Thyroid Function and Risk for AF: A Linear Relation

Patients with overt hyperthyroidism (suppressed thyroid-stimulating hormone [TSH] and elevated free thyroxine [T₄] levels) have excess risk for developing atrial fibrillation (AF). However, the relations between subclinical hyperthyroidism (suppressed TSH and normal T₄), overt hypothyroidism (elevated TSH and low T₄), and subclinical hypothyroidism (elevated TSH and normal T₄) are unclear.

In a population-based cohort study, nearly 590,000 primary care patients (mean age, 50; 39% men) underwent thyroid function blood testing from 2000 through 2010. Overall, 0.3% of patients had overt hypothyroidism, 2.0% had subclinical hypothyroidism, 96.0% were euthyroid, 1.0% had subclinical hyperthyroidism, and 0.7% had overt hyperthyroidism. During a me…