Initial experience with hyperoxemic reperfusion after primary angioplasty for acute myocardial infarction: results of a pilot study utilizing intracoronary aqueous oxygen therapy

Cardioprotective Strategies After Ischemia-Reperfusion Injury

Acute myocardial infarction (AMI) is associated with high morbidity and mortality worldwide. Although early reperfusion is the most effective strategy to salvage ischemic myocardium, reperfusion injury can develop with the restoration of blood flow. Therefore, it is important to identify protection mechanisms and strategies for the heart after myocardial infarction. Recent studies have shown that multiple intracellular molecules and signaling pathways are involved in cardioprotection. Meanwhile, device-based cardioprotective modalities such as cardiac left ventricular unloading, hypothermia, coronary sinus intervention, supersaturated oxygen (SSO2), and remote ischemic conditioning (RIC) have become important areas of research. Herein, we review the molecular mechanisms of cardioprotection and cardioprotective modalities after ischemia-reperfusion injury (IRI) to identify potential approaches to reduce mortality and improve prognosis in patients with AMI.

Novel Intracoronary Infusion of Supersaturated Oxygen Therapy in Patients Presenting With Acute ST Elevation Myocardial Infarction: Does It Help?

Supersaturated oxygen (SSO₂) is one of the emerging therapies that has shown benefit for patients suffering from acute ST elevation myocardial infarction (STEMI) in terms of reducing infarct size, which has been used as a prognostic indicator for future heart failure and hospitalizations. Trials investigating SSO₂ therapy have shown improvement in infarct size when used as an adjunct therapy to percutaneous trans-luminal coronary angioplasty (PTCA) or percutaneous coronary intervention (PCI) in patients presenting with acute myocardial infarction (aMI).  Here we present a patient with a mid left anterior descending artery (mLAD) STEMI who underwent SSO₂ therapy. The patient presented with new onset angina and ST elevations on EKG. He underwent emergent coronary angiography, which confirmed an mLAD complete vessel occlusion. Successful PCI was done with a drug-eluting stent followed by supersaturated oxygen therapy. On follow-up evaluation, the patient had improved left ventricular (LV) ejection fraction from 35% to 60%. This case highlights the safety and efficacy of SSO₂ therapy for patients suffering from acute anterior wall myocardial infarction. We recommend further investigation of this therapy for its routine use, safety, and prognostic utility. We also recommend routine use of adjunctive SSO₂ therapy for patients suffering acute anterior STEMI.

The Use of Cardioprotective Devices and Strategies in Patients Undergoing Percutaneous Procedures and Cardiac Surgery

In the United States, about one million people are seen to visit the operating theater for cardiac surgery annually. However, nearly half of these visits result in complications such as renal, neurological, and cardiac injury of varying degrees. Historically, many mechanisms and approaches have been explored in attempts to reduce injuries associated with cardiac surgery and percutaneous procedures. Devices such as cardioplegia, mechanical circulatory support, and other methods have shown promising results in managing and preventing life-threatening cardiac-surgery-related outcomes such as heart failure and cardiogenic shock. Comparably, cardioprotective devices such as TandemHeart, Impella family devices, and venoarterial extracorporeal membrane oxygenation (VA-ECMO) have also been proven to show significant cardioprotection through mechanical support. However, their use as interventional agents in the prevention of hemodynamic changes due to cardiac surgery or percutaneous interventions has been correlated with adverse effects. This can lead to a rebound increased risk of mortality in high-risk patients who undergo cardiac surgery. Further research is necessary to delineate and stratify patients into appropriate cardioprotective device groups. Furthermore, the use of one device over another in terms of efficacy remains controversial and further research is necessary to assess device potential in different settings. Clinical research is also needed regarding novel strategies and targets, such as transcutaneous vagus stimulation and supersaturated oxygen therapy, aimed at reducing mortality among high-risk cardiac surgery patients. This review explores the recent advances regarding the use of cardioprotective devices in patients undergoing percutaneous procedures and cardiac surgery.

Device-Based Approaches Targeting Cardioprotection in Myocardial Infarction: The Expanding Armamentarium of Innovative Strategies

Coronary reperfusion therapy has played a pivotal role for reducing mortality and heart failure after acute myocardial infarction. Although several adjunctive approaches have been studied for reducing infarct size further, both ischemia-reperfusion injury and microvascular obstruction are still major contributors to both early and late clinical events after acute myocardial infarction. The progress in the field of cardioprotection has found several promising proof-of-concept preclinical studies. However, translation from bench to bedside has not been very successful. This comprehensive review discusses the importance of infarct size as a driver of clinical outcomes post-acute myocardial infarction and summarizes recent novel device-based approaches for infarct size reduction. Device-based interventions including mechanical cardiac unloading, myocardial cooling, coronary sinus interventions, supersaturated oxygen therapy, and vagal stimulation are discussed. Many of these approaches can modify ischemic myocardial biology before reperfusion and offer unique opportunities to target ischemia-reperfusion injury.

