Concordant improvements in coronary flow reserve and ST-segment resolution during percutaneous coronary intervention for acute myocardial infarction: a benefit of postconditioning

Myocardial Ischemia-Reperfusion Injury: Unraveling Pathophysiology, Clinical Manifestations, and Emerging Prevention Strategies

Myocardial ischemia-reperfusion injury (MIRI) remains a challenge in the context of reperfusion procedures for myocardial infarction (MI). While early revascularization stands as the gold standard for mitigating myocardial injury, recent insights have illuminated the paradoxical role of reperfusion, giving rise to the phenomenon known as ischemia-reperfusion injury. This comprehensive review delves into the intricate pathophysiological pathways involved in MIRI, placing a particular focus on the pivotal role of endothelium. Beyond elucidating the molecular intricacies, we explore the diverse clinical manifestations associated with MIRI, underscoring its potential to contribute substantially to the final infarct size, up to 50%. We further navigate through current preventive approaches and highlight promising emerging strategies designed to counteract the devastating effects of the phenomenon. By synthesizing current knowledge and offering a perspective on evolving preventive interventions, this review serves as a valuable resource for clinicians and researchers engaged in the dynamic field of MIRI.

Effect of ischaemic postconditioning on markers of myocardial injury in ST-elevation myocardial infarction: a meta-analysis

OBJECTIVES

This study aimed to perform a meta-analysis of the short-term impact of ischaemic postconditioning (IPoC) on myocardial injury in ST elevation myocardial infarction (STEMI) using surrogate cardiac biomarkers.

METHODS

Eligible studies were identified using several article databases. Randomised controlled trials published between 1 January 2000 and 1 December 2021 comparing IPoC to standard of therapy in STEMI patients were included in the search. Outcomes included surrogates of myocardial injury, specifically peak troponin, creatine-kinase (CK) and CK myoglobin binding (CK-MB) enzyme levels.

RESULTS

11 articles involving 1273 patients reported on CK-MB and 8 studies involving 505 patients reported on CK. Few studies used troponin as an outcome, thus, a subanalysis of troponin dynamics was not performed. Meta-regression analysis demonstrated no significant effect of IPoC on peak CK-MB (effect size -0.41, 95% CI -1.15 to 0.34) or peak CK (effect size -0.42, 95% CI -1.20 to 0.36). Linear regression analysis demonstrated a significant correlation between a history of smoking and CK-MB in the IPoC group (p=0.038).

CONCLUSIONS

IPoC does not seem to protect against myocardial injury in STEMI, except possibly in smokers. These results resonate with some studies using imaging techniques to ascertain myocardial damage. More research using troponin and cardiac imaging should be pursued to better assess the effects of IPoC on cardiovascular outcomes in STEMI.

Ischemic Postconditioning Confers No Benefit to Left Ventricular Systolic Function: A Meta-Analysis of Cardiac Magnetic Resonance Imaging Results

Ischemic postconditioning (IPoC) is a technique suggested to reduce reperfusion injury in patients suffering acute ST-elevation myocardial infarction (STEMI), although its use is highly controversial. This meta-analysis aimed to evaluate the effect of IPoC with percutaneous coronary intervention in patients with acute STEMI, as measured by follow-up left ventricular ejection fraction (LVEF) on cardiac magnetic resonance imaging. The investigators searched PubMed, Embase, and Web of Science for all randomized controlled trials published during the last 2 decades. After the removal of duplicates, 2,021 articles from online databases had been identified using relevant search criteria. The included randomized controlled trials had studied patients with acute STEMI and Thrombolysis in Myocardial Infarction flow 0 to 1 at presentation and had measured follow-up LVEF using cardiac magnetic resonance imaging. Overall, 11 studies (n = 1,339 patients) qualified for inclusion. In each study, the control group did not differ significantly from the experimental group. The pooled data from included studies were analyzed using standardized mean difference between IPoC and control groups, and the 95% confidence interval for LVEF; the results were visualized using a forest plot. Bivariate regression analyses and 1-way analyses of LVEF coefficient ratios were done to isolate for various clinical and procedural parameters. An analysis of pooled data of the IPoC (n = 674) and control (n = 665) groups showed that IPoC did not significantly impact follow-up LVEF (using standardized mean difference 0.10, 95% confidence interval 0.00 to 0.21). Further analysis showed that IPoC did not improve follow-up LVEF when isolating for relevant clinical and procedural parameters. In conclusion, the use of IPoC as an adjunctive therapy to percutaneous coronary intervention seemingly provides no benefit to left ventricular systolic function, as quantified with cardiac magnetic resonance imaging, in patients with acute STEMI with Thrombolysis in Myocardial Infarction flow 0 to 1.

Signaling Pathways Involved in Myocardial Ischemia-Reperfusion Injury and Cardioprotection: A Systematic Review of Transcriptomic Studies in Sus scrofa

Myocardial damage in acute myocardial infarctions (AMI) is primarily the result of ischemia−reperfusion injury (IRI). Recognizing the timing of transcriptional events and their modulation by cardioprotective strategies is critical to address the pathophysiology of myocardial IRI. Despite the relevance of pigs for translational studies of AMI, only a few have identified how transcriptomic changes shape cellular signaling pathways in response to injury. We systematically reviewed transcriptomic studies of myocardial IRI and cardioprotection in Sus scrofa. Gene expression datasets were analyzed for significantly enriched terms using the Enrichr analysis tool, and statistically significant results (adjusted p-values of <0.05) for Signaling Pathways, Transcription Factors, Molecular Functions, and Biological Processes were compared between eligible studies to describe how these dynamic changes transform the myocardium from an injured and inflamed tissue into a scar. Then, we address how cardioprotective interventions distinctly modulate the myocardial transcriptome and discuss the implications of uncovering gene regulatory networks for cardiovascular pathologies and translational applications.

Comparison of infarction size, complete ST-segment resolution incidence, mortality and re-infarction and target vessel revascularization between remote ischemic conditioning and ischemic postconditioning in ST-segment elevation myocardial infarction patients undergoing primary percutaneous coronary intervention

Introduction

Due to higher morbidity and mortality, ST-segment elevation myocardial infarction (STEMI) causes many public health problems.

Aim

To observe effects of remote ischemic conditioning (RIC) and ischemic postconditioning (IPC) on patients diagnosed as STEMI undergoing primary percutaneous coronary intervention (pPCI).

Material and methods

This meta-analysis was conducted using indirect comparison by conducting a network meta-analysis (NMA). We conducted searches by utilizing PubMed and the other databases to identify randomized controlled trials (RCTs) that described IPC or RIC treated patients diagnosed with STEMI during processes of pPCI. Enzymatic infarct size and infarction size were evaluated and cardiac events were assessed during the follow-up.

Results

Pooled results showed that lower enzymatic infarction size was associated with the RIC group compared to the IPC group (IPC vs. RIC: standardized mean difference (SMD) = 1.126; 95% confidence interval (CI): 0.756–1.677). Compared with IPC, RIC significantly reduced infarction size, which was assessed using cardiac magnetic resonance (CMR) (SMD = 1.113; 95% CI: 0.674–1.837). We noted a potential toward greater complete ST-segment resolution in RIC patients compared with IPC patients (odds ratio (OR) = 0.821; 95% CI: 0.166–4.051). No significant difference existed in all-cause mortality (OR = 2.211; 95% CI: 0.845–5.784), Target vessel revascularization (TVR) (OR = 0.045; 95% CI: 0.001–.662) or re-infarction (OR = 1.763; 95% CI: 0.741–4.193).

Conclusions

This meta-analysis suggested RIC was correlated with significantly smaller infarction size compared to IPC. No significant superiority between RIC and IPC has been observed in this study on cSTR incidence, mortality and re-infarction or TVR.

