Ischemic preconditioning attenuates postischemic coronary artery endothelial dysfunction in a model of minimally invasive direct coronary artery bypass grafting

Endothelial Cell Apoptosis but Not Necrosis Is Inhibited by Ischemic Preconditioning

This study aimed to assess the influence of ischemic preconditioning (IP) on hypoxia/reoxygenation (HR)-induced endothelial cell (EC) death. Human umbilical vein endothelial cells (HUVECs) were subjected to 2 or 6 h hypoxia with subsequent reoxygenation. IP was induced by 20 min of hypoxia followed by 20 min of reoxygenation. Necrosis was assessed by the release of lactate dehydrogenase (LDH) and apoptosis by double staining with propidium iodide/annexin V (PI/AV), using TUNEL test, and Bcl-2 and Bax gene expression measured using RT-PCR. In PI/AV staining, after 24 h of reoxygenation, 30-33% of EC were necrotic and 16-21% were apoptotic. In comparison to HR cells, IP reduced membrane apoptosis after 24 h of reoxygenation by 50% but did not influence EC necrosis. Nuclear EC apoptosis affected about 15-17% of EC after 24 h of reoxygenation and was reduced with IP by 55-60%. IP was associated with a significantly higher Bcl-2/Bax ratio, at 8 h 2-4 times and at 24 h 2-3 times as compared to HR. Longer hypoxia was associated with lower values of Bcl-2/Bax ratio in EC subjected to HR or IP. IP delays, without reducing, the extent of HR-induced EC necrosis but significantly inhibits their multi-level evaluated apoptosis.

Myocardial ischaemia-reperfusion injury and cardioprotection in perspective

Despite the increasing use and success of interventional coronary reperfusion strategies, morbidity and mortality from acute myocardial infarction are still substantial. Myocardial infarct size is a major determinant of prognosis in these patients. Therefore, cardioprotective strategies aim to reduce infarct size. However, a perplexing gap exists between the many preclinical studies reporting infarct size reduction with mechanical and pharmacological interventions and the poor translation into better clinical outcomes in patients. This Review revisits the pathophysiology of myocardial ischaemia-reperfusion injury, including the role of autophagy and forms of cell death such as necrosis, apoptosis, necroptosis and pyroptosis. Other cellular compartments in addition to cardiomyocytes are addressed, notably the coronary microcirculation. Preclinical and clinical research developments in mechanical and pharmacological approaches to induce cardioprotection, and their signal transduction pathways, are discussed. Additive cardioprotective interventions are advocated. For clinical translation into treatments for patients with acute myocardial infarction, who typically are of advanced age, have comorbidities and are receiving several medications, not only infarct size reduction but also attenuation of coronary microvascular obstruction, as well as longer-term targets including infarct repair and reverse remodelling, must be considered to improve patient outcomes. Future clinical trials must focus on patients who really need adjunct cardioprotection, that is, those with severe haemodynamic alterations.

Cardiac donation after circulatory death

PURPOSE OF REVIEW

Increasing number of patients with end-stage heart failure and those with improved survivorship from selective utilization of implantable mechanical circulatory support devices have added further burden and complexity to the transplant waitlist and on the rate-limiting availability of donor hearts from the standard pathway of donation after brain death. Unlike this conventional route, the increasing clinical use of donation after circulatory death (DCD) donor hearts necessitates a closer understanding of the logistics involved in the DCD process as well as of the risks associated with the unique pathophysiological consequences in this setting.

RECENT FINDINGS

Notwithstanding a higher incidence of delayed graft function, the clinical utilization of DCD hearts for cardiac transplantation over the past five years has demonstrated this to be a well-tolerated and strategic alternative with excellent medium-term clinical outcomes.

SUMMARY

The uptake of DCD heart transplantation remains selective and currently confined to Australia, the United Kingdom, Belgium, and more recently the USA. A more significant adoption will only come about through: a concerted effort to resolve the ethical and clinical controversies; a better understanding of postconditioning strategies; continued resolve to reduce the obligatory period of warm ischemia; and from better extracorporeal platforms that permit functional viability assessment of the DCD donor heart.

