Terminal magnesium cardioplegia: protective effect in the isolated rat heart model using calcium accentuated ischemic...

We have developed a modified isolated working rat heart model to study the effect of potassium and magnesium cardioplegia given just prior to reperfusion, "terminal cardioplegia," on preservation of aortic flow following a standard ischemic insult. The model incorporates a short-term calcium challenge at the beginning of reperfusion to accentuate ischemic injury. All hearts were given initial potassium cardioplegia and subjected to 30 min of normothermic ischemia. Terminal cardioplegia was given for the 2 min prior to reperfusion. Calcium-challenged hearts were reperfused initially with calcium-enriched reperfusate and then switched to standard reperfusate. Aortic flow prior to and 60 min after ischemia was used to determine functional protection. Hearts recovered 82 +/- 3% of preischemic aortic flow when reperfused with normocalcemic reperfusate. When the initial reperfusate was enriched with calcium, aortic flow was only 43 +/- 4% of control. Hearts given terminal magnesium cardioplegia and then challenged with calcium-enriched reperfusate recovered 79 +/- 4% of control aortic flow. Hearts given terminal potassium cardioplegia recovered only 53 +/- 5% of control aortic flow when challenged with calcium-enriched initial reperfusate. Our results indicate that the recovery of aortic flow is significantly reduced by short-term postischemic calcium challenge. This damage is blocked by terminal magnesium cardioplegia, but not by terminal potassium cardioplegia.