What is the investigation of choice for Pulmonary Thromboembolism (PTE) in a pregnant female?

Investigation of Choice for Pulmonary Thromboembolism in Pregnant Females

Ventilation/Perfusion (V/Q) scanning is the recommended first-line imaging modality for diagnosing pulmonary thromboembolism (PTE) in pregnant women when available, due to lower maternal breast radiation exposure compared to CT pulmonary angiography (CTPA). 1, 2

Diagnostic Algorithm for PTE in Pregnancy

1. Initial Assessment:

   • Apply modified Wells score (cutoff ≥6 points is most appropriate for pregnancy) 2
   • Consider pregnancy-adapted YEARS algorithm with D-dimer levels 2
   • Initiate anticoagulation therapy while diagnostic workup is ongoing unless contraindicated 2

2. Imaging Selection:

   • If chest X-ray is normal: V/Q scan (preferred)
   • If chest X-ray is abnormal: CTPA
   • If DVT symptoms present: Consider bilateral compression ultrasound of lower extremities first to avoid radiation 2

Comparison of Imaging Modalities

V/Q Scan vs. CTPA Radiation Exposure:

Modality	Maternal Breast Radiation	Fetal Radiation Exposure
V/Q scan	0.28-1.07 mGy [2,3]	0.25-0.40 mGy [3,4]
CTPA	10-60 mGy [2,3]	0.003-0.46 mGy [2,3]

Performance Metrics:

• V/Q scan has a negative predictive value of 100% in pregnancy 5
• CTPA has a negative predictive value of 97.5% in pregnancy 5

Key Considerations

• Both V/Q scanning and CTPA deliver radiation doses well below the threshold for fetal harm 1
• V/Q scanning exposes maternal breast tissue to significantly less radiation than CTPA, reducing long-term breast cancer risk 1, 2
• CTPA is an acceptable alternative when V/Q scanning is not available 1
• CTPA may be preferred in patients with abnormal chest radiographs 1
• Low-dose perfusion scanning (LDQ) without ventilation imaging may be sufficient in patients with normal chest X-rays, further reducing radiation exposure 5

Special Populations

• Patients with asthma: Both V/Q scan and CTPA have high negative predictive values (100%) in pregnant women with asthma 5
• Patients with suspected DVT: Consider additional investigations including serial compression ultrasound or magnetic resonance venography after an initial negative ultrasound 1

Clinical Pitfalls to Avoid

• Do not delay imaging: Failure to investigate symptoms suggestive of PE is a consistent finding in maternal death inquiries 6
• Do not rely solely on clinical symptoms: Clinical symptoms are insufficient to exclude or diagnose VTE in pregnancy 6
• Do not withhold anticoagulation: Initiate treatment while awaiting definitive diagnosis unless contraindicated 2
• Do not forget about other diagnoses: Pneumonia was diagnosed in 12% of pregnant patients with suspected PE in one study 4

The American Society of Hematology and European Society of Cardiology guidelines align in recommending V/Q scanning as the preferred first-line imaging test for suspected PTE in pregnant women when available, with CTPA as an acceptable alternative when V/Q scanning is unavailable or when chest X-ray is abnormal.