the following detailed description includes references to the accompanying drawings , which form a part of the detailed description . the drawings show , by way of illustration , specific embodiments in which the invention may be practiced . these embodiments , which are also referred to herein as “ examples ,” are described in enough detail to enable those skilled in the art to practice the invention . the embodiments may be combined , other embodiments may be utilized , or structural , logical and electrical changes may be made without departing from the scope of the present invention . the following detailed description is , therefore , not to be taken in a limiting sense , and the scope of the present invention is defined by the appended claims and their equivalents . in this document , the terms “ a ” or “ an ” are used , as is common in patent documents , to include one or more than one . in this document , the term “ or ” is used to refer to a nonexclusive or , unless otherwise indicated . furthermore , all publications , patents , and patent documents referred to in this document are incorporated by reference herein in their entirety , as though individually incorporated by reference . in the event of inconsistent usages between this document and those documents so incorporated by reference , the usage in the incorporated reference ( s ) should be considered supplementary to that of this document ; for irreconcilable inconsistencies , the usage in this document controls . fig1 is a schematic drawing illustrating generally one example of an implantable cardiac function management device 100 that is coupled to a heart 102 using one or more intravascular leads 104 . in this illustrative example , a lead 104 a has its proximal end connected to a header 106 portion of the device 100 , with the header 106 , in turn , connected to a hermetically sealed electronics unit 108 . in this illustrative example , the distal portion of multi - conductor lead 104 a extends into a right ventricle of the heart 102 , and includes a tip electrode 110 , a ring electrode 112 , a distal shock electrode 114 and a proximal shock electrode 116 . this example also shows a lead 104 b that has its proximal end connected to the header 106 . the distal portion of the lead 104 b extends into a coronary sinus or great cardiac vein , and provides four electrodes 118 a - d located near the left ventricle of the heart 102 . other leads may extend elsewhere , such as lead 104 c extending into the right atrium , for example , to provide a distal tip electrode 124 and a slightly more proximal ring electrode 126 . the electronics unit 108 of the device 100 may also include electrodes , such as a can electrode 120 or a header electrode 122 , or one or more other electrodes located at the device 100 or nearby , or one or more epicardial electrodes , or any other suitable configuration of electrodes . such electrodes may be individually connected back to the device 100 or , in certain circumstances , may share one or more common conductors back to the device 100 . fig2 is a schematic drawing illustrating generally an example of a distributed patient management system 200 for managing multiple implantable devices 100 a - n , which are generally , but not necessarily , located in different patients 202 a - n . each implantable device 100 communicates with a server 204 , which can be remote from one or all of the patients 202 . the example of fig2 shows intermediary transceivers 206 a - n for each of the implantable devices 202 a - n , however , this is not necessary . for example , the transceiver 206 a communicates wirelessly with the implanted device 100 a , such as by a radio frequency ( rf ) link , an inductive link , or otherwise . the transceiver 206 a also provides wired or rf or other wireless communication with the server 204 , such as through a telecommunications or computer network 208 . in this example , the patient management system 200 includes one or more computer or other user interfaces 210 a - n , which communicate with the server 204 over the network 208 , such as via a wired or wireless link . such a user interface 210 permits a physician or other user to connect to the server 204 , such as for interacting with one or more of the implantable cardiac function management devices 100 a - n . this may include reviewing or using physiological data or device settings communicated from an implantable cardiac function management device 100 to the server 204 , or even for remotely programming an implantable cardiac rhythm management device 100 . the server 204 generally includes a processor 212 and data storage 214 to help the user analyze cardiac function management device status , settings , and physiological data . fig3 is a flow chart illustrating generally an example of using the server 204 for managing the electrode configuration of various implantable cardiac function management devices 100 a - n , such as for ensuring the integrity and proper functioning of such electrodes by monitoring electrode impedance . although fig3 focuses on the interaction between the server 204 and a particular cardiac function management device 100 a , the server 204 will generally interact with multiple such cardiac function management devices 100 a - n , which are generally respectively implanted in different patients , although a single patient could have multiple devices 100 . in the example of fig3 , at 300 , an implantable cardiac function management device 100 a tests interelectrode impedance for various specified combinations of two or more electrodes . an exemplary illustrative list specifying combinations of electrodes for which impedance is to be tested is given in table 1 , which is provided by way of example only , and not by way of limitation . in certain examples , the impedance will be tested between combinations of multiple electrodes , such as between ( 1 ) electrodes 118 a and 118 b ( in common with each other ) and ( 2 ) electrodes 118 c and 118 d ( in combination with each other ). moreover , certain electrodes may appear in more than one combination . for example , an electrode that appears in a failed or failing electrode combination may nonetheless also appear in one or more of the backup electrode combinations being tested , and may appear either alone , or in combination with one or more other electrodes . in certain examples , an indication of interelectrode impedance is measured by delivering a specified fixed amplitude ( e . g ., typically biphasic ) test current pulse between one or more commonly connected first electrodes and one or more commonly connected second electrodes , and measuring the resulting voltage between the first and second electrode ( s ). the impedance is given by the measured voltage divided by the specified current , and the actual impedance need not be calculated since the resulting voltage gives a signal that is proportional to , and therefore indicative of , the interelectrode impedance . the delivered test current is optionally subthreshold in amplitude and frequency ( e . g ., 80 microamperes , 78 microsecond per phase of a four - phase biphasic pulse train ), such that it does not evoke a resulting heart contraction . the test current can be generated , in certain examples , using a circuit that is also used for performing thoracic impedance measurements , such as for performing minute ventilation ( mv ) regulation of pacing rate . in other examples , the impedance measurement is made using , as a test energy or excitation energy , the energy delivered during a pacing pulse . in certain examples , the test current can be delivered at a single electrode , and received by multiple electrodes . in certain other examples , the test current can be delivered at multiple electrodes and received by multiple other electrodes . in certain further examples , the test current can be delivered at multiple electrodes and received by a single electrode . a list of candidate electrode combinations to be tested is typically used to operate a multiplexer in the electronics unit 108 to connect to the desired electrodes for performing the desired impedance measurements . the interelectrode impedance testing at 300 is typically performed recurrently , such as periodically with a specified frequency . at 302 , after the interelectrode impedance data has been collected for all the electrode combinations specified on a list , such as the list shown in table 1 , or a pre - specified subset thereof , then the resulting impedance data is uploaded to the server 204 and stored in the data storage 214 , such as in a record associated with the particular implantable cardiac function management device 100 a from which it was obtained . the uploading at 302 is typically performed recurrently , such as periodically with a specified frequency , which may be different from the frequency of testing interelectrode impedance at 300 . thus , at 302 , the data uploaded may include interelectrode impedance test data acquired over a period of time between uploading events . in certain examples , the uploading at 302 is initiated by the server 204 , which “ polls ” the implantable cardiac function management devices 100 . in other examples , the uploading at 302 is initiated by the particular implantable cardiac function management device 100 , which “ pushes ” data out to the server 204 . at 304 , the interelectrode impedance data is compared to a history of such data previously obtained from the same implantable cardiac function management device 100 . this generally involves comparing data from each tested electrode configuration to previously obtained data for the same electrode configuration , such as to determine whether there has been a statistically significant change . this may involve comparing the most recent data ( or a short term average or the like ) to earlier or longer term data ( such as an initial measurement , a long term average , or the like ). at 306 , if such a change in interelectrode impedance has been detected , then at 308 the changed interelectrode impedance data is optionally compared to patient or population data . patient data includes other data previously obtained from the same patient . such a comparison helps determine whether the observed change in interelectrode impedance in a particular patient is significant with respect to previously observed measurement or trend data such that it represents an actual or impending failure . if no patient data is yet available ( e . g ., for a newly implanted lead ), then predictive laboratory or simulation modeled data or other data can be used for performing this comparison . population data generally includes interelectrode impedance data from a like electrode configuration used by other implantable cardiac function management devices , e . g ., 100 b - n , that use the same type ( e . g ., model ) of lead . such a comparison helps determine whether the observed not - insignificant change in interelectrode impedance in a particular patient represents an actual or impending failure already being observed in other patients . if no population data is yet available ( e . g ., for a new lead model ), then predictive laboratory or simulation modeled data or other data can be used for performing this comparison . in making the comparison at 308 to population data , it may be desirable to normalize the interelectrode impedance data , such as to initial or earlier data obtained from the same patient , such that it is a change in interelectrode impedance for a particular patient that is being compared to corresponding changes in interelectrode