A 52-year-old man presents with progressive dyspnea and right-sided heart failure 8 months after an acute pulmonary embolism treated with anticoagulation. Echocardiography shows elevated right ventricular systolic pressure. The structure marked **D** in the diagram represents the category of pulmonary hypertension most likely responsible for his clinical presentation. Which of the following is the most appropriate FIRST-LINE imaging modality to confirm this diagnosis and guide further management?

Explanation

## Why V/Q scan is correct Group 4 PH (CTEPH) is the only potentially curable form of pulmonary hypertension, and early diagnosis is critical to identify surgical candidates. The clinical anchor mandates that V/Q scan is the FIRST-LINE imaging modality for screening persistent dyspnea >3 months post-PE, with superior sensitivity compared to CTPA for detecting CTEPH. Multiple segmental and subsegmental mismatched perfusion defects on V/Q scan are the hallmark finding that triggers further investigation with right heart catheterization and pulmonary angiography (gold standard for surgical evaluation). This patient's 8-month post-PE timeline with progressive RV dysfunction fits the typical presentation of CTEPH developing in ~3% of acute PE survivors due to organized non-resolving thromboembolic material causing progressive vascular obstruction. ## Why each distractor is wrong - **HRCT of chest**: While useful for evaluating parenchymal lung disease (Group 3 PH), HRCT is not the first-line screening tool for CTEPH. It may show mosaic perfusion pattern but lacks the sensitivity of V/Q scan for detecting mismatched perfusion defects characteristic of CTEPH. - **CTPA with 3D reconstruction**: Although CTPA can visualize thromboembolic material, it is less sensitive than V/Q scan for detecting CTEPH and is not recommended as first-line imaging per current guidelines. CTPA is reserved for confirming findings or when V/Q scan is inconclusive. - **Transthoracic echocardiography with contrast**: While echocardiography is useful for estimating RV systolic pressure and assessing RV function (as already done in this case), it cannot diagnose the underlying cause of PH or detect the perfusion defects specific to CTEPH. It is a screening tool, not a diagnostic tool for CTEPH. **High-Yield:** CTEPH is the ONLY curable form of PH — screen ALL post-PE patients with persistent dyspnea >3 months using V/Q scan (mismatched defects = positive); confirm with RHC + pulmonary angiography; treat with PTE at specialized centers or riociguat if inoperable. [cite: Robbins 10e Ch 15; Harrison 21e Ch 282]