In atrial fibrillation, embolic strokes most commonly originate from thrombus in which site?

• A. Left atrium
• B. Right atrium
• C. Left ventricle
• D. Left atrial appendage thrombus

Answer: (D)

In atrial fibrillation the irregular, ineffective atrial contractions cause blood to pool, especially in the left atrial appendage, a small, pouch-like area of the left atrium. This stasis promotes thrombus formation there. A clot that forms in the left atrial appendage can dislodge and travel through the arterial system to the brain, causing an embolic stroke. The left atrial appendage is the most common source of these emboli because of its anatomy and tendency to slow flow, making it an especially fertile site for clot formation in AF. Other sites, like the right atrium or left ventricle, are less typical sources of AF-related embolic strokes (right-sided clots tend to cause pulmonary events, and LV clots are more linked to post–MI states).