The coronary circulation in acute myocardial ischaemia/reperfusion injury: a target for cardioprotection

The coronary circulation is both culprit and victim of acute myocardial infarction. The rupture of an epicardial atherosclerotic plaque with superimposed thrombosis causes coronary occlusion, and this occlusion must be removed to induce reperfusion. However, ischaemia and reperfusion cause damage not only in cardiomyocytes but also in the coronary circulation, including microembolization of debris and release of soluble factors from the culprit lesion, impairment of endothelial integrity with subsequently increased permeability and oedema formation, platelet activation and leucocyte adherence, erythrocyte stasis, a shift from vasodilation to vasoconstriction, and ultimately structural damage to the capillaries with eventual no-reflow, microvascular obstruction (MVO), and intramyocardial haemorrhage (IMH). Therefore, the coronary circulation is a valid target for cardioprotection, beyond protection of the cardiomyocyte. Virtually all of the above deleterious endpoints have been demonstrated to be favourably influenced by one or the other mechanical or pharmacological cardioprotective intervention. However, no-reflow is still a serious complication of reperfused myocardial infarction and carries, independently from infarct size, an unfavourable prognosis. MVO and IMH can be diagnosed by modern imaging technologies, but still await an effective therapy. The current review provides an overview of strategies to protect the coronary circulation from acute myocardial ischaemia/reperfusion injury. This article is part of a Cardiovascular Research Spotlight Issue entitled 'Cardioprotection Beyond the Cardiomyocyte', and emerged as part of the discussions of the European Union (EU)-CARDIOPROTECTION Cooperation in Science and Technology (COST) Action, CA16225.

The Coronary Circulation as a Target of Cardioprotection

The atherosclerotic coronary vasculature is not only the culprit but also a victim of myocardial ischemia/reperfusion injury. Manifestations of such injury are increased vascular permeability and edema, endothelial dysfunction and impaired vasomotion, microembolization of atherothrombotic debris, stasis with intravascular cell aggregates, and finally, in its most severe form, capillary destruction with hemorrhage. In animal experiments, local and remote ischemic pre- and postconditioning not only reduce infarct size but also these manifestations of coronary vascular injury, as do drugs which recruit signal transduction steps of conditioning. Clinically, no-reflow is frequently seen after interventional reperfusion, and it carries an adverse prognosis. The translation of cardioprotective interventions to clinical practice has been difficult to date. Only 4 drugs (brain natriuretic peptide, exenatide, metoprolol, and esmolol) stand unchallenged to date in reducing infarct size in patients with reperfused acute myocardial infarction; unfortunately, for these drugs, no information on their impact on the ischemic/reperfused coronary circulation is available.

Protective effect of maternal uteroplacental insufficiency on oxygen-induced retinopathy in offspring: removing bias of premature birth

To address the hypothesis that maternal uteroplacental insufficiency (UPI) increases severity of retinopathy of prematurity, we developed a composite rat model of UPI and oxygen-fluctuations and removed premature birth as a confounding factor. Timed-pregnant Sprague-Dawley dams underwent bilateral uterine artery ligation or anesthesia (control) at e19.5. Full-term pups developed in room air (RA) or an oxygen-induced retinopathy (OIR) model. Isolectin-stained retinal flat-mounts were analyzed for percent of areas of avascular/total retina (AVA) and of intravitreal neovascular/total retina (IVNV). Pup weights and serum and mRNA of liver and kidney VEGF, IGF-1, and erythropoietin (EPO) were determined. Multivariable mixed effects linear regressions and Pearson correlations were performed using STATA14. Postnatal growth restriction occurred in pups in UPI/RA, but not in UPI/OIR. Weight gain was similar between UPI/OIR and control/OIR pups. AVA was reduced and a trend toward reduced IVNV was seen in UPI/OIR compared to control/OIR. No difference in birth weights of UPI/OIR vs. control/OIR pups occurred. Serum and renal IGF-1 and EPO were significantly increased in UPI/OIR compared to control/OIR pups. In the absence of prematurity, UPI increased angiogenic factors in association with reduced OIR severity, suggesting that ischemia from UPI could yield protective angiogenic effects by offspring.

