A 62-year-old man with a history of atrial fibrillation and hypertension presents with acute left-sided weakness and speech difficulty. Imaging confirms acute ischemic stroke. Which is the most common site of thrombus formation in this patient?

Explanation

## Most Common Site of Thrombus in Atrial Fibrillation **Key Point:** The left atrial appendage (LAA) is the most common site of thrombus formation in patients with atrial fibrillation, accounting for >90% of cardioembolic thrombi in AF. ### Pathophysiology 1. Atrial fibrillation causes loss of organized atrial contraction 2. Blood stasis develops, particularly in the low-flow LAA 3. Virchow's triad is satisfied: stasis (flow), endothelial injury (from AF), and hypercoagulability (AF-induced) 4. Thrombus forms and embolizes to systemic circulation (especially cerebral vessels) ### Comparison of Common Thrombotic Sites | Site | Condition | Frequency | Mechanism | |------|-----------|-----------|----------| | Left atrial appendage | Atrial fibrillation | Most common (>90% in AF) | Blood stasis in low-flow chamber | | Left ventricular apex | Anterior MI, dilated cardiomyopathy | Common in LV dysfunction | Akinetic/dyskinetic wall segment | | Aortic arch | Atherosclerosis, hypercoagulable states | Less common | Atherosclerotic plaque ulceration | | Carotid bifurcation | Atherosclerotic disease | Arterial thrombosis, not cardiac | Plaque rupture and endothelial injury | **High-Yield:** Atrial fibrillation increases stroke risk 5-fold; anticoagulation (warfarin or DOAC) reduces this risk by ~64%. LAA thrombi are the source in the vast majority of cardioembolic strokes in AF patients. **Clinical Pearl:** Even paroxysmal AF carries significant thromboembolic risk because LAA dysfunction persists between episodes. CHA₂DS₂-VASc score guides anticoagulation decisions in AF. **Mnemonic:** **LAA-AF** — Left Atrial Appendage is the Achilles' Foot in Atrial Fibrillation.