Ischaemic preconditioning by partial occlusion without intermittent reperfusion

OBJECTIVE: The aim was to investigate whether ischaemic preconditioning can be obtained by a partial coronary artery occlusion without intermittent reperfusion. METHODS: In seven anaesthetised open chest pigs, the flow in the proximal left anterior descending coronary artery was reduced to 30% of baseline during 30 min before the vessel was occluded completely for 60 min (60 min total coronary occlusion, TCO). After 2 h of reperfusion, the area at risk (AR) and infarct size (IS) were determined using standard procedures. Infarct sizes were compared to those observed in control animals (n = 12), which were subjected to 60 min TCO and 2 h reperfusion, and to infarct sizes determined in animals preconditioned by 10 min TCO with either 15 min (n = 10) or 60 min (n = 5) of reperfusion before the 60 min TCO and 2 h reperfusion. In the last three groups of animals, area at risk was varied by occluding the coronary artery or its branches at different sites. RESULTS: In the control animals infarct size was linearly related (r = 0.99, p < 0.001) to the area at risk with a positive intercept on the AR axis: IS/LVmass (x100%) = 0.88 AR/LVmass (x100%)-3.6. At comparable areas at risk, the infarct size of the animals preconditioned with a 10 min TCO was less than for the control animals. For the animals preconditioned with 10 min TCO and 15 min reperfusion, the relationship between infarct size and area at risk was again linear (r = 0.88) and also had a positive intercept on the AR axis: IS/LVmass (x100%) = 0.68 AR/LVmass (x100%)-4.8. All animals with the flow reduction to 30% of baseline immediately preceding the 60 min TCO had infarct sizes smaller (p < 0.05) than predicted from the regression equation for the control animals, but the infarct size limitation could not be simply related to variables such as changes in regional systolic and postsystolic segment length shortening, ATP, or ADP during the partial occlusion period. CONCLUSIONS: Myocardium can be preconditioned with a flow reduction to 30% of baseline for 30 min without intermittent reperfusion (two stage Harris model). The positive intercept on the AR axis of the IS-AR relationship warrants caution of the use of IS/AR as an index for infarct size limitation.