Pulmonary Embolism (PE)

Risk factors

• Virchow triad: venous stasis, endothelial injury, hypercoagulability
• Recent surgery (especially orthopedic, abdominopelvic, neurosurgery), trauma, immobilization
• Malignancy (especially pancreatic, gastric, brain, lung, hematologic)
• Pregnancy/postpartum, estrogen therapy (OCPs, HRT)
• Prior VTE, family history
• Inherited thrombophilias: factor V Leiden, prothrombin G20210A, antithrombin/protein C/S deficiency; acquired: antiphospholipid syndrome (warfarin preferred over DOACs, especially if triple-positive)
• Obesity, advanced age, smoking, long travel (>4 h)

Pathophysiology

Thromboembolus lodges in pulmonary arteries → mechanical obstruction + neurohumoral vasoconstriction → increased pulmonary vascular resistance. Right ventricular afterload rises; severe RV strain can cause hypotension, shock, and death. Occluded arteries leave ventilated but unperfused alveoli (dead space, high V/Q); blood diverted to the remaining lung overperfuses those units (low V/Q), and together with atelectasis/shunt and low mixed-venous O2 this causes hypoxemia, with hyperventilation (hypocapnia) and a widened A-a gradient.

Clinical presentation

Differential diagnosis

• Acute coronary syndrome — Substernal pressure rather than pleuritic; ECG ischemic changes; troponin rise pattern; coronary anatomy on cath
• Pneumonia — Fever, productive cough, lobar consolidation on CXR; positive cultures
• Pneumothorax — Unilateral absent breath sounds, hyperresonance; CXR diagnostic
• Aortic dissection — Tearing pain radiating to back, BP differential, widened mediastinum on CXR/CT
• Heart failure exacerbation — Orthopnea, PND, elevated BNP, bilateral edema; echocardiogram
• Musculoskeletal chest pain — Reproducible with palpation; normal vitals and oxygenation
• Pericarditis/tamponade — Pleuritic pain improved leaning forward, diffuse ST elevation; pericardial effusion on echo
• Anxiety/hyperventilation — Diagnosis of exclusion; normal ABG except respiratory alkalosis; no risk factors

Diagnostic workup

Diagnostic algorithm

flowchart TD
  A[Suspected PE] --> B{Hemodynamically<br/>unstable?}
  B -->|Yes| C[Bedside echo<br/>RV strain?]
  C -->|Yes| D[Systemic thrombolysis<br/>or embolectomy]
  B -->|No| E[Wells / Geneva<br/>pretest probability]
  E -->|Low + PERC negative| F[PE excluded]
  E -->|"PE unlikely (two-tier Wells 4 or less)"| G[D-dimer<br/>age-adjusted]
  G -->|Negative| F
  G -->|Positive| H[CTPA]
  E -->|"PE likely (two-tier Wells over 4)"| H
  H -->|Negative| I[Consider alternative dx]
  H -->|Positive| J[Anticoagulation<br/>DOAC preferred]

Treatment

Complications

• Cardiogenic shock, cardiac arrest (PEA most common arrest rhythm)
• Chronic thromboembolic pulmonary hypertension (CTEPH) — occurs in ~3% post-PE; treat with pulmonary endarterectomy (curative) or riociguat
• Recurrence (~30% over 10 years without secondary prevention)
• Bleeding from anticoagulation, including intracranial hemorrhage
• Heparin-induced thrombocytopenia (HIT) with platelet drop >50%

PANCE pearls

• PERC rule rules out PE without D-dimer in low-pretest-probability patients meeting all 8 criteria: age <50, HR <100, SpO2 >94%, no hemoptysis, no estrogen, no prior VTE, no recent surgery/trauma, no unilateral leg swelling.
• Massive PE = hemodynamic instability; submassive = stable BP but RV dysfunction or troponin+; low-risk = stable, no RV strain. Risk-stratification (sPESI, PESI) drives disposition. The 2026 AHA/ACC guideline uses clinical categories A-E in place of these terms: A asymptomatic (incidental), B symptomatic low risk, C symptomatic elevated risk, D incipient cardiopulmonary failure (transient hypotension or normotensive shock), E cardiopulmonary failure (persistent hypotension, refractory shock, or cardiac arrest; roughly the old massive PE).
• ECG findings of severe PE: S1Q3T3 (S in I, Q and inverted T in III), new RBBB, T-wave inversions in anterior leads. Sinus tach remains the most common ECG finding.
• Wells criteria + age-adjusted D-dimer (age × 10 ng/mL if >50) safely reduce CTPA imaging in low-probability patients (ADJUST-PE).
• DOACs are first-line for most non-pregnant patients with normal renal function; apixaban and rivaroxaban require no parenteral lead-in.

References

• CHEST 2021 — Antithrombotic Therapy for VTE Disease: CHEST Guideline and Expert Panel Report (Stevens et al., Chest 2021)
• ESC 2019 — 2019 ESC Guidelines for the Diagnosis and Management of Acute Pulmonary Embolism (Konstantinides et al., Eur Heart J 2020)
• PEITHO Trial — Fibrinolysis for Patients with Intermediate-Risk Pulmonary Embolism (Meyer et al., NEJM 2014)
• ADJUST-PE — Age-Adjusted D-Dimer Cutoff Levels to Rule Out Pulmonary Embolism (Righini et al., JAMA 2014)
• AHA/ACC 2026 — 2026 AHA/ACC/ACCP/ACEP/CHEST/SCAI/SHM/SIR/SVM/SVN Guideline for the Evaluation and Management of Acute Pulmonary Embolism in Adults (Creager et al., Circulation 2026)