The Mechanisms of Digitalis-Induced Ventricular Fibrillation

¹ Assistant Professor of Medicine, University of Miami School of Medicine
² Associate Professor of Medicine, University of Miami School of Medicine
³ Department of Medicine (Section of Cardiology), University of Miami School of Medicine, the Division of Electrophysiology, Jackson Memorial Hospital, Miami, Florida; and the Veterans Administration Hospital, Coral Gables, Florida

Two cases of digitalis induced ventricular fibrillation in which the onset of the arrhythmia was recorded electrocardiographically are presented. In the first patient, fibrillation evolved from a rapidly progressing bidirectional ventricular tachycardia. The arrhythmia was due to acetyl strophanthidin administered at five minute intervals, as recommended in 1954. The patient had not been receiving digitalis previously. In the second case, ventricular fibrillation appeared suddenly when a ventricular extrasystole fell in the vulnerable phase of the preceding contraction. This occurred after the intravenous administration of digoxin to a patient with an undiagnosed digitalis induced arrhythmia. Both episodes occurred before the era of transthoracic electric countershock. It seems that in man, as well as in the laboratory animal, there are at least two types of digitalis related ventricular fibrillation. One appears suddenly and responds to electric countershock. The other from of ventricular fibrillation is preceded by a gradual widening of the QRS complexes. The latter cannot be abolished electrically. Aggressive antiarrhythmic drug treatment during the tachycardia stage is probably the treatment of choice.