Evaluation of the effect of L-thyroxin therapy on cardiac functions by using novel tissue Doppler-derived indices in patients with subclinical hypothyroidism.

Objectives: Subclinical hypothyroidism (SH) is characterized by normal serum free T4 (fT4), free T3 (fT3) levels and increased serum thyroid stimulating hormone (TSH) levels.The aim of this study was to assess the validity of tissue Doppler imaging (TDI) in evaluating cardiac effects of SH and to demonstrate the improving effects of L-thyroxin(L-T4) on TDI parameters.

Methods: Twenty-seven patients with SH and 22 healthy controls were evaluated by standard echocardiography and TDI. TDI-derived systolic velocities [isovolumic myocardial acceleration (IVA), peak myocardial velocity during isovolumic contraction (IW), peak systolic velocity during ejection period (Sa)] and diastolic indices (peak early (Ea) and late diastolic (Aa) velocities, Ea/Aa, E/Ea ratios and Tei index) were measured. After restoring euthyroidism, all measurements were repeated.

Results: At baseline, left ventricular (LV) systolic velocities (IW and IVA) and diastolic indices were significantly impaired in the SH group. After L-T4 therapy, left ventricular systolic and diastolic functions were improved. Right ventricular (RV) systolic velocities were similar between the study group and the healthy controls but diastolic functions were impaired in the SH group, at baseline. Tei index of the RV was improved after L-T4 therapy. RV IVA remained unchanged after hormone replacement therapy.

Conclusions: SH is associated with biventricular systolic and diastolic dysfunction. IVA which is an accurate estimate of subclinical systolic dysfunction, was significantly impaired in the left ventricle and had improved after L-T4 therapy. We found that IVA is able to detect early effects of subclinical hypothyroidism on LV systolic functions and L-T4 therapy can improve ventricular functions.