Enhanced Detection of Underlying, Covert ATrial Fibrillation Using 7-day Holter Electrocardiogram in Patients With Embolic Stroke of Undetermined Source

Inclusion Criteria: 1. Recent ESUS (within 3 months of onset) defined as: A. Recent ischemic stroke (including transient ischemic attack with positive neuroimaging) visualized by brain imaging that is not lacunar B. Abscence of ≥ 50% stenosis or occlusion in cervical and intracranial arteries supplying ischemic area C. No atrial fibrillation after ≥ 24-hour Holter monitoring D. No intra-cardiac thrombus on transthoracic echocardiography E. No other major cardioembolic sources F. No other specific cause of stroke (for example, arteritis, dissection, migraine/vasospasm, drug abuse) 2. 20 years of age or older 3. Signed written informed consent Exclusion Criteria: 1. Previously documented atrial fibrillation 2. Untreated hyperthyroidism 3. Pacemaker or implantable cardioverter defibrillator implanted or planned to implant 4. Estimated life expectancy \< 12 months 5. Examination of seven-day Holter ECG not applicable within 3 months after stroke onset. 6. Patients considered inappropriate to participate in the study