The Effect Of Remote Ischemic Precondition Induced By Limb On Vessel And Myocardial Ischemia-reperfusion Injury And The Assessment Of Myocardial Ischemia-reperfusion Injury

Reperfusion therapy, including primary percutaneous coronary intervention(PPCI) and thrombolytic therapy, effectively open the infarct-related coronary artery to reduce the infarct size and the death rate as well as improve the prognosis in patients with ST-elevation myocardial infarction(STEMI), which has become the pivotal treatment for STEMI. However, the process of myocardial reperfusion itself induces ischemia-reperfusion(IR) injury, which can attenuate the full benefits of the reperfusion therapy. Prolonged myocardial ischemia gives rise to endothelium swelling, cardiocytes swelling and interstitial edema, which cause microvascular compression. A massive infiltration of coronary microcirculation by neutrophils and platelets occurs at the time of reperfusion to result in activating endothelial cell, neutrophils, and platelets. Subsequently they release oxygen free radicals, proteolytic enzymes, and proinflammatory mediators, which make the synthesis of nitric oxide decrease and the production of superoxide increase. This leads to an exacerbation of the inflammatory state, an injury to myocytes, and a disturbance of coronary microcirculation. Meanwhile, IR injury causes intracellular Ca2+ overloading, opening of the mitochondrial permeability transition pore(m PTP), and enhancing cardiocytes swelling, which damage myocytes. Moreover, the extracellular osmolality is rapidly normalized by reperfusion, contributing to subsequent rupture of the cell membrane. In addition, IR injury causes a decease in flow-mediated dilation(FMD), which indicate that vascular endothelial function is damaged by IR injury. In the end, IR injury damages endothelial function, exacerbates myocardial reperfusion, and extends the final infarct size in STEMI. Ischemic precondition(IPC), being brief periods of ischemia preceding long-lasting ischemia, reduces the susceptibility of myocardium and vascular endothelium for IR injury, and it also does infarct size in STEMI. At present, IPC always is exploited in experimental animal models because it is the logistical difficulties to apply IPC in vital organs or spontaneous cardiovascular events in high-risk patients(such as STEMI). Remote ischemic precondition(RIPC), induced by several episodes of brief ischemia and reperfusion at a distance, can avoid or relieve IR injury to protect vascular endothelial function and reduce infarct size in STEMI. Whereas, at present, the study about the protection of RIPC for vascular endotheial function manily focused on brachial artery, and it rarely did on radial artery. Foreign scholars demonstrated that RIPC induced by limb before hospital admission increased myocardial salvage assessed by Single Photon Emission Computed Tomography(SPECT) in patients with STEMI. Nonetheless, SPECT doesn’t exactly quantify myocardial IR injury and infarct size for patients with STEMI. Cardiovascular magnetic resonance imaging(CMR) accurately assesses IR injury, microvascular obstruction(MO) and infarct size in STEMI. Nevertheless, up to date, there is no a study to evaluate the effect of RIPC on IR injury and infarct size using the early MO of CMR in patients with STEMI. Although CMR is an accurate imaging technique to be used to identify and quantify IR injury, but there is no biomarker to assess the extent of IR injury at present. IR injury induces long-lasting permeability transition pore opening and mitochondrial membrane rupturing so as to gives rise to promoting additional release of cytochrome c into the blood circulation. Cytochrome c is detectable in the circulating blood during the early stages of STEMI. Moreover, the levels of serum cytochrome c were negatively correlated with myocardial reperfusion. So, cytochrome c may become a biomarker that is easily detectable in serum and related to myocardial IR injury.In sum, the present study include: 1) a role of RIPC induced by limb in protecting the endothelial function of radial artery against IR injury. 