Chronic myocardial and coronary arterial effects of intracoronary supersaturated oxygen therapy in swine with normal and ischemic-reperfused myocardium

The study assessed chronic myocardial, coronary and systemic effects of intracoronary supersaturated oxygen (SSO2) therapy. Left anterior descending coronary arteries of 40 swine were stented and randomized to 90-min selective intracoronary infusion of SSO2 (pO2 760-1000 mmHg) or normoxemic saline. In 20 out of 40 animals, SSO2 delivery followed a 60-min balloon occlusion to induce myocardial infarction (MI). In both normal and MI models, intracoronary treatment with hyperoxemic SSO2 therapy showed no evidence of coronary thrombosis. There were no biologically relevant differences between treatments at either time point in regard to coronary intervention site healing and neointimal growth. No signs of any myocardial or systemic toxicity were observed after 7 or 30 days. A trend was observed toward reduced incidence of microscopic MI scars and reduced infarct size in histopathology, as well as toward better recovery of echocardiographically evaluated global and regional contractility at 30 days. No treatment related infarcts or thromboemboli were observed in the downstream organs.

Intracoronary Application of Super-Saturated Oxygen to Reduce Infarct Size Following Myocardial Infarction

Optimal medical therapy for secondary prevention following acute myocardial infarction reduces non-fatal ischaemic events. Intensive antithrombotic or lipid-lowering approaches have failed to significantly lower mortality. In the past, reduction of infarct size in patients undergoing primary percutaneous revascularisation for acute myocardial infarction had been considered as a surrogate outcome marker. However, infarct size measured by magnetic resonance imaging or SPECT is strongly associated with all-cause mortality and hospitalization for heart failure within the first year after an acute myocardial infarction. Intracoronary administration of super-saturated oxygen (SSO₂) immediately after revascularisation is an approach that can be used to reduce infarct size and, therefore, improve cardiovascular outcome in patients with acute myocardial infarction. In this article, we describe the modulation of pathophysiology by SSO₂, review the existing trial data and present our first impressions with the technique in real clinical practice.

IDENTIFYING THE EFFECTS OF SUPPLEMENTAL OXYGEN ADMINISTRATION ON THE HEALTH OUTCOMES OF PATIENTS PRESENTING WITH ACUTE CORONARY SYNDROME AND OXYGEN SATURATION >93% - A SYSTEMATIC REVIEW

OBJECTIVES

Oxygen was commonly used in the early management of patients presenting with Acute Coronary Syndrome (ACS) regardless of their oxygen saturation. Inappropriate administration of supplemental oxygen could potentially result in adverse patient health outcomes.

AIM

To identify the effects of supplemental oxygen administration on the health outcomes of patients presenting with ACS and oxygen saturations >93%.

METHOD

Systematic review. The CINAHL, PubMed, Cochrane and Medline databases were searched for relevant literature. Inclusion criteria included articles published from 2008-2019, adult participants, primary studies, and participants with uncomplicated ACS and have oxygen saturation >93%. Eligible studies were assessed for rigour using a critical appraisal tool.

RESULTS

Seven randomised controlled studies were included for analysis. Themes were also used to group the assessed endpoints. The three main outcomes analysed were: infarct size and cardiac function; adverse cardiac events; and mortality. Two of the seven studies found a statistically significant relationship between oxygen administration, infarct size, and adverse cardiac events. Conversely, five of the seven studies reported that supplemental oxygen did not have statistically significant benefit over room air.

CONCLUSION

This review identified that oxygen should not be administered to patients who present with ACS and have oxygen saturations >93%. This is due to the potential risk of adverse outcomes: increased infarct size, mortality, and adverse events.

IMPACT STATEMENT

Recent update of guidelines despite evidence opposing oxygen delivery in ACS means the education of nurses is imperative for safe practice.

Update on Cardioprotective Strategies for STEMI: Focus on Supersaturated Oxygen Delivery

Despite the fact that door-to-balloon times have been greatly reduced, the rates of death and the incidence of heart failure in patients with ST-segment elevation myocardial infarction (MI) have plateaued. There is still an unmet need to further reduce MI size in the reperfusion era. Most adjunctive therapies to enhance myocardial salvage have failed, but some have shown promise. Currently, the only adjunctive therapy in a pivotal trial that has demonstrated reductions in infarct size is localized delivery of supersaturated oxygen (SSO₂) therapy. This review provides background on prior infarct size reduction efforts. The authors describe the preclinical data that shows the effectiveness of SSO₂ in reducing MI size, improving regional myocardial blood flow and cardiac function, and reducing adverse left ventricular remodeling-presumably by reducing patchy areas of residual ischemia within the reperfused risk zone. Potential mechanisms by which SSO₂ is beneficial are described, including the delivery of high levels of dissolved oxygen through plasma to ischemic, but viable, vascular and myocardial cells, thus allowing their survival and function. The authors then describe the SSO₂ clinical trials, demonstrating that in patients with anterior ST-segment elevation MI, SSO₂ therapy safely and effectively reduces infarct size, improves cardiac function, and reduces adverse left ventricular remodeling.

Controlling Reperfusion Injury With Controlled Reperfusion: Historical Perspectives and New Paradigms

Cardiac reperfusion injury is a well-established outcome following treatment of acute myocardial infarction and other types of ischemic heart conditions. Numerous cardioprotection protocols and therapies have been pursued with success in pre-clinical models. Unfortunately, there has been lack of successful large-scale clinical translation, perhaps in part due to the multiple pathways that reperfusion can contribute to cell death. The search continues for new cardioprotection protocols based on what has been learned from past results. One class of cardioprotection protocols that remain under active investigation is that of controlled reperfusion. This class consists of those approaches that modify, in a controlled manner, the content of the reperfusate or the mechanical properties of the reperfusate (e.g., pressure and flow). This review article first provides a basic overview of the primary pathways to cell death that have the potential to be addressed by various forms of controlled reperfusion, including no-reflow phenomenon, ion imbalances (particularly calcium overload), and oxidative stress. Descriptions of various controlled reperfusion approaches are described, along with summaries of both mechanistic and outcome-oriented studies at the pre-clinical and clinical phases. This review will constrain itself to approaches that modify endogenously-occurring blood components. These approaches include ischemic postconditioning, gentle reperfusion, controlled hypoxic reperfusion, controlled hyperoxic reperfusion, controlled acidotic reperfusion, and controlled ionic reperfusion. This review concludes with a discussion of the limitations of past approaches and how they point to potential directions of investigation for the future.

