Electrical Alternans in Single Ventricular Fibers of the Frog Heart

Abstract

Electrical alternation was produced in single ventricular fibers of the frog heart in 14 experiments by means of l-thyroxine, triiodothyronine and acute anoxia. The phenomenon was transitory, unrelated to heart rate, and more often than not associated with decreased cardiac contractility. Four types were observed: alternation in a) the rate of depolarization, b) the rate of repolarization, c) the magnitude of the action potential and d) hyperpolarization. Usually the alternation involved several phases of the membrane action potential. The exact mechanism by which the agents used produced the phenomenon is unknown.