Thyroid Function and Risk for AF: A Linear Relation
Patients with even subclinical hyperthyroidism had excess risk for atrial fibrillation.
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 median follow-up of 5.5 years, >17,000 participants received first diagnoses of AF. Compared with euthyroid patients, patients with overt hypothyroidism had less risk for AF (incidence rate ratio, 0.67), as did those with subclinical hypothyroidism (IRR, 0.87); risk for AF was higher in patients with subclinical hyperthyroidism (IRR, 1.31) or overt hyperthyroidism (IRR, 1.42) than for euthyroid patients. Stratifying data by age, sex, or both did not change the associations.
Comment: In this large prospective study, a linear relation was observed between thyroid function and risk for AF: hypothyroid patients had lower risk and hyperthyroid patients had excess risk. The authors suggest that patients with overt and subclinical hyperthyroidism should be screened routinely for AF.
Paul S. Mueller, MD, MPH, FACP
Published in Journal Watch General Medicine December 18, 2012
Citation(s): Selmer C et al. The spectrum of thyroid disease and risk of new onset atrial fibrillation: A large population cohort study. BMJ 2012 Nov 27; 345:e7895. (http://dx.doi.org/10.1136/bmj.e7895)