of therapy. One feature of the described embodiments is the ability to sense and store a relatively large amount of data (e.g., from the data acquisition system  252 ), which data may then be used for subsequent analysis to guide the programming of the device. 
     Advantageously, the operating parameters of the implantable device  100  may be non-invasively programmed into the memory  260  through a telemetry circuit  264  in telemetric communication via communication link  266  with the external device  254 , such as a programmer, transtelephonic transceiver, or a diagnostic system analyzer. The microcontroller  220  activates the telemetry circuit  264  with a control signal  268 . The telemetry circuit  264  advantageously allows intracardiac electrograms (IEGM) and other information (e.g., status information relating to the operation of the device  100 , etc., as contained in the microcontroller  220  or memory  260 ) to be sent to the external device  254  through an established communication link  266 . 
     The stimulation device  100  can further include one or more physiologic sensors  270 . For example, the device  100  may include a “rate-responsive” sensor that may provide, for example, information to aid in adjustment of pacing stimulation rate according to the exercise state of the patient. However, the one or more physiological sensors  270  may further be used to detect changes in cardiac output (see, e.g., U.S. Pat. No. 6,314,323, entitled “Heart stimulator determining cardiac output, by measuring the systolic pressure, for controlling the stimulation”, to Ekwall, issued Nov. 6, 2001, which discusses a pressure sensor adapted to sense pressure in a right ventricle and to generate an electrical pressure signal corresponding to the sensed pressure, an integrator supplied with the pressure signal which integrates the pressure signal between a start time and a stop time to produce an integration result that corresponds to cardiac output), changes in the physiological condition of the heart, or diurnal changes in activity (e.g., detecting sleep and wake states). Accordingly, the microcontroller  220  responds by adjusting the various pacing parameters (such as rate, AV Delay, V-V Delay, etc.) at which the atrial and ventricular pulse generators,  222  and  224 , generate stimulation pulses. 
     While shown as being included within the stimulation device  100 , it is to be understood that one or more of the physiologic sensors  270  may also be external to the stimulation device  100 , yet still be implanted within or carried by the patient. Examples of physiologic sensors that may be implemented in device  100  include known sensors that, for example, sense respiration rate, pH of blood, ventricular gradient, cardiac output, preload, afterload, contractility, and so forth. Another sensor that may be used is one that detects activity variance, where an activity sensor is monitored diurnally to detect the low variance in the measurement corresponding to the sleep state. For a complete description of the activity variance sensor, the reader is directed to U.S. Pat. No. 5,476,483 which is hereby incorporated by reference. 
     The one or more physiological sensors  270  optionally include sensors for detecting movement and minute ventilation in the patient. Signals generated by a position sensor, a MV sensor, etc., may be passed to the microcontroller  220  for analysis in determining whether to adjust the pacing rate, etc. The microcontroller  220  may monitor the signals for indications of the patient&#39;s position and activity status, such as whether the patient is climbing upstairs or descending downstairs or whether the patient is sitting up after lying down. 
     The stimulation device  100  additionally includes a battery  276  that provides operating power to all of the circuits shown in  FIG. 2 . For the stimulation device  100 , which employs shocking therapy, the battery  276  is capable of operating at low current drains for long periods of time (e.g., preferably less than 10 μA), and is capable of providing high-current pulses (for capacitor charging) when the patient requires a shock pulse (e.g., preferably, in excess of 2 A, at voltages above 200 V, for periods of 10 seconds or more). The battery  276  also desirably has a predictable discharge characteristic so that elective replacement time can be detected. 
     The stimulation device  100  can further include magnet detection circuitry (not shown), coupled to the microcontroller  220 , to detect when a magnet is placed over the stimulation device  100 . A magnet may be used by a clinician to perform various test functions of the stimulation device  100  and/or to signal the microcontroller  220  that the external programmer  254  is in place to receive or transmit data to the microcontroller  220  through the telemetry circuits  264 . 
     The stimulation device  100  further includes an impedance measuring circuit  278  that is enabled by the microcontroller  220  via a control signal  280 . The known uses for an impedance measuring circuit  278  include, but are not limited to, lead impedance surveillance during the acute and chronic phases for proper lead positioning or dislodgement; detecting operable electrodes and automatically switching to an operable pair if dislodgement occurs; measuring respiration or minute ventilation; measuring thoracic impedance for determining shock thresholds; detecting when the device has been implanted; measuring stroke volume; and detecting the opening of heart valves, etc. The impedance measuring circuit  278  is advantageously coupled to the switch  226  so that any desired electrode may be used. 
     In the case where the stimulation device  100  is intended to operate as an implantable cardioverter/defibrillator (ICD) device, it detects the occurrence of an arrhythmia, and automatically applies an appropriate therapy to the heart aimed at terminating the detected arrhythmia. To this end, the microcontroller  220  further controls a shocking circuit  282  by way of a control signal  284 . The shocking circuit  282  generates shocking pulses of low (e.g., up to 0.5 J), moderate (e.g., 0.5 J to 10 J), or high energy (e.g., 11 J to 40 J), as controlled by the microcontroller  220 . Such shocking pulses are applied to the patient&#39;s heart  102  through at least two shocking electrodes, and as shown in this embodiment, selected from the left atrial coil electrode  126 , the RV coil electrode  132 , and/or the SVC coil electrode  134 . As noted above, the housing  200  may act as an active electrode in combination with the RV electrode  132 , or as part of a split electrical vector using the SVC coil electrode  134  or the left atrial coil electrode  126  (i.e., using the RV electrode as a common electrode). 
     Cardioversion level shocks are generally considered to be of low to moderate energy level (so as to minimize pain felt by the patient), and/or synchronized with an R-wave and/or pertaining to the treatment of tachycardia. Defibrillation shocks are generally of moderate to high energy level (e.g., corresponding to thresholds in the range of approximately 5 J to 40 J), delivered asynchronously (since R-waves may be too disorganized), and pertaining exclusively to the treatment of fibrillation. Accordingly, the microcontroller  220  is capable of controlling the synchronous or asynchronous delivery of the shocking pulses. 
     As already mentioned, the implantable device  100  includes impedance measurement circuitry  278 . Such a circuit may measure impedance or electrical resistance through use of various techniques. For example, the device  100  may deliver a low voltage (e.g., about 10 mV to about 20 mV) of alternating current between the RV tip electrode  128  and the case electrode  200 . During delivery of this energy, the device  100  may measure resistance between these two electrodes where the resistance depends on any of a variety of factors. For example, the resistance may vary inversely with respect to volume of blood along the path. 
     In another example, resistance measurement occurs through use of a four terminal or electrode technique. For example, the exemplary device  100  may deliver an alternating current between one of the RV tip electrode  128  and the case electrode  200 . During delivery, the device  100  may measure a potential between the RA ring electrode  121  and the RV ring electrode  130  where the potential is proportional to the resistance between the selected potential measurement electrodes. 
     With respect to two terminal or electrode techniques, where two electrodes are used to introduce current and the same two electrodes are used to measure potential, parasitic electrode-electrolyte impedances can introduce noise, especially at low current frequencies; thus, a greater number of terminals or electrodes may be used. For example, aforementioned four electrode techniques, where one electrode pair introduces current and another electrode pair measures potential, can cancel noise due to electrode-electrolyte interface impedance. Alternatively, where suitable or desirable, a two terminal or electrode technique may use larger electrode areas (e.g., even exceeding about 1 cm 2 ) and/or higher current frequencies (e.g., above about 10 kHz) to reduce noise. 
       FIG. 3  shows an exemplary method  300  for acquiring position information and calculating one or more stability metrics  330 . In the example of  FIG. 3 , the method  300  includes a configurations block  310  that includes intraoperative configurations  312  and chronic configurations  314 . The intraoperative configurations  312  pertain to configurations that may be achieved during an operative procedure. For example, during an operative procedure, one or more leads (and/or catheter(s)) may be positioned in a patient where the one or more leads are connected to, or variously connectable to, a device configured to acquire information and optionally to deliver electrical energy to the patient (e.g., to the heart, to a nerve, to other tissue, etc.). The chronic configurations  314  pertain to configurations achievable by a chronically implanted device and its associated lead or leads. In general, intraoperative configurations include those achievable by physically re-positioning a lead (or catheter) in a patient&#39;s body while chronic configurations normally do not allow for re-positioning as a lead or leads are usually anchored during implantation or become anchored in the weeks to months after implantation. Chronic configurations do, however, include selection of a subset of the multiple implanted electrodes, for example using the tip electrode versus the first ring electrode as a cathode or using the tip and first ring as a bipolar pair versus using the tip and ring as two independent cathodes. Thus, intraoperative configurations include configurations available by changing device settings, electrode selection, and physical position of electrodes, while chronic configurations include only those configurations available by changing device settings and electrode selection, or “electronic repositioning” of one or more stimulation electrodes. 
     As indicated in  FIG. 3 , an acquisition block  320  includes acquisition of position information  322  and optionally acquisition of pacing and/or other information  324  (e.g., electrical information as to electrical activity of the heart, biosensor information, etc.). While an arrow indicates that a relationship or relationships may exist between the configurations block  310  and the acquisition block  320 , acquisition of information may occur by using in part an electrode (or other equipment) that is not part of a configuration. For example, the acquisition block  320  may rely on one or more surface electrodes that define a coordinate system or location system for locating an electrode that defines one or more configurations. For example, three pairs of surface electrodes positioned on a patient may be configured to deliver current and define a three-dimensional space whereby measurement of a potential locates an electrode in the three-dimensional space. 
     As described herein, an electrode may be configured for delivery of energy to the body; for acquisition of electrical information; for acquisition of position information; for acquisition of electrical information and position information; for delivery of energy to the body and for acquisition of electrical information; for delivery of energy to the body and for acquisition of position information; for delivery of energy to the body, for acquisition of electrical information and for acquisition of position information. 
