Factors responsible for such differences in longevity are many.

Epicardial electrode impedances are lower than for endocardial electrodes by a factor of 1.5 to 2; and, therefore, current drain for epicardial electrodes is higher.

The average heart rate of the younger child is higher, and in atrial triggered pacing the average number of generator discharges is higher enhancing battery depletion. These are probably the two most important factors in determining generator longevity.

Epicardial electrodes often have higher pacing thresholds but the difference is not great in many patients. Yet in some patients this can decrease generator longevity. As a consequence of this, especially for epicardial pacing, the use of generators with the largest battery capacity should be preferred even though this results in a some what larger generator. Larger generator size is often acceptable in epicardial pacing where the generator is implanted in the abdomen.

To what degree atrial pacing rather than atrial sensing as in DDDR pacing and the use of enhanced generator functionality such as enhanced patient diagnostic capabilities impact upon generator longevity is unclear.