Evaluation of Levothyroxine Treatment for Subclinical Hypothyroidism and Its Impact on Cardiac Function: A Meta-analysis

Qiang ZhangQingyang LiuYiwen LaiZhimin WangXueying ChenWu JiabaoBingchen WeiYi WenTianshu Gao^*

• Liaoning University of Traditional Chinese Medicine, Shenyang, China

Abstract: Introduction: the clinical efficacy of levothyroxine (L-T4) in treating subclinical hypothyroidism (SH) and its specific effects on cardiac function remain controversial. Material and Methods: clinical studies on L-T4 for the treatment of SH were retrieved from online databases. Basic information from the literature, patient demographics, efficacy evaluation indicators (serum thyroid-stimulating hormone (TSH), free thyroxine (FT4), and FT3 levels), cardiac function assessment parameters (ejection fraction (EF) and E/A ratio), and cardiovascular parameters were collected. The quality of the studies was assessed utilizing the Risk of Bias Tool for Randomized Controlled Trials. Meta-analysis was conducted using RevMan5.3, with heterogeneity evaluated through Q-test and I² statistics, and publication bias analyzed employing funnel plots. Results: a total of 11 studies involving 1,915 patients with SH were included. Of these, 968 patients were in the L-T4 experimental group (EG) and 947 patients were in placebo control group (CG). The TSH levels in EG (MD=-2.80, 95% CI: -3.49 to -2.12; Z=8.01, P<0.00001) were markedly inferior to those in CG, while the FT4 levels (mean difference (MD) =3.14, 95% CI: 1.11 to 5.17; Z=3.03, P=0.002) were greatly superior in EG to CG. No significant differences were found between EG and CG in terms of FT3 levels (MD=0.12, 95% CI: -0.39 to 0.63; Z=0.46, P=0.65), EF (MD=-0.40, 95% CI: -2.01 to 1.21; Z=0.49, P=0.63), or E/A ratio (MD=0.00, 95% CI: -0.05 to 0.06; Z=0.17, P=0.86). Conclusion: L-T4 treatment effectively improves thyroid function indicators in patients with SH, but there is no clear evidence of significant changes in cardiac function.