Pulmonary Embolism

Detailed Overview

PE is a life-threatening manifestation of venous thromboembolism (VTE). The clot blocks blood flow to a segment of the lung, preventing gas exchange and severely increasing pulmonary vascular resistance. If the clot burden is large enough, the rapid increase in right ventricular afterload causes acute right heart failure, decreased left ventricular filling, cardiogenic shock, and sudden death. It is a leading cause of preventable hospital mortality.

Epidemiology & Demographics

Incidence is roughly 60-70 per 100,000 population annually. Risk increases exponentially with age, particularly after 60 years. Slight male predominance in older age, but female predominance in childbearing years (due to pregnancy and oral contraceptives).

Etiological Mechanism

The majority (>90%) of pulmonary emboli originate as Deep Vein Thromboses (DVT) in the popliteal, femoral, or iliac veins. Emboli can also consist of fat (post long-bone fracture), air (central line placement), or amniotic fluid, though these are rare.

Primary Causes

Provoked PE is caused by transient risk factors: surgery, trauma, immobility, pregnancy, or estrogen use. Unprovoked PE occurs in the absence of transient risks and is often linked to active malignancy or undiagnosed inherited thrombophilias.

• Immobility: Bed rest > 3 days, long-haul flights (>4 hours), or casting of a lower extremity promotes venous stasis.
• Surgery/Trauma: Major orthopedic surgery (hip/knee replacement) causes massive endothelial injury and hypercoagulability.
• Malignancy: Cancers (especially pancreatic, lung, gastric, brain) secrete procoagulants like tissue factor.
• Hypercoagulable States: Factor V Leiden mutation, Prothrombin G20210A mutation, Antiphospholipid Syndrome, or use of Combined Oral Contraceptives.

Pathogenesis follows Virchow's Triad: endothelial injury, venous stasis, and hypercoagulability. A thrombus forms in a deep vein, fragments, and embolizes through the right heart into the pulmonary arterial tree. Obstruction of the artery causes a ventilation-perfusion (V/Q) mismatch (ventilated alveoli are not perfused - alveolar dead space), leading to hypoxemia. The body releases serotonin and thromboxane A2 from platelets, causing further pulmonary vasoconstriction. The sudden rise in pulmonary vascular resistance forces the right ventricle to generate higher pressures. A massive PE causes acute RV dilation and failure; the interventricular septum bows into the left ventricle, reducing left ventricular end-diastolic volume, dropping cardiac output, and causing obstructive shock.

Characteristic Clinical Presentation

• Sudden Dyspnea: Acute onset shortness of breath at rest or exertion; the most common symptom.
• Pleuritic Chest Pain: Sharp chest pain that worsens with deep inspiration or coughing, indicating peripheral lung infarction.
• Hemoptysis: Coughing up blood, seen in roughly 10% of cases when pulmonary infarction occurs.
• Syncope: Fainting or sudden collapse, a classic presentation for massive, hemodynamically unstable PE.

Physical Examination Signs

• Tachypnea
• Tachycardia
• Unilateral Leg Swelling

• Cardiogenic/Obstructive Shock: Rapid cardiovascular collapse due to right heart failure.
• Pulmonary Infarction: Death of lung tissue supplied by the occluded artery, causing pain and hemoptysis.
• Chronic Thromboembolic Pulmonary Hypertension (CTEPH): Occurs in ~2-4% of survivors where the clot fails to dissolve, fibroses, and causes chronic high pulmonary pressures.

Diagnostic Criteria & Guidelines

Clinical probability assessed via Wells Score or Geneva Score. Low probability: normal D-dimer rules out PE. High probability or positive D-dimer: CT Pulmonary Angiography (CTPA) is the gold standard diagnostic test, demonstrating a filling defect in the pulmonary arteries.

Differential Diagnosis

• Acute Myocardial Infarction
• Aortic Dissection
• Pneumothorax
• Pneumonia
• Asthma/COPD exacerbation

Laboratory Tests & Biomarkers

• D-dimer: Elevated (typically > 500 ng/mL); highly sensitive but poorly specific.
• Troponin I/T: Elevated in submassive/massive PE indicating right ventricular myocardial microinfarction.
• Arterial Blood Gas: Hypoxemia (PaO2 < 80 mmHg) and respiratory alkalosis (low PaCO2) due to hyperventilation.

Imaging Modalities & Findings

• CT Pulmonary Angiography (CTPA): Intraluminal filling defects in the main, lobar, segmental, or subsegmental pulmonary arteries. May show RV enlargement (RV/LV ratio > 1.0).
• ECG: Sinus tachycardia is most common. Classic S1Q3T3 pattern (S wave in I, Q wave in III, inverted T in III) is highly specific but rare, indicating right heart strain.

• Low Risk (Non-massive)
  Normal blood pressure, normal right heart function on Echo, negative cardiac biomarkers.
• Submassive (Intermediate Risk)
  Normal blood pressure, but evidence of Right Ventricular dysfunction (on Echo or CT) or elevated cardiac biomarkers (Troponin, BNP).
• Massive (High Risk)
  Hemodynamic instability: Systolic BP < 90 mmHg for >15 mins, requiring inotropes, or pulselessness.

Second-Line & Adjunctive Therapy

For Massive PE (hemodynamically unstable): Systemic thrombolysis with Alteplase (tPA) 100 mg IV over 2 hours. If thrombolysis is contraindicated (e.g., recent surgery, bleeding risk), catheter-directed thrombectomy or surgical pulmonary embolectomy is indicated.

Surgical & Procedural Management

Inferior Vena Cava (IVC) Filter placement if anticoagulation is strictly contraindicated (e.g., active GI bleed) or if recurrent PE occurs despite therapeutic anticoagulation.

Recommended Lifestyle Changes

• Early ambulation post-surgery and during hospitalization.
• Use of graduated compression stockings during long flights.
• Adequate hydration and taking breaks to walk during long sedentary periods.

Patient Counseling & Advice

Educate on the signs of bleeding while on anticoagulation (melena, hematuria, severe headaches). Advise avoiding contact sports. Counsel women of childbearing age to stop estrogen-containing oral contraceptives immediately.

Follow-Up & Monitoring Schedule

Outpatient follow-up within 2-4 weeks to assess bleeding compliance. Minimum anticoagulation duration is 3 months for provoked PE; lifetime therapy may be needed for unprovoked PE or recurrent VTE. Follow-up echocardiogram at 3-6 months to screen for CTEPH.

Preventive Strategies

VTE prophylaxis in hospitalized patients using Enoxaparin 40 mg SC daily or Heparin 5000 U SC TID. Mechanical prophylaxis (SCDs) if bleeding risk is high.

Untreated PE has a mortality rate up to 30%. With timely anticoagulation, mortality drops to 2-8%. Massive PE presenting with shock carries a 30-50% short-term mortality.