Thyroid and the Heart: A Historical Perspective

It has long been known that thyroid hormones exert marked effects on the cardiac structure and function and that most of its clinical signs and symptoms occur as a consequence of thyroid hormone action in the heart and cardiovascular system (Klein and Ojamaa, N Engl J Med 344:501–509, 2001; Razvi et al., J Am Coll Cardiol 24:1781–1796, 2018). Since the first connection between the thyroid and the heart by Caleb Hillier Parry (Underwood 2:110, 1825), in 1825, many studies in humans and in animals have documented the heart abnormalities in consequence of thyroid hormone excess or deficiency. Typically, hyperthyroidism is often associated with increased cardiac contractility and cardiac output, decreased peripheral vascular resistance, systolic arterial hypertension, tachycardia, atrial fibrillation, left ventricular hypertrophy, and heart failure (Kahaly and Dillmann, Endocr Rev 26:704–728, 2005). On the other hand, hypothyroidism is associated with decreased cardiac contractility, increased peripheral vascular resistance, diastolic arterial hypertension, bradycardia, dilatation of all chambers, pericardial effusion, and heart failure (Kahaly and Dillmann, Endocr Rev 26:704–728, 2005). All of these abnormalities reverse to a condition close to normal after the appropriated treatment and reestablishment of the euthyroid state.