Antiarrhythmic Prophylaxis with Procainamide in Acute Myocardial Infarction

The effectiveness of prophylactic therapy with procainamide in preventing active ventricular arrhythmias after acute myocardial infarction was determined in a double-blind study using electrocardiographic monitoring of 70 patients with acute infarctions uncomplicated by shock, heart block or severe heart failure. After a loading dose, 250, 375 or 500 mg of procainamide or placebo were administered every three hours according to patient weight. Procainamide afforded highly significant protection against all types of active ventricular arrhythmias, markedly reduced the need for acute therapy of arrhythmias, and prevented death from active arrhythmias. Adverse effects of procainamide therapy occurred only in patients with excessive plasma concentrations. The effective plasma procainamide concentration for suppressing active ventricular arrhythmias after acute myocardial infarction is 4 to 6 mg per liter. Lower plasma levels protect incompletely whereas concentrations above 7 mg per liter can produce adverse cardiovascular effects. Plasma procainamide concentrations vary widely among patients, and their measurement is helpful in establishing proper individual dosage.