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.

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.