Many of the deleterious aspects of reperfusion, such as calcium overload, myo-cyte edema, and free radical production, occur very rapidly during the first few minutes of reperfusion, as demonstrated by electron spin resonance studies.55 Just as they were investigated in the setting of preservation perfusate, modifications of the reperfusate vehicle base (blood vs. asanguinous) and chemical composition (acalcemic, leukocyte depleted, additives) have been investigated both experimentally and clinically in an attempt to abrogate the entire spectrum of the ischemic-reperfusion syndrome. The "oxygen paradox" and "calcium paradox" of reperfusion (that is, the paradoxically deleterious effects of reperfusion with oxygen and without calcium) have been demonstrated in cardiac transplantation, as in other organ transplants.

Resuscitative Effects of Controlled Reperfusion Convincing evidence exists regarding the reanimation and engraftment of asys-tolic heart donors in the laboratory setting, in primate, rat and rabbit heart models.56-58 The prototypical animal model preparation uses a period of prolonged, sublethal normothermic ischemia followed by preservative perfusion and prolonged storage. This is followed by engraftment with controlled reperfusion (with substrate enriched blood cardioplegic solutions typically) immediately preceding uncontrolled reperfusion with normothermic unmodified blood.

Secondary Blood Cardioplegia

The administration of oxygenated blood cardioplegia during reimplantation of the transplanted heart functionally decreases the ischemic interval without changing the time to conventional reperfusion.59, 60 The largest series (n = 99 patients) reporting on secondary blood cardioplegia, given in an antegrade route, demonstrated benefit in terms of catecholamine requirements, endomyocardial biopsy evidence of ischemic injury, and a decrease in operative mortality from 21% to 9%, with graft failure mediated deaths reduced from 13% to 4.9%.61

0 0

Post a comment