[Prolonged hyperthyroidism and recurrent atrio-ventricular block].

The authors report the case of a patient with hyperthyroidism who had three episodes of grade 2 and 3 atrio-ventricular block over a 6-year period. After he recovered from hyperthyroidism, the atrio-ventricular conduction returned to normal and remained so throughout a 5-year follow-up. A grade 1 atrio-ventricular block is found in 6 to 8 p. 100 of hyperthyroid patients, but grade 2 and 3 blocks are rare in such patients. Case reports in which thyrotoxicosis alone seemed to be responsible for disorders of conduction are exceptional; frequently, other factors likely to induce such disorders were present. In 90 p. 100 of the cases hyperthyroidism was due to Graves' disease; it lasted for more than one year and thyrotoxicosis was often severe. These facts suggest the possibility of a thyrotoxic myocarditis and/or an autoimmune focal myocarditis. Although rare, atrio-ventricular block in hyperthyroid subjects is a possibility that warrants electrocardiographic monitoring, notably when negative dromotropic drugs are prescribed.