Second and third degree atrioventricular block with Graves' disease: a case report and review of the literature.

A previously healthy woman experienced Adams-Stokes attacks ten weeks after the initiation of antithyroid medication for Graves' disease. The patient manifested advanced atrioventricular (A-V) block requiring a temporary transvenous pacemaker. The site of heart block was localized to the A-V node by utilizing a His bundle electrogram. With control of the hyperthyroid state, normal A-V conduction was restored. Review of the literature identified twenty-five additional cases of second or third degree A-V block associated with Graves' disease, ten of whom had Adams-Stokes syncope or convulsive seizures. The A-V nodal block was reversible with cure of the primary endocrine disease. It is postulated that excessive thyroid hormone has a direct effect on the cardiac conduction system, specifically, the region of the A-V node and bundle of His. Recommendations are made regarding the recognition and management of patients at risk for developing heart block associated with Graves' disease.