Update your Knowledge with MKSAP Q&A: Answer and Critique

Answer

D: Ventilation-perfusion scanning

Educational Objective

Diagnose chronic thromboembolic pulmonary hypertension.

Critique

The most appropriate diagnostic test to perform next in this patient with precapillary pulmonary hypertension (PH) is ventilation-perfusion (V/Q) scanning (Option D). Causes of PH are divided into five groups:

  1. Pulmonary arterial hypertension
  2. PH due to left-sided heart disease
  3. PH due to lung diseases or chronic hypoxia
  4. Chronic thromboembolic PH (CTEPH) and other pulmonary artery obstructions
  5. PH with unclear or multifactorial causes

CTEPH is an underrecognized cause of PH because previous pulmonary embolism (PE) is not always evident, requiring a high index of suspicion for diagnosis. Untreated CTEPH can lead to right-sided heart failure and death; however, it is potentially treatable through pulmonary thromboendarterectomy. All patients with PH without an obvious cause should undergo evaluation for possible CTEPH; V/Q scanning is the most appropriate first test in these patients because in the absence of parenchymal lung disease, a normal V/Q scan excludes CTEPH with a negative predictive value of 98%. This patient with precapillary PH has no clear underlying cause and should be evaluated for CTEPH with V/Q scanning despite the lack of history of PE.

CT angiography (Option A) would not be the most appropriate diagnostic test to perform next in this patient. Despite rapidly improving CT imaging techniques, guidelines recommend V/Q scanning as the initial test to rule out CTEPH in patients being evaluated for PH. In patients in whom V/Q scanning results suggest CTEPH, however, CT angiography is an appropriate next test because it can identify pertinent vascular anomalies, such as webs, intimal irregularities, and luminal narrowing.

Assessment of functional status with the 6-minute walk test (Option B) provides prognostic information and a baseline for assessment of therapeutic response in patients with PH. Although this test is an important marker of prognosis and disease severity, it is not helpful in differentiating the potential causes of PH, which is the more appropriate current focus in this patient.

Pulmonary angiography (Option C) may be indicated later in the evaluation of this patient but is not an appropriate test at this time. It is invasive, costly, and associated with adverse effects. It was previously used to confirm the diagnosis after a suggestive V/Q scan, but its use in this role has been largely supplanted by CT angiography.

Key Points

All patients suspected of having pulmonary hypertension without an obvious cause should be evaluated for chronic thromboembolic pulmonary hypertension with ventilation-perfusion scanning.

A normal ventilation-perfusion scan rules out chronic thromboembolic pulmonary hypertension.

Bibliography

Humbert M, Kovacs G, Hoeper MM, et al; ESC/ERS Scientific Document Group. 2022 ESC/ERS guidelines for the diagnosis and treatment of pulmonary hypertension. Eur Respir J. 2023;61. [PMID: 36028254] doi:10.1183/13993003.00879-2022

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