     In various examples, acquisition of position information occurs by measuring one or more potentials where the measuring relies on an electrode that assists in determining a position of the electrode or other item (e.g., a lead or sensor) where the electrode may also be configured to sense signals and/or deliver energy to the body (e.g., electrical energy to pace a chamber of the heart). For example, an electrode may deliver energy sufficient to stimulate the heart and then be tracked along one or more dimensions to monitor the position information resulting from the stimulation. Further, such an electrode may be used to acquire electrical information (e.g., an IEGM that evidences an evoked response). Such an electrode can perform all three of these tasks with proper circuitry and control. For example, after delivery of the energy, the electrode may be configured for acquiring one or more potentials related to position and for acquiring an electrogram. To acquire potentials and an electrogram, circuitry may include gating or other sampling techniques (e.g., to avoid circuitry or interference issues). Such circuitry may rely on one sampling frequency for acquiring potentials for motion tracking and another sampling frequency for acquiring an electrogram. 
     The method  300  of  FIG. 3  includes a metrics block  330  that includes electrode stability metrics  332 , lead stability metrics  334  and implanted device stability metrics  336 . 
     As shown in the example of  FIG. 3 , the conclusion block  340  may perform actions such as to assess stability  342  and/or to optimize or monitor patient and/or device condition  344 . These options are described in more detail with respect to  FIG. 4 . 
       FIG. 4  shows an exemplary method  400  with various configurations  410  (C 1 , C 2 , . . . , Cn) and options  450 . As mentioned, a configuration may be defined based on factors such as electrode location (e.g., with respect to some physiological feature of the heart or another electrode), stimulation parameters for an electrode or electrodes and, where appropriate, one or more interelectrode timings. Hence, with reference to  FIG. 1 , C 1  may be a configuration that relies on the RV tip electrode  128 , the RV ring electrode  130 , the LV tip electrode  122  and the LV ring electrode  124  while C 2  may be a configuration that relies on the same electrodes as C 1  but where the stimulation polarity for the LV electrodes is reversed. Further, C 3  may rely on the same electrodes where the timing between delivery of a stimulus to the RV and delivery of a stimulus to the LV is different compared to C 1 . Yet further, C 4  may rely on the same electrodes where the duration of a stimulus to the RV is different compared to C 1 . In these foregoing examples, configurations provide for one or more electrodes to deliver energy to stimulate the right ventricle and for one or more electrodes to deliver energy to stimulate the left ventricle. In other examples, configurations may provide for stimulation of a single chamber at one or more sites, stimulation of one chamber at a single site and another chamber at multiple sites, multiple chambers at multiple sites per chamber, etc. 
     As mentioned, configurations can include one or more so-called “stimulators” and/or “sensors”. Thus, the configurations block  410  may select a configuration that includes one or more of an electrode, a lead, a catheter, a device, etc. In various examples, a stimulator or a sensor can include one or more electrodes configured to measure a potential or potentials to thereby directly or indirectly provide position information for the stimulator or the sensor. For example, a lead-based oximeter (oxygen sensor) may include an electrode configured to measure a potential for providing position information for the oximeter or a lead-based RF applicator may include electrodes configured to measure potentials for providing position information for the RF applicator or a tip of the lead. 
     In an acquisition block  420 , acquisition occurs for information where such information includes position information that pertains to one or more electrodes of a configuration. In a determination block  430 , one or more stability metrics are determined based at least in part on the acquired information (see, e.g., the metrics block  330  of  FIG. 3 ). A conclusions block  430  provides for therapeutic or other action, which may be selected from one or more options  450 . 
     In the example of  FIG. 4 , the one or more options  450  include selection of a configuration  452  (e.g., Cx, where x is a number selected from 1 to n), issuance of a patient and/or device alert  454  that pertains to condition of a patient or a condition of a device or associated lead(s) or electrode(s), and storage of conclusion(s) and/or data  456 . The options  450  may be associated with the configurations  410 , as indicated by an arrow. For example, storage of conclusions and/or data  456  may also store specific configurations, a generalization of the configurations (e.g., one or more shared characteristics), a device/system arrangement (e.g., where the number and types of configurations would be known based on the arrangement), etc. With respect to an alert per block  454 , an exemplary method may determine a stability limit as an indicator of instability or risk of instability. Such a limit may be a metric or index, for example, based on impedance of a known unstable configuration (e.g., a standard deviation of impedance measurements) as acquired in an acute setting. Accordingly, where impedance measured in a chronic setting exhibits a metric or index that exceeds the limit, an alert may be issued. 
     As described herein, an exemplary method can include: locating one or more electrodes within the heart and/or surrounding space (e.g., intra-chamber, intra-vascular, intrapericardial, etc., which may be collectively referred to as “cardiac space”); and acquiring information (e.g., via one or more measured potentials) to calculate one or more stability metrics for at least one of the one or more electrodes using an electroanatomic mapping system (e.g., the ENSITE® NAVX® system or other system with appropriate features). In such a method, the located electrodes may be configured for acquisition of electrical information indicative of physiological function (e.g., IEGMs, muscle signals, nerve signals, etc.). Further, with respect to acquisition of information, an acquisition system may operate at an appropriate sampling rate. For example, an acquisition system for position information may operate at a sampling rate of about 100 Hz (e.g., the ENSITE® NAVX® system can sample at about 93 Hz) and an acquisition system for electrical information may operate at a sampling rate of about 1200 Hz (e.g., in unipolar, bipolar or other polar arrangement). 
     An exemplary method may include preparing a patient for both implant of a device such as the device  100  of  FIGS. 1 and 2  and for electroanatomic mapping study. Such preparation may occur in a relatively standard manner for implant prep, and using the ENSITE® NAVX® system or other similar technology for the mapping prep. As described herein, any of a variety of electroanatomic mapping or locating systems that can locate indwelling electrodes in and around the heart may be used. 
     Once prepped, a clinician or robot may place leads and/or catheters in the patient&#39;s body, including any leads to be chronically implanted as part of a therapy system (e.g., CRT), as well as optional additional electrodes that may yield additional information (e.g., to increase accuracy by providing global information or other information). 
     After an initial placement of an electrode-bearing catheter or an electrode-bearing lead, a clinician may then connect one or more electrodes to an electroanatomic mapping or localizing system. The term “connection” can refer to physical electrical connection or wireless connection (e.g., telemetric, RF, ultrasound, etc.) with the electrodes or wireless connection with another device that is in electrical contact with the electrodes. 
     Once an appropriate connection or connections have been made, real-time position data for one or more electrodes may be acquired for various configurations or conditions. For example, position data may be acquired during normal sinus rhythm; pacing in one or more chambers; advancing, withdrawing, or moving a location of an electrode; pacing one or more different electrode configurations (e.g. multisite pacing); or varying inter-stimulus timing (e.g. AV delay, VV delay). 
     In various examples, simultaneous to the position recording, an intracardiac electrogram (IEGM) from each electrode can also be recorded and associated with the anatomic position of the electrode. While various examples refer to simultaneous acquisition, acquisition of electrical information and acquisition of position information may occur sequentially (e.g., alternate cardiac cycles) or interleaved (e.g., both acquired during the same cardiac cycle but offset by sampling time or sampling frequency). 
     In various exemplary methods, electrodes within the cardiac space may be optionally positioned at various locations (e.g., by continuous movement or by discrete, sequential moves), with a mapping system recording the real-time position information at each electrode position in a point-by-point manner. Such position data can by associated with a respective anatomic point from which it was collected. By moving the electrodes from point to point during an intervention, the position data from each location can be incorporated into a single map, model, or parameter. 
     As explained, an exemplary method may include mapping one or more stability metrics and/or parameters. In turn, an algorithm or a clinician may select a configuration (e.g., electrode location, multisite arrangement, AV/VV timing) that yielded the best value for an electromechanical delay parameter and use the selected configuration as a chronic configuration for the CRT system. Such a chronic configuration may be optionally updated from time to time (e.g., during a follow-up visit, in a patient environment, etc., depending on specific capabilities of a system). 
     Various exemplary methods, using either a single metric or a combination of more than one metric, may automatically select a configuration, present an optimal configuration for acknowledgement by a clinician, or present various configurations to a clinician along with pros and cons of each configuration (e.g., in objective or subjective terms). For example, a particular configuration may be associated with a high power usage that may excessively drain a power source of an implantable device (e.g., device battery  276 ). Other pros and cons may pertain to patient comfort (e.g., pain, lack of pain, overall feeling, etc.). As described herein, various decisions are based on stability of one or more of an electrode or a lead. 
     An exemplary method may rely on certain equipment at time of implant or exploration and other equipment after implantation of a device to deliver a cardiac therapy. For example, during an intraoperative procedure, wireless communication may not be required; whereas, during a follow-up visit, measured potentials for position of chronically implanted electrodes (e.g., mechanical information) and of measured IEGMs using chronically implanted electrodes (e.g., electrical information) may be communicated wirelessly from an implanted device to an external device. With respect to optimization or assessment of a chronically implanted system, in general, electrode location will not be altered (e.g., except for dislocation or failure), but other parameters altered to result in an optimal configuration (e.g., single- or multi-site arrangement, polarity, stimulation energy, timing parameters, etc.). 
     As discussed herein, various exemplary techniques deliver current and measure potential where potential varies typically with respect to cardiac mechanics (e.g., due to motion). For example, electrodes for delivery of current may be placed at locations that do not vary significantly with respect to cardiac mechanics or other patient motion (e.g., breathing) while one or more electrodes for measuring potential may be placed at a location or locations that vary with respect to cardiac mechanics or other patient motion. Alternatively, electrodes for measuring potential may be placed at locations that do not vary significantly with respect to cardiac mechanics or other patient motion while one or more electrodes for delivery of current may be placed at a location or locations that vary with respect to cardiac mechanics or other patient motion. Various combinations of the foregoing arrangements are possible as well. Electrodes may be associated with a catheter or a lead. In some instances, an electrode may be a “stand-alone” electrode, such as a case electrode of an implantable device (see, e.g., the case electrode  200  of the device  100  of  FIGS. 1 and 2 ). 