Myocardial ischaemia-reperfusion injury and cardioprotection in perspective

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

Effects of ischaemic postconditioning on outcomes of patients with ST-segment elevation myocardial infarction who underwent primary percutaneous coronary intervention: a meta-analysis

OBJECTIVE

The aim of this meta-analysis was to evaluate the effects of ischaemic postconditioning (IPC) therapy on hard clinical endpoints in ST-segment elevation myocardial infarction (STEMI) patients who underwent primary percutaneous coronary intervention (PPCI).

DESIGN

Systematic review and meta-analysis to evaluate the effects of IPC on the outcomes of patients with STEMI.

DATA SOURCES

PubMed, Embase and the Cochrane Library were systematically searched for relevant articles published prior to May 1, 2018.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Randomised trials comparing conventional PPCI to PPCI combined with IPC in STEMI patients were included. The primary endpoint was heart failure. Secondary endpoints were all-cause mortality and major adverse cardiac events (MACE), including cardiac death, heart failure and MI. The Cochrane Reviewer's Handbook 4.2 was used to assess the risk of bias.

DATA EXTRACTION AND SYNTHESIS

Relevant data were extracted by two independent investigators. We derived pooled risk ratios (RRs) with random effects models. Sensitivity and subgroup analyses were performed.

RESULTS

Ten studies that had enrolled 3137 patients were included. PPCI combined with IPC failed to reduce heart failure (RR: 0.88, 95% CI: 0.61 to 1.26, p=0.47; absolute risk: 3.64% in the IPC group and 4.11% in the PPCI only group), all-cause mortality (RR: 0.94, 95% CI: 0.69 to 1.27, p=0.68; absolute risk: 5.07% in the IPC group and 5.27% in the PPCI onlygroup), MACE (RR: 1.05, 95% CI: 0.83 to 1.32, p=0.69; absolute risk: 9.37% in the IPC group and 8.93% in the PPCI only group), cardiac death (RR: 1.28, 95% CI: 0.85 to 1.93, p=0.24; absolute risk: 4.28% in the IPC group and 3.25% in the PPCI only group) and MI (RR: 1.08, 95% CI: 0.38 to 3.12, p=0.88; absolute risk: 3.61% in the IPC group and 3.44% in the PPCI only group).

CONCLUSIONS

IPC combined with PPCI does not reduce heart failure, MACE and all-cause mortality compared with traditional PPCI in patients with STEMI.

TRIAL REGISTRATION NUMBER

CRD42017063959.

Clinical translation of myocardial conditioning

Rapid admission and acute interventional treatment combined with modern antithrombotic pharmacologic therapy have improved outcomes in patients with ST elevation myocardial infarction. The next major target to further advance outcomes needs to address ischemia-reperfusion injury, which may contribute significantly to the final infarct size and hence mortality and postinfarction heart failure. Mechanical conditioning strategies including local and remote ischemic pre-, per-, and postconditioning have demonstrated consistent cardioprotective capacities in experimental models of acute ischemia-reperfusion injury. Their translation to the clinical scenario has been challenging. At present, the most promising mechanical protection strategy of the heart seems to be remote ischemic conditioning, which increases myocardial salvage beyond acute reperfusion therapy. An additional aspect that has gained recent focus is the potential of extended conditioning strategies to improve physical rehabilitation not only after an acute ischemia-reperfusion event such as acute myocardial infarction and cardiac surgery but also in patients with heart failure. Experimental and preliminary clinical evidence suggests that remote ischemic conditioning may modify cardiac remodeling and additionally enhance skeletal muscle strength therapy to prevent muscle waste, known as an inherent component of a postoperative period and in heart failure. Blood flow restriction exercise and enhanced external counterpulsation may represent cardioprotective corollaries. Combined with exercise, remote ischemic conditioning or, alternatively, blood flow restriction exercise may be of aid in optimizing physical rehabilitation in populations that are not able to perform exercise practice at intensity levels required to promote optimal outcomes.

The pathophysiology of acute myocardial infarction and strategies of protection beyond reperfusion: a continual challenge

The incidence of ST segment elevation myocardial infarction (STEMI) has decreased over the last two decades in developed countries, but mortality from STEMI despite widespread access to reperfusion therapy is still substantial as is the development of heart failure, particularly among an expanding older population. In developing countries, the incidence of STEMI is increasing and interventional reperfusion is often not available. We here review the pathophysiology of acute myocardial infarction and reperfusion, notably the temporal and spatial evolution of ischaemic and reperfusion injury, the different modes of cell death, and the resulting coronary microvascular dysfunction. We then go on to briefly characterize the cardioprotective phenomena of ischaemic preconditioning, ischaemic postconditioning, and remote ischaemic conditioning and their underlying signal transduction pathways. We discuss in detail the attempts to translate conditioning strategies and drug therapy into the clinical setting. Most attempts have failed so far to reduce infarct size and improve clinical outcomes in STEMI patients, and we discuss potential reasons for such failure. Currently, it appears that remote ischaemic conditioning and a few drugs (atrial natriuretic peptide, exenatide, metoprolol, and esmolol) reduce infarct size, but studies with clinical outcome as primary endpoint are still underway.

cGMP-Elevating Compounds and Ischemic Conditioning Provide Cardioprotection Against Ischemia and Reperfusion Injury via Cardiomyocyte-Specific BK Channels

BACKGROUND

The nitric oxide-sensitive guanylyl cyclase/cGMP-dependent protein kinase type I signaling pathway can afford protection against the ischemia/reperfusion injury that occurs during myocardial infarction. Reportedly, voltage and Ca²⁺-activated K⁺ channels of the BK type are stimulated by cGMP/cGMP-dependent protein kinase type I, and recent ex vivo studies implicated that increased BK activity favors the survival of the myocardium at ischemia/reperfusion. It remains unclear, however, whether the molecular events downstream of cGMP involve BK channels present in cardiomyocytes or in other cardiac cell types.

METHODS

Gene-targeted mice with a cardiomyocyte- or smooth muscle cell-specific deletion of the BK (CMBK or SMBK knockouts) were subjected to the open-chest model of myocardial infarction. Infarct sizes of the conditional mutants were compared with litter-matched controls, global BK knockout, and wild-type mice. Cardiac damage was assessed after mechanical conditioning or pharmacological stimulation of the cGMP pathway and by using direct modulators of BK. Long-term outcome was studied with respect to heart functions and cardiac fibrosis in a chronic myocardial infarction model.

RESULTS

Global BK knockouts and CMBK knockouts, in contrast with SMBK knockouts, exhibited significantly larger infarct sizes compared with their respective controls. Ablation of CMBK resulted in higher serum levels of cardiac troponin I and elevated amounts of reactive oxygen species, lower phosphorylated extracellular receptor kinase and phosphorylated AKT levels and an increase in myocardial apoptosis. Moreover, CMBK was required to allow beneficial effects of both nitric oxide-sensitive guanylyl cyclase activation and inhibition of the cGMP-degrading phosphodiesterase-5, ischemic preconditioning, and postconditioning regimens. To this end, after 4 weeks of reperfusion, fibrotic tissue increased and myocardial strain echocardiography was significantly compromised in CMBK-deficient mice.

CONCLUSIONS

Lack of CMBK channels renders the heart more susceptible to ischemia/reperfusion injury, whereas the pathological events elicited by ischemia/reperfusion do not involve BK in vascular smooth muscle cells. BK seems to permit the protective effects triggered by cinaciguat, riociguat, and different phosphodiesterase-5 inhibitors and beneficial actions of ischemic preconditioning and ischemic postconditioning by a mechanism stemming primarily from cardiomyocytes. This study establishes mitochondrial CMBK channels as a promising target for limiting acute cardiac damage and adverse long-term events that occur after myocardial infarction.

The Coronary Circulation as a Target of Cardioprotection

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

Ischemic postconditioning during primary percutaneous coronary intervention

BACKGROUND

Although some studies have shown potential benefit for ischemic postconditioning (IPoC) during primary percutaneous coronary intervention (PCI) in improving surrogate markers of reperfusion and infarction size, the benefit of this approach on clinical outcomes remains unknown.

