The serum reverse triiodothyronine (rT₃) values of heart failure patients who died during hospitalization were found significantly higher than the upper limit of the biological reference interval in the clinical work of the author. The prediction of thyroid hormones, especially rT₃, on death during hospitalization of heart failure patients was rare reported in the previous studies, it is of great clinical significance to explore the indicators with predictive value for death during hospitalization in patients with heart failure.

To investigate the relationship between serum thyroid hormones and prognosis during hospitalization in patients with heart failure.

A total of 197 patients with heart failure admitted to Dongzhimen Hospital of Beijing University of Chinese Medicine from April 2019 to April 2022 were included in the study. Baseline data of the study subjects were collected by the electronic medical record system. Fasting venous blood of all subjects was collected within 24 h after admission for total triiodothyronine (TT₃), total thyroxine (TT₄), free triiodothyronine (FT₃), free thyroxine (FT₄), thyroid stimulating hormone (TSH), rT₃ and N-terminal brain natriuretic peptide precursor (NT-pro-BNP). Subjects were divided into death group (n=18) and non-death group (n=179) according to the occurrence of death during hospitalization. Multivariate Logistic regression analysis was used to investigate the influencing factors of death during hospitalization in patients with heart failure. Receiver operating curve (ROC curve) was plotted to evaluate the predictive value of related indicators on death during hospitalization in patients with heart failure, and the area under curve (AUC) of each indicator was calculated and compared by Delong test.

The age and rT₃ of death group were higher than those of non-death group, while FT₃, TT₃ and TSH of death group were lower than those of non-death group, with statistically significant differences (P<0.05). In the non-death group, 66 patients had normal thyroid function, 87 patients had low T₃ syndrome, 15 patients had high FT₄ alone, 3 patients had high TT₄ alone, 5 patients had both high TT₄ and FT₄, 1 patient had low TT₄ alone, 1 patient had high TT₃ alone, and 1 patient had high FT₃ alone. In the death group, 1 patient had normal thyroid function, 14 patients had low T₃ syndrome, and 3 patients had high FT₄ alone. There was significant difference in the incidence of low T₃ syndrome between the two groups (P<0.05). The results of multivariate Logistic regression analysis showed that rT₃ was an influencing factor for death during hospitalization in patients with heart failure〔OR=5.245, 95%CI (2.283, 12.050), P<0.05〕. ROC curve results showed that the AUC of rT₃ was 0.914〔95%CI (0.865, 0.962) 〕, which was higher than that of age (Z=3.137, P=0.002), FT₃ (Z=2.389, P=0.017), TT₃ (Z=2.123, P=0.034) and TSH (Z=3.056, P=0.002) .

Low T₃ syndrome may be a risk factor for death during hospitalization in patients with heart failure. Serum rT₃ is of high predictive value for the prognostic evaluation of patients with heart failure during hospitalization, which need more attention in clinical work.