Effects of thyroxin therapy on cardiac function in patients with subclinical hypothyroidism: index of myocardial performance in the evaluation of left ventricular function

Objective: We investigated the effects of thyroxine (T4) therapy on the cardiac function in subclinical hypothyroidism (SHT) by using the index of myocardial performance (IMP) and the conventional echocardiographic parameters. Methods: Forty-five SHT patients (F/M:38/7, age 39.9±7.9) and 29 healthy subjects (F/M:25/4, age 38.3±8.6) were studied. Patients were randomly assigned, in a double-blind manner to receive T4 therapy (group I) or a placebo (group II) and for a period of up to 12 months, were followed up using thyroid function tests and both conventional and Doppler echocardiographic measurements. Results: At the baseline, the SHT patients has a significantly higher isovolumic relaxation time (IRT) (98.3±23.7 vs. 81.7±14.7<0.01), IMP (0.52±0.06 vs. 0.42±0.05; P<0.001), A max (late mitral peak velocity) (83.4±12.6 vs. 74.3±13.5; P<0.01) and significantly lower (early mitral peak velocity) Emax/Amax ratio (1.19±0.18 vs. 1.34±0.17; P<0.01) than the individuals in the control group. In group I, the thyroid hormone profile became normalized after 1 year of L-T4 therapy, but there was no significant change in the left ventricular (LV) morphology or systolic function. After 1 year of follow-up, group I showed a significant reduction of MPI (0.53±0.05 vs. 0.42±0.07; P<0.001), Amax (84.2±13.7 vs. 74.5±11; P<0.001) and IRT (98.6±23.7 vs. 82.9± 23.3; P<0.001) along with a normalization of the E/A ratio (1.17±0.16 vs. 1.33±0.19; P<0.001). Conversely, no change was observed in group II. Conclusions: An impairment of left ventricular diastolic function, which may be reversible with T4 therapy, was observed in the SHT patients, and IMP may be useful in the evaluation of LV myocardial dysfunction in these patients.