METHODS AND RESULTS

Electronic databases were searched for randomized clinical trials that compared IPoC versus conventional treatment during primary PCI. Random effects DerSimonian-Laird risk ratios (RR) were calculated for different clinical and surrogate outcomes. The main outcome of this analysis was all-cause mortality. A total of 25 trials involving 3,619 patients were included in the analysis. At a mean follow up of 14 months (95% confidence interval (CI) 8.6-19.4 months), the incidence of all-cause mortality was 4.9% [95% CI 3.8-6.0%] in the IPoC group versus 3.8% [95% CI 1.9-5.7%] in the control group (RR 0.92, 95% CI 0.68-1.24, P = 0.74). The risk of reinfarction (2.7% [95% CI 1.1-4.3%] vs. 2.3% [0.6-4.0%]; RR 1.29, 95% CI 0.62-2.68, P = 0.72), heart failure (3.6% [95% CI 2.0-5.1%] vs. 5.7% [95% CI 3.3-8.2%]; RR 0.77, 95% CI 0.58-1.06, P = 0.24), target vessel revascularization (3.2% [95% CI 1.7-4.7%] vs. 2.4% [95% CI 1.4-3.3%]; RR 1.40, 95% CI 0.90-2.20, P = 0.20), and stent thrombosis (2.4% [95% CI 1.1-3.8%] vs. 1.8% [95% CI 0.5-3.2%]); RR 1.50, 95% CI 0.60-3.70, P = 0.40) was similar in both groups.

CONCLUSIONS

IPoC does not appear to reduce the risk of clinical adverse events in patients with ST-elevation myocardial infarction undergoing primary PCI. © 2017 Wiley Periodicals, Inc.

State of the Science of Cardioprotection: Challenges and Opportunities— Proceedings of the 2010 NHLBI Workshop on Cardioprotection

The National Heart, Lung, and Blood Institute convened a Workshop on September 20-21, 2010, “New Horizons in Cardioprotection,” to identify future research directions for cardioprotection against ischemia and reperfusion injury. Since the early 1970s, there has been evidence that the size of a myocardial infarction could be altered by various interventions. Early coronary artery reperfusion has been an intervention that consistently reduces myocardial infarct size in animal models as well as humans. Most cardiologists agree that the best way to treat acute ST-segment elevation myocardial infarction is to reperfuse the infarct artery as soon as possible and to keep the infarct artery patent. In general, stenting is superior to angioplasty, which is superior to thrombolysis. There is no accepted adjunctive therapy to acutely limit myocardial infarct size along with reperfusion that is routinely used in clinical practice. In the Kloner experimental laboratory, some adjunctive therapies have reproducibly limited infarct size (regional hypothermia, preconditioning, cariporide, combinations of the above, remote preconditioning, certain adenosine agonists, and late sodium current blockade). In clinical trials, a host of pharmacologic adjunctive therapies have failed to either reduce infarct size or improve clinical outcome. Potential reasons for the failure of these trials are discussed. However, some adjunctive therapies have shown promise in data subanalyses or subpopulations of clinical trials (adenosine, therapeutic hypothermia, and hyperoxemic reperfusion) or in small clinical trials (atrial natriuretic peptide, ischemic postconditioning, and cyclosporine, the mitochondrial permeability transition pore inhibitor). A recent clinical trial with remote conditioning induced by repetitive inflation of a brachial artery cuff begun prior to hospitalization showed promise in improving myocardial salvage and there are several reports in the cardiothoracic literature, suggesting that remote preconditioning protects hearts during surgery. Thus, in 2011, there is hope that applying some of the body’s own conditioning mechanisms may provide protection against ischemic damage.

Ultrasonic Transducer-Guided Electrochemical Impedance Spectroscopy to Assess Lipid-Laden Plaques

Plaque rupture causes acute coronary syndromes and stroke. Intraplaque oxidized low density lipoprotein (oxLDL) is metabolically unstable and prone to induce rupture. We designed an intravascular ultrasound (IVUS)-guided electrochemical impedance spectroscopy (EIS) sensor to enhance the detection reproducibility of oxLDL-laden plaques. The flexible 2-point micro-electrode array for EIS was affixed to an inflatable balloon anchored onto a co-axial double layer catheter (outer diameter = 2 mm). The mechanically scanning-driven IVUS transducer (45 MHz) was deployed through the inner catheter (diameter = 1.3 mm) to the acoustic impedance matched-imaging window. Water filled the inner catheter to match acoustic impedance and air was pumped between the inner and outer catheters to inflate the balloon. The integrated EIS and IVUS sensor was deployed into the ex vivo aortas dissected from the fat-fed New Zealand White (NZW) rabbits (n=3 for fat-fed, n= 5 normal diet). IVUS imaging was able to guide the 2-point electrode to align with the plaque for EIS measurement upon balloon inflation. IVUS-guided EIS signal demonstrated reduced variability and increased reproducibility (p < 0.0001 for magnitude, p < 0.05 for phase at < 15 kHz) as compared to EIS sensor alone (p < 0.07 for impedance, p < 0.4 for phase at < 15 kHz). Thus, we enhanced topographic and EIS detection of oxLDL-laden plaques via a catheter-based integrated sensor design to enhance clinical assessment for unstable plaque.

Time to Give Up on Cardioprotection?

The mortality from acute myocardial infarction (AMI) remains significant, and the prevalence of post-myocardial infarction heart failure is increasing. Therefore, cardioprotection beyond timely reperfusion is needed. Conditioning procedures are the most powerful cardioprotective interventions in animal experiments. However, ischemic preconditioning cannot be used to reduce infarct size in patients with AMI because its occurrence is not predictable; several studies in patients undergoing surgical coronary revascularization report reduced release of creatine kinase and troponin. Ischemic postconditioning reduces infarct size in most, but not all, studies in patients undergoing interventional reperfusion of AMI, but may require direct stenting and exclusion of patients with >6 hours of symptom onset to protect. Remote ischemic conditioning reduces infarct size in patients undergoing interventional reperfusion of AMI, elective percutaneous or surgical coronary revascularization, and other cardiovascular surgery in many, but not in all, studies. Adequate dose-finding phase II studies do not exist. There are only 2 phase III trials, both on remote ischemic conditioning in patients undergoing cardiovascular surgery, both with neutral results in terms of infarct size and clinical outcome, but also both with major problems in trial design. We discuss the difficulties in translation of cardioprotection from animal experiments and proof-of-concept trials to clinical practice. Given that most studies on ischemic postconditioning and all studies on remote ischemic preconditioning in patients with AMI reported reduced infarct size, it would be premature to give up on cardioprotection.

Involvement of exogenous H2S in recovery of cardioprotection from ischemic post-conditioning via increase of autophagy in the aged hearts

BACKGROUND

Hydrogen sulfide (H2S), which is a member of the gasotransmitter family, plays an important physiological and pathological role in cardiovascular system. Ischemic post-conditioning (PC) provides myocardial protective effect in the young hearts but not in the aged hearts. Exogenous H2S restores PC-induced cardioprotection by inhibition of mitochondrial permeability transition pore (mPTP) in the aged hearts. However, whether H2S contributes to the recovery of PC-induced cardioprotection via up-regulation of autophagy in the aged hearts is unclear.

METHODS

The isolated aged rat hearts (24-months-old, 450-500g) and aged cardiomyocytes-induced by d-galactose were exposed to an ischemia/reperfusion (I/R) and PC protocol.

RESULTS

We found PC lost cardioprotection in the aged hearts and cardiomyocytes. NaHS (a H2S donor) significantly restored cardioprotection of PC through decreasing myocardial damage, infarct size, and apoptosis, improving cardiac function, increasing cell viability and autophagy in the aged hearts and cardiomyocytes. 3-MA (an autophagy inhibitor) abolished beneficial effect of NaHS in the aged hearts. In addition, in the aged cardiomyocytes, NaHS up-regulated AMPK/mTOR pathway, and the effect of NaHS on PC was similar to the overexpression of Atg 5, treatment of AICAR (an AMPK activator) or Rapamycin (a mTOR inhibitor, an autophagy activator), respectively.