The role of myocardial ischaemic preconditioning during beating heart surgery: biological aspect and clinical outcome

Short periods of ischaemia consecutive to reperfusion periods before a sustained ischaemic condition, the so-called ischaemic preconditioning (IP), aim to protect myocardial cells against prolonged ischaemia. IP appears as a considerable endogenous cardioprotective mechanism decreasing the infarct size after total occlusion in either experimental models or humans. Angina periods before an acute coronary syndrome limit the myocardial infarction being protective for the myocardium. Our report aims to review the international bibliography of the IP during off-pump coronary artery bypass grafting.

Inflammatory response and cardioprotection during open-heart surgery: the importance of anaesthetics

Open-heart surgery triggers an inflammatory response that is largely the result of surgical trauma, cardiopulmonary bypass, and organ reperfusion injury (e.g. heart). The heart sustains injury triggered by ischaemia and reperfusion and also as a result of the effects of systemic inflammatory mediators. In addition, the heart itself is a source of inflammatory mediators and reactive oxygen species that are likely to contribute to the impairment of cardiac pump function. Formulating strategies to protect the heart during open heart surgery by attenuating reperfusion injury and systemic inflammatory response is essential to reduce morbidity. Although many anaesthetic drugs have cardioprotective actions, the diversity of the proposed mechanisms for protection (e.g. attenuating Ca(2+) overload, anti-inflammatory and antioxidant effects, pre- and post-conditioning-like protection) may have contributed to the slow adoption of anaesthetics as cardioprotective agents during open heart surgery. Clinical trials have suggested at least some cardioprotective effects of volatile anaesthetics. Whether these benefits are relevant in terms of morbidity and mortality is unclear and needs further investigation. This review describes the main mediators of myocardial injury during open heart surgery, explores available evidence of anaesthetics induced cardioprotection and addresses the efforts made to translate bench work into clinical practice.

Diazoxide preconditioning attenuates global cerebral ischemia-induced blood-brain barrier permeability

Brain edema formation due to blood-brain barrier (BBB) disruption is a major consequence of cerebral ischemia. Previously, we demonstrated that targeting mitochondrial ATP-sensitive potassium channels (mitoK(ATP)) protects neuronal tissues in vivo and in vitro, however, the effects of mitoK(ATP) openers on cerebral endothelial cells and on BBB functions have never been examined. We investigated the effects of mitoK(ATP) channel opener diazoxide on BBB functions during ischemia/reperfusion injury (I/R). Rats were treated with 6, 20 or 40 mg/kg diazoxide ip for 3 days then exposed to global cerebral ischemia for 30 min. BBB permeability was assessed by administering Evan's-blue (EB) and Na-fluorescein (NaF) at the beginning of the 30 min reperfusion. I/R increased BBB permeability for the large molecular weight EB (ng/mg) in the cortex (control: 146 +/- 12, n = 7; I/R: 1049 +/- 152, n = 11) which was significantly attenuated in diazoxide-treated rats (575 +/- 99, n = 9; 582 +/- 104, n = 8; 20 and 40 mg/kg doses). Diazoxide pretreatment also significantly inhibited the extravasation of the low molecular weight NaF. Edema formation in the cortex was also decreased after diazoxide pretreatment. In cultured cerebral endothelial cells, diazoxide depolarized the mitochondrial membrane, suggesting a direct diazoxide effect on the endothelial mitochondria. Our results demonstrate that preconditioning of cerebral endothelium with diazoxide protects the BBB against ischemic stress.

