Pulmonary Embolism: Flashcards for Doctors and Medical Students

1. What is a Pulmonary Embolism (PE), and what is its most common origin?

A PE occurs when a blood clot (thrombus) becomes lodged in an artery in the lung, blocking blood flow.
It is not a disease itself, but a complication of underlying venous thrombosis.
Most commonly, PEs arise from a thrombus in the deep venous system of the lower extremities, particularly calf veins and venous valve pockets, traveling through the right side of the heart to the lungs.

2. What are the three primary influences (Virchow's Triad) that predispose a patient to blood clot formation, leading to PE?

The three primary influences are:

Endothelial injury (injury to the inner lining of blood vessels).
Stasis or turbulence of blood flow (slow or turbulent blood flow).
Blood hypercoagulability (increased tendency for blood to clot).

3. List key risk factors for developing a PE.

Key risk factors include:

Immobilization (e.g., prolonged bed rest, surgery).
Surgery and Trauma (especially leg amputations, hip, pelvic, spinal surgery, femur/tibia fractures, major trauma, severe burns).
Malignancy (identified in 17% of patients; pancreatic, bronchogenic, GU, colon, stomach, breast cancers are common).
Pregnancy and Postpartum period (leading cause of death in this group, higher risk postpartum).
Oral contraceptives and estrogen replacement therapy.
Hereditary factors (e.g., Factor V Leiden mutation – most common genetic risk factor, Protein C/S deficiency, Antithrombin III deficiency).
Acute medical illnesses (e.g., Congestive Heart Failure, Myocardial Infarction, HIV, AIDS, Systemic Lupus Erythematosus).
Smoking.
Previous history of DVT or PE.
Central venous instrumentation (especially in children).
Travel of 4 hours or more in the past month.

4. What are the classic and atypical signs and symptoms of PE, and what should always raise suspicion?

Classic presentation: Abrupt onset of pleuritic chest pain, shortness of breath (dyspnea), and hypoxia.
Important note: Most patients with PE have no obvious symptoms at presentation. Symptoms can range from catastrophic hemodynamic collapse to gradually progressive dyspnea.
Atypical symptoms may include: Seizures, Syncope, Abdominal pain, Fever, Productive cough, Wheezing, Decreasing level of consciousness, New onset of atrial fibrillation, Hemoptysis (coughing blood), Flank pain, Delirium (in elderly patients).
Suspicion should be raised in patients with respiratory symptoms unexplained by an alternative diagnosis. Unexplained dyspnea, tachypnea, or chest pain, especially with risk factors, warrant diagnostic tests.

5. What are common physical signs found in patients with PE?

Common physical signs include:

Tachypnea (respiratory rate >20/min): 96% of patients.
Rales (crackling lung sounds): 58%.
Accentuated second heart sound: 53%.
Tachycardia (heart rate >100/min): 44%.
Fever (temperature >37.8°C [100.04°F]): 43%.

Other signs: Diaphoresis, S3 or S4 gallop, clinical signs/symptoms suggesting thrombophlebitis, lower extremity edema, cardiac murmur, cyanosis.

6. What are the primary diagnostic tests for PE, and when are they used?

Clinical Scoring Systems: Used to determine the pre-test probability of PE before testing.
D-dimer Test: A blood test that can exclude PE in patients with low clinical risk (high negative predictive value). It is not helpful in high-risk patients, where further investigation is mandatory even if normal.
Computed Tomography Pulmonary Angiography (CTPA): The first-line and primary diagnostic test for PE. It is the criterion standard for diagnosis when available, visualizing emboli and alternative diagnoses.
Ventilation-Perfusion (V/Q) Scan: Used when CT scanning is not available or is contraindicated (e.g., renal impairment, contrast allergy).
Duplex Ultrasonography (Colour Doppler ultrasound) of leg veins: Non-invasive test to demonstrate the presence of a DVT, as most PEs originate from leg clots.
Electrocardiogram (ECG): Often normal, but can show tachycardia, non-specific ST-T wave changes, or signs of right heart strain (S1Q3T3 pattern, RBBB). Useful for ruling out acute myocardial infarction or pericarditis.
Echocardiography: Can identify central pulmonary embolism and assess right heart function (dilation) in massive PE, also helps in differential diagnosis of circulatory collapse.

