An Analysis of Arrhythmias Induced by Ouabain in Intact Dogs.

• The mechanism of cardiac arrhythmias induced by digitalis compounds has been investigated recently by the microelectrode technique. Coraboeuf et al. found that the automaticity of the canine "tissu nodal" was enhanced by administration of digitalis. This finding was confirmed by Dudel and Trautwein for canine Purkinje fibers. Also, the action of glycosides on transmembrane potentials of ventricular muscle fibers has been studied extensively." In a comparative study canine Purkinje fibers and ventricular muscle fibers were exposed to ouabaiu in vitro under identical experimental conditions. It was found that the transmembrane potential of the Purkinje fibers is markedly modified by ouabain and that this tissue quite often develops a fast rhythm at a time when the transmembrane action potentials of ventricular muscle fibers show only minor changes. No electrophysiological evidence that ventricular muscle fibers develop automaticity under the influence of ouabain was found. The sensitivity of the specialized conducting system to ouabain suggested that a similar increase in automaticity of Purkinje fibers might be observed in vivo at an early stage of ouabain administration. Since ventricular muscle fiber action potentials showed little change when Purkinje fibers exhibited fast rhythms, one could expect an increase in automaticity of the specialized system of the