CONCLUSIONS

These results suggest that exogenous H2S restores cardioprotection from PC by up-regulation of autophagy via activation of AMPK/mTOR pathway in the aged hearts and cardiomyocytes.

Effects of ischemic postconditioning on expressions of pentraxin-related protein 3 and neutrophil CD11b in the plasma of patients with acute myocardial infarction after percutaneous coronary intervention

OBJECTIVE

To evaluate the effects of ischemic postconditioning on expressions of pentraxin-related protein 3 (PTX3) and neutrophil CD11b in the plasma of patients with acute myocardial infarction (AMI) after percutaneous coronary intervention (PCI).

METHODS

Fifty-six patients who had AMI with ST-segment elevation were randomly divided into a control group and an ischemic postconditioning group (n=28). Both groups received emergency PCI. After recanalization of infarct-related arteries, the control group did not receive intervention within three minutes, while the ischemic postconditioning group was treated by low-pressure filling and emptying of balloon within one minute. The plasma expressions of PTX3 before and 24 hour after PCI were detected by ELISA, and those of neutrophil CD11b were detected by flow cytometry.

RESULTS

PTX3 and neutrophil CD11b expressions of the two groups were similar before PCI, but those of the ischemic postconditioning group significantly decreased 24 hour after PCI (P<0.05).

CONCLUSION

Ischemic postconditioning lowered the expressions of PTX3 and neutrophil CD11b in AMI patients after PCI, inhibited inflammatory response, reduced the adhesion between leukocytes and endothelial cells, and protected the ischemic-reperfused myocardium.

Short-and long-term effects of ischemic postconditioning in STEMI patients: a meta-analysis

Background

Compelling evidence from large randomized trials demonstrates the salutary effects of ischemic postconditioning on cardioprotection against ischemic/reperfusion injury. However, some studies appear negative findings.

This study was designed to assess the short-and long-term effects of postconditioning (Poc) in studies including evolving ST-elevation myocardial infarction (STEMI).

Methods

Relevant studies were identified through an electronic literature search from the PubMed, Library of Congress, Embase, Cochrane Central Register of Controlled Trials, and ISI Web of Science. Studies published up to December 2014 were eligible for inclusion. Patients older than 18 years presenting within 12 h of the first STEMI and eligible for angioplasty were considered for the study.

Results

The 25 trials allocated 1136 patients to perform locational postconditioning cycles at the onset of reperfusion and 1153 patients to usual percutaneous coronary intervention (PCI). Ischemic postconditioning demonstrated a decrease in serum cardiac enzymes creatine kinase (CK) and CK-MB (P < 0.00001 and P =0.25, respectively) in the subgroup analysis based on direct stenting. Reduction in infarct size by imaging was showed during7 days after myocardial infarction (P =0.01), but not in the longterm (P = 0.08). The wall motion score index was improved in both the short term within 7 days (P = 0.009) and the long term over 6 months after receiving Poc (P = 0.02). All included studies were limited by the high risk of performance and publication bias.

Conclusions

Ischemic postconditioning by brief interruptions of coronary blood flow at the onset of reperfusion after PCI appears to be superior to PCI alone in reducing myocardial injury and improving left ventricular function, especially in patients who have received direct stenting in PCI.

Interaction of risk factors, comorbidities, and comedications with ischemia/reperfusion injury and cardioprotection by preconditioning, postconditioning, and remote conditioning

Pre-, post-, and remote conditioning of the myocardium are well described adaptive responses that markedly enhance the ability of the heart to withstand a prolonged ischemia/reperfusion insult and provide therapeutic paradigms for cardioprotection. Nevertheless, more than 25 years after the discovery of ischemic preconditioning, we still do not have established cardioprotective drugs on the market. Most experimental studies on cardioprotection are still undertaken in animal models, in which ischemia/reperfusion is imposed in the absence of cardiovascular risk factors. However, ischemic heart disease in humans is a complex disorder caused by, or associated with, cardiovascular risk factors and comorbidities, including hypertension, hyperlipidemia, diabetes, insulin resistance, heart failure, altered coronary circulation, and aging. These risk factors induce fundamental alterations in cellular signaling cascades that affect the development of ischemia/reperfusion injury per se and responses to cardioprotective interventions. Moreover, some of the medications used to treat these risk factors, including statins, nitrates, and antidiabetic drugs, may impact cardioprotection by modifying cellular signaling. The aim of this article is to review the recent evidence that cardiovascular risk factors and their medication may modify the response to cardioprotective interventions. We emphasize the critical need to take into account the presence of cardiovascular risk factors and concomitant medications when designing preclinical studies for the identification and validation of cardioprotective drug targets and clinical studies. This will hopefully maximize the success rate of developing rational approaches to effective cardioprotective therapies for the majority of patients with multiple risk factors.

Recent advances in the diagnosis and treatment of acute myocardial infarction

The Third Universal Definition of Myocardial Infarction (MI) requires cardiac myocyte necrosis with an increase and/or a decrease in a patient’s plasma of cardiac troponin (cTn) with at least one cTn measurement greater than the 99^th percentile of the upper normal reference limit during: (1) symptoms of myocardial ischemia; (2) new significant electrocardiogram (ECG) ST-segment/T-wave changes or left bundle branch block; (3) the development of pathological ECG Q waves; (4) new loss of viable myocardium or regional wall motion abnormality identified by an imaging procedure; or (5) identification of intracoronary thrombus by angiography or autopsy. Myocardial infarction, when diagnosed, is now classified into five types. Detection of a rise and a fall of troponin are essential to the diagnosis of acute MI. However, high sensitivity troponin assays can increase the sensitivity but decrease the specificity of MI diagnosis. The ECG remains a cornerstone in the diagnosis of MI and should be frequently repeated, especially if the initial ECG is not diagnostic of MI.

There have been significant advances in adjunctive pharmacotherapy, procedural techniques and stent technology in the treatment of patients with MIs. The routine use of antiplatelet agents such as clopidogrel, prasugrel or ticagrelor, in addition to aspirin, reduces patient morbidity and mortality. Percutaneous coronary intervention (PCI) in a timely manner is the primary treatment of patients with acute ST segment elevation MI. Drug eluting coronary stents are safe and beneficial with primary coronary intervention. Treatment with direct thrombin inhibitors during PCI is non-inferior to unfractionated heparin and glycoprotein IIb/IIIa receptor antagonists and is associated with a significant reduction in bleeding. The intra-coronary use of a glycoprotein IIb/IIIa antagonist can reduce infarct size. Pre- and post-conditioning techniques can provide additional cardioprotection. However, the incidence and mortality due to MI continues to be high despite all these recent advances. The initial ten year experience with autologous human bone marrow mononuclear cells (BMCs) in patients with MI showed modest but significant increases in left ventricular (LV) ejection fraction, decreases in LV end-systolic volume and reductions in MI size. These studies established that the intramyocardial or intracoronary administration of stem cells is safe. However, many of these studies consisted of small numbers of patients who were not randomized to BMCs or placebo. The recent LateTime, Time, and Swiss Multicenter Trials in patients with MI did not demonstrate significant improvement in patient LV ejection fraction with BMCs in comparison with placebo. Possible explanations include the early use of PCI in these patients, heterogeneous BMC populations which died prematurely from patients with chronic ischemic disease, red blood cell contamination which decreases BMC renewal, and heparin which decreases BMC migration. In contrast, cardiac stem cells from the right atrial appendage and ventricular septum and apex in the SCIPIO and CADUCEUS Trials appear to reduce patient MI size and increase viable myocardium. Additional clinical studies with cardiac stem cells are in progress.

Long-term effects of ischemic postconditioning on clinical outcomes: 1-year follow-up of the POST randomized trial

BACKGROUND

In the Effects of Postconditioning on Myocardial Reperfusion in Patients with ST-segment Elevation Myocardial Infarction (POST) trial, ischemic postconditioning failed to improve myocardial reperfusion. However, long-term effects of ischemic postconditioning on clinical outcomes are not known in patients with ST-segment elevation myocardial infarction.

