Evaluation Of The Protective Effects Of Ischemic Postconditioning On Ischemia-reperfused Heart With Myocardial Contrast Echocardiography, Real-Time Three-dimensional Echocardiography, And Doppler Tissue Imaging

ObjectiveAlthough the prognosis of acute myocardial infarction (AMI) has significantly improved, it represents a major cause of death and heart failure in industrialized countries. Reperfusion therapy for AMI has been shown to reduce mortality , yet it may also induce myocardium ischemia - reperfusion injury ( MI-RI). It is important to reduce MIRI for improving curative effect of reperfusion therapy.Repeated brief episodes of ischemia - reperfusion after the prolonged ische-mic insult, and before reperfusion may induce protective effect on myocardium. The phenomenon was termed myocardial ischemic postconditioning (IPostC ). The ischemic postconditioning is feasible clinically, especially during percutaneous coronary intervention ( PCI). In this case, inflation and deflation of the an-gioplasty balloon after reopening of the coronary artery can mimic repetitive coronary artery clamping performed in animal model. It was hypothesized that ATP sensitive K⁺ channel ( K_ATP⁺) play an important role in the process, and Gliben-camide (Gli) is K_ATP⁺, blocker.Therefore, the objective of the present study was to evaluate the protective effects of IPostC on canine and human hearts with myocardial contrast echocar-diography ( MCE ) , real - time three - dimensional echocardiography ( RT — 3DE) , and Doppler tissue imaging (DTI).MethodsPart one:Three groups open - chest canines ( n = 21) endured 3 hours left anterior descending artery ( LAD) occlusion followed by 2 hours reperfusion;Con group (n =7) , no intervention;IPostC group (n =7) , 3 cycles of 10 seconds reperfusion - 10 seconds reocclusion were imposed immediately upon reperfusion;Gli group (n =7) , 10 min before LAD reperfusion, glibencamide was injected intravenously with a dosage of 0. 3 mg/kg, then the same as the IPostC group.MCE protocol: Intermittent harmonic imaging was performed in the para -sternal short - axis plain at mid - papillary muscle level with the HP 5500 Sonos system. Water bath was placed on heart as an acoustic interface. Mechanical index was set to 1. 6 at the beginning of the experiment, the gain, the depth, and focus were adjusted at the baseline, and the myocardium was almost black and only endocardial borders was visible. The adjustments were kept unchanged throughout the procedure. The baseline images were acquired. Self - made contrast media was injected intravenously as bolus infusion. End - diastolic images , triggered by ECG R wave were obtained at pulse intervals ranging of 7 9 cycles. And images of end diastolic phase at AD Time - Intensity mode were recorded with papillary muscle level at short axis plain. And MCE parameters of time - intensity curve were measured at before and after acetylcholine ( Ach) injection on each point for representing myocardial microvascular endothelium -dependent relaxation (EDR). All of the data were stored on magnetic optic disk for later retrieval.MCE data sampling and analysis: acoustic densitometry ( AD ) program was used for offline analysis. Myocardial video density time - intensity curves were analyzed for calculation of peak intensity (PI) , half time of descent (HT) , descending slope (DS) , and area under the curve (AUC). The EDR parameters of PIr and AUCr were calculated. Areas of contrast media loss during ischemia (indicating risk area, RA) and during reperfusion (indicating necrosis area, NA) were calculated also. The ratios of necrosis area to risk area (NA/ RA)were calculated for comparison with pathologic stain results.DTI and RT-3DE protocol: Before ischemia (baseline) , during ischemi-a, 30min, 60min, and 120min after reperfusion, the DTI parameters of systolic velocity Sa at anterior left ventricular wall were measured, and left ventricular e-jection fraction (EF) was measured using RT-3DE method. And the ejection fraction recovery rate was calculated with the formula ( EF at 120min after reperfusion/ baseline EF).Plasma lipid peroxidation product Malondialdehyde ( MDA) , Creatine ki-nase enzyme ( CK) , and Superoxide dismutase ( SOD) were measured in each group at baseline, during ischemia, and at 120rain after reperfusion.Pathologic stain for infarction evaluation: at the completion of the experiment , the heart was arrested by intravenous administration of saturated KCL and then was removed. Evans blue dye was injected into left and right coronary artery , with LAD re - occluded. Then the heart was cut into slices with 3 5mm thickness. The slices were immersed in a solution of 2% triphenyltetrazolium chloride (TTC) at 37X1 for 30min. The infarct myocardium (necrosis area, NA) was identified as the region of white color, while the risk area ( RA) was labeled as brick red. Both of the NA and RA were calculated and ratio of NA/ RA was calculated also.Part two:Twenty - three patients, submitted to coronary angioplasty for ongoing acute myocardial infarction, contributed to the study. Patients were randomly assigned to either a control (Con group, n = 12) or a ischemic postconditioning group (IPostC group, n = 11). Before reperfusion by stenting, control subjects underwent no further intervention, whereas postconditioning subjects was performed within 1 minutes of reflow by 3 episoded of 10 - seconds inflation and 10 - seconds deflation of the angioplasty balloon.DTI and RT -3DE protocol: at 3 ⁷days, and 3 months after angioplasty, the DTI parameters of systolic velocity Sa at anterior left ventricular wall were measured, and left ventricular global ejection fraction and regional ejection fraction (rEF) was measured using RT-3DE method.Plasma MDA, CK, and SOD were measured in each group before angio-plasty, 1 hour, and 72 hours after angioplasty. Infarct size was assessed by measuring total CK release over 72 hours.ResultsPart oneThe infarct size in the IPostC group was significantly smaller than that in the Con group, and the infarction area measured by MCE was well correlated with the result from pathological stain analysis. MCE analysis showed that myo-cardial perfusion at micro vascular level was better ameliorated in IPostC group, reflected by higher PI, DS, and AUC, and shorter HT in the group (p < 0.05). and the EDR in IPostC group was significant increased, reflected by higher PIr and AUCr. And the systolic velocity Sa at anterior left ventricular and EF were well preserved in IPostC group. Plasma CK and MDA were less, whereas SOD was more, in IPostC group. These protection effects by IPostC were partly blocked by the K^p blocker Glibencamide.Part TwoDeterminants of infarct size, including ischemia time, CK release, and collateral flow, were comparable between the 2 groups before angioplasty. Plasma CK release was significantly reduced in the IPostC group compared with the Con group, representing a 33% reduction in infarction size. Plasma MDA was less, whereas SOD was more, in IPostC group.The systolic velocity Sa at anterior left ventricular wall, EF, and rEF were well preserved in IPostC group.ConclusionsIschemic postconditioning at onset of reperfusion can reduce the infarct size, ameliorate micro vascular perfusion, protect myocardial microvascular en-dothelium - dependent relaxation, and preserve myocardium and left ventricular systolic function of canine and human hearts.Cardioprotective effects of postconditioning may be mediated, in part, byinhibiting oxidant generation and oxidant mediated injury.Cardioprotective effects of postconditioning may be achieved partly by activating KAVMyocardial contrast echocardiography can not only observe the risk and in-farct area dynamically, but also evaluate the myocardial perfusion at micro vascular level, indicating the MCE may be used as an effective technique in the research of myocardial ischemic and reperfusion.RT -3DE and DTI could quantitatively evaluate left ventricular and regional myocardial systolic function.