Preconditioning does not attenuate myocardial stunning

Background. Despite numerous reports that one or more episodes of brief coronary artery occlusion preconditions the myocardium and dramatically reduces myocardial infarct size produced by a subse-quent prolonged ischemia, we recently demonstrated that preconditioning does not attenuate contractile dysfunction in the peri-infarct tissue. However, the specific effects of preconditioning on myocardium in which wall motion has not been compromised by the preconditioning regimen per se and is further submitted to a short ischemic insult (that is, not confounded by necrosis) remain unknown. Methods and Results. We addressed these issues in the canine model of myocardial stunning. Eighteen anesthetized dogs underwent 15 minutes of coronary occlusion followed by 3 hours of reperfusion. Before the 15-minute coronary occlusion, each dog received one of three treatments: no intervention (control group, n=6), one episode of 5-minute coronary occlusion/S-minute reperfusion (PC5 group, n=6), or one episode of 2.5-minute coronary occlusion/S-minute reperfusion (PC2.j group, n=6). Segment shortening (SS) in the ischemic/reperfused midmyocardium was monitored by sonomicrometry, and myocardial blood flow was assessed by injection of radiolabeled microspheres. All three groups were equally ischemic during the 15-minute coronary occlusion: Midmyocardial blood flow averaged 0.05±0.02, 0.07+0.04, and 0.08±0.03 ml/min/g in control, PC", and PC5 groups, respectively. Before the 15-minute coronar