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.
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.
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
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.