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Deprivation of a constant and regulated supply of oxygen to cells initiates a progressive series of detrimental events often referred to as the ischemic cascade. This process is unavoidable when a tissue or organ is severed from its blood supply after circulatory arrest and/or excision for transplantation. The cascade of injurious pathways is initiated within minutes of the cessation of oxygen supply. Avoidance or minimization of the intricate interrelated pathways calls for strategic intervention that historically has been centered upon the application of hypothermia in the field of transplantation. In other fields, such as traumatic brain injury and stroke, neuroprotection has been centered on chemical/drug suppression of detrimental pathways in an attempt to avert the cascade of processes that ultimately result in cell death by necrosis, apoptosis, or a combination of these mechanisms. Such strategies are focused on short-term events and transient ischemic attacks. However, in the context of the long-term preservation of tissues and organ banking for transplantation, the application of hypothermia has proved to be the bedrock strategy providing effective methods of preservation and storage to meet the current practices of organ transplantation. This approach is not without severe limitations since hypothermia is a double-edged sword. Hypothermia is globally protective due to its inherent suppression of chemical pathways on the basis of thermodynamics and Arrhenius kinetics. In this way, the demand for oxygen is markedly reduced due to the suppression of metabolic processes and detrimental pathways are also slowed by reduction of temperature. However, cooling per se causes undesirable responses in the cell such that as interventionalists (clinicians and researchers) we have learned to strike a balance to counteract the detrimental effects of cooling in order to harness the protective properties of hypothermia during ischemia and hypoxia. The name of the game is to understand how a cell responds to cold in relation to the ischemic cascade and translate this into how we can control the environment of the cell directly, and the internal environment indirectly, in order to optimize preservation and protection. This is the principle upon which organ preservation solutions have been designed and developed and formed the basis of current methods that have existed for several decades. Future developments are unlikely to come from further minor modifications to the present-day base formulations. Nevertheless, these tried-and-tested solutions provide the necessary baseline for including additional cytoprotective agents aimed at targeting specific pathways in the ischemia/reperfusion cascade. Such additives will include pharmacologics, biochemicals, oxygen-carriers and cryoprotective agents added to the baseline preservation solutions to enhance cellular preservation-protection-resuscitation. Delivery of these agents to the cells comprising complex tissues and organs will demand new technologies with a wide range of potential candidates on the horizon.

Although the management of stroke has improved remarkably over the last decade due mainly to the advent of thrombolysis, most neuroprotective agents, although successful in animal studies, have failed in humans. Our increasing knowledge concerning the ischemic cascade is leading to a considerable development of pharmacological tools suggesting that each step of this cascade might be a target for cytoprotection. Glutamate has long been recognized to play key roles in the pathophysiology of ischemia. However, although some trials are still ongoing, the results from several completed trials with drugs interfering with the glutamatergic pathway have been disappointing. Regarding the inhibition of glutamate release as a possible target for cytoprotection, it might be afforded either by decreasing glutamate efflux or by increasing glutamate uptake. In this context, it has been shown that glutamate transport is the primary and only mechanism for maintaining extracellular glutamate concentrations below excitotoxic levels. This transport is executed by the five high-affinity, sodium-dependent plasma membrane glutamate transporters. Among them, the transporter EAAT2 is responsible for up to 90% of all glutamate transport. We will discuss the effect of different neuroprotective tools (membrane stabilizers or endogenous neuroprotection) affecting glutamate efflux and/or expression of EAAT2. We will also describe the finding of a novel polymorphism in the EAAT2 promoter region which could be responsible for differences in both gene function and regulation under pathological conditions such as cerebral ischemia, and which might well account for the failure of glutamate antagonists in the clinical practice. These results may possess important therapeutic implications in the management of patients at risk of ischemic events, since it has been demonstrated that those patients with progressing stroke have higher plasma concentrations of glutamate which remain elevated up to 24 h when compared to the levels in patients without neurological deterioration.

Ischemic stroke is a common clinical emergency, with thrombolysis and neuroprotection as its cardinal treatment, and nowadays the latter is more and more stressed by stroke researchers. On the basis of pathophysiology and ischemic cascade of ischemic stroke, we now try to analyze the conceivable mechanism of intervention by tradition Chinese medicine (TCM) and hopefully provide experience for experimental and clinical research in the future.

Coronary artery disease (CAD) with its clinical appearance of stable or unstable angina and acute myocardial infarction is the leading cause of death in developed countries. In view of increasing costs and the rising number of CAD patients, there has been a major interest in reliable non-invasive imaging techniques to identify CAD in an early (i.e. asymptomatic) stage. Since myocardial perfusion deficits appear very early in the “ischemic cascade”, a major breakthrough would be the non-invasive quantification of myocardial perfusion before functional impairment might be detected. Therefore, there is growing interest in other, target-organ-specific parameters, such as relative and absolute myocardial perfusion imaging. Magnetic resonance (MR) imaging has been proven to offer attractive concepts in this respect. However, some important difficulties have not been resolved so far, which still causes uncertainty and prevents the broad application of MR perfusion imaging in a clinical setting. This review explores recent technical developments in MR hardware, software and contrast agents, as well as their impact on the current and future clinical status of MR imaging of first-pass myocardial perfusion imaging.

