Atrial fibrillation diagnosed after stroke and dementia risk: cohort study of first-ever ischaemic stroke patients aged 65 or older

Aims Atrial fibrillation (AF) is a risk factor for dementia among ischaemic stroke patients in whom the AF was known before the stroke (KAF). Atrial fibrillation detected after stroke (AFDAS) has a different profile compared to KAF, including less frequent cardiovascular comorbidities and lower CHA2-DS2-VASC scores. Currently, it is unknown if AFDAS is also associated with increased dementia risk. We assessed the association between AFDAS and the incident risk of dementia. We also evaluated whether the use of oral anticoagulants (OAC) was associated with lower dementia risk among AFDAS patients. Methods and results In this cohort study, we classified 9791 first-ever ischaemic stroke patients from the Ontario Stroke Registry into four groups: (i) No AF, (ii) KAF, (iii) Inpatient AFDAS (diagnosed during admission), and (iv) Outpatient AFDAS (diagnosed after discharge). We used multivariable Cox proportional models to estimate hazard ratios (HR) for the association between AFDAS and incident dementia risk. Dementia was determined through administrative datasets based on previously validated algorithms. In adjusted analyses, the dementia risk was higher for inpatient AFDAS [HR 1.78, 95% confidence interval (CI) 1.51–2.10] and outpatient AFDAS (HR 1.74, 95% CI 1.47–2.05) relative to no AF. Oral anticoagulants use was associated with lower dementia risk among patients with inpatient AFDAS (HR 0.58, 95% CI 0.43–0.79) and outpatient AFDAS (HR 0.60, 95% CI 0.43–0.83). Conclusion Atrial fibrillation detected after stroke was independently associated with higher risk of dementia relative to no AF. Among patients with AFDAS, the use of OACs was associated with lower dementia risk.