Which of the following is the most common source of pulmonary embolism in clinical practice?

Explanation

## Source of Pulmonary Embolism **Key Point:** Deep vein thrombosis (DVT) of the lower extremities is the source of >90% of clinically significant pulmonary emboli. Thrombi form in the deep veins of the legs (popliteal, femoral, and iliac veins) and embolize to the pulmonary circulation. **High-Yield:** The classic triad for DVT formation (Virchow's triad) applies: - Venous stasis - Endothelial injury - Hypercoagulability **Clinical Pearl:** Upper extremity DVT accounts for only 5–10% of PE cases and is often associated with central venous catheters or malignancy. Right atrial thrombi are rare and usually occur secondary to severe right ventricular dysfunction or arrhythmias, not as a primary source. **Mnemonic: DVT → PE** — Deep Vein Thrombosis is the Direct Path to Pulmonary Embolism. ## Why Lower Limb DVT Dominates 1. **Anatomical factors:** Leg veins are prone to stasis due to gravity and dependency. 2. **Hemodynamic factors:** Slow flow in deep leg veins favors thrombus formation. 3. **Risk factors:** Immobility, surgery, malignancy, and hypercoagulable states preferentially affect the lower extremities.