 Based on the previous data, ATTICUS is designed as multicentre, national, parallel groupactive controlled, phase III randomized 2x2 factorial, clinical trial to demonstrate the superiority of apixaban against the current standard of treatment acetylsalicylic acid for the longterm treatment after ESUS. ATTICUS will follow a dynamic treatment protocol implementing conversion from the acetylsalicylic acid arm to the apixaban arm in case of detection of relevant episodes of AF during the course of the study. 