PURPOSE: The thyroid hormone system may be downregulated temporarily in patients 
who are severely ill. This "euthyroid sick syndrome" may be an adaptive response 
to conserve energy. However, thyroid hormone also has beneficial effects on the 
cardiovascular system, such as improving cardiac function, reducing systemic 
vascular resistance, and lowering serum cholesterol levels. We investigated 
whether thyroid hormone levels obtained at the time of myocardial infarction are 
associated with subsequent mortality.
PATIENTS AND METHODS: Serum levels of thyroid hormones (triiodothyronine [T3], 
reverse T3, free thyroxine [T4], and thyroid-stimulating hormone) were measured 
in 331 consecutive patients with acute myocardial infarction (mean age [+/- SD], 
68 +/- 12 years), from samples obtained at the time of admission.
RESULTS: Fifty-three patients (16%) died within 1 year. Ten percent (16 of 165) 
of patients with reverse T3 levels (an inactive metabolite) >0.41 nmol/L (the 
median value) died within the first week after myocardial infarction, compared 
with none of the 166 patients with lower levels (P <0.0004). After 1 year, the 
corresponding figures were 24% (40 of 165) versus 7.8% (13 of 166; P <0.0001). 
Reverse T3 levels >0.41 nmol/L were associated with an increased risk of 1-year 
mortality (hazard ratio = 3.0; 95% confidence interval: 1.4 to 6.3; P = 0.005), 
independent of age, previous myocardial infarction, prior angina, heart failure, 
serum creatinine level, and peak serum creatine kinase-MB fraction levels.
CONCLUSION: Determination of reverse T3 levels may be a valuable and simple aid 
to improve identification of patients with myocardial infarction who are at high 
risk of subsequent mortality.