       FIG. 5  shows an arrangement and method  500  that may rely in part on a commercially available system marketed as ENSITE® NAVX® navigation and visualization system (see also LocaLisa system). The ENSITE® NAVX® system is a computerized storage and display system for use in electrophysiology studies of the human heart. The system consists of a console workstation, patient interface unit, and an electrophysiology mapping catheter and/or surface electrode kit. By visualizing the global activation pattern seen on color-coded isopotential maps in the system, in conjunction with the reconstructed electrograms, an electrophysiologist can identify the source of an arrhythmia and can navigate to a defined area for therapy. The ENSITE® system is also useful in treating patients with simpler arrhythmias by providing non-fluoroscopic navigation and visualization of conventional electrophysiology (EP) catheters. 
     As shown in  FIG. 5 , electrodes  532 ,  532 ′, which may be part of a standard EP catheter  530  (or lead), sense electrical potential associated with current signals transmitted between three pairs of surface electrode patches  522 ,  522 ′ (x-axis),  524 ,  524 ′ (y-axis) and  526 ,  526 ′ (z-axis). An addition electrode patch  528  is available for reference, grounding or other function. The ENSITE® NAVX® System can also collect electrical data from a catheter and can plot a cardiac electrogram from a particular location (e.g., cardiac vein  103  of heart  102 ). Information acquired may be displayed as a 3-D isopotential map and as virtual electrograms. Repositioning of the catheter allows for plotting of cardiac electrograms from other locations. Multiple catheters may be used as well. A cardiac electrogram or electrocardiogram (ECG) of normal heart activity (e.g., polarization, depolarization, etc.) typically shows atrial depolarization as a “P wave”, ventricular depolarization as an “R wave”, or QRS complex, and repolarization as a “T wave”. The ENSITE® NAVX® system may use electrical information to track or navigate movement and construct three-dimensional (3-D) models of a chamber of the heart. 
     A clinician can use the ENSITE® NAVX® system to create a 3-D model of a chamber in the heart for purposes of treating arrhythmia (e.g., treatment via tissue ablation). To create the 3-D model, the clinician applies surface patches to the body. The ENSITE® NAVX® system transmits an electrical signal between the patches and the system then senses the electrical signal using one or more catheters positioned in the body. The clinician may sweep a catheter with electrodes across a chamber of the heart to outline structure. Signals acquired during the sweep, associated with various positions, can then be used to generate a 3-D model. A display can display a diagram of heart morphology, which, in turn, may help guide an ablation catheter to a point for tissue ablation. 
     With respect to the foregoing discussion of current delivery and potential measurement, per a method  540 , a system (e.g., such as the ENSITE® NAVX® system) delivers low level separable currents from the three substantially orthogonal electrode pairs ( 522 ,  522 ′,  524 ,  524 ′,  526 ,  526 ′) positioned on the body surface (delivery block  542 ). The specific position of a catheter (or lead) electrode within a chamber of the heart can then be established based on three resulting potentials measured between the recording electrode with respect to a reference electrode, as seen over the distance from each patch set to the recording tip electrode (measurement block  544 ). Sequential positioning of a catheter (or lead) at multiple sites along the endocardial surface of a specific chamber can establish that chamber&#39;s geometry, i.e., position mapping (position/motion determination block  546 ). Where the catheter (or lead)  530  moves, the method  540  may also measure motion. 
     In addition to mapping at specific points, the ENSITE® NAVX® system provides for interpolation (mapping a smooth surface) onto which activation voltages and times can be registered. Around 50 points are required to establish a surface geometry and activation of a chamber at an appropriate resolution. The ENSITE® NAVX® system also permits the simultaneous display of multiple catheter electrode sites, and also reflects real-time motion of both ablation catheters and those positioned elsewhere in the heart. 
     The ENSITE® NAVX® system relies on catheters for temporary placement in the body. Various exemplary techniques described herein optionally use one or more electrodes for chronic implantation. Such electrodes may be associated with a lead, an implantable device, or other chronically implantable component. Referring again to  FIG. 3 , the configuration block  310  indicates that intraoperative configurations  312  and chronic configurations  314  may be available. Intraoperative configurations  312  may rely on a catheter and/or a lead suitable for chronic implantation. 
     With respect to motion (e.g., change in position with respect to time), the exemplary system and method  500  may track motion of an electrode in one or more dimensions. For example, a plot  550  of motion versus time for three dimensions corresponds to motion of one or more electrodes of the catheter (or lead)  530  positioned in a vessel  103  of the heart  102  where the catheter (or lead)  530  includes the one or more electrodes  532 ,  532 ′. Two arrows indicate possible motion of the catheter (or lead)  530  where hysteresis may occur over a cardiac cycle. For example, a systolic path may differ from a diastolic path. An exemplary method may analyze hysteresis for any of a variety of purposes including assessing stability of an electrode of a catheter (or lead), assessing stability of a catheter (or lead), selection of a stimulation site, selection of a sensing site, diagnosis of cardiac condition, etc. 
     The exemplary method  540 , as mentioned, includes the delivery block  542  for delivery of current, the measurement block  544  to measure potential in a field defined by the delivered current and the determination block  546  to determine position or motion based at least in part on the measured potential. According to such a method, position or motion during systole and/or diastole may be associated with electrical information or other information (e.g., biosensor, loading of a catheter or lead, intrinsic/paced activation, etc.). Alone, or in combination with other information, the position or motion information may be used for various assessments (e.g., stability assessments), selection of optimal stimulation site(s), determination of hemodynamic surrogates (e.g., surrogates to stroke volume, contractility, etc.), optimization of CRT, placement of leads, determination of pacing parameters (AV delay, VV delay, etc.), etc. 
     The system  500  may use one or more features of the aforementioned ENSITE® NAVX® system. For example, one or more pairs of electrodes ( 522 ,  522 ′,  524 ,  524 ′,  526 ,  526 ′ and optionally  528 ) may be used to define one or more dimensions by delivering an electrical signal or signals to a body and/or by sensing an electrical signal or signals. Such electrodes (e.g., patch electrodes) may be used in conjunction with one or more electrodes positioned in the body (e.g., the electrodes  532 ,  532 ′). 
     The exemplary system  500  may be used to track position or motion of one or more electrodes due to systolic function, diastolic function, respiratory function, etc. Electrodes may be positioned along the endocardium and/or epicardium during a scouting or mapping process for use in conjunction with electrical information. Such information may also be used alone, or in conjunction with other information (e.g., electrical information), for assessing stability of an electrode or electrodes for use in delivering a therapy or for identifying the optimal location of an electrode or electrodes for use in delivering a therapy. For example, a location may be selected for optimal stability, for optimal stimulation, for optimal sensing, or for other purposes. 
     With respect to stimulation, stimulation may be delivered to control cardiac mechanics (e.g., contraction of a chamber of the heart) and position or motion information may be acquired where such information is associated with the controlled cardiac mechanics. An exemplary selection process may identify the best stimulation site based on factors such as electrical activity, electromechanical delay, extent of motion, synchronicity of motion where motion may be classified as motion due to systolic function or motion due to diastolic function. In general, motion information corresponds to motion of an electrode or electrodes (e.g., endocardial electrodes, epicardial electrodes, etc.) and may be related to motion of the heart or other physiology. 
     As described with respect to  FIG. 5 , a localization system can acquire position information for one or more electrodes on a lead or catheter. The ENSITE® NAVX® system can operate at a sampling frequency around 100 Hz (10 ms), which, for a cardiac rhythm of 60 bpm, allows for 100 samples per electrode per cardiac cycle. In various examples, sampling may be gated to occur over only a portion of a cardiac cycle. Gating may rely on fiducial markers such as peaks, gradients, crossings, etc., in an electrogram of heart activity. Other techniques for gating can include accelerometer techniques, impedance techniques, pressure techniques, flow techniques, etc. For example, an accelerometer signal slope above a threshold value (e.g., due to cardiac contraction or relaxation) can be used to commence acquisition of information or to terminate acquisition of information during a cardiac cycle. Such a technique may be repeated over multiple cardiac cycles with or without application of electrical stimuli, medication, body position changes, etc. 
     As described herein, for one or more electrodes, a localization system provides four-dimensional information (e.g., x, y, z and time). The four-dimensional information describes a three-dimensional trajectory in space that can be analyzed or displayed in part, in whole or at one or more key points in time. As mentioned, various other types of information may be used to gate acquisition or to delineate points or segments of a trajectory. For example, information provided by a surface EKG, an intracardiac EGM, or other biosignal can delineate a point or event such as QRS onset or pacing pulse or a segment (e.g., QRS complex, QT interval, etc.). 
     Where an electrode is position in a vessel of the heart such as a vein (e.g., cardiac sinus (CS) vein or a tributary thereto), the trajectory of the electrode will follow cardiac motion of nearby myocardium. For example, a CS lead electrode will trace the path traversed by epicardium adjacent the CS or adjacent the particular CS tributary. If the lead position is stable in a branch, the trajectory for consecutive beats will typically remain within a bounded spatial volume; however, if the lead dislodges grossly, a shift in the CS lead electrode&#39;s position will be apparent in a display or analysis of the acquired information. 
