Is the risk of ischemic stroke lower in atrial flutter compared to atrial fibrillation?

Background Previous literature has suggested that patients with atrial flutter (AFL) may have a lower risk of ischemic stroke (IS) compared to patients with atrial fibrillation (AF). Purpose In this study we compared the risk of ischemic stroke in three groups: patients with only AF, patients with only AFL, and those with both AF and AFL (AF&AFL). Methods The registry-linkage Finnish AntiCoagulation in Atrial Fibrillation (FinACAF) study included all patients with AF in Finland from 2007 to 2018. Those with digitally documented electrocardiograms (ECGs) were selected. Based on the digitally recorded ECGs, three groups were created: patients with AF only, patients with AFL only, and those with AF&AFL. The ischemic stroke rates and rate ratios (RRs) for these three groups were calculated using possion regression model. Results A total of 40,986 patients with new-onset AF and digitally documented ECGs were identified. The only AF group included 30,261 patients (48.2% women, mean age 71.8 years), the only AFL group included 2,409 patients (38.8% women, mean age 70.7 years), and the AF&AFL group included 8,316 patients (53.9% women, mean age 72.4 years). Of all the groups, 31,795 (77.6%) patients initiated anticoagulation during follow-up. The crude rate of IS was higher in the AF&AFL group (2.1 per 100 patient-years, confidence interval (CI)1.01-1.19) compared to only AF (1.9 per 100 patient-years, CI 1.0-1.0) and only AFL (1.1 per 100 patient-years, CI 0.46-0.71). After adjusting for patient characteristics and anticoagulant use, AFL was associated with a lower stroke rate (RR 0.599 [0.484 to 0.742]), and AF&AFL was associated with a higher stroke rate (RR 1.105 [1.018 to 1.199]) when compared to patients with AF only. The results were not changed when only time without anticoagulant use was considered in the analysis; however, in these analyses, the difference between AF and AF&AFL was not statistically significant. Conclusion AFL patients had lower risk of IS than those with AF, while those with AF and AFL had the highest risk of IS. These findings have important clinical implications for customizing stroke prevention strategies in patients with different arrhythmia profiles.