Risk of stroke or systemic embolism in atrial fibrillation patients treated with warfarin: a systematic review and meta-analysis

Abstract

Background and purpose: 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.