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

Abstract

Predicted heart mass (PHM) ratio has become the standard donor-recipient size matching method in heart transplantation. Although use of small PHM ratio hearts is associated with increased 1-year mortality, the underlying mechanisms and time horizon of mortality remain uncertain. A single-institution analysis of 334 isolated heart transplant recipients (January 2019-July 2022) was performed. Patients were stratified by PHM ratio: undersized (<0.86; n = 106), matched (0.86-1.15; n = 175), and oversized (>1.15; n = 53). Survival within PHM ratio groups was further stratified by complex transplant group (preoperative left ventricular assist device, adult congenital, or preoperative extracorporeal membrane oxygenation) and noncomplex transplant group (all others). Donor and recipient variables were similar. However, undersized patients were more likely to have a durable left ventricular assist device (P = .022). Although postoperative primary graft dysfunction and inotrope score were similar between groups, there was a trend toward increased need for postoperative dialysis with undersized hearts (P = .056). Overall, 30-day (P = .012) and 1-year survival (P = .002) was significantly worse in the undersized group compared with the matched or oversized groups. However, subset analysis showed these differences only remained among the complex transplant recipients (P = .013) but not the noncomplex transplant recipients (P = .428). Median mixed venous oxygen saturations at serial time points were maintained between 65% and 70% in all heart size groups, with cardiac indices between 2.4 and 2.8 L/min/m². Small PHM ratio hearts are associated with increased 1-year mortality, driven by complex transplant operations. Recipients who received undersized PHM ratio hearts from noncomplex transplant operations had a similar hemodynamic profile and survival as those who received matched and oversized hearts. Small PHM ratio hearts may be selectively safe for transplantation.