The aim of this study is to determine the diagnostic yield of continuous 7-day Holter ECG for detecting covert paroxysmal atrial fibrillation in patients with recent embolic stroke or transient ischemic attack (TIA) of undetermined cause after completion of a standard clinical work up including an initial 24-hour Holter monitoring.

Covert atrial fibrillation (AF) is a relevant potential cause of a recently proposed clinical construct, "Embolic Stroke of Undetermined Source (ESUS)". However, routine post-stroke work up including 24-hour Holter monitoring may fail to detect paroxysmal AF. A recent systematic review has shown an increased AF detection rate with longer monitoring durations. The aim of this study is to evaluate the effectiveness of a novel ambulatory 7-day Holter ECG (EV-201, Parama-Tech inc.) for detecting AF in patients with recent ESUS after completion of a standard clinical examination.

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

Patients with recent embolic stroke of undetermined source