Intravascular ultrasound analysis of spontaneous pulmonary artery lumen enlargement after balloon pulmonary angioplasty in patients with chronic thromboembolic pulmonary hypertension.

BACKGROUND: Balloon pulmonary angioplasty (BPA) is an important therapeutic strategy for chronic thromboembolic pulmonary hypertension (CTEPH) requiring staged procedures. Notably, incompletely expanded pulmonary artery lumens enlarge spontaneously between sessions, but the mechanism remains unclear. OBJECTIVES: To investigate the morphological mechanisms of spontaneous lumen enlargement after BPA and their association with vasoactive mediators. METHODS: A total of 151 pulmonary artery segments from 92 BPA procedures in 24 CTEPH patients were included for analysis. Intravascular ultrasound (IVUS) was used to assess the same vascular segments immediately after the first BPA procedure and again before the second BPA procedure. Plasma levels of vasoactive mediators were also measured in the corresponding pulmonary artery segments at both time points. RESULTS: Before the second procedure, IVUS showed significant increases in lumen area (LA, 10.2 → 16.8 mm2, p < 0.001) and vascular area (VA, 16.4 → 25.5 mm2, p < 0.001), and a reduction in lesion burden (LB, 35.9% → 32.1%, p < 0.001). Linear mixed-effects model analysis showed that changes in VA and LB were independently associated with the change in LA. Plasma nitrate-nitrite (NOx) levels were higher and plasma endothelin-1 concentrations were lower before the second procedure compared with immediately after the first procedure. Mixed-effects model analysis showed that only plasma NOx difference was independently associated with LA difference. CONCLUSION: Spontaneous lumen enlargement after BPA was associated with vascular enlargement and reduced lesion burden, suggesting a morphological basis for this phenomenon. Pulmonary vascular enlargement may be associated with increased plasma NOx levels.