The Bottom Line: Subclinical hyperthyroidism is associated with increased heart rate, atrial arrhythmias, increased LV mass, impaired ventricular relaxation, reduced exercise performance, and increased risk of cardiovascular mortality. Subclinical hypothyroidism is associated with impaired LV diastolic function and subtle systolic dysfunction and an enhanced risk for atherosclerosis and myocardial infarction.
Summary: Thyroid dysfunction causes remarkable cardiovascular derangements. Because signs and symptoms referable to the cardiovascular system may be the only manifestations of overt thyroid dysfunction and because persistent subclinical thyroid dysfunction may notably increase the cardiovascular risk, thyroid status should be systematically investigated in all patients with newly diagnosed or worsening cardiovascular disease, especially the elderly. In addition, patients with acute or chronic cardiovascular disorders have abnormalities in peripheral thyroid hormone metabolism that may alter cardiac function. The finding that administration of thyroid hormone or its analog 3,5-diiodothyropropionic acid may greatly benefit these patients should foster further investigation in this area.