Cardiac Systolic Time Intervals in Thyroid Disorders

Hyperthyroidism and hypothyroidism, particularly when long-standing or severe, produce substantial changes in cardiac performance that are largely reversible with appropriate therapy. Recently, it has become possible to quantitate the effects of thyroid hormone deficiency or excess on the heart by measurement of systolic time intervals (STI). Furthermore, serial STI measurements can provide insight into the time course and efficacy of therapy for these thyroid disorders. Thus, the STI offer a simple and inexpensive noninvasive technique for assessing the cardiac status of patients with certain thyroid diseases. Although other noninvasive tests of cardiac function have also become available in recent years, the STI most likely will remain a major method for following up the cardiac status of patients with hyperthyroidism or hypothyroidism, principally because of the high degree of sensitivity of the test to the effects of pharmacologicn intervention. However, as with any other laboratory test, the clinician must be aware