SELECTIVE FUNCTIONAL-PROPERTIES OF DUAL ATRIOVENTRICULAR NODAL INPUTS- ROLE IN NODAL CONDUCTION, REFRACTORINESS, SUMMATION, AND RATE-DEPENDENT FUNCTION IN RABBIT HEART

Background The atrioventricular node receives its activation signal fr om the low crista terminalis and low interatrial septum, the summation of which is believed to favor conduction. A functional asymmetry betw een the inputs is also believed to be involved in nodal reentrant rhyt hms. We studied the selective functional characteristics of nodal inpu ts and determined their role in nodal conduction, refractoriness, summ ation, and rate-dependent function. Methods and Results The nodal prop erties of recovery, facilitation, and fatigue were characterized with stimulation protocols applied with varying phases between the two inpu ts in isolated rabbit heart preparations. The effects of the input pha se, nodal functional state, and input reference on the nodal conductio n time, recovery time, and refractory periods were assessed with multi factorial ANOVAs. It was found that the phase of stimulation significa ntly affected nodal conduction time but not the refractory periods or the time constant of the recovery. Each input could show longer and sh orter conduction time than the other depending on the stimulation phas e, input reference, and coupling interval. These effects were similar for different nodal functional states. However, pacing and recording f rom the low crista resulted in similar conduction and refractory value s than did pacing and recording from the low septum. Input summation d id not increase the otherwise equal efficacy of individual input in ac tivating the node. Nodal surface recordings confirmed this functional symmetry and equivalent efficacy of the inputs and showed that input e ffects were confined to the proximal node. Conclusions The two nodal i nputs have equivalent functional properties and are equally effective in activating the rate-dependent portion of the node. Input interactio n affects perinodal activation but not the rate-dependent nodal functi on.