A clinically relevant sheep model of orthotopic heart transplantation 24 h after donor brainstem death
Authors: See Hoe Louise E. , Wildi Karin , Obonyo Nchafatso G. , Bartnikowski Nicole , McDonald Charles , Sato Kei , Heinsar Silver , Engkilde-Pedersen Sanne , Diab Sara , Passmore Margaret R. , Wells Matthew A. , Boon Ai-Ching , Esguerra Arlanna , Platts David G. , James Lynnette , Bouquet Mahe , Hyslop Kieran , Shuker Tristan , Ainola Carmen , Colombo Sebastiano M. , Wilson Emily S. , Millar Jonathan E. , Malfertheiner Maximillian V. , Reid Janice D. , O’Neill Hollier , Livingstone Samantha , Abbate Gabriella , Sato Noriko , He Ting , von Bahr Viktor , Rozencwajg Sacha , Byrne Liam , Pimenta Leticia P. , Marshall Lachlan , Nair Lawrie , Tung John-Paul , Chan Jonathan , Haqqani Haris , Molenaar Peter , Li Bassi Gianluigi , Suen Jacky Y. , McGiffin David C. , Fraser John F. 
Published: December 2021

Abstract
Background
Heart transplantation (HTx) from brainstem dead (BSD) donors is the gold-standard therapy for severe/end-stage cardiac disease, but is limited by a global donor heart shortage. Consequently, innovative solutions to increase donor heart availability and utilisation are rapidly expanding. Clinically relevant preclinical models are essential for evaluating interventions for human translation, yet few exist that accurately mimic all key HTx components, incorporating injuries beginning in the donor, through to the recipient. To enable future assessment of novel perfusion technologies in our research program, we thus aimed to develop a clinically relevant sheep model of HTx following 24 h of donor BSD.

Methods
BSD donors (vs. sham neurological injury, 4/group) were hemodynamically supported and monitored for 24 h, followed by heart preservation with cold static storage. Bicaval orthotopic HTx was performed in matched recipients, who were weaned from cardiopulmonary bypass (CPB), and monitored for 6 h. Donor and recipient blood were assayed for inflammatory and cardiac injury markers, and cardiac function was assessed using echocardiography. Repeated measurements between the two different groups during the study observation period were assessed by mixed ANOVA for repeated measures.

Results
Brainstem death caused an immediate catecholaminergic hemodynamic response (mean arterial pressure, p = 0.09), systemic inflammation (IL-6 - p = 0.025, IL-8 - p = 0.002) and cardiac injury (cardiac troponin I, p = 0.048), requiring vasopressor support (vasopressor dependency index, VDI, p = 0.023), with normalisation of biomarkers and physiology over 24 h. All hearts were weaned from CPB and monitored for 6 h post-HTx, except one (sham) recipient that died 2 h post-HTx. Hemodynamic (VDI - p = 0.592, heart rate - p = 0.747) and metabolic (blood lactate, p = 0.546) parameters post-HTx were comparable between groups, despite the observed physiological perturbations that occurred during donor BSD. All p values denote interaction among groups and time in the ANOVA for repeated measures.

Conclusions
We have successfully developed an ovine HTx model following 24 h of donor BSD. After 6 h of critical care management post-HTx, there were no differences between groups, despite evident hemodynamic perturbations, systemic inflammation, and cardiac injury observed during donor BSD. This preclinical model provides a platform for critical assessment of injury development pre- and post-HTx, and novel therapeutic evaluation.