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Difficulty: HardDiagnostic Workup and Test Sequencing

A 29-year-old G1P0 woman at 22 weeks gestation presents to the emergency department complaining of sudden-onset shortness of breath and right-sided chest pain that worsens with deep inspiration. The symptoms started 3 hours ago. She has no significant past medical history. Vital signs show a temperature of 37.1°C (98.8°F), heart rate of 118/min, blood pressure of 112/72 mmHg, respiratory rate of 24/min, and oxygen saturation of 94% on room air. Physical examination reveals clear lung fields bilaterally. Cardiac auscultation reveals tachycardia with a regular rhythm and no murmurs. Examination of the lower extremities demonstrates mild, asymmetric swelling of the left calf with localized tenderness. An electrocardiogram shows sinus tachycardia. A chest radiograph is unremarkable. Which of the following is the most appropriate next diagnostic test?

  1. Compression ultrasonography of the bilateral lower extremitiesAnswer
  2. B
    Computed tomography pulmonary angiography
  3. C
    Measurement of serum D-dimer
  4. D
    Ventilation-perfusion scanning
  5. E
    Transthoracic echocardiography

Answer

The most appropriate next step is compression ultrasonography of the bilateral lower extremities.
The correct sequence for evaluating suspected pulmonary embolism in a pregnant patient prioritizes minimizing radiation exposure to the fetus and mother. Guidelines recommend a chest radiograph as the initial study. If the radiograph is normal, the next best step is bilateral lower extremity compression ultrasonography, particularly when the patient has clinical signs of a deep vein thrombosis (DVT) such as calf swelling and tenderness. Confirming a DVT establishes the diagnosis of venous thromboembolism (VTE) and provides sufficient indication to initiate therapeutic anticoagulation, making further tests like CT pulmonary angiography (CTPA) or V/Q scanning unnecessary.

Step-by-Step Solution

1
Identify the primary clinical presentation.
A pregnant patient presents with pleuritic chest pain, dyspnea, and an asymmetrically swollen, tender calf, highly suggestive of venous thromboembolism (VTE).
Recognizing the high pre-test probability for both deep vein thrombosis (DVT) and pulmonary embolism (PE) dictates the diagnostic algorithm.
2
Evaluate the constraints of diagnostic testing in pregnancy.
Maternal and fetal radiation exposure must be minimized. The initial test for suspected PE in pregnancy is a chest radiograph, which was normal.
A normal chest radiograph rules out common alternative diagnoses (e.g., pneumonia, pneumothorax) but does not rule out PE.
3
Determine the optimal sequencing to confirm the diagnosis safely.
Select bilateral lower extremity compression ultrasonography.
Because the patient has signs of DVT, a positive ultrasound will confirm a VTE diagnosis and provide an immediate indication for therapeutic anticoagulation, successfully bypassing the need for radiation-based thoracic imaging.

Key Concept

In pregnant patients with suspected pulmonary embolism and a normal chest radiograph, bilateral lower extremity compression ultrasonography is the most appropriate next step, especially if symptoms of deep vein thrombosis are present, as a positive finding circumvents the need for radiation-based imaging.
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Diagnostic Workup and Test Sequencing

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