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Difficulty: HardDiagnostic Workup and Test Sequencing

A 42-year-old woman is evaluated in the ambulatory clinic for an 8-month history of progressively worsening exertional dyspnea and fatigue. She has no prior medical conditions, takes no medications, and has never smoked. Vital signs include a blood pressure of 118/76 mmHg, heart rate of 88/min, and respiratory rate of 16/min. Pulse oximetry is 96% on room air.

Cardiovascular examination reveals a regular rate and rhythm, a prominently loud pulmonic component of the second heart sound, and a grade 2/6 holosystolic murmur at the left lower sternal border that increases in intensity with inspiration. The lungs are clear to auscultation bilaterally. There is no jugular venous distention or peripheral edema.

An electrocardiogram demonstrates right axis deviation and right ventricular hypertrophy. A transthoracic echocardiogram reveals an estimated pulmonary artery systolic pressure of 62 mmHg, right ventricular enlargement, and normal left ventricular size and systolic function with no left-sided valvular abnormalities.

Subsequent pulmonary function testing, including spirometry and diffusing capacity of the lungs for carbon monoxide (DLCO), is within normal limits. High-resolution computed tomography of the chest reveals clear lung fields without interstitial lung disease or emphysema.

Which of the following is the most appropriate next step in the diagnostic workup of this patient's condition?

  1. A
    Computed tomography pulmonary angiography
  2. B
    Right heart catheterization with vasoreactivity testing
  3. Ventilation-perfusion (V/Q) lung scanAnswer
  4. D
    Lower extremity venous duplex ultrasonography
  5. E
    Empiric initiation of a pulmonary vasodilator

Answer

Ventilation-perfusion (V/Q) lung scan
The correct answer is a ventilation-perfusion (V/Q) lung scan. This patient has echocardiographic evidence of unexplained pulmonary hypertension (PH). The diagnostic workup for PH follows a strict sequence to categorize the disease into one of five World Health Organization (WHO) groups. Group 2 (left heart disease) and Group 3 (lung disease/hypoxia) are the most common causes and have been effectively ruled out in this patient by the normal left ventricular function on echocardiography, normal pulmonary function tests, and a normal high-resolution CT of the chest. The next mandatory step in the diagnostic sequence is to evaluate for Group 4 PH, which is chronic thromboembolic pulmonary hypertension (CTEPH). A V/Q scan is the guideline-recommended initial screening test of choice for CTEPH because it is significantly more sensitive than computed tomography pulmonary angiography (CTPA) for detecting the distal, organized, and often subtle thromboembolic disease characteristic of chronic chronicity.

Step-by-Step Solution

1
Identify the patient's primary syndrome based on clinical and objective findings.
The patient has clinical and echocardiographic evidence of pulmonary hypertension without left-sided heart disease or parenchymal lung disease.
Establishing the presence of unexplained pulmonary hypertension dictates the subsequent specific diagnostic algorithmic sequence.
2
Determine which etiologic groups of pulmonary hypertension remain in the differential diagnosis.
Group 2 (left heart disease) and Group 3 (lung disease) have been ruled out. Group 4 (chronic thromboembolic disease) and Group 1 (pulmonary arterial hypertension) remain.
Systematically ruling out common causes prevents premature invasive testing and guides the selection of targeted non-invasive screening.
3
Select the appropriate next non-invasive screening test to differentiate between the remaining diagnostic possibilities.
A ventilation-perfusion (V/Q) scan is selected.
A V/Q scan is the strictly guideline-mandated screening test for chronic thromboembolic pulmonary hypertension (CTEPH) because it is more sensitive than a CT pulmonary angiogram for chronic, distal thromboembolic disease.

Key Concept

The diagnostic workup for unexplained pulmonary hypertension requires a ventilation-perfusion (V/Q) scan to screen for chronic thromboembolic pulmonary hypertension (CTEPH) prior to performing a diagnostic right heart catheterization.
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Diagnostic Workup and Test Sequencing

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