An Austrian cohort study included 23,638 subjects. The subjects were classified according to their serum thyrotropin concentrations: group 1 comprised those with normal values of serum thyrotropin concentration (>0.4-5.0 mU/L) and free tri-iodothyronine and free thyroxine concentrations were within the normal range (22,300 subjects), group 2 comprised those with both low serum thyrotropin values (
A population-based study of 5860 subjects 65 years and older excluded those being treated for thyroid dysfunction and those with previous hyperthyroidism. Fourteen subjects (0.2%) had previously undiagnosed overt hyperthyroidism and 126 (2.2%), subclinical hyperthyroidism; 5519 (94.4%) were euthyroid; and 167 (2.9%) had subclinical hypothyroidism and 23 (0.4%), overt hypothyroidism. The prevalence of AF in the whole cohort was 6.6% in men and 3.1% in women (odds ratio, 2.23; P<.001). After adjusting for sex, logistic regression showed a higher prevalence of AF in those with subclinical hyperthyroidism compared with euthyroid subjects (9.5% vs 4.7%; adjusted odds ratio, 2.27; P=.01). Logistic regression showed serum free T(4) concentration, increasing category of age, and male sex all to be independently associated with AF. Similar independent associations were observed when analysis was confined to euthyroid subjects with normal TSH values.
Similar results have been consistently found in other studies.
Comment: The quality of evidence is upgraded by very strong association and no plausible confounders.
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