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ELECTROCARDIOGRAPHIC CHANGES IN HYPERTHYROIDISM AFTER ADRENERGIC BLOCKADE WITH RESERPINE AND PROPRANOLOL

The type and the frequency of changes seen in the electrocardiograms of patients with hyperthyroidism treated with reserplne and propranolol is little known. In this study, electrocardiograms were recorded in 15 hyperthyroid patients before and after treatment with reserpine and propranolol alternatively for a period of two weeks each on a double‐blind basis. Typical electrocardiographic changes in hyperthyroidism such as increased heart rate, an increase in height and duration of P wave in lead II, an increase in total voltage of St and RB and in QTc interval were noted in patients before treatment. It was found in our present study that the electrocardiographic changes other than heart rate were not corrected by either reserpine or propranolol therapy though it was well known that similar electrocardiographic changes were significantly corrected when euthyroidism was achieved by specific antithyroid treatment. Adequate adrenergic blockade with reserpine or propranolol only slowed the heart rate but did not revert the tachycardia completely back to normal. These findings support the concept that the tachycardia in hyperthyroidism is caused partly by the direct action of the thyroid hormone on the myocardium and partly by increased sensitivity to the catecholamines, whereas the other electrocardiographic changes are mainly due to the direct action of thyroid hormone on the myocardium. As both reserpine and propranolol block the action only of catecholamines at the adrenergic receptors and do not in any way interfere with the production of thyroid hormones, therefore they do not correct the cardiac abnormalities due to direct action of thyroid hormones.