What investigation has the highest diagnostic value for a patient with pulmonary hypertension being evaluated for chronic thromboembolic disease?

Ventilation-Perfusion (V/Q) Lung Scan Has the Highest Diagnostic Value for CTEPH

For a patient with pulmonary hypertension being evaluated for chronic thromboembolic disease, the ventilation-perfusion (V/Q) lung scan is the investigation with the highest diagnostic value and should be performed as the primary screening test.

Diagnostic Performance of V/Q Scanning

The V/Q scan demonstrates superior sensitivity for detecting chronic thromboembolic pulmonary hypertension (CTEPH) compared to other imaging modalities:

• V/Q scanning carries 96-97% sensitivity and 90-95% specificity for CTEPH diagnosis 1
• The test shows mismatched wedge-shaped, segmental perfusion defects characteristic of CTEPH 1
• A normal or low-probability V/Q scan essentially excludes CTEPH with 90-100% sensitivity and 94-100% specificity 1
• V/Q single-photon emission CT (SPECT) further improves accuracy to 94% 1

Why V/Q Scan Outperforms CT

While spiral CT chest with contrast has become widely used, it has critical limitations:

• CT pulmonary angiography alone may miss the diagnosis of CTEPH 1, 2
• CT sensitivity ranges from only 37-51% in some studies, though specificity remains high at 95-100% 1
• More recent studies with expert interpretation show CT can achieve 92-100% sensitivity, but this requires specialized expertise not available in all centers 1, 3
• The 2015 ESC/ERS Guidelines explicitly state that CT pulmonary angiography alone cannot exclude CTEPH 1

Guideline-Recommended Diagnostic Algorithm

The European Society of Cardiology/European Respiratory Society guidelines establish a clear hierarchy:

1. V/Q scanning is mandatory as the main first-line imaging modality for all patients with unexplained pulmonary hypertension 1, 2
2. If V/Q scan shows multiple segmental perfusion defects, proceed to CT pulmonary angiography for confirmation and anatomic detail 2
3. CT angiography serves to confirm CTEPH and assess surgical accessibility, but should not be used alone for screening 1
4. Right heart catheterization provides definitive hemodynamic diagnosis 1, 2

Role of Other Investigations

Echocardiography serves as the initial screening tool for pulmonary hypertension itself, but cannot differentiate CTEPH from other causes of pulmonary hypertension 2. It identifies patients who need further evaluation but lacks diagnostic specificity for chronic thromboembolic disease 1.

Electrocardiography has no role in diagnosing CTEPH specifically, though it may show signs of right ventricular strain in pulmonary hypertension 2.

Spiral CT with contrast is valuable for confirming CTEPH and planning surgical intervention, showing findings like eccentric thrombus, webs, bands, and mosaic perfusion patterns 1. However, its role is complementary to V/Q scanning rather than replacing it 1.

Critical Clinical Pitfall

The most important pitfall is relying on CT alone to exclude CTEPH. A relatively normal CT can be observed despite significant abnormalities on V/Q scintigraphy 1. This can lead to missed diagnoses of a potentially curable condition, as pulmonary endarterectomy surgery offers definitive treatment with mortality rates as low as 4.7% in experienced centers 1.

Answer: D. Ventilation-perfusion lung scan

The V/Q scan has the highest diagnostic value because it provides the best sensitivity for detecting CTEPH while maintaining excellent negative predictive value to exclude the disease 1.