Relationship between body mass index and traditional size-matching in heart transplantation.

Abstract

Background: Donor-recipient size matching is an important consideration for heart allocation, of which predicted heart mass ratio (PHMR) was found to be the most optimal metric. However, the PHM formula has not been validated in a cohort that included obese recipients. Therefore, our study seeks to add further granular data on this topic by investigating acute survival in PHM categories across multiple body mass index (BMI) groups.

Methods: Adult heart transplant recipients were analyzed using the United Network for Organ Sharing database. BMI groups included: normal (18.5-24.9 kg/m²), overweight (25.0-29.9 kg/m²), obese class I (30.0-34.9 kg/m²), and obese class II+ (≥35.0 kg/m²). PHMR categories were: severely undersized (U2): <0.85, undersized (U1): 0.85-0.95, approximately equally sized (R): 0.95-1.05, oversized (O1): 1.05-1.25, and severely oversized (O2): ≥1.25. All-cause acute mortality was the primary outcome of interest.

Results: A total of 46,141 recipients were included in our analysis. The percentage of obese patients and donors increased over the years, from 21.5 % and 17.2 % in 2000 to 34.4 % and 33.1 % in 2022, respectively. Survival analysis found that as BMI increased, a stepwise reduction in mortality risk for severely undersized grafts was observed (normal: HR = 1.59, p < 0.001; overweight: HR = 1.20, p = 0.029), until ultimately reaching insignificant levels in obese groups across all PHMR categories.

Conclusion: Patients with a normal to overweight BMI were susceptible to increased mortality with a severely undersized graft. Conversely, obese groups appeared to be resistant to the hazards of organ size mismatching by PHMR. The clinical implications of this study may enable recruitment from a larger donor pool and improve challenges in transplantation for obese patients.