Defining the Criteria for ISIS Strokes

The classification of Embolic Stroke of Undetermined Source (ISIS) hinges on three key criteria: first, the stroke must be non-Lakunar as confirmed by brain imaging; second, there should be no significant narrowing (over 50%) in intracranial or extracranial arteries affecting the stroke territory; and third, there must be an absence of any high-risk cardioembolic sources, such as atrial fibrillation or mechanical heart valves. Proper patient workup is essential, which includes a 24-hour monitoring for atrial fibrillation and imaging of blood vessels to exclude significant stenosis.