       FIG. 6  shows a plot  600  of trajectories based on position information acquired for four electrodes  623 - 1 ,  623 - 2 ,  623 - 3  and  622  of a quadpolar LV lead in a CS branch of a canine model over a number of cardiac cycles. Each of the trajectories can be characterized as defining a first cluster (“A”) and a second cluster (“B”). In the example of  FIG. 6 , for the electrode  623 - 1 , the direction of the shift from cluster A to cluster B differs from that of the other electrodes  623 - 2 ,  623 - 3  and  622 . An analysis of shift direction for a lead (e.g., on an electrode-by-electrode basis) can indicate mechanisms underlying a shift. For example, if slack exists in a lead between two adjacent electrodes, a shift may reduce the slack where the two adjacent electrodes move in substantially opposite directions. Another mechanism is dislodgement, which may occur for any of a variety of reasons including body or organ movements caused by coughing, phrenic nerve stimulation or delivery of a defibrillation shock. Dislodgement may also occur where a lead or electrode anchor fails. Further, a shift may occur upon withdrawal of a stylet (e.g., consider a lead body that has greater flexibility after withdrawal of a stylet). 
       FIG. 7  shows a plot  700  of a stable trajectory and an unstable trajectory based on position information acquired for a cardiac lead of a patient. Lead electrodes in good stable contact with the epicardium or endocardium tend to trace similar trajectories for every cardiac cycle (e.g., especially for a consistent beat). To the contrary, lead electrodes in poor contact with the epicardium or endocardium (e.g., if a CS lead is not securely wedged in a branch), tend to bounce around erratically from beat to beat, even when general position of the lead appears stable. 
     As described herein, various exemplary methods acquire and analyze position information to indicate whether an electrode is stable. Stability criteria may be applied to analyzed information acquired during an intraoperative procedure (e.g., acute state) to increase the probability that an electrode will be stable after the intraoperative procedure (e.g., chronic state). 
     After implant, the body responds to the foreign electrode. The response can be similar to a wound healing process characterized by inflammation and collagen formation (e.g., fibrous encapsulation). The body&#39;s response to an implanted electrode can be tracked to some extent by measuring capture threshold for an electrode configuration that uses the electrode or by measuring impedance of a circuit that includes the electrode. Often, the capture threshold rises over the first few days following implant and then declines to a relatively constant value over a period of weeks (e.g., six to ten weeks). As the capture threshold depends on contact between the electrode and the body, stability of the electrode-myocardial interface may also be understood via capture threshold and impedance measurements. Factors such as electrode location, size, shape, chemical composition and surface structure can affect how the body responds post-implant. 
     Given sufficient data for specific or general electrode types, stability criteria can be determined and applied to data acquired in an acute state. For example, an electrode known to have few stability issues post-implant may have stability criteria that allow for larger trajectories or more erratic trajectories whereas an electrode known to have more stability issues post-implant may have stability criteria that dictate small trajectories with small standard deviation. Further, stability criteria may be applied regionally and optionally with respect to electrode function. For example, an electrode to be used for sensing may have a greater tolerance to instability while an electrode to be used for pacing may have a lesser tolerance to instability. Thus, as described herein, stability criteria may depend on any of a variety of factors. 
     To assess stability of an electrode, an exemplary method may determine one or more exemplary metrics.  FIG. 8  shows an exemplary method  800  along with position information  805 , a length equation  810  and an area equation  820  that may be used to determine a length metric “L j ” and an area metric “A j ”, respectively. To illustrate how these two metrics may be used alone or in combination, position information  805  is shown for two paths: Path A and Path B. For the j th  cardiac cycle, sampled at N s  time points, the path length L 4  can be determined based on the length equation  810 , i.e., by the integral of an electrode position vectors {right arrow over (s)} over a trajectory length (dl) or by its discrete approximation of position {right arrow over (x)} over the number of sampled time points N s . Given Path A and Path B, which are shown in respective planes that correspond to maximum area, length metrics per the length equation  810  indicate that the length of Path A is approximately the same as the length of Path B. To distinguish characteristics of Path A from Path B, the area equation  820  may be used. The area equation  820  is given in  FIG. 8  as an integral of the electrode position vector {right arrow over (s)} over an area (dA) (e.g., consider the planes as shown for Path A and Path B). In various instances, area enclosed by a swept path can be used as a single cycle indicator as an electrode normally returns to approximately the same point. In the example of  FIG. 8 , the area metrics per the area equation  820  indicate that Path B sweeps a larger area than Path A. As described herein, path metrics such as path length and path area can indicate whether an electrode is in a stable location or an unstable location (e.g., based on one or more stability criteria). Further, such metrics can help determine an optimal electrode location that accounts for stability and desired therapeutic function (e.g., sensing, pacing, shocking, etc.). 
       FIG. 9  shows an exemplary method  900  that computes various stability index metrics. Specifically, given position information  905 , the method  900  can compute a stability index sum metric, a stability index mean metric and a stability index standard deviation metric, for example, per a SI sum  equation  910 , a SI mean  equation  920  and a SI stadev  equation  930 , respectively. In the equations  910  and  920 , an index j represents a number of cardiac cycles from 1 to N 0  while an index i represents a number of time fiducials from 1 to N f . The position information  905  is shown with labels that indicate a number of cardiac cycles from 1 to N c  and a number of time fiducials from 1 to N f . In the equations  910  and  920 , the vector {right arrow over (x)} represents a particular position of an electrode in a three-dimensional space for a given cardiac cycle and for a time fiducial within the given cardiac cycle. 
     As described herein, for a lead of which stability is desired to be known, position information is acquired at one or more gated points in a cardiac cycle. In a particular implementation, position of an electrode at a single fiducial time point is the only required information; in another implementation, position of an electrode is traced as a complete trajectory for all samples (e.g., for multiple fiducial time points). Over the course of two or more cardiac cycles (e.g., consecutive, alternate, etc.), electrode position at each corresponding gated point is noted. 
     With respect to stability metrics, an exemplary method may compute distance in three dimensions between positions at like time points of different cardiac cycles. In implementations that utilize a single or a small number of time points, the distance between like time points, or the sum or average of distances between multiple like time points, is an index of stability, such that the smaller the distance or sum or average of distances, the more stable the position. The equation  910  can be used to determine such a sum where a reference cardiac cycle may be selected for calculating distance between a position for a fiducial point in the reference cardiac cycle and a position for the same fiducial point in another cardiac cycle. The equation  920  can be used to determine a stability index mean in a similar manner. 
     With respect to standard deviation, such a statistical measure may be applied to various forms of position information. Per the equation  930 , a standard deviation stability index can be determined for a length L j . In this example, the standard deviation corresponds to changes in path length of an electrode over multiple cardiac cycles. Similarly, standard deviation may be determined for a swept area, a cycle-to-cycle distance at a time fiducial (e.g., given a reference position), etc. 
     As mentioned, differing pacing interventions as well as external forces on an electrode-bearing lead can affect stability in a given location. A stability index can be calculated from the electrode(s) motion stability during intrinsic and paced rhythm or with zero mechanical loading and some mechanical loading to the lead by pulling a proximal portion of the lead. For example, predictors of lead dislodgement can be derived as follows: (SI intrinsic −SI paced )/SI intrinsic  or (SI no load −SI loaded )/SI no load . 
     As described herein, various stability metrics may be mapped with respect to one or more anatomical markers.  FIG. 10  shows an exemplary stability index map  1000  where contours indicate stability metric values at various regions of the heart  102 . In cases where a clinician desires to map various CS lead locations in order to find an acceptable location, the inclusion of a point-wise stability indicator on a map is possible. For example, at each candidate location, position information may be acquired for two or more cardiac cycles. Such information may be analyzed to provide one or more stability metrics (e.g., consider a local stability index). As each candidate location is probed for stability, a patch of color can be displayed on an anatomic map showing, for example, relative stability at that location. Such a map can be overlaid with other electroanatomic or physio-anatomic map data such as voltage map data, activation time map data, hemodynamic response map data, etc. 
     Referring again to the map  1000  of  FIG. 10 , a left ventricular lead  1006  is shown as including various electrodes  1022 ,  1023 - 1  to  1023 - 4 , and  1024  located in the coronary sinus or a tributary vein of the coronary sinus (e.g., along a lateral wall of the left ventricle) and a right ventricular lead  1008  is shown as including various electrodes  1030 - 1  to  1030 - 9 , some of which contact the septal wall between the right ventricle and the left ventricle. The contours indicate stability index values, which may be dimensionless and normalized such that a higher number corresponds to increased stability. 
       FIG. 10  also shows a plot  1040  of stability index versus electrode position (or electrode order) on the RV lead  1008  and a plot  1060  of stability index versus electrode position (or electrode order) on the LV lead  1006 . In each of the plots  1040  and  1060 , a threshold value is shown, which, in this example, is specific to the right ventricle or specific to the left ventricle. Such a threshold may assist a clinician in site selection for an electrode or in programming an implantable device for sensing cardiac electrical activity and/or delivering electrical energy to the heart  102 . For example, where an implantable device relies on accurate IEGM data to adjust a pacing parameter, a criterion may exist that prohibits use of an electrode having a stability index below a threshold value. Thus, given the plot  1040 , a clinician may program an implantable device to prohibit use of the electrodes  1030 - 5 ,  6 ,  7  and  9  from sensing for the particular purpose of adjusting the pacing parameter. In this example, the values of the thresholds may be based on historic stability data or physiological models that may indicate signal-to-noise ratio or other criteria germane to sensing (e.g., if stability is less than Y, then SNR will exceed Z). 
       FIG. 11  shows an exemplary method  1100  with two sub-methods, one method  1104  for acquiring position information during intrinsic activation of the heart and another method  1108  for acquiring position information during paced activation of the heart. Further, as indicated in  FIG. 11 , information acquired from the method  1104  and the method  1108  may be relied up in a hybrid method  1106 . 
     The method  1104  commences in a configuration selection block  1110 , which is followed by an information acquisition block  1114 . After or during acquisition, an analysis block  1118  analyzes the position information and a conclusion block  1122  makes one or more conclusions based on the analysis. The method  1108  operates in a similar manner to the method  1104  but includes pacing. As shown in  FIG. 11 , the method  1108  commences in a configuration selection block  1130 , which is followed by an implementation block  1132  that implements pacing. An information acquisition block  1134  follows where, after or during acquisition, an analysis block  1138  analyzes the position information and a conclusion block  1142  makes one or more conclusions based on the analysis. 
