Functional Properties of the Atrioventricular Conduction System

Abstract

Experiments were designed to study A-V transmission of premature atrial responses by recording electrical activity directly from selected parts of the conducting system. This experimental design permits a more exact interpretation of results than is the case when records are obtained only from the atria and ventricles. Two types of experiments have been conducted in studies of the response of the specialized conducting system of the mammalian heart to premature activation. Records of transmembrane potentials from single fibers of the A-V node and Purkinje system show that premature responses may show a reduced rate of rise and amplitude and thus may be conducted slowly or may decrement completely. Under other conditions, premature responses may show local delay or block because they arise from a local response of considerable duration. Records obtained directly from different parts of the in situ specialized conducting system show that the same phenomena probably occur in the intact, normal heart. These properties of the various fibers of the conducting system, in conjunction with the normal local differences in action potential duration, conduction velocity, and excitability, seem to account quite adequately for the variations which have been noted during A-V propagation of premature responses. On the basis of these results, it seems unnecessary to postulate a dual A-V conducting system in the mammalian heart.