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

Reperfusion Injury in Patients With Acute Myocardial Infarction: JACC Scientific Statement

Despite impressive improvements in the care of patients with ST-segment elevation myocardial infarction, mortality remains high. Reperfusion is necessary for myocardial salvage, but the abrupt return of flow sets off a cascade of injurious processes that can lead to further necrosis. This has been termed myocardial ischemia-reperfusion injury and is the subject of this review. The pathologic and molecular bases for myocardial ischemia-reperfusion injury are increasingly understood and include injury from reactive oxygen species, inflammation, calcium overload, endothelial dysfunction, and impaired microvascular flow. A variety of pharmacologic strategies have been developed that have worked well in preclinical models and some have shown promise in the clinical setting. In addition, there are newer mechanical approaches including mechanical unloading of the heart prior to reperfusion that are in current clinical trials.

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.

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.

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.

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.

Hyperoxia Is Associated With Poor Outcomes in Pediatric Cardiac Patients Supported on Venoarterial Extracorporeal Membrane Oxygenation

OBJECTIVES

Patients who require venoarterial extracorporeal membrane oxygenation because of cardiac failure frequently have supranormal blood oxygen tensions (hyperoxia). Recent studies have suggested worse outcomes in patients with hyperoxia after resuscitation from cardiac or respiratory arrests, presumably because of oxidative stress. There are limited data regarding the effect of hyperoxia on outcomes in pediatric patients on venoarterial extracorporeal membrane oxygenation.

DESIGN

Retrospective chart review.

SETTING

Pediatric cardiothoracic ICU.

PATIENTS

Cardiac surgery patients less than 1 year old requiring venoarterial extracorporeal membrane oxygenation in the postoperative period from 2007 to 2013.

MEASUREMENTS AND MAIN RESULTS

In 93 infants (median time on extracorporeal membrane oxygenation, 5 d), mortality at 30 days post surgery (primary outcome) was 38%. Using a receiver operating characteristic curve, a mean PaO2 of 193 mm Hg in the first 48 hours of extracorporeal membrane oxygenation was determined to have good discriminatory ability with regard to 30-day mortality. Univariate analysis identified a mean PaO2 greater than 193 mm Hg (p = 0.001), longer cardiopulmonary bypass times (p = 0.09), longer duration of extracorporeal membrane oxygenation (p < 0.0001), and higher extracorporeal membrane oxygenation pump flows (p = 0.052) as possible risk factors for 30-day mortality. In multivariable analysis controlling for the variables listed above, a mean PaO2 greater than 193 mm Hg remained an independent risk factor for mortality (p = 0.03). In addition, a mean PaO2 greater than 193 mm Hg was associated with the need for renal dialysis (p = 0.02) but not with neurologic injury (p = 0.41) during the hospitalization.

CONCLUSIONS

In infants with congenital heart disease who are placed on venoarterial extracorporeal membrane oxygenation postoperatively, hyperoxia (defined as a mean PaO2 > 193 mm Hg in the first 48 hr of extracorporeal membrane oxygenation) was an independent risk factor for 30-day mortality after surgery. Future studies are needed to delineate the causative or associative role of hyperoxia with outcomes, especially in children with baseline cyanosis who may be more susceptible to the effects of oxidative stress.

Approaches to Improving Cardiac Structure and Function During and After an Acute Myocardial Infarction: Acute and Chronic Phases

While progress has been made in improving survival following myocardial infarction, this injury remains a major source of mortality and morbidity despite modern reperfusion therapy. While one approach has been to develop therapies to reduce lethal myocardial cell reperfusion injury, this concept has not translated to the clinics, and several recent negative clinical trials raise the question of whether reperfusion injury is important in humans undergoing reperfusion for acute ST segment elevation myocardial infarction. Therapy aimed at reducing myocardial cell death while the myocytes are still ischemic is more likely to further reduce myocardial infarct size. Developing new therapies to further reduce left ventricular remodeling after the acute event is another approach to preserving structure and function of the heart after infarction. Such therapy may include chronic administration of pharmacologic agents and/or therapies developed from the field of regenerative cardiology, including cellular or non-cellular materials such as extracellular matrix. The optimal therapy will be to administer agents that both reduce myocardial infarct size in the acute phase of infarction as well as reduce adverse left ventricular remodeling during the chronic or healing phase of myocardial infarction. Such a dual approach will help optimize the preservation of both cardiac structure and function.

