Rivaroxaban Versus Warfarin in Acute Ischemic Stroke With Atrial Fibrillation

Inclusion Criteria: All of below * Acute ischemic stroke or TIA presumed to be cardioembolic origin (within 5 days from stroke onset) with mild severity: infarct size on DWI less than 1/3 of MCA territory, 1/2 of ACA territory, 1/2 of PCA territory, and 1/2 of one cerebellar hemisphere * Atrial fibrillation including paroxysmal atrial fibrillation: atrial fibrillation must be documented by ECG evidence (e.g., 12-lead ECG, rhythm strip, Holter, pacemaker interrogation) within 30 days before randomization. This could be obtained from a notation in the subject's record (e.g., medical chart, hospital discharge summary). * Age ≥19 years * Informed consent Exclusion Criteria: Any of below * Chronic renal failure (GFR less than 30ml/min) or severe hepatic impairment * Significant hemorrhagic transformation (parenchymal hematoma type I or II by the ECASS definition) * Stroke mechanism of presumed small vessel occlusion: single small subcortical infarct in the perforating artery territory * Large hemispheric or cerebellar infarction; larger than 1/3 of MCA territory, 1/2 of ACA territory, 1/2 of PCA territory, and 1/2 of one cerebellar hemisphere * Mechanical valve requiring warfarin therapy * Active internal bleeding * Prior history of symptomatic intracranial bleeding : patients with asymptomatic bleedings or microbleedings on MRI are eligible for inclusion * Major surgery or major trauma within 30 days that might be associated with increased bleeding risk * Clinically significant gastrointestinal bleeding within 6 months * Intravenous tissue plasminogen activator use or mechanical embolectomy within 48 hours plus 'significant hemorrhagic transformation as described above (exclusion criteria 2)' or 'large hemispheric infarction or cerebellar infarction as described above (exclusion criteria 4)' : patients achieving successful reperfusion without hemorrhage nor large infarction are eligible for enrollment * Severe anemia: hemoglobin \<10 g/dL * Bleeding diathesis; thrombocytopenia (\<90,000/µL, prolonged PT (INR\>1.7) * Sustained uncontrolled hypertension: SBP \>180 mmHg or DBP \>100 mmHg * Severe devastating illness, such terminal cancer, hepatic failure; therefore, the participants have a life expectancy less than 6 months. * Planned invasive procedure with potential for uncontrolled bleeding, including major surgery