THE ELECTROCARDIOGRAM IN MYXOEDEMA

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Abstract
The changing pattern of the electrocardiogram was studied in 7 patients with myxedema before and during the early stages of thyroid substitution therapy. In 1 patient a previously masked left strain pattern became manifest 48 hr. after the start of therapy with a rapidly acting thyroid compound (tri-iodothyronine). In 4 patients the cardiogram displayed distinct changes 24 hr. (or earlier) after the 1st dose of 40 [mu]g (or less) of tri-iodothyronine, this being the 1st sign of effective replacement therapy. In 2 of them the tracing progressively reverted to normal while the clinical signs also regressed. In the other 2 patients the early electrocardiographs response was followed by a period of unresponsiveness during which the other symptoms and signs of myxedema disappeared. In these last 2 patients the electrocardiogram displayed a delayed response indicating that in them the heart muscle was comparatively more refractory to thyroid hormone than were the other peripheral tissues. The implications of these observations are discussed. It is emphasized that the short-term effects of small amounts of thyroid upon the myxedema electrocardiogram argue in favor of the following a primary action of thyroid hormone upon the cardio-circulatory system independent of the metabolic activities of the hormone; minute changes in the intracardlac water balance as the patho-physlological foundation of the occurrence and regression of the electrocardiographic anomalies in myxedema; the suitability of rapidly-acting thyroid compounds for the introduction of therapy, in contradistinction to their inferiority to desiccated thyroid for purposes of long-term treatment. The role of the peripheral target organs in determining the mode and extent of hormonal activity is discussed afresh in the light of these observations.

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