The potential relevance of neuroprotective and recovery enhancing therapies after acute ischemic stroke to vascular dementia (VaD) must be considered from several perspectives. The goal of acute neuroprotective therapy for ischemic stroke is to impede one or more aspects of the ischemic cascade of cell injury induced by focal brain ischemia (1). It is presumed that inhibiting the ischemic cascade will reduce the extent of infarction and improve ultimate functional outcome. Recovery-enhancing therapies are designed to enhance brain recovery after stroke and to improve functional outcome but not necessarily to affect infarct size (2). It can be assumed that both neuroprotection and recovery enhancement might lessen the incidence of VaD development after stroke by several mechanisms. This chapter overviews current concepts of ischemic injury related to acute focal brain ischemia and the current status of efforts to develop effective neuroprotective and recovery-enhancing therapies for acute ischemic stroke.

Retinal ischemia is a common cause of visual impairment and blindness. At the cellular level, ischemic retinal injury consists of a self-reinforcing destructive cascade involving neuronal depolarisation, calcium influx and oxidative stress initiated by energy failure and increased glutamatergic stimulation. There is a cell-specific sensitivity to ischemic injury which may reflect variability in the balance of excitatory and inhibitory neurotransmitter receptors on a given cell. A number of animal models and analytical techniques have been used to study retinal ischemia, and an increasing number of treatments have been shown to interrupt the "ischemic cascade" and attenuate the detrimental effects of retinal ischemia. Thus far, however, success in the laboratory has not been translated to the clinic. Difficulties with the route of administration, dosage, and adverse effects may render certain experimental treatments clinically unusable. Furthermore, neuroprotection-based treatment strategies for stroke have so far been disappointing. However, compared to the brain, the retina exhibits a remarkable natural resistance to ischemic injury, which may reflect its peculiar metabolism and unique environment. Given the increasing understanding of the events involved in ischemic neuronal injury it is hoped that clinically effective treatments for retinal ischemia will soon be available.

A wide variety of imaging modalities is available for the diagnosis of ischemic coronary artery disease (CAD). Myocardial hypo-perfusion is one of the first steps in the ischemic cascade and can be detected before clinical symptoms, ECG alterations or wall motion abnormalities occur. Currently, nuclear medicine techniques (scintigraphy) such as single-photon emission computed tomography using Thalium-201 or TC-99 m sestamibi are most frequently used for the imaging of myocardial perfusion. Positron emission tomography (PET) is the reference standard for myocardial perfusion imaging. These techniques attain a sensitivity and specificity for the detection of myocardial ischemia of, respectively, 83–95 and 53–95%. However, PET is not widely available, which makes it relatively inaccessible. Other disadvantages of myocardial perfusion imaging scintigraphy are: high costs, long-time commitment, radiation exposure, specificity depending on quality control of laboratory and trained readers and low specificity in presence of left bundle branch block. As a result of the fast hardware and software development magnetic resonance imaging (MRI) has become a promising new technique for perfusion imaging. This paper will give an introduction to myocardial perfusion MRI for the detection of ischemic heart disease followed by an overview of the post-processing procedures.

While the relationship between coronary blood flow and myocardial function is complex and multifaceted, it can be summarized in one simplistic statement: reduction in coronary flow results in reduced myocardial perfusion leading to an ischemic cascade, the end-point of which is compromised ventricular function. Different methods used for the diagnosis of coronary heart disease are based on detection of these changes, either at rest or under stress. However, most of them focus on a single parameter, such as wall motion or myocardial perfusion, rather than providing comprehensive diagnosis based on the combined assessment of multiple variables. Thus, coronary angiography focuses on coronary anatomy to estimate coronary flow, nuclear imaging provides information on myocardial perfusion, and the echocardiographic diagnosis of ischemic heart disease is mainly based on the assessment of regional wall motion. It has been recognized that a technique capable of evaluating more than one variable in a single test would likely provide a more accurate and reliable diagnostic tool [1–2], and undoubtedly have an impact on the prognosis and risk stratification of patients with suspected ischemic heart disease. In addition, such a technique would be advantageous for the diagnosis of conditions characterized by a mismatch between blood supply and myocardial function, such as hibernating or stunned myocardium [3–5].

A target for treatment of acute ischemic stroke is the penumbra, a territory of critically reduced blood flow between the core zone of an evolving infarction and the still sufficiently perfused brain. Unless there is early reperfusion of the ischemic area, neurons in the penumbra are destined to die in the ensuing hours to days, due to a cascade of biochemical events, the so-called ischemic cascade [1, 2]. Key steps in this cascade are uncontrolled depolarizations of neurons, build-up of extracellular glutamate, intracellular calcium overload, formation of nitric oxide and free radicals, and inflammation. Some forms of cell death in the ischemic penumbra also involve apoptosis [1, 2]. Studies in patients using positron emission tomography, combined perfusion and diffusion magnetic resonance imaging (MRI), and MR spectroscopy indicate that the penumbra in humans may remain viable for several (up to 48) hours after stroke onset [3-6].

