Temporal trends of ischemic stroke rates in atrial fibrillation without anticoagulation: a nationwide cohort study from 2007 to 2018

Abstract Background Atrial fibrillation (AF) is a major risk factor for ischemic stroke (IS), but whether the magnitude of this risk has changed over time is unknown. Purpose To evaluate temporal trends in IS rates in patients with AF who have not initiated oral anticoagulant (OAC) therapy. Methods The registry-linkage Finnish AntiCoagulation in Atrial Fibrillation (FinACAF) study covers all patients with incident AF in Finland from 2007 to 2018. A four-week quarantine period from AF diagnosis was applied and only follow-up time without OAC therapy was included. IS incidence rates were computed in four-year intervals. Results In total, 129 789 patients with new-onset AF (49.2% women; mean age 71.4 years) were identified. The IS incidence rate trends according to sex and the CHA2DS2-VA score are depicted in the Figure, along with the previously estimated treatment thresholds for direct oral anticoagulants (red broken line) and warfarin therapy (blue broken line). Between the calendar year intervals of 2007-2010 and 2015-2018, their mean CHA2DS2-VA score increased from 2.5 to 3.0, while concurrently the overall IS rate decreased by 25% from 36.7 (95% CI 34.5-39.0) to 27.6 (95% CI 26.1-29.0) events per 1000 patient years. This trend was driven by a 32% decrease in women, particularly among those with high CHA2DS2-VA scores. The overall IS rate in patients with a CHA2DS2-VA score of 1 was 8.2 (95% CI 7.2-9.4) events per 1000 patient years and it remained stable across the study period. Conclusions The IS rates in AF patients without OAC therapy have decreased by 25% between 2007 and 2018, despite their rising stroke risk scores. In patients with a CHA2DS2-VA score of 1 the IS rate appears to be lower than previously assumed and approximately at the threshold at which the potential benefits and harms of OAC therapy have been estimated to overlap.