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Mortality is increased in patients with heart disease who have low serum free triiodothyronine concentrations

(July 2003)

The background of the study. Many patients with nonthyroidal illness have abnormal pituitary-thyroid function, most often low serum triiodothyronine (T3) concentrations. In this study, the relationship between serum T3 concentrations and mortality was determined in patients with heart disease.

How the study was done. The study subjects were 573 consecutive patients hospitalized for diagnosis and treatment of heart disease during a one-year period. Among them, 129 had heart muscle dysfunction (cardiomyopathy), 51 an acute myocardial infarction, 91 a previous myocardial infarction, 189 myocardial ischemia, 60 an abnormal heart rhythm, and 53 other disorders. Serum free thyroxine (T4) and total and free T3 were measured two to five days after admission. The patients were divided into two groups, those with low serum free T3 concentrations (<0.20 ng/dl) and those with normal concentrations (0.20 to 0.42 ng/dl). Outcome was determined from patient records, interviews, examinations, and review of death certificates. Death was considered to be of cardiac origin if the patient died from major arrhythmia, cardiac arrest, congestive heart failure, or myocardial infarction.

The results of the study. The serum free T3 concentration was low in 173 patients (30 percent) and normal in 400 patients (70 percent); the serum total T3 concentrations were low and normal, respectively, in all patients with low and normal serum free T3 concentrations. The patients in the low serum free T3 group had poorer cardiac function, and more of them had multiple symptoms of heart disease (84 vs. 70 percent). Only 11 patients (2 percent) had a low serum free T4 concentration.

The 573 patients were followed for an average of 11 months. Among the patients in the low serum free T3 group, 13 patients (7 percent) died from heart disease, as compared with 6 patients (2 percent) in the normal serum free T3 group. Overall, there were 25 deaths in the low serum free T3 group (14 percent) and 12 deaths (3 percent) in the normal serum free T3 group.

The conclusions of the study. A low serum T3 concentration is associated with higher mortality in patients with heart disease.

The original article. Iervasi G, Pingitore A, Landi P, Raciti M, Ripoli A, Scarlattini M, L'Abbate A, Donato L. Low-T3 syndrome: a strong prognostic predictor of death in patients with heart disease. Circulation 2003;107:708-13.

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Nonthyroidal Illness