Hypoxia-Reperfusion in a Rodent Model of DCD Cardiac Resuscitation Leads to Improved Myocyte Function Compared to Conventional Ischemia Reperfusion Injury

Abstract

Purpose Hypoxia, as opposed to ischemia, precedes circulatory arrest in DCD donors. Our aim was to identfy any differences in cardiac myocyte function following hypoxia-reperfusion in comparison to ischemia-reperfusion. Methods Rats were subjected to hypoxic cardiac arrest (DD30, n = 6) via tracheal occlusion or ischemic cardiac arrest (IR30, n = 6) from aortic clamping. After 30 minutes of warm ischemia, cardiac reperfusion was achieved using a miniature ECMO circuit. LV myocytes isolated from each group were stimulated with 50% suprathreshold voltage at 0.5 Hz for analysis of sarcomeric contractility, expressed as percentage of sarcomere shortening. Contractile reserve was assessed by stimulation with Isoproterenol. Calcium transients were measured in myocytes from the fluorescence of the dye Fura-2. Reperfusion injury was assessed by measurement of superoxide using dihydroethidium fluorescence confocal microscopy. Results Sarcomere shortening was greater in DD30 myocytes compared to IR30 myocytes (figure 1). Myocytes from the IR30 group demonstrated the least shortening and poor contractile reserve. Velocity of contraction and relaxation was also significantly greater in DD30. There was enhanced sensitivity of myofilaments to calcium in DD30 and reduced sensitivity in IR30. The rate of calcium release and uptake was greater in DD30 as was the peak calcium concentration. Superoxide production was significantly greater in IR30. Conclusion There are concerns that exposure of the DCD heart to warm ischemia may adversely impact allograft function. However, prior to circulatory arrest the DCD heart is exposed primarily to hypoxia as opposed to ischemia. We identified that myocytes subjected to hypoxia-reperfusion demonstrated superior contractility and enhanced sensitivity of myofilaments to calcium. DCD myocytes also exhibited less production of superoxide free radicals suggesting less reperfusion injury.