TOPLINE

In patients with heart failure with mildly reduced ejection fraction (HFmrEF), subclinical hypothyroidism, subclinical hyperthyroidism, and low triiodothyronine (T3) syndrome were independent predictors of long-term all-cause mortality but were not associated with the risk for HF-related rehospitalisation.

METHODOLOGY

• Researchers evaluated how thyroid function affected clinical outcomes in 1568 patients hospitalised with HFmrEF, using data from a large single-centre registry between 2016 and 2022.
• Patients were grouped by thyroid function: euthyroidism (n = 1186; median age, 75 years), subclinical hypothyroidism (n = 95; median age, 74 years), subclinical hyperthyroidism (n = 139; median age, 77 years), and isolated low T3 syndrome (n = 148; median age, 77 years).
• Euthyroidism and the subclinical conditions were defined using thyroid-stimulating hormone and free thyroxine levels, and isolated low T3 syndrome was defined using free T3 and thyroxine levels.
• HFmrEF was diagnosed according to the 2021 European Society of Cardiology guidelines for the diagnosis and treatment of acute and chronic HF.
• The primary outcome was all-cause mortality at 30 months; secondary outcomes included in-hospital mortality and all-cause mortality at 12 months and HF-related rehospitalisation at 12 and 30 months.

TAKEAWAY

• At 30 months, the rate of all-cause mortality was significantly higher in patients with low T3 syndrome, subclinical hypothyroidism, and subclinical hyperthyroidism than in those with euthyroidism (51.4%, 38.9%, and 36.7%, respectively, vs 26.6%; P = .001). Similar findings were observed for the rates of in-hospital mortality and all-cause mortality at 12 months.
• In a multivariable Cox regression analysis, subclinical hypothyroidism (adjusted hazard ratio [aHR], 1.454; P = .049), subclinical hyperthyroidism (aHR, 1.458; P = .026), and isolated low T3 syndrome (aHR, 1.594; P = .002) were independent predictors of all-cause mortality at 30 months.
• Low T3 syndrome was linked to a worse prognosis than subclinical hyperthyroidism (aHR, 1.553; P = .015).
• At 30 months, patients with low T3 syndrome, subclinical hypothyroidism, and subclinical hyperthyroidism had higher rates of major adverse cardiac and cerebrovascular events (MACCE) than those with euthyroidism (56.1%, 43.2%, and 41.0%, respectively, vs 34.3%; P = .001). No significant association was seen between thyroid status and the risk for HF-related rehospitalisation at 30 months.

IN PRACTICE

"In our analysis, clinical outcomes, including in-hospital, long-term mortality, and MACCE, were more frequent in HFmrEF patients with subclinical hypothyroidism as well as those with isolated low T3 syndrome," the authors wrote.

"Further studies are warranted to determine optimal treatment strategies for these conditions in patients with HFmrEF in order to improve clinical outcomes," they added.

SOURCE

This study was led by Mohammad Abumayyaleh, Department of Cardiology, Haemostaseology and Medical Intensive Care, University Medical Centre Mannheim, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany. It was published online on July 13, 2026, in Endocrine.

LIMITATIONS

The retrospective design may have introduced confounding. The study lacked data on the effects of thyroid hormone therapy on outcomes and the reasons for thyroid dysfunction. Thyroid status was classified based only on biochemical parameters.

DISCLOSURES

The study received open access funding from Projekt DEAL. The authors declared having no conflicts of interest.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.