Pulmonary Embolism: Wells Score, D-dimer, CTPA and Treatment

Pulmonary embolism (PE) occurs when a blood clot, usually from the deep veins of the legs, travels to the lungs and blocks part of the pulmonary arterial circulation. Together with deep vein thrombosis (DVT) it forms venous thromboembolism (VTE). PE can be rapidly fatal, yet it is often missed because its symptoms are non-specific.

Risk factors

Remember Virchow's triad: stasis of blood, damage to the vessel wall and increased clotting tendency.

• Recent surgery (especially orthopaedic and pelvic) or trauma.
• Immobility and long-distance travel.
• Active cancer.
• Pregnancy and the postpartum period.
• Oestrogen-containing contraception and hormone therapy.
• Previous VTE.
• Thrombophilia (for example factor V Leiden, antiphospholipid syndrome).
• Obesity.
• Heart failure.

Clinical features

The most common symptoms:

• sudden breathlessness
• pleuritic chest pain
• haemoptysis
• syncope

Signs:

• tachycardia
• tachypnoea
• low oxygen saturation
• a low-grade fever
• signs of DVT, such as a swollen, tender calf

A large PE may cause hypotension, a raised JVP and cardiac arrest.

Diagnostic approach

1. Assess clinical probability with a validated tool such as the two-level Wells score (PE "likely" or "unlikely").
2. If PE is unlikely, do a D-dimer. A negative D-dimer makes PE very unlikely. D-dimer is non-specific and is raised by many conditions, including infection, cancer, pregnancy and recent surgery.
3. If PE is likely or the D-dimer is positive: CT pulmonary angiography (CTPA). A V/Q scan is an alternative when CT is unsuitable, for example in kidney impairment, contrast allergy or some pregnant patients.

Other tests:

• ECG: sinus tachycardia is most common. The S1Q3T3 pattern and right heart strain are classic but uncommon.
• Chest X-ray: often normal; helps exclude other causes.
• Arterial blood gases: hypoxaemia and low CO₂.
• Echocardiography and troponin: look for right ventricular strain in unstable or high-risk patients.

Management

• Supportive: oxygen, analgesia and fluids with care.
• Anticoagulation: start promptly when PE is strongly suspected, unless there is a contraindication. Direct oral anticoagulants (for example apixaban or rivaroxaban) are first-line for most patients. Low molecular weight heparin is used in pregnancy and often in cancer. Treatment lasts at least 3 months; longer if the PE was unprovoked or the risk factor persists.
• High-risk (massive) PE with shock or hypotension: systemic thrombolysis unless contraindicated. Surgical embolectomy or catheter-directed therapy are alternatives.
• An IVC filter only when anticoagulation is impossible.

Prevention

• Risk assessment for every admitted patient.
• Thromboprophylaxis (for example low molecular weight heparin).
• Early mobilisation.
• Mechanical methods when drugs are contraindicated.

Exam pearls

• Unexplained tachycardia and hypoxia after surgery: think PE.
• Do not use D-dimer in patients with a high (likely) clinical probability; go straight to imaging.
• Thrombolysis is reserved for PE with haemodynamic compromise.

For more, see the respiratory and cardiovascular chapters of the Medicine Companion and our CT Scan Interpretation Simplified note.

Test yourself

5 exam-style single-best-answer questions. Choose your answer, then tap “Show answer”.

1. Two-level Wells score says 'PE likely'. Next step?

   1. No investigation
   2. Echocardiogram only
   3. CT pulmonary angiography
   4. Chest X-ray only
   5. D-dimer and discharge if negative
   Show answer

   Answer: C. CT pulmonary angiography
   If PE is likely, go straight to imaging. D-dimer is used only when PE is unlikely.

2. Most common ECG finding in PE:

   1. ST elevation
   2. Sinus tachycardia
   3. Right bundle branch block
   4. S1Q3T3
   5. Atrial flutter
   Show answer

   Answer: B. Sinus tachycardia
   Sinus tachycardia is most common; S1Q3T3 is classic but uncommon.

3. Massive PE with hypotension and no contraindications. Treatment?

   1. IVC filter first
   2. DOAC and discharge
   3. Aspirin
   4. Observation
   5. Systemic thrombolysis
   Show answer

   Answer: E. Systemic thrombolysis
   High-risk PE with haemodynamic compromise is treated with thrombolysis unless contraindicated.

4. Imaging alternative to CTPA in a patient with severe kidney impairment:

   1. Abdominal ultrasound
   2. V/Q scan
   3. MRI brain
   4. Coronary angiography
   5. Plain X-ray
   Show answer

   Answer: B. V/Q scan
   V/Q scanning avoids iodinated contrast.

5. Minimum anticoagulation duration for a provoked PE:

   1. 6 weeks
   2. Lifelong always
   3. At least 3 months
   4. None
   5. 2 weeks
   Show answer

   Answer: C. At least 3 months
   At least 3 months, longer if unprovoked or the risk factor persists.

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Disclaimer

For education and exam preparation only. This is not medical advice and must not be used to diagnose or treat patients. Always follow current clinical guidelines and the advice of qualified senior colleagues.