Duration of ischaemic preconditioning and importance of size of area at risk in pigs

An explanation of the preconditioning phenomenon must account for the biolo gy of the phenomenon. Here we provide a more thorough characterization of i schaemic preconditioning (IPC), examining temporal characteristics and the importance of the size of area at risk. IPC was induced by two 10-min LAD o cclusions separated by 30 min reperfusion in pentobarbital anaesthetized op en-chest pigs. The last brief occlusion was followed by either 30 min, 2 h or 4h of reperfusion, The degree of protection was evaluated by measuring i nfarct size after either 45 or 60 min LAD occlusion followed by 2 h of repe rfusion. To examine the importance of the size of area at risk, the occlusi on site on LAD was varied between pigs, IPC followed by 30 min and 2 h of r eperfusion 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 promi nent when a test ischaemic period of 45 min was used (47 +/- 5% vs 13 +/- 1 %: P<0.05). IPC was paralleled by an increased incidence of ventricular fib rillation during the early phase of the prolonged LAD occlusion after 30 mi n, 2 h and 4 h of reperfusion. Although no correlation was found between in farct size (as a percentage of area at risk) and area at risk (as a percent age of Ventricular weight) in control pigs, a positive correlation was foun d between these variables in preconditioned pigs. We conclude that the infa rct size-limiting effect of IPC lasts at least 4 h and that it is parallele d by profibrillatory effects in open-chest pigs. Furthermore, the infarct s ize-limiting effect of IPC depends on the size of area at risk, being most pronounced when area at risk is small. (C) 1999 Academic Press.