Evaluation of metoprolol in suppressing complex ventricular arrhythmias

This study documents the extent of suppression of premature ventricular beats which can be achieved with metoprolol, a semiselective beta-adrenergic blocking agent, at doses of 100 to 200 mg daily, utilizing a single-blind placebo-controlled 10-day protocol with continuous ambulatory electrocardiographic recording of 20 patients with cardiac disease and complex ventricular arrhythmias. Metoprolol (200 mg/day) resulted in suppression of 60% of total premature ventricular beats, with couplets (pairs) and ventricular tachycardia decreased 84% and 94%, respectively (all p < 0.01). Exercise-induced premature ventricular beats, especially ventricular tachycardia, were effectively suppressed. The peak plasma metoprolol level to achieve these results was 72 ± 34 ng/ml (mean ± 1 standard deviation). At this plasma concentration, the mean 24-hour heart rate during normal activity was reduced from 78 ± 8 beats/min (placebo) to 62 ± 4 (metoprolol 200 mg/day)(p < 0.001). Beta blockade also was demonstrated by a 20% reduction in heart rate during maximal Bruce exercise testing with metoprolol 200 mg/day. Although resting left ventricular function was not affected by metoprolol, pulmonary function tests show a statistically significant decrease in forced vital capacity, forced expiratory volume in 1 second, and forced expiratory flow rates (25-75) reversible with a beta-2 agonist.