Temporal Trends of Ischemic Stroke Risk in Patients With Incident Atrial Fibrillation Before Anticoagulation

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. Objectives: This study sought to investigate temporal trends in IS rates in patients with incident AF before oral anticoagulant agent (OAC) therapy. Methods: The nationwide FinACAF (Finnish Anticoagulation in Atrial Fibrillation) study covers patients with AF at all levels of care in Finland from 2007 to 2018. A 4-week quarantine period from AF diagnosis was applied, and only follow-up time without OAC therapy was included. Incidence rates of IS were computed in 4-year intervals in relation to sex and non-sex CHA₂DS₂-VASc (ie, CHA₂DS₂-VA) score values. Results: In total, 129,789 patients with new-onset AF were identified (49.2% women; mean age: 71.4 ± 14.5 years). Between the calendar year intervals of 2007-2010 and 2015-2018, the patients’ mean CHA₂DS₂-VA score increased from 2.5 to 3.0, and concurrently the overall IS rate decreased by 25% from 36.7 to 27.6 events per 1,000 patient-years. This trend was driven by a 32% decrease of IS rate in women, particularly among those with higher age and CHA₂DS₂-VA scores. The IS rate in patients with a CHA₂DS₂-VA score of 1 was 8.2 events per 1,000 patient-years and remained stable across the study period. Conclusions: The initial IS risk in AF patients, before the initiation of OAC therapy, has decreased by 25% between 2007 and 2018 despite an increase in both age and stroke risk scores. The decrease has been most pronounced in older women with high stroke risk scores.