impedance for the same electrode configuration as observed in other patients in the population . in certain examples , it is a trend over time of such normalized values from a particular patient that is compared to one or more trends over time of such normalized values from other patients in the population . since various patients in the population may have experienced different lead failure modes , in certain examples , the population data is analyzed such that data from patients deemed to exhibit the same failure mode are used together , such as in a composite trend over time for that particular failure mode . data from a particular patient can be compared to multiple such composite trends to determine whether the patient is exhibiting the signs of a particular failure mode . the ability to separately represent and test for different failure modes separately may increase the predictive capability of the present techniques . since interelectrode impedance data is generally obtained and uploaded for all possible electrode configurations , a failed or failing electrode can be positively identified by comparing interelectrode impedance data for the various electrode combinations , and may not even require testing all such electrode configurations in order to make such a positive identification . at 310 , if the comparison at 308 indicates an abnormal interelectrode impedance for a particular electrode configuration , and that particular electrode configuration is being used by the implantable cardiac function management device 100 a for sensing or delivering electrical energy , then at 312 an alternative electrode configuration can be selected . in certain examples , the particular electrode configuration having an abnormal impedance reading has a list of backup electrode configurations that can be substituted for sensing or delivering electrical energy . in certain examples , a particular backup electrode configuration is selected by comparing interelectrode impedance data for such alternative backup electrode configurations , and selecting a particular backup electrode configuration using the comparison . in other examples , the list of backup electrode configurations is ordered , for example , by similarity of locations of the electrodes in the backup electrode configuration to the locations of the electrode configuration for which it is being substituted , and the impedance data is only used to choose between backup electrode configurations that are similarly located . at 314 , after a failed or failing electrode configuration has been identified at 310 , and the most suitable backup electrode configuration has been selected at 312 , then , at 314 , the particular implantable cardiac function management device 100 a is automatically reprogrammed to the selected backup electrode configuration , and an alert notifying of the same is automatically generated and communicated to one or more of the patient , the patient &# 39 ; s physician , the manufacturer of the cardiac function management device 100 a , or the manufacturer of the lead being used by the cardiac function management device 100 a . after 314 , a “ no change ” determination at 306 , or a “ not abnormal ” determination at 310 , process flow then returns to 300 , after an optional delay 316 . fig4 is a graph of impedance ( e . g ., axis 400 ) vs . time ( e . g ., axis 402 ) illustrating generally one conceptualization of how population ( or simulation or other predictive ) information can be used , such as at 308 in fig3 , or otherwise . in the example of fig4 , population - based impedance data for a particular electrode combination of a particular lead model is aggregated into population impedance data 404 . in this conceptualization , lead impedance is initially stable over time , then increases to a plateau , and then abruptly increases beyond a failure threshold 406 . in comparing an individual patient to the population data , an individual patient &# 39 ; s location on the population curve 404 can be located . if such location indicates impending failure , a corresponding alert can be issued to the patient , caregiver , manufacturer , regulatory agency , or another . if such location indicates that the patient is an “ outlier ” on the population curve 404 , a corresponding alert can be issued to the patient , caregiver , manufacturer , regulatory agency or another . moreover , as seen in the illustrative example of fig4 , a predicted time - to - failure , t 2 - t 1 , can be computed . such information can be provided , for example , to a physician to help the physician schedule an appointment to replace the lead before the predicted failure time , if desired . moreover , as additional data is acquired from various patients , the threshold 406 can be adjusted in response , either automatically , or upon intervention by a human failure analysis engineer . furthermore , a patient &# 39 ; s predicted future change in electrode impedance can be used to adjust one or more device parameters of the patient &# 39 ; s cardiac rhythm management device , either automatically , or using caregiver control . for example , pacing energy can be automatically increased , depolarization sensing sensitivity can be automatically increased . similarly , if caregiver control is to be used , a recommendation of device parameter setting changes can be automatically provided to the caregiver to alert and perform triage for the caregiver . fig5 is a flow chart illustrating examples of various responses to determining that a particular interelectrode impedance measurement is abnormal , such as by comparison to population data , previous patient data , or otherwise . in this example , at 500 , impedance is tested between specified electrodes . at 502 , such information is uploaded to the server 