     As described herein, the methods  1104  and  1108  may be performed successively or alternately (e.g., perform method  1104  for three minutes, perform method  1108  for two minutes, etc.). As mentioned, the hybrid method  1106  may include acquiring information from the acquisition blocks  1114  and  1134  and analyzing such acquired information in an analysis block  1150  where the analyzed information can be relied on to make one or more conclusions per a conclusions block  1154 . 
     According to the hybrid method  1106 , with respect to the analysis block  1150 , a linear dislodgement intrinsic/paced index may be calculated and with respect to the conclusions block  1154 , conclusions may be instability for a configuration with intrinsic activation and increased stability for the configuration with paced activation. In another instance, an area dislodgement intrinsic/paced index may be calculated and conclusions made that a small trajectory exists for a configuration with intrinsic activation and a larger trajectory exists for the configuration with paced activation. Such conclusions may indicate that pacing can alter the stability of the configuration, for example, possibly creating an environment that is likely to decrease stability of the configuration. 
       FIG. 12  shows an exemplary method  1200  that can determine whether an electrode sensing configuration is suitable for gating acquisition for position information of one or more other electrodes. The method  1200  commences in a selection block  1210  that selects an electrode sensing configuration (e.g., for IEGM acquisition). In an acquisition block  1220 , position information is acquired for the selected electrode sensing configuration, for example, using a localization system such as the ENSITE® NAVX® system. The selected electrode sensing configuration may correspond to a unipolar arrangement where one electrode is positioned in the heart and another electrode positioned in or on the body but not in the heart (e.g., an extracardiac electrode). In an alternative scenario, the selected electrode sensing configuration may rely on bipolar or other multipolar sensing. 
     After the acquisition block  1220 , the method  1200  enters a decision block  1230  that decides whether the selected configuration is stable. If the decision block  1230  decides that the selected configuration is not stable, the method  1200  enters a selection block  1235  that selects a different configuration. However, if the decision block  1230  decides that the selected configuration is stable, the method  1200  continues to a selection block  1240  for selection of a test electrode configuration, which may include one or more electrodes that are not part of the selected sensing electrode configuration. 
     After selection of a test electrode configuration, the method  1200  enters a gated acquisition block  1250  that relies on sensed electrical activity of the heart to gate acquisition of position information for the test electrode configuration (see, e.g., the IEGM with dashed lines indicating a gate). As shown in  FIG. 12 , a decision block  1260  follows the gated acquisition block  1250  to decide if the selected test electrode configuration is stable. If the decision block  1260  decides that the test electrode configuration is not stable, the method  1200  continues at a selection block  1265  to select another test configuration. Such a selection may or may not require repositioning of a lead when the method  1200  is performed in an intraoperative setting (e.g., acute state). For example, where a lead includes multiple electrodes, the selection block  1265  may select an electrode configuration that includes an electrode that was not part of the unstable test configuration. If repositioning of a lead is required and such repositioning effects the gating (e.g., the previously determined stable sensing electrode configuration), the method  1200  may require a return to the selection block  1210 . 
     In the instance the decision block  1260  decides that the selected test configuration is stable (e.g., according to one or more criteria), the method  1200  continues at a selection block  1270  that may select the stable test electrode configuration, for example, for chronic or other use (e.g., further testing, etc.). 
       FIG. 13  shows an exemplary method  1300  for addressing dislodgment of an electrode or lead. Specifically, the method  1300  addresses situations where dislodgment may cause an electrode or lead to move to a more stable location. The method  1300  commences in a selection block  1310  where an electrode or lead configuration is selected. An acquisition block  1320  follows that acquires position information for the electrode or one or more electrodes associated with the lead. A decision block  1330  decides, based at least in part on the acquired information, whether the selected configuration is stable (e.g., optionally using one or more stability criteria). If the decision block  1330  decides that the selected configuration is stable, the method  1300  enters a conclusion block  1340  that concludes the selected configuration is stable. During implant of a pacing device (e.g., the device  100  of  FIGS. 1 and 2 ), such a conclusion may be required prior to use of the selected configuration for chronic sensing, pacing, shocking, etc. 
     In the instance the decision block  1330  decides that the selected configuration is not stable, the method  1300  proceeds to another decision block  1350 . The decision block  1350  decides whether dislodgment occurred. For example, a modal analysis of position information may reveal a bi-modal distribution as exhibited in the plot  600  of  FIG. 6 . A bi-modal distribution may include two position averages (e.g., a first distinct position average for a first set of cardiac cycles and a second distinct position average for a second set of cardiac cycles). Evidence of a bi-modal or other multimodal distribution may indicate dislodgement, especially where data sets or metrics show a correspondence to distinct time frames (e.g., sets of cardiac cycles). 
     Referring again to the decision block  1350  of  FIG. 13 , if a decision is made that dislodgment did not occur, the method  1300  returns to the selection block  1310 , which may act to select another configuration. However, if the decision block  1350  decides that dislodgement occurred, the method  1300  proceeds to an acquisition block  1360  that acquires position information for the configuration in its current condition, optionally while applying a load. As mentioned, stability may be assessed while applying a load to a lead (e.g., tension or compression at a proximal end, away from the heart). A dislodgement stability index may be calculated, for example, based on the equation: (SI no load −SI loaded )/SI no load . 
     As described herein, an exemplary method may include applying techniques to assess or improve accuracy of a metric such as a stability index. For example, if a pacing algorithm changes pacing rate during acquisition of position information for an electrode, the change can be expected to alter the electrode&#39;s trajectory. Further, a change in pacing rate is likely to alter time fiducials in instances where they are used to trigger acquisition of position data. In instances where one or more events (e.g., as noted in an IEGM) are used to gate acquisition of position information, a change in pacing rate may affect relative timing of the events. To increase accuracy, an exemplary method can apply a constant pacing rate that exceeds the intrinsic rate of the heart (e.g., overdrive pacing). Such a technique helps ensure a reproducible position of an electrode at like time points across cardiac cycles. 
     As described herein, an exemplary method implements overdrive pacing by pacing the heart using a single ventricle or biventricular electrode configuration, noting that a biventricular electrode configuration may inherently provide a more regular pattern of contraction. The selected electrode configuration may correspond to a configuration intended to be used chronically. For example, if biventricular pacing is indicated for a patient, a biventricular electrode configuration can be selected for patient to more closely mimic the chronic state. 
       FIG. 14  shows an exemplary method  1400  for assessing chronic stability along with a computing device  1430  and one or more databases  1450  and  1460 . The method  1400  commences in a selection block  1410  that selects a chronic configuration, which may be an electrode configuration implemented in conjunction with an implanted device to sense, pace or shock the heart. In an alternative example, the electrode configuration may be implemented in conjunction with an implanted device to sense, pace or shock a nerve or other tissue (e.g., vagal nerve, phrenic nerve, diaphragm, etc.). In an acquisition block  1414 , position information is acquired. For example, patches may be placed on a patient&#39;s body to deliver current where the implanted device senses potentials related to the current. In turn, the sensed potentials may be communicated from the implanted device to an external device such as an implantable device programmer (see, e.g., the telemetry circuit of the device  100  of  FIG. 2 ). 
     According to the method  1400 , a comparison block  1418  compares the acquired chronic state information to information associated with the same configuration in an acute state (e.g., as acquired during an intraoperative procedure) or to information associated with the same configuration in a historic chronic state (e.g., a week earlier, a month earlier, during a post-operative period, etc.). In a conclusions block  1422 , the method  1400  may make one or more conclusions based on the comparison of block  1418 . 
     As mentioned, the example of  FIG. 14  also shows the computing device  1430  and the databases for acute data  1450  and chronic data  1460 . The acute database  1450  may store stability index or other stability metric data for various configurations examined during an acute procedure. For example, for each configuration, the acute database  1450  may store metrics in a relational format along with a stability tolerance (ST). The stability tolerance indicates a tolerable percent deviation for one or more of the metrics as determined in a chronic state. For example, for configuration C 1 , the stability index sum is 2.4 and the ST is 4%; thus, a chronic state stability index sum of 2.3 or less will exceed the stability tolerance and optionally give rise to an alert. An example of out-of-tolerance stability metrics is shown for C 2  in the chronic state data  1460  where SI sum , SI mean  decreased and SI stddev  increased. The method  1400  may be implemented in the form of computer-executable instructions stored in memory, for example, of the computing device  1430 , which may be a device programmer configured to store or otherwise access the data of the acute database  1450  or the data of the chronic database  1460 . 
     While the data is shown for individual configurations in the example of  FIG. 14 , data may be stored additionally or alternatively for leads. For example, stability metrics may be determined and stored for a lead based on position information acquired for one or more individual electrodes of the lead. Further, lead metrics may account for length, electrode spacing, material properties, etc., of a lead. For example, position information or metric(s) for an unanchored tip electrode of a left ventricular lead may be allowed greater tolerance or weighted less than an intermediate electrode of the lead. 
     According to the method  1400 , lead stability can be determined, for example, during an in-clinic follow-up visit. Such a method may rely on telemetric or RF communication between a localization system (e.g., the ENSITE® NAVX® system) and information sensed using electrodes on an implanted lead connected to an implanted device. 
     An exemplary method includes, at a post-implant follow-up visit, a clinician placing various patches on a patient where the patches carry energy sufficient to generate a localization field within the patient&#39;s body. Upon delivery of energy, an implanted device senses signals associated with the delivered energy using one or more electrodes, converts the signals to digital data and then wirelessly communicates the data to an external computing device. The communicated data may be analyzed or stored and analyzed at a later time. 
