title: Risk of stroke or systemic embolism in atrial fibrillation patients treated with warfarin: a systematic review and meta-analysis.
abstract: OBJECTIVE
  Although oral anticoagulants (OACs) are highly effective in reducing stroke risk in atrial fibrillation, some patients still sustain stroke despite being on an OAC. Our aim was to identify the risk factors that contribute to stroke risk in atrial fibrillation, although patients were taking OACs in a clinical trial setting.
  
  
  METHODS
  We identified contemporary clinical trials that investigated OACs in patients with atrial fibrillation. Event rates per year from each study and pooled event rates and relative risks, all with a 95% confidence interval, were calculated. Statistical heterogeneity was assessed using the I(2) test.
  
  
  RESULTS
  Six trials were included in the meta-analysis, with a total of 58 883 patients randomized. Characteristics associated with a higher relative risk of stroke while on an OAC included age ≥ 75 years (relative risk, 1.46 [95% confidence interval, 1.25-1.69]), female sex (1.30 [1.15-1.49]), previous stroke/transient ischemic attack (1.85 [1.32-2.60]), vitamin K-antagonist naive status (for vitamin K antagonist experienced, 0.85 [0.74-0.97]), moderate and severe renal impairment (1.54 [1.30-1.81] and 2.22 [1.85-2.66], respectively, compared with normal renal function), previous aspirin use (1.19 [1.04-1.37]), Asian race (1.70 [1.42-2.03]), and a CHADS2 score of ≥ 3 (1.64 [1.18-2.27]).
  
  
  CONCLUSIONS
  Stroke rates are higher on OACs with some patient clinical characteristics, that is, older age, female sex, previous stroke/transient ischemic attack, vitamin K-antagonist naive status, renal impairment, previous aspirin use, and higher CHADS2 score. The identified risk factors for stroke while on an OAC could potentially be used to consider a risk assessment tool to flag up high-risk patients while on an OAC (in this case, warfarin). Whether these risk factors apply to novel OACs is uncertain.
authors.affiliation: Department of Cardiology, Aalborg AF Study Group, Aalborg University Hospital, Aalborg, Denmark.
authors.forename: Ida Ehlers
authors.initials: IE
authors.lastname: Albertsen
authors.forename: Lars Hvilsted
authors.initials: LH
authors.lastname: Rasmussen
authors.forename: Thure Filskov
authors.initials: TF
authors.lastname: Overvad
authors.forename: Tina
authors.initials: T
authors.lastname: Graungaard
authors.forename: Torben Bjerregaard
authors.initials: TB
authors.lastname: Larsen
authors.forename: Gregory Y H
authors.initials: GY
authors.lastname: Lip
mesh_terms: D000368:Aged; D000925:Anticoagulants / Q000009:adverse effects* / Q000627:therapeutic use; D001281:Atrial Fibrillation / Q000150:complications / Q000188:drug therapy*; D004617:Embolism / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012306:Risk; D018570:Risk Assessment; D020521:Stroke / Q000209:etiology*; D014859:Warfarin / Q000009:adverse effects* / Q000627:therapeutic use
chemical_list: D000925:Anticoagulants; D014859:Warfarin