M1. Association between Subclinical Hypothyroidism and Heart Failure: A Systematic Review and Meta-Analysis

The correlation between subclinical hypothyroidism and heart failure has been increasingly investigated, but still controversial. We performed a systematic review and meta-analysis to evaluate the association between subclinical hypothyroidism and the incidence of heart failure.

Two reviewers systematically searched literature evaluating the association between subclinical hypothyroidism and heart failure on PubMed from inception to June 2021. Subclinical hypothyroidism was defined as thyroid-stimulating hormone (TSH) of 4.5 to 19.9 mIU/L with normal T4 level in the absence of symptoms. The quality of the studies was reported using the Newcastle-Ottawa scale (NOS). A meta-analysis was conducted using RevMan 5.4 software by analyzing the hazard ratio (HR) with 95% confidence intervals (95%CIs) using a random and fixed-effects model. 

A total of six cohort studies involving 602,176 subjects were included. Among the participants, 14,995 (2.5%) had subclinical hypothyroidism. Our pooled analysis showed that individuals with subclinical hypothyroid had an increased risk of heart failure compared to those with euthyroid (HR = 1.03; 95%CI = 0.95-1.11, p = 0.50); however, it was not statistically significant. Furthermore, subgroup analysis was done based on TSH level divided into 4.5-6.9 mIU/L, 7.0-9.9 mIU/L, and ≥10.0 mIU/L. Increased risk of heart failure was significantly associated with TSH level of ≥ 10.0 mIU/L (HR = 1.93; 95%CI = 1.24-3.01, p = 0.004).

Higher TSH level in subclinical hypothyroidism is associated with an increased risk of heart failure, particularly for TSH ≥10 mIU/L.