Complete heart block complicating thyrotoxicosis.

.~ SUMMARY Two cases of complete heart block complicating thyro­ toxicosis are recorded. In both cases intercurrent febrile illnesses were related to the development of this com­ plication. It appears that while first and second degree atrioventricular block may occur not uncommonly in uncomplicated thyrotoxicosis, the presence of an additional factor which may further compromise atrioventricular conduction, is required for the development of complete heart block. S. Afr. Med. l., 47, 513 (1973). Whereas the association of first and second degree atrioventricular (A V) block with thyrotoxicosis is well recognized,' complete (third degree) A V block is an infrequently reported association. Before 1937, II cases were reported in which the diagnosis of the thyrotoxi­ cosis was based on .clinical grounds, in some instances supported by basal metabolic measurements' Recently the first 2 cases of complete heart block in association with biochemically proved thyrotoxicosis were reported,' and in this paper we document the case histories of a further 2 patients in whom this association was noted.