Background: This study aimed to determine whether use of oral anticoagulants (OACs) was associated with a reduced risk of recurrent stroke compared with use of antiplatelets (APs) in patients with embolic stroke of undetermined source (ESUS) having no potential source of embolism. Methods: Of 8,790 patients with acute ischemic stroke registered at 7 centers in the Fukuoka Stroke Registry from June 2007 to May 2017, we included 681 patients (mean age 69.7 [SD 14.1] years, 48.3% men) who experienced ESUS without a potential source of embolism and received OAC alone or AP alone. We estimated hazard ratios (HRs) and 95% confidential intervals (CIs) of recurrent ischemic stroke or any stroke after discharge using a Cox proportional hazards model and Fine and Gray model. Results: During a mean follow-up of 3.4 (SD 1.7) years, event rates of recurrent ischemic stroke were 4.4 per 100 person-years in 489 patients treated with AP and 2.0 per 100 person-years in 192 patients treated with OAC. OAC use was associated with a reduced risk of recurrent ischemic stroke, even after adjusting for potential confounding factors (multivariable-adjusted HR [95% CI], 0.42 [0.23-0.80]) and when additionally considering death as a competing risk (0.45 [0.24-0.85]). The reduced risk of recurrent ischemic stroke was still observed in patients treated with OAC (0.32 [0.15-0.67]) in reference to propensity score-matched patients treated with AP. These associations were maintained for all types of stroke, including ischemic and hemorrhagic stroke. Conclusions: This nonrandomized observational study suggests that anticoagulation therapy might be associated with a reduced risk of recurrent stroke compared with antiplatelet therapy in patients with ESUS in whom no potential source of embolism was identified. Further study should be performed in consideration of a potential source of embolism even in patients with ESUS.
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