Background and Purpose— The absence of a widely available and sensitive diagnostic test for acute cerebral ischemia remains a significant limitation in the diagnosis and management of stroke. The objective of this study was to examine the feasibility of developing a diagnostic panel of blood-borne biochemical markers of cerebral ischemia. Methods— Serial blood samples were obtained from patients (n=65 with suspected ischemic stroke, n=157 control subjects) presenting to an academic medical center emergency department. We analyzed 26 blood-borne markers believed to play a role in the ischemic cascade and created a 3-variable logistic regression model to predict the clinical diagnosis of stroke, defined as persistent neurological symptoms of cerebral ischemia lasting >24 hours. Results— Of the 26 blood-borne markers analyzed, univariate logistic analysis revealed that 4 were highly correlated with stroke ( P P =0.1, our logistic model provided a sensitivity and specificity of 90% for predicting stroke. Conclusions— A panel of blood-borne biochemical markers may be helpful in identifying patients with acute cerebral ischemia who could benefit from urgent care. Such a test may also be helpful in identifying stroke patients in the prehospital setting so that they could be fast-tracked to an institution equipped to care for patients with acute stroke.

The premise of neuroprotective therapy for acute ischemic stroke is based upon the possibility to interfere with the cellular ischemic cascade, so the understanding of the mechanisms and consequences of cerebral ischemia is necessary. The relationship between lipid peroxidation and acidosis was investigated in several regions of rat brain following ischemia without reperfusion. Male Wistar rats (280-300 g) were anaesthetised (Ketalar 33 mg/kg and Rompun 6.66 mg/kg) or not and underwent a four-vessel occlusion for 5 minutes. Then, thiobarbituric acid-reactive substances (TBARS) and lactate levels were measured in different brain regions (cerebellum, bulb, striatum, hippocampus, cortex). Induction of ischemia by ligation of two common carotid arteries and two vertebral arteries resulted in a production of TBARS (40-120%, p < 0.05) and lactate (20-60%, p < 0.05) in all cerebral regions of awake rats, especially in striatum, suggesting a potential link between lipid peroxidation and acidosis. When ischemia was realised on anaesthetised animals, an increase of lactate levels (30-50%, p < 0.05) was shown in all brain regions but TBARS were produced only in striatum (82%, p < 0.05). These data showed the particular vulnerability of striatum to ischemia and the possible opposite effects of an anaesthesia.

Modern scientific and technological advances give reason to revise the previous pessimistic opinion about the therapeutic possibilities for acute focal brain ischemia, i.e. ischemic stroke.

To keep ischemic brain cells alive, neuroprotective agents target events in the ischemic cascade that might be injurious to the cells. They can be divided broadly into groups that restore ion balance, block receptors, prevent reperfusion injury, or promote neuronal healing. To date, neuroprotective agents have either shown a lack of efficacy in clinical stroke trials or been limited by side effects. Ongoing clinical trials with novel agents are trying to enroll a more homogeneous population of stroke patients in an effort to demonstrate treatment benefit.

Acute stroke can be classified as ischemic, hemorrhagic, or both and result in the occurrence of multiple pathophysiological processes. These pathophysiological events develop over the subsequent hours to days, as the original core of the infarct develops into the surrounding penumbral area (1, 2). Initial cell death results from the deprivation of blood supply to the brain. However, a significant portion of the brain damage occurs later when secondary deleterious mechanisms come into play (2). The recent progress made in defining the mechanisms involved in the pathophysiology of stroke will probably lead to the identification of new strategies for intervention in the ischemic cascade. Therefore, it becomes increasingly important to initially consider how these new therapeutics may be delivered into the target tissue in brain and secondly to speculate on new strategies that would target ischemic brain tissue.

The pursuit of targeting multiple pathways in the ischemic cascade of cerebral stroke is a promising treatment option. We examined the regenerative potential of conditioned medium derived from rat and human apoptotic mononuclear cells (MNC), rMNCapo sec and hMNCapo sec, in experimental stroke.We performed middle cerebral artery occlusion on Wistar rats and administered apoptotic MNC-secretomes intraperitoneally in two experimental settings. Ischemic lesion volumes were determined 48 hours after cerebral ischemia. Neurological evaluations were performed after 6, 24 and 48 hours. Immunoblots were conducted to analyze neuroprotective signal-transduction in human primary glia cells and neurons. Neuronal sprouting assays were performed and neurotrophic factors in both hMNCapo sec and rat plasma were quantified using ELISA.Administration of rat as well as human apoptotic MNC-secretomes significantly reduced ischemic lesion volumes by 36% and 37%, respectively. Neurological examinations revealed improvement after stroke in both treatment groups. Co-incubation of human astrocytes, Schwann cells and neurons with hMNCapo sec resulted in activation of several signaling cascades associated with the regulation of cytoprotective gene products and enhanced neuronal sprouting in vitro. Analysis of neurotrophic factors in hMNCapo sec and rat plasma revealed high levels of brain derived neurotrophic factor (BDNF).Our data indicate that apoptotic MNC-secretomes elicit neuroprotective effects on rats that have undergone ischemic stroke.