204 . at 504 , the information is compared to one or more criteria , such as to a simple impedance threshold value or band , or to population or predicted ( e . g ., computer - simulated ) impedance data , which may represent one or more failure modes . if , at 506 , the a particular interelectrode impedance is deemed abnormal , then at 508 , a responsive act is carried out , such as delivering an alert at 508 a , predicting and communicating a time - to - failure at 508 b , reprogramming or recommending a different electrode configuration at 508 c , reprogramming or recommending one or more other changed device parameters ( e . g ., increase pacing energy , increase depolarization detection gain , etc .) at 508 d , or triggering another device feature ( e . g ., trigger an automatic pacing threshold test to ensure proper pacing energy is being delivered ) at 508 e . process flow returns to 500 , after any desired delay 510 . fig6 is a flow chart illustrating an example that is similar to fig3 and 5 , but in which certain functions are performed within the implantable device 100 , rather than in the remote server 204 . in this example , at 600 , the implantable device 100 tests impedance or other characteristics between specified combinations of electrodes , such as discussed above . at 602 , resulting information is optionally uploaded to the remote server 204 , such as for storing the device history , by itself , or as part of population data , or both . at 604 , the remote server 204 downloads impedance related information to the implantable device 100 . this may include , for example , criteria against which the measured impedance is to be compared to detect an actual or impending failure . it may include , for example , information by which to predict a time - to - failure . it may include , for example , information about which responsive action to take in the event of an actual or impending lead failure . the information may be based on population - derived data , the particular implantable device &# 39 ; s own historical data , simulated or predicted data , or the like . at 606 , the impedance or one or more other characteristics is compared to one or more criteria , such as to determine whether there is an actual or impending lead failure . if a particular electrode configuration fails such a test , then at 608 a failure response is initiated , such as issuing an alert , predicting a time to failure , reprogramming an electrode configuration , recommending or reprogramming one or more other device parameters ( e . g ., pacing energy ), triggering another device function ( e . g ., a pacing threshold test ), or the like . otherwise , after an optional delay at 610 , process flow returns to 600 . although fig6 illustrates a particular example of task division between the implantable device 100 and the remote server 204 , other allocations will also be suitable . in general , the remote server 204 advantageously permits population - based data to be used for a particular device , since the remote server 204 will typically communicate with and obtain information from multiple implantable devices 100 in various patients . it is to be understood that the above description is intended to be illustrative , and not restrictive . for example , the above - described embodiments ( and / or aspects thereof ) may be used in combination with each other . many other embodiments will be apparent to those of skill in the art upon reviewing the above description . the scope of the invention should , therefore , be determined with reference to the appended claims , along with the full scope of equivalents to which such claims are entitled . in the appended claims , the terms “ including ” and “ in which ” are used as the plain - english equivalents of the respective terms “ comprising ” and “ wherein .” also , in the following claims , the terms “ including ” and “ comprising ” are open - ended , that is , a system , device , article , or process that includes elements in addition to those listed after such a term in a claim are still deemed to fall within the scope of that claim . moreover , in the following claims , the terms “ first ,” “ second ,” and “ third ,” etc . are used merely as labels , and are not intended to impose numerical requirements on their objects . for example , reciting first , second , third , fourth , fifth , and sixth electrodes in a claim does not mean that there must be six electrodes . the abstract is provided to comply with 37 c . f . r . § 1 . 72 ( b ), which requires that it allow the reader to quickly ascertain the nature of the technical disclosure . it is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims . also , in the above detailed description , various features may be grouped together to streamline the disclosure . this should not be interpreted as intending that an unclaimed disclosed feature is essential to any claim . rather , inventive subject matter may lie in less than all features of a particular disclosed embodiment . thus , the following claims are hereby incorporated into the detailed description , with each claim standing on its own as a separate embodiment .
this document discusses , among other things , systems and methods for automatic electrode integrity management . interelectrode impedance is measured for various electrode combinations of an implantable cardiac function management device . the impedance data is processed , such as at an external remote server , to determine whether an electrode is failing or has failed , to select an alternate electrode configuration , to alert a physician or patient , to predict a time - to - failure such as by using population data , or to reprogram electrode configuration or other device parameters of the implantable cardiac function management device .