Assessment of Extended Criteria Donor Hearts with Resonance Raman Spectroscopy During Normothermic Machine Perfusion

Purpose: Normothermic Machine Perfusion (NMP) is an excellent method for the assessment of Extended Criteria Donor (ECD) organs, with the possibility of improving the supply of organs for heart transplantation. Resonance Raman Spectroscopy (RRS) is a real-time assessment technique, easily applied during NMP, that enables non-invasive quantification of the mitochondrial redox state and oxygen usage, as proxies for heart viability.
Methods: Four human hearts (three Donation by Circulatory Death(DCD), one Donation by Brain Death(DBD)), rejected for transplant, were perfused retrograde using a pulsatile pump (VentriFlo, Pelham, NH) for ~6 hr at 37°C. Using RRS, the ratio of reduced to total mitochondria (Raman reduced mitochondrial ratio - 3RMR) was compared with biochemical and functional metrics obtained during NMP to determine the correlation between mitochondrial function and cardiac graft health.
Results: The results obtained from RRS indicate hearts with longer cold ischemia times (CIT) contain larger ratios of reduced mitochondria (C & D) 1 hr after initiating the perfusion (Fig. 1A & E), when compared to hearts with shorter CIT (A & B). Furthermore, RRS predicts hearts B and C would be the best performing hearts based on lower 3RMR values. This prediction is supported by the acquired functional data where heart B and C had higher left ventricular function when compared to heart A and D (Fig 1B). Conventional perfusate-based metrics (lactate and oxygen uptake) do not correlate with the acquired heart functionality metrics (Fig. 1C & D).
Conclusion: These results indicate that hearts with extended cold storage times may have some mitochondrial dysfunction that can be reversed during NMP. Lower 3RMR numbers seem to correlate with better heart functionality, suggesting RRS has potential as an assessment tool in NMP.