Higher Risk of Incident Hyperthyroidism in Patients With Atrial Fibrillation

Background: Atrial fibrillation (AF) has been linked to increased hyperthyroidism risk, but contributing factors are unclear. Objective: We aimed to investigate whether AF could predict hyperthyroidism and related risk factors. Methods: This retrospective cohort study was conducted in a tertiary medical institution and included patients aged 18 years or older with AF but without hyperthyroidism at diagnosis. The endpoint was defined as newly diagnosed hyperthyroidism during the follow-up period. Results: The study cohort included 8552 participants. Patients who developed new hyperthyroidism were younger and the proportion of females was higher. They had fewer comorbidities, including diabetes (26% vs 29%, P = .121), hypertension (51% vs 58%, P < .001), coronary artery disease (17% vs 25%, P < .001), stroke (16% vs 22%, P < .001), and end-stage renal disease (ESRD) (6% vs 10%, P = .001). The CHADS2 score was lower in patients with hyperthyroidism (1.74 vs 2.05, P = .031), but there was no statistically significant difference in the CHA2DS2-VASc and HAS-BLED score. Cox regression analysis identified younger age, female gender, history of congestive heart failure, hypertension, diabetes, non-ESRD status, and lower CHADS2 score but not CHA2DS2-VASc as independent predictors of incident hyperthyroidism during follow-up. We also propose a novel, simple risk stratification score (SAD HEC2 score) with excellent predictive power for incident hyperthyroidism during follow-up. Conclusion: Our results provide insight into clinical risk factors for the development of hyperthyroidism in AF patients, as identified by the novel SAD HEC2 score. AF appears to be a common precursor of hyperthyroidism.