Abstract:
Individual implantable medical device (IMD) follow-up support unit supports follow-up session for IMD. IMD includes a data input for receiving IMD data which includes an IMD identification code identifying an individual IMD and IMD type, and IMD irregularity messages including data identifying type/date of irregularity, a database for storing IMD, a follow-up history dataset that includes date(s) of latest follow-up session. Includes a data processor that generates a list of irregularities taking place after previous follow-up session, calculate an individual IMD irregularity index for each type of irregularity based on IMD irregularity messages for an individual IMD via IMD identification code, calculate for type of irregularity an average irregularity index over the same irregularity over all IMD irregularity messages associated to the same type of IMD, compare calculated individual IMD irregularity index (IIII) with the calculated average irregularity index (ARI) and generate an indication if IIII significantly differs from the ARI.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention refers to an integrated bidirectional data communication and follow-up system for at least one implanted medical device (IMD). The invention relates in particular to follow up systems for an implantable cardiac pacemaker an implantable pulse generator (IPG) or an implantable cardioverter/defibrillator (ICD). 
         [0003]    2. Description of the Related Art 
         [0004]    Implantable heart stimulators can be used for treating a variety of heart disorders like bradycardia, tachycardia or fibrillation by way of electric stimulation pulses delivered to the heart tissue, the myocardium. Strong enough a stimulation pulse outside a heart chamber&#39;s refractory period leads excitation of the myocardium of that heart chamber, which in turn is followed by a contraction of the respective heart chamber. 
         [0005]    Depending on the disorder to be treated, such heart stimulator generates electrical stimulation pulses that are delivered to the heart tissue (myocardium) of a respective heart chamber according to an adequate timing regime. Delivery of stimulation pulses to the myocardium is usually achieved by means of an electrode lead that is electrically connected to a stimulation pulse generator inside a heart stimulator&#39;s housing and that carries a stimulation electrode in the region of its distal end. A stimulation pulse also is called a pace. Similarly, pacing a heart chamber means stimulating a heart chamber by delivery of a stimulation pulse. 
         [0006]    Parameters defining a therapy to be delivered by a heart stimulator need to be adapted to a patient&#39;s need. After adapting all parameters there may occur nevertheless irregularities such as unsuccessful attempts of treating a tachycardia by means of an antitachycardia therapy (antitachycardia pacing; ATP). This may necessitate reprogramming the antitachycardia therapy during a next follow up session. 
         [0007]    IMDs may feature a telemetry unit for wireless access to the implanted medical device. Usually IMDs such as pacemakers offer a plurality of operation modes and feature a number of adjustable parameters to best match the IMDs configuration to a patient&#39;s individual need. Further, state of the art pacemakers collect a number of operational and physiological data such as, inter alia, data representing an intracardiac electogram. Operational data collected and stored by the IMD include irregularity indicators indicating irregularities such as incidents of tachycardia etc. These indicators are at least temporarily stored in an IMDs memory. 
         [0008]    During follow-up sessions, a patient having an IMD meets a physician that checks the patient&#39;s health state and the state of the IMD. By means of a programmer or a similar device for wireless data communication with the IMD and an IMD&#39;s telemetry unit connected to the IMD&#39;s memory the physician is able to read out the IMD&#39;s memory and to reprogram the IMD if necessary. 
         [0009]    Irregularities felt by the patient are noted by the physician during follow-up and may entice the physician to adapt the operational parameters of the IMD. 
         [0010]    Between the follow-up sessions the IMD may wirelessly communicate data to an external device in the patient proximity. The external device can be linked to a remote service center for collection of data collected or generated by the IMD. 
         [0011]    Such a system is, for example, disclosed in United States Patent Application Publication Serial No. 2003/0028082. 
       SUMMARY OF THE INVENTION 
       [0012]    The inventors have noted a number of problems that render dealing with irregularities during follow-up sessions inefficient: 
         [0013]    During follow-up examination of patients with a cardiac implant (ICD, IPG) the examining physician has the problem to address all irregularities of the patient have which occurred after the previous follow-up examination. This is difficult because
       1. The physician conducting the follow-up is not always the same person thus doesn&#39;t always know the complete patient history.   2. The physician has possibly a lot of patients to examine per day. Time and schedule is tight.   3. There is not only a short list of possible irregularities (together with standard solutions) which can occur, so that the task to solve irregularities is not easy.   4. The information about irregularities of the patient has to be accessible at exactly that place where the patient is during follow-up examination and not where the clinic is located in which he received the implant.       
 
