Enhanced left ventricular diastolic function in hyperthyroidism: noninvasive assessment and response to treatment

Hyperthyroidism is associated with a marked effect on the cardiovascular system. Despite enhanced resting ventricular systolic performance, thyrotoxicosis has been implicated as a primary cause of cardiomegaly, congestive heart failure, and decreased exercise tolerance. To further assess potential alterations in ventricular function we have noninvasively studied diastolic performance in nine newly diagnosed and untreated hyperthyroid patients. Parameters including diastolic flow velocities, isovolumic relaxation time (IVRT), and the rate of diastolic flow deceleration were compared to those of an age- and sex-matched control population, and then repeat determinations were made after beta-adrenergic blockade and again when the patients were chemically and clinically euthyroid. Before treatment the IVRT was 33.0 ms, which was significantly (P less than 0.005) shorter than the control value (57.9 ms) and in combination with other measures of diastolic function indicated enhanced left ventricular relaxation. beta-Adrenergic blockade slowed the resting heart rate from 97 to 80 beats/min (P less than 0.005) and partially normalized the rate of diastolic deceleration, but had no effect on the IVRT (33.8 ms). When patients were euthyroid, the IVRT was 51.7 ms, and other measures of diastolic performance were the same as those in controls. The current data assessing resting diastolic function in hyperthyroidism are similar to those previously reported for systolic function. Our findings of enhanced cardiac diastolic performance do not support the hypothesis that thyrotoxicosis is associated with compromised left ventricular function and suggest the possibility that the cardiac symptoms that accompany hyperthyroidism may be due to noncardiac mechanisms.