Usefulness of labetalol in chronic atrial fibrillation

Beta-adrenergic blocking agents are useful in controlling excessive ventricular rate in chronic atrial fibrillation (AF) but often reduce exercise capacity. To investigate the advantage of labetalol—a unique β blocker with α-blocking property—in chronic AF, 10 patients without underlying structural heart disease were studied with treadmill test, 12-minute walk and 24-hour ambulatory electrocardiographic monitoring. Patients were randomized and crossed over to receive 4 phases of treatment (placebo, digoxin, digoxin with half-dose labetalol, and full-dose labetalol). Exercise durations were 14.1 ± 1.5, 14.2 ± 1.5, 16.1 ± 1.1 and 15.6 ± 1.1 minutes, respectively, indicating that labetalol did not reduce exercise tolerance. Although digoxin had no advantage over placebo in controlling maximal heart rate (177 ± 2 vs 175 ± 3 beats/ min), labetalol, both as monotherapy or as an adjunct to digoxin, was advantageous (156 ± 4 vs 177 ± 2 beats/min, p < 0.01, and 154 ± 4 vs 177 ± 2 beats/min, p < 0.01, respectively). The rate-pressure product was consistently lowered by labetalol at rest and during exercise. At peak exercise, the addition of labetalol to digoxin reduced the maximal rate-pressure product achieved from 30,900 ± 1300 to 24,100 ± 2,000 mm Hg min (p < 0.01) and the maximal rate-pressure product was lowest with full-dose labetalol (22,300 ± 1,600 mm Hg/min). During submaximal exercise on treadmill or during the 12-minute walk, the combination of labetalol and digoxin produced the best heart rate control, whereas labetalol monotherapy was comparable to digoxin therapy. During daily activities, digoxin failed to control the maximal ventricular rate (172 ± 5 vs 174 ± 7 beats/min with placebo) but the addition of labetalol was efficacious (141 ± 5 vs 172 ± 5 beats/min; p < 0.01). No bradycardia was recorded during labetalol treatment. Thus, labetalol improves heart rate control in chronic AF without decreasing exercise tolerance.