Effect of Levothyroxine on Cardiac Function and Structure in Subclinical Hypothyroidism: A Double Blind, Placebo-Controlled Study

Abstract

Subclinical hypothyroidism (sHT) affects 5-15% of the general population; however, the need of lifelong L-T(4) therapy is still controversial. As myocardium is a main target of thyroid hormone action, we investigated whether sHT induces cardiovascular alterations. Twenty sHT patients were randomly assigned to receive placebo or L-T(4) therapy and were followed for 1 yr. Twenty sex- and age-matched normal subjects served as controls. Doppler echocardiography and videodensitometric analysis were performed in all subjects. Myocardium textural parameters were obtained as mean gray levels, which were then used to calculate the cyclic variation index (CVI; percent systolic/diastolic change in mean gray levels). Patients had a significantly higher isovolumic relaxation time (3.1 +/- 0.5 vs. 2.6 +/- 0.6; P < 0.03), peak A (0.77 +/- 0.16 vs. 0.56 +/- 0.13 m/s; P < 0.01), and preejection/ejection time (PEP/ET) ratio (0.72 +/- 0.05 vs. 0.57 +/- 0.06; P < 0.03) and a lower CVI (P < 0.0001) than controls. CVI was inversely related to TSH level (P < 0.0001) and PEP/ET ratio (P < 0.01). L-T(4)-treated patients showed a significant reduction of the PEP/ET ratio (P < 0.05), peak A (P < 0.05), and isovolumic relaxation time (P < 0.05) along with a normalization of CVI. Conversely, no changes were observed in the placebo-treated group. In conclusion, sHT affects both myocardial structure and contractility. These alterations may be reversed by L-T(4) therapy.

Evaluation of Cardiovascular Status in Thyroid Disorders

“…Rawat et al [17] also reported significant increase in LVPW in hypothyroid subjects. Bello et al [18] and Monzani et al [19] did not find similar incidence.…”

Coronary Flow Reserve Is Impaired in Subclinical Hypothyroidism

“…16,17 However, this suggestion was not confirmed by other studies. 13,15 Second, previous studies have clearly shown that patients with SHT have left ventricular diastolic dysfunction at rest that is reversible with thyroxine therapy 18,19 and systolic dysfunction on effort, which may result in poor physical exercise capacity. In the present study, we revealed that left ventricular diastolic function was impaired in patients with SHT as compared with controls.…”

Clinical practice guidelines for the management of hypothyroidism

“…SH has been consistently associated with mild diastolic dysfunction at rest and on effort, but the studies are limited by their small size, design and selection bias (148)(149)(150)(151)(152)(153)(154) (B,B,B,B,C,C,C,). In a moderate-sized community-based sample, no association was observed between higher serum TSH concentrations and echocardiographic measurements (155) (A).…”