Value of the fT3/fT4 ratio and its combination with the GRACE risk score in predicting the prognosis in euthyroid patients with acute myocardial infarction undergoing percutaneous coronary intervention: a prospective cohort study

BACKGROUND: Thyroid hormones deeply influence the cardiovascular system; however, the association between the fT3/fT4 ratio and the clinical outcome in euthyroid patients with acute myocardial infarction (AMI) undergoing percutaneous coronary intervention (PCI) is not well defined. Therefore, the present study aimed to assess the prognostic performance of the fT3/fT4 ratio in predicting the long-term prognosis in euthyroid patients with AMI undergoing PCI. METHODS: In a prospective cohort study with a 1-year follow-up, according to the clinical end point, 953 euthyroid individuals (61.0 ± 11.6; female, 25.8%) were divided into two groups: (1) the survival group (n = 915) and (2) the death group (n = 38). RESULTS: According to Cox regression multivariate analysis, fT4 (HR: 1.249, 95% CI: 1.053–1.480, p = 0.010) and the fT3/fT4 ratio (HR: 3.546, 95% CI: 1.705–7.377, p = 0.001) were associated with an increased risk of 1-year all-cause mortality. The prognostic performance of the fT3/fT4 ratio was similar to the Global Registry of Acute Coronary Events (GRACE) score in predicting 1-year all-cause mortality (C-statistic: z = 0.261, p = 0.794; IDI: -0.017, p = 0.452; NRI: -0.049, p = 0.766), but better than fT4 (C-statistic: z = 2.438, p = 0.015; IDI: 0.053, p = 0.002; NRI: 0.656, p < 0.001). The fT3/fT4 ratio also significantly improved the prognostic performance of the GRACE score (GRACE score vs GRACE score + fT3/fT4 ratio: C-statistic: z = 2.116, p = 0.034; IDI: 0.0415, p = 0.007; NRI: 0.614, p < 0.001). CONCLUSIONS: In euthyroid patients with AMI undergoing PCI, the fT3/fT4 ratio was an independent predictor of 1-year all-cause mortality. Its prognostic performance was similar to the GRACE score, and also improved its prognostic performance (GRACE score vs GRACE score + fT3/fT4 ratio).