A conceptual basis for pacing waveforms

A model is developed that allows evaluation of the pacing efficacy of different stimulus waveforms. it treats the heart as having a first order time constant and enables ready visualization of the time course of the effective voltage within the heart. For pacemakers, where the stimulus pulse is produced by the discharge of a capacitor the voltage within the heart rapidly rises to a peak and then more slowly decays to zero. The time interval at which the peak occurs defines the optimal duration, i.e., the shortest duration with minimal pacing voltage. Characteristics are developed that show the changes in optimal duration and pacing threshold for changes in the pacemaker's output capacitor and for differences in lead impedance and time constant of the heart.