Vascular dysfunction in ischemia-reperfusion injury

Microvascular dysfunction mediates many of the local and systemic consequences of ischemic-reperfusion (I/R) injury, with a spectrum of changes specific to arterioles, capillaries, and venules. This review discusses the specific changes in the endothelium during I/R injury; describes the differential responses of the various levels of the vasculature including arterioles, capillaries, and venules; and explores mechanisms for remote organ injury. Vascular dysfunction is largely a consequence of changes in the endothelial cells themselves, affecting the integrity of barrier function, cytokine and adhesion molecule expression, and vascular tone. The bioavailability of nitric oxide, an important mediator of vasodilation, is profoundly decreased during the reperfusion period, resulting in impaired vasodilation of arterioles. Release of inflammatory mediators and increased expression of adhesion molecules initiate inflammatory and coagulation cascades that culminate in the occlusion of capillaries, known as the "no-reflow''" phenomenon. In postcapillary venules, the recruitment and transmigration of leukocytes further compromise the integrity of the endothelial barrier and increase the oxidative burden, resulting in leakage and tissue edema. I/R injury can have significant and untoward consequences beyond the affected tissue, with such conditions as systemic inflammatory response syndrome. This review highlights recent progress in understanding of the varied phenomena of vascular dysfunction in I/R injury and some promising advances in the understanding and application of ischemic preconditioning and other potential therapies.

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 (microM), 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).

Role of reactive oxygen species in ischemic preconditioning of subcellular organelles in the heart

Ischemic preconditioning (IPC) is an endogenous adaptive mechanism and is manifested by early and delayed phases of cardioprotection. Brief episodes of ischemia-reperfusion during IPC cause some subtle functional and structural alterations in sarcolemma, mitochondria, sarcoplasmic reticulum, myofibrils, glycocalyx, as well as nucleus, which render these subcellular organelles resistant to subsequent sustained ischemia-reperfusion insult. These changes occur in functional groups of various receptors, cation transporters, cation channels, and contractile and other proteins, and may explain the initial effects of IPC. On the other hand, induction of various transcriptional factors occurs to alter gene expression and structural changes in subcellular organelles and may be responsible for the delayed effects of IPC. Reactive oxygen species (ROS), which are formed during the IPC period, may cause these changes directly and indirectly and act as a trigger of IPC-induced cardioprotection. As ROS may be one of the several triggers proposed for IPC, this discussion is focused on the current knowledge of both ROS-dependent and ROS-independent mechanisms of IPC. Furthermore, some events, which are related to functional preservation of subcellular organelles, are described for a better understanding of the IPC phenomenon.

The protective effects of preconditioning on cerebral endothelial cells in vitro

Ischemic preconditioning (PC) can markedly reduce ensuing ischemic damage. Although most attention has focused on the neuronal effects of PC, the authors have recently shown that ischemic PC reduces ischemia-induced cerebrovascular damage. In vivo, it is difficult to ascertain whether this is a direct cerebrovascular effect of PC. This study, therefore, examined whether cerebral endothelial cells can be preconditioned in vitro in the absence of other cell types. Experiments were performed on an immortalized mouse brain endothelial cell line or primary cultures of mouse brain microvessel endothelial cells. Cells were exposed to oxygen glucose deprivation (OGD) of either short duration, as a PC stimulus, or a long duration (5 hours) with or without reoxygenation to induce endothelial damage. Endothelial injury was assessed by measuring lactate dehydrogenase release and the expression of intercellular adhesion molecule-1 at the protein and mRNA levels. Experiments indicated that 1 hour of OGD was the optimal PC stimuli and that a 1 or 3 day interval was the optimal time interval between the PC stimulus and the injurious event. Preconditioned cells had less lactate dehydrogenase release during OGD (+/- reoxygenation) and reduced intercellular adhesion molecule-1 expression after OGD with reoxygenation. This study shows that cerebral endothelial cells can be directly preconditioned. The importance of this phenomenon in the overall effects of PC on the brain remains to be elucidated. Understanding the protective mechanisms elicited by PC may give insight into how to prevent ischemia-induced vascular damage (e.g., hemorrhagic transformation).