         [0018]    Possible solutions and their disadvantages are:
       1. The examining physician can ask the patient about symptoms he felt during the last months (after the previous follow-up).   Disadvantage: Symptoms do not necessarily stand for irregularities, symptoms can be forgotten. Furthermore, irregularities sometimes are not symptomatic.   2. The examining physician can consult a clinical information system in which all irregularities of patients are entered as soon as they become known to any the clinic.   Disadvantage: someone has to feed the clinical information system with irregularities. The patient must log all symptoms.   3. For each patient a paper file is kept which travels together with the patient as long as the patient has the implant.       
 
         [0024]    Disadvantage: The file might get lost. The patient might forget the file which will sooner or later render it incomplete (and thus useless). 
         [0025]    It is an object of the invention to provide an integrated bi-directional data communication and follow-up system for at least one implanted medical device (IMD) that facilitates a follow-up session conducted by a physician. 
         [0026]    According to the present invention the object of the invention is achieved by an IMD follow-up support unit for supporting a follow-up session for an individual implantable medical device (IMD). The IMD follow-up support unit comprises:
       a data input for receiving IMD data, said IMD data including an IMD identification code identifying an individual IMD and an IMD type, and IMD irregularity messages including data identifying type and date of an irregularity,   a database for storing IMD data received via said data input and a follow-up history dataset comprising at least a date of a latest follow-up session for an individual IMD, and   a data processor having access to said data base.       
 
         [0030]    The processor is adapted to:
       generate a list of irregularities which took place after a previous follow-up session,   calculate an individual IMD irregularity index for each type of irregularity based on IMD irregularity messages associated to an individual IMD by way of said IMD identification code,   calculate for each type of irregularity an average irregularity index over the same irregularity over all IMD irregularity messages associated to the same type of IMD,   compare said calculated individual IMD irregularity index with said calculated average irregularity index and   generate an indication if said individual IMD irregularity index significantly differs from said average irregularity index.       
 
         [0036]    Thus, the follow up support unit is able to automatically generate useful information about irregularities that are not available to any device that only is considering information received from an individual IMD. 
         [0037]    The irregularity index can be a composed variable or a one or more digit number. 
         [0038]    Also it is possible to create and compare irregularity indices associated not only to the same type of irregularity but to the same IMD in order to compare alternative therapy mode or setups of an individual IMD. In such case individual irregularity indices would be create for different therapies or IMD setups in order to compare these setups with each other. Thus it is possible e.g. to determine which mode of antitachycardia therapy (ATP) is more successful for an individual patient, burst or ramp? 
         [0039]    Preferably, the data processor is further adapted to calculate a list of hints upon generating said indication, wherein said list of hints is calculated on the basis of said irregularity messages stored in said data base and wherein said list of hints comprises at least one of:
       static suggestions which are always associated with the irregularity leading to said indication and   dynamic suggestions, wherein said data processor is adapted to calculate for each dynamic suggestion an IMD setting index of the device settings currently configured to treat said irregularity and to compare said IMD setting index to an average index over all device settings of IMDs of this type.       
 
         [0042]    Such suggestions can help the physician during a follow up session. 
         [0043]    In a further preferred embodiment the IMD follow-up support unit is part of or is at least remotely connected to an IMD follow-up workstation comprising
       a display for displaying said hints calculated by said data processor   input means for entering of commands and/or data by a user, and   a telemetry link adapted for wireless transmission of data to an IMD.       
 
         [0047]    The telemetry link may either be a direct link as is provided by a programmer directly communicating with an IMD or an indirect link via a remote service center. 
         [0048]    The IMD follow-up support unit is adapted to generate display messages that include a hint generated and may include response buttons that allow a user to respond to said hints. The follow-up system can further be adapted to process a response and to eventually initiate reprogramming of the IMD according to the hint, if possible. 
         [0049]    The response buttons can be actuated by means of e.g. a computer mouse. Alternatively, the display may be touch sensitive allowing direct actuation of the buttons displayed. Another alternative would be means for voice control of the IMD follow-up unit to respond to the messages displayed. 
         [0050]    Preferably, the follow-up support system is adapted to gives the physician conducting the follow-up the possibility
       to rate the given hint as unimportant, preferably either for one time only or generally.   to tell the assistant that the issue is being handled   to automatically re-program the IMD as suggested.       
 