ContextElucidation of the ischemic cascade has helped stimulate development of neuroprotective drugs aimed at limiting brain injury in the hours following an ischemic stroke. To date, none of these drugs has shown clinical efficacy.ObjectiveTo examine the efficacy of gavestinel (GV150526), an antagonist of the glycine site of the N-methyl-D-aspartate receptor, as a neuroprotective therapy for acute ischemic stroke when administered within 6 hours of symptom onset.DesignThe Glycine Antagonist in Neuroprotection (GAIN) Americas trial, a randomized, double-blind placebo-controlled trial with enrollment from April 1998 to October 1999.SettingOne hundred thirty-two hospital centers across the United States and Canada.PatientsThe primary efficacy population consisted of 1367 ischemic stroke patients with a predefined level of limb weakness and functional independence prior to stroke, stratified at randomization by age (≤75 vs >75 years) and initial stroke severity (National Institutes of Health [NIH] Stroke Scale scores of 2-5, 6-13, or ≥14).InterventionPatients were randomly assigned to receive an intravenous loading dose (800 mg) plus 5 maintenance doses (200 mg every 12 hours) of gavestinel (n = 701) or placebo (n = 666) for 3 days.Main Outcome MeasureFunctional capability at 3 months, measured by the Barthel Index (BI), with scores trichotomized as dead/0-55, 60-90, and 95-100, compared between the gavestinel and placebo groups.ResultsTreatment groups were well matched for baseline characteristics. For each group, median NIH Stroke Scale was 12, median age was 72 years, and median time to treatment was 5.2 hours. No statistically significant improvement on the 3-month BI trichotomy was demonstrated for gavestinel (P = .79). The proportion who were functionally independent (BI score = 95-100) was 39% in the gavestinel group and 37% in the placebo group. No statistically significant difference in 3-month survival was observed using Kaplan-Meier curves (P = .11). No other secondary end point suggested an advantage for gavestinel. Among the 333 patients (24%) who received recombinant tissue-type plasminogen activator, there was also no benefit for gavestinel (P = .53). There were no serious safety issues.ConclusionIn this study, gavestinel administered up to 6 hours after an acute ischemic stroke did not improve functional outcome at 3 months.

Stress cine function and vasodilating stress perfusion are commonly used approaches for the evaluation of ischemic heart disease. Both imaging approaches, using either stress echocardiography or stress nuclear scintigraphy, have stood the test of time as highly accurate in diagnosing coronary artery stenosis and as prognostic tools in patients with symptoms suspicious of myocardial ischemia.1,2 When epicardial coronary flow is interrupted and leads to an imbalance between myocardial oxygen supply and demand, reduced myocardial perfusion, regional ventricular dysfunction, and ECG change occur in quick succession; hence, the term “ischemic cascade” has been described.3 This phenomenon has been well described after acute balloon inflation during percutaneous coronary intervention and also during demand ischemia induced by dobutamine stress. Consequently, capturing abnormalities of both perfusion and function, in an attempt to improve the diagnostic performance of noninvasive tests, has been the focus of investigation using echocardiography and nuclear scintigraphy, with encouraging results.4–6 Article p 122 In this issue of Circulation: Cardiovascular Imaging , Gebker et al7 described the diagnostic utility of cardiac MRI (CMR) for evaluation of coronary artery disease using both myocardial perfusion (DSMRP) and function (DSMR) assessments during high-dose dobutamine stress testing. As shown in their work, CMR has technical features that are well suited for imaging both perfusion and regional function during a single, high-dose dobutamine infusion. With advances in imaging speed and algorithms of accelerated data reconstruction, gated cine steady-state free precession imaging can capture regional left ventricular dysfunction from ischemia at high temporal resolution and contrast-to-noise ratio. At target heart rates during peak stress, first-pass perfusion can sample myocardial …

Geoffrey A. Donnan MD, FRACP Stephen M. Davis MD, FRACP Section Editors: Neuroprotective agents disrupting the ischemic cascade and salvaging the ischemic penumbra are being explored as a potential therapeutic option for stroke. Although a number of agents are neuroprotective in animal studies, none of the human trials have been positive, with the exception of the SAINT I trial.1 Unfortunately, the follow-up SAINT II trial had a negative result,2 and a great deal of pessimism regarding the future of neuroprotection has been generated. However, before abandoning neuroprotection as a strategy, it is important to examine where research in neuroprotection has brought us and how we can better design future animal and clinical studies. The main reason for failure has been poor translation from animal studies to clinical trials. Clinical trials often had prolonged therapeutic windows, small sample sizes, and failed to achieve adequate plasma levels of study medications. These problems lead to the Stroke Therapy Academic Industry Roundtable (STAIR) recommendations,3,4 which have greatly improved …

