Risk of Ischaemic Stroke in Patients with Atrial Fibrillation and Concomitant Hyperthyroidism: A Nationwide Cohort Study

Background: Hyperthyroidism is associated with atrial fibrillation (AF) and the latter confers a significant risk for stroke. However, conflicting evidence was found in the association between hyperthyroidism and stroke in AF patients.&nbsp;<br><br>Methods: Admissions with AF between January 2010 and December 2019 was retrospectively collected from National Hospital Discharge Database. Incidence rates of ischaemic stroke and bleeding were calculated and compared in AF patients with and without hyperthyroidism. The associations of risk factors with ischaemic stroke were assessed by Cox regression.&nbsp;<br><br>Results: The yearly incidence of ischaemic stroke was 2.6 (95% confidence interval CI: 2.5-2.8) in hyperthyroid AF patients, and 2.3 (95%CI: 2.3-2.4) in non-thyroid AF patients over a mean follow-up of 2.0 (SD: 2.2) years. Hyperthyroidism was an independent risk factor for ischaemic stroke (adjusted hazard ratio HR: 1.133, 95%CI: 1.080-1.189, p&lt;0.001) overall, particularly within the first year of hyperthyroidism diagnosis (HR 1.203, 95%CI 1.120-1.291) with a non-significant association beyond 1 year (HR 1.047, 95%CI 0.980-1.118). Major bleeding incidence was lower in hyperthyroid AF group (incidence ratio IR: 5.1%/year) as compared to non-thyroid AF group (IR: 5.4%/year, p&lt;0.001). The predictive value of CHA2DS2VASc and HAS-BLED scores for ischaemic stroke and bleeding events respectively did not significantly differ between AF patients with or without hyperthyroidism.<br><br>Interpretation: Hyperthyroidism was independent risk factor of ischaemic stroke among AF patients, within the first year of hyperthyroidism diagnosis. Beyond 1 year, there was no independent contribution of hyperthyroidism to ischaemic stroke in AF.<br><br>Funding: None.<br><br>Declaration of Interests: GYHL: Consultant and speaker for BMS/Pfizer, Boehringer Ingelheim and Daiichi-Sankyo. No fees are received personally. LF: reports personal fees from Bayer, personal fees from BMS Pfizer, personal fees from Boehringer Ingelheim, personal fees from Medtronic, personal fees from Novartis, outside the submitted work. Other authors have no conflicts of interest to disclose.<br><br>Ethics Approval Statement: The medical information contained in the database is anonymous and protected by professional confidentiality. Consequently, ethics review was not required. Patient consent was not sought. The study was conducted retrospectively, patients were not involved in its conduct, and there was no impact on their care. This type of study was approved by the institutional review board of the Pole Coeur Thorax Vaisseaux from the Trousseau University Hospital (Tours, France) on December 1, 2015, and registered as a clinical audit. Procedures for data collection and management were approved by the Conseil National de l’Informatique et des Libertés, the independent national ethics committee protecting human rights in France, which ensures that all information is kept confidential and anonymous (authorization no. 1749007).