title: Net clinical benefit of warfarin in individuals with atrial fibrillation across stroke risk and across primary and secondary care.
abstract: To investigate net clinical benefit (NCB) of warfarin in individuals with atrial fibrillation (AF) across stroke risk and across primary and secondary care.
  
  
  
  We conducted a linked electronic health record cohort study of 70 206 individuals with initial record of diagnosis of AF in primary (n=29 568) or secondary care (n=40 638) in England (1998-2010). We defined stroke risk according to the CHA2DS2-VASc score, and followed individuals over a median 2.2 years for 7005 ischaemic strokes (IS) and for 906 haemorrhagic strokes (HS). We calculated incidence rates (IRs) and 95% CIs per 100 person-years (PYs) (IR (95% CI)/100 PY) of IS and HS, with and without use of warfarin, and the NCB (ie, number of IS avoided) per 100 PYs of warfarin use (NCB (95% CI)/100 PY).
  
  
  
  Compared with individuals with initial record of diagnosis in secondary care, those in primary care had lower scores of IS risk (CHA2DS2-VASc≤2: 30.8% vs 20.6%), and lower overall incidence of IS (IR (95% CI)/100 PY: 2.3 (2.2 to 2.4) vs 4.3 (4.2 to 4.4), p value=0.00); however among individuals with CHA2DS2-VASc=0, 1 or 2 there were no differences in IS rate between those with initial record of diagnosis in primary care or secondary care (IR (95% CI)/100 PY: 0.2 (0.1 to 0.3) vs 0.3 (0.2 to 0.5), p value=0.16), (IR (95% CI)/100 PY: 0.6 (0.4 to 0.7) vs 0.7 (0.6 to 0.9), p value=0.08) and (IR (95% CI)/100 PY: 1.1 (1.00 to 1.3) vs 1.4 (1.2 to 1.6), p value=0.05), respectively. For CHA2DS2-VASc=0, 1 and 2, IRs of IS with versus without warfarin were (IR (95% CI)/100 PY: 0.4 (0.2 to 0.8) vs 0.2 (0.1 to 0.3), p value=0.16), (IR (95% CI)/100 PY: 0.4 (0.3 to 0.7) vs 0.7 (0.6 to 0.8), p value=0.03) and (IR (95% CI)/100 PY: 0.8 (0.7 to 1.0) vs 1.4 (1.3 to 1.6), p value=0.00), respectively. We found a significant positive NCB of warfarin from CHA2DS2-VASc≥2 in men (NCB (95% CI)/100 PY: 0.5 (0.1 to 0.9)) and from CHA2DS2-VASc≥3 in women (NCB (95% CI)/100 PY: 1.5 (1.1 to 1.9)).
  
  
  
  CHA2DS2-VASc accurately stratifies IS risk in individuals with AF across both primary and secondary care. However, the incidence rate of ischaemic stroke at CHA2DS2-VASc=1 are lower than previously reported, which may change the decision to start anticoagulation with warfarin in these individuals.
authors: Farr Institute of Health Informatics Research, Institute of Health Informatics, University College London, London, UK.
authors: Victoria
authors: 0000-0002-3284-8896
authors: V
authors: Allan
authors: Farr Institute of Health Informatics Research, Institute of Health Informatics, University College London, London, UK.
authors: Amitava
authors: A
authors: Banerjee
authors: Farr Institute of Health Informatics Research, Institute of Health Informatics, University College London, London, UK.
authors: Anoop Dinesh
authors: AD
authors: Shah
authors: Farr Institute of Health Informatics Research, Institute of Health Informatics, University College London, London, UK.
authors: Riyaz
authors: R
authors: Patel
authors: Farr Institute of Health Informatics Research, Institute of Health Informatics, University College London, London, UK.
authors: Spiros
authors: S
authors: Denaxas
authors: Farr Institute of Health Informatics Research, Institute of Health Informatics, University College London, London, UK.
authors: Juan-Pablo
authors: JP
authors: Casas
authors: Farr Institute of Health Informatics Research, Institute of Health Informatics, University College London, London, UK.
authors: Harry
authors: H
authors: Hemingway
mesh_terms: D000284:Administration, Oral; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000008:administration & dosage* / Q000009:adverse effects; D001281:Atrial Fibrillation / Q000175:diagnosis / Q000188:drug therapy* / Q000453:epidemiology; D003661:Decision Support Techniques; D057286:Electronic Health Records; D004739:England / Q000453:epidemiology; D005260:Female; D006470:Hemorrhage / Q000139:chemically induced; D006801:Humans; D015994:Incidence; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D011320:Primary Health Care; D018570:Risk Assessment; D012307:Risk Factors; D063127:Secondary Health Care; D020521:Stroke / Q000175:diagnosis / Q000453:epidemiology / Q000517:prevention & control*; D013997:Time Factors; D016896:Treatment Outcome; D014859:Warfarin / Q000009:adverse effects / Q000627:therapeutic use*
chemical_list: D000925:Anticoagulants; D014859:Warfarin
keywords: Stroke