Duration of Ischaemic Preconditioning and Importance of Size of Area at Risk in Pigs

An explanation of the preconditioning phenomenon must account for the biology of the phenomenon. Here we provide a more thorough characterization of ischaemic preconditioning (IPC), examining temporal characteristics and the importance of the size of area at risk. IPC was induced by two 10-min LAD occlusions separated by 30 min reperfusion in pentobarbital anaesthetized open-chest pigs. The last brief occlusion was followed by either 30 min, 2 h or 4 h of reperfusion. The degree of protection was evaluated by measuring infarct size after either 45 or 60 min LAD occlusion followed by 2 h of reperfusion. To examine the importance of the size of area at risk, the occlusion site on LAD was varied between pigs. IPC followed by 30 min and 2 h of reperfusion reduced infarct size from 58±2% of area at risk to 15±4% (P<0.05) and 15±6% (P<0.05), respectively, by 45 min of LAD occlusion. After 4 h of reperfusion the infarct size-limiting effect of IPC was still prominent when a test ischaemic period of 45 min was used (47±5%vs13±1%P<0.05). IPC was paralleled by an increased incidence of ventricular fibrillation during the early phase of the prolonged LAD occlusion after 30 min, 2 h and 4 h of reperfusion. Although no correlation was found between infarct size (as a percentage of area at risk) and area at risk (as a percentage of ventricular weight) in control pigs, a positive correlation was found between these variables in preconditioned pigs. We conclude that the infarct size-limiting effect of IPC lasts at least 4 h and that it is paralleled by profibrillatory effects in open-chest pigs. Furthermore, the infarct size-limiting effect of IPC depends on the size of area at risk, being most pronounced when area at risk is small.