Electrophysiological Properties of the Canine Peripheral A-V Conducting System

Action potential durations and local refractory periods were mapped along the course of canine conducting tissue from bundle branches to the termination of false tendons in ventricular muscle. Standard microelectrode techniques were used. Areas of maximum action potential duration, which coincided with areas of maximum local refractory periods, were consistently found 2 to 3 mm proximal to the termination of conducting fibers in muscle. The refractory periods at the areas of maximum action potential duration were quantitatively identical in the multiple false tendons of a segment of the conducting system, providing a uniform functional limit for the propagation of premature impulses across the distal end of the conducting system of the segments studied. It was demonstrated that appropriately timed premature impulses could be confined within conducting tissue either proximal or distal to the area of maximum action potential duration. This occurred when the area of maximum duration was still refractory, after other areas of the conducting system had recovered excitability. In most preparations, maximum action potential durations and functional refractory periods across distal false tendons were longer in tissue from the right side than from the left side of the conducting system.