2) an effect of RIPC induced by limb on myocardial IR injury in patients with STEMI. 3) a role of serum cytochrome c in evaluating myocardial IR injury in patients with STEMI.Part I The effect of remote ischemic precondition induced by limb on ischemia-reperfusion injury for radial arteryObjectives: The aim of this study was to discuss that the effect of RIPC induced by limb on radial artery against IR injury.Methods: Twenty healthy nonsmoking volunteers(14 men, 6 women, mean age: 32.7±8.3 years old) were enrolled from January 2012 to December 2012. They were divided into baseline group, RIPC group, and RIPC24 h group according to whether undergoing RIPC. IR injury was implemented immediately after RIPC in RIPC group, while it was done at 24 hours after RIPC in RIPC24 h group. IR injury was induced by inflating a blood pressure cuff placed around the upper arm to a pressure of 200 mm Hg for 20 minutes in all three groups. RIPC was performed by three cycles that a blood pressure cuff placed around the upper part of the contralateral arm was inflated to 200 mm Hg for 5 minutes(ischemia) and then deflated for 5 minutes. Baseline blood flow, reactive hyperemia, and FMD were measured before and after IR injury in three groups.Results: There were no significant difference in radial artery diameter, baseline blood flow, and reactive hyperemia before and after IR injury in three groups. The change of radial diameter before IR injury had more significant difference than after IR injury in baseline group(P < 0.0001). Compared with baseline group, there were distinct difference in RIPC24 h group(P<0.0001) and RIPC group(P < 0.01) for the change of radial diameter after IR injury.IR injury significantly blunted FMD(pre-IR: 6.8±1.3% vs. post-IR: 4.7±2.1%, P<0.0001). RIPC protected endothelial function immediately(FMD pre-IR: 7.4±1.7% vs. post-IR: 6.7±1.9%, P>0.05) and at 24h(FMD pre-IR: 7.3±1.6% vs post-IR: 6.8±1.7%, P>0.05).Conclusions:1 IR injury damages endothelial function of radial artery.2 RIPC induced by limb protects endothelial function of radial artery against IR Injury in Human.Part II The effect of remote schemic preconditioning induced by limb before primary percutaneous coronary intervention on myocardial ischemia-reperfusion injury in patients with ST-elevation myocardial infarctionObjectives: The purpose of this study was to evaluate the influence of RIPC induced by limb before PPCI on myocardial IR injury in patients with STEMI.Methods: From January, 2012 to March, 2013, one hundred and twenty consecutive patients with STEMI were randomly received PPCI without RIPC(PPCI group, n=60) versus with RIPC(R-PPCI group, n=60)(intermittent arm ischaemia through four cycles of 5-min inflation and 5-min deflation of a blood-pressure cuff). Peripheral venous blood in all patients was drawn to measure the plasma creatine kinase-MB isoenzyme(CK-MB) at hospital presentation and once every 6 h until the peak plasma CK-MB appeared. Myocardial blush grade(MBG) were also assessed after PPCI in all patients. The CMR was performed in patients with anterior myocardial infarction to assess MO, left ventricular ejection fraction(LVEF), and infarct size. The primary endpoints were the occurrence of MO. Follow-up was conducted for 6 months to assess the clinical end point that was the occurrence of major adverse cardiovascular events(MACE): cardiac death, reinfarction, or new congestive heart failure.Results: There were no significant differences in baseline characteristics: age, male sex, current smoking, hypertension, Hypercholesterolemia, diabetes mellitus, renal failure, family history, and prior myocardial infarction between the two groups. Patients in R-PPCI group had a lower CK-MB peak level(P=0.043), a higher occurrence of MBG(2-3)(P=0.032). CMR demonstrated that there were a significantly better cardiac function(LVEF, 49.7%±6.0% vs.45.5%±6.3%, P=0.043), a significantly lower occurrence of early MO(31.6% vs.72.2%, P=0.013), a smaller extent of early MO(MO% left ventricle, 0.45(0-0.9) vs. 