Baseline pressure ratio predicts adequacy of reference balloon sizing during balloon pulmonary angioplasty for inoperative chronic thromboembolic pulmonary hypertension

Background/Introduction Balloon pulmonary angioplasty (BPA) is an established treatment for patients with inoperable chronic thromboembolic pulmonary hypertension (CTEPH). However, insufficient dilation may limit haemodynamic improvement, whereas excessive dilation may increase the risk of complications, including delayed pulmonary haemorrhage. A post-procedural distal-to-proximal pressure ratio (Pd/Pa) ≥0.7 is widely used as a physiological indicator of adequate lesion expansion, yet determining the optimal balloon size to achieve it remains unclear. Purpose We aimed to identify predictors of achieving Pd/Pa ≥0.7 following dilation with intravascular ultrasound (IVUS)-guided reference balloon diameter and to determine a clinically relevant baseline factor. Methods We retrospectively analysed pulmonary vessels in patients with inoperable CTEPH who underwent BPA with pressure catheter assessment between November 2022 and September 2025. Among 225 vessels evaluated, those requiring balloon dilation before baseline pressure ratio measurement (pre-dilatation) were excluded (n=50), leaving 175 vessels for the primary analysis. Reference vessel diameter was determined by IVUS. BPA was initially performed using a balloon matching the IVUS-derived reference diameter, followed by repeat pressure ratio assessment. The primary endpoint was the achievement of Pd/Pa ≥0.7. Predictors were evaluated using multivariable logistic regression. Receiver operating characteristic (ROC) analysis was performed to identify the optimal baseline pressure ratio cutoff. External validation was performed in vessels requiring pre-dilatation. Results The study included 36 patients (mean age 64.1±12.8 years; 58% female). Pd/Pa ≥0.7 was achieved in 106 vessels (61%), whereas 69 vessels (39%) did not reach the target ratio. In multivariable analysis, baseline pressure ratio independently predicted target achievement (OR per 0.1 increase 1.796, 95%CI 1.341–2.406, p<0.001). Reference vessel diameter (OR 1.796, 95%CI 1.217–2.651, p=0.003) was also independently associated with the outcome. Compared with ring-type lesions, web or subtotal lesions were associated with lower odds of achieving Pd/Pa ≥0.7 (OR 0.329, 95%CI 0.134–0.804, p=0.015). ROC analysis regarding baseline pressure ratio demonstrated modest discrimination (AUC 0.683, 95%CI 0.603–0.763, p<0.001). A baseline pressure ratio threshold of approximately 0.54 provided the best balance between sensitivity (61%) and specificity (68%), suggesting that lesions with lower baseline values may require balloon size escalation beyond the IVUS-derived reference diameter. Similar discriminative performance was observed in the pre-dilatation cohort (AUC 0.695), supporting the robustness of this threshold. Conclusion Baseline pressure ratio is an independent predictor of physiological adequacy following reference balloon sizing during BPA and may help identify lesions requiring balloon size escalation.