Novel intracoronary supersaturated oxygen treatment for anterior myocardial infarction

Primary percutaneous coronary intervention (PCI) is now the recommended reperfusion technique for patients with acute ST-segment elevation myocardial infarction. However, despite early reperfusion in the majority of patients, PCI does not achieve effective myocardial reperfusion in a significant proportion of patients due to the prevalence of coronary microvascular obstruction. The amount of infarcted myocardium has been considered to be a reliable indicator of major adverse cardiovascular events and resultant adverse left ventricular remodeling. The purpose of this paper is to review the clinical benefits of supersaturated oxygen therapy following PCI for ST-segment elevation myocardial infarction.

Reperfusion Microvascular Ischemia After Prolonged Coronary Occlusion: Implications And Treatment With Local Supersaturated Oxygen Delivery

Following a prolonged coronary arterial occlusion, heterogeneously scattered, focal regions of low erythrocyte flow are commonly found throughout the reperfused myocardium. Experimental studies have also demonstrated the presence of widespread, focally patchy regions of microvascular ischemia during reperfusion (RMI). However, the potential contribution of RMI to tissue viability and function has received little attention in the absence of practical clinical methods for its detection. In this review, the anatomic/functional basis of RMI is summarized, along with the evidence for its presence in reperfused myocardium. Advances in microcirculation research related to obstructive responses of vascular endothelial cells and blood elements to the effects of hypoxia and low shear stress are discussed, and a potential cycle of intensification of RMI from such responses and progressive loss of functional capillary density is presented. In capillaries with impaired erythrocyte flow, compensatory increases in the delivery of oxygen, because of its low solubility in plasma, are effective only at high partial pressures. As discussed herein, attenuation of the cycle with oxygen at hyperbaric levels in plasma is, very likely, responsible for improved tissue level perfusion noted experimentally. Observed clinical benefits from intracoronary SuperSaturated oxygen (SSO₂) delivery, including infarct size reduction, can be attributed to attenuation of RMI with improvement in microvascular blood flow.

Intravenous oxygen: a novel method of oxygen delivery in hypoxemic respiratory failure?

INTRODUCTION

Hypoxemic respiratory failure is a common problem in critical care. Current management strategies, including mechanical ventilation and extracorporeal membranous oxygenation, can be efficacious but these therapies put patients at risk for toxicities associated with invasive forms of support. Areas covered: In this manuscript, we discuss intravenous oxygen (IVO₂), a novel method to improve oxygen delivery that involves intravenous administration of a physiologic solution containing dissolved oxygen at hyperbaric concentrations. After a brief review of the physiology behind supersaturated fluids, we summarize the current evidence surrounding IVO₂. Expert commentary: Although not yet at the stage of clinical testing in the United States and Europe, IVO₂ has been used safely in Asia. Furthermore, preliminary laboratory data have been encouraging, suggesting that IVO₂ may play a role in the management of patients with hypoxemic respiratory failure in years to come. However, significantly more work needs to be done, including definitive evidence that such a therapy is safe, before it can be included in an intensivist's arsenal for hypoxemic respiratory failure.

Improved arterial blood oxygenation following intravenous infusion of cold supersaturated dissolved oxygen solution

BACKGROUND

One of the primary goals of critical care medicine is to support adequate gas exchange without iatrogenic sequelae. An emerging method of delivering supplemental oxygen is intravenously rather than via the traditional inhalation route. The objective of this study was to evaluate the gas-exchange effects of infusing cold intravenous (IV) fluids containing very high partial pressures of dissolved oxygen (>760 mm Hg) in a porcine model.

METHODS

Juvenile swines were anesthetized and mechanically ventilated. Each animal received an infusion of cold (13 °C) Ringer’s lactate solution (30 mL/kg/hour), which had been supersaturated with dissolved oxygen gas (39.7 mg/L dissolved oxygen, 992 mm Hg, 30.5 mL/L). Arterial blood gases and physiologic measurements were repeated at 15-minute intervals during a 60-minute IV infusion of the supersaturated dissolved oxygen solution. Each animal served as its own control.

RESULTS

Five swines (12.9 ± 0.9 kg) were studied. Following the 60-minute infusion, there were significant increases in PaO₂ and SaO₂ (P < 0.05) and a significant decrease in PaCO₂ (P < 0.05), with a corresponding normalization in arterial blood pH. Additionally, there was a significant decrease in core body temperature (P < 0.05) when compared to the baseline preinfusion state.

CONCLUSIONS

A cold, supersaturated dissolved oxygen solution may be intravenously administered to improve arterial blood oxygenation and ventilation parameters and induce a mild therapeutic hypothermia in a porcine model.

Pharmacologic Therapy for Reducing Myocardial Infarct Size in Clinical Trials

In patients with acute ST-segment elevation myocardial infarction, early, successful, and durable reperfusion therapy optimizes the likelihood of favorable outcomes. Fibrinolysis and primary percutaneous coronary intervention improve survival compared to no reperfusion therapy in large part by reducing infarct size (IS) and preserving left ventricular ejection fraction. There is direct correlation between IS and clinical outcomes. In this article, we will review some of the more promising pharmacological agents geared toward reduction in IS, discuss the major pathways that can lead to this desirable outcome, and evaluate the results of clinical trials performed with these and other compounds.

