A 62-year-old man with atrial fibrillation presents with acute onset of severe pain and coldness in the right lower limb. Clinical examination reveals absent pulses and mottled skin. What is the most common cause of acute limb ischemia in this patient?

Explanation

## Most Common Cause of Acute Limb Ischemia ### Epidemiology **Key Point:** Thromboembolism from a cardiac source accounts for approximately 50% of acute limb ischemia cases, making it the single most common etiology. ### Cardiac Sources of Embolism | Cardiac Condition | Relative Frequency | Mechanism | | --- | --- | --- | | Atrial fibrillation | 45–50% | Stasis in fibrillating atrium | | Acute MI with wall motion abnormality | 10–15% | Mural thrombus formation | | Dilated cardiomyopathy | 5–10% | Ventricular stasis | | Prosthetic valve | 3–5% | Thrombosis on prosthesis | | Endocarditis | 2–5% | Septic emboli | ### Clinical Presentation **High-Yield:** The classic presentation of embolic acute limb ischemia is **sudden onset** (often within hours) of the "6 Ps": Pain, Pallor, Pulselessness, Paresthesia, Paralysis, and Perishing cold. ### Why Atrial Fibrillation? **Clinical Pearl:** Atrial fibrillation causes blood stasis in the left atrial appendage, promoting thrombus formation. The patient's AF history in this vignette is the key clinical clue pointing to embolic origin. ### Distinguishing Features from Other Causes | Feature | Embolic | Thrombotic | Dissection | | --- | --- | --- | --- | | Onset | Sudden (minutes–hours) | Gradual (hours–days) | Sudden but often with preceding trauma | | Prior claudication | Absent | Often present | Absent | | Collateral circulation | Poor (sudden occlusion) | Better developed | Variable | | Imaging | Proximal occlusion at bifurcation | Distal occlusion on atherosclerotic plaque | Intimal flap on CTA | **Key Point:** Emboli lodge at arterial bifurcations (aortic, iliac, femoral, popliteal) because the vessel narrows abruptly; the femoral bifurcation is the most common site in the lower limb. ### Management Implications **Tip:** Embolic occlusions are amenable to **embolectomy** (Fogarty catheter) if performed within 6–8 hours, whereas thrombotic occlusions may require thrombolysis or bypass grafting.