This communication reports the results of investigations on the effect of low molecular weight heparin (LMWH) on intraneuronal calcium release, and considers its possible relevance to the treatment of ischemic stroke. It previously was shown that intraneuronal injection of conventional heparin (MW 12,000) in vitro prevents glutamate-induced calcium release from intracellular stores through its blocking action on IP3 (inositol-1,4,5-triphosphate) receptors, and thus interferes with events occurring in the ischemic cascade. In the experiments reported herein, a LMWH of MW 4500 was shown to have these same effects when injected into a Purkinje cell in an in vitro cerebellar slice preparation, and also when administered externally (bath application). By contrast, conventional heparin works only when injected into the cell; bath application has no effect. The results are interpreted to mean that the larger conventional heparin molecule cannot pass through the cell membrane, while the smaller LMWH molecule does indeed enter the cell. In a clinical trial, LMWH begun within 48 hours of ischemic stroke onset in humans improved outcome at 6 months; conventional heparin given in a similar trial was without benefit. That one anticoagulant was beneficial while another failed suggests the possibility that the difference was independent of effect on the clotting system. The experimental data herein reported support the view that LMWH may benefit stroke victims by an action directly cytoprotective against the consequences of neuronal ischemia.

Imaging the ischemic cascade for diagnostic purposes can be done with different techniques focusing on perfusion defects and/or wall motion abnormalities. Tests based on perfusion imaging require malperfusion as a positivity criterion, with a relative difference in hyperemic flow which does not need myocardial ischemia for positivity (Fig. I). Tests based on wall motion abnormalities do require myocardial ischemia and therefore more advanced levels of flow reserve impairment (Fig. 1). Besides magnetic resonance imaging (MRI, see Chap. 32), several methods based on ionizing radiations have been proposed to diagnose coronary artery disease using the marker of wall motion and/or malperfusion. These methods include fast computed tomography (CT), radionuclide ventriculography, standard perfusion scintigraphy, and positron emission tomography (PET) [I]. Perfusion defects allow an earlier detection of atherosclerotic disease, probably at the expense of lower specificity. Wall motion changes allow detection of more advanced forms of obstructive disease, allowing more prognostically meaningful forms of disease to picked up (Fig. 2 in Chap. 3). This enormous potential should be used with parsimony, since in the words of Skorton [2]

Publisher Summary This chapter elaborates mechanisms of antiplatelet agents and the prevention of stroke. The role of antiplatelet agents in cerebrovascular disease (stroke) is that of treatment for its acute and chronic phase. Treatment for stroke is based upon diagnosis and stroke diagnosis is based upon pathology and pathogenesis. Antiplatelet agents may have a role in the treatment of acute cerebral infarction, with the aim of treatment being limitation of tissue damage through interruption of the final ischemic cascade. At the no reflow stage of brain ischemia, platelet and erythrocyte aggregation, polymorphonuclear leukocyte-endothelial adhesion, and in situ thrombosis may cause microvascular occlusion. The use of antiplatelet therapy is defined by the white clot-red clot paradigm. If the clinician can determine that a particular patient is at risk for formation of white thrombi, then antiplatelet therapy can rationally be chosen for prevention of its occurrence. Both red and white thrombus potential may coexist in the same individual, and the presence of red thrombi may predispose to white thrombus. Recombinant leech antiplatelet protein blocks platelet deposition on collagen surfaces under flow conditions. Such therapy may be far more advantageous than therapy aimed uniquely at inhibiting the red or white clot formation specifically. Attention to common dietary substances and their potential effect on thrombosis may help the antithrombosis campaign.

