What are the next steps to confirm pulmonary embolism in a pregnant female beyond initial 2D echocardiography, ECG, and D-dimer test?

Diagnostic Algorithm for Pulmonary Embolism in Pregnant Women

For pregnant women with suspected pulmonary embolism (PE), a chest radiograph (CXR) should be the first radiation-associated procedure, followed by lung scintigraphy (V/Q scan) if the CXR is normal, or CT pulmonary angiography (CTPA) if the CXR is abnormal. 1, 2

Initial Assessment

When evaluating a pregnant woman at 5 months gestation with suspected PE who has already had 2D echocardiography, ECG, and D-dimer testing:

• Echocardiogram alone is insufficient for diagnosing PE in pregnancy 2
• D-dimer should not be used to exclude PE in pregnant women due to poor specificity (15%) and inadequate sensitivity (73%) 1, 2

Diagnostic Algorithm

Step 1: Assess for DVT symptoms

• If leg symptoms are present:
  • Perform bilateral compression ultrasound (CUS) of lower extremities 1, 2
  • If CUS positive → Begin anticoagulation treatment
  • If CUS negative → Proceed to Step 2

Step 2: Chest Radiograph (CXR)

• Perform CXR as the first radiation-associated procedure 1, 2
• CXR helps rule out other causes of dyspnea and guides selection of subsequent imaging

Step 3: Based on CXR results

• If CXR is normal:

  • Proceed to lung scintigraphy (V/Q scan) 1, 2
  • V/Q scan exposes the mother to lower radiation dose compared to CTPA
  • Breast tissue radiation: 0.98-1.07 mGy with V/Q scan vs. 10-60 mGy with CTPA 1

• If CXR is abnormal:

  • Proceed to CT pulmonary angiography (CTPA) 1, 2
  • CTPA is preferred when CXR is abnormal as V/Q scan is likely to be nondiagnostic

Step 4: Follow-up based on V/Q scan results

• If V/Q scan is diagnostic (positive or negative) → Management based on results
• If V/Q scan is nondiagnostic:
  • Perform further diagnostic testing rather than clinical management alone 1
  • CTPA is recommended rather than digital subtraction angiography (DSA) 1

Important Considerations

Radiation Exposure

• V/Q scan exposes the mother to lower radiation dose than CTPA:
  • Breast tissue: 0.98-1.07 mGy (V/Q) vs. 10-60 mGy (CTPA)
  • Lung tissue: 5.7-13.5 mGy (V/Q) vs. 39.5 mGy (CTPA) 1
• Fetal radiation exposure is minimal with both tests when proper shielding is used

Clinical Pitfalls to Avoid

• Do not rely on D-dimer to exclude PE in pregnancy 1, 2
• Do not rely solely on echocardiography for diagnosis or exclusion of PE 2
• Do not rely on clinical features alone, as no single clinical feature or combination reliably predicts PE in pregnancy 2
• Do not perform CTPA as the first imaging test when CXR is normal 1

Warning Signs Requiring Immediate Attention

• Tachycardia, hypoxemia, abnormal alveolar-arterial gradient (>15 mm Hg)
• Hemoptysis, syncope, or unexplained hypotension 2

This evidence-based diagnostic algorithm provides a systematic approach to investigating suspected PE in pregnant women while minimizing radiation exposure to both mother and fetus. The approach prioritizes diagnostic accuracy while considering the unique physiological changes of pregnancy.