Low tri-iodothyronine syndrome improve the risk prediction of mortality in patients with acute heart failure

Background Clinical studies have suggested that low tri-iodothyronine (T3) syndrome negatively affects the clinical outcomes of patients with acute heart failure (AHF). The aim of this prospective cohort study was to evaluate the effect of low T3 syndrome in terms of prognosis and risk predictive potential in AHF.Methods Low T3 syndrome was defined by a low free T3 level (<3.1 pmol/L) accompanied by a normal thyroid-stimulating hormone level. The association between the free T3 level and mortality and the incremental risk prediction were estimated in adjusted models.Results In total, 312 patients with AHF for whom detailed thyroid hormone profiles were available were prospectively enrolled. Seventy-two patients exhibited low T3 syndrome. Over a median follow-up period of 35 months, 121 cumulative deaths occurred. Cardiovascular death was observed in 94 patients. After extensive adjustment for confounders, the low T3 syndrome associated hazard ratio (95% confidence interval) was 1.74 (1.16-2.61, P =0.007) for all-cause mortality and 1.90 (1.21-2.98, P =0.005) for cardiovascular mortality. The regression splines suggested a negative linear relationship between the free T3 level and mortality risk. Considering reclassification, adding low T3 syndrome to the fully adjusted model improved the risk prediction for all-cause mortality (Integrated discrimination improvement [IDI] 2.0%, P = 0.030; net reclassification improvement [NRI] 8.9%, P = 0.232) and cardiovascular mortality (IDI = 2.5%, P = 0.030; NRI 21.3%, P = 0.013).Conclusions Low T3 syndrome reclassified risk prediction for mortality beyond traditional risk factors.