To prevent stroke recurrence, we treat patients based on the presumed underlying etiology; however, in clinical practice, the underlying mechanism remains undetermined in up to 30% of patients.1 Atrial fibrillation (AF), a known and frequent culprit for cardioembolic stroke, can be transient and not present at the time of evaluation following a stroke. Treatment differs for patients who have strokes caused by AF because of the high risk of recurrent stroke with AF and the high degree of effectiveness of oral anticoagulants to reduce cardioembolic stroke risk. Several guidelines recommend a minimum of 24 to 48 hours of Holter monitoring in all patients with stroke to identify AF as the underlying source of stroke.2 Previous studies found that Holter ECG monitoring (24–72 hours) detects paroxysmal AF in approximately 5% of patients with stroke, and longer duration ECG monitoring detects AF in an additional 5% to 30% of patients depending on the type and duration of monitoring.2–4

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