Temporal dispersion of recovery of excitability in atrium and ventricle as a function of heart rate.

Abstract Temporal dispersion of recovery of excitability, measured as the range of local refractory period durations at numerous sites on the atrial and ventricular surfaces, was found to be a direct function of the basic cycle length except at very rapid driving frequencies. In the atrium, spontaneous ectopic activity followed early premature stimuli at slow but not at fast driving frequencies. In the ventricle, the fibrillation threshold was significantly lower at slow than at high basic frequencies. It was concluded that spontaneous closely coupled beats occurring at slow ventricular rates in A-V dissociation may result from asynchrony in the repolarization of adjacent excitable units.