Triiodothyronine (T3), inflammation and mortality risk in patients with acute myocardial infarction.

OBJECTIVES: To study the relationship between serum free T3 (FT3), C-reactive protein (CRP), and all-cause mortality in patients with acute myocardial infarction (AMI).

DESIGN: Prospective multicentre longitudinal cohort study.

METHODS: Between December 2014 and December 2016, thyroid function and CRP were analysed in AMI (both ST- and non-ST-elevation) patients from the ThyrAMI-1 study. The relationship of FT3 and CRP at baseline with all-cause mortality up to June 2020 was assessed. Mediation analysis was performed to evaluate if CRP mediated the relationship between FT3 and mortality.

RESULTS: In 1919 AMI patients [29.2% women, mean (SD) age 64.2 (12.1) years and 48.7% STEMI] followed over a median (inter-quartile range) period of 51 (46 to 58) months, there were 277 (14.4%) deaths. Overall, lower serum FT3 and higher CRP levels were associated with higher risk of mortality. When divided into tertiles based on levels of FT3 and CRP, the group with the lowest FT3 and highest CRP levels had 2.5-fold increase in mortality risk [adjusted hazard ratio (95% confidence interval) of 2.48 (1.82 to 3.16)] compared to the group with the highest FT3 and lowest CRP values. CRP mediated 9.8% (95% confidence interval 6.1 to 15.0%) of the relationship between FT3 and mortality.

CONCLUSIONS: In AMI patients, lower serum FT3 levels on admission are associated with a higher mortality risk, which is partly mediated by inflammation. Adequately designed trials to explore potential benefits of T3 in AMI patients are required.