Arrhythmogenic effects of antiarrhythmic drugs: a study of 506 patients treated for ventricular tachycardia or fibrillation.

Antiarrhythmic therapy in 506 consecutive patients undergoing 1,268 antiarrhythmic drug trials for ventricular tachycardia or ventricular fibrillation was reviewed for evidence of arrhythmogenic drug effect defined as the occurrence of a new form of ventricular tachyarrhythmia temporally associated with initiation of drug therapy or dosage increase. Arrhythmogenic effects occurred in 6.9% of patients and 3.4% of drug trials. This ranged from a high of 11.8% caused by encainide to none occurring with procainamide, tocainide or beta-adrenergic blocking drugs. The incidence of arrhythmogenesis was significantly greater in patients whose presenting arrhythmia was sustained ventricular tachycardia than it was in those who presented with nonsustained ventricular tachycardia or ventricular fibrillation (p = 0.02). Decreased systolic function measured echocardiographically at the base of the left ventricle was associated with an increased incidence of arrhythmogenic effects (p = 0.006) whereas global left ventricular ejection fraction was not. Age, gender, cardiac diagnosis, location of prior myocardial infarction and New York Heart Association functional class for heart failure were not related to the occurrence of drug-induced arrhythmias. These findings emphasize the need for in-hospital cardiac monitoring during initiation of antiarrhythmic drug therapy for ventricular tachyarrhythmias.