Stroke rates in non-anticoagulated individuals with and without atrial fibrillation and one non-sex CHA2DS2-VASc risk factor: a nationwide registry-based cohort (Atrial Fibrillation in Norway – AFNOR)
Authors: Anjum M , Ariansen I , Hjellvik V , Kjerpeseth L J , Selmer R , Skovlund E , Ellekjaer H , Christophersen I E , Myrstad M , Tveit A , Berge T 
Published: October 2022

Abstract

Background
Stroke prevention is fundamental in the management of atrial fibrillation (AF). However, in patients with intermediate risk of stroke (CHA2DS2-VASc score 2 in women; 1 in men) the net clinical benefit of oral anticoagulant (OAC) treatment is uncertain, as the treatment effect must be carefully balanced against the potential bleeding risk. Moreover, multiple risk factors included in the CHA2DS2-VASc score increase the risk of stroke independent of AF.

Purpose
We aimed to compare rates of ischemic and haemorrhagic stroke between non-anticoagulated individuals with and without AF in a nationwide cohort of individuals at intermediate risk of stroke.

Method
We identified a cohort of non-anticoagulated Norwegian individuals with and without non-valvular AF aged ≥18 years, with one non-sex CHA2DS2-VASc risk factor linking data from the Norwegian Population Registry, Patient Registry, Prescription Database and Cause of Death Registry. AF and comorbidities were identified with minimum three-year look-back period at study start and successively during follow up. Individuals without AF entered the study at date of first registered non-sex CHA2DS2-VASc risk factor while individuals with AF entered at the first date when both AF and first CHA2DS2-VASc risk factor were registered. Individuals with and without AF were followed from study start in 2011 until occurrence of stroke, death, emigration, OAC claim, increased CHA2DS2-VASc score or end of follow-up on December 31, 2018. Rates of ischemic and haemorrhagic stroke were calculated as the number of stroke cases per 100 person-years with 95% confidence intervals (CI).

Results
During 2011–2018, a total of 61,762 individuals with AF at intermediate risk of stroke and no previous OAC use were identified (mean age 63.2±7.6 years (SD); 37% women). In the AF population, a total of 1,304 ischemic strokes were registered during 109,881 person-years, and 127 haemorrhagic strokes during 109,559 person-years. In the corresponding intermediate risk non-AF population, 1,099,655 individuals (mean age 59.5±10.2 years (SD); 49.5% women) were identified, with a total of 6,081 ischemic strokes during 4,037,940 person-years and 3,037 haemorrhagic strokes during 4,022,952 person-years.
The rate of ischemic stroke was 1.19 (95% CI, 1.12–1.25) in AF-patients and 0.15 (95% CI, 0.15–0.15) in non-AF individuals per 100 person-years, corresponding to a rate difference of 1.04 excess stroke cases per 100 person-years in AF patients. The haemorrhagic stroke rate was 0.12 (95% CI, 0.10–0.14) in AF-patients and 0.08 (95% CI, 0.07–0.08) per 100 person-years in non-AF individuals. Similar rate differences were seen in both men and women.

Conclusion
In a nationwide population with one non-sex CHA2DS2-VASc risk factor and without OAC treatment, we found higher stroke rate in AF patients compared to the rest of the population without AF, with a stroke rate difference of ∼1% per year. Haemorrhagic stroke rates were generally low.

Funding Acknowledgement
Type of funding sources: Public Institution(s). Main funding source(s): South-Eastern Norway Regional Health Authority