METHODS

A total of 700 patients undergoing primary percutaneous coronary intervention (PCI) were randomly assigned to the postconditioning group or the conventional primary PCI group in a 1:1 ratio. Postconditioning was performed immediately after restoration of coronary flow by balloon occlusion 4 times for 1 minute. Complete follow-up data for major clinical events at 1 year were available in 695 patients (99.3%), and analyses were done by the intention to treat principle. The primary outcome was a composite of death, myocardial infarction, severe heart failure, or stent thrombosis at 1 year.

RESULTS

At 1 year, a composite of death, myocardial infarction, severe heart failure, or stent thrombosis occurred in 21 patients (6.1%) in the postconditioning group and 16 patients (4.6%) in the conventional PCI group (hazard ratio [HR] 1.32, 95% CI 0.69-2.53, P = .40). The risk of death (4.9% vs 3.7%, HR 1.32, 95% CI 0.64-2.71, P = .46), heart failure (2.6% vs 2.3%, HR 1.13, 95% CI 0.44-2.94, P = .80), and stent thrombosis (2.3% vs 1.7%, HR 1.34, 95% CI 0.46-3.85, P = .59) did not differ significantly between the 2 groups.

CONCLUSIONS

Ischemic postconditioning does not seem to improve the 1-year clinical outcomes in patients with ST-segment elevation myocardial infarction undergoing primary PCI.

The Third DANish Study of Optimal Acute Treatment of Patients with ST-segment Elevation Myocardial Infarction: Ischemic postconditioning or deferred stent implantation versus conventional primary angioplasty and complete revascularization versus treatment of culprit lesion only: Rationale and design of the DANAMI 3 trial program

BACKGROUND

In patients undergoing primary percutaneous coronary intervention for ST-segment elevation myocardial infarction, ischemic postconditioning has been shown to reduce infarct size, but the effect on clinical outcome has not been tested in a large randomized trial. In addition, deferring stent implantation in the infarct-related lesion 1 to 3 days after acute opening of the infarct-related artery could have protective effects, by reducing the risk of injury caused by distal embolization and microvascular obstruction. Finally, a considerable fraction of patients present with lesions in other coronary artery branches than the infarct-related artery. Whether a strategy of complete or partial revascularization of these patients should be preferred remains uncertain.

STUDY DESIGN

The DANAMI 3 trial program was designed to investigate 3 different randomized treatment strategies in patients with ST-segment elevation myocardial infarction: (1) ischemic postconditioning versus conventional treatment with a primary end point of death and hospitalization for heart failure; (2) deferring stent implantation in the infarct-related lesion versus conventional treatment with a primary end point of death, hospitalization for heart failure, reinfarction, and repeat revascularization; and (3) treatment of the culprit lesion only versus fractional flow reserve-guided complete revascularization in patients with multivessel disease, with a primary end point of death, reinfarction, and repeat revascularization.

SUMMARY

The DANAMI 3 trial program will determine whether either of 2 approaches to reduce reperfusion injury and distal microvascular obstruction with postconditioning or deferred stent implantation will translate into improved clinical outcome and whether patients with multivessel disease undergoing primary percutaneous coronary intervention will benefit from a strategy of complete or partial revascularization.

The role of post-translational modifications in acute and chronic cardiovascular disease

Cardiovascular disease (CVD) in one of the leading causes of mortality and morbidity worldwide, accounting for both primary diseases of the heart and vasculature and arising as a co-morbidity with numerous pathologies, including type 2 diabetes mellitus (T2DM). There has been significant emphasis on the role of the genome in CVD, aiding in the definition of 'at-risk' patients. The extent of disease penetrance however, can be influenced by environmental factors that are not detectable by investigating the genome alone. By targeting the transcriptome in response to CVD, the interplay between genome and environment is more apparent, however this implies the level of protein expression without reference to proteolytic turnover, or potentially more importantly, without defining the role of PTMs in the development of disease. Here, we discuss the role of both brief and irreversible PTMs in the setting of myocardial ischemia/reperfusion injury. Key proteins involved in calcium regulation have been observed as differentially modified by phosphorylation/O-GlcNAcylation or phosphorylation/redox modifications, with the level of interplay dependent on the physiological or pathophysiological state. The ability to modify crucial sites to produce the desired functional output is modulated by the presence of other PTMs as exemplified in the T2DM heart, where hyperglycemia results in aberrant O-GlcNAcylation and advanced glycation end products. By using the signalling events predicted to be critical to post-conditioning, an intervention with great promise for the cardioprotection of the ischemia/reperfusion injured heart, as an example, we discuss the level of PTMs and their interplay. The inability of post-conditioning to protect the diabetic heart may be regulated by aberrant PTMs influencing those sites necessary for protection.

Molecular basis of cardioprotection: signal transduction in ischemic pre-, post-, and remote conditioning

Reperfusion is mandatory to salvage ischemic myocardium from infarction, but reperfusion per se contributes to injury and ultimate infarct size. Therefore, cardioprotection beyond that by timely reperfusion is needed to reduce infarct size and improve the prognosis of patients with acute myocardial infarction. The conditioning phenomena provide such cardioprotection, insofar as brief episodes of coronary occlusion/reperfusion preceding (ischemic preconditioning) or following (ischemic postconditioning) sustained myocardial ischemia with reperfusion reduce infarct size. Even ischemia/reperfusion in organs remote from the heart provides cardioprotection (remote ischemic conditioning). The present review characterizes the signal transduction underlying the conditioning phenomena, including their physical and chemical triggers, intracellular signal transduction, and effector mechanisms, notably in the mitochondria. Cardioprotective signal transduction appears as a highly concerted spatiotemporal program. Although the translation of ischemic postconditioning and remote ischemic conditioning protocols to patients with acute myocardial infarction has been fairly successful, the pharmacological recruitment of cardioprotective signaling has been largely disappointing to date.

Ischaemic conditioning: pitfalls on the path to clinical translation

The development of novel adjuvant strategies capable of attenuating myocardial ischaemia-reperfusion injury and reducing infarct size remains a major, unmet clinical need. A wealth of preclinical evidence has established that ischaemic 'conditioning' is profoundly cardioprotective, and has positioned the phenomenon (in particular, the paradigms of postconditioning and remote conditioning) as the most promising and potent candidate for clinical translation identified to date. However, despite this preclinical consensus, current phase II trials have been plagued by heterogeneity, and the outcomes of recent meta-analyses have largely failed to confirm significant benefit. As a result, the path to clinical application has been perceived as 'disappointing' and 'frustrating'. The goal of the current review is to discuss the pitfalls that may be stalling the successful clinical translation of ischaemic conditioning, with an emphasis on concerns regarding: (i) appropriate clinical study design and (ii) the choice of the 'right' preclinical models to facilitate clinical translation.

Effect of ischemic postconditioning on myocardial salvage in patients undergoing primary percutaneous coronary intervention for ST-segment elevation myocardial infarction: cardiac magnetic resonance substudy of the POST randomized trial

In the effects of postconditioning on myocardial reperfusion in patients with ST-segment elevation myocardial infarction (POST) trial, ischemic postconditioning did not improve myocardial reperfusion in 700 patients with STEMI undergoing primary PCI. However, the impact of postconditioning on myocardial salvage and infarct size still needs to be addressed. The aim of this study was to investigate the effect of ischemic postconditioning on myocardial salvage using cardiac magnetic resonance (CMR) in patients with STEMI undergoing primary PCI. For the CMR substudy, a total of 111 patients was analyzed, 56 in the postconditioning group and 55 undergoing conventional primary PCI in the control group. Postconditioning was performed immediately after restoration of coronary flow by four cycles of 1-min balloon occlusion separated by 1 min of deflation. The primary end point was myocardial salvage measured by CMR 3 days after the index event. The myocardial salvage index was not improved by ischemic postconditioning compared with conventional PCI (46.3 ± 18.5 vs. 45.7 ± 20.5%, p = 0.86). The infarct size was not significantly different between the two groups (18.8 ± 10.3 vs. 20.2 ± 11.0%, p = 0.52). Moreover, there was no significant difference in the rates of microvascular obstruction or hemorrhagic infarction between the groups. CMR study demonstrated that ischemic postconditioning during primary PCI in STEMI patients did not improve myocardial salvage or reduce infarct size. These findings further support the results of the POST trial which showed no benefit of ischemic postconditioning as an adjunctive treatment of primary PCI.

