Etiology

Driven by Virchow Triad: Endothelial injury, venous stasis, hypercoagulability.
Acquired risks: Recent surgery/trauma, immobilization, malignancy, OCPs/HRT, pregnancy, smoking, obesity, prior VTE.
Hereditary risks: Factor V Leiden (most common), Prothrombin G20210A, Antithrombin III deficiency, Protein C/S deficiency.
Most commonly arise from deep vein thrombosis (DVT) in proximal LE (femoral/iliac veins).

Tip

Up to 30% of cases may present with no apparent risk factors (eg, hypercoagulability).

Pathophysiology

Dual Blood Supply: The lungs are supplied by two circulations:
1. Pulmonary Arteries: Low-pressure system carrying deoxygenated blood from the RV for gas exchange.
2. Bronchial Arteries: High-pressure system arising from the aorta; supplies oxygenated blood to the lung parenchyma (bronchi, connective tissue).
Pulmonary Infarction:
- Due to the dual blood supply, PE does not always cause pulmonary infarction (tissue death). The bronchial circulation can often sustain the lung tissue.
- Infarction is more likely to occur if the bronchial circulation is compromised (e.g., in left-sided heart failure) or if the embolus is very peripheral.
- When it occurs, it’s typically a hemorrhagic (red) infarct because some blood from the bronchial circulation still leaks into the necrotic area.
- Clinically, it presents with pleuritic chest pain and hemoptysis. Radiologically, it may appear as a wedge-shaped infiltrate (Hampton’s Hump).

Algorithm:
- Wells score (≤4 = PE unlikely; >4 = PE likely)
  - +3 points
    - Clinical signs of DVT
    - Alternate diagnosis less likely than PE
  - +1.5 points
    - Previous PE or DVT
    - Heart rate >100/min
    - Recent surgery or immobilization
  - +1 point
    - Hemoptysis
    - Cancer
- Hemodynamically Unstable: Bedside Echo -> if RV strain -> Treat.
- Stable + Low Prob (Wells ≤4): D-dimer (High sensitivity, low specificity). If (-) -> Stop. If (+) -> CTPA.
- Stable + High Prob (Wells >4): CTPA immediately. Start empiric anticoagulation before imaging if no contraindications.
Initial/Adjuncts:
- CXR: Usually normal. Rare signs: Hampton Hump (wedge opacity), Westermark Sign (oligemia).
- ECG: Sinus tach (most common). S1Q3T3 (specific but rare, indicates RV strain).
- ABG: Respiratory alkalosis (hypocapnia), hypoxia, widened A-a gradient.
Confirmatory/Gold Standard:
- CT Pulmonary Angiography (CTPA): Best initial test for most pts.
- V/Q Scan: Use if renal failure (Cr elevated), severe contrast allergy, or pregnancy (sometimes).
- Lower Extremity US: Useful if CTPA contraindicated/unavailable; (+) DVT treats as PE.

Tension Pneumothorax: Diff by absent breath sounds, tracheal deviation, hyperresonance on percussion. c

Stabilization: Oxygen, IVF (cautious to avoid RV overload).
Anticoagulation (AC):
- Start empirically if Wells >4 and no CI to AC, even before imaging.
- Stable pts: LMWH (Enoxaparin) or Fondaparinux, followed by DOACs (Rivaroxaban, Apixaban) for 3–6 months.
- Renal failure (CrCl <30): Use Unfractionated Heparin (UFH) (easier to monitor/reverse). c
Thrombolysis (tPA): Only for Massive PE (hemodynamic instability/hypotension) with no major CI. c
Embolectomy: For massive PE when thrombolysis is contraindicated or failed.
IVC Filter: Only if pt has proven PE/DVT AND absolute contraindication to AC (e.g., active GI bleed, recent hemorrhagic stroke).

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