Ischemic preconditioning does not improve myocardial preservation during off-pump multivessel coronary operation

BACKGROUND

The value of ischemic preconditioning during coronary operations has remained controversial. The aim of this study was to evaluate the effects of ischemic preconditioning on myocardial energy metabolism and tissue injury during off-pump multivessel coronary surgery.

METHODS

Eleven patients with preceding preconditioning were compared with 11 patients without it. The preconditioning group underwent a 5-minute period of ischemia followed by a 5-minute reperfusion period before coronary occlusion for each of the first two anastomoses.

RESULTS

The transmyocardial differences (coronary sinus - arterial) in inosine and the sum of adenine degradation products increased in both groups, but the differences in xanthine and hypoxanthine increased only in the preconditioning group. Myocardial lactate production increased to a maximum of 0.09 mmol/L with preconditioning and to a maximum of 0.17 mmol/L without it. Transmyocardial pH differences increased to 0.03 U in both groups. The maximum postoperative concentration of creatine kinase-MB mass was 14.8 microg/L with preconditioning and 6.3 microg/L without preconditioning, and that of troponin I 7.4 microg/L and 5.2 microg/L, respectively. There were no statistically significant differences between the groups, however.

CONCLUSIONS

Ischemic preconditioning of 5 minutes followed by reperfusion of 5 minutes during off-pump multivessel coronary artery surgery did not prevent myocardial metabolic derangement and tissue injury and thus cannot be routinely recommended.

Regional ischemic preconditioning enhances myocardial performance in off-pump coronary artery bypass grafting

OBJECTIVES

We intended to investigate whether ischemic preconditioning (IP) enhances myocardial performance in patients who undergo off-pump coronary artery bypass grafting (CABG).

DESIGN

A controlled, randomized, prospective study.

SETTING

A university hospital.

PATIENTS

Thirty-two patients with left anterior descending coronary artery (LAD) or two-vessel heart disease (including LAD) who were to undergo off-pump CABG were randomized into an IP group and a control group.

INTERVENTIONS

IP was induced by occluding the LAD twice for a 2-min period followed by 3-min LAD reperfusion before bypass grafting of the first coronary vessel.

MEASUREMENTS AND RESULTS

Registration included hemodynamic data from the peripheral artery and the pulmonary artery, and the measurement of cardiac troponin I (CTnI) and creatine kinase isoenzyme MB (CK-MB) values. IP resulted in a complete recovery of the mean stroke volume index (SVI) after the operation. In the control subjects, the mean SVI showed a significant reduction postoperatively (p = 0.039). On the first postoperative day, the increase in the mean heart rate (HR) was also significantly lower in the IP patients. The CTnI level was statistically significantly lower in the IP group (p = 0.043), and IP patients tended to have a smaller CK-MB release after surgery (not significant). The duration of mechanical ventilation, the length of stay in the ICU, and the use of inotropic medication did not increase after the IP protocol.

CONCLUSIONS

Two cycles of regional 2-min IP in the LAD, followed by 3 min of reperfusion, proved to be applicable and safe in patients undergoing off-pump myocardial revascularization, it tended to decrease the immediate myocardial enzyme release, it prohibited the postoperative increase in HR, and it enhanced the recovery of SVI.

Preserved myocardial blood flow and oxygen supply-demand balance with active coronary perfusion during simulated off-pump coronary artery bypass grafting

BACKGROUND

During off-pump coronary artery bypass surgery, concern remains about the possible myocardial injury associated with the transient occlusion and stabilization of the target vessels. Although intraluminal shunts are used to avoid ischemia during graft anastomosis, blood flow through the shunts can be affected by upstream pressure and inherent resistance, resulting in reduced blood flow during hypotension or severe proximal stenosis.

METHODS

In anesthetized dogs regional myocardial blood flow (microspheres), oxygen consumption, lactate extraction, and systolic shortening (sonomicrometry) were measured in the myocardium served by the left anterior descending coronary artery with native perfusion after interposition of a 2.25-mm shunt (> or = 90% of left anterior descending diameter) and during active coronary perfusion with a constant flow pump. Measurements were made under normotension and hypotension produced by partial caval occlusion to reduce arterial pressure by 50%.

