Reversible Atrioventricular Block in Myxedema

¹ Cardiovascular Units, Boston University and Harvard Medical Services, Boston City Hospital; Department of Cardiology, the Memorial Hospital, Worcester, Mass

Disturbances in atrioventricular conduction with myxedema have been described. The present study describes three such cases with varying degrees of atrioventricular block, which reverted to normal sinus rhythm following thyroid hormone replacement. There is a strong likelihood that myxedema and reversible atrioventricular block following therapy represent a significant association. In view of the rarity of pharmacologic reversibility in atrioventricular block, the need to screen patients for myxedema is stressed. Microscopic examination of the cardiac muscle in one case revealed the presence of PAS positive material in a perinuclear distribution in the cytoplasm of a myocardial fiber.