Conditioning the heart to prevent myocardial reperfusion injury during PPCI

For patients presenting with a ST-segment elevation myocardial infarction (STEMI), early myocardial reperfusion by primary percutaneous coronary intervention (PPCI) remains the most effective treatment strategy for limiting myocardial infarct size, preserving left ventricular systolic function, and preventing the onset of heart failure. Recent advances in PCI technology to improve myocardial reperfusion and the introduction of novel anti-platelet and anti-thrombotic agents to maintain the patency of the infarct-related coronary artery continue to optimize PPCI procedure. However, despite these improvements, STEMI patients still experience significant major adverse cardiovascular events. One major contributing factor has been the inability to protect the heart against the lethal myocardial reperfusion injury, which accompanies PPCI. Past attempts to translate cardioprotective strategies, discovered in experimental studies to prevent lethal myocardial reperfusion injury, into the clinical setting of PPCI have been disappointing. However, a number of recent proof-of-concept clinical studies suggest that the heart can be 'conditioned' to protect itself against lethal myocardial reperfusion injury, as evidenced by a reduction in myocardial infarct size. This can be achieved using either mechanical (such as ischaemic postconditioning, remote ischaemic preconditioning, therapeutic hypothermia, or hyperoxaemia) or pharmacological (such as cyclosporin-A, natriuretic peptide, exenatide) 'conditioning' strategies as adjuncts to PPCI. Furthermore, recent developments in cardiac magnetic resonance (CMR) imaging can provide a non-invasive imaging strategy for assessing the efficacy of these novel adjunctive therapies to PPCI in terms of key surrogate clinical endpoints such as myocardial infarct size, myocardial salvage, left ventricular ejection fraction, and the presence of microvascular obstruction or intramyocardial haemorrhage. In this article, we review the therapeutic potential of 'conditioning' to protect the heart against lethal myocardial reperfusion injury in STEMI patients undergoing PPCI.

Oxygen therapy in acute coronary syndrome: are the benefits worth the risk?

Oxygen supplementation is a standard treatment for all patients who present with acute coronary syndrome, regardless of oxygen saturation levels. Most of the data regarding the function of oxygen in myocardial infarction is based on a limited number of basic and clinical studies. We performed a systematic literature review that explores the basic and clinical data on the function of oxygen in ischaemic heart disease and myocardial infarction. This review discusses many aspects of oxygen treatment: (i) basic studies on the effects of oxygen in ischaemia and the potential cardiovascular effects of oxygen metabolites; (ii) clinical trials that have assessed the value of inhaled oxygen, supersaturated oxygen, and intracoronary injection of hyperoxaemic solutions in myocardial infarction; and (iii) the haemodynamic effects of oxygen in various clinical scenarios and its direct effects on the coronary vasculature. Our findings suggest that there are conflicting data on the effects of oxygen treatment. Further, the potential harmful effects of oxygen must be considered, particularly in myocardial infarction. These findings question the current guidelines and recommendations and emphasize the need for large clinical trials.

Lethal myocardial reperfusion injury: a necessary evil?

Despite being the most effective means of limiting infarct size, coronary reperfusion comes at a price and induces additional damage to the myocardium. Lethal reperfusion injury (death of myocytes that were viable at the time of reperfusion) is an increasingly acknowledged phenomenon. There are many interconnected mechanisms involved in this type of cell death. Calcium overload (generating myocyte hypercontracture), rapid recovery of physiological pH, neutrophil infiltration of the ischemic area, opening of the mitochondrial permeability-transition-pore (PTP), and apoptotic cell death are among the more important mechanisms involved in reperfusion injury. The activation of a group of proteins called reperfusion injury salvage kinases (RISK) pathway confers protection against reperfusion injury, mainly by inhibiting the opening of the mitochondrial PTP. Many interventions have been tested in human trials triggered by encouraging animal studies. In the present review we will explain in detail the main mechanism involved in reperfusion injury, as well as the various approaches (pre-clinical and human trials) performed targeting these mechanisms. Currently, no intervention has been consistently shown to reduce reperfusion injury in large randomized multicenter trials, but the research in this field is intense and the future is highly promising.

Hyperbaric oxygen: its application in cardiology: a historical perspective and personal journey

Hyperbaric oxygen (HBO) was first used by placing a patient with the "bends" in a pressure chamber and increasing the pressure to 3 atm with 100% oxygen. It was soon recognized that HBO could also facilitate wound healing in infected ischemic extremities. Before the pump oxygenator was developed, it was also shown to facilitate corrective surgery, especially in congenital heart disease. In 1997, after encouraging animal work, HBO therapy was used in conjunction with thrombolytics to reduce the magnitude of injury in patients with acute myocardial infarction. The benefit is probably due to the decrease in reperfusion injury, which has been shown to be a major cause of myocardial cell death when the culprit artery is opened with a catheter. The most recent development is to infuse saline saturated with HBO into the opened coronary artery immediately after angioplasty. An advantage of this treatment has been demonstrated in experimental animals and in man. Future applications of HBO treatment in cardiovascular disease await more research, but at this time it seems to have considerable promise.

