Prevention of Silent Cerebral Thromboembolism by Oral Anticoagulation With Dabigatran After Pulmonary Vein Isolation for Atrial Fibrillation

Inclusion criteria: 1. Written informed consent 2. Patients undergoing circumferential antral PV ablation for non-valvular (mitral regurgitation less than moderate- severe insufficiency; no relevant mitral stenosis with a mean pressure gradient \>5mmHg) symptomatic, paroxysmal AF or persistent AF (duration \< 12 months) with risk factors resulting in a CHA2DS2VASc score ≥2, using a cooled tip RF-, laser- or cryo-balloon-catheter. 3. CHA2DS2VASc score ≥2 Randomization criteria: 1. Sinus rhythm (as assessed by 72h Holter ECG) following the 3 months blanking and 3 months observation period after first or second pulmo-nary vein ablation procedure 2. No clinical evidence of recurrent AF after completing 3 months blanking and 3 months observation period as assessed by symptoms 3. No other relevant contraindication for OAC assessed by randomization MRI of the brain Exclusion criteria: 1. Severe mental retardation or psychiatrical disorder resulting in incapabil-ity to adequately understand nature, significance, implications and risks of study parcipitation (i.e. bipolar disorders, severe depression, suicidal tendencies, among others) as judged by the local physician, ongoing drug or alcohol addiction (\> 8 drinks/week) 2. Pregnancy /breast feeding 3. Severely impaired renal function, GFR \< 30 ml/min 4. Impaired liver function (ALT/AST transaminase count 3fold higher than normal values) or liver disease with reduced life expectancy \<1 year 5. Valvular AF (moderate- severe mitral insufficiency; relevant mitral steno-sis with a mean pressure gradient \>5mmHg) 6. Long standing persistent (\>12 months) and permanent AF 7. NSTEMI/STEMI/implantated drug eluting stent with indication for dual antiplatelet therapy within 12 months before enrolment 8. History of complex left atrial ablation procedures. One previous PVI al-lowed. 9. Clinical indication for extended left atrial ablation procedures (CFAE-, rotor-ablation) 10. History or presence of left atrial or ventricular thrombus 11. History of stroke / TIA independent from etiology 12. Acute major bleedings 13. Lesion or condition, if considered a significant risk factor for major bleeding. This may include current or recent gastrointestinal ulceration, presence of malignant neoplasms at high risk of bleeding, recent brain or spinal injury, recent brain, spinal or ophthalmic surgery, recent intracranial haemorrhage, known or suspected oesophageal varices, arteriovenous malformations, vascular aneurysms or major intraspinal or intracerebral vascular abnormalities 14. Need for concomitant anitcoagulation in addition to dabigatran 15. History of previous surgery resulting in contraindication for OAC 16. History of malignoma resulting in contraindication for OAC 17. Mechanical prosthetic heart valve or other indication for permanent OAC 18. Contraindication for MRI (i.e. metal implants unsuitable for MRI, wearing of magnetic or metallic objects that cannot be removed from the body (such as body piercing, implanted electrodes, contraceptive coil), inabil-ity to lie on the back for an extended period of time, uncontrollable claustrophobia, hypersensitivity to noise etc.). Pacemaker and ICD-patients may be included at the discretion of the local investigators/radiologists if MRI is warranted 19. Hypersensitivity against dabigatran or other ingredients of the medical product 20. Concomitant medication with dronedarone, ketoconazole, itraconazole, cyclosporine, tacrolimus or other interacting drugs as specified in the drug information 21. Simultaneous participation in any clinical trial involving administration of an investigational medicinal product within 30 days prior to clinical trial beginning 22. Females of childbearing potential, who are not using or not willing to use medically reliable methods of contraception for the entire study duration (such as oral, injectable, or implantable contraceptives, or intrauterine contraceptive devices) unless they are surgically sterilized / hysterectomized or there are any other criteria considered sufficiently reliable by the investigator in individual cases 23. Conditions which interfere with the study treatment at the discretion of the investigator