     In various exemplary methods, at implant and at subsequent follow-ups visits, relative positions of an electrode associated with a known stable lead (e.g., an RA lead) and an electrode associated with a lead susceptible to instability (e.g., a CS lead) can be noted, for example as the distance between the two electrodes at a fiducial time point. Where more than two electrodes are compared, the angle made between electrodes at a fiducial time point can be noted (e.g., an angle formed between three electrodes). Given such information, one or more exemplary stability indexes can be computed, for example, as a difference in a distance or an angle at one fiducial time point or as a sum or an average of differences at multiple time points. In this exemplary approach, even if localization system patches are not placed in identical location on the body of a patient (e.g., which would cause a shift in absolute positional coordinate values), a chronic stability trend may still be determined, for example, by using a stable reference point within the heart. 
     As described herein, data acquired for a stable heart rhythm with a somewhat varying rate (e.g., within specified normal limits of deviation) may be corrected by normalizing common time points to duration of each cardiac cycle. For example, an acquisition system may sample an electrode position in tenths or other fractions of a cardiac cycle rather than according to a set interval (e.g., every 75 ms). In a more complex manner, sampling may space points according to slope or other features, for example, to more accurately sample a QRS complex. An exemplary technique may optionally, for intrinsic or paced cycles, rely on ECG or IEGM morphology as a prerequisite for inclusion of data from a beat (e.g., cardiac cycle) in a stability index calculation. Such an approach can act to filter out or exclude data from beats having certain types of morphology such as PVC morphology. 
     In various instances, depending on placement of electrodes that generate a localization field, respiration may affect accuracy of position data. For example, referring to  FIG. 5 , as a patient breathes, the torso changes shape, which can alter the alignment of the electrodes  522 ,  522 ′,  524 ,  524 ′,  526 ,  526 ′ and  528 . Further, as respiration introduces air into the body, dielectric properties of media between electrodes of a directional pair may change. To account for the affects of respiration, an exemplary data acquisition technique may include an algorithm that compensates for respiratory motion. Alternatively, compensation of filtering may be performed after data acquisition, for example, using one or more algorithms that identify frequencies in data that are likely related to respiration and adjust the data (e.g., filter or normalize) to compensate for respiration. In other instances, respiration gating may be used during data acquisition, for example, akin to techniques used during acquisition of nuclear magnetic resonance data (e.g., NMR or MRI data). For example, beats to be included in a stability index metric may be gated to a particular portion of the respiratory cycle. 
     The ENSITE® NAVX® system includes a so-called “RespComp” algorithm that uses a combination of impedance between various pairs of patches, which create the localization field, as a measure of respiratory motion. In yet another alternative, motion of electrodes that are known to be stable can be used to ascertain respiratory motion. For example, position data with respect to time may have low frequency content (approximately 0.1 Hz to approximately 0.5 Hz) that can be due to respiration, which can be subtracted from the motion of the electrode of which stability is of interest. 
     Instantaneous fluid status, among other variables, can cause some drift in position as measured by a localization system such as the ENSITE® NAVX® system. An exemplary method can include a correction factor that accounts for fluid status drift, which may be found by comparing position of a stable electrode from one cycle to the next and applying any measured offset to an electrode of interest. 
     As described herein, an exemplary method includes calculating one or more stability metrics for an electrode. For example, an exemplary method includes selecting an electrode located in a patient; acquiring position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculating a stability metric for the electrode based on the acquired position information with respect to time; mapping the stability metric to a map that includes one or more anatomical features; and, based in part on the mapping, deciding if the selected electrode is in a stable location for sensing biological electrical activity, for delivering electrical energy or for sensing biological electrical activity and delivering electrical energy (e.g., as associated with a cardiac therapy, nerve therapy or other therapy). 
     In various exemplary methods, acquiring position information with respect to time may include repeatedly measuring electrical potentials over multiple cycles (e.g., cardiac cycles, respiratory cycles, cycles defined by delivering electrical energy to the patient, cycles defined by sensing biological electrical activity, etc.). 
     As described herein, a stability metric can be a path length metric associated with a cycle, for example, where variation in the path length metric over multiple cycles provides an indication of stability of an electrode as located in the patient. As described herein, a stability metric can be an area metric associated with a cycle, for example, where variation in the area metric over multiple cycles provides an indication of stability of an electrode as located in the patient. As described herein, a stability metric can be a standard deviation metric for multiple cycles that provides an indication of stability of an electrode as located in the patient. 
     In various examples, fiducials may be used during acquisition of information, for position determinations, or stability metric calculations. For example, a fiducial may be one or more discrete times or time intervals, based on percentages or fractions of a cycle (e.g., a cardiac, respiratory or other cycle), based on one or more events in an electrogram (e.g., an “event fiducial” based on a muscle activity electrogram or a neuroelectrogram). 
     An exemplary stability metric optionally relies on cycle-to-cycle fiducial-associated position differentials for positions of the electrode over multiple cycles. For example, a stability metric may be a stability index sum that divides a sum of the position differentials by number of cycles. In another example, a stability metric may be a stability index mean that divides a sum of the position differentials by number of cycles and by number of fiducials per cycle. 
     As described herein, an exemplary method can include, during some or all cycles, delivering energy to a patient via a lead or a catheter positioned in the patient. Such a method may include calculating a stability metric for cycles associated with delivery of energy and calculating a stability metric for the cycles not associated with delivery of energy. For example, a method can include intrinsic cardiac cycles and paced cardiac cycles and associated intrinsic and paced stability metrics. With respect to pacing, a method may include acquiring position information with respect to time during paced activation of the heart at an overdrive pacing rate. 
     As described herein, various techniques can be used to improve accuracy of a stability metric. For example, a method may include sensing biological electrical activity and, prior to calculating a stability metric, excluding at least some acquired position information for a selected electrode based on the sensed biological electrical activity. In another example, a method may include filtering position information to remove respiratory motion, filtering position information to remove drift artifact or the like. 
     As described herein, one or more exemplary computer-readable storage media can include processor-executable instructions to configure a computing device to: select an electrode located in a patient based upon user input; acquire position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculate a stability metric for the electrode based on the acquired position information with respect to time; map the stability metric to a map that includes one or more anatomical features; and, based in part on the map, decide if the selected electrode is in a stable location for sensing biological electrical activity, for delivering electrical energy or for sensing biological electrical activity and delivering electrical energy. 
     As described herein, an exemplary system can include one or more processors; memory; and control logic configured to: select an electrode located in a patient; acquire position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculate a stability metric for the electrode based on the acquired position information with respect to time; map the stability metric to a map that includes one or more anatomical features; and, based in part on the map, decide if the selected electrode is in a stable location for sensing biological electrical activity, for delivering electrical energy or for sensing biological electrical activity and delivering electrical energy. Such control logic may be stored as instructions on one or more computer-readable media (e.g., memory) and/or be implemented by one or more devices (e.g., an implanted device and an external device). 
     Where an exemplary method includes intrinsic and paced activation of the heart (see, e.g.,  FIG. 11 ), such a method may include selecting an electrode located in a patient; during intrinsic activation of the heart, acquiring position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; during paced activation of the heart, acquiring position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculating an intrinsic activation stability metric for the electrode based on the acquired position information with respect to time during the intrinsic activation of the heart; calculating a paced activation stability metric for the electrode based on the acquired position information with respect to time during the paced activation of the heart; and comparing the intrinsic activation stability metric to the paced activation stability metric to decide whether the electrode, as located in the patient, is in a stable location for delivery of a therapy that includes paced activation of the heart. Such a method can further include mapping the intrinsic activation stability metric and the paced activation stability metric to a map (e.g., a map that includes one or more anatomical features). 
     As described herein, a method may include calculating an intrinsic-paced stability differential based on an intrinsic activation stability metric and a paced activation stability metric. For example, where the stability metric is a path length metric, a differential may be a distance, where the stability metric is an area metric, a differential may be an area and where a stability metric is a standard deviation or other statistical parameter, a differential may be a difference between two such parameters. Further, a differential may be mapped to a map (e.g., a map that includes one or more anatomical features). 
     As described herein, an exemplary system can include one or more processors; memory; and control logic configured to: select an electrode located in a patient; during intrinsic activation of the heart, acquire position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; during paced activation of the heart, acquire position information with respect to time by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculate an intrinsic activation stability metric for the electrode based on the acquired position information with respect to time during the intrinsic activation of the heart; calculate a paced activation stability metric for the electrode based on the acquired position information with respect to time during the paced activation of the heart; and compare the intrinsic activation stability metric to the paced activation stability metric to decide whether the electrode, as located in the patient, is in a stable location for delivery of a therapy that includes paced activation of the heart. Such control logic may be stored as instructions on one or more computer-readable media (e.g., memory) and/or be implemented by one or more devices (e.g., an implanted device and an external device). 
     As described herein, an exemplary method may include loading of a lead or catheter (see, e.g.,  FIG. 13 ). Such an exemplary method can include selecting an electrode located in a patient where the electrode is a lead-based electrode; acquiring position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; during application of force to the lead, acquiring position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculating an unloaded stability metric for the electrode based on the acquired position information with respect to time; calculating a loaded stability metric for the electrode based on the acquired position information with respect to time during the application of force to the lead; and comparing the unloaded stability metric to the loaded stability metric to decide whether the electrode, as located in the patient, is in a stable location for delivery of a therapy. Such a method may also include mapping the unloaded stability metric and the loaded stability metric to a map (e.g., a map that includes one or more anatomical features). Such a method may include sensing biological electrical activity, paced activation of the heart, nerve stimulation, muscle stimulation, etc. 
     A method that includes loading a lead or a catheter may include calculating an unloaded-loaded stability differential based on an unloaded stability metric and a loaded activation stability metric. For example, where the stability metric is a path length metric, a differential may be a distance, where the stability metric is an area metric, a differential may be an area and where a stability metric is a standard deviation or other statistical parameter, a differential may be a difference between two such parameters. Further, a differential may be mapped to a map (e.g., a map that includes one or more anatomical features). 
