Interaction of the input atrial excitatory waves and conduction through the atrioventricular node. I. Changes in the cellular electrical activity.

Extrasystoles were applied only at the posterior input, only at the anterior input and jointly at both AVN-inputs in preparations from rabbit right atrium, after 10 basic beats. The effect of the interaction of the input excitatory waves was evaluated by the changes in the cellular electrical activity and in the output H1H2-interval. It has been demonstrated that both the summation effects (shortening of the H1H2-interval) and the inhibition effects (prolongation of the H1H2-interval) are accompanied by substantial changes in the spatial-temporal organization of conduction within the node. The summation of excitatory waves leads to higher velocity of AP increase (most frequently in the N-zone), to changes in the shape of AP as a result of electrotonic influences, to changes in the sequence of activation of cellular group forming different conduction pathways. The inhibition of the excitatory waves is related to the increase in the inhomogeneity of conduction, manifested in the formation of competitive conduction pathways. In addition to the changes in the AP-front, a typical characteristic is the hill-structure reflecting the effect of the excitatory fronts. The formation of conduction pathways under the effect of each of the input excitatory waves probably takes place on the background (spatial and temporal) of the disappearing refractoriness, related to another excitatory wave. The interaction between the input excitatory waves, taking places through the proposed model, could also be present in a normally functioning heart provided the phasic correlations between the moments of activation of the posterior and anterior inputs are optimal for such an interaction.