A 58-year-old man from Delhi presents with acute onset left-sided weakness and slurred speech. He has a history of atrial fibrillation (not on anticoagulation) and hypertension. CT head shows no hemorrhage. MRI brain reveals acute infarction in the left middle cerebral artery territory. On examination, irregular pulse is noted. What is the most likely source of the thrombus in this patient?

Explanation

## Clinical Scenario Analysis This patient presents with acute ischemic stroke in the setting of **untreated atrial fibrillation**. The irregular pulse on examination confirms AF. ### Pathophysiology of Cardioembolic Stroke in AF **Key Point:** Atrial fibrillation causes loss of organized atrial contraction, leading to blood stasis particularly in the **left atrial appendage (LAA)**. Stasis promotes thrombus formation. **High-Yield:** The left atrial appendage is the source of thrombi in 90% of cardioembolic strokes due to AF. The LAA has a narrow neck and complex anatomy that traps blood during AF. ### Why LAA Thrombus Forms 1. **Loss of atrial contractility** → blood stasis in LAA 2. **Endothelial injury** from abnormal flow patterns 3. **Hypercoagulability** (AF itself increases thrombotic tendency) 4. **Virchow's triad satisfied:** stasis (primary), endothelial injury (secondary), hypercoagulability (tertiary) ### Comparison of Cardioembolic Sources | Source | Clinical Context | Frequency in AF | |--------|------------------|------------------| | LAA thrombus | AF without anticoagulation | 90% of cardioemboli | | Mural thrombus | Post-MI with akinetic segment | Acute MI phase | | Atherosclerotic plaque | Carotid stenosis >50% | Arterial source, not cardiac | | PFO paradoxical embolism | Venous thromboembolism + PFO | Requires VTE source | **Clinical Pearl:** This patient has no history of recent MI (no mural thrombus), no evidence of carotid disease (no TIA/amaurosis fugax prodrome), and no mention of DVT/PE (no PFO paradoxical route). The **irregular pulse + AF history + no anticoagulation** = LAA thrombus. **Mnemonic:** **CHADS₂** score predicts stroke risk in AF; this patient has C (CHF/LV dysfunction risk), H (Hypertension), A (Age ≥75 or 65–74 with risk factors), D (Diabetes), S (prior Stroke/TIA/thromboembolism). Even one point warrants anticoagulation; this patient should have been on warfarin or DOAC. ### Prevention & Management - **Anticoagulation** (warfarin INR 2–3 or DOAC) reduces stroke risk by ~65% in AF - **LAA closure devices** (Watchman, LAAC) for patients with contraindications to anticoagulation - **Aspirin alone** is insufficient in AF with stroke risk factors