Syncope induced by propranolol in hypertrophic cardiomyopathy.

A patient with chest pain was found to have obstructive hypertrophic cardiomyopathy. After the first oral dose of propranolol, syncope developed together with atrioventricular block. An electrophysiologic study revealed an intermittent advanced (His-Purkinje) block within the atrioventricular conduction system. Caution is recommended when treatment is initiated in patients with hypertrophic cardiomyopathy in whom there is any suspicion of abnormalities in the atrioventricular conduction tissues.