Preadmission antithrombotic treatment and stroke severity in patients with atrial fibrillation and acute ischaemic stroke: an observational study

Background: Vitamin K antagonists (eg, warfarin) substantially reduce the risk of ischaemic stroke in patients with atrial fibrillation. Additionally, therapeutic anticoagulation at time of acute stroke admission might reduce in-hospital mortality and disability. We assessed the association between preadmission antithrombotic treatment and initial stroke severity, neurological deterioration, major vascular events during hospital stay, and death or disability at discharge in patients with acute ischaemic stroke and atrial fibrillation. Methods: We identified consecutive patients with acute ischaemic stroke and atrial fibrillation, admitted to 11 hospitals in Ontario, Canada, from the Registry of the Canadian Stroke Network (2003-05). Logistic regression was used to assess the association between antiplatelet treatment, subtherapeutic warfarin treatment (admission international normalised ratio [INR] <2), therapeutic warfarin treatment (admission INR ≥2), and clinical outcome. Stroke severity was measured using the Canadian neurological scale (CNS) and was categorised into mild (CNS >7) and severe stroke (CNS ≤7). Disability was measured with the modified-Rankin scale (mRS) and was categorised into strokes associated with no or mild-moderate dependency (mRS 0-3) and with severe dependency or death (mRS 4-6). Results: Of 948 patients, 306 (32%) were not on antithrombotic treatment, 292 (31%) were receiving antiplatelet treatment, 238 (25%) were receiving warfarin with a subtherapeutic INR, and 112 (12%) were receiving warfarin with a therapeutic INR on admission. Compared with those not receiving antithrombotic therapy, antiplatelet therapy (odds ratio 0·7; 95% CI 0·5-0·995) and therapeutic warfarin (0·4; 0·2-0·6) were associated with a reduction in severe stroke at admission. Therapeutic warfarin was also associated with a reduction in the odds of severe disability or death at discharge (0·5; 0·3-0·9). Interpretation: Therapeutic warfarin is associated with reduced severity of ischaemic stroke at presentation and reduced disability or death at discharge in patients with atrial fibrillation. Antiplatelet treatment is associated with a more modest reduction than warfarin in baseline stroke severity.