PRECONDITIONING IMPROVES ENERGY-METABOLISM DURING REPERFUSION BUT DOES NOT ATTENUATE MYOCARDIAL STUNNING IN PORCINE HEARTS

Background. It has been reported that a brief period of coronary occlu sion and reperfusion slows the rate of ATP depletion during subsequent sustained ischemia as well as limiting infarct size. However, it has not yet been determined whether ischemic preconditioning also has an e ffect on the functional and metabolic recovery of stunned myocardium. Our study was designed to address this problem. Methods and Results. F arm pigs were anesthetized with fluothane and randomly assigned to eit her a control group or a preconditioned group. The control group (n=15 ) underwent 15 minutes of coronary occlusion followed by 120 minutes o f reperfusion. The preconditioned group (n=14) underwent two episodes of 5-minute occlusion and 5-minute reperfusion followed by 15 minutes of occlusion and 120 minutes of reperfusion. This protocol was designe d to exclude the stunning effect of the preconditioning procedure itse lf as much as possible besides preconditioning the heart. A pair of ul trasonic crystals was implanted in the area at risk perfused by the le ft anterior descending coronary artery. P-31-nuclear magnetic resonanc e spectroscopy and sonomicrometry were performed alternately. Regional myocardial blood flow (RMBF) was determined with colored microspheres . At 15 minutes of sustained ischemia, phosphocreatine (Pcr), ATP, and intracellular pH were significantly better preserved in the precondit ioned group (Pcr: control/preconditioned, 1+/-1%/14+/-1%; ATP:control/ preconditioned, 66+/-2%/74+/-2%; pH:control/preconditioned, 6.32+/-0.0 7/6.52+/-0.05; P<.05). After reperfusion, ATP increased progressively and was almost normalized at 120 minutes of reperfusion in the precond itioned group (control/preconditioned, 73+/-4%/95+/-3%; P<.05). Oversh oot of Pcr (which indicates that the energy generating system is opera ting better than energy utilizing system) persisted in preconditioned hearts but disappeared rapidly in controls (control/preconditioned, 10 4+/-3%/130+/-3% after 120 minutes of reperfusion). There was no signif icant difference in percent segment shortening (%SS), RMBF, and hemody namics between the two groups throughout the experiment (%SS: control/ preconditioned, 29.8+/-5.9%/28. 8+/-6.3% of baseline after 120 minutes of reperfusion). Conclusions. Preconditioning improves energy metabol ism during reperfusion, although it does not attenuate myocardial stun ning for at least 2 hours after reperfusion. (Circulation 1993;88:223- 234)