Ischaemic stroke in atrial flutter vs fibrillation: a Finnish nationwide study.

BACKGROUND AND AIMS: Previous literature has suggested that the risk of ischaemic stroke (IS) is lower in patients with atrial flutter (AFL) compared with patients with atrial fibrillation (AF), but large-scale studies with electrocardiogram (ECG) documentation are not available. METHODS: The registry-linkage Finnish AntiCoagulation in Atrial Fibrillation study included all patients with AF and AFL in Finland from 2007 to 2018. Based on the digitally recorded ECGs, patients were categorized into AF-only, AFL-only, or combined AF and AFL groups. IS rates and adjusted incidence rate ratios (IRRs) were calculated. RESULTS: A total of 40 986 patients with new-onset AF/AFL and 532 041 digitally documented ECGs were identified. The AF-only group included 30 261 patients (48.2% women, mean age 71.8 years), the AFL-only group 2409 patients (38.8% women, mean age 70.8 years), and the AF & AFL group 8316 patients (53.9% women, mean age 72.4 years). Of these, 31 795 (77.6%) initiated anticoagulation during a mean follow-up of 1.2 years. Overall, IS was observed in 3165 (7.7%) patients. The crude rate of IS was highest in the AF & AFL group [2.1 per 100 patient-years, 95% confidence interval (CI) 1.9-2.2] compared to the AF-only group (1.9 per 100 patient-years, 95% CI 1.8-1.9) and AFL-only group (1.1 per 100 patient-years, 95% CI 0.9-1.3). Adjusted IRR of IS was lower in the AFL-only group (0.60, 95% CI 0.49-0.74) and slightly higher in the AF & AFL group (1.11, 95% CI 1.02-1.20) compared with patients with AF-only. These findings were consistent in analyses restricted to follow-up time without anticoagulation and before catheter ablation, as well as across CHA2DS2-VA score categories. CONCLUSIONS: In this large cohort of patients, those with AFL-only had a substantially lower risk of IS than patients with AF-only, suggesting clinically meaningful differences in thromboembolic risk between these arrhythmias.