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.