Alterations in left ventricular mass and performance in patients treated effectively for thyrotoxicosis. A comparative echocardiographic study.

The effect of successful therapy for thyrotoxicosis on left ventricular mass in human subjects has not been documented. Furthermore, assessment of intrinsic left ventricular pathophysiologic changes associated with hyperthyroidism has been limited by the difficulty of justifying invasive studies in these patients. Echocardiography is a suitable method of assessing cardiac dimensions and function in patients with thyrotoxicosis.Echocardiographic studies were performed on 15 thyrotoxic patients, mean age 36 years, prior to and 12 months after the initiation of effective antithyroid therapy. The clinical diagnosis and results of therapy were confirmed by the measurement of serum thyroxine levels. Therapy produced a significant decrease in heart rate (108 to 78 beats/min; p < 0.001), arterial pulse pressure (60 to 45 mm Hg; p < 0.02) and echocardiographically estimated cardiac output (6.49 to 3.84 liters/min; p < 0.001).There was a significant reduction in left ventricular mass from 135 to 96 g (p < 0.001). The mean velocity of circumferential fiber shortening was reduced from 1.13 to 0.81 cire/sec (p < 0.001), a change that correlated significantly with the decrease in heart rate (r = 0.66, p < 0.01). A minimal reduction in left ventricular diameter was found (4.7 to 4.5 cm; p < 0.05), whereas end-systolic diameter and shortening fraction remained unchanged. Four patients failed to repond to initial antithyroid therapy. The size of the left ventricular mass increased in these patients after unsuccessful therapy.This study shows that effective treatment for thyrotoxicosis is associated with a reduction in the size of the left ventricular mass. The correlation between alterations in heart rate and mean velocity of circumferential fiber shortening following effective therapy suggests that the changes in myocardial contractility in these hyperthyroid patients may be predominantly a negative chronotropic effect. Minimal changes in end-diastolic diameter without changes in end-systolic diameter tend to confirm that myocardial contractility is altered by the state of thyroid activity independent of the Frank-Starling mechanism.