Common functional origin for simple and complex responses of atrioventricular node in dogs.

The possibility that variations in atrioventricular nodal conduction time observed during transient and steady-state nodal responses share common characteristics was examined in six anesthetized dogs. Atrioventricular conduction times (AV intervals) obtained during transient (incremental atrial pacing rates, short frequency steps, and Wenckebach cycles) and steady state (periodic premature stimulation performed at 5 basic rates) responses were plotted together against the corresponding preceding ventriculoatrial (VA) intervals on a graph for each dog. Despite their diversity, nodal responses consistently resulted in AV intervals that fell within a well-defined, relatively narrow, crescent-shaped zone on the graphs. AV interval variations were small in the long VA interval range and increased slightly but predictably as the VA intervals decreased. AV intervals of transient and steady state nodal responses overlapped markedly. These results show that AV intervals of transient and steady-state nodal responses vary within a given common functional domain despite the diversity of their sequential patterns and suggest that the AV node may be obeying the same set of conduction rules during these very distinct responses.