Longevity of programmable energy output pacemakers. Early results and experiences.

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Abstract
To solve the problem of pacemaker longevity, current output and pulse width programmable pacing systems were introduced for clinical use in 1972. Patients (37) with such systems were serially assessed in this pacemaker follow-up clinic for an average of 23 mo. (range 6-36 mo.). Patients (25) received the Cordis Omnicor system (programmable current output), while 12 patients received the Medtronic 5961 system (programmable pulse width). Pacemaker failure caused by battery exhaustion occurred in 5 Omnicor units (average 29.0 mo.) with an average current output of 4.8 mA in 4. One Medtronic 5961 unit failed after 19 mo. (0.8 ms pulse width) because of a manufacturing defect in the battery sealing. The 31 remaining programmable pacers remain functional (average 22 mo.). Special problems encountered included increased early incidence of cardiac perforation attributable to small surface area endocardial electrodes (6 patients); ventricular fibrillation induced by unipolar fixed rate pacing (2 patients) representing the 1st report of cathode provoked ventricular tachyarrhythmias caused by the R on T phenomenon and pacemaker vulnerability to direct current countershock resulting in fixed rate pacing (1 patient). Despite lack of sufficient prolongation of pacemaker life, unique advantages of the programmable systems constitute ability to alter heart rate to allow evaluation of patients'' intrinsic rhythm and QRS complexes, overdrive suppression of ventricular tachyarrhythmias and determination of chronic threshold and early detection of exit block. This experience to date with the programmable Omnicor system does not appear to provide inproved pacemaker lifetime compared with our 22 nonprogrammable Cordis and Medtronic demand pacemakers with an average longevity of 31.5 mo. Attention to alternate power sources such as lithium iodide batteries may be a more promising approach to increasing pacemaker life.