Acute hypothyroidism slows the rate of left ventricular diastolic relaxation

Abstract

The effect of acute thyroid hormone deficiency on left ventricular diastolic filling was studied by radionuclide ventriculography with simultaneous right heart catheterization in nine athyreotic patients without cardiovascular disease. The patients were studied when they were hypothyroid and when they were euthyroid on replacement therapy. Peak filling rate and the time to peak filling were used to characterize diastolic function. The time to peak filling was defined as the interval from end-systole on the radionuclide time–volume curve to the time of occurrence of peak filling. The peak filling rate was determined in absolute terms from the normalized radionuclide peak filling rate and from the end-diastolic volume, which was derived from the radionuclide ejection fraction and from the thermodilution stroke volume. In all patients, the values for peak filling rate were lower in the hypothyroid than in the euthyroid state (287 ± 91 mL/s vs. 400 ± 118 mL/s, Δ = 41 ± 13%, p < 0.01). Peak filling always occurred during the first half of the diastolic interval. The time to peak filling was not significantly affected by the thyroid state (170 ± 10 ms vs. 159 ± 21 ms, Δ = 7 ± 10%). Left ventricular filling pressure as reflected by the pulmonary capillary wedge pressure and end-systolic volume were similar in both thyroid states (6 ± 2 mmHg vs. 8 ± 2 mmHg (1 mmHg = 133.32 Pa) and 32 ± 11 mL vs. 32 ± 7 mL, respectively). The data suggest that the rate of active diastolic relaxation is decreased in short-duration hypothyroidism. This may be due to a depressed activity of the sarcoplasmic reticular calcium pump which is under thyroid control.Key words: hypothyroidism, left ventricular diastolic function, radionuclide ventriculography.