Optimal Antiplatelet Therapy Following Left Atrial Appendage Closure

Inclusion Criteria: * Successful left atrial appendage occlusion with Amplatzer or WATCHMAN device within 37 days before randomization * Treatment with dual antiplatelet therapy (clopidogrel and acetylsalicylic acid) between left atrial appendage closure and randomization * Participant's age 18 years or older at the time of signing the informed consent form * Participant is willing to follow all study procedures; especially the randomized antiplatelet treatment regimen * Participant is willing to sign the study informed consent form Exclusion Criteria: * Indications to dual antiplatelet therapy other than atrial fibrillation and/or left atrial appendage occlusion at the time of enrollment or predicted appearance of such indications within the duration of the trial (e.g. planned coronary revascularization) * Indications to anticoagulation at the time of enrollment and/or predicted appearance of such indications within the duration of the trial (e.g. pulmonary embolism) * Known allergy to clopidogrel and/or acetylsalicylic acid precluding its administration as specified by the protocol * Any known inborn or acquired coagulation disorders * Peridevice leak \>5mm on imaging study preceding enrollment * Left atrial thrombus on an imaging study performed after successful left atrial appendage closure but before enrollment * Life expectancy of fewer than 18 months * Participation in other clinical studies with experimental therapies at the time of enrollment and preceding 3 months * Chronic kidney disease stage IV and V * Women who are pregnant or breastfeeding; women of childbearing potential who do not consent to apply at least two methods of contraception. This criterion does not apply to women 2 years post menopause (with negative pregnancy test 24 hours prior to randomization if \<55 years old) or after surgical sterilization