Myocardial cooling for reperfusion injury protection achieved by organ specific hypothermic autologous perfusion

OBJECTIVE

Whole body hypothermia has been suggested to reduce myocardial injury in patients with ST-segment elevation myocardial infarction. Because of the large human thermal mass, induction of generalized hypothermia is slow and the technique has encountered considerable side effects. The aim was to develop and validate a method for regional cooling during myocardial reperfusion using hypothermic autologous blood.

DESIGN

In a myocardial ischemia-reperfusion pig model (n = 10), arterial blood was cooled in a closed circuit, and returned to the myocardium during reperfusion either through a perfusion catheter or through the guiding catheter. Myocardial temperatures were recorded using temperature electrodes.

RESULTS

Stabile regional myocardial cooling was induced without complications within 4 min. Both flow rate and blood temperature had significant impact on temperature in the reperfused myocardium but did not influence systemic temperature.

CONCLUSION

A method for organ specific hypothermic autologous arterial blood reperfusion has been developed and validated. The method is a simple and much faster alternative to systemic cooling and may have the potential to reduce myocardial injury in patients with acute myocardial infarction.

Oxygen therapy in stroke: past, present, and future

Oxygen is frequently administered to patients with suspected stroke. However, the role of oxygen therapy in ischemic stroke remains controversial in light of the failure of three clinical trials of hyperbaric oxygen therapy to show efficacy, and the fear of exacerbating oxygen free radical injury. The previous trials had several shortcomings, perhaps because they were designed on basis of anecdotal case reports and little preclinical data. Most animal studies concerning oxygen therapy in stroke have been conducted over the last 6 years. Emerging data suggests that hyperbaric and even normobaric oxygen therapy can be effective if used appropriately, and raises the tantalizing possibility that hyperoxia can be used to extend the narrow therapeutic time window for stroke thrombolysis. This article reviews the history, rationale, mechanisms of action and adverse effects of hyperoxia, the key results of previous hyperoxia studies, and the potential role of oxygen therapy in contemporary stroke treatment.

Percutaneous coronary intervention and the no-reflow phenomenon

No-reflow during percutaneous coronary intervention (PCI) is observed most commonly during saphenous vein graft intervention, rotational atherectomy and primary PCI for acute ST-elevation myocardial infarction. The contributions of distal embolization and ischemia/reperfusion injury to the pathogenesis of no-reflow vary in these settings, as does prevention and management. Prevention of no-reflow in these high-risk groups is the best treatment strategy, employing antiplatelet agents, vasodilators and/or mechanical devices to prevent distal embolization. Once mechanical factors are excluded as a cause for reduced epicardial flow, the treatment of established no-reflow is mainly pharmacologic, since the obstruction occurs at the level of the microvasculature. Compared with patients in whom no-reflow is transient, refractory no-reflow is associated with a markedly increased risk of 30-day mortality.

Acute Myocardial Infarction With Hyperoxemic Therapy (AMIHOT)

OBJECTIVES

This study sought to determine whether hyperoxemic reperfusion with aqueous oxygen (AO) improves recovery of ventricular function after percutaneous coronary intervention (PCI) for acute myocardial infarction (AMI).

BACKGROUND

Hyperbaric oxygen reduces myocardial injury and improves ventricular function when administered during ischemia-reperfusion.

METHODS

In a prospective, multicenter study, 269 patients with acute anterior or large inferior AMI undergoing primary or rescue PCI (<24 h from symptom onset) were randomly assigned after successful PCI to receive hyperoxemic reperfusion (treatment group) or normoxemic blood autoreperfusion (control group). Hyperoxemic reperfusion was performed for 90 min using intracoronary AO. The primary end points were final infarct size at 14 days, ST-segment resolution, and delta regional wall motion score index of the infarct zone at 3 months.

RESULTS

At 30 days, the incidence of major adverse cardiac events was similar between the control and AO groups (5.2% vs. 6.7%, p = 0.62). There was no significant difference in the incidence of the primary end points between the study groups. In post-hoc analysis, anterior AMI patients reperfused <6 h who were treated with AO had a greater improvement in regional wall motion (delta wall motion score index = 0.54 in control group vs. 0.75 in AO group, p = 0.03), smaller infarct size (23% of left ventricle in control group vs. 9% of left ventricle in AO group, p = 0.04), and improved ST-segment resolution compared with normoxemic controls.

CONCLUSIONS

Intracoronary hyperoxemic reperfusion was safe and well tolerated after PCI for AMI, but did not improve regional wall motion, ST-segment resolution, or final infarct size. A possible treatment effect was observed in anterior AMI patients reperfused <6 h of symptom onset.

Post-Reperfusion Myocardial Infarction

OBJECTIVES

The purpose of this study was to assess the safety and efficacy of the adenosine regulating agent (ARA) acadesine for reducing long-term mortality among patients with post-reperfusion myocardial infarction (MI).

BACKGROUND

No prospectively applied therapy exists that improves long-term survival after MI associated with coronary artery bypass graft (CABG) surgery-a robust model of ischemia/reperfusion injury. Pretreatment with the purine nucleoside autocoid adenosine mitigates the extent of post-ischemic reperfusion injury in animal models. Therefore, we questioned whether use of the ARA acadesine-by increasing interstitial adenosine concentrations in ischemic tissue-would improve long-term survival after post-reperfusion MI.

METHODS

At 54 institutions, 2,698 patients undergoing CABG surgery were randomized to receive placebo (n = 1,346) or acadesine (n = 1,352) by intravenous infusion (0.1 mg/kg/min; 7 h) and in cardioplegia solution (placebo or acadesine; 5 microg/ml). Myocardial infarction was prospectively defined as: 1) new Q-wave and MB isoform of creatine kinase (CK-MB) elevation (daily electrocardiography; 16 serial CK-MB measurements); or 2) autopsy evidence. Vital status was assessed over 2 years, and outcomes were adjudicated centrally.

