Effectiveness and safety of oral verapamil to control exercise-induced tachycardia in patients with atrial fibrillation receiving digitalis.

The safety and efficacy of oral verapamil to control exercise tachycardia in 27 patients with atrial fibrillation and 3 with atrial flutter receiving digitalis was evaluated in a double-blind, randomized, crossover study. The heart rate in patients who received verapamil compared with placebo group was lower at rest (mean 69 +/- 13 versus 87 +/- 20 beats/min, p less than 0.01), as was the degree of tachycardia at the end of 3 minutes of a standardized exercise test (104 +/- 14 versus 136 +/- 23 beats/min, p less than 0.01). Doses of verapamil required to achieve suppression of tachycardia were 240 mg/day in 18 patients, 320 mg/day in 6 patients, and 480 mg/day in 3 patients. Only 3 patients complained of adverse effects from verapamil during the double-blind phase of the study. Two patients were discontinued from the study because of adverse reactions. No clinically significant changes during verapamil therapy were observed on the electrocardiogram, chest roentgenogram, echocardiogram or in the laboratory evaluation. Digoxin blood levels were higher in patients who received concomitant verapamil compared with placebo (1.23 +/- 0.59 versus 0.85 +/- 0.46 ng/ml, p less than 0.01), but no patient had signs or symptoms of digitalis toxicity. Thus, oral verapamil given in addition to digitalis is a safe and effective agent in the treatment of patients with chronic atrial fibrillation or flutter to decrease exercise-induced tachycardia.