Electrophysiologic effects of beta blockers in ventricular arrhythmias

Beta-adrenergic receptor blocking agents are effective antiarrhythmic drugs in patients with ventricular arrhythmias. However, these agents exert little or no measurable electrophysiologic effect on normal Purkinje and ventricular muscle fibers when administered acutely. They prevent catecholamine-induced increases in Purkinje fiber automaticity and may interfere with catecholamine-dependent slow responses. beta-adrenergic blocking drugs also prevent the decrease in ventricular fibrillation threshold induced by catecholamines. In the acutely ischemic ventricle, some beta blockers selectively depress conduction within the ischemic zone. The long-term administration of some beta blockers has, in contrast to their short-term effects, been shown to prolong action potential duration and effective refractory period in the ventricle. Which of these observed electrophysiologic effects, either alone or in combination, contributes to the ventricular antiarrhythmic effects of beta-blocking drugs in man is at present unknown.