Spontaneous Enlargement in Balloon Pulmonary Angioplasty With Undersized Balloon for Chronic Thromboembolic Pulmonary Hypertension

Background Balloon pulmonary angioplasty (BPA) has emerged as an effective treatment for chronic thromboembolic pulmonary hypertension (CTEPH). Recent studies have reported progressive improvements in hemodynamic and clinical parameters during follow‐up, even without additional interventions. However, the exact mechanisms underlying these delayed effects remain unclear. Methods This retrospective study analyzed 114 lesions from 31 CTEPH patients who underwent initial BPA with undersized balloons. Quantitative pulmonary angiography analysis was performed at three time points: pre‐procedure, immediately post‐procedure, and at follow‐up. Vessel diameters were measured and compared across different lesion types. Results Among the analyzed lesions, 78.2% demonstrated spontaneous pulmonary artery enlargement at a median follow‐up of 56 days. The median enlargement in diameter increased by 0.16 (0.00–0.36) mm from pre‐procedure to immediately post‐procedure, and further increased by 0.31 (0.03–0.76) mm at follow‐up. The magnitude of spontaneous enlargement during follow‐up was significantly greater than immediate post‐procedural changes ( p = 0.003). Web lesions showed the highest rate of spontaneous enlargement (77.7%), compared to ring‐like stenosis lesions (57.1%). No restenosis was observed during the follow‐up period. Conclusions In the initial BPA for CTEPH patients, even with the use of small balloons, the treated vessels demonstrated significant spontaneous enlargement from post‐procedure to follow‐up without additional interventions, particularly in web lesions.