Pulmonary Embolism (PE)

Definition & Epidemiology

Pathophysiology

1. Venous stasis — prolonged immobility, uterine compression of IVC
2. Hypercoagulability — inherited (Factor V Leiden, protein C/S deficiency, antithrombin deficiency, prothrombin G20210A) or acquired (malignancy, antiphospholipid syndrome, OCP use, pregnancy)
3. Endothelial injury — surgery, trauma, catheter placement

• Right ventricular (RV) afterload increases acutely
• RV dilation → interventricular septal deviation → compresses the left ventricle
• LV filling decreases → reduced cardiac output → systemic hypotension
• Coronary perfusion falls → RV ischemia → spiral of cardiac failure
• Respiratory consequences: dead-space ventilation, hypoxemia, reflex bronchoconstriction

Autopsy: massive PE occluding the RV outflow — Rosen's Emergency Medicine

Risk Factors

Clinical Presentation

Symptoms

• Dyspnea is the most common symptom but absent in ~25% of patients — do not rule out PE based on its absence
• Pleuritic pain suggests peripheral PE causing pulmonary infarction
• Fever from PE is low-grade; temperature >38.6°C (101.5°F) suggests infection
• Syncope alone, especially with risk factors, can be a PE presentation

Vital Signs

⚠ Normal O₂ saturation cannot rule out PE. Normalization of vital signs does not reduce PE probability.

Physical Examination

• Usually unremarkable
• DVT signs (unilateral edema, leg asymmetry, vein tenderness) are the only findings that reliably increase PE probability
• Wheezing → favors bronchospasm over PE; bilateral rales → favors LV failure

Cardiac Arrest from PE

• PEA (pulseless electrical activity) is the most common ECG finding in PE-related arrest
• Survival rate from PE cardiac arrest ≈ 20% even with witnessed arrest and thrombolytics

Diagnosis

Clinical Pre-test Probability

• Low: ≤1 | Moderate: 2–6 | High: ≥7
• Two-level version: ≤4 = PE unlikely; >4 = PE likely

• Age <50, HR <100, SpO₂ ≥95%, no unilateral leg swelling, no hemoptysis, no recent trauma/surgery, no prior DVT/PE, no exogenous estrogen use

Laboratory Tests

• D-dimer: High sensitivity (~98%), low specificity. A negative D-dimer (<500 ng/mL) with low pre-test probability effectively rules out PE. Not useful if probability is high. In the elderly, age-adjusted cutoff = age × 10 ng/mL (e.g., age 70 → cutoff 700 ng/mL).
• Troponin I/T and BNP/NT-proBNP: Markers of RV strain — useful for risk stratification, not diagnosis. Elevated troponin indicates RV myocardial injury and portends worse prognosis.
• ABG: May show hypoxemia, hypocapnia (respiratory alkalosis), increased A-a gradient — nonspecific

ECG

• Sinus tachycardia (most common)
• S1Q3T3 pattern (S wave in lead I, Q wave and T-wave inversion in lead III) — classic but insensitive (~20%)
• Right bundle branch block (complete or incomplete)
• T-wave inversions in V1–V4 (RV strain pattern)
• New right axis deviation

Chest X-Ray

• Westermark sign: Focal oligemia (hypovascular zone distal to obstructed vessel)
• Hampton's hump: Peripheral wedge-shaped opacity (pulmonary infarction)
• Palla sign: Enlarged right descending pulmonary artery
• Elevated hemidiaphragm, atelectasis, small pleural effusion

Imaging

• Sensitivity ~96%, specificity ~98% for segmental/larger PE
• Shows hypodense intraluminal filling defects within pulmonary arteries

CTPA: bilateral filling defects (arrows) in both main pulmonary arteries — massive PE

• Preferred when CTPA is contraindicated (renal failure, contrast allergy, pregnancy)
• In pregnancy: halving the perfusion dose is standard practice; fetal radiation exposure ≈ 0.011–0.022 cGy
• Results: Normal (rules out PE), High probability, Indeterminate

Risk Stratification

Treatment

General Supportive Care

• Supplemental oxygen; mechanical ventilation if needed (use low tidal volumes to avoid worsening RV dilation from high intrathoracic pressures)
• IV fluids cautiously — excessive volume can worsen RV dilation
• Vasopressors (norepinephrine preferred) for hemodynamic instability

Anticoagulation (cornerstone of treatment)

• Provoked (reversible risk factor): 3 months
• Unprovoked or high-recurrence risk: ≥3–6 months, often indefinite
• Cancer-associated VTE: indefinite (LMWH or DOAC preferred)

Thrombolysis (Systemic)

• Alteplase 100 mg IV over 2 hours (or 0.6 mg/kg for cardiac arrest)
• Contraindications: recent surgery (<10 days), intracranial pathology, active bleeding, recent stroke
• Survival from PE arrest ≈ 20% even with witnessed arrest + thrombolytics

Catheter-Directed Therapy (CDT)

• Catheter-directed thrombolysis or mechanical thrombectomy
• Considered for submassive PE with high bleeding risk for systemic thrombolysis, or failed systemic lysis
• Effective at restoring patency (as seen in pre/post angiography images of bilateral PE treatment)

Surgical Embolectomy

• Reserved for massive PE with absolute contraindication to thrombolysis or failed thrombolysis
• High-risk procedure

IVC Filter

• Indicated when anticoagulation is absolutely contraindicated (e.g., active hemorrhage)
• Preferred: retrievable filters; permanent filters have long-term complications (IVC thrombosis)

Special Populations

Pregnancy

• VTE risk is 5× higher than non-pregnant age-matched controls
• Diagnosis complicated by: physiological dyspnea, elevated baseline D-dimer
• Left-sided DVT predominates (88% in one series) due to gravid uterus compressing left iliac vein
• A pregnancy-adapted YEARS algorithm has been studied but no strategy can fully safely exclude PE in pregnancy given catastrophic consequences of a missed diagnosis
• Treatment: LMWH throughout pregnancy and ≥6 weeks postpartum (warfarin and DOACs contraindicated)

Cancer

• Highest VTE risk; LMWH (dalteparin) or DOACs (edoxaban, rivaroxaban) preferred
• A 2024 meta-analysis found significant VTE risk in lung cancer (PMID 39183726)

Complications

• Pulmonary hypertension (chronic thromboembolic pulmonary hypertension, CTEPH) — ~4% of PE survivors
• Recurrent VTE — ~30% at 10 years if anticoagulation stopped
• Post-thrombotic syndrome (from underlying DVT)
• Right heart failure (acute cor pulmonale)

Key Mnemonics & Pearls

• "PERC all 8 criteria" — if ALL met with low clinical suspicion, no further workup needed
• Shock index >1 (HR > SBP) — suggests high-risk PE requiring urgent intervention
• Normal SpO₂ does not exclude PE (~50% of PE patients have normal oxygen saturation)
• Normal D-dimer in a low-probability patient effectively rules out PE
• Age-adjusted D-dimer (age × 10 ng/mL for age >50) improves specificity without sacrificing sensitivity
• PEA arrest in an undifferentiated patient → think PE, tension pneumothorax, cardiac tamponade