BACKGROUND: Overt thyroid dysfunction, hypothyroidism in particular, may lead to 
coronary artery disease (CAD). Whether more subtle anomalies of thyroid hormone 
metabolism influence the progression of CAD remains a matter of speculation.
HYPOTHESIS: The occurrence of CAD and long-term prognosis in patients without a 
history of either primary thyroid disease, myocardial infarction, or chronic 
heart failure is related to serum levels of biologically active free 
triiodothyronine (fT3).
METHODS: The cohort consisted of 1047 clinically and biochemically euthyroid 
patients (median age 65.6 y and 69% male) who underwent coronary angiography in 
our institute for suspected CAD.
RESULTS: Lower fT3 levels were predictive of both single-vessel (p = 0.012) and 
multivessel (p = 0.009) CAD. Through a multivariate logistic regression 
analysis, fT3 was still linked to the presence of CAD (hazard ratio [HR]: 0.48, 
95% confidence interval [CI]: 0.34-0.68, p < 0.001). After a mean follow-up of 
31 months, the survival rate was 95% and total mortality (log-rank 6.75, p = 
0.009), as well as cardiac mortality (log-rank 8.26, p = 0.004), was greater 
among patients with low T3 (fT3 < 2.10 pg/mL) syndrome. At subsequent 
multivariate Cox regression analysis, the association between low T3 syndrome 
and survival was maintained (total mortality HR: 1.80, 95% CI: 1.05-3.10, p = 
0.034; cardiac mortality HR: 2.58, 95% CI: 1.13-5.93, p = 0.025).
CONCLUSIONS: In this selected population, fT3 levels were inversely correlated 
to the presence of CAD and low T3 syndrome conferred an adverse prognosis, even 
after adjusting for traditional coronary risk factors.