Subclinical hypothyroidism: a new predictor of heart failure with improved ejection fraction in HFrEF patients

Heart failure (HF) with improved ejection fraction (HFimpEF) has gradually attracted widespread attention in recent years for its better clinical prognosis. In this study, we attempted to investigate the relationship between subclinical hypothyroidism (SCH) and HFimpEF. This study retrospectively collected clinical data on patients with HF with reduced ejection fraction (HFrEF) hospitalized at the First Affiliated Hospital of USTC from March 2015 to September 2023, and divided into two groups as euthyroidism or SCH according to the baseline thyroid function. Then patients were further categorized into HFimpEF (follow-up LVEF > 40% and absolute increase ≥ 10%) and persistent HFrEF based on their LVEF on the echocardiograms during the follow-up period. Afterward, logistic regression was used to estimate the effect of SCH on HFimpEF. A total of 916 patients with HFrEF met the inclusion and exclusion criteria, and 396 patients (43.2%) progressed to HFimpEF status during the follow-up period. Compared with HFrEF patients, the prevalence of SCH is lower in HFimpEF patients (9.3% vs. 14.4%, P = 0.020). Univariate logistic regression analysis indicates that SCH was a potential predictor for HFimpEF (OR: 0.612 [95% CI 0.403-0.928], P = 0.021). After adjusting for multiple factors in logistic regression, the odds ratios of HFrEF patients with SCH progressing to HFimpEF decreased by 37.8% (OR: 0.622 [95% CI 0.397-0.974], P = 0.038) compared with patients with euthyroidism. This study suggests that thyroid function affects the improvement of cardiac function in patients with HFrEF and SCH is an independent predictor for HFimpEF.