Myocardial Protection With Postconditioning is Not Enhanced by Ischemic Preconditioning

BACKGROUND: Ischemic preconditioning (IPC) has been used in off-pump coronary artery bypass surgery (OPCAB) to reduce potential injury secondary to ligation of the target vessel. Previous studies have shown that a brief period of repetitive coronary occlusion applied at the onset of reperfusion, postconditioning (postcon), attenuates myocardial injury. This study tested the hypothesis that coincident application of IPC and postcon would provide more cardioprotection than either intervention alone by inhibiting oxidant-mediated injury after ischemia and reperfusion.

METHODS: Four groups of open-chest canines endured 60 minutes coronary occlusion followed by 3 hours reperfusion: control (n = 10), no intervention; IPC (n = 9), 5 minutes left anterior descending coronary artery occlusion preceded 10 minutes of reperfusion before prolonged occlusion; postcon (n = 10), 3 cycles of 30 seconds reperfusion-30 seconds reocclusion were imposed immediately upon reperfusion; IPC+postcon (n = 8), IPC and postcon algorithms were combined.

RESULTS: Collateral blood flow during ischemia was similar in all groups. Compared to control (24% ± 2%), infarct size was comparably reduced in IPC (13% ± 2%* [* denotes p less than 0.05 compared with control]), and postcon (10% ± 1%*), consistent with a reduction in plasma creative kinase activity in these groups; infarct size was not further reduced by IPC+postcon (12% ± 3%*). Tissue water content in ischemic myocardium was comparably reduced in IPC, postcon, and IPC+postcon compared to control. Superoxide anion generation detected by dihydroethidium staining in area at risk myocardium was comparably reduced in all intervention groups relative to control. Plasma malondialdehyde (µM), a lipid peroxidation byproduct of oxidant injury, was less at 1 hour of reperfusion in IPC (2.2 ± 0.2*), postcon (2.1 ± 0.2*), and IPC+postcon (2.5 ± 0.2*) relative to control (3.3 ± 0.2). Ventricular fibrillation occurred less often in all intervention groups.

CONCLUSIONS: No additive cardioprotective effects by IPC and postcon were observed in a canine model of regional ischemia and reperfusion. The potent attenuation of myocardial injury by postcon may suggest a clinically applicable strategy during some surgical revascularization procedures (ie, OPCAB).