     As described herein, an exemplary system can include one or more processors; memory; and control logic configured to: select an electrode located in a patient where the electrode is a lead-based electrode; acquire position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; during application of force to the lead, acquire position information with respect to time for the electrode by using the electrode for repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculate an unloaded stability metric for the electrode based on the acquired position information with respect to time; calculate a loaded stability metric for the electrode based on the acquired position information with respect to time during the application of force to the lead; and compare the unloaded stability metric to the loaded stability metric to decide whether the electrode, as located in the patient, is in a stable location for delivery of a therapy. Such control logic may be stored as instructions on one or more computer-readable media (e.g., memory) and/or be implemented by one or more devices (e.g., an implanted device and an external device). 
     As described herein, an exemplary method may perform stability determinations in association with gated acquisition of information (see, e.g.,  FIG. 12 ). For example, an exemplary method can include selecting an electrode located in a patient; acquiring position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculating a stability metric for the electrode based on the acquired position information with respect to time; deciding if the selected electrode, as located in the patient, is in a stable location for sensing cardiac electrical activity; and, if the deciding decides that the selected electrode is in a stable location for sensing cardiac electrical activity, selecting a different electrode located in the patient, sensing cardiac electrical activity using the electrode at the stable location, gating acquisition of position information for the different electrode based on the sensed cardiac electrical activity, calculating a stability metric for the different electrode, and deciding if the different electrode, as located in the patient, is in a stable location for use in a cardiac therapy. Such a method may include delivering energy to the heart using either or both of the electrodes. In a particular example, a cardiac therapy may include use of the electrode for sensing biological electrical activity and use of the different electrode for paced activation of the heart. Such a method may further include mapping the stability metrics to a map (e.g., a map that includes one or more anatomical features). 
     In the foregoing method, a stability metric for the electrode or the different electrode may be a path length metric associated with a cycle, for example, where variation in the path length metric over multiple cycles provides an indication of stability of an electrode as located in the patient. In another example, a stability metric for the electrode or the different electrode may be an area metric associated with a cycle, for example, where variation in the area metric over multiple cycles provides an indication of stability of an electrode as located in the patient. In yet another example, a stability metric for the electrode or the different electrode may be a standard deviation metric for multiple cycles, for example, that provides an indication of stability of an electrode as located in the patient. 
     As described herein, an exemplary system can include one or more processors; memory; and control logic configured to: select an electrode located in a patient; acquire position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculate a stability metric for the electrode based on the acquired position information with respect to time; decide if the selected electrode, as located in the patient, is in a stable location for sensing cardiac electrical activity; and, in response to a decision that the selected electrode is in a stable location for sensing cardiac electrical activity to select a different electrode located in the patient, sense cardiac electrical activity using the electrode at the stable location, gate acquisition of position information for the different electrode based on the sensed cardiac electrical activity, calculate a stability metric for the different electrode, and decide if the different electrode, as located in the patient, is in a stable location for use in a cardiac therapy. Such control logic may be stored as instructions on one or more computer-readable media (e.g., memory) and/or be implemented by one or more devices (e.g., an implanted device and an external device). 
     As described herein, an exemplary method can include calculation of stability metrics for acute and chronic scenarios (see, e.g.,  FIG. 14 ). For example, exemplary method can include selecting an electrode located in a patient; during an intraoperative, acute state, acquiring position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; during a post-operative, chronic state, acquiring position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculating an acute state stability metric for the electrode based on the acquired position information with respect to time during the acute state; calculating a chronic state stability metric for the electrode based on the acquired position information with respect to time during the chronic state; and comparing the acute state stability metric to the chronic state stability metric to decide whether the electrode, as located in the patient in the chronic state, is in a stable location for delivery of a therapy. Such a method may include mapping the acute state stability metric and the chronic state stability metric to a map (e.g., a map that includes one or more anatomical features). 
     A method that acquires acute and chronic state information may include calculating an acute state-chronic state stability differential based on an acute state stability metric and a chronic state stability metric. For example, where the stability metric is a path length metric, a differential may be a distance, where the stability metric is an area metric, a differential may be an area and where a stability metric is a standard deviation or other statistical parameter, a differential may be a difference between two such parameters. Further, a differential may be mapped to a map (e.g., a map that includes one or more anatomical features). 
     As described herein, an exemplary can include one or more processors; memory; and control logic configured to: select an electrode located in a patient; during an intraoperative, acute state, acquire position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; during a post-operative, chronic state, acquire position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculate an acute state stability metric for the electrode based on the acquired position information with respect to time during the acute state; calculate a chronic state stability metric for the electrode based on the acquired position information with respect to time during the chronic state; and compare the acute state stability metric to the chronic state stability metric to decide whether the electrode, as located in the patient in the chronic state, is in a stable location for delivery of a therapy. Such control logic may be stored as instructions on one or more computer-readable media (e.g., memory) and/or be implemented by one or more devices (e.g., an implanted device and an external device). 
     As described herein, an exemplary method may include comparing current chronic state information to historic chronic state information (see, e.g.,  FIG. 14 ). For example, an exemplary method can include selecting a chronically implanted electrode located in a patient; acquiring position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculating a stability metric for the electrode based on the acquired position information with respect to time; and comparing the stability metric to a previously calculated stability metric for the selected electrode to decide whether stability of the chronically implanted electrode, as located in the patient, has changed. Such a method may further include mapping the stability metric and the previously calculated stability metric to a map (e.g., a map that includes one or more anatomical features). 
     A method that acquires chronic state information over time may include calculating a chronic state-chronic state stability differential based on a current chronic state stability metric and a historic chronic state stability metric. For example, where the stability metric is a path length metric, a differential may be a distance, where the stability metric is an area metric, a differential may be an area and where a stability metric is a standard deviation or other statistical parameter, a differential may be a difference between two such parameters. Further, a differential may be mapped to a map (e.g., a map that includes one or more anatomical features). 
     As described herein, an exemplary system can include one or more processors; memory; and control logic configured to: select a chronically implanted electrode located in a patient; acquire position information with respect to time for the electrode by repeatedly measuring electrical potentials in an electrical localization field established in the patient; calculate a stability metric for the electrode based on the acquired position information with respect to time; and compare the stability metric to a previously calculated stability metric for the selected electrode to decide whether stability of the chronically implanted electrode, as located in the patient, has changed. Such control logic may be stored as instructions on one or more computer-readable media (e.g., memory) and/or be implemented by one or more devices (e.g., an implanted device and an external device). 
     Various exemplary techniques may include deriving a lead stability metric to more effectively place coronary sinus leads. As described herein, a stability metric may be a stability index computed as the distance between an electrode location at a fiducial time point for two different cardiac cycles, a stability index computed as the sum or the mean of distances between respective electrode locations at more than one fiducial or relative time point of different cardiac cycles. 
     As described herein, a stability metric may be computed as the standard deviation of path length or area enclosed by a swept electrode trajectory over the course of each of several cardiac cycles. A stability metric may be optionally measured in a point-by-point manner by moving a lead or catheter to various location, for example, where a value of the stability index is encoded along a color scale and displayed on a map at each respective anatomic location. 
     With respect to data analysis, ECG, IEGM or other biosignal morphology may be used to exclude information associated with inconsistent beats or other artifacts from a calculation of a stability metric. Various methods may optionally use filtering to remove artifacts such as respiratory motion or drift from a location signal prior to calculating a stability metric. 
     With respect to chronic electrode stability, an exemplary method may include tracking at finite intervals by noting relative positions (distance, angle) of two or more electrodes, for example, where at least one landmark or electrode is known or assumed to be stable. 
     Exemplary External Programmer 
       FIG. 15  illustrates pertinent components of an external programmer  1500  for use in programming an implantable medical device  100  (see, e.g.,  FIGS. 1 and 2 ). The external programmer  1500  optionally receives information from other diagnostic equipment  1650 , which may be a computing device capable of acquiring location information and other information. For example, the equipment  1650  may include a computing device to deliver current and to measure potentials using a variety of electrodes including at least one electrode positionable in the body (e.g., in a vessel, in a chamber of the heart, within the pericardium, etc.). Equipment may include a lead for chronic implantation or a catheter for temporary implantation in a patient&#39;s body. Equipment may allow for acquisition of respiratory motion and aid the programmer  1500  in distinguishing respiratory motion from cardiac. 
     Briefly, the programmer  1500  permits a clinician or other user to program the operation of the implanted device  100  and to retrieve and display information received from the implanted device  100  such as IEGM data and device diagnostic data. Where the device  100  includes a module such as the position detection module  239 , then the programmer  1500  may instruct the device  100  to measure potentials and to communicate measured potentials to the programmer via a communication link  1653 . The programmer  1500  may also instruct a device or diagnostic equipment to deliver current to generate one or more potential fields within a patient&#39;s body where the implantable device  100  may be capable of measuring potentials associated with the field(s). 
     The external programmer  1500  may be configured to receive and display ECG data from separate external ECG leads  1732  that may be attached to the patient. The programmer  1500  optionally receives ECG information from an ECG unit external to the programmer  1500 . As already mentioned, the programmer  1500  may use techniques to account for respiration. 
     Depending upon the specific programming, the external programmer  1500  may also be capable of processing and analyzing data received from the implanted device  100  and from ECG leads  1732  to, for example, render diagnosis as to medical conditions of the patient or to the operations of the implanted device  100 . As noted, the programmer  1500  is also configured to receive data representative of conduction time delays from the atria to the ventricles and to determine, therefrom, an optimal or preferred location for pacing. Further, the programmer  1500  may receive information such as ECG information, IEGM information, information from diagnostic equipment, etc., and determine one or more metric (e.g., consider the method  300 ). 
