Abstract Body (Do not enter title and authors here): Introduction/Background:
Atrial fibrillation (AF), a common postoperative arrhythmia, is associated with increased morbidity and mortality across various surgical populations. In patients undergoing orthotopic liver transplantation (LT), the presence of AF has been linked to poorer clinical outcomes. However, data on the prognostic significance of new-onset AF during early post-transplant readmissions in orthotopic LT recipients remain limited.

Hypothesis:
We postulated that incident AF occurring during 90-day post-LT readmissions is independently associated with increased in-hospital mortality, prolonged length of stay, and higher healthcare costs.

Methods:
We conducted a retrospective cohort study using data from the National Readmission Database (2016–2019). Adult LT recipients (aged >18 years) readmitted within 90 days were identified via ICD-10 coding. Patients who developed new-onset atrial fibrillation (AF) during readmission were compared to those without AF. Primary outcomes included in-hospital mortality, length of stay (LOS), and total hospitalization costs. Multivariable logistic and linear regression models, adjusted for demographic and clinical confounders, were used.

Results:
Of 31,557 adult LT recipients (mean age 55.5 years, 35% female), 8,449 (27.6%) (mean age 55.3 years, 36.7% women) were readmitted within 90 days. Among those readmitted, 222 patients (2.6%) developed new-onset atrial fibrillation (AF), and 84 (1.0%) died during the readmission period. New-onset AF was associated with a 7.6-fold increased risk of in-hospital mortality (95% CI: 3.0–19.0; P < 0.05). Additionally, AF onset was linked to a mean increase in LOS of 6.2 days (95% CI: 6.2–7.1; P = 0.001) and an average increase in hospitalization costs of $75,396 (95% CI: $11,932–$138,860; P = 0.02). All associations achieved statistical significance.

Conclusion(s):
New-onset AF during early post-transplant readmissions is associated with significantly worse clinical outcomes and increased healthcare utilization. These findings underscore the need for proactive rhythm monitoring and risk-stratified arrhythmia management during the liver transplant recovery period.