Complete heart block with myocardial membrane-bound glycogen and normal peripheral α-glucosidase activity

Although many metabolic and infiltrative diseases are associated with conduction disturbances in children and young adults, these conduction abnormalities are rarely the presenting feature of disease. We describe a young man presenting with complete atrioventricular nodal block in whom an endomyocardial biopsy showed membrane-bound glycogen resembling glycogen storage disease type II (GSD-II, Pompe disease). The glycogenosis appeared to be limited to the myocardium because the rest of the physical examination, as well as histology and enzyme studies of muscle and of skin fibroblasts, were normal.