Abstract Body (Do not enter title and authors here): Background:
In single ventricle (SV) cases with pulmonary stenosis or atresia, where pulmonary blood flow is supplied by major aortopulmonary collateral arteries (MAPCAs), early unifocalization may help establish a low-resistance pulmonary vascular bed. This study aims to describe the postoperative outcomes of patients with SV and MAPCAs who undergo early unifocalization and to identify factors associated with successful completion of total cavopulmonary connection (Fontan procedure).

Methods:
This is a retrospective cohort study of all patients with SV and MAPCAs who underwent initial unifocalization at a single institution with intention to treat along the single ventricle pathway from 2006 to 2024. The primary outcome of successful SV palliation was defined as survival to discharge following Fontan completion, or superior cavopulmonary connection (Glenn) with encouraging hemodynamic assessment for Fontan completion.

Results:
The cohort included 43 patients, with median follow up of 5.3 years. Surgical outcomes are depicted in Figure 1, and intracardiac diagnoses in Figure 2. Total anomalous pulmonary venous return (TAPVR) was present in 14 (33%) patients, of whom 5 (36%) had significant obstruction, and heterotaxy syndrome was present in 25 (58%). A dominant right ventricle was present in 29 (68%), a dominant left ventricle in 13 (30%) and an indeterminate ventricle in 1 (2%). Preoperative respiratory support was used in 19 (44%) patients, of whom 4 (9%) were intubated.

Of the study cohort, 35 (81%) patients survived unifocalization, 15 (35%) survived Glenn anastomosis, and 10 (23%) survived Fontan completion. Overall, 14 (33%) underwent successful SV palliation. None of the above factors demonstrated a significant association with survival to Glenn, survival to Fontan or successful SV palliation. Of the 5 patients with obstructed TAPVR, none achieved successful SV palliation. Overall mortality was 61% overall (Figure 3A). Mortality in the group with obstructed TAPVR was 40% compared to 67% in the group without pulmonary venous obstruction (p = 0.062, Figure 3B).

Conclusion:
Patients with SV and MAPCAs represent a high-risk population. Despite early unifocalization at a specialized center, outcomes remain guarded relative to overall SV outcomes, with a subset of patients still being candidates for Glenn and Fontan procedures. Obstructed TAPVR may be associated with worse outcomes in this high-risk group.