Effect of propranolol on ventricular rate during atrial fibrillation in the Wolff-Parkinson-White syndrome.

Atrial fibrillation was induced during an electrophysiology study in 10 patients with the Wolff-Parkinson-White (WPW) syndrome, after determination of baseline properties of the accessory atrioventricular (AV) connection; intravenous propranolol (0.2 mg/kg) was then administered. Atrial fibrillation terminated during the drug infusion in three patients, allowing determination of propranolol's effects on conduction and refractoriness during sinus rhythm, before atrial fibrillation was reinduced. In these three patients propranolol had no effect on refractoriness or conduction properties of the accessory AV connection during sinus rhythm. The mean ventricular rate during atrial fibrillation was slowed by 15-56 beats/min in six patients, had no effect on the mean rate in three patients, and markedly increased the ventricular rate (203 to 267 beats/min) in one patient. In this patient, 54% of QRS complexes during atrial fibrillation were narrow, compared to 0-25% in the other patients. Propranolol reduced the percentage of QRS complexes that were narrow from 13 +/- 16% to 1 +/- 2% (mean +/- standard deviation, p less than 0.05). We conclude that propranolol may slow the ventricular rate during atrial fibrillation in some patients with the WPW syndrome, probably by blocking the effects of adrenergic activation. However, propranolol should not be used in patients with the WPW syndrome who have atrial fibrillation, if most QRS complexes during atrial fibrillation are preexcited. When a large percentage of QRS complexes are narrow, propranolol may increase the ventricular rate, probably by eliminating concealed retrograde conduction in the accessory AV connection.