     Now, considering the components of programmer  1500 , operations of the programmer are controlled by a CPU  1702 , which may be a generally programmable microprocessor or microcontroller or may be a dedicated processing device such as an application specific integrated circuit (ASIC) or the like. Software instructions to be performed by the CPU are accessed via an internal bus  1704  from a read only memory (ROM)  1706  and random access memory  1730 . Additional software may be accessed from a hard drive  1708 , floppy drive  1710 , and CD ROM drive  1712 , or other suitable permanent or removable mass storage device. Depending upon the specific implementation, a basic input output system (BIOS) is retrieved from the ROM  1706  by CPU  1702  at power up. Based upon instructions provided in the BIOS, the CPU  1702  “boots up” the overall system in accordance with well-established computer processing techniques. 
     Once operating, the CPU  1702  displays a menu of programming options to the user via an LCD display  1614  or other suitable computer display device. To this end, the CPU  1702  may, for example, display a menu of specific programming parameters of the implanted device  100  to be programmed or may display a menu of types of diagnostic data to be retrieved and displayed. In response thereto, the clinician enters various commands via either a touch screen  1616  overlaid on the LCD display or through a standard keyboard  1618  supplemented by additional custom keys  1620 , such as an emergency VVI (EVVI) key. The EVVI key sets the implanted device to a safe VVI mode with high pacing outputs. This ensures life sustaining pacing operation in nearly all situations but by no means is it desirable to leave the implantable device in the EVVI mode at all times. 
     With regard to the determination of location stability (e.g., for pacing, sensing, etc.), CPU  1702  includes a metric analysis system  1741  and a 3-D mapping system  1747 . The systems  1741  and  1747  may receive information from the implantable device  100  and/or diagnostic equipment  1650 . The parameter analysis system  1741  optionally includes control logic to associate information and to make one or more conclusions based on a map of a metric or metrics (e.g., consider the block  330  of  FIG. 3 ). 
     Where information is received from the implanted device  100 , a telemetry wand  1728  may be used. Other forms of wireless communication exist as well as forms of communication where the body is used as a “wire” to communicate information from the implantable device  100  to the programmer  1500 . 
     If information is received directly from diagnostic equipment  1650 , any appropriate input may be used, such as parallel  10  circuit  1740  or serial  10  circuit  1742 . Motion information received via the device  100  or via other diagnostic equipment  1650  may be analyzed using the mapping system  1747 . In particular, the mapping system  1747  (e.g., control logic) may identify positions within the body of a patient and associate such positions with one or more electrodes where such electrodes may be capable of delivering stimulation energy to the heart. 
     A communication interface  1745  optionally allows for wired or wireless communication with diagnostic equipment  1650  or other equipment. The communication interface  1745  may be a network interface connected to a network (e.g., intranet, Internet, etc.). 
     A map or model of cardiac motion may be displayed using display  1614  based, in part, on 3-D heart information and optionally 3-D torso information that facilitates interpretation of motion information. Such 3-D information may be input via ports  1740 ,  1742 ,  1745  from, for example, a database, a 3-D imaging system, a 3-D location digitizing apparatus (e.g., stereotactic localization system with sensors and/or probes) capable of digitizing the 3-D location. According to such an example, a clinician can thereby view the stability of a location on a map of the heart to ensure that the location is acceptable before an electrode or electrodes are positioned and optionally fixed at that location. While 3-D information and localization are mentioned, information may be provided with fewer dimensions (e.g., 1-D or 2-D). For example, where motion in one dimension is insignificant to one or more other dimensions, then fewer dimensions may be used, which can simplify procedures and reduce computing requirements of a programmer, an implantable device, etc. The programmer  1500  optionally records procedures and allows for playback (e.g., for subsequent review). For example, a heart map and all of the electrical activation data, mechanical activation data, parameter data, etc., may be recorded for subsequent review, perhaps if an electrode needs to be repositioned or one or more other factors need to be changed (e.g., to achieve an optimal configuration). Electrodes may be lead based or non-lead based, for example, an implantable device may operate as an electrode and be self powered and controlled or be in a slave-master relationship with another implantable device (e.g., consider a satellite pacemaker, etc.). An implantable device may use one or more epicardial electrodes. 
     Once all pacing leads are mounted and all pacing devices are implanted (e.g., master pacemaker, satellite pacemaker, biventricular pacemaker), the various devices are optionally further programmed. 
     The telemetry subsystem  1722  may include its own separate CPU  1724  for coordinating the operations of the telemetry subsystem. In a dual CPU system, the main CPU  1702  of programmer communicates with telemetry subsystem CPU  1724  via internal bus  1704 . Telemetry subsystem additionally includes a telemetry circuit  1726  connected to telemetry wand  1728 , which, in turn, receives and transmits signals electromagnetically from a telemetry unit of the implanted device. The telemetry wand is placed over the chest of the patient near the implanted device  100  to permit reliable transmission of data between the telemetry wand and the implanted device. 
     Typically, at the beginning of the programming session, the external programming device  1500  controls the implanted device(s)  100  via appropriate signals generated by the telemetry wand to output all previously recorded patient and device diagnostic information. Patient diagnostic information may include, for example, motion information (e.g., cardiac, respiratory, etc.) recorded IEGM data and statistical patient data such as the percentage of paced versus sensed heartbeats. Device diagnostic data includes, for example, information representative of the operation of the implanted device such as lead impedances, battery voltages, battery recommended replacement time (RRT) information and the like. 
     Data retrieved from the implanted device(s)  100  can be stored by external programmer  1500  (e.g., within a random access memory (RAM)  1730 , hard drive  1708 , within a floppy diskette placed within floppy drive  1710 ). Additionally, or in the alternative, data may be permanently or semi-permanently stored within a compact disk (CD) or other digital media disk, if the overall system is configured with a drive for recording data onto digital media disks, such as a write once read many (WORM) drive. Where the programmer  1500  has a communication link to an external storage device or network storage device, then information may be stored in such a manner (e.g., on-site database, off-site database, etc.). The programmer  1500  optionally receives data from such storage devices. 
     A typical procedure may include transferring all patient and device diagnostic data stored in an implanted device  100  to the programmer  1500 . The implanted device(s)  100  may be further controlled to transmit additional data in real time as it is detected by the implanted device(s)  100 , such as additional motion information, IEGM data, lead impedance data, and the like. Additionally, or in the alternative, telemetry subsystem  1722  receives ECG signals from ECG leads  1732  via an ECG processing circuit  1734 . As with data retrieved from the implanted device  100 , signals received from the ECG leads are stored within one or more of the storage devices of the programmer  1500 . Typically, ECG leads output analog electrical signals representative of the ECG. Accordingly, ECG circuit  1734  includes analog to digital conversion circuitry for converting the signals to digital data appropriate for further processing within programmer  1500 . Depending upon the implementation, the ECG circuit  1743  may be configured to convert the analog signals into event record data for ease of processing along with the event record data retrieved from the implanted device. Typically, signals received from the ECG leads  1732  are received and processed in real time. 
     Thus, the programmer  1500  is configured to receive data from a variety of sources such as, but not limited to, the implanted device  100 , the diagnostic equipment  1650  and directly or indirectly via external ECG leads (e.g., subsystem  1722  or external ECG system). The diagnostic equipment  1650  includes wired  1654  and/or wireless capabilities  1652  which optionally operate via a network that includes the programmer  1500  and the diagnostic equipment  1650  or data storage associated with the diagnostic equipment  1650 . 
     Data retrieved from the implanted device(s)  100  typically includes parameters representative of the current programming state of the implanted devices. Under the control of the clinician, the external programmer displays the current programming parameters and permits the clinician to reprogram the parameters. To this end, the clinician enters appropriate commands via any of the aforementioned input devices and, under control of CPU  1702 , the programming commands are converted to specific programming parameters for transmission to the implanted device  100  via telemetry wand  1728  to thereby reprogram the implanted device  100  or other devices, as appropriate. 
     Prior to reprogramming specific parameters, the clinician may control the external programmer  1500  to display any or all of the data retrieved from the implanted device  100 , from the ECG leads  1732 , including displays of ECGs, IEGMs, statistical patient information (e.g., via a database or other source), diagnostic equipment  1650 , etc. Any or all of the information displayed by programmer may also be printed using a printer  1736 . 
     A wide variety of parameters may be programmed by a clinician. In particular, for CRT, the AV delay and the W delay of the implanted device(s)  100  are set to optimize cardiac function. In one example, the VV delay is first set to zero while the AV delay is adjusted to achieve the best possible cardiac function, optionally based on motion information. Then, W delay may be adjusted to achieve still further enhancements in cardiac function. 
     Programmer  1500  optionally includes a modem to permit direct transmission of data to other programmers via the public switched telephone network (PSTN) or other interconnection line, such as a T1 line or fiber optic cable. Depending upon the implementation, the modem may be connected directly to internal bus  1704  may be connected to the internal bus via either a parallel port  1740  or a serial port  1742 . 
     Other peripheral devices may be connected to the external programmer via the parallel port  1740 , the serial port  1742 , the communication interface  1745 , etc. Although one of each is shown, a plurality of input output (IO) ports might be provided. A speaker  1744  is included for providing audible tones to the user, such as a warning beep in the event improper input is provided by the clinician. Telemetry subsystem  1722  additionally includes an analog output circuit  1746  for controlling the transmission of analog output signals, such as IEGM signals output to an ECG machine or chart recorder. 
     With the programmer  1500  configured as shown, a clinician or other user operating the external programmer is capable of retrieving, processing and displaying a wide range of information received from the ECG leads  1732 , from the implanted device  100 , the diagnostic equipment  1650 , etc., and to reprogram the implanted device  100  or other implanted devices if needed. The descriptions provided herein with respect to  FIG. 15  are intended merely to provide an overview of the operation of programmer and are not intended to describe in detail every feature of the hardware and software of the device and is not intended to provide an exhaustive list of the functions performed by the device. 
     CONCLUSION 
     Although exemplary methods, devices, systems, etc., have been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described. Rather, the specific features and acts are disclosed as exemplary forms of implementing the claimed methods, devices, systems, etc.