SUN-391 Endogenous and Iatrogenic Thyrotoxicosis and the Risk of Atrial Fibrillation in Older Adults

Abstract Disclosure: N. Mhaimeed: None. P. Babar: None. J. Vaidya: None. R. Adams: None. J.S. Mammen: None. Background:Atrial fibrillation (AF) affects 8-10% of patients aged 65 or older and is linked to significant morbidity and mortality. While endogenous hyperthyroidism is a well-recognized risk factor for AF, the role of iatrogenic thyrotoxicosis remains controversial. Thyroid hormone, among the most frequently prescribed medications in the US, is used by 7% of the population, with up to 20% potentially overtreated. A trend toward aggressive prescribing coupled with the vulnerability of an aging population, underscores the need for clarity on the impacts of thyroid hormone overtreatment on this critical health outcome to improved thyroid hormone management and reduce iatrogenic harm.Objective:Determine whether endogenous thyrotoxicosis (ET) and iatrogenic thyrotoxicosis (IT) are associated with equivalent risks of AF.Methods:This cohort study performed a longitudinal analysis of EHR data for patients receiving care in a regional, community-based primary care network since 1/1/2014. Eligible patients were age 50 or older with at least two outpatient visits, one TSH measure, and no AF within 3 months of the first included visit. Thyrotoxicosis cases were categorized as ET and IT as previously described (Adams, 2023). Time-varying Cox regression models were used to calculate the risk of AF and adjusted for age, sex, race, and comorbidities.Results:We had an eligible cohort of 137,879 patients, 61.6% female, 63.2% White, with mean age 59. Men were at a higher risk of AF than women (cumulative incidence by age 90 of 60% for men compared to 45% for women). A protective effect was seen for Blacks (aHR 0.81, p<0.001), Asian (aHR 0.46, p<0.001), and female sex (aHR 0.57, p<0.001). Those with low TSH were more likely to be women (79.4%, p<0.001) and older age (60 vs. 58, p<0.001). ET rates were similar by sex, but IT was more common in women (cumulative incidence by age 90 55% for women compared to 25% for men). IT explained three quarters of all low TSH events. Low TSH of any origin was associated with AF diagnosis (8.4% vs. 7.0%, p<0.001). In adjusted models for ET aHR=1.51 (p=0.002) while IT was not associated with a significant increase (aHR 1.09, p=0.2). There was insufficient power to analyze a dose response among the ET subgroup. Conclusion:Low TSH is an independent predictor of AF, with a higher risk in patients with endogenous thyrotoxicosis compared to iatrogenic thyrotoxicosis. These findings underscore the importance of monitoring of the treatment of thyroid disease to mitigate AF risk in older adults. Citation: Adams R, Oh ES, Yasar S, Lyketsos CG, Mammen JS. Endogenous and Exogenous Thyrotoxicosis and Risk of Incident Cognitive Disorders in Older Adults. JAMA Intern Med. 2023 Dec 1;183(12):1324-1331. doi: 10.1001/jamainternmed.2023.5619. PMID: 37870843; PMCID: PMC10594176. Presentation: Sunday, July 13, 2025