AF Risk Tied to Thyroid Function

High free thyroxine (fT4) levels were associated with an increased risk for atrial fibrillation (AF) among individuals with normal thyroid function, according to the findings of a recent study.

In their systematic review, the researchers analyzed data from 11 cohort studies that measured the thyroid function of 30,085 participants at baseline and assessed incident AF. The researchers defined the euthyroid state as thyroid-stimulating hormone (TSH) levels from 0.45 to 4.49 mIU/L. Subclinical hypothyroidism was defined as TSH levels from 4.5 to 19.9 mIU/L with fT4 levels within the reference range.
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Overall, 1958 participants (6.5%) had subclinical hypothyroidism, and 2574 (8.6%) had developed AF during follow-up.

Baseline TSH was not significantly associated with incident AF among euthyroid patients or with subclinical hypothyroidism. However, higher fT4 levels at baseline were associated with increased AF risk among euthyroid patients after the researchers adjusted for sex and age. The association between fT4 and AF risk did not differ substantially after adjusting for preexisting cardiovascular disease.

“In euthyroid individuals, higher circulating fT4 levels, but not TSH levels, are associated with increased risk of incident AF,” the researchers concluded.

—Melissa Weiss

Reference:

Baumgartner C, da Costa BR, Collet TH, et al; the Thyroid Studies Collaboration. Thyroid function within the normal range, subclinical hypothyroidism and the risk of atrial fibrillation [published online October 23, 2017]. Circulation. https://doi.org/10.1161/CIRCULATIONAHA.117.028753.