The diminished cardiac performance in severe thyrotoxicosis. Parabolic correlation of LVET/PEP to the circulating levels of thyroid hormones.

Fifteen patients with thyrotoxicosis, 8 patients with primary hypothyroidism and 15 normal subjects were studied to assess the correlation between systolic time intervals and serum levels of thyroid hormones. In hypothyroid patients, prolongation of PEPc (corrected pre-ejection period), shortening of LVETc (corrected left ventricular ejection time) and low values of LVET/PEP ratio and cardiac output were improved after restoration of thyroid function. In thyrotoxic patients, shortening of PEPc, high values of LVET/PEP ratio and cardiac output were normalized after correction of thyroid function. As contrasted with these observations, in 5 severely thyrotoxic patients, low values of LVET/PEP ratio and cardiac output for thyrotoxicosis were observed; these were not significantly decreased after antithyroid drug treatment, but appeared to have a tendency to increase. Performing polynomial regression analysis, a significant parabolic correlation was found between LVET/PEP and serum T4 or T3 (p less than 0.0001). From these results, it might be concluded that large amounts of thyroid hormones suppress cardiac performance.