RESULTS

Interposition of the shunt reduced blood flow by 67.8%, regional oxygen delivery by 59.8%, and systolic shortening by 45.6% relative to baseline, but lactate extraction (31.0% vs 31.2%) and oxygen supply-consumption (O(2)S/myocardial oxygen consumption ratio, 2.7 +/- 0.5 vs 2.6 +/- 0.5) were comparable with baseline values. Hypotension further decreased these physiologic values and was associated with local lactate production (-67.4% extraction) and decreased O(2)S/myocardial oxygen consumption ratio (1.3 +/- 0.1). Active coronary perfusion was associated with regional blood flow, oxygen delivery, systolic shortening, and lactate extraction comparable with baseline values. In contrast to the shunt, active perfusion maintained myocardial flow, oxygen delivery, and lactate extraction during hypotension and normalized the O(2)S/myocardial oxygen consumption ratio, although systolic shortening decreased as a result of ventricular unloading.

CONCLUSION

Intraluminal shunts may impede oxygen delivery to the target myocardium, which precipitates regional ischemia during transient hypotension. Active coronary perfusion provides adequate oxygen supply independent of systemic blood pressure.

Ischemic preconditioning prevents endothelial injury and systemic neutrophil activation during ischemia-reperfusion in humans in vivo

BACKGROUND

Endothelial dysfunction leading to neutrophil infiltration of tissues has been implicated in tissue injury caused by ischemia-reperfusion (IR). Tissue injury during IR can be reduced by prior ischemic preconditioning (IPC). In humans, it is unclear whether endothelial dysfunction occurs during IR or whether IPC offers protection against endothelial dysfunction and inflammatory cell activation. We studied the effects of experimental IR on endothelial and neutrophil function in the human forearm in vivo and examined the protection afforded by IPC.

METHOD AND RESULTS

The forearm was made ischemic for 20 minutes by inflating a blood pressure cuff to 200 mm Hg. We assessed endothelial function of conduit (radial artery flow-mediated dilation) and resistance vessels (blood flow responses to intra-arterial infusion of the endothelium-dependent dilator acetylcholine) in healthy volunteers before and after IR. IR reduced flow-mediated dilation of the radial artery at 15 minutes of reperfusion (7.7+/-1.5% to 3.5+/-0.9%) and the dilator response of resistance vessels to acetylcholine at 15, 30, and 60 minutes of reperfusion. IR did not reduce the dilator response of the radial artery to glyceryltrinitrate and only caused a small reduction of glyceryltrinitrate-induced dilation of resistance vessels at 60 minutes of reperfusion. IR caused an increase in neutrophil CD11b expression and platelet-neutrophil complexes in the circulating blood. IPC (three 5-minute episodes of ischemia) before IR prevented endothelial dysfunction and neutrophil activation.

CONCLUSIONS

A clinically relevant period of ischemia-reperfusion causes profound and sustained endothelial dysfunction and systemic neutrophil activation. IPC attenuates both of these effects in humans.

Myocardial protection for off-pump coronary artery bypass surgery

Myocardial protection during off-pump coronary artery bypass surgery (OPCAB) is a multifactorial problem. Careful, individualized choice of graft sequence and maintenance of stable systemic hemodynamics are of central importance. Recently refined techniques for atraumatic rotation of the heart and visualization of coronary anastomoses allow precise and controlled grafting of all coronary territories without cardiopulmonary bypass in the large majority of cases. Perfusion-assisted direct coronary artery bypass (PADCAB) techniques, in which coronary perfusion pressure is independent of systemic arterial pressure, can avoid or abort a downward hemodynamic spiral, which may occasionally occur during complex, multivessel OPCAB. PADCAB promotes collateral myocardial perfusion and avoids the cumulative global effect of sequential episodes of regional ischemia, improving myocardial protection during OPCAB.

