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.
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