Pulse duration variation and electrode size as factors in pacemaker longevity.

For the past 4 years, we have used highly efficient Medtronic electrodes (Nos. 6901 and 6907), with small surface areas, for cardiac pacemakers. We have found that chronic thresholds average 1.6 Ma. at a 1 msec. pulse duration, compared to 4.9 Ma. for the conventional Medtronic No. 5816 electrodes. These electrodes have been used in association with Medtronic Models 5961 and 5931, ventricular-inhibited and asynchronous pulse generators in which output current and voltage are fixed and pulse duration is variable. Drain from the generator battery is directly related to impulse duration and is reduced at shorter durations. The strength-duration curve of cardiac stimulation suggests and actual long-term pacing has been achieved at an average of 0.2 to 0.3 msec., rather than the conventional 1.0 msec. Drain from the battery is one fourth that of pacemakers of 1970 and one half that of present day, conventional units. This fact suggests that a realistic average life of the pulse generator is 4 years or more.