Prolongation of the P-R interval has been reported in uncomplicated hyperthyroidism,1-5 and some of the patients show, in addition, large and tall P waves in leads II, III, and aVF.
Transient complete heart block has been described also in hyperthyroid patients, particularly in association with acute inflammatory diseases.6-11 Electrocardiographic abnormalities usually disappear when the patients become euthyroid.
We are reporting the cases of two hyperthyroid patients without signs of heart disease who had first-degree heart block with tall and large P waves; in one of these patients, a left bundle-branch block and a transient complete heart block with Stokes-Adams episodes also occurred without clear-cut evidence of acute inflammatory disease.
Both patients eventually showed a normal electrocardiographic pattern when they became euthyroid.
—A 19-year-old woman was admitted with symptoms of weakness, fatigue, fine tremors, and palpitations. She had been found to be hyperthyroid one
Campus S, Rappelli A, Malavasi A, Satta A. Heart Block and Hyperthyroidism: Report of Two Cases. Arch Intern Med. 1975;135(8):1091–1095. doi:10.1001/archinte.1975.00330080093015
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