         [0054]    It is further preferred that the follow-up support unit is adapted to group and prioritize the irregularities according to an internally stored irregularity priority list and to initiate displaying of the irregularities highest priority first. 
         [0055]    A further aspect of the invention relates to a workstation (e.g., the programmer itself) comprising a follow up support unit as disclosed herein before. Alternatively, the follow-up support unit can be part of a remote service center that can be linked to an external device for communicating with an IMD. The external device preferably is a workstation that is adapted for wireless data communication with the IMD. 
         [0056]    According to another aspect of the invention, the problem if solved by a method of generating support hints assisting in a follow-up session for an implantable medical device, said method comprising:
       selecting an IMD and indicating that a follow-up is about to be performed,   generating a list of irregularities which took place after a previous follow-up, said list of irregularities containing every type of irregularity which was detected   calculating for each detected irregularity an irregularity index which makes the irregularity inter-IMD comparable   calculating for each detected irregularity an average index over the same irregularity over all patients which have the same type of IMD.   comparing said calculated irregularity index with said calculated average index and displaying it to a user conducting the follow-up if said irregularity indices significantly differ from each other   and, if there is a significant difference, calculating a list of hints which can help a user to improve therapy of this irregularity.       
 
         [0063]    Preferably said hints comprise
       static suggestions which are always associated with the irregularity   dynamic suggestions that are generated by calculating an index of the device setting currently configured to treat the irregularity and comparing it to an average index over all device settings of IMDs of this type.       
 
         [0066]    The method preferably includes:
       giving the physician conducting the follow-up the possibility   to rate the given hint as unimportant (either for this time only or generally)   to tell the assistant that the issue is being handled   to automatically re-program the IMD as suggested.       
 