New therapeutic approaches are urgently needed to treat stroke patients. According to the World Health Organization this devastating disease affects 15 million people each year, among them about 10 million will die or live as functionally-disabled stroke survivors. Despite these devastating numbers, only pharmacological and mechanical reperfusion therapies to restore the blood flow have proven to save lives and improve the neurological outcome of ischemic stroke patients.1 On the other side, hundreds of neuroprotective drugs targeting inflammation, oxidative stress, apoptosis and other cell-death triggers of the ischemic cascade, have failed to prove efficacy in clinical trials after obtaining encouraging supporting data from pre-clinical studies. Hence, enormous disappointment has struck researchers, neurologists and industry partners when translating basic science findings to the clinical practice. This shocking reality has opened the eyes of many stroke researchers to look for new targets, and most importantly, to find new ways to validate potential therapeutic benefits in a bedside-to-bench strategy. In this regard, the main endpoint of stroke clinical trials designed to prove efficacy is to demonstrate improvement of neurological function in stroke survivors. In recent publications from Bargiotas and colleagues2,3 the authors show this new vision in the stroke research field: the authors focus their interest in pannexins, a family of proteins involved in basic cell-signaling functions, to demonstrate their role not only in brain injury but also in modifying functional outcome in a mouse model of stroke. It is known that cell-to-cell communication occurs directly through gap-junctions between cells or by indirect paracrine signaling when cells release molecules such as ATP, ions or small metabolites into the extracellular space. With a structure similar to gap-junction forming connexins, recently discovered pannexins are membrane channels described to connect the cytosol with the extracellular space.4 Pannexin 1 (Px1) and pannexin 2 (Px2) are known to be expressed in the cerebral nervous system, in contrast to the other member of the family, pannexin 3.4 Interestingly, pannexins have been shown to be expressed in the brain both in neurons and astrocytes2,5 while other authors have recently demonstrated their expression in vascular cells of the rat brain (Px1 expression in smooth muscle cells and Px2 in both endothelium and smooth muscle cells).6 Regarding function, channel activity has been demonstrated to be dependent on pannexins in neurons,2 whereas channel activity in astrocytes has been reported to be both independent and dependent on pannexins by different authors.2,7 Interestingly, Px1- and Px2-deficient mice, but not single knockouts, have recently shown to be protected in front of ischemia in an experimental model reproducing cortical infarcts, by reducing lesion volume and improving neurological outcome at short-term.2 Why do pannexins become involved in brain damage? Several authors speculate that K+ efflux, accumulation of reactive oxygen species and caspase expression after ischemia might activate and open these membrane channels leading to cell death,8 although the precise mechanisms still need to be fully characterized. The knowledge on pannexin functions is incipient and continuously evolving. However Bargiotas and colleagues2,3 have already explored the final consequences of knocking-out these proteins in the context of cerebral ischemia. Their results position pannexins as therapeutic targets to improve functional outcome in sensorimotor, anxiety and exploration functions after stroke. Certainly these are exciting results, but from a bedside-to-bench point of view it is still required to demonstrate if the reported neurological protection is sustained long-term, in old animals, in females or in other species and should be validated by independent researchers in other stroke models. Finally, it would be interesting to explore the pharmacological inhibition of pannexins to demonstrate functional benefits in pre-clinical models before we move to the clinical setting.

In this review paper on the pathophysiology of myocardial ischaemia, the recent concepts of the ischaemic cascade, as well as the concepts of stunning and hibernating myocardium, are discussed. It is clear that painful ischaemia is the final phenomenon in the ischaemic cascade and that it is preceded by biochemical disturbances, diastolic and systolic dysfunction and electrocardiographic abnormalities. Silent ischaemia remains a difficult research field.

Many substances act in an antiischemic manner, e g membrane-stabilizing drugs, cationic amphiphilic compounds,such as β-sympathicolytics, local anesthetics and all agents that suppress cardiac function, e.g. calcium entry blockers. However, high concentrations are necessary, and the side effects are pronounced. It would be desirable to find agents which affect only the pathophysiological processes observed during ischemia without influencing physiological processes. The optimal stage of interaction would be early in the ischemic cascade.

Background: Previous studies have shown that transmural myocardial ischemia caused by sudden epicardial coronary artery occlusion determines a typical sequence of events characterized, in order, by left ventricular wall motion abnormalities, ST segment ischemic modifications and, only at the end, angina. In this study, we investigate if this typical "ischemic cascade" presents with the same modalities also during subendocardial ischemia induced by dipyridamole infusion. Patients and Methods: A total of 41 patients (63±9 years; 12 women) with chronic stable angina and angiographically documented coronary artery disease (1-vessel: 14 [34%]; 2-vessel: 8 [19%]; 3-vessel: 19 [46%]) underwent dipyridamole stress echocardiography (total dose: 0,84 mg/kg iv). Cardiac images were acquired by a 2.5 MHZ probe connected to a Toshiba set, Power Vision 8000. Results: During test, 39 patients (95%) had left ventricular wall motion abnormalities, 31 patients (75%) had ST segment depression and 32 patients (78%) had angina. The first manifestation of ischemia was left ventricular wall motion abnormalities in 7 patients (17%), ST segment depression in 16 patients (39%) and angina in 9 patients (22%). When considering only the 21 patients who developed all three manifestations of ischemia during dipyridamole stress echocardiography, left ventricular wall motion abnormalities were the first manifestation of ischemia (alone or in association with ST segment depression or angina) in 5 patients (24%), ST segment depression was the first manifestation of ischemia (alone or in association with left ventricular wall motion abnormalities or angina) in 14 patients (66%) and angina was the first manifestation of ischemia (alone or in association with left ventricular wall motion abnormalities or ST segment depression) in 8 patients (38%). Conclusion: Our data indicate that dipyridamole induced subendocardial ischemia results in a very variable sequence of events, which doesn’t seem to reproduce the typical "ischemic cascade" described after sudden coronary artery occlusion. The heterogeneity of the response among patients likely depends on a variable association of interindividual differences in the extension of ischemia, in the sensitivity of cardiac neuronal algogenic receptors and in the adenosine-mediated effects of dipyridamole on cardiac perception of pain and on electrophysiological characteristics of myocardial cells. 735 Cultural evolution of digital description of coronary artery disease severity potential of inducing myocardial ischemia during exercise stress echocardiography.

