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

To solve the problem of pacemaker longevity, current output, and pulse width programmable pacing systems were introducedfor clinical use in 1972. Thirty-seven patients with such systems were serially assessed in our pacemakerfollow-up clinicfor an average of 23 months (range 6 to 36 months). Twenty-five patients 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 Omnnicor units (average 29 0 months) with an average current output of 4-8 mA in 4. One Medtronic 5961 unit failed after 19 months (0.8 ms pulse width) because of a manufacturing defect in the battery sealing. The 31 re- maining programmable pacers remainfunctional (average 22 months). Specialproblems encountered included increased early incidence of cardiac perforation attributable to small surface area endocardial electrodes (6 patients); ventricularfibrillation induced by unipolarfixed rate pacing (2 patients) representing the first report of cathode provoked ventricular tachyarrhythmias caused by the R on T phenomenon and pacemaker vulnerability to direct current countershock resulting infixed 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 improved pace- maker lifetime compared with our 22 nonprogrammable Cordis and Medtronic demand pacemakers with an average longevity of 31.5 months. Attention to alternatepower sources such as lithium iodide batteries may be a more promising approach to increasing pacemaker life.