Complete heart block complicating hyperthyroidism: a case report.

Complete heart block developed in a 29-year-old man with hyperthyroidism and acute febrile illness. The definite cause of acute febrile illness was unknown. The results of bacteriological and viral studies were negative. Endomyocardial biopsy revealed no evidence of carditis which is the common cause of heart block. All the abnormalities resolved completely after the fever subsided and the patient was treated with an antithyroid drug. Available information indicates that a high degree of heart block can sometimes occur in hyperthyroidism in either the presence or absence of additional factors which can independently impair atrioventricular conduction. This course of events which occurred in this patient suggest that complete heartblock may have been the direct manifestation of the hyperthyroid state, however, the acute febrile illness may have been an aggravating factor in the development of abnormal atrioventricular conduction.