The Spread of Sinus Activation During Potassium Administration

Abstract

Electrodes were chronically implanted in intact dogs at several locations on the atria and ventricles, and studies made of the effect of an elevated extracellular K⁺ concentration on the spread of the sinus impulse throughout the atria. It was found that sinus activity propagates to the coronary sinus and ventricles at a time when the atrial muscle fibers have been rendered inexcitable. The finding of such a sino-ventricular rhythm supports the existence of a specialized conducting path between the sinus and the atrio-ventricular node; this path is particularly resistant to depolarization by potassium. Potassium-induced 2:1 sino-atrial block was described. In vitro experiments provided a demonstration that such block is frequency-dependent and due to marked prolongation of the refractory period provoked by high [K]₀. It appears that the lengthened refractory period may be due to a marked reduction of the reactivation rate of the "sodium carrying system."