         [0071]    Further, the method may include grouping and prioritizing the irregularities according to a stored irregularity priority list and presenting the irregularities highest priority first. 
         [0072]    It is to be appreciated that features of preferred embodiments of the invention may be combined in any useful manner thus arriving at further preferred embodiments of the invention not explicitly mentioned in this disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0073]    The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
           [0074]      FIG. 1  is a system including an implantable medical device, and external device/programmer and a remote service center. 
           [0075]      FIG. 2  shows a dual chamber pacemaker/atrial defibrillator/cardioverter connected to leads placed in a heart. 
           [0076]      FIG. 3  is a block diagram of the device of  FIG. 1 . 
           [0077]      FIG. 4  is a more detailed representation of an external device/programmer of the system of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0078]    The following description is of the best mode presently contemplated for carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
         [0079]    In  FIG. 1 , a system comprising an implantable medical device  10 , an external device  2  and a remote service center  4  are shown. The implantable medical device  10  is an implantable heart stimulator that can act as a biventricular pacemaker and cardioverter/defibrillator. The heart stimulator  10  comprises a telemetry unit  82  for wireless data communication with the external device. The external device can wirelessly communicate with the heart stimulator  10  and thus can act as a programmer for the heart stimulator. Further, the external device  2  provides for a link to the remote service center  4  to upload data to the service center  4  and to download data from the service center  4 . Thus it is possible that the external device  2  reads out data from the heart stimulator  10  and uploads the data to the service center. The external device  2  is a workstation. 
         [0080]    The service center collects data received from different external devices belonging to different heart stimulators. The service center processes these data in order to calculate irregularity indices. The data uploaded to the service center IMD includes an identification code identifying an individual IMD and an IMD type, and IMD irregularity messages including data identifying type and date of an irregularity. 
         [0081]    The service center calculates both, a device specific irregularity index and 
         [0082]    From  FIG. 2  it is apparent that stimulator  10  comprises a case  12  and header  14 . 
         [0083]    The heart stimulator  10  is connected to three electrode leads, namely a right ventricular electrode lead for  16 , a right atrial electrode lead  18  and a left ventricular electrode lead  20 . The left ventricular electrode lead  20  is designed to pass trough the coronary sinus of heart  22 . 
         [0084]    Left ventricular electrode lead  20  comprises a left ventricular tip electrode  24  at the distal end a left ventricular electrode lead  20  and a left ventricular ring electrode  26 . 
         [0085]    Atrial electrode lead  18  comprises a right atrial tip electrode  28  at the distal end of right atrial electrode lead  18  and a right atrial ring electrode  30 . 
         [0086]    The right ventricular electrode lead  16  comprises right ventricular tip electrode  32  at the distal end of right ventricular electrode lead  16  and a right ventricular ring electrode  34 . 
         [0087]    In order to illustrate that heart stimulator  10  may be adapted to act as an implantable cardioverter/defibrillator (ICD) ventricular electrode lead  16  also exhibits a ventricular shock coil  36  for the delivery of defibrillation shocks to right ventricle  38  of heart  22  and an atrial shock coil  40  for the delivery of atrial defibrillation shocks to a right atrium  42  of heart  22 . 
         [0088]    Each electrode and shock coil of electrode leads  16  to  20  is separately connected to an electric circuit enclosed by case  12  of heart stimulator  10  by way of electrical contacts of a plaque (not shown) at the proximal end of each electrode lead  16  to  20  and corresponding contacts (not shown) in header  14  of heart stimulator  10 . 
         [0089]    Right atrial shock coil  40  is connected to right atrial shock generator  50  (see  FIG. 2 ) that is controlled by a control unit  52  of heart stimulator  10 . 
         [0090]    Similarly right ventricular shock coil  36  is connected to a right ventricular shock generator  54  that is also connected to control unit  52 . 
         [0091]    Right atrial tip electrode  28  and right atrial ring electrode  30  are both connected to a right atrial stimulation pulse generator  56  and a right atrial sensing stage  58  that internal both connected to control unit  52 . 
         [0092]    Sensing stages are provided in order to be able to sense a contraction a heart chamber that naturally occurs without artificial stimulation and that is called intrinsic. An intrinsic excitation of a heart chamber results in characteristic electrical potentials that can be picked up via the sensing electrode and that can be evaluated by the sensing stage in order to determine whether an intrinsic excitation—called: intrinsic event—has occurred. 
         [0093]    Separate sensing stages  58 ,  62  and  66  are provided for the right atrium RA  42 , right ventricle RV  38  and left ventricle LV  70 . 
         [0094]    By means of a sensing stage for a heart chamber to be stimulated, the pacemaker is able to only trigger stimulation pulses when needed that is when no intrinsic excitation of the heart chamber occurs in time. Such mode of pacing a heart chamber is called demand mode. In the demand mode the pacemaker schedules an atrial or a ventricular escape interval that causes triggering of an atrial or ventricular stimulation pulse when the escape interval times out. Otherwise, if an intrinsic atrial or ventricular event is detected prior to time out of the respective atrial or ventricular escape interval, triggering of the atrial or ventricular stimulation pulse is inhibited. Such intrinsic (natural, non-stimulated) excitation are manifested by the occurrence of recognizable electrical signals that accompany the depolarization or excitation of a cardiac muscle tissue (myocardium). The depolarization of the myocardium is usually immediately followed by a cardiac contraction. For the purpose of the present application, depolarization and contraction may be considered as simultaneous events and the terms “depolarization” and “contraction” are used herein as synonyms. 
