Cardioversion and digitalis drugs: changed threshold to electric shock in digitalized animals.

• Cardioversion is now widely accepted as the method of choice for terminating a number of atrial, nodal and ventricular arrhythmias." The technique consists of administering from a capacitor a specific underdamped monophasic electrical pulse across the intact chest. When the heart is exposed to electrical energy, there is a risk of producing ventricular fibrillation. With this new technique, such risk is minimized by programming the discharge to fall outside the ventricular vulnerable period of the cardiac cycle. In 450 patients reverted to sinus rhythm during the past three years at the Peter Bent Brigham Hospital, there has not been a single episode of cardiac standstill, ventricular fibrillation or death. Transient arrhythmias, however, have been frequently noted after delivery of the electric shock. These have consisted of varying degrees of A-V block, atrial, nodal and ventricular extrasystoles occurring either singly or assuming a bigeminal pattern, nodal rhythm, nodal tachycardia and rarely paroxysms of ventricular tachycardia. In reviewing the cardioversion experience at the Peter Bent Brigham Hospital, it was found that patients with evidence of digitalis toxicity were more prone to manifest "shock induced" disorders of rhythm.