Nonvalvular Atrial Fibrillation

The aim of this observational study is to evaluate safety and therapeutic adherence during anticoagulant prophylaxis with apixaban in patients with nonvalvular atrial fibrillation. The main questions it aims to answer are: * What is the incidence of major bleeding and clinically relevant non-major bleeding during anticoagulant prophylaxis with apixaban in patients with nonvalvular atrial fibrillation? * What is therapy adherence during anticoagulant prophylaxis with apixaban in patients with nonvalvular atrial fibrillation? * What is frequency and types of other adverse reactions, excluding bleeding, during anticoagulant prophylaxis with apixaban in patients with nonvalvular atrial fibrillation? Participants will be followed for six months through four measurements. The first and fourth measurements will be performed in person, while the remaining measurements can also be recorded by telephone, if the patient's condition allows. Any bleeding or serious adverse reactions to the medication being administered will be recorded immediately, through unscheduled measurements. Adverse reactions will be recorded at each measurement. Adherence to the medication being administered will be evaluated using the BARS scale.

The goal of this clinical trial is to verify that Non-Antithrombotic Therapy (NAPT) followed by Oral Anticoagulants (OAC) monotherapy for 45 days after Left Atrial Appendage Closure (LAAC) is non-inferior to Single Antiplatelet Therapy (SAPT) with aspirin during the period from randomization to the end of observational period (4 years at the maximum) in non-valvular atrial fibrillation subjects with high bleeding risk. The primary endpoint is a composite endpoint consisting of all-cause mortality, myocardial infarction, stroke, systemic embolism, major bleeding, or clinically relevant non-fatal bleeding from randomization to the end of study observation (up to a maximum follow-up of 4 years). * Participants will be enrolled in this study until the day following the implementation of LAAC and will be randomized to the SAPT arm and NAPT arm in a 1:1 ratio. * Participants will be observed for 4 years from the time the first subject is enrolled in this study. * Participants will visit the hospital at 45 days, 1 year, and 2 years after enrollment, and will also be followed up by telephone, basically at the end of the observation period (up to a maximum follow-up of 4 years). \<Study treatment duration\> In both arms, OAC monotherapy will be initiated in the first 24 hours of enrollment and continued for 45 days (allowed window period: plus 2 weeks).. * SAPT arm will continue to receive 45 days of OAC monotherapy followed by low-dose aspirin (75～100 mg/day) as an antithrombotic agent required through the end of the study observation period. * NAPT arm do not receive antithrombotic medication after 45 days of OAC monotherapy through the end of the study observation period.