RESULTS

Perioperative MI occurred in 100 patients (3.7%), conferring a 4.2-fold increase in 2-year mortality (p < 0.001) compared with those not suffering MI. Acadesine treatment, however, reduced that mortality by 4.3-fold, from 27.8% (15 of 54; placebo) to 6.5% (3 of 46; acadesine) (p = 0.006), with the principal benefit occurring over the first 30 days after MI. The acadesine benefit was similar among diverse subsets, and multivariable analysis confirmed these findings.

CONCLUSIONS

Acadesine is the first therapy proven to be effective for reducing the severity of acute post-reperfusion MI, substantially reducing the risk of dying over the 2 years after infarction.

Aqueous Oxygen Near the Homogeneous Nucleation Limit of Water: Stabilization With Submicron Capillaries

Previous studies have demonstrated that the metastability threshold of aqueous oxygen (AO) is inversely dependent on the internal diameter of capillary tubes used to deliver it into blood. The hypothesis was tested herein that significantly higher thresholds are attainable with capillaries having markedly smaller dimensions (submicron) than those previously studied. Water was equilibrated with oxygen over a 0.3- to 0.7-k bar range. Inert gases (argon, helium) facilitated studies at pressures to 2.5 k bar. An argon-ion laser was used to visualize fluorescein in the liquid effluent from silica capillaries that were tapered at the distal end to a submicron internal diameter (0.5 +/- 0.3 microns). During infusion of the fluorescent effluent into host water at 21 degrees C and atmospheric pressure, integrity of the effluent and lack of microbubbles were monitored by videomicroscopy. No microbubbles were noted at AO concentrations ranging from 7.5 to 12.8 ml O2/g (0.34 to 0.68 k bar, respectively) or in the aqueous argon effluent at concentrations to 14 ml Ar/g (0.75 k bar). For aqueous helium, effluent nucleation was not observed at a mean concentration of 13 +/- 3 ml He/g (2.0 +/- 0.5 k bar), with an upper value of 15.2 ml He/g (2.4 k bar). The data represent the highest values of the tensile strength of water ever observed and approximate its theoretical homogeneous nucleation limit. Thus, remarkably high metastable concentrations of AO and other gases are attainable with the use of submicron capillaries.

Hyperoxemic perfusion of the left anterior descending coronary artery after primary angioplasty in anterior ST-elevation myocardial infarction

OBJECTIVES

To assess left ventricle function recovery, ST-segment changes, and enzyme kinetic in ST-elevation myocardial infarction patients treated with intracoronary hyperoxemic perfusion (IHP) after primary percutaneous coronary intervention and compare them with the results obtained in control patients.

BACKGROUND

IHP has been shown to attenuate microvascular reperfusion injury, which may result in poor LV function recovery despite successful primary percutaneous coronary intervention.

METHODS

Twenty seven anterior ST-elevation myocardial infarction patients treated < or = 12 hr after symptom onset by primary percutaneous coronary intervention were subjected to selective IHP into the left anterior descending coronary artery for 90 min. They were compared with 24 anterior ST-elevation myocardial infarction control patients matched in clinical and angiographic characteristics and treated with conventional primary percutaneous coronary intervention. Left ventricular function recovery was evaluated by serial 2D contrast echocardiography.

RESULTS

Left anterior descending coronary artery recanalization was successful in all patients. After IHP (100% successful, duration 90 +/- 5.4 min), patients showed a 4.8 +/- 2.2 hr shorter time-to-peak creatine kinase release (P = 0.001), a shorter creatine kinase half-life period (23.4 +/- 8.9 hr vs. 30.5 +/- 5.8 hr, P = 0.006), and a higher rate of complete ST-segment resolution (78% vs. 42%, P = 0.01). A significant improvement of mean left ventricular ejection fraction (from (44 +/- 9)% to (55 +/- 11)%, P < 0.001) and wall motion score index (from 1.77 +/- 0.2 to 1.39 +/- 0.4, P < 0.001) was observed at 3 months in IHP patients only.

CONCLUSION

After successful primary coronary intervention, IHP is associated with significant left ventricular function recovery when compared to conventional treatment. Enzyme kinetic and ST-segment changes suggest faster and more complete microvascular reperfusion and may explain the salutary effects of this new therapy on left ventricular function.

Promising though not yet proven: Emerging strategies to promote myocardial salvage

Remarkable advances in our ability to achieve early and sustained culprit vessel patency in acute myocardial infarction have been satisfying, but our enthusiasm must be tempered by the knowledge that the overall treatment strategy often leaves an inadequate long term clinical result. Early success of percutaneous therapy as judged at angiography does not ensure recovery of normal left ventricular function, the most important determinant of survival in acute myocardial infarction. That congestive heart failure and death still complicate apparently successful percutaneous procedures underscores the need to develop novel therapies which salvage jeopardized myocardium, limit infarct size and preserve left ventricular function. An ever-increasing body of data demonstrates a multifactorial mechanism of myocyte injury and microvascular collapse and also demonstrates that these injuries seem to have a profound impact on long-term outcomes. Given these findings, microvascular protection during the acute event has become the focus of a variety of emerging technologies. The goal of these mechanical and pharmacologic therapies is the restoration of normal metabolic function at the myocyte level. The acute pathologic mechanisms which contribute to sustained left ventricular dysfunction despite angiographically successful revascularization will be reviewed as will be several strategies being developed to counter these pathologic mechanisms.

