Differences in Chronic Pulmonary Embolism Burden in Chronic Thromboembolic Disease with and Without Pulmonary Hypertension.

Background: Chronic thromboembolic disease is a recognised sequela of acute pulmonary embolism and may occur with or without pulmonary hypertension. The purpose of this study was to evaluate differences in chronic thromboembolic burden, lesion type, and distribution between chronic thromboembolic pulmonary disease without pulmonary hypertension (CTEPD) and chronic thromboembolic pulmonary hypertension (CTEPH). Methods: This retrospective single-centre study included patients with CTEPD or CTEPH by right heart catheterisation using 2022 ESC/ERS criteria between 2021 and 2022. Two CTEPH patients were randomly selected per CTEPD patient. CTPA studies were reviewed by a blinded thoracic radiologist, assessing 32 pulmonary vessels from the main to segmental arteries for chronic thromboembolic lesions. Groups were compared by disease distribution, most proximal lesion level, Qanadli obstruction index, lesion type, and location. Exploratory receiver operating characteristic (ROC) analysis assessed discriminatory performance. Results: The 44 CTEPD and 88 CTEPH patients included had no differences in age, BMI, or sex. CTEPH patients had shorter six-minute walk distance (p = 0.001), greater right ventricular dilation/dysfunction (p < 0.001), and lower prevalence of deep vein thrombosis (p = 0.03). CTPA identified more lesions in CTEPH (21.2 vs. 10.0 lesions/case, p < 0.001) across more lobes (4.8 vs. 3.4, p < 0.001), with more proximal main/lobar disease (p < 0.001). CT obstruction index was 51% in CTEPH and 26% in CTEPD (p < 0.001). Total lesion number best discriminated CTEPH from CTEPD (AUC 0.91; optimal cutoff, 16 lesions). Conclusions: CTEPH demonstrates a greater, more diffuse, and more proximal chronic thromboembolic lesion burden on CTPA than CTEPD.