Pulmonary Embolism Lecture Notes

Overview

• Discusses signs and symptoms, risk factors, pathophysiology, investigations, diagnosis, and treatment/management of pulmonary embolism.

Signs and Symptoms

• Dyspnea (shortness of breath)
• Pleuritic chest pain
• Tachycardia (rapid heart rate)
• Hypotension (low blood pressure)
• Signs of deep vein thrombosis (DVT):
  • Swollen leg
  • Pain in the lower legs
• DVT is a major cause (~90-95%) of pulmonary embolism

Risk Factors

• Surgery (abdominal, pelvic, orthopedic)
• Obstetric factors (e.g., pregnancy)
• Cardiorespiratory issues (COPD, congestive heart failure)
• Lower limb problems (varicose veins, fractures)
• Malignant diseases
• Increasing age
• Immobility
• Thrombotic disorders (focus due to their significant role in causing PE)

Sources of Thrombi

• Common: External iliac vein, femoral vein, deep femoral vein, popliteal vein, posterior tibial vein
• Less common: Right side of the heart, gonadal veins, uterine veins, great saphenous vein

Pathophysiology

• Thrombus: Collection of RBCs, platelets, and fibrin
• Virchow's Triad: Abnormal blood flow, hypercoagulability, altered vessel wall
• Outcomes of thrombus formation:
  • Resolution
  • Propagation
  • Embolization (most relevant for PE)
  • Recanalization
  • Organization

Events Leading to PE

1. Thrombus forms (often in deep veins of the lower limbs)
2. Thrombus breaks off, travels through inferior vena cava to the heart
3. Embolus lodges in the pulmonary artery, causing PE

Cardiovascular Effects

• Increased pulmonary vascular pressure → Increased right ventricular pressure → Ventricular dilation → Right-sided heart failure → Decreased stroke volume and cardiac output → Decreased blood pressure
• Sympathetic response: Increases heart rate (tachycardia) and vasoconstriction, but overall hypotension persists

Respiratory Effects

• Ventilation-Perfusion (V/Q) mismatch and inflammation → Bronchoconstriction → Hyperventilation → Hypocapnia (reduced CO2) → Hypoxemia (reduced O2) → Respiratory alkalosis
• Detected through arterial blood gas (ABG) test

Diagnostic Investigations

• X-ray: Often normal, used to exclude other conditions (pneumonia, pneumothorax); may show enlarged pulmonary artery, wedge-shaped opacity, elevated hemidiaphragm, pleural effusion
• ECG: Often normal, used to exclude myocardial infarction and pericarditis; may show:
  • Sinus tachycardia (50% of cases)
  • Right ventricular strain (T-wave inversion in leads V1-V4)
  • S1Q3T3 pattern (deep S wave in lead 1, deep Q and T waves in lead 3)
• CT Pulmonary Angiogram: Gold standard for diagnosis
• Ventilation-Perfusion (V/Q) Scan: Less commonly used, not definitive
• Echocardiogram: Bedside test
• D-dimer assay: Blood test to rule out PE when negative

Important Points

• Differentiating PE from other conditions is challenging
• Emphasis on assessing patient risk factors for accurate diagnosis