Nonanticoagulant heparin inhibits NF-kappaB activation and attenuates myocardial reperfusion injury

Heparin reduces ischemia-reperfusion injury to myocardium. This effect has been attributed to complement inhibition, but heparin also has other activities that might diminish ischemia-reperfusion. To further probe these mechanisms, we compared heparin or an o-desulfated nonanticoagulant heparin with greatly reduced anticomplement activity. When given at the time of coronary artery reperfusion in a canine model of myocardial infarction, heparin or o-desulfated heparin equally reduced neutrophil adherence to ischemic-reperfused coronary artery endothelium, influx of neutrophils into ischemic-reperfused myocardium, myocardial necrosis, and release of creatine kinase into plasma. Heparin or o-desulfated heparin also prevented dysfunction of endothelial-dependent coronary relaxation following ischemic injury. In addition, heparin and o-desulfated heparin inhibited translocation of the transcription nuclear factor-kappaB (NF-kappaB) from the cytoplasm to the nucleus in human endothelial cells and decreased NF-kappaB DNA binding in human endothelium and ischemic-reperfused rat myocardium. Thus heparin and nonanticoagulant heparin decrease ischemia-reperfusion injury by disrupting multiple levels of the inflammatory cascade, including the novel observation that heparins inhibit activation of the proinflammatory transcription factor NF-kappaB.

Near-infrared monitoring of myocardial oxygenation during ischemic preconditioning

BACKGROUND

Ischemic preconditioning has been advocated as a method of cardioprotection for minimally invasive direct coronary artery bypass. This study was performed to estimate the cardioprotective effect of ischemic preconditioning before ischemia by examining the changes in myocardial tissue oxygenation and also to examine whether adenosine triphosphate-sensitive potassium channel opener enhances the cardioprotective effect of ischemic preconditioning.

METHODS

Myocardial ischemia was induced in three groups of 6 dogs by temporary occlusion of the left anterior descending coronary artery. Group 1 dogs received a 30-minute coronary occlusion and subsequent 3-hour reperfusion. Groups 2 and 3 dogs underwent three periods of 5-minute coronary occlusion and 5-minute reperfusion and then received 30-minute sustained ischemia and 3-hour reperfusion. In group 3, nicorandil was administered during the procedure. Myocardial oxygenation was measured using three-wavelength near-infrared spectroscopy. Myocardial blood flow was measured by the colored microsphere method.

RESULTS

During ischemic preconditioning the myocardial tissue oxygen saturation decreased rapidly at coronary occlusion and increased at reperfusion. It was increased stepwise at the second and third coronary occlusion. Myocardial oxygen saturation during 30-minute sustained ischemia was significantly higher in groups 2 and 3 than in group 1 (p < 0.05). The myocardial tissue hemoglobin concentration showed similar changes to myocardial oxygen saturation. During 30-minute sustained ischemia, it was significantly higher in group 2 than in group 1 (p < 0.001), and it was significantly higher in group 3 than in groups 1 and 2 (p < 0.05). Regional myocardial blood flow showed no difference after 30 minutes of sustained ischemia among the three groups. Troponin-T levels were significantly lower in groups 2 and 3 than in group 1 (p < 0.01).

CONCLUSIONS

Ischemic preconditioning had beneficial effects on myocardial oxygenation during sustained ischemia, and the protected state of the myocardium could be monitored with the use of near-infrared spectroscopy. Ischemic preconditioning coupled with nicorandil administration might provide protection for minimally invasive direct coronary bypass.

Ischaemic preconditioning of the vasculature: an overlooked phenomenon for protecting the heart?

Exposing the heart to brief episodes of ischaemia protects the myocardium and vascular endothelial cells against functional damage and cell death caused by subsequent prolonged ischaemia. Elucidation of the mechanisms that are involved in this phenomenon known as 'ischaemic preconditioning' and identification of drugs that mimic the protective response have the potential to improve the prognosis of myocardial infarction and other cardiac syndromes dramatically. This article focuses on recent findings on the effects of ischaemic preconditioning of the coronary vasculature, which highlight the endothelium as an important target for a successful therapeutic approach to myocardial ischaemia-reperfusion injury.