Assessment of cardiac reserve in patients with hyperthyroidism.

Radionuclide multigated cardiac imaging was performed to assess functional cardiac reserve in patients with hyperthyroidism. In 11 normal individuals, submaximl supine exercise increased heart rate (HR) by 60 percent, systolic blood pressure (BP) by 54 percent, and the left ventricular ejection fraction (LVEF) by 13 percent. All of these increments were statistically significant (p < 0.001). Eight patients with hyperthyroidism were studied. Their mean +/- standard error of the mean (SEM) serum thyroxine level was 17.7 +/- 0.5 micrograms percent. There was a negative correlation between serum thyroxine levels and LVEF, both at rest and during exercise, in the patients with hyperthyroidism. Our data suggest that hyperthyroidism is associated with impaired functional cardiac reserve.