Thyroid Research Thyroid Research Archive Hyperthyroidism

Atrial fibrillation is common in patients with subclinical hyperthyroidism

(March 2002)

The background of the study. Hyperthyroidism is a well-known cause of atrial fibrillation, which is a common cause of an irregular heartbeat. This study was undertaken to determine the frequency of atrial fibrillation in patients with both overt and subclinical hyperthyroidism.

How the study was done. The study subjects were 725 patients with overt hyperthyroidism (low serum thyrotropin [TSH] concentrations and high serum free thyroxine [T4] and free triiodothyronine [T3] concentrations), 613 patients with subclinical hyperthyroidism (low serum TSH concentrations alone), and 22,300 patients with normal serum TSH concentrations. All the patients were ≥45 years old; the reasons for testing included "screening, suspected thyroid disease, concomitant disease. Atrial fibrillation was diagnosed by electrocardiography.

The results of the study. The frequency of atrial fibrillation was 2.3 percent in the euthyroid patients, 13.8 percent in the patients with overt hyperthyroidism, and 12.7 percent in those with subclinical hyperthyroidism. Among the patients with atrial fibrillation, there were no differences in the frequency of coexisting cardiovascular diseases such as hypertension and coronary heart disease.

After antithyroid treatment, 24 percent of the patients with overt hyperthyroidism and 19 percent of those with subclinical hyperthyroidism had a normal heart rhythm. The rate of conversion was higher in patients who had no cardiovascular disease.

The conclusions of the study. Atrial fibrillation is as common in patients with subclinical hyperthyroidism as in those with overt hyperthyroidism.

The original article. Auer J, Scheibner P, Mische T, Langsteger W, Eber O, Eber B. Subclinical hyperthyroidism as a risk factor for atrial fibrillation. Am Heart J 2001;142:838-42.