Abstract Body (Do not enter title and authors here): Introduction: Ebstein’s anomaly (EA) patients are at risk of arrhythmias. However, data regarding cardiac magnetic resonance (CMR) for predicting arrhythmic events using anatomic and functional parameters are scarce.

Goal/Aims: To assess whether CMR-derived anatomical and functional data can predict arrhythmias in EA.

Methods: Retrospective single-center cohort assessing EA patients referred for CMR between June 2016 and December 2023. Anatomic, volumetric and functional ventricular parameters were obtained from the CMR, and arrhythmias were found in the medical records. Arrhythmia occurrence was assessed from the CMR date (time-0), excluding pre-existing arrhythmias. Normality was assessed with Shapiro-Wilk for continuous variables, followed by a t-test or Wilcoxon. For categorical variables, we calculated chi-square or Fisher exact test. Receiver Operating Characteristic curves evaluated CMR predictors for arrhythmia occurrence. The 95% confidence interval lower bound must be > 0.5 to be statistically significant.

Results: Forty-two patients were included (mean age 24.1 years±15.3); 21 (50.0%) were males. Other parameters are presented in Table1. There were 11 (26.2%) patients with arrhythmias after CMR: 72.7%patients developed supraventricular tachycardia, 18,2% atrial flutter, and 9.1% patients for each of the following: sustained ventricular tachycardia, atrial fibrillation and high-grade AV block. True tricuspid annulus (AUC=80.4, CI: 65.0-95.7) was a good predictor. In contrast, GOSE index (AUC=77.9, CI:63.3-92.5), apical displacement (AUC=76.4, CI:59.2-93.6), Ebstein’s angle (AUC=70.5, CI: 52.5-88.6), right atrial size (AUC=70.9, CI:54.6- 87.2) and right ventricular ejection fraction (AUC=74.2, CI:56.4-92.0) had fair predictive capacity (Figure1).

Conclusion: CMR metrics predict arrhythmias in EA patients, with anatomic variables outperforming volumetric, but not functional ones. Larger studies are needed to confirm these findings.