The Basic And Clinical Study Of Myocardial Ischemic Postconditioning

Objective:The research is aimed at evaluating cardioprotective effects of ischemic postconditioning and further exploring its mechanisms by establishing a model of ischemia and reperfusion in rabbit heart in vivo. This basic study can provide theoretical basis for the clinical application of postconditioning.Methods:A model of ischemia/reperfusion(I/R)was established by left anterior descending artery( LAD) occlusion for 30 min using the method of two sutures and two knots followed by reperfusion for 180 min.Sixty New Zealand rabbits are randomly allocated to five groups(n=12):(1)control group: LAD occlusion and reperfusion only, with no other intervention; (2)ischemic postconditioning group(IPostC group): Four episodes of 30s reperfusion and 30s oclusion after 30 min ischemic and before 180 min reperfusion; (3) IpostC+ERK1/2 inhibitor PD98059 group(IPostC+PD98059 group) and (4) IpostC+PI3K inhibitor LY294002 group (IPostC+LY294002 group): ERK1/2 inhibitor PD98059 and PI3K inhibitor LY294002 were given as intravenous boluses just 10 min before the onset of reperfusion which was the only difference between these two groups and IPostC group. (5)shame operation group( shame group): There was a thread through muscles around LAD which was not ligated. Electrocardiogram (ECG) were performed during the experiment. Blood was drawn from femoral vein to evaluate cardiac troponin I(cTnI) values with enzyme-linked immunosorbent assay (ELISA) before operation and 60 min after reperfusion in ischemia-reperfusion groups. In shame group blood was drawn through the same way before threading and 60 min after threading. At the end of the experiment cardiac muscle tissues of six rabbits in each group were determined myocardial infarct size by staining with triphenyltetrazolium chloride dye . Morphologic examination of cardiac muscle tissues of another six rabbits in each group was done using optical microscope and transmission electron microscope. At the same time western blot analysed several protein expressions such as Bad,Akt,P-Akt,ERK1/2 and P-ERK1/2 of cardiac muscle tissues.Results:1. There were no significant differences in sex, weight and heart rate among five groups at baseline. During coronary occlusion, there were trends for an increase in heart rate. But this change were not significant compared with the baseline value( P>0.05).2. There were ST-segment elevations after LAD occlusion and ST-segment resolutions 120 min after reperfusion in ischemia-reperfusion groups. There were 8 rabbits in control group and 6 rabbits in IPostC+PD98059 group having ST-segment resolution≥50%. Ten rabbits had ST-segment resolution≥50% in IPostC group and IPostC+LY294002 group. But there were no significant difference among four groups (P>0.05).3. The cardiac arrhythmia scores were significantly decreased in IPostC group and IPostC+LY294002 group compared with control group (P<0.05). There was no difference between control group and IPostC+PD98059 group (P>0.05).4. There were no significant differences in cTnI values among four groups before LAD occlusion(P>0.05). Sixty minutes after reperfusion cTnI values of control group , IPostC group, IPostC+PD98059 group and IPostC+LY294002 group were 6.63±2.32, 3.04±1.10, 7.12±2.30 and 3.52±1.67ng/ml respectively. cTnI values of IPostC group and IPostC+LY294002 group were significantly lower than that of control group (P<0.05). But there was no difference in cTnI value between control group and IPostC+PD98059 group (P>0.05). 5. Morphologic examination indicated that there were milder injuries of the cardiomyocyte of rabbits in IPostC group and IPostC+LY294002 group compared with IPostC group and IPostC+ PD98059 group.6. Mycardial infarct sizes of control group , IPostC group, IPostC+PD98059 group and IPostC+LY294002 group were 23.63±12.08%, 10.96±2.07%, 25.16±9.3% and 12.65±2.0% respectively. Compare to control group infarct sizes of IPostC group and IPostC+LY294002 group were significantly redued (P<0.05). But there was no difference between control group and IPostC+PD98059 group (P>0.05).7. IPostC group and IPostC+LY294002 group were associated with a significant decrease in the expression of Bad