Relation of hypothyroidism and incident atrial fibrillation (from the Framingham Heart Study)

BACKGROUND: Hyperthyroidism has a well-described association with atrial fibrillation (AF). However, the relation of hypothyroidism to AF has had limited investigation. Hypothyroidism is associated with cardiovascular risk factors, subclinical cardiovascular disease, and overt cardiovascular disease, all of which predispose to AF. We investigated 10-year incidence of AF in a community-dwelling cohort. METHODS: Among 6,653 Framingham heart Study participants, 5,069 participants, 52% female, with mean age of 57 ± 12 years, were eligible after excluding those with missing thyroid-stimulating hormone (TSH), TSH 19.9 μU/L, or prevalent AF. Thyroid-stimulating hormone was categorized by range (≥0.45 to <4.5, 4.5 to <10.0, 10.0 to ≤19.9 μU/L) and by quartiles. We examined the associations between TSH and 10-year risk of AF using multivariable-adjusted Cox proportional hazards analysis. RESULTS: Over 10-year follow-up, we observed 277 cases of incident AF. A 1-SD increase in TSH was not associated with increased risk of AF (hazard ratio 1.01, 95% CI 0.90-1.14, P = .83). In categorical analysis, using TSH ≥0.45 to <4.5 μU/L as the referent (equivalent to euthyroid state), we found no significant association between hypothyroidism and 10-year AF risk. Comparing the highest (2.6 < TSH < 19.9 μU/L) to lowest (0.45 < TSH