Abstract Body (Do not enter title and authors here): Introduction: Despite medical advances in congenital heart surgery, disparities in outcomes remain. Social determinants of health (SDoH) are known contributors to healthcare inequities, but their cumulative impact in geographically diverse populations remains understudied.

Research Question: We hypothesized that children undergoing congenital heart surgery with lower SDoH indices and greater distance to care have increased morbidity, mortality at 30 days and 1 year, and longer length of stay.

Methods: We conducted a retrospective cohort study of children undergoing cardiac surgery at a tertiary Heart Center from 2014-2024. Exposures included race, ethnicity, primary language, insurance status, Childhood Opportunity Index (COI), and distance traveled. Age at time of surgery, STAT category, and single ventricle status were also studied. Primary outcomes were 30-day and 1-year morbidity and mortality; the secondary outcome was postoperative length of stay. Univariable and multivariable logistic regression models assessed associations.

Results: Among 3,141 patients, 84.7% were white and 94.3% listed English as their primary language. COI distribution was: 8.5% Very Low, 20.3% Low, 28.7% Moderate, 32.4% High, 10.2% Very High. Most patients had private insurance (63.0%). In univariable models, unknown race was associated with higher odds of complications (OR 1.57, p=0.002), 30-day mortality (OR 2.99, p<0.001), and 1-year mortality (OR 3.96, p<0.001). Unavailable ethnicity predicted increased 30-day (OR 4.24, p=0.002) and 1-year mortality (OR 2.52, p=0.043). No significant associations were found between language, COI, or distance to care and primary outcomes. These associations did not maintain significance in the multivariable model. Compared to white patients, Black (OR 1.78, p=0.015) and Native Hawaiian/Pacific Islander patients (OR 1.67, p=0.028) had significantly longer postoperative length of stay in a multivariable model. Insurance status was not significantly associated with outcomes.

Conclusions: Unreported race and ethnicity data were strongly associated with worse surgical outcomes, highlighting reporting gaps that may mask inequities. While other SDoH factors such as COI and distance traveled were not predictive of morbidity or mortality, race-based disparities in hospital length of stay underscore the need for targeted interventions to improve equity in the care of patients with congenital heart disease.