The Role of Intraoperative Pulmonary Blood Flow Assessment and 3D Imaging in Unifocalization for PA/VSD/MAPCAs

Introduction: Tetralogy of Fallot with pulmonary atresia and major aortopulmonary collateral arteries (TOF/PA/MAPCAs) is a highly complex congenital heart defect. It involves a ventricular septal defect (VSD), overriding aorta, complete pulmonary atresia, and variable pulmonary blood supply from MAPCAs. The diverse pulmonary artery anatomy and perfusion patterns create significant diagnostic and therapeutic challenges. Surgical management focuses on unifocalization and establishing a reliable right ventricle–to–pulmonary artery connection for complete repair, aiming to preserve long-term right ventricular function. Previous studies suggested that intraoperative mean pulmonary artery pressure (mPAP) <30 mmHg predicts successful VSD closure. This study aimed to re-evaluate intraoperative pulmonary blood flow assessment reliability, identify conditions causing over/underestimation of pulmonary vascular load, and assess the role of three-dimensional (3D) imaging in surgical decision-making. Methods: We retrospectively reviewed 56 TOF/PA/MAPCAs patients undergoing unifocalization between 2011 and 2025. Data collected included baseline characteristics (MAPCA anatomy, prior palliation, demographics), intraoperative mPAP (at 3 L/min/m² flow), and postoperative right ventricular–to–systemic pressure ratios. Preoperative 3D imaging reconstructions were used to calculate Nakata index and highest surgically achievable total neopulmonary artery index (TNPAI), correlating these with flow study results and outcomes. Serial flow studies were compared in patients with deferred VSD closure. We specifically analyzed cases where flow study predictions conflicted with actual VSD closure outcomes (e.g., reopening despite low mPAP, closure despite elevated mPAP). Results: Fifty-six patients (42.9% male; median age 9.3 months, median weight 7.33 kg at unifocalization) were included; 21 (37.5%) had prior shunt palliation. VSD was closed at unifocalization in 27 patients (48.2%; median mPAP 22 mmHg, IQR 18–24), left open in 24 (42.9%; median mPAP 35 mmHg, IQR 32.5–39.5), and reopened/enlarged in 4 (7.1%), with half (2/4) having mPAP <30 mmHg at initial closure. At final follow-up, 13 patients (23.2%) had a fully or partially open VSD. Hospital mortality was 1.8% (1/56). Five patients required postoperative ECMO, all survived. Ten-year survival was 94.7% (95% CI 85.2–100%) for VSD closure at unifocalization, 100% for delayed closure, and 41.6% (95% CI 5.1–65.4%) for an open defect at final follow-up (p<0.001). Prior shunt palliation did not affect mortality or successful VSD closure. Among six patients with subsequent closure, repeat flow studies showed decreased mPAP in half, with stable/increased mPAP in the rest; all but one achieved successful closure. In discrepant cases, 3D imaging revealed uneven pulmonary blood flow or incomplete vascular recruitment, explaining misleading mPAP values. Preoperative CT scans were available for 42 patients (75%). A TNPAI <200 mm²/m² strongly correlated with a VSD left open (p<0.001); 3 of 4 patients requiring reopening had TNPAI <200 (one lacked CT data). Conclusions: TOF/PA/MAPCAs patients remain surgically complex, despite excellent early/mid-term survival. Persistent open VSD at final follow-up identifies a high-risk subgroup with significantly increased mortality. Intraoperative pulmonary blood flow study is valuable for estimating VSD closure feasibility but can over/underestimate pulmonary vascular capacity. Integrating 3D imaging improves anatomical interpretation of flow study results, supporting VSD closure decisions, especially in patients with borderline or acceptable mPAP.