What is a pulmonary embolism?

Pulmonary Embolism

A pulmonary embolism (PE) is a potentially life-threatening condition characterized by the blockage of one or more pulmonary arteries by blood clots that typically originate from deep vein thrombosis in the legs, causing impaired blood flow to the lungs and resulting in right ventricular dysfunction and hemodynamic consequences.

Definition and Pathophysiology

Pulmonary embolism occurs when emboli (usually blood clots) travel through the venous system and lodge in the pulmonary arteries, obstructing blood flow. The key pathophysiological consequences include:

• Obstruction of pulmonary arterial blood flow
• Increased pulmonary vascular resistance
• Right ventricular pressure overload and potential failure
• Ventilation/perfusion mismatch leading to hypoxemia
• Potential hemodynamic collapse in severe cases

When more than 30-50% of the pulmonary arterial bed becomes occluded, significant hemodynamic consequences can occur 1. The right ventricle, which is not designed to pump against high resistance, may fail under the sudden pressure load.

Classification

For clinical purposes, PE can be classified into:

1. Massive (High-risk) PE:

   • Characterized by shock and/or hypotension (systolic BP <90 mmHg or a drop of ≥40 mmHg for >15 minutes)
   • May require cardiopulmonary resuscitation
   • Associated with high mortality (up to 30% if untreated)

2. Submassive (Intermediate-risk) PE:

   • Normal blood pressure but evidence of right ventricular dysfunction
   • Higher risk than non-massive PE

3. Non-massive (Low-risk) PE:

   • Normal blood pressure
   • No evidence of right ventricular dysfunction

Epidemiology

PE is the third most common cardiovascular disease with an annual incidence of 100-200 per 100,000 inhabitants 1. It represents a major cause of mortality, morbidity, and hospitalization in Europe, with an estimated 317,000 deaths related to venous thromboembolism in six European Union countries in 2004 1.

The risk of PE increases with age, approximately doubling with each decade after age 40 1.

Risk Factors

The major predisposing factors for PE include:

Strong predisposing factors (odds ratio >10):

• Fractures of hip or leg
• Hip or knee replacement
• Major general surgery
• Major trauma
• Spinal cord injury

Moderate predisposing factors (odds ratio 2-9):

• Arthroscopic knee surgery
• Central venous lines
• Chemotherapy
• Chronic heart or respiratory failure
• Hormone replacement therapy
• Malignancy
• Oral contraceptive therapy
• Paralytic stroke
• Pregnancy/postpartum
• Previous venous thromboembolism

Weak predisposing factors (odds ratio <2):

• Bed rest >3 days
• Immobility (prolonged car or air travel)
• Increasing age
• Laparoscopic surgery
• Obesity
• Pregnancy/antepartum
• Varicose veins

1

Clinical Presentation

The clinical presentation of PE can range from asymptomatic to sudden death. Common symptoms and signs include:

• Dyspnea (sudden onset)
• Chest pain (typically pleuritic)
• Hemoptysis
• Syncope
• Tachypnea
• Tachycardia
• Hypoxemia
• Signs of deep vein thrombosis
• Fever

In severe cases, patients may present with:

• Shock
• Hypotension
• Right heart failure
• Cardiac arrest

Diagnosis

Diagnosis of PE relies on a combination of:

1. Clinical assessment and probability scoring
2. Laboratory tests (D-dimer)
3. Imaging studies:
   • CT pulmonary angiography (gold standard)
   • Ventilation/perfusion scan
   • Echocardiography (especially in unstable patients)
   • Compression ultrasonography of lower extremities

For hemodynamically unstable patients, bedside echocardiography is often the first diagnostic test to identify right ventricular overload 1.

Management

Treatment depends on risk stratification:

High-risk (Massive) PE:

• Thrombolytic therapy is the first-line treatment for patients with cardiogenic shock and/or persistent arterial hypotension 1
• Surgical pulmonary embolectomy for patients with contraindications to thrombolysis or failed thrombolysis
• Catheter-directed interventions as an alternative when surgical expertise is not available

Non-high-risk PE:

• Anticoagulation is the mainstay of treatment
• Initial parenteral anticoagulation followed by oral anticoagulants
• Direct oral anticoagulants (DOACs) are increasingly used for at least 3 months 2
• Extended anticoagulation may be considered for unprovoked PE due to high recurrence risk

Complications and Long-term Outcomes

• Mortality: 3-month mortality rates range from 8.6% to 17% 1
• Recurrence: Up to 30% after 10 years, with recurrences more likely to be PE than DVT 3
• Chronic thromboembolic pulmonary hypertension (CTEPH): Occurs in approximately 1.5% of patients after PE 1
• Post-PE syndrome: Characterized by persistent symptoms, decreased quality of life, and functional limitations 4

Special Considerations

Non-thrombotic PE

Several types of non-thrombotic PE exist:

• Fat embolism (typically after long bone fractures)
• Air embolism
• Amniotic fluid embolism
• Septic embolism
• Tumor embolism
• Foreign body embolism

These forms of PE have different pathophysiology and may require specific management approaches 1.

Prevention

Prevention strategies focus on:

• Early mobilization
• Mechanical prophylaxis (compression stockings, intermittent pneumatic compression)
• Pharmacological prophylaxis with anticoagulants in high-risk patients
• Risk assessment for hospitalized patients

Despite evidence supporting prophylaxis, it remains underused in many at-risk hospitalized patients 5.