Redox signalling and cardioprotection: translatability and mechanism

The morbidity and mortality from coronary artery disease (CAD) remain significant worldwide. The treatment for acute myocardial infarction has improved over the past decades, including early reperfusion of culprit coronary arteries. Although it is mandatory to reperfuse the ischaemic territory as soon as possible, paradoxically this leads to additional myocardial injury, namely ischaemia/reperfusion (I/R) injury, in which redox stress plays a pivotal role and for which no effective therapy is currently available. In this review, we report evidence that the redox environment plays a pivotal role not only in I/R injury but also in cardioprotection. In fact, cardioprotective strategies, such as pre- and post-conditioning, result in a robust reduction in infarct size in animals and the role of redox signalling is of paramount importance in these conditioning strategies. Nitrosative signalling and cysteine redox modifications, such as S-nitrosation/S-nitrosylation, are also emerging as very important mechanisms in conditioning cardioprotection. The reasons for the switch from protective oxidative/nitrosative signalling to deleterious oxidative/nitrosative/nitrative stress are not fully understood. The complex regulation of this switch is, at least in part, responsible for the diminished or lack of cardioprotection induced by conditioning protocols observed in ageing animals and with co-morbidities as well as in humans. Therefore, it is important to understand at a mechanistic level the reasons for these differences before proposing a safe and useful transition of ischaemic or pharmacological conditioning. Indeed, more mechanistic novel therapeutic strategies are required to protect the heart from I/R injury and to improve clinical outcomes in patients with CAD.

Ischemic preconditioning-an unfulfilled promise

Myocardial reperfusion injury has been identified as a key determinant of myocardial infarct size in patients undergoing percutaneous or surgical interventions. Although the molecular mechanisms underpinning reperfusion injury have been elucidated, attempts at translating this understanding into clinical benefit for patients undergoing cardiac interventions have produced mixed results. Ischemic conditioning has been applied before, during, or after an ischemic insult to the myocardium and has taken the form of local induction of ischemia or ischemia of distant tissues. Clinical studies have confirmed the safety of differing conditioning techniques, but the benefit of such techniques in reducing hard clinical event rates has produced mixed results. The aim of this article is to review the role of ischemic conditioning in patients undergoing percutaneous and surgical coronary revascularization.

Postconditioning signalling in the heart: mechanisms and translatability

The protective effect of ischaemic postconditioning (short cycles of reperfusion and reocclusion of a previously occluded vessel) was identified over a decade ago commanding intense interest as an approach for modifying reperfusion injury which contributes to infarct size in acute myocardial infarction. Elucidation of the major mechanisms of postconditioning has identified potential pharmacological targets for limitation of reperfusion injury. These include ligands for membrane-associated receptors, activators of phosphokinase survival signalling pathways and inhibitors of the mitochondrial permeability transition pore. In experimental models, numerous agents that target these mechanisms have shown promise as postconditioning mimetics. Nevertheless, clinical studies of ischaemic postconditioning and pharmacological postconditioning mimetics are equivocal. The majority of experimental research is conducted in animal models which do not fully portray the complexity of risk factors and comorbidities with which patients present and which we now know modify the signalling pathways recruited in postconditioning. Cohort size and power, patient selection, and deficiencies in clinical infarct size estimation may all represent major obstacles to assessing the therapeutic efficacy of postconditioning. Furthermore, chronic treatment of these patients with drugs like ACE inhibitors, statins and nitrates may modify signalling, inhibiting the protective effect of postconditioning mimetics, or conversely induce a maximally protected state wherein no further benefit can be demonstrated. Arguably, successful translation of postconditioning cannot occur until all of these issues are addressed, that is, experimental investigation requires more complex models that better reflect the clinical setting, while clinical investigation requires bigger trials with appropriate patient selection and standardization of clinical infarct size measurements.

Cardioprotective role of ischemic postconditioning in acute myocardial infarction: a systematic review and meta-analysis

BACKGROUND

Evidence suggests that ischemic postconditioning (IPoC) may reduce the extent of reperfusion injury. We performed a meta-analysis of randomized controlled trials, which compared the role of IPoC during primary percutaneous coronary intervention (PCI) to PCI alone (control group) in ST-segment elevation myocardial infarction.

METHODS

Several databases were searched, which yielded 19 studies. The outcomes of interest were measures of myocardial damage (serum cardiac enzymes and infarct size by imaging) and left ventricular function (left ventricular ejection fraction and wall motion score index). Mean difference (MD) and standardized mean difference (SMD) were used to assess the treatment effect. An inverse variance method was used to pool data into a random-effects model.

RESULTS

Ischemic postconditioning demonstrated a decrease in serum cardiac enzymes (SMD -0.48, 95% CI -0.92 to -0.05, I(2) = 92%), reduction in infarct size by imaging (SMD -0.30, 95% CI -0.58 to -0.01, I(2) = 80%), wall motion score index (MD -0.19, 95% CI -0.29 to -0.09, I(2) = 44%), and showed improvement in left ventricular ejection fraction (IPoC 52 ± 0.4, control 49.7 ± 0.4) (MD 2.78, 95% CI 0.66-4.91, I(2) = 69%). All included studies were limited by high risk of performance and publication bias.

CONCLUSIONS

Ischemic postconditioning during PCI in ST-segment elevation myocardial infarction appears to be superior to PCI alone in reduction of both myocardial injury or damage and improvement in global and regional left ventricular function. The effect seems to be more pronounced when a greater myocardial area is at risk. Given the limitations of the current available evidence, additional data from large randomized controlled trials are warranted.

Meta-analysis of randomized trials of postconditioning in ST-elevation myocardial infarction

Clinical benefit of postconditioning in patients with ST-elevation myocardial infarction (STEMI) treated by primary percutaneous coronary intervention is still controversial. We performed a meta-analysis of available randomized clinical trials (RCTs) to define the role of postconditioning in STEMI. Fourteen RCTs evaluating postconditioning in a total of 778 patients with STEMI were identified in PubMed, EMBase, and Cochrane databases from January 1998 to February 2014. Overall, postconditioning was found to be cardioprotective in term of infarct size reduction (weighted standardized mean differences -0.5837, 95% confidence interval -0.9609 to -0.2066, p <0.05), but significant heterogeneity across the trials was detected (I(2) = 84%). Univariate meta-regression analysis did not identify clinical or procedural variables associated with a more pronounced effect of postconditioning effects on infarct size with the exception of using cardiac magnetic resonance (CMR) to evaluate infarct size (p <0.01). Restricting the analysis to 6 RCTs including a total of 448 patients and evaluating the postconditioning effect on infarct size by means of CMR led to the disappearance of benefit of postconditioning on infarct size. In conclusion, the results of this meta-analysis of RCTs suggested that postconditioning reduces infarct size, as expressed by weighted standardized mean differences. However, if the analysis was limited to trials with a more accurate quantification of infarct size reduction, namely by CMR, the benefit was lost. More data are required before adoption of postconditioning in clinical practice.

Novel therapeutic strategies for ischemic heart disease

Despite significant advances in the physician's ability to initiate myocardial reperfusion and salvage heart tissue, ischemic heart disease remains one of the leading causes of death in the United States. Consequently, alternative therapeutic strategies have been intensively investigated, especially methods of enhancing the heart's resistance to ischemic cell death - so called "cardioprotective" interventions. However, although a great deal has been learned regarding the methods and mechanisms of cardioprotective interventions, an efficacious therapy has yet to be successfully implemented in the clinical arena. This review discusses the current understanding of cardioprotection in the context of ischemic heart disease pathophysiology, highlighting those elements of ischemic heart disease pathophysiology that have received less attention as potential targets of cardioprotective intervention.

