After four hours of cold ischemia and cardioplegic protocol, the heart can still be rescued with postconditioning

There is evidence that ischemia lasting more than 4 hours affects cardiac allograft survival. Ischemia and reperfusion are associated with additional deleterious effects. Protective effects of preconditioning are already being used but protocols based on postconditioning have not been evaluated. We tested the impact of postconditioning on hearts maintained in the cold for a long period of total global ischemia and we compared the results with those obtained with pyruvate, a cardioprotective molecule.

Isolated working rat hearts were subjected to a global total ischemia (4 h/4 degrees C), followed by 45 min of reperfusion. Postconditioning consisted of brief total global ischemia applied three times during the onset of reperfusion (ischemia: 30 sec, reperfusion: 30 sec). Superoxide anion production and collagen content were evaluated on cryosections.

Our results showed that postconditioning led to improvements in cardiac functions that were comparable to those conferred by pyruvate. Postconditioning reduced myocardial damage, gave better functional recovery, and better preserved the collagen content. It reduced the duration of arrhythmias at the onset of reperfusion. In the postconditioning group, this improvement was associated with a reduction in superoxide production.

In conclusion, our study showed that postconditioning induced good cardioprotective effects in a long cold (4 hr/4 degrees C) ischemia protocol and led to lower O2 production in part mediated by the reduction in NAPDH oxidase activity. It is interesting to note that, in our experimental conditions, the beneficial effects of postconditioning were comparable to those produced by pyruvate.