Abstract Body (Do not enter title and authors here): Background: Advanced directives are important tools for ensuring patient autonomy in healthcare decision-making, yet little is known about their prevalence among adults with congenital heart disease (ACHD).

Objective: To determine the prevalence of advanced directives among ACHD patients and identify associated clinical and demographic factors.

Methods: We conducted a cross-sectional analysis of 295 unique ACHD patients. Demographic data, congenital heart disease complexity, surgical history, comorbidities, and lifestyle factors were collected. Univariable screening followed by multivariable logistic regression was used to identify factors associated with having an advanced directive.

Results: Among 295 ACHD patients (49.32% male, median age 30 years [IQR 23-37]), most had severe complexity ACHD (50.85%), while 29.15% had moderate complexity and 20% had simple ACHD. Genetic syndromes were present in 13.89% of patients. Most patients (78.64%) had undergone at least one cardiac procedure. Only 42 patients (14.24%) had an advanced directive. Univariable screening identified older age (p=0.0345) and the presence of a genetic syndrome (p=0.0001) as a potential predictor. Of these, both were found to be significant at the 0.05 level in the final, multivariable adjusted model (Age p=0.0105, Genetic Syndrome p<0.0001). Adjusted for age, the presence of a genetic syndrome in patients was associated with 5.38 times the odds of having an advanced directive (95% CI: (2.420, 11.950)). Adjusted for the presence of a genetic syndrome, every one-year increase in patient age corresponded to a 3.7% increase in the odds of having an advanced directive (95% CI: (1.009, 1.066)).

Conclusions: Despite high disease complexity, advanced directive completion rates among ACHD patients remain low at only 14.35%. Notably, older age and the presence of a genetic syndrome were found to be significant factors influencing the likelihood of having an advanced directive. These findings highlight the need for targeted interventions to increase advanced care planning in this growing population.