Abstract Body (Do not enter title and authors here): Introduction: Supraventricular tachycardia (SVT) is common and poorly tolerated in patients who have undergone Fontan procedure. Recurrence rates after catheter ablation in these patients are high. Recent data on the outcomes of SVT ablation and the predictors of recurrence in this population is lacking.

Objective: Our study aimed to characterize clinical variables in patients with a Fontan undergoing EP ablation, investigate long-term outcomes, and determine factors that are associated with recurrence.

Methods: Charts of patients who had undergone Fontan procedure and underwent SVT ablation between January 1, 1995, and October 1, 2023, at a tertiary care center were reviewed. Demographic, clinical, and outcome variables over 5 years were compared between patients with and without SVT recurrence.

Results: Mean age of 25 patients (56% male) at time of SVT ablation was 31.5 ± 7.2 years. Ablation success rate was 92%. Recurrence occurred in 12 (48%) patients, with 7 (28%) requiring repeat ablations repeat within 5 years. Rate of recurrence did not differ between those who had the procedure before or after 2018. During the 5-year follow up period, 13 (59%) patients with follow up had cardiovascular (CV) hospitalization and 1 patient died. Atrial Tachycardia (70%) and Typical Atrial Flutter (65%) were the most common SVTs ablated. A trans-baffle puncture during the ablation was performed in 6 (23%) patients. Tricuspid atresia and elevated BNP levels were associated with increased risk of SVT recurrence (Table).

Conclusion: Recurrence and cardiac hospitalization rates after SVT ablation in this population remain high. This study underscores the need for risk stratification in patients with Fontan physiology undergoing SVT ablation and informs future research directions for enhancing ablation outcomes.