BACKGROUND: Previous studies have suggested that hypothyroidism correlated with 
coronary heart diseases (CHD) mortality in long-term cohort, but whether the 
thyroid function status is associated with myocardial injury in acute 
ST-elevation myocardial infarction (STEMI) has not been investigated 
sufficiently.
METHODS: Five hundred and eighty-two hospitalized patients from January 2010 to 
December 2011, with the diagnosis of STEMI, were enrolled in this study. All 
patients underwent testing for thyroid function status, cardiac troponin I 
(cTnI), cardiac enzymes, C-reactive protein (CRP). We investigated the 
association between thyroid hormone levels and cardiac markers (creatine 
kinase-MB and cTnI), and thus evaluated the potential role of thyroid function 
status in predicting the myocardial injury.
RESULTS: There were 76 patients (13.06%) who had hypothyroidism including 
low-T3-syndrome (34 patients, 5.84%), subclinical hypothyroidism (28 patients, 
4.81%) and clinical hypothyroidism (14 patients, 2.41%). After adjusting for 
conventional risk factors (age, gender, smoking, diabetes mellitus, 
dyslipidemia, hypertension), free triiodothyronine (FT3) was significantly and 
negatively correlated with log-CKMB (r = -0.244, P < 0.001) and log-cTnI (r = 
-0.290, P < 0.001), indicating that the lower thyroid hormone level correlates 
with the severer cardiac injury in STEMI patients. FT3 also had a moderate 
negative correlation with CRP (r = -0.475, P < 0.001), which might indicate that 
hypothyroidism may activate the inflammation response. No significant 
correlation was found between other thyroid parameters (TSH, FT4) and cardiac 
markers.
CONCLUSIONS: As the lower FT3 level correlates with higher level of cardiac 
markers and lower left ventricular ejection fraction (LVEF), the hypothyroidism 
may be a predictor for myocardial injury in STEMI. And these results may warrant 
further study to investigate whether reversing the hypothyroidism could benefit 
the STEMI patients.