Syncope with prolonged QT interval.

Four children with syncope had a prolonged QT interval on the electrocardiogram. Neurologic studies were negative. One patient had associated deaf mutism, one had a family history of sudden death and prolonged QT interval, and two had ventricular arrhythmias while being monitored in the hospital. Treatment with propranolol hydrochloride eliminated the syncope in all patients, although the ECGs remained abnormal.