Atrial Fibrillation in Cryptogenic Stroke and TIA

Inclusion Criteria: 1. Cryptogenic ischemic stroke patients or symptomatic TIA \< 21 days from symptom start. 2. A stroke/TIA is considered to be cryptogenic if no cause can be determined despite an extensive workup according to the standard protocol of the participating center. Before inclusion to the study, the following tests are required as standard tests to establish the diagnosis of cryptogenic stroke or TIA: 1. Brain MRI or CT† 2. 12-lead ECG for AF detection 3. 24-h ECG monitoring for AF detection and premature atrial complex analysis (e.g. Holter) 4. TEE (transesophageal echocardiography) highly recommended or TTE (transthoracic echocardiography) 5. Colour Duplex ultrasound examination of the pre-cerebral arteries 6. CTA or MRA of head and neck to rule out other causes of stroke pathologies 3. Age 18 to 80 at onset of TIA/stroke 4. A participation consent form signed by the patient or a legally authorized representative. * TIA cases with acute non-lacunar infarct on Diffusion Weighted Imaging are included as TIA events. Exclusion Criteria: 1. Known etiology of TIA or stroke. 2. TIA without documented cerebral ischemia on Diffusion Weighed Imaging. 3. Untreated hyperthyroidism 4. Myocardial infarction less than 1 month prior to the stroke or TIA. 5. Coronary bypass grafting less than 1 month prior to the stroke or TIA. 6. Valvular heart disease requiring immediate surgical intervention. 7. History of atrial fibrillation or atrial flutter. 8. Patent Foramen Ovale (PFO) or PFO where there is or was an indication to start oral anticoagulation 9. Permanent indication for OAC treatment at enrollment. 10. Permanent contra-indication for OAC. 11. Life expectancy less than 1 year. 12. Pregnancy 13. An indication for an Implantable Pulse Generator (IPG), Implantable Cardioverter-Defibrillator (ICD), Cardiac Resynchronization Therapy (CRT) or an implantable hemodynamic monitoring system. 14. Patient otherwise not eligible for the study or adherent for follow-up (e.g. non-resident) or has concurrent disease which may affect clinical outcome (e.g. multiple sclerosis, cancer).