Effect of suboptimal anticoagulation treatment with antiplatelet therapy and warfarin on clinical outcomes in patients with nonvalvular atrial fibrillation: a population-wide cohort study

BACKGROUND: The actual consequence of suboptimal anticoagulation management in patients with non-valvular atrial fibrillation(NVAF) is unclear in the real-life practice.

OBJECTIVE: To identify the prevalence of suboptimally anticoagulated patients with NVAF, and compare the effectiveness and safety of antiplatelet drugs with warfarin.

METHODS: We performed a retrospective cohort study using a population-wide database managed by the Hong Kong Hospital Authority. Patients newly diagnosed with NVAF during 2010-2013 were included in the analysis. Cox proportional hazards regression model with 1:1 propensity-score-matching was used to compare the risk of ischemic stroke, intracranial hemorrhage(ICH), gastrointestinal bleeding(GIB), and all-cause mortality between patients on antiplatelet drugs and warfarin stratified by level of international normalized ratio(INR) control.

RESULTS: Among the 35,551 patients with NVAF, 30,294(85.2%) had CHA2DS2-VASc≥2(target group for anticoagulation). Of these, 7,029(23.2%) received oral anticoagulants and 18,508 (61.1%) received antiplatelet drugs alone. There were 67.7% of warfarin users had poor INR control (time-in-therapeutic-range[2.0-3.0]<60%). Patients on warfarin had comparable risks of ICH(hazard ratio,1.24;95%confidence interval,0.65-2.34) and GIB(1.23;0.84-1.81); lower risk of ischemic stroke(0.40;0.28-0.57) and all-cause mortality(0.45;0.36-0.57) when compared to patients on antiplatelet drugs alone. Good INR control was associated with reduced risk of ischemic stroke(0.48;0.27-0.86) compared to poor control. Modelling analyses suggested that ~40,000 stroke cases could be potentially prevented per year in the Chinese population if patients were optimally treated.

CONCLUSIONS: Over three-quarters of high-risk patients were not anticoagulated or had poor INR control in this Chinese NVAF population. There is an urgent need to improve the optimization of anticoagulation for stroke prevention in AF patients.