The safety and efficacy of the intravenous (IV)
calcium channel blocker,
verapamil, in controlling the ventricular response or converting to sinus rhythm patients with
atrial flutter or
atrial fibrillation were assessed. Seventeen patients (nine with
atrial flutter and eight with
atrial fibrillation) with these arrhythmias that were difficult to control pharmacologically were chosen for the study. All patients at the time of study were receiving
digoxin. Either
verapamil or placebo was chosen randomly and a bolus of 0.075 mg/kg (up to 5 mg) was administered. Twelve patients had a marked reduction in their ventricular response after IV administration of
verapamil (seven with
atrial flutter and five with
atrial fibrillation). None of these 12 patients converted (nonconverters). The average reduction in heart rate was from 120 +/- 6 beats per minute to a minimum of 83 +/- 13 beats per minute within 20 minutes after
drug administration.
Verapamil was found to convert five patients with atrial arrhythmias to sinus rhythm (two with
atrial flutter and three with
atrial fibrillation) (converters). In addition, three patients with atrial arrhythmias of less than one month who did not convert with parenteral
drug therapy converted within 24 hours while receiving the oral
drug. Converters had their supraventricular arrhythmias of significantly shorter duration (median, three hours v 30 days) and tended to have smaller left atrial size (3.8 +/- 0.7 cm v 4.3 +/- 1.3 cm) compared with the nonconverters. We conclude that
verapamil is safe and effective when administered IV to patients with
atrial flutter and fibrillation for control of ventricular response. In short duration atrial arrhythmias, conversion to sinus rhythm is likely once the ventricular response is controlled.