Evaluating Matching by Predicted Heart Mass in Adolescent Heart Transplantation: Analysis of the United Network for Organ Sharing Database

Abstract

<h3>Purpose</h3> Predicted Heart Mass (PHM) has emerged as an attractive size matching metric in adult cardiac transplantation. However, since PHM was derived from a healthy adult cohort, its generalizability to the pediatric population is unclear. We hypothesize that PHM can be extended to older adolescents, and potentially broaden the donor pool available to this group. <h3>Methods</h3> The United Network for Organ Sharing database was retrospectively analyzed for patients aged 13-18 undergoing heart transplantation. Recipients were divided into quintiles (Q1-Q5) based on donor-to-recipient predicted heart mass ratios (PHMR). Primary endpoint was graft survival at five years. <h3>Results</h3> 1727 adolescent heart transplant recipients between January 1994 and September 2019 were retrospectively analyzed. The median PHMR's for each quintile was 0.85 (0.60 to 0.92), 0.98 (0.92 to 1.03), 1.08 (1.03 to 1.14), 1.22 (1.14 to 1.31), and 1.44 (1.31 to 2.3). Kaplan-Meier survival curves demonstrated comparable survival across all quintiles of PHMR (p=0.9). Multivariate Cox regression showed no significant difference in graft failure of the outer quintiles when compared to the middle quintile (Q1: 0.98 HR, p=0.93; Q2: 0.93 HR, p=0.69; Q4: 1.14 HR, p=0.46; Q5: 1.05 HR, p=0.79). Significant covariates included transplant year (HR: 0.95, p<0.0001), serum bilirubin (HR: 1.06, p=0.002), ECMO at transplantation (HR: 1.89, p=0.035), recipient age (HR: 1.14, p=0.0013), number of previous transplantations (HR: 1.59, p=0.007), and underlying diagnosis of congenital heart disease (vs. dilated cardiomyopathy, HR: 1.69, p=0.0005). Ischemic time in hours (HR: 1.08, p=0.17) and mechanical circulatory support at transplantation (HR: 0.91, p=0.49) were not significant. <h3>Conclusion</h3> Matching by PHM is not associated with survival or risk in adolescent heart transplant recipients. Our results underscore the ongoing need to develop an improved size-matching method in pediatric heart transplantation.