1.17(0.45-1.8), P=0.025), and a smaller infart size(% left ventricle, 14.0±4.3 vs. 17.7±5.5, P=0.032) in R+PPCI group compared to PPCI group. The incidence of cardiac death(PPCI group vs R-PPCI group, 5.0% vs. 0%, P=0.081) and MACE(PPCI group vs R-PPCI group, 11.7% vs. 3.3%, P=0.084) had no difference between two groups.Conclusions:1 It is safe and feasible for remote ischemic preconditioning induced by limb to be applied in patients with STEMI.2 Remote ischemic preconditioning induced by limb before PPCI alleviates the intensity of microvascular obstruction, ischemia-reperfusion injury, and improves myocardial reperfusion in patients with STEMI.3 Remote ischemic preconditioning induced by limb before PPCI reduces infarct size and improves cardiac function in patients with STEMI.Part III The role of serum cytochrome c level in assessing myocardial ischemia-reperfusion injuryObjectives: The aim of our study was to investigate the relationship between systemic cytochrome c levels and myocardial microvascular obstruction(MO) so as to evalutate the relationship between systemic cytochrome c and myocardial IR injury in patients with STEMI after PPCI.Methods: One hundred and sixty consecutive patients with STEMI undergoing PPCI were randomly chosen during June, 2010 – May, 2011. Peripheral venous blood was drawn to measure the plasma creatine kinase-MB isoenzyme(CK-MB) and serum cytochrome c levels at hospital presentation and once every 6 h until their peak plasma were identified. Patients were divided into a less than mean peak level of cytochrome c group(CC<mean, n=87) and an at least mean peak level of cytochrome c group(CC3mean, n=73) defined by the mean cytochrome c peak level after PPCI. Myocardial reperfusion was assessed by myocardial blush grade(MBG), and electrocardiographic ST-resolution(STR) after PPCI. CMR was performed in all patients to evaluate myocardial MO, LVEF, and myocardial infarct size. The primary end points were MO and the occurrence of MBG. Follow-up was conducted for 1 year to assess the clinical end point of major adverse cardiovascular events(MACE): cardiac death, reinfarction, or new congestive heart failure.Results: On admission, cytochrome c was detectable in the blood of 92 patients and was not detectable in 68 patients. TIMI flow grade in patients with no detectable cytochrome c was less than in patients with detectable cytochrome c(P=0.001). The peak CK-MB level in the CC3mean group was significantly higher than that in CC<mean group(P=0.044). There were no significant differences in other baseline characteristic including age, current smoking, male sex, hypertension, hypercholesterolemia, diabetes mellitus, prior myocardial infarction, and anterior myocardial infarction, symptom onset to reperfusion, number of diseased vessels, creatinine clearance, and use of thrombus aspiration device between two groups(P>0.05).Patients in CC<mean group had a higher incidence of final MBG 2–3 than patients in CC3mean group(P=0.017). Patients in CC3mean group had a lower LVEF(P=0.029), a significantly higher occurrence of early MO(P=0.008), and a significantly larger extent of early MO(%LV, P=0.020). The cytochrome c peak level was elevated in patients with early MO(1.60±0.44 vs 1.44±0.42 ng/ml, P=0.025), a final MBG(0–1)(1.73±0.44 vs 1.48±0.43 ng/ml, P=0.002), and STR(<30%)(1.81±0.48 ng/ml vs 1.50±0.42 ng/ml, P=0.003) after PPCI. The cardiac death had obviously higher mean cytochrome c peak values than surviving patients(2.05±0.34 ng/ml vs. 1.52±0.43 ng/ml, P=0.003). Patients in CC3mean group had a higher incidence of cardiac death(8.2% vs. 1.1%,log rank, P=0.029) than patients in CC<mean group. However, there was no difference in MACE between two groups at 1 year.Conclusions:1 The level of the serum cytochrome c is elevated and has significant relation with myocardial microvascular obstruction and MBG in patients with STEMI, so assessing the severity of myocardial ischemic injury and myocardial reperfusion.2 The elevated level of serum cytochrome c indicates an increase of mortality in patients with STEMI.