Attenuation of reperfusion microvascular ischemia by aqueous oxygen: experimental and clinical observations

It is being increasingly recognized that, in patients with acute myocardial infarction, angiographically successful recanalization of the occluded artery cannot be used as a reliable indicator of successful myocardial perfusion. Postischemic myocardial reperfusion is commonly associated with focal regions of microvascular impairment, even when global coronary artery flow is normal. This problem ranges in severity from microvascular stunning to no reflow, depending principally on the duration and severity of ischemia. Reperfusion microvascular ischemia is not an instantaneous single event that occurs just at the moment of reperfusion. Rather, it is a progressive process that increases with time. Of importance, it is associated with poor recovery of left ventricular (LV) function and a worsened clinical outcome at follow-up. An increasing body of experimental and clinical data suggests a valuable role for high concentrations of oxygen (O2), delivered directly to the coronary artery, in reducing microvascular injury. Recently, a catheter-based method has been developed for infusion of O2 , dissolved in a crystalloid solution at extremely high concentrations (ie, 1-3 mL O2 /g [aqueous oxygen {AO}]), into blood without bubble formation to provide hyperoxemic treatment of tissue ischemia. In experimental studies, AO hyperoxemia has been found to improve LV function and electrocardiographic evidence of ischemia. This is thought to be the result of augmentation of oxygen delivery in plasma. Marked improvement in myocardial flow has been consistently found. These observations may explain the improvement of LV function after AO treatment noted in clinical studies.

Myocardial and pulmonary effects of aqueous oxygen with acute hypoxia

BACKGROUND

The purpose of this paper was to evaluate myocardial and pulmonary effects of aqueous oxygen (AO) delivered directly into the pulmonary circulation in acute hypoxia.

METHODS

Six calves (2 months old, 68.0 +/- 2.2 kg) after general anesthesia, mechanical ventilation, and median sternotomy underwent total right heart bypass using fixed flow with continuous pressure and blood gas measurements in carotid and femoral arteries, left atrium, the coronary sinus and PA. Measurements of systemic and PA pressures and O2 saturations; myocardial O2 atrioventricular (AV) differences; and O2 extraction were made. After base line measurements, hypoxic ventilation reducing the mean arterial PO2 from 277 +/- 102 mm Hg to 47 +/- 4 mm Hg (p < 0.0005) was maintained for 30 minutes. Without changes in the hypoxic ventilation (mean arterial PO2 = 49 +/- 11 mm Hg) 3 ml/min of hyperbaric aqueous oxygen (AO = oxygen diluted in saline solution) was administered into the PA for 30 minutes. Pulmonary blood flow was maintained during the entire experiment (3.7 +/- 0.3 L/min).

RESULTS

Hypoxic ventilation significantly raised (p < 0.05) the systolic (30 +/- 7 vs 21 +/- 4 mm Hg), diastolic (20 +/- 6 vs 12 +/- 3 mm Hg), and mean (23 +/- 7 vs 15 +/- 3 mm Hg) PA pressure; PA/systemic pressure ratio for systolic (0.37 +/- 0.08 vs 0.25 +/- 0.06) and mean (0.56 +/- 0.19 vs 0.29 +/- 0.11) pressures; and pulmonary vascular resistance (PVR) (5.63 +/- 1.06 vs 3.53 +/- 0.75 U). Aqueous oxygen (AO) infusion significantly reduced (p < 0.05) the values obtained with hypoxic ventilation; systolic (23 +/- 5 vs 30 +/- 7 mm Hg), diastolic (11 +/- 4 vs 20 +/- 6 mm Hg), and mean (14 +/- 3 vs 23 +/- 7 mm Hg) PA pressure; PA/systemic pressure ratio for systolic (0.25 +/- 0.05 vs 0.37 +/- 0.08) and mean pressures (0.29 +/- 0.12 vs 0.56 +/- 0.19); and PVR (3.41 +/- 1.01 vs 5.63 +/- 1.06 U). AO infusion in the pulmonary circulation did not influence the myocardial O2 atrioventricular (AV) difference or the O2 extraction.

CONCLUSIONS

Infusion of hyperbaric AO solution into the PA can completely reverse the negative effects of acute hypoxia on the pulmonary circulation without affecting the myocardial metabolism.

Aqueous Oxygen Attenuation of Reperfusion Microvascular Ischemia in a Canine Model of Myocardial Infarction

Uncorrected microvascular ischemia may contribute to left ventricular impairment during reperfusion after prolonged coronary artery occlusion. Attenuation of such ischemia in microvessels with impaired erythrocyte flow may require delivery of oxygen at high levels in plasma. Intraarterial infusion of aqueous oxygen (AO) can be used in a site specific manner to achieve hyperoxemic levels of oxygenation in the perfusate. With this new approach, the hypothesis was tested that reperfusion microvascular ischemia can be attenuated. After a 90 min coronary balloon occlusion in a canine model, AO hyperoxemic intracoronary perfusion was performed for 90 min after a 30 min period of autoreperfusion. Control groups consisted of normoxemic reperfusion, both passive (autoreperfusion) and active (roller pump). A significant improvement in left ventricular ejection fraction (p < 0.05) at 2 hr of reperfusion was noted only in the AO hyperoxemia group (17 +/- 6% by two dimensional echo), without a significant reduction in the improvement 1 hr after termination of treatment. During AO hyperoxemic perfusion, ECG ST segment isoelectric deviation normalized, and frequency of ventricular premature contractions was significantly reduced, in contrast to the autoreperfusion control group (p < 0.05). Microvascular blood flow, measured as the ischemic/normal left ventricular segment ratio by radiolabeled microspheres immediately after AO hyperoxemic perfusion, was double the value of the autoreperfusion control group at 2 hr of reperfusion (p < 0.05). We conclude that reperfusion microvascular ischemia is attenuated by intracoronary AO hyperoxemic perfusion and acutely improves left ventricular function in this model.

