ELECTROCARDIOGRAPHIC VOLTAGE CHANGES DURING HYPER-THYROIDISM

Abstract

ECG of 67 thyrotoxic patients were studied and subsequent ECG during euthyroidism in 16 patients permitted an analysis of voltage changes. Decreases in voltages after radioiodine therapy were significant (P < 0.01) for the P wave in lead V1, R wave in leads II, AVF, V4, V5 and V6, maximal RS wave and maximal R wave and were present in all but 1 patient. Criteria for left ventricular hypertrophy (sum of S wave in V1 plus R wave in V5 or V6 > 35 mm), present in 21% of patients, regressed in all 5 patients who had later ECG during euthyroidism. Left ventricular hypertrophy or high-voltage R waves in the absence of usual causes may suggest the presence of hyperthyroidism. The concept that cardiac voltage is determined in part by thyroid hormone is reviewed; this relationship may be the basis for increased voltage in hyperthyroidism and decreased voltage in hypothyroidism.