Blood Clotting Markers and Heart Ultrasound in People With Device-Detected Atrial Fibrillation

Inclusion Criteria: * Age \> 50 years at inclusion * Presence of a cardiac implanted electronic device, either: * A pacemaker or internal cardiac defibrillator with an atrial lead * An implantable cardiac monitor * ≥1 episode of device-detected atrial fibrillation lasting ≥30 seconds within the previous 12 months, indentified: * During routine cardiac implantable electronic device interrogation for patients with a pacemaker or implantable cardiac defibrillator. * Through remote monitoring for patients with an implantable cardiac monitor * The longest episode of device-detected atrial fibrillation must be confirmed by the investigator by review of the stored intracardiac electrogram (EGM) for pacemakers and implantable cardiac defibrillators or review of the single-lead electrogardiogram for implantable cardiac monitors. * Written informed consent obtained prior to inclusion Exclusion Criteria: * History of ECG-documented atrial fibrillation at any time prior to inclusion * Use of oral anticoagulation or dual antiplatelet therapy within 6 months prior to inclusion, irrespective of indication * Current treatment with oral contraceptives or hormone replacement therapy * Pregnancy or breastfeeding * End-stage renal disease (creatinine clearance \<15 mL/min, calculated using the Cockcroft-Gault equation) * Active malignancy, defined as cancer diagnosis not followed by curative treatment within 6 months of diagnosis * Major surgery within the last 3 months * Connective tissue disease requiring treatment * Acute coronary syndrome, stroke/transient ischemic attack, or venous thromboembolism within 3 months prior to inclusion * Known thrombophilia * Clinically significant hepatic or hematological disease requiring treatment and/or specialist follow-up * Mechanical heart valve, moderate-to-severe mitral stenosis, or other valvular disease requiring intervention