Postconditioning in ST-elevation myocardial infarction: a systematic review, critical appraisal, and meta-analysis of randomized clinical trials

Objective

We aimed to summarize the evidence from randomized clinical trials studies examining the efficacy of ischemic postconditioning (IPost) in ST-elevation myocardial infarction.

Design

The study was a systematic review and critical appraisal, with meta-analysis of randomized clinical trials.

Materials and methods

We searched the literature. A total of 21 randomized clinical trials were identified. Both fixed effect and random effects models were used to synthesize the results of individual studies. Heterogeneity between studies was examined by subgroup and random effects meta-regression analyses, considering ptient-related and study-level variables. Publication bias, or “small-study effect”, was evaluated.

Results

Substantial heterogeneity was present. The random effects model pooled estimate for the outcome infarct size assessed by cardiac magnetic resonance was estimated by the standardized mean difference (SMD) =−0.06, 95% confidence interval (CI): −0.34 to 0.21, ie, no effect of IPost. For the end point infarct size, estimated by biomarkers of myocardial necrosis, an overall pooled effect was SMD =−0.58, 95% CI: −0.96 to −0.19. This effect disappeared in powered and nonbiased studies (SMD =0.03, 95% CI: −0.48 to 0.55). Finally, for the outcome left ventricular ejection fraction, SMD =0.47 95% CI: 0.20 to 0.74. Unfortunately, selection bias (small-study effect) was present. For this outcome, the meta-regression showed that both presence of hypertension and the inclusion of nonbiased studies explained 28.3% of the heterogeneity among the studies. Simulation by the “trim and fill” method, which controlled for selection bias using random effects model, diluted the effect (SMD =0.17 95% CI: −0.13 to 0.48). No effects by IPost on ST-segment resolution or on the majority of adverse clinical events were observed during follow up, except the incidence of congestive heart failure was found.

Conclusion

Evidence from this study suggests no cardioprotection from IPost, on surrogate and the majority of clinical end points. A possible beneficial effect on the incidence of congestive heart failure needs to be replicated by a large clinical trial.

Surrogate and clinical outcomes following ischemic postconditioning during primary percutaneous coronary intervention of ST--segment elevation myocardial infarction: a meta-analysis of 15 randomized trials

OBJECTIVES

To conduct a meta-analysis on surrogate and clinical outcomes with myocardial ischemic postconditioning (IPoC) following revascularization with primary percutaneous intervention (PPCI) for ST-segment myocardial infarction (STEMI) compared with PPCI alone.

BACKGROUND

Reperfusion injury remains an important problem following PPCI for STEMI. Trials of IPoC have mainly focused on cardiac biomarkers; the impact on clinical outcomes is unknown.

METHODS

Clinical trials that randomized STEMI patients to IPoC as compared with conventional PPCI were included for analysis.

RESULTS

A total of 15 randomized trials with 1,545 patients met our selection criteria (785 underwent IPoC + PPCI, 760 PPCI alone). Mean follow-up for clinical outcomes was 4.7 months. The mean ischemic time was 225 min. ST-segment resolution (Relative Risk [RR] = 0.98; 95% Confidence Intervals [CI] 0.85-1.13; P = 0.75) and infarct size (Weighted mean difference [WMD] = -2.53%, 95% CI -6.10 to 1.05; P = 0.17) were similar between the IPoC + PPCI vs. PPCI arms. Left ventricular ejection fraction at follow-up was marginally higher in the IPoC (WMD = 4.15%, 95% CI 0.19-8.12%, P = 0.04). No differences were noted in any of the clinical outcomes studied, including mortality (RR = 1.52; 95% CI 0.77-2.99; P = 0.23), recurrent MI (RR = 3.04; 95% CI 0.74-12.54; P = 0.12); stent thrombosis (RR = 1.24, 95% CI 0.51-3.04; P = 0.83) or the composite MACE outcome (RR = 1.53; 95% CI 0.89-2.63; P = 0.13).

CONCLUSIONS

IPoC following PPCI is not associated with improvements in surrogate or clinical outcomes at 5 months as compared with PPCI alone. Our findings indicate no role for IPoC in the routine management of patients with STEMI.

Remote ischemic post-conditioning of the lower limb during primary percutaneous coronary intervention safely reduces enzymatic infarct size in anterior myocardial infarction: a randomized controlled trial

OBJECTIVES

This study sought to evaluate whether remote ischemic post-conditioning (RIPC) could reduce enzymatic infarct size in patients with anterior ST-segment elevation myocardial infarction undergoing primary percutaneous coronary intervention (pPCI).

BACKGROUND

Myocardial reperfusion injury may attenuate the benefit of pPCI. In animal models, RIPC mitigates myocardial reperfusion injury.

METHODS

One hundred patients with anterior ST-segment elevation myocardial infarction and occluded left anterior descending artery were randomized to pPCI + RIPC (n = 50) or conventional pPCI (n = 50). RIPC consisted of 3 cycles of 5 min/5 min ischemia/reperfusion by cuff inflation/deflation of the lower limb. The primary endpoint was infarct size assessed by the area under the curve of creatinine kinase-myocardial band release (CK-MB). Secondary endpoints included the following: infarct size assessed by cardiac magnetic resonance delayed enhancement volume; T2-weighted edema volume; ST-segment resolution >50%; TIMI (Thrombolysis In Myocardial Infarction) frame count; and myocardial blush grading.

RESULTS

Four patients (2 RIPC, 2 controls) were excluded due to missing samples of CK-MB. A total of 96 patients were analyzed; median area under the curve CK-MB was 8,814 (interquartile range [IQR]: 5,567 to 11,325) arbitrary units in the RIPC group and 10,065 (IQR: 7,465 to 14,004) arbitrary units in control subjects (relative reduction: 20%, 95% confidence interval: 0.2% to 28.7%; p = 0.043). Seventy-seven patients underwent a cardiac magnetic resonance scan 3 to 5 days after randomization, and 66 patients repeated a second scan after 4 months. T2-weighted edema volume was 37 ± 16 cc in RIPC patients and 47 ± 22 cc in control subjects (p = 0.049). ST-segment resolution >50% was 66% in RIPC and 37% in control subjects (p = 0.015). We observed no significant differences in TIMI frame count, myocardial blush grading, and delayed enhancement volume.

CONCLUSIONS

In patients with anterior ST-segment elevation myocardial infarction, RIPC at the time of pPCI reduced enzymatic infarct size and was also associated with an improvement of T2-weighted edema volume and ST-segment resolution >50%. (Remote Postconditioning in Patients With Acute Myocardial Infarction Treated by Primary Percutaneous Coronary Intervention [PCI] [RemPostCon]; NCT00865722).

Effect of ischemic postconditioning on infarct size in patients with ST-elevation myocardial infarction treated by primary PCI results of the POSTEMI (POstconditioning in ST-Elevation Myocardial Infarction) randomized trial

Background

Reduction of infarct size by ischemic postconditioning (IPost) has been reported in smaller proof‐of‐concept clinical studies, but has not been confirmed in other smaller studies. The principle needs to be evaluated in larger groups of ST‐elevation myocardial infarction (STEMI) patients before being implemented in clinical practice. This study assessed the effect of ischemic postcoditioning (IPost) on infarct size in patients with STEMI treated by primary percutaneous coronary intervention (PCI).