The concept of neuroprotection is based on the understanding that delayed neuronal damage occurs after ischemia. Each step along the ischemic cascade provides an opportunity for therapeutic intervention. Based on the excellent results obtained in experimental models of ischemia, many clinical trials have been conducted with different neuroprotective drugs. The results obtained in most studies were negative and in some cases the studies were terminated due to safety problems. However, the mechanisms that underlie the development of ischemic damage are still being discovered, creating new therapeutic possibilities for neuroprotection that might be clinically applicable in the future. This article reviews the mechanisms of ischemic neuronal injury, the mechanism of action of neuroprotective agents, current neuroprotective clinical trials, and probable reasons for the failure of clinical neuroprotection. (c) 2003 Prous Science. All rights reserved.

In this article we review the concept of ischemic penumbra and emphasize the potentially reversible aspect as a function of time, which is the basis of the concept of a therapeutic window. Also, we briefly consider the physiopathology of the ischemic cascade, emphasizing the levels at which the different neuroprotector drugs under investigation have their effect.

The author reviews the major biochemical events that follow in the wake of a significant brain ischemic insult. Evidence is presented that establishes lactic acidosis as a significant accelerant of the ischemic cascade and that proposes that uncontrolled entry of calcium into the vulnerable neuron triggers cell death.

The effects of mannitol, nimodipine, and indomethacin on ischemic neuronal injury were examined in 45 rats divided equally into nine groups subjected to 10 minutes of forebrain ischemia. Of two control groups, one received maintenance fluids while the other received a normal saline bolus. In the remaining seven groups, mannitol, nimodipine, and indomethacin were administered singly or in combination 5 minutes before forebrain ischemia. Seven days after ischemia, the brains were perfusion-fixed, sectioned coronally into 2.8-mm slices, and stained with hematoxylin and eosin. Ischemic neurons were directly counted on predetermined regions of standardized serial sections. Considerable amelioration of ischemic injury (ischemic neurons/total neurons) was observed with mannitol (ischemic injury, 7 +/- 5% in the hippocampal CA1/CA2 sectors and 28 +/- 17% in the CA3 sector). This is in contrast to control values of 64 +/- 11% and 80 +/- 6%, respectively, and those obtained in the normal saline group of 70 +/- 10% and 59 +/- 13%, respectively. The beneficial effect with nimodipine reached significance in only the hippocampal CA3 sector (ischemic injury, 35 +/- 21%). Indomethacin showed no significant benefit. Combining the agents resulted in significantly reduced neuronal injury compared with control groups, although the effect was not greater than that achieved with mannitol alone. The degree of ischemic injury was least when all three agents were used in combination (ischemic injury, 12 +/- 12% in the hippocampal CA1/CA2 sectors and 4 +/- 4% in the CA3 sector). Our data support the concept that successfully blocking the ischemic cascade with a single, diversely acting agent or multiple agents will evoke the best beneficial response.

The development of an ischemic event, whether silent or painful, represents the cumulative impact of a sequence of pathophysiologic events. Each ischemic episode is initiated by an imbalance between myocardial oxygen supply and demand that may ultimately be manifested as angina pectoris. This sequence of events can be termed the ischemic cascade. The significance of this concept resides in the fact that it redirects the focus from the end result—angina—to the more fundamental, underlying pathophysiologic factors that precede it. Specifically, these events include diminished left ventricular compliance, decreased myocardial contractility, increased left ventricular end-diastolic pressure, ST-segment changes and, occasionally, angina pectoris.

Despite the widespread use of the exercise stress test in diagnosing asymptomatic myocardial ischemia, exercise radionuclide imaging remains useful for detecting silent ischemia in numerous patient populations, including those who are totally asymptomatic, those who have chronic stable angina, those who have recovered from an episode of unstable angina or an uncomplicated myocardial infarction, and those who have undergone angioplasty or received thrombolytic therapy. Studies show that thallium scintigraphy is more sensitive than exercise electrocardiography in detecting ischemia, i.e., in part, because perfusion defects occur more frequently than ST depression and before angina in the ischemic cascade. Thallium-201 scintigraphy can be performed to differentiate a true- from a false-positive exercise electrocardiographic test in patients with exercise-induced ST depression and no angina. The development of technetium-labeled isonitriles may improve the accuracy of myocardial perfusion imaging.

