Cardioversion and Digitalis

CARDIOVERSION has proved an effective and safe method for reverting ectopic arrhythmias to sinus rhythm.1'-" However, there is increasing evidence that capacitor electrical discharge may provoke arrhythmias in experimental animals12"-4 as well as in man.2' 6, 15 The majority of abnormal rhythms immediately following cardioversion are atrial in origin and are not serious. They generally represent one of three mechanisms: (1) a delayed "warm-up" of the sinus node manifested by sinus bradycardia, nodal rhythm, or escape beats, (2) increased atrial automaticity as demonstrated by individual or multiple atrial premature beats occurring either singly or in paroxysms of tachycardia, and (3) a defect in elaboration or conduction of the sinus impulse characterized by chaotic atrial activity with changing P wave contour and bradycardia interspersed with multiple and recurring ectopic beats with runs of atrial or nodal tachycardia. The first two mechanisms are transient and generally result in stable sinus rhythm within 1 to 5 minutes. The third mechanism almost invariably reverts to atrial flutter or fibrillation. The ventricular arrhythmias following cardioversion are less common but may be more serious. These are of two types: The first occurs immediately after the shock and involves development of ventricular fibrillation usually the result of improper synchronization. The second occurs after a delay of several or