Beta-adrenoceptor blockade: electrophysiology and antiarrhythmic mechanisms.

Beta-adrenoceptor-blocking agents reduce beta-adrenergic activity and depress sinoatrial and atrioventricular nodal conduction. These agents are thus useful for controlling supraventricular tachyarrhythmias. For the treatment of ventricular arrhythmias, beta-adrenoceptor-blocking agents possess antifibrillatory properties, depress diastolic depolarization of ectopic pacemaker activity, reduce electrical instability associated with prolongation of the QT interval, and are specifically effective in suppressing ventricular arrhythmias that are rate (tachycardia) dependent and/or caused by catecholamine-sensitive automaticity. Furthermore, beneficial hemodynamic effects of beta-adrenoceptor blockade on ischemic myocardium may also contribute to the antiarrhythmic potency of these agents.