The Safety and Late Hemodynamics of Donor Cardiac Undersizing in Heart Transplantation.

Background: Predicted heart mass ratio (PHMr) has become the standard donor-recipient size matching method in heart transplantation. While utilization of small PHMr hearts is associated with increased one-year mortality, the underlying mechanisms and time horizon of mortality remain uncertain.

Methods: A single institution analysis of isolated heart transplant recipients (01/2019-7/2022) was performed (N=334). Patients were stratified by PHMr: undersized (<0.86) (n=106), matched (0.86-1.15) (n=175), and oversized (>1.15) (n=53). Survival within PHMr groups was further stratified: complex transplant group (preoperative LVAD, adult congenital, or preoperative ECMO) and non-complex transplant group (all others).

Results: Donor and recipient variables were similar. However, undersized patients were more likely to have a durable LVAD (P=0.022). While postoperative PGD and inotrope score were similar between groups, there was a trend toward increased postoperative dialysis need with undersized hearts (P=0.056). Overall, thirty-day (P=0.012) and one-year survival (P=0.002) was significantly worse in the undersized group compared to matched or oversized groups. However, on subset analysis, these differences only remained among the complex transplant recipients (P=0.013), but not the non-complex transplant recipients (P=0.428). Median mixed venous oxygen saturations at serial time-points were maintained between 65-70% in all heart size groups, with cardiac indices between 2.4-2.8 LPM/m2.

Conclusions: Small PHMr hearts are associated with increased one-year mortality, driven by complex transplant operations. Recipients who received undersized PHMr hearts from non-complex transplant operations had a similar hemodynamic profile and survival as those who received matched and oversized hearts. Small PHMr hearts may be selectively safe for transplantation.