Real-time assessment of myocardial perfusion during balloon angioplasty of the left anterior descending coronary artery

Balloon occlusion and release during elective percutaneous coronary intervention (PCI) provides a unique opportunity to study dynamic temporal alterations in myocardial perfusion in a controlled setting. These changes in flow and volume mimic those that occur during presentation with, and successful therapy of, ST-segment elevation acute myocardial infarction (AMI). Eleven patients underwent myocardial contrast echocardiography (MCE) using a continuous infusion of Definity at baseline, during coronary occlusion, and during reactive hyperemia immediately after balloon deflation. Fifty separate flow state sequences were acquired, and off-line analysis was performed to determine myocardial contrast intensity within a region of interest in the distribution of the left anterior descending artery (LAD). A reader blinded to flow state also performed qualitative evaluation (perfusion or lack of perfusion). Quantitative analysis demonstrated significant differences in myocardial contrast intensity by flow state (p = 0.0001 for occlusion vs reperfusion). Qualitative assessment demonstrated a high rate of correct classification (92%). Real-time myocardial perfusion assessment using MCE accurately differentiates coronary occlusion and reactive hyperemia in humans by qualitative and quantitative assessment. This technique may be clinically useful in assessing the efficacy of thrombolytic therapy in ST-segment elevation AMI and in clinical trial assessment of new drugs and devices aimed at limitation of infarct size.

Acute myocardial infarction

Acute myocardial infarction is a common disease with serious consequences in mortality, morbidity, and cost to the society. Coronary atherosclerosis plays a pivotal part as the underlying substrate in many patients. In addition, a new definition of myocardial infarction has recently been introduced that has major implications from the epidemiological, societal, and patient points of view. The advent of coronary-care units and the results of randomised clinical trials on reperfusion therapy, lytic or percutaneous coronary intervention, and chronic medical treatment with various pharmacological agents have substantially changed the therapeutic approach, decreased in-hospital mortality, and improved the long-term outlook in survivors of the acute phase. New treatments will continue to emerge, but the greatest challenge will be to effectively implement preventive actions in all high-risk individuals and to expand delivery of acute treatment in a timely fashion for all eligible patients.

Hyperoxemic perfusion for treatment of reperfusion microvascular ischemia in patients with myocardial infarction

In patients with acute myocardial infarction (AMI) primary angioplasty and stent placement is a more effective and better tolerated treatment than thrombolysis, and therefore, when logistics allow, this treatment is preferred and routinely used. However, successful reopening of an occluded coronary artery does not necessarily lead to recovery of left ventricular (LV) function. Post-AMI reduction in contractile function and ventricular remodeling may result in heart failure. There is evidence that reduced contractile function in the infarct zone is related to poor microvascular perfusion even after normalization of large-vessel flow by angiographic criteria following coronary recanalization. Failure to re-establish adequate tissue perfusion may be because of reperfusion injury, ischemia-induced microvascular damage, and plugging of the microcirculation by thrombus and plaque during mechanical recanalization. Experimental data support the hypothesis that reperfusion microvascular ischemia contributes to myocardial tissue injury over a prolonged time period. Hyperbaric oxygen therapy (HBO) attenuates microvascular dysfunction and reperfusion microvascular ischemia, as demonstrated in both experimental models and patients with AMI. However, treating patients in an HBO chamber or with a conventional oxygenator is impractical and difficult. Aqueous oxygen (AO) is a newly developed solution containing extremely high oxygen concentrations (1-3 ml O(2)/mL saline). The AO system mixes AO solution with a patient's blood from an arterial puncture and delivers the hyperoxemic blood to targeted ischemic myocardium via an infusion catheter for regional correction of hypoxemia and production of hyperoxemia. The system precisely controls the level of pO(2) without clinically significant microbubble formation. Hyperoxemic coronary infusion of AO in experimental models of AMI improved LV function and reduced infarct size compared with normoxemic controls,very likely as a result of microvascular blood flow improvement. The first clinical experiences with intracoronary infusion of AO solution demonstrated the therapy to be a safe and well tolerated in the setting of AMI after successful primary percutaneous transluminal coronary angioplasty. Its use was associated with significant progressive improvement in LV function as measured by ejection fraction and wall motion score index. Interestingly, such improvement was primarily due to functional recovery of infarct zone contractility. A larger randomized trial is currently underway to define the role of hyperoxemic coronary infusion in patients with AMI.

Pharmacologic reperfusion therapy for acute myocardial infarction

Acute myocardial infarction (MI) remains a significant problem in terms of morbidity, mortality and healthcare costs. Pharmacologic reperfusion therapies for MI are becoming increasingly complex. This review therefore places contemporary pharmacologic MI developments into perspective. An historical overview of pharmacologic reperfusion therapy for MI is provided, followed by an analysis of current limitations, treatment options, and present and likely future pharmacologic therapies. Adjunctive percutaneous and other treatments are also discussed, to clarify what is becoming a rapidly changing field.