and a significant increase in the expression of P-ERK1/2 compared with control group (P<0.05). But there was no difference between control group and IPostC+LY294002 group (P>0.05). There was no difference in the expression of P-Akt among five groups.Conclusions:1. The method of two sutures and two knots can conveniently and successfully establish a model of ischemia and reperfusion in rabbit heart in vivo.2. Ischemic postconditioning at onset of reperfusion can obviously reduce myocardial reperfusion injury.3. ERK1/2 rather than PI3-kinase/Akt involved in the protective effect of ischemic postconditioning. Objective:It had been proved in animal models that ischemic postconditioning(IPostC) was a mechanical strategy to attenuate reperfusion injury. But there are not many clinical researches on the application of IPostC in percutaneous coronary intervention (PCI) . This study researched its value in emergent PCI.Methods:Forty-three patients diagnosed as acute myocardial infarction(AMI) were randomly assigned to two groups: the control group (18 cases) receiving conventional PCI and the IPostC group (25 cases) receiving IPostC in PCI. Blood sampling for creatine kinase isoenzyme MB (CKMB) were performed at 0, 8, 16, 24, 32, 40, 48 and 72 hours after PCI. Venous blood samples for high sensitive C-reactive protein (hsCRP) were obtained on admission and 24 hours after PCI. Electrocardiogram (ECG) was recorded at presentation and 2 hours after PCI. A 24h Holter monitoring was performed after PCI. The presence of arrhythmias was then analyzed. All patients received Doppler ultrasound examination and rest 99mTc-sestamibi (99mTc-MIBI ) myocardial perfusion single-photon emission computed tomography (SPECT) seven days and six months after PCI.Results:1. There were no significant differences between two groups with regard to the baseline clinical , angiographic and procedural characteristics(P>0.05).2. Patients in the control group presented with higher peak CKMB as compared with patients in the IPostC group (374.9±146.8 vs 280.7±120.0U/L, P=0.026). So was the area under the curve (AUC) of CKMB (8643±3779 vs 6125±2136, P=0.017).3. On admission the levels of hsCRP were similar in both groups(5.0±2.8 vs 4.8±2.2 mg/L, P=0.156). But IPostC group was associated with a lower level of hsCRP in comparison with the control group (6.1±4.8 vs 9.6±5.0 mg/L, P=0.025). 4. In the IPostC group more patients had complete ST-segment resolutions than patients in the control group(88% vs 55.6%, P=0.04).5. Incidences of arrhythmias during 24 hours of the IPostC group were less than that of the control group(P<0.05)。6. Left ventricle ejection fraction (LVEF) of patients in the IPostC group which were quantified by echocardiography seven days and six months after PCI were both better than that in the control group (55.04±11.23% vs 47.81±7.78%, P=0.025; 54.70±4.62% vs 49.27±5.57%, P=0.024). WMSI of patients having undergone IPostC quantified by echocardiography was less than that of patients having received conventional PCI not only seven days but also six months after PCI(1.27±0.22 vs 1.44±0.30, P=0.039; 1.15±0.12 vs 1.33±0.18, P=0.01).7. Ischemic size, infarct size and the ratio of infart and ischemic size of patients in the IPostC group that was measured by SPECT seven days after PCI were 27±15%,14±11% and 46±29% respectively. Six months after PCI these three values were 23±11%,10±8% and 38±29% respectively. These three values of patients in control group were 37±14%,25±11% and 67±20% respectively seven days after PCI. Six months after PCI these three values were 34±9%,16±7% and 45±17% respectively. Comparing with the control group IPostC greatly reduced ischemic size, infarct size and the ratio of infart and ischemic size seven days after PCI (P<0.05). But six months after PCI there were significant difference in ischemic size between control and IPostC group only(P<0.05).Conclusions:This study indicated that postconditioning the human heart in emergent PCI was a modification of conventioal PCI. It is a relatively novel , effective and safe method of cardioprotection to improve myocardial perfusion , attenuate inflammation and decrease myocardial necrosis. Maybe the effect of postconditioning has long-term benefit.