Comparison of the posterior and anterior activation of the atrioventricular node in rabbit heart with identical prematurity--microelectrode investigation.

The present work evaluates the input prematurity of AVN-activation as a determinant atrioventricular condition. The cellular organization of conduction is studied by consecutive stimulation of the posterior input (crista terminalis) and the anterior input (interatrial septum) with identical prematurity. The results obtained demonstrate the existence of essential differences in conduction upon posterior and anterior stimulation. Above all, separate activation of the two inputs leads to different timing of the cell excitation from the adjacent AN-zones; different sections of the AN-area may prove to be excluded from the conduction process to the His-bundle. Moreover, upon changing the direction of the excitatory wave (even if the prematurity of the extrastimulus is preserved unchanged), temporal and spatial reorganization occurs in the N-zone of the node, the concurrent changes in the shape of the action potentials and the intervals between them. The activation of only one AVN input (by electrical stimulation) could cause passive or active excitation of the other. In the first case the passively activated input may participate in the retrograde conduction of the excitation to the atrium (re-entry); in the second case, under definite conditions, the two antegrade input waves may interact within the AVN. Knowledge only of the absolute values of the stimulation prematurity is not sufficient for description of the conduction through AVN.