7. How is PE severity classified, and what are the associated mortality rates?

PE severity is commonly classified into three categories based on clinical variables:

High-risk PE: Defined by hypotension (systolic arterial pressure < 90 mmHg or a drop of > 40 mmHg for ≥ 15 minutes) and/or the need for vasopressor support.
- Accounts for ~5% of PEs.
- 30-day mortality rate: Approximately 65%.
Intermediate-risk PE: Defined by being normotensive with evidence of right ventricular (RV) dysfunction or myocardial ischemia.
- Accounts for ~40% of PEs.
- 30-day mortality rate: 5% to 25%.
Low-risk PE: Patients who do not meet the criteria for intermediate-risk.
- Accounts for ~55% of PEs.
- 30-day mortality rate: Approximately 1%.

8. What is the immediate and long-term management for PE?

Immediate Management:

Prompt recognition and treatment are potentially life-saving.
Immediate full anticoagulation is mandatory for all patients suspected of having DVT or PE, and diagnostic investigations should not delay this empirical therapy.
Oxygen therapy for hypoxemic patients (maintain arterial O2 saturation above 90%).
Intravenous fluids/plasma expander for circulatory shock (avoid diuretics/vasodilators).
Opiates for pain/distress (use with caution in hypotensive patients).

Pharmacologic Management:

Anticoagulation medications (blood thinners):
- Unfractionated heparin
- Low-molecular-weight heparin
- Factor Xa inhibitors
- Fondaparinux
- Warfarin
Thrombolytic therapy (Clot Busters): Indicated in acute massive PE with cardiogenic shock/hypotension (systolic BP < 90 mmHg) without high bleeding risk. May be considered in selected normotensive patients with RV dysfunction/severe hypoxemia and low bleeding risk. (e.g., Alteplase, Reteplase). High risk of intracranial hemorrhage.

Surgical/Procedural Options:

Catheter-directed thrombolysis.
Surgical embolectomy (surgical removal of the clot): Considered in selected patients, but carries high mortality.
Vena Cava Filters: Reserved for patients where anticoagulation is contraindicated, who experience massive hemorrhage on anticoagulation, or have recurrent VTE despite adequate anticoagulation. Retrievable filters are preferred for temporary risk factors.

Long-term Management:

Long-term anticoagulation is critical to prevent recurrence. A significant reduction in recurrence is associated with 3-6 months of anticoagulation.

9. What is the prognosis for PE, and what is the risk of recurrence?

Mortality:

Untreated PE can lead to sudden death in approximately 25% of individuals.
Anticoagulant treatment significantly decreases mortality to less than 5%.
Mortality in undiagnosed PE is 30%.

Resolution: Lung scan defects often resolve rapidly with treatment (e.g., 73% resolved within 3 months). Most treated patients do not develop long-term complications.

Recurrence:

The risk of recurrence is highest in the first 6-12 months after the initial event.
Approximately one-third of individuals may experience another embolic event within 10 years.
Long-term anticoagulation is critical to prevent recurrence.

Chronic Complications: In a small proportion of patients, PE may not fully resolve, leading to chronic thromboembolic pulmonary arterial hypertension.

10. What are specific considerations for PE in special populations like children, the elderly, and pregnant/postpartum women?

Children:
- DVT/PE are rare but associated with significant morbidity/mortality.
- 98% have an identifiable risk factor or serious underlying disorder.
- Common risk factors include indwelling central venous catheters (up to 36%), and inherited coagulation disorders (5-10%).
- Dehydration, especially hyperosmolar, is typically observed in younger infants.
Elderly Patients:
- Increasingly prevalent, but diagnosis is often missed because respiratory symptoms are dismissed as chronic.
- Appropriate therapy may be inappropriately withheld due to bleeding concerns.
- Appropriate diagnostic workup and therapeutic anticoagulation with a careful risk-to-benefit assessment is recommended. Delirium can be an atypical symptom.
Pregnant and Postpartum Women:
- Incidence of thromboembolic disease is increased.
- It is the leading cause of death in pregnant and postpartum women.
- The annual incidence of venous thromboembolism is 5 times higher in postpartum women than in pregnant women.
- PE is relatively less common during pregnancy than postpartum.
- There is an association between increasing rates of PE and increasing rates of cesarean delivery.