OBJECTIVESThe purpose of this study was to explore interactions between paracrine angiotensin II (Ang-II) and tumor necrosis factor-alpha (TNF-alpha) during myocardial ischemia.BACKGROUNDIschemic myocardium releases significant amounts of TNF-alpha. This paracrine release correlated with postischemic myocardial injury. Other studies showed myocardial protection obtained by the use of angiotensin-converting enzyme inhibitors (i.e., captopril) and the Ang-II type 1 receptor antagonist losartan after ischemia. The possibility that these agents decrease TNF-alpha synthesis has not yet been investigated.METHODSUsing the modified Langendorff model, isolated rat hearts underwent either 90 min of nonischemic perfusion (control group) or 1 h of global cardioplegic ischemia. In both groups, either captopril (360 μmol/liter) or losartan (182.2 μmol/liter) was added before ischemia. The hearts were assayed for messenger ribonucleic acid (mRNA) expression and effluent TNF-alpha levels. In addition, cardiac myocytes were incubated in cell culture with Ang-II.RESULTSAfter ischemia, TNF-alpha mRNA expression intensified from 0.63 ± 0.06 (control group) to 0.92 ± 0.12 (p < 0.03), and effluent TNF-alpha levels were 711 ± 154 pg/ml. The TNF-alpha mRNA expression declined to 0.46 ± 0.07 (p < 0.01) and 0.65 ± 0.08 (p < 0.02) in captopril- and losartan-treated hearts, respectively. Effluent TNF-alpha was below detectable levels. Concentrations of TNF-alpha in supernatants of incubated cardiac myocytes treated with 10 and 50 nmol/liter of Ang-II were 206.0 ± 47.0 pg/ml and 810 ± 130 pg/ml, respectively (p < 0.004). When pretreated with 700 μmol/liter of losartan, TNF-alpha was below detectable levels.CONCLUSIONSThis study presents an original explanation for previously reported myocardial protection after ischemia, obtained by the use of captopril and losartan. These drugs reduce TNF-alpha synthesis, providing strong evidence of active interactions between paracrine TNF-alpha and Ang-II in the evolution of the ischemic cascade.

Echocardiographic diagnosis of myocardial ischemia is based on visualizing hypokinesis, which occurs late in the ischemic cascade. We hypothesized that temporal changes in endocardial motion may constitute sensitive early markers of ischemia. Two protocols were performed in 19 anesthetized pigs. Protocol 1 included 54 intracoronary balloon occlusions. Transthoracic images were acquired at baseline and every 15 s during 5 min of occlusion and reperfusion. In protocol 2, ischemia was induced in 12 animals by use of graded dobutamine infusion, after creating significant partial occlusions without a resting wall motion abnormality. Systolic and diastolic endocardial motion was color encoded using color kinesis and analyzed using custom software. All ischemic episodes caused detectable and reversible changes. The earliest sign of ischemia was tardokinesis in 31/54 occlusions, whereas hypokinesis appeared first in 23/54 cases. Dobutamine-induced ischemia caused tardokinesis first in 9/12 and hypokinesis in 3/12 animals. Reversible ischemic changes in regional left ventricular performance can be objectively detected using analysis of echocardiographic images and will likely improve the early noninvasive diagnosis of acute ischemia.

Tissue damage following acute focal cerebral ischemia results from multiple pathophysiological mechanisms called the ischemic cascade. This is a complex series of neurochemical processes involving cellular bioenergetic failure, excitotoxicity, oxidative stress, blood-brain barrier dysfunction, microvascular injury, hemostatic activation, post-ischemic inflammation and finally cell death of neurons, glial and endothelial cells. These key biochemical pathways are targets for the development of improved stroke treatments and novel diagnostic tools.

Acute ischemic stroke is usually caused by thromboembolic occlusion of an intracranial artery.1 The arterial occlusion and the consequent lowering of CBF result in a complex series of events that transform ischemic tissue into infarction.2,3 The survival time of tissue after ischemia depends mainly on the residual CBF through collaterals and on selective neuronal vulnerability to ischemia.3 The time window from ischemia to neuronal death therefore varies widely. It may be a few minutes, e.g., in brain tissue with a residual CBF below 10 ml/100 g/min (the so-called threshold for energy failure), or several hours, e.g., in tissue with CBF values between 10 and 20 ml/100 mg/min (the ischemic penumbra). In the context of penumbra tissue, the electrical neuronal function is abolished but the neurons themselves are viable4 until the amount of ATP produced falls below 50% of normal values and the breakdown of energy-producing metabolites causes lactoacidosis, ion pump failure, and eventually irreversible membrane damage5 (figure 1). As a consequence, tissue that at a certain point in time is alive or can be saved from ischemia may be irreversibly damaged soon after. In other words, there is a "point of no return" in the ischemic cascade, a factor that is crucial for both the so called therapeutic window6 and for acute stroke treatments. Figure 1. Main steps of the ischemic cascade. EAA= excitatory amino acids, Cai = intracellular calcium, Nai= intracellular sodium, Ke = extracellular potassium, ICAM-1 = intercellular adhesion molecules. Ischemia may be reversed by reperfusion.7 However, on return of blood flow, together with the resumption of the principal neuronal functions (e.g., oxygen delivery, provision of substrates for metabolism), interactions between blood and the already damaged tissue can be responsible for further tissue …