Thyroid status, cardiac function, and mortality in patients with idiopathic dilated cardiomyopathy

Context: Previous studies claiming a relationship between thyroid dysfunction and poor prognosis of heart failure (HF) had a major limitation in that they included patients with different etiologies. Objective: With complete information of thyroid function profile from 458 consecutive patients with idiopathic dilated cardiomyopathy, we tested the hypothesis that thyroid status can independently influence mortality in patients with HF. Design, Patients, and Outcome Measure: The original cohort consisted of 572 consecutive patients with idiopathic dilated cardiomyopathy, and 458 patients remained at the end of follow-up. All patients took thyroid function tests and other regular examinations in hospital. The risk of mortality was evaluated based on free T<inf>3</inf>, TSH, and the whole thyroid function profile, respectively. Results: The most frequent thyroid dysfunction was subclinical hypothyroidism (n = 41), followed by subclinical hyperthyroidism (n = 35), low-T<inf>3</inf> syndrome (n = 17), and hypothyroidism (n = 12). Logistic analysis showed log-TSH and free T<inf>3</inf> as independent predictors of exacerbated cardiac function (New York Heart Association stages III-IV vs New York Heart Association stages I-II). During the follow-up (17 ± 8 mo), 111 cumulative deaths occurred. Hypothyroidism was the strongest predictor of mortality [hazard ratio (HR) 4.189; 95% confidence interval (CI) 2.118- 8.283)], followed by low-T<inf>3</inf> syndrome (HR 3.147; 95% CI 1.558-6.355) and subclinical hypothyroidism (HR 2.869; 95% CI 1.817- 4.532). Subclinical hyperthyroidism showed no significant impact. Conclusions: We found a clear association between thyroid dysfunction and increased risk of mortality in idiopathic dilated cardiomyopathy with HF. These results suggest that monitoring thyroid function in HF patients is necessary, and further studies on the treatment of HF with thyroid dysfunction are needed.