Association between Low Free Triiodothyronine Levels and Poor Prognosis in Patients with Acute ST-Elevation Myocardial Infarction

Abstract

Background: Low free triiodothyronine (fT3) levels are generally associated with poor prognosis in patients with heart diseases, but this is controversial and there is a lack of data about ST-elevation myocardial infarction (STEMI) in Chinese patients.

Objective: To assess the association between fT3 levels and the prognosis of patients with STEMI.

Methods: This was a prospective observational study of 699 consecutive patients with STEMI treated at the Xinqiao Hospital between January 1, 2013, and December 31, 2014. The patients were divided into the low fT3 (fT3 < 3.1 pmol/L; n = 179, 27.5%) and normal fT3 (fT3 ≥ 3.1 pmol/L; n = 473, 72.5%) groups according to fT3 levels at admission. Patients were followed up at 1, 3, 6, and 12 months for all-cause death and major adverse cardiac events (MACE).

Results: During the 1-year follow-up, there were 70 all-cause deaths (39.1%) in the low fT3 group and 40 (8.5%) in the normal fT3 group (P < 0.001). MACE occurred in 105 patients (58.7%) in the low fT3 group and 74 (15.6%) in the normal fT3 group (P < 0.001). Multivariate Cox proportional hazards regression analysis indicated that fT3 levels were independently associated with 30-day and 1-year all-cause death [30-day: hazard ratio (HR) = 0.702, 95% confidence interval (95% CI): 0.501-0.983, P = 0.04; 1-year: HR = 0.557, 95% CI: 0.411-0.755, P < 0.001] and MACE (30-day: HR = 0.719, 95% CI: 0.528-0.979, P = 0.036; 1-year: HR = 0.557, 95% CI: 0.445-0.698, P < 0.001).

Conclusion: Low fT3 levels were strongly associated with poor prognosis in patients with STEMI. Measurement of fT3 levels may be a valuable and simple way to identify high-risk STEMI patients.

Figure 1

Kaplan-Meier survival curves for (a) 30-day mortality, (b) 1-year mortality, (c) 30-day major adverse cardiac events (MACE), and (d) 1-year MACE in patients in the low and normal fT3 groups. The log-rank tests showed that all four parameters (mortality and MACE occurrence) were higher in the low fT3 group than in the normal fT3 group (all P < 0.001). After adjustment for age and sex, all associations remained significant, except for 30-day and 1-year mortality and 30-day MACE in female >75 years of age (all P > 0.05); only the difference in 1-year MACE remained significant (P = 0.019).