Postural heart block.

A patient presented with orthostatic dizziness and syncope caused by postural heart block. When the patient was supine, atrioventricular conduction was normal and he was asymptomatic; when he was standing he developed second degree type II block and symptoms. The left bundle-branch block on his electrocardiogram and intracardiac electrophysiological study findings suggest that this heart block occurred distal to the His bundle. Orthostatic symptoms are usually presumed to be secondary to an inappropriate distribution of intravascular volume or to autonomic nervous system abnormalities. As shown in this patient, these symptoms may be the result of orthostatic heart block. Ambulatory monitoring may be useful in patients with orthostatic neurological symptoms, particularly when conduction abnormalities are present on the electrocardiogram.