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August 24, 1970

Hypercalcemia, Heart-Block, And Hyperthyroidism

Author Affiliations

Bethlehem, Pa

JAMA. 1970;213(8):1342. doi:10.1001/jama.1970.03170340064017

To the Editor.—  In their paper, "Complete Heart Block Complicating Hyperthyroidism" (212:2117, 1970), the authors suggest that other factors, such as infection or digitalis therapy, may contribute to the development of the arrhythmia. Another predisposing factor might be hypercalcemia which occurs in about 15% of the patients with hyperthyroidism.1 Variations in the calcium concentration of cardiac muscle are fundamental for excitation-contraction coupling in muscle and may represent the basic mechanism for drug action.2

Report of a Case.—  A 52-year-old woman was recently hospitalized at this institution following the onset of atrial fibrillation with a ventricular response of 140 beats per minute. There was no history of previous cardiac disease and the only other complaint was a weight loss of 140 lb in six months prior to admission. Results of routine laboratory studies were normal. (The serum calcium level determination was not requested.)Digoxin therapy, 1.5 mg in