Dilated cardiomyopathy masquerading as long QT syndrome.

Atrioventricular block has been described in association with cases of long QT syndrome and mortality is increased in this subgroup. We describe an infant with congenital QT prolongation and atrioventricular block with normal cardiac function, leading to the initial diagnosis of long QT syndrome. She subsequently developed dilated cardiomyopathy requiring cardiac transplantation. We postulate that the presenting electrocardiograph abnormalities were early manifestations of the myocardial disease, preceding the development of myocardial dysfunction by several months. The need for heightened surveillance in cases of QT prolongation with atrioventricular block is amplified by the possibility of an evolving cardiomyopathy.