[Hyperthyroidism and atrioventricular block. Pathogenic hypothesis. Apropos of a case and review of the literature].

The authors report the case of a 26-year old male patient who had Graves' disease with a first degree atrioventricular block (AVB) and intermittent episodes of a second degree AVB of the Lucciani-Wenckebach type. These disorders of conduction had features characteristic of a nodal block and disappeared after treatment of the hyperthyroidism. The pathogenesis of atrioventricular conduction disorders in hyperthyroidism remains controverted. The authors put forward the following hypothesis: under the influence of thyroid hormones in excessive amounts, the autonomic nervous system would act by reciprocal excitation and exacerbate a patent or latent hypervagotonia which was pre-existent to the hyperthyroidism. This hypothesis needs to be tested by intracardiac electrophysiological studies with atrial stimulation.