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Difficulty: HardDiagnostic Workup and Test Sequencing

A 28-year-old woman, G2P1, at 33 weeks gestation presents to the emergency department with sudden-onset shortness of breath and right-sided pleuritic chest pain that began 4 hours ago. Her temperature is 37.1°C (98.8°F), blood pressure is 118/76 mmHg, pulse is 112/min, respiratory rate is 24/min, and oxygen saturation is 95% on room air. The patient appears anxious but is in no acute respiratory distress. Lungs are clear to auscultation bilaterally. Cardiac examination reveals regular tachycardia but is otherwise unremarkable. The right calf appears slightly more edematous than the left and is mildly tender to palpation. A plain chest radiograph performed with abdominal shielding shows no abnormalities. An electrocardiogram demonstrates sinus tachycardia with no ischemic changes. Which of the following is the most appropriate next step in the diagnostic workup?

  1. A
    Computed tomography pulmonary angiography
  2. B
    Plasma D-dimer assay
  3. Compression ultrasonography of the lower extremitiesAnswer
  4. D
    Ventilation-perfusion (V/Q) scan
  5. E
    Transthoracic echocardiography

Answer

Compression ultrasonography of the lower extremities is the correct next step in a pregnant patient with suspected pulmonary embolism and symptomatic deep vein thrombosis.
The correct answer is compression ultrasonography of the lower extremities. The diagnostic workup of pulmonary embolism (PE) in pregnancy is heavily influenced by the need to minimize fetal and maternal radiation exposure. When a pregnant patient presents with symptoms of PE and concomitant signs of deep vein thrombosis (DVT), such as unilateral leg swelling and tenderness, the preferred initial diagnostic step is lower extremity compression ultrasonography. If the ultrasound is positive for a DVT, the diagnosis of venous thromboembolism is established, and the patient can be started on therapeutic anticoagulation. This completely circumvents the need for thoracic imaging (e.g., CT pulmonary angiography or V/Q scan) and its associated radiation risks.

Step-by-Step Solution

1
Identify the primary clinical suspicion based on the presentation.
The patient has sudden-onset dyspnea, pleuritic chest pain, tachycardia, and a normal chest radiograph, making pulmonary embolism (PE) the most likely diagnosis.
Establishing the pre-test probability is essential before selecting a diagnostic algorithm.
2
Recognize the special population constraints and physical exam findings.
The patient is pregnant (requires minimizing radiation) and has unilateral calf swelling and tenderness (suspicious for deep vein thrombosis).
Pregnancy alters the standard diagnostic sequence for venous thromboembolism (VTE) to protect the fetus from teratogenic radiation effects.
3
Determine the optimal diagnostic test sequence.
Because treatment for deep vein thrombosis and PE is identical (anticoagulation), demonstrating a lower extremity deep vein thrombosis via non-invasive ultrasound confirms the need for treatment and safely avoids the need for pulmonary imaging.
In pregnant patients with suspected PE who have leg signs/symptoms, bilateral or symptomatic leg ultrasound is the standard-of-care first step.

Key Concept

In pregnant patients with suspected pulmonary embolism who exhibit signs of a deep vein thrombosis, bilateral lower extremity compression ultrasonography is the most appropriate first diagnostic step to avoid unnecessary fetal and maternal radiation exposure.
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Topics

Diagnostic Workup and Test Sequencing

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