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Topic Library / Compendium / Pulmonary Embolism & Venous Thromboembolism
Core Clinical Level 1–3 Step 1–3 High Yield

Pulmonary Embolism & Venous Thromboembolism

Virchow triad, Wells criteria, PERC rule, CTA vs V/Q scanning, emergent anticoagulation, and systemic thrombolysis for massive PE.

Virchow Triad

Endothelial injury, Stasis, Hypercoagulability

Diagnostic Gold Standard

CT Pulmonary Angiography (CTPA) (or V/Q scan if renal failure/contrast allergy)

Massive PE Definition

PE with sustained hypotension (SBP < 90 mmHg) → Emergent Thrombolysis

ECG Hallmark

Sinus tachycardia (most common); S1Q3T3 (classic right ventricular strain pattern)

Clinical Risk Stratification: Wells Score & PERC Rule

Evaluating suspected pulmonary embolism begins with pre-test probability scoring to avoid inappropriate imaging:

Wells Criteria for PE

Clinical signs of DVT (3 pts), Alternative diagnosis less likely than PE (3 pts), Heart rate > 100 bpm (1.5 pts), Immobilization ≥ 3 days or surgery in past 4 weeks (1.5 pts), Previous DVT/PE (1.5 pts), Hemoptysis (1 pt), Malignancy (1 pt). Score > 4: PE Likely → proceed directly to CTPA. Score ≤ 4: PE Unlikely → High-sensitivity D-dimer.

PERC Rule (Pulmonary Embolism Rule-Out Criteria)

In patients with very low clinical suspicion, if ALL 8 criteria are met (Age < 50, HR < 100, SaO2 ≥ 95%, No prior DVT/PE, No recent surgery/trauma, No hemoptysis, No estrogen use, No unilateral leg swelling), PE is ruled out without even ordering a D-dimer.

Diagnostic Modalities: CTPA vs. V/Q Scanning

Selecting the appropriate imaging test for confirmed high-probability candidates:
Imaging TestIndicationsContraindications / LimitationsDiagnostic Finding
CT Pulmonary Angiogram (CTPA)First-line test for majority of patientsSevere renal impairment (eGFR < 30), severe anaphylactic iodinated contrast allergyIntraluminal filling defect in pulmonary arterial branches
Ventilation-Perfusion (V/Q) ScanRenal failure, pregnancy, severe contrast allergyAbnormal baseline chest X-ray (COPD, pneumonia, effusion reduces accuracy)Wedge-shaped perfusion defect with preserved normal ventilation (mismatch)
Lower Extremity Duplex UltrasoundPregnant patients or bedside unstable DVT checkNegative scan does not rule out PE (clot already embolized)Non-compressible deep vein lumen

Anticoagulation & Reperfusion Protocols

Management is categorized by hemodynamic stability (Submassive vs. Massive):

Hemodynamically Stable (Low / Intermediate Risk)

Immediate therapeutic anticoagulation: DOACs (Apixaban, Rivaroxaban) are first-line for most patients without cancer or severe renal disease. LMWH (Enoxaparin) is preferred in malignancy or pregnancy.

Massive PE (Hemodynamically Unstable)

Presents with sustained SBP < 90 mmHg, cardiogenic shock, or cardiac arrest. Requires emergent systemic thrombolysis (Alteplase / tPA) or surgical/catheter-directed embolectomy if thrombolysis is contraindicated.
COMLEX / OMM Integration NBOME High-Yield Correlate

Rib Somatic Dysfunctions & Pulmonary Autonomics

- Autonomics: Pulmonary sympathetics originate from T2–T7. Parasympathetics are supplied by the Vagus nerve (CN X).
- Rib Restrictions: Patients with acute PE or infarction develop localized rib exhalation somatic dysfunctions and diaphragmatic splinting over the affected lung segment.
Board Traps & Common Distractors
  • Trap: Delaying anticoagulation to wait for imaging in a patient with high clinical probability of PE. If suspicion is high and there are no absolute bleeding contraindications, administer anticoagulation immediately while awaiting CTPA.
  • Trap: Ordering a D-dimer in a patient with a Wells score > 4. High-risk patients require immediate CTPA regardless of what D-dimer shows.