         [0095]    Right atrial stimulation pulse generator  56  is adapted to generate atrial stimulation pulses of sufficient strength to cause an excitation of atrial myocardium by an electrical stimulation pulse delivered via right atrial tip electrode  28  and right atrial ring electrode  30 . Preferably, means are provided to adapt the right atrial stimulation pulse strength to the stimulation threshold. 
         [0096]    Right atrial sensing stage  58  is adapted to pick up myocard cardial potentials indicating an intrinsic atrial excitation that corresponds to a natural atrial contraction. By way of right atrial sensing stage  58 , it is possible to stimulate the right atrium  42  of heart  22  in a demand mode wherein a right atrial stimulation pulse is inhibited if an intrinsic atrial event (intrinsic atrial excitation) is sensed by right atrial sensing stage  58  prior to expiration of an atrial escape interval. 
         [0097]    In a similar manner, right ventricular ring electrode  34  and right ventricular tip electrode  32  are connected to right ventricular stimulation pulse generator  60  and to a right ventricular sensing stage  62  that in turn are connected to control unit  52 . By way of right ventricular tip electrode  32 , right ventricular ring electrode  34 , right ventricular stimulation generator  60  and right ventricular sensing stage  62 , right ventricular stimulation pulses can be delivered in a demand mode to the right ventricle  38  of heart  22 . 
         [0098]    In the same way left ventricular tip electrode  32  and left ventricular ring electrode  26  are connected to the left ventricular stimulation pulse generator  64  and the left ventricular sensing stage  66  that internal connected to control unit  52  and that allow for stimulating a left ventricle  70  of heart  22 . 
         [0099]    Triggering and inhibition of delivery of stimulation pulses to the right atrium, the right ventricle or the left ventricle is controlled by control unit  52  in a manner generally known to the man skilled in the art. The timing that schedules delivery of stimulation pulses if needed is controlled by a number of intervals, that at least partly may depend on a hemodynamic demand of a patient that is sensed by means of an activity sensor  72  that is connected to control unit  52 . Activity sensor  72  allows for rate adaptive pacing wherein a pacing rate (the rate of consecutive ventricular stimulation pulses for a duration of consecutive atrial stimulation pulses) depends on a physiological demand of a patient that is sensed by a way of activity sensor  72 . Details of rate adaptation are known to the man skilled in the art but need not to be explained in detail in this description. 
         [0100]    Whereas an actual stimulation rate determines the timing from one (paced) heart cycle to another, intervals like an atrioventricular delay interval and an interventricular delay interval determine the timing within one heart cycle. Starting with an atrial event, the right ventricle would be excited (either intrinsically or paced) at the end of an atrioventricular delay interval. A left ventricular contraction should follow the right ventricular contraction at the end of an interventricular delay interval. This shall include the case, wherein the right ventricle and the left ventricle are excited the same time resulting in an interventricular delay interval duration of zero. Also, it is possible that the left ventricle is excited prior to the right ventricle resulting in an negative interventricular delay interval duration. 
         [0101]    In any case, the atrioventricular delay interval duration and the interventricular delay interval duration need to be adapted to an individual heart in order to achieve an optimized cardiac output. 
         [0102]    Adaptation of these and other parameters is performed during implantation and during follow-up sessions taking into account irregularities that may have occurred since implantation or a previous follow-up session. 
         [0103]    To assist a physician during a follow-up session, either the external device  2  or the remote service center is adapted to allow the following scenario:
       1. The physician selects the patient and indicates that he is about to perform a follow-up.   2. The external device  2  or the service center  4  generates a list of irregularities which took place after the previous follow-up so that the physician knows which problems to address. This list of irregularities contains every type of irregularity which was detected by Home Monitoring.   3. For each detected irregularity the external device  2  or the service center  4  calculates an irregularity index which makes it inter-patient comparable or makes comparable for alternative modes or setups of an individual IMD.   4. For each detected irregularity the external device  2  or the service center  4  calculates an average index over the same irregularity. The average index may be calculated over all patients in the external device  2  or the service center  4  which have the same type of implant (given that there is a substantial base of other patients with this implant type) in order to make the index inter-patient comparable.   5. The external device  2  or the service center  4  compares said calculated irregularity index with said calculated average index and displays it to the physician conducting the follow-up if it significantly differs.   6. In that case, the external device  2  or the service center  4  furthermore calculates a list of hints which can help the physician to improve therapy of this irregularity. These hints may comprise
           static suggestions which are always associated with the irregularity   dynamic suggestions: A dynamic suggestion calculates an index of the device setting currently configured to treat the irregularity and either compares it to an average index over all device settings of implants (IMDs) of this type or compares it to a corresponding index for an alternative setup or mode of operation of the same implant.   
               