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.

Effect of Supersaturated Oxygen Delivery on Infarct Size After Percutaneous Coronary Intervention in Acute Myocardial Infarction

Background— Myocardial salvage is often suboptimal after percutaneous coronary intervention in ST-segment elevation myocardial infarction. Posthoc subgroup analysis from a previous trial (AMIHOT I) suggested that intracoronary delivery of supersaturated oxygen (SSO 2 ) may reduce infarct size in patients with large ST-segment elevation myocardial infarction treated early.

Methods and Results— A prospective, multicenter trial was performed in which 301 patients with anterior ST-segment elevation myocardial infarction undergoing percutaneous coronary intervention within 6 hours of symptom onset were randomized to a 90-minute intracoronary SSO 2 infusion in the left anterior descending artery infarct territory (n=222) or control (n=79). The primary efficacy measure was infarct size in the intention-to-treat population (powered for superiority), and the primary safety measure was composite major adverse cardiovascular events at 30 days in the intention-to-treat and per-protocol populations (powered for noninferiority), with Bayesian hierarchical modeling used to allow partial pooling of evidence from AMIHOT I. Among 281 randomized patients with tc-99m-sestamibi single-photon emission computed tomography data in AMIHOT II, median (interquartile range) infarct size was 26.5% (8.5%, 44%) with control compared with 20% (6%, 37%) after SSO 2 . The pooled adjusted infarct size was 25% (7%, 42%) with control compared with 18.5% (3.5%, 34.5%) after SSO 2 ( P Wilcoxon =0.02; Bayesian posterior probability of superiority, 96.9%). The Bayesian pooled 30-day mean (�SE) rates of major adverse cardiovascular events were 5.0�1.4% for control and 5.9�1.4% for SSO 2 by intention-to-treat, and 5.1�1.5% for control and 4.7�1.5% for SSO 2 by per-protocol analysis (posterior probability of noninferiority, 99.5% and 99.9%, respectively).

Conclusions— Among patients with anterior ST-segment elevation myocardial infarction undergoing percutaneous coronary intervention within 6 hours of symptom onset, infusion of SSO 2 into the left anterior descending artery infarct territory results in a significant reduction in infarct size with noninferior rates of major adverse cardiovascular events at 30 days.

Clinical Trial Registration— clinicaltrials.gov Identifier: NCT00175058

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.

Impact of cardiac and renal dysfunction on inhospital morbidity and mortality of patients with acute myocardial infarction undergoing primary angioplasty

BACKGROUND

Risk stratification of patients with ST-elevation myocardial infarction (STEMI) undergoing primary angioplasty is important in order to predict outcomes and to delineate targeted therapeutic strategies. Although the prognostic implications of reduced left ventricular ejection fraction (LVEF) and creatinine clearance (CrCl) have been recognized, the clinical and prognostic impact of their combination has never been prospectively evaluated.

METHODS

We stratified 467 patients with STEMI undergoing primary angioplasty according to LVEF and CrCl values at admission: CrCl > 60 mL/min and LVEF > 40% (group 1, n = 261); CrCl < or = 60 mL/min and LVEF > 40% (group 2, n = 113); CrCl > 60 mL/min and LVEF < or = 40% (group 3, n = 60); CrCl < or = 60 mL/min and LVEF < or = 40% (group 4, n = 33).

RESULTS

Inhospital mortality was different in the 4 groups (1% in group 1, 3% in group 2, 15% in group 3, 30% in group 4) (P < .001). The incidence of combined end point of death, acute pulmonary edema, cardiogenic shock, and acute renal failure requiring mechanical support increased progressively from group 1 to group 4 (5%, 17%, 33%, and 48%, respectively) (P < .001). We found a significant gradient of risk in terms of inhospital mortality and combined end point when patients outcome was evaluated according to the presence of both normal LVEF and CrCl (group 1), impairment in only 1 of these 2 parameters (group 2 and 3 pooled together), and combined LVEF and CrCl reductions (group 4).

CONCLUSIONS

Reduced LVEF and CrCl are strong independent predictors of increased inhospital morbidity and mortality, and their combined evaluation provides a simple tool for early risk stratification in patients with STEMI treated with primary angioplasty.

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.