Impact of low triiodothyronine syndrome on long-term outcomes in patients with myocardial infarction with nonobstructive coronary arteries

BACKGROUND: Low triiodothyronine syndrome (LT3S), frequently seen in patients with acute myocardial infarction (AMI), has been regarded as a predictor of poor outcomes after AMI. However, little is known about the prognostic value of LT3S in euthyroid patients with myocardial infarction with nonobstructive coronary arteries (MINOCA). METHODS: A total of 1162 MINOCA patients were enrolled and divided into LT3S and no-LT3S groups. LT3S was defined as decreased free T3 (fT3 < 2.36 pg/mL) with normal values of thyroid-stimulating hormone. The primary endpoint was a composite of major adverse cardiovascular events (MACE), including all-cause death, nonfatal MI, stroke, revascularization, and hospitalization for unstable angina or heart failure. Kaplan–Meier, Cox regression, propensity score matching (PSM), and receiver-operating characteristic analyses were performed. RESULTS: Patients with LT3S (prevalence of 17.5%) had a significantly higher incidence of MACE (19.6% vs. 12.9%; p = .013) than patients without during the median follow-up of 41.7 months. LT3S was closely associated with an increased risk of MACE even after multivariable adjustment (HR 1.50, 95% CI: 1.03–2.18, p = .037). After PSM, 197 pairs of patients with or without LT3S were identified, and LT3S remained a robust risk factor of worse outcomes (HR 1.53, 95% CI: 1.02–2.65, p = .042). Moreover, LT3S had an area under the curve (AUC) of 0.60 for predicting MACE. When adding LT3S to the thrombolysis in myocardial infarction (TIMI) risk score, the combined model yielded a significant improvement in discrimination for MACE. CONCLUSIONS: LT3S was independently associated with poor outcomes after MINOCA. Routine assessment of LT3S may provide valuable prognostic information in this specific population.