Abstract Body (Do not enter title and authors here): Background: The prevalence of both obesity and the use of left ventricular assist devices (LVAD) is increasing in pediatrics, but what impact obesity has on post-heart transplant (HT) outcomes when using an LVAD as a bridge to transplant (BTT) is unknown.

Methods: Retrospective cohort study of patients 12-18 years old in the UNOS database with a durable LVAD and listed for heart transplant (HT) between 7/1/2004-12/31/2021. Demographic and clinical variables were assessed. Patients were classified as overweight (BMI≥85-<95% percentile), Class I obesity (BMI≥95-<120% of the 95^th %), and Class II/III obesity (≥120% of the 95^th% or BMI≥35) at time of listing and transplant. The primary outcome was 1-year post-HT survival; additional outcomes included post-HT length of stay (LOS), rejection, and waitlist removal. A multivariable analysis was performed to identify the independent association of morbid obesity with 1-year post HT survival.

Results: Of 539 adolescent BTT patients, 41% had a BMI ≥85^th percentile at time of listing: 76 were overweight, 84 were Class I, and 60 were Class II/III. Class II/III patients, compared to overweight, demonstrated a decrease in BMI between listing and transplant (△BMI -0.2, IQR -2.6–0.5 vs 0.0, IQR -0.5–2.6, p= 0.003) with similar improvement in functional status (27% vs 32-36%, p=0.37) and equivalent post-HT LOS (17 vs 15-17 days, p =0.09). However, these patients were more frequently inactivated (13% vs 4-7%, p=0.04). In adjusted analysis, the highest BMI cohort had lower likelihood of reaching HT (OR 0.65, 95% CI 0.48-0.88) and increased 1-year post-HT graft failure (OR 4.47, 95% CI 1.22-14.78) (Fig. 1A). The 5-year mortality of these patients was nearly twice that of other adolescents (29% vs 18%, p=0.06) (Fig. 1B).

Conclusions: Class II/III obese adolescent VAD patients have an increased risk of waitlist inactivation and 1-year graft failure. Use of VADs and HT in obese adolescents may be reasonable (71% 5-year survival) if the team, patient, and family are aware of the higher risk profile. Given the socioeconomic contributions to obesity in children, further studies examining if obesity can be a modifiable risk factor in VAD and HT is critical.