 
         [0112]    The external device  2  or the service center  4  gives the physician conducting the follow-up the possibility
       to rate the given hint as unimportant (either for this time or generally)   to tell the assistant that the issue is being handled       
 
         [0115]    Further, the external device  2  or the service center  4  may give the physician conducting the follow-up the possibility to automatically re-program the implant as suggested. 
         [0116]    The external device  2  or the service center  4  groups and prioritizes the irregularities according to an internally stored irregularity priority list and presents the irregularities highest priority first. 
         [0117]    If the external device is not designed as a stand-alone device but designed to cooperate with the remote service center, follow-up support unit is accessible over any internet-connected computer and for every physician who has the right to view and change the patient&#39;s data. 
         [0118]    This scenario provides for the following advantages of the invention over the prior art:
       1. Patient compliance is no longer necessary. The invention doesn&#39;t rely on the patient memorizing or writing down all symptoms.   2. It is no longer necessary for the attending physician to browse through cardio reports collected since the last follow-up examination.   3. The problem of keeping several copies of one patient file up to date and consistent with one another is solved.       
 
         [0122]      FIG. 4  shows a workstation  2  that is used as the external device of  FIG. 1 . Workstation  2  comprises a touch sensitive display  90  that allows displaying of the hints generated and of response buttons  92  that can be actuated by a physician. 
         [0123]    The following table gives another example of hints o be displayed and possible response buttons: 
         [0000]    
       
         
               
             
               
             
               
               
             
               
             
               
               
             
           
               
                   
               
               
                 Home Monitoring Service Center Follow-Up Assistant 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 Follow-Up Assistant 
               
             
          
           
               
                 Patient: 
                 David Labraccio 
               
               
                 SN: 
                 60209071 
               
               
                 Device type: 
                 Lumax 340 HF-T 
               
               
                 Implantation: 
                 Sep 13, 2005 
               
               
                 Today: 
                 Jan, 15, 2007 
               
               
                 Date of last follow-up: 
                 Aug, 12, 2006 
               
               
                 Length of follow-up interval: 
                 186 days. 
               
               
                 Average length of follow-up interval in your user group: 
                 172 days. 
               
               
                 Average length of follow-up interval over all patients with this implant type: 
                 322 days. 
               
             
          
           
               
                 The following irregularities were detected within this follow-up interval: 
               
             
          
           
               
                 Ineffective shocks 
                 Not of interest 
               
               
                 There were 7 ineffective shocks reported during the current follow- 
                 Reprogram device 
               
               
                 up interval. This is above average. 
                 Ok 
               
               
                 Suggestion: 
               
               
                 Change course of therapy? First shock now is 10 J. Consider 25 J. 
               
               
                 Ineffective ATP 
                 Not of interest 
               
               
                 Only 5% of all conducted ATP ramps were ineffective. But 78% of 
                 Reprogram device 
               
               
                 all conducted ATP bursts were effective. 
                 Ok 
               
               
                 Suggestion: 
               
               
                 Change course of therapy? Exchange all programmed ramps into 
               
               
                 bursts. 
               
               
                 Many VT1 
                 Not of interest 
               
               
                 38 ventricular tachycardia (VT1) detected since last follow-up. This 
                 Reprogram device 
               
               
                 is above average (average for this implant type within the same 
                 Ok 
               
               
                 time: 4). 
               
               
                 Suggestion: 
               
               
                 Examine IEGMs for T-wave oversensing 
               
               
                 Examine patient medication 
               
               
                 Change programmed VT1 zone (currently: 120 bpm) to 140 bpm. 
               
               
                 CHF worsened 
                 Not of interest 
               
               
                 The CHF index for this patient changed from 1.3 to 4.5 (on a scale 
                 Ok 
               
               
                 from 1 . . . 10). This is above average (average increase for this implant 
               
               
                 type within the same time: 0.3). 
               
               
                 Suggestion: 
               
               
                 Examine patient medication. 
               
               
                   
               
             
          
         
       
     
         [0124]    Although an exemplary embodiment of the present invention has been shown and described, it should be apparent to those of ordinary skill in the art that a number of changes and modifications to the invention may be made without departing from the spirit and scope of the invention. In particular, it is possible to implement the features of the claimed transceiver unit into state of the art implantable medical devices such as implantable pacemakers or implantable cardioverter/defibrillator. This invention can readily be adapted to such devices by following the present teachings. All such changes, modifications and alterations should therefore be recognized as falling within the scope of the present invention.