Methods and Results

Patients with first‐time STEMI, <6 hours from symptom onset, referred to primary PCI were randomized to IPost or control groups. IPost was administered by 4 cycles of 1‐minute reocclusion and 1‐minute reperfusion, starting 1 minute after opening, followed by stenting. In the control group, stenting was performed immediately after reperfusion. The primary endpoint was infarct size measured by cardiac magnetic resonance after 4 months. A total of 272 patients were randomized. Infarct size (percent of left ventricular mass) after 4 months (median values and interquartile range) was 14.4% (7.7, 24.6) and 13.5% (8.1, 19.3) in the control group and IPost group, respectively (P=0.18). No significant impact of IPost was found when controlling for baseline risk factors of infarct size in a multivariate linear regression model (P=0.16). The effects of IPost on secondary endpoints, including markers of necrosis, myocardial salvage, and ejection fraction, as well as adverse cardiac events during follow‐up, were consistently neutral.

Conclusions

In contrast to several smaller trials reported previously, we found no significant effects of IPost on infarct size or secondary study outcomes.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov Unique identifier: NCT.No.PO1506.

Molecular mechanisms of ischemic conditioning: translation into patient outcomes

Following the initiation of an ischemic insult, reperfusion injury (RI) can result in numerous deleterious cardiac effects, including cardiomyocyte death. Experimental data have suggested that ischemic conditioning, when delivered either before or after the ischemic event, can provide considerable cardioprotection against RI. Ischemic conditioning involves delivering brief repetitive cycles of ischemia to the myocardium (local) or to another distal organ or structure (remote). This review will discuss recent advances in the molecular mechanisms involved in RI, the signaling pathways recruited by ischemic conditioning and conclude with an appraisal of the evidence for the use of ischemic conditioning in current clinical practice.

Phosphomimetic modulation of eNOS improves myocardial reperfusion and mimics cardiac postconditioning in mice

Objective

Myocardial infarction resulting from ischemia-reperfusion injury can be reduced by cardiac postconditioning, in which blood flow is restored intermittently prior to full reperfusion. Although key molecular mechanisms and prosurvival pathways involved in postconditioning have been identified, a direct role for eNOS-derived NO in improving regional myocardial perfusion has not been shown. The objective of this study is to measure, with high temporal and spatial resolution, regional myocardial perfusion during ischemia-reperfusion and postconditioning, in order to determine the contribution of regional blood flow effects of NO to infarct size and protection.

Methods and Results

We used myocardial contrast echocardiography to measure regional myocardial blood flow in mice over time. Reperfusion after myocardial ischemia-reperfusion injury is improved by postconditioning, as well as by phosphomimetic eNOS modulation. Knock-in mice expressing a phosphomimetic S1176D form of eNOS showed improved myocardial reperfusion and significantly reduced infarct size. eNOS knock-out mice failed to show cardioprotection from postconditioning. The size of the no-reflow zone following ischemia-reperfusion is substantially reduced by postconditioning and by the phosphomimetic eNOS mutation.

Conclusions and Significance

Using myocardial contrast echocardiography, we show that temporal dynamics of regional myocardial perfusion restoration contribute to reduced infarct size after postconditioning. eNOS has direct effects on myocardial blood flow following ischemia-reperfusion, with reduction in the size of the no-reflow zone. These results have important implications for ongoing clinical trials on cardioprotection, because the degree of protective benefit may be significantly influenced by the regional hemodynamic effects of eNOS-derived NO.

Ischemic postconditioning during primary percutaneous coronary intervention: the effects of postconditioning on myocardial reperfusion in patients with ST-segment elevation myocardial infarction (POST) randomized trial

BACKGROUND

Ischemic postconditioning has been reported to reduce infarct size in patients with ST-segment-elevation myocardial infarction. However, cardioprotective effects of postconditioning have not been demonstrated in a large-scale trial.

METHODS AND RESULTS

We performed a multicenter, prospective, randomized, open-label, blinded end-point trial. A total of 700 patients undergoing primary percutaneous coronary intervention (PCI) for ST-segment-elevation myocardial infarction within 12 hours after symptom onset were randomly assigned to the postconditioning group or to the conventional primary PCI group in a 1:1 ratio. Postconditioning was performed immediately after restoration of coronary flow as follows: The angioplasty balloon was positioned at the culprit lesion and inflated 4 times for 1 minute with low-pressure (<6 atm) inflations, each separated by 1 minute of deflation. The primary end point was complete ST-segment resolution (percentage resolution of ST-segment elevation >70%) measured at 30 minutes after PCI. Complete ST-segment resolution occurred in 40.5% of patients in the postconditioning group and 41.5% of patients in the conventional PCI group (absolute difference, -1.0%; 95% confidence interval, -8.4 to 6.4; P=0.79). The rate of myocardial blush grade of 0 or 1 and the rate of major adverse cardiac events (a composite of death, myocardial infarction, severe heart failure, or stent thrombosis) at 30 days did not differ significantly between the postconditioning group and the conventional PCI group (17.2% versus 22.4% [P=0.20] and 4.3% versus 3.7% [P=0.70], respectively).

CONCLUSION

Ischemic postconditioning did not improve myocardial reperfusion in patients with ST-segment-elevation myocardial infarction undergoing primary PCI with current standard practice.

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.

The impact of ischemia-reperfusion injury on the effectiveness of primary angioplasty in ST-segment elevation myocardial infarction

The most effective method of reperfusion in patients with ST-segment elevation myocardial infarction (STEMI) is primary percutaneous coronary intervention (PCI), assisted by aspiration thrombectomy and administration of antiplatelet agents and anticoagulants. However, effective restoration of blood flow in the infarct-related artery may paradoxically result in further damage to the heart muscle. This phenomenon, called ischemia-reperfusion injury (IRI), can significantly reduce the beneficial effects of reperfusion therapy. The rapid restoration of blood flow to the previously ischemic area causes a number of pathophysiological mechanisms leading to increased necrosis of myocytes still viable at the end of the ischemic period. It has been postulated that there are several strategies that can reduce damage to the heart muscle. Attempts to translate the results of experimental trials has been disappointing. More recently, however, some of the clinical benefits of ischemic postconditioning in which reperfusion in patients with STEMI who are undergoing PCI is interrupted with short episodes of ischemia were demonstrated. This renewed the interest in the reperfusion phase as a target for cardioprotective therapy. Research in this field has also been reinforced by the discovery of new potential targets for treatment that protects against IRI, such as the kinase pathway to protect against damage (reperfusion injury salvage kinases – RISK) and mitochondrial permeability transition pore. It seems that these findings will help to develop strategies that will improve the efficiency of mechanical reperfusion and may translate into long-term clinical effects.

Long-term impact of postconditioning on infarct size and left ventricular ejection fraction in patients with ST-elevation myocardial infarction

Background

Ischemic postconditioning (PostC), reperfusion in brief cycles, is known to induce short-term reduction in infarct size in patients with ST elevation myocardial infarction (STEMI), especially among those with large myocardium at risk (MaR). The aim of the present study was to investigate the long-term effect of PostC on infarct size and left ventricular ejection fraction (LVEF).

Methods

Sixty-eight patients with a first STEMI were randomised to primary percutaneous coronary intervention (PCI) (n = 35) or PCI followed by PostC (n = 33). MaR was determined as abnormally contracting segments on left ventricular angiogram. Cardiac magnetic resonance was performed at 3 and 12 months for the determination of infarct size and LVEF.

Results

Overall there was no difference in infarct size expressed in percentage of MaR between patients randomised to the control (31%; 23, 41) and PostC (31%; 23, 43) groups at 12 months. Likewise there was no difference in LVEF between control (49%; 41, 55) and PostC (52%; 45, 55). In contrast, patients in the PostC group with MaR in the upper quartile had a significantly smaller infarct size (29%; 18, 38) than those in the control group (40%; 34, 48; p < 0.05) at 12 months. In these patients LVEF was higher in the PostC (47%; 43, 50) compared to the control group (38%; 34, 42; p < 0.01).

Conclusions

In this long-term follow-up study PostC did not reduce infarct size in relation to MaR or improved LVEF in the overall study population. However, the present data suggest that PostC exerts long-term beneficial effects in patients with large MaR thereby extending previously published short-term observations.

Trial registration

Karolinska Clinical Trial Registration (http://www.kctr.se). Unique identifier: CT20080014