Pulmonary Embolism (PE)

Definition and Overview

Pathophysiology

• Redistribution of blood flow to non-obstructed zones, creating low V/Q areas
• Shunt (from atelectasis and surfactant loss) appearing hours to days later
• Markedly low mixed venous PO2 from depressed cardiac output (amplifies venous admixture)
• Loss of surfactant causing atelectasis in the infarcted zone

Risk Factors (Virchow's Triad)

Clinical Presentation

Symptoms

• Dyspnea: most common symptom (75-80%), but absent in ~25%
• Chest pain: 2nd most common; can be pleuritic (sharp, respirophasic - seen in ~20%, usually with peripheral/infarction PE), dull, or vague
• Hemoptysis, cough, fever: suggest pulmonary infarction; fever > 38.6°C (101.5°F) suggests infection rather than PE
• Syncope: PE in <5% of patients presenting with syncope, but unexplained syncope with risk factors should prompt consideration
• Unilateral leg swelling: present in <30%, but highly specific when combined with dyspnea or chest pain

Vital Signs

Physical Examination

Autopsy specimen: massive PE completely occluding the right ventricular outflow tract. - Rosen's Emergency Medicine, Fig. 74.7

Diagnosis

Step 1 - Pretest Probability (Clinical Decision Rules)

• Score > 4 = PE likely
• Score ≤ 4 = PE unlikely (proceed to D-dimer)

Step 2 - D-Dimer

• High sensitivity (~95%), low specificity
• A negative D-dimer in a low-pretest-probability patient effectively excludes PE
• Age-adjusted D-dimer threshold: age × 10 ng/mL (in patients > 50 years) - increases specificity without significantly reducing sensitivity
• YEARS algorithm: combines 3 criteria (DVT signs, hemoptysis, PE as most likely diagnosis) with D-dimer thresholds (< 500 ng/mL if any YEARS item present; < 1000 ng/mL if none present) to rule out PE safely in many patients

Step 3 - Imaging

• High sensitivity and specificity for PE down to the segmental level
• Preferred in most non-pregnant patients
• Can identify alternative diagnoses
• Maternal breast radiation exposure is significant (7-70 mSv); consider V/Q in young women

• Preferred in pregnancy (lower maternal breast dose) and when contrast is contraindicated
• Results: normal (excludes PE), high probability (diagnoses PE), or indeterminate
• In pregnancy: perfusion-only scan with half-dose is standard practice

• Bedside TTE/TEE: RV dilation, septal bowing, reduced RV function, McConnell sign (RV free wall hypokinesis with preserved apex)
• Not sensitive for PE itself but useful for risk stratification and resuscitation guidance
• May directly visualize saddle embolus in massive PE

• Usually normal or non-specific
• Classic signs: Hampton's hump (wedge-shaped opacity - infarction), Westermark sign (oligemia)

• If positive for DVT in a patient with clinical suspicion for PE, may be sufficient to start treatment without CTPA

Biomarkers

• Troponin (I or T): elevated = RV myocardial injury; strongly predicts short-term adverse outcomes and mortality - Murray & Nadel's, p. 893
• BNP/NT-proBNP: elevated with RV strain; used for risk stratification
• D-dimer: see above

Risk Stratification

Management

1. Immediate Resuscitation

• Supplemental O2; intubation if respiratory failure (caution: intubation drops preload and can precipitate RV collapse)
• IV fluids (cautiously - RV is preload dependent but volume overload worsens septal shift)
• Vasopressors for refractory hypotension: norepinephrine preferred

2. Anticoagulation (All confirmed PE without contraindication)

3. Reperfusion Therapy

• Alteplase (tPA) 100 mg IV over 2 hours (or 0.6 mg/kg over 15 min in arrest)
• Reduces clot burden, RV dilation, and hemodynamic instability
• Major bleeding (including intracranial hemorrhage ~2-3%) is the principal risk
• Contraindicated with recent surgery, active bleeding, recent stroke

4. Duration of Anticoagulation

5. Outpatient vs. Inpatient Treatment

Pregnancy-Specific Considerations

• D-dimer is physiologically elevated in pregnancy; standard thresholds unreliable
• Pregnancy-adapted YEARS algorithm may reduce unnecessary imaging in some patients, but limited data means caution is warranted
• LMWH is the anticoagulant of choice throughout pregnancy (DOACs are contraindicated; warfarin crosses placenta)
• Imaging: Start with lower-limb CUS; if negative, proceed to CTPA or V/Q (V/Q preferred by some due to lower maternal breast dose)
• Fetal radiation from CTPA is low (0.01-0.66 mSv) vs. natural background (~0.5-1.0 mSv/gestation) - Rosen's Emergency Medicine, Table 74-6

Key ECG Findings

• Sinus tachycardia - most common
• S1Q3T3 pattern - classic but present in minority
• New right bundle branch block (RBBB)
• T-wave inversions in V1-V4 (RV strain pattern)
• PEA in cardiac arrest

Summary Algorithm

Suspected PE
    │
    ├─ Hemodynamically unstable?
    │       YES → Immediate resuscitation + CTPA/bedside echo
    │               Massive PE confirmed → Systemic thrombolysis (if no CI)
    │
    └─ Hemodynamically stable?
            │
            ├─ Wells Score
            │       Low/Moderate (PE unlikely, score ≤4) → D-dimer
            │           Negative → PE excluded
            │           Positive → CTPA
            │
            └─ High (PE likely, score >4) → CTPA directly
                    PE confirmed → Anticoagulation ± risk stratify
                    Low risk → Consider outpatient DOAC
                    Submassive → Anticoagulation ± CDT

• Rosen's Emergency Medicine: Concepts and Clinical Practice, Chapter 74 (Pulmonary Embolism)
• Murray & Nadel's Textbook of Respiratory Medicine (Chapters 81-82 on PE, pathophysiology of hypoxemia)
• Murray & Nadel's Textbook of Respiratory Medicine (Chapter on PE in pregnancy)
• Recent evidence: anticoagulation vs. thrombolysis meta-analysis (PMID 39267429); DOACs in cancer-associated VTE (PMID 40578592)