Patient Selection

This is a predefined substudy nested within CROMIS‐2 AF, a multicenter prospective observational study of patients with AF‐related cardioembolic stroke or TIA, as described previously.20, 21 Briefly, this was a study of adults (aged ≥18 years) presenting with ischemic stroke or TIA with nonvalvular AF (confirmed by electrocardiography), who were eligible to start anticoagulation following their ischemic event.20, 21 Patients who could not have an MRI scan, had contraindications to anticoagulation, or had previously received therapeutic anticoagulation, were excluded.20, 21 The study was approved by the National Research Ethics Service (IRAS reference 10/H0716/61). Written informed consent was obtained in all cases.