Letter to the editor

Lesion morphological classification by OCT to predict therapeutic efficacy after balloon pulmonary angioplasty in CTEPH

Chronic thromboembolic pulmonary hypertension is a form of precapillary pulmonary hypertension resulting from the incomplete resolution of pulmonary thromboemboli and formation of chronic, fibrotic, flow-limiting obstructions within the pulmonary vasculature. The progression of chronic thromboembolic disease is associated with the development of pulmonary hypertension, right heart failure, and diminished patient function. Surgical pulmonary thromboendarterectomy to extract thromboembolic disease is curative and the primary treatment option for chronic thromboembolic pulmonary hypertension. For patients who are not surgical candidates, balloon pulmonary angioplasty (BPA) is a percutaneous treatment option that uses angioplasty techniques to dilate diseased pulmonary arteries, disrupt organized flow-limiting obstructions, revascularize underperfused lung regions, improve pulmonary vascular hemodynamics, and restore patient function. BPA has undergone refinement and worldwide adoption since its inception, leading to advancements in the equipment used, technical approach, and complication management for each procedure. The approach to modern BPA, its attendant complications, and contemporary treatment outcomes are discussed in this state-of-the-art review.

Chronic thromboembolic pulmonary hypertension (CTEPH), classified as group 4 pulmonary hypertension (PH), is caused by stenosis and obstruction of the pulmonary arteries by organized thrombi that are incompletely resolved after acute pulmonary embolism. The prognosis of patients with CTEPH is poor if untreated; however, in expert centers with multidisciplinary teams, a treatment strategy for CTEPH has been established, dramatically improving its prognosis. CTEPH is currently not a fatal disease and is the only curable form of PH. Despite these advances and the establishment of treatment approaches, early diagnosis is still challenging, especially for non-experts, for several reasons. One of the reasons for this is insufficient knowledge of the various diagnostic imaging modalities, which are essential in the clinical practice of CTEPH. Imaging modalities should detect the following pathological findings: lung perfusion defects, thromboembolic lesions in pulmonary arteries, and right ventricular remodeling and dysfunction. Perfusion lung scintigraphy and catheter angiography have long been considered gold standards for the detection of perfusion defects and assessment of vascular lesions, respectively. However, advances in imaging technology of computed tomography and magnetic resonance imaging have enabled the non-invasive detection of these abnormal findings in a single examination. Cardiac magnetic resonance (CMR) is the gold standard for evaluating the morphology and function of the right heart; however, state-of-the-art techniques in CMR allow the assessment of cardiac tissue characterization and hemodynamics in the pulmonary arteries. Comprehensive knowledge of the role of imaging in CTEPH enables appropriate use of imaging modalities and accurate image interpretation, resulting in early diagnosis, determination of treatment strategies, and appropriate evaluation of treatment efficacy. This review summarizes the current roles of imaging in the clinical practice for CTEPH, demonstrating the characteristic findings observed in each modality.

Chronic Thromboembolic Pulmonary Hypertension (CTEPH) is a progressive pulmonary vascular disease which can lead to right heart failure and death, if left untreated. CTEPH is caused by persistent obstruction of large, middle-sized, or distal pulmonary arteries due to limited thromboembolic resolution in the pulmonary vascular arterial tree. Every patient with CTEPH should undergo evaluation for Pulmonary Endarterectomy (PEA) after referral to institutions with an experienced multidisciplinary CTEPH team. Although management of distal thromboembolic lesions with PEA remains a challenge due to their difficult accessibility, limited distal CTEPH is not considered an absolute contraindication for PEA, as more expertise surgical teams operate on them successfully. Furthermore, in up to 30–50% of patients who undergo PEA, curative treatment is not achieved due to incomplete thrombi removal or extensive pulmonary microvascular disease. Medical therapies that target the underlying pulmonary microvascular disease can offer symptomatic and hemodynamic benefits, although they do not deal with the core mechanism of the disease which is the removal of thromboembolic material from pulmonary vasculature. Recent research has provided evidence suggesting balloon pulmonary angioplasty (BPA) is a reasonable treatment option for inoperable CTEPH and recurrent/persistent pulmonary hypertension after PEA. Advancements in diagnostic modalities and refinements of BPA technique have decreased the complication rate and increased its beneficial effects in hemodynamics, symptoms, right ventricular function and long-term survival. Ongoing trials and future prospective cohorts will provide evidence regarding the optimal selection of patients and lesions prone to BPA treatment along with hybrid therapeutic strategies combining pharmacological therapy, PEA and BPA, which can potentially change the standard of care in CTEPH.

To evaluate the feasibility of two-dimensional parametric parenchymal blood flow (2D-PPBF) to quantify perfusion changes in the lung parenchyma following balloon pulmonary angioplasty (BPA) for treatment of chronic thromboembolic pulmonary hypertension.

Overall, 35 consecutive interventions in 18 patients with 98 treated pulmonary arteries were included. To quantify changes in pulmonary blood flow using 2D-PPBF, the acquired digital subtraction angiography (DSA) series were post-processed using dedicated software. A reference region of interest (ROI; arterial inflow) in the treated pulmonary artery and a distal target ROI, including the whole lung parenchyma distal to the targeted stenosis, were placed in corresponding areas on DSA pre- and post-BPA. Half-peak density (HPD), wash-in rate (WIR), arrival to peak (AP), area under the curve (AUC), and mean transit time (MTT) were assessed. The ratios of the reference ROI to the target ROI (HPD_parenchyma/HPD_inflow, WIR_parenchyma/WIR_inflow; AP_parenchyma/AP_inflow, AUC_parenchyma/AUC_inflow, MTT_parenchyma/MTT_inflow) were calculated. The relative differences of the 2D-PPBF parameters were correlated to changes in the pulmonary flow grade score.

The pulmonary flow grade score improved significantly after BPA (1 versus 3; p<0.0001). Likewise, the mean HPD_parenchyma/HPD_inflow (–10.2%; p<0.0001), AP_parenchyma/AP_inflow (–24.4%; p=0.0007), and MTT_parenchyma/MTT_inflow (–3.5%; p=0.0449) decreased significantly, whereas WIR_parenchyma/WIR_inflow (+82.4%) and AUC_parenchyma/AUC_inflow (+58.6%) showed a significant increase (p<0.0001). Furthermore, a significant correlation between changes of the pulmonary flow grade score and changes of HPD_parenchyma/HPD_inflow (ρ=–0.21, p=0.04), WIR_parenchyma/WIR_inflow (ρ=0.43, p<0.0001), AP_parenchyma/AP_inflow (ρ=–0.22, p=0.03), AUC_parenchyma/AUC_inflow (ρ=0.48, p<0.0001), and MTT_parenchyma/MTT_inflow (ρ=–0.39, p<0.0001) could be observed.

The 2D-PPBF technique is feasible for the quantification of perfusion changes following BPA and has the potential to improve monitoring of BPA.