What is the equivalent of the PERC (Pulmonary Embolism Rule-out Criteria) test for risk assessment of pulmonary embolism in pregnant patients?

Diagnostic Algorithm for Pulmonary Embolism in Pregnant Patients

There is no direct equivalent to the PERC rule for pregnant patients with suspected pulmonary embolism (PE). Instead, clinicians should follow a specific diagnostic algorithm that includes clinical assessment, chest radiography, and appropriate imaging based on radiographic findings. 1

Clinical Assessment and Initial Approach

• Unlike the general population, D-dimer testing should not be used to exclude PE in pregnant women due to its poor specificity (15%) and inadequate sensitivity (73%) during pregnancy 1
• Pregnant women commonly present with shortness of breath, pleuritic chest pain, hypoxemia, and tachycardia when experiencing PE 1
• There are no validated clinical prediction rules (like Wells or Geneva criteria) specifically for determining pre-test probability of PE in pregnant patients 1
• Clinicians must maintain a high index of suspicion as normal pregnancy can mimic some PE symptoms (mild dyspnea, tachycardia, leg edema) 1

Recommended Diagnostic Algorithm

Step 1: Assess for DVT symptoms

• In pregnant women with suspected PE and signs/symptoms of deep venous thrombosis (DVT), perform bilateral venous compression ultrasound (CUS) of lower extremities 1
• If CUS is positive, initiate anticoagulation treatment 1
• If CUS is negative, proceed to chest radiography 1

Step 2: Chest Radiography

• For all pregnant women with suspected PE, chest radiography (CXR) should be the first radiation-associated procedure 1
• CXR helps triage between lung scintigraphy and CT pulmonary angiography (CTPA) 1

Step 3: Choose appropriate imaging based on CXR results

• If CXR is normal: Perform lung scintigraphy (V/Q scan) rather than CTPA 1

  • V/Q scanning delivers lower radiation dose to maternal breast tissue (0.98-1.07 mGy vs. 10-60 mGy with CTPA) 1
  • For women with normal chest X-rays, V/Q scanning is more likely to yield diagnostic results than CTPA (94.4% vs. 70% diagnostic rate) 2

• If CXR is abnormal: Perform CTPA rather than lung scintigraphy 1

  • CTPA provides better diagnostic yield in this scenario and can identify alternative diagnoses 1

Step 4: Follow-up for non-diagnostic results

• If V/Q scan is non-diagnostic: Perform further diagnostic testing rather than clinical management alone 1
• For non-diagnostic V/Q scans requiring further investigation, CTPA is recommended over digital subtraction angiography (DSA) 1

Important Considerations

• Technically inadequate CTPA studies occur in 6-36% of pregnant women, primarily due to suboptimal vascular opacification and respiratory motion artifacts 1
• At facilities with high rates of inadequate CTPA studies, V/Q scanning may be preferable even with abnormal CXRs 1
• Repeat CTPA after a non-diagnostic study should be undertaken cautiously unless technical improvements can be made 1
• For unstable patients or when studies are not available promptly, empiric anticoagulation should be considered while awaiting diagnostic results 1

Radiation Concerns

• CTPA delivers higher radiation dose to maternal breast tissue compared to V/Q scanning (10-60 mGy vs. 0.98-1.07 mGy) 1
• The lifetime relative risk of radiation-induced breast cancer in a 25-year-old woman undergoing a single CTPA is estimated at 1.011 1
• Both imaging modalities are considered safe in pregnancy, but radiation exposure should be minimized when possible 3

This diagnostic approach prioritizes minimizing radiation exposure while maintaining diagnostic accuracy, which is crucial for reducing maternal mortality from PE, a leading cause of pregnancy-related deaths 1, 3.