Plasma Modifications Associated With Rivaroxaban® Treatment for Stroke Prevention

Inclusion Criteria: * The patient was correctly informed about the study, its implementation, objectives, associated restrictions and patient rights * The patient must have given his/her informed and signed consent * The patient must be insured or beneficiary of a health insurance plan * The patient is available for 1 month of follow-up * The patient has non-valvular atrial fibrillation that was diagnosed within the last 3 months. Documentation of atrial fibrillation by a 12-lead ECG, an ECG rhythm strip, atrial fibrillation episode lasting at least 30 seconds. * The patient has a CHA2-DS2-VASc score = 1, that is to say the presence of at least one of the following risk factors: (1) congestive heart failure or moderate to severe systolic dysfunction of the left ventricle; (2) history of systolic blood pressure\> 160 mmHg; (3) diabetes; (4) history of ischemic stroke or systemic embolism; (5) vascular disease (myocardial infarction, arterial disease); (6) age \> 65 years; (7) female. * The patient will start Rivaroxaban (Xarelto®) at the Nîmes University Hospital Exclusion Criteria: * The patient is participating in another interventional study * The patient has participated in another interventional study within the past three months * The patient is in an exclusion period determined by a previous study * The patient is under judicial protection, under tutorship or curatorship * The patient refuses to sign the consent * It is impossible to correctly inform the patient * The patient is pregnant, parturient, or breastfeeding * Presence of a mechanical heart valve or valve disease * Patient who recieved another new direct oral anticoagulant other than Xarelto® in the previous three months