Optimal Antiplatelet Therapy Following Left Atrial Appendage Closure

Who May Qualify: - 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 willing to sign a consent form form - Participant is willing to follow all study procedures; especially the randomized antiplatelet treatment regimen - Participant is willing to sign the study willing to sign a consent form form Who Should NOT Join This Trial: - 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 Always talk to your doctor about whether this trial is right for you.