Controlled reperfusion of cardiac grafts from non-heart beating donors

Background. Hearts harvested from non-heart-beating donors sustain severe injury during procurement and implantation, mandating interventions to preserve their function. We tested the hypothesis that limiting oxygen delivery during initial reperfusion of such hearts would reduce free-radical injury. Methods. Rabbits sustained hypoxic arrest after ventilatory withdrawal, followed by 20 minutes of in vivo ischemia. Hearts were excised and reperfused with blood under conditions of high arterial oxygen tension (PaO₂) (approximately 400 mm Hg), low PaO₂ (approximately 60 to 70 mmHg), high pressure (80 mm Hg), and low pressure (40 mm Hg), with or without free-radical scavenger infusion. Non-heart-beating donor groups were defined by the initial reperfusion conditions: high PaO₂/high pressure (n = 8), low PaO₂/high pressure (n = 7), high PaO₂/low pressure (n = 8), low PaO₂/low pressure (n = 7), and high PaO₂/high pressure/free-radical scavenger infusion (n = 7). Results. After 45 minutes of reperfusion, low PaO₂/high pressure and high PaO₂/low pressure had a significantly higher left ventricular developed pressure (63.6 ± 5.6 and 63.1 ± 5.6 mm Hg, respectively) than high PaO₂/high pressure (40.9 ± 4.5 mm Hg; p < 0.0000001 versus both). However, high PaO₂/high pressure/free radical scavenger infusion displayed only a trend toward improved ventricular recovery compared with high PaO₂/high pressure. Conclusions. Initially reperfusing nonbeating cardiac grafts at low PaO₂ or low pressure improves recovery, but may involve mechanisms other than decreased free-radical injury.