ST-Segment resolution and clinical outcome with ischemic postconditioning and comparison to magnetic resonance

Mechanisms of myocardial reverse remodelling and its clinical significance: A scientific statement of the ESC Working Group on Myocardial Function

Cardiovascular disease (CVD) is the leading cause of morbimortality in Europe and worldwide. CVD imposes a heterogeneous spectrum of cardiac remodelling, depending on the insult nature, that is, pressure or volume overload, ischaemia, arrhythmias, infection, pathogenic gene variant, or cardiotoxicity. Moreover, the progression of CVD-induced remodelling is influenced by sex, age, genetic background and comorbidities, impacting patients' outcomes and prognosis. Cardiac reverse remodelling (RR) is defined as any normative improvement in cardiac geometry and function, driven by therapeutic interventions and rarely occurring spontaneously. While RR is the outcome desired for most CVD treatments, they often only slow/halt its progression or modify risk factors, calling for novel and more timely RR approaches. Interventions triggering RR depend on the myocardial insult and include drugs (renin-angiotensin-aldosterone system inhibitors, beta-blockers, diuretics and sodium-glucose cotransporter 2 inhibitors), devices (cardiac resynchronization therapy, ventricular assist devices), surgeries (valve replacement, coronary artery bypass graft), or physiological responses (deconditioning, postpartum). Subsequently, cardiac RR is inferred from the degree of normalization of left ventricular mass, ejection fraction and end-diastolic/end-systolic volumes, whose extent often correlates with patients' prognosis. However, strategies aimed at achieving sustained cardiac improvement, predictive models assessing the extent of RR, or even clinical endpoints that allow for distinguishing complete from incomplete RR or adverse remodelling objectively, remain limited and controversial. This scientific statement aims to define RR, clarify its underlying (patho)physiologic mechanisms and address (non)pharmacological options and promising strategies to promote RR, focusing on the left heart. We highlight the predictors of the extent of RR and review the prognostic significance/impact of incomplete RR/adverse remodelling. Lastly, we present an overview of RR animal models and potential future strategies under pre-clinical evaluation.

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.

Coronary No-Reflow after Primary Percutaneous Coronary Intervention-Current Knowledge on Pathophysiology, Diagnosis, Clinical Impact and Therapy

Coronary no-reflow (CNR) is a frequent phenomenon that develops in patients with ST-segment elevation myocardial infarction (STEMI) following reperfusion therapy. CNR is highly dynamic, develops gradually (over hours) and persists for days to weeks after reperfusion. Microvascular obstruction (MVO) developing as a consequence of myocardial ischemia, distal embolization and reperfusion-related injury is the main pathophysiological mechanism of CNR. The frequency of CNR or MVO after primary PCI differs widely depending on the sensitivity of the tools used for diagnosis and timing of examination. Coronary angiography is readily available and most convenient to diagnose CNR but it is highly conservative and underestimates the true frequency of CNR. Cardiac magnetic resonance (CMR) imaging is the most sensitive method to diagnose MVO and CNR that provides information on the presence, localization and extent of MVO. CMR imaging detects intramyocardial hemorrhage and accurately estimates the infarct size. MVO and CNR markedly negate the benefits of reperfusion therapy and contribute to poor clinical outcomes including adverse remodeling of left ventricle, worsening or new congestive heart failure and reduced survival. Despite extensive research and the use of therapies that target almost all known pathophysiological mechanisms of CNR, no therapy has been found that prevents or reverses CNR and provides consistent clinical benefit in patients with STEMI undergoing reperfusion. Currently, the prevention or alleviation of MVO and CNR remain unmet goals in the therapy of STEMI that continue to be under intense research.

Renal Dysfunction as a Predictor of Slow-Flow/No-Reflow Phenomenon and Impaired ST Segment Resolution After Percutaneous Coronary Intervention in ST-Elevation Myocardial Infarction With Initial Thrombolysis in Myocardial Infarction Grade 0

BACKGROUND

The slow-flow/no-reflow phenomenon and impaired ST segment resolution (STR) following primary percutaneous coronary intervention (PCI) in ST-elevation myocardial infarction (STEMI) predict unfavorable prognosis and are characterized by obstruction of the coronary microvascular. Several predictors of slow-flow/no-reflow have been revealed, but few studies have investigated predictors of slow-flow/no-reflow and STR exclusively in acute myocardial infarction patients with initial Thrombolysis in Myocardial Infarction (TIMI) Grade 0.

METHODS AND RESULTS

In all, 279 STEMI patients with initial TIMI Grade 0 were enrolled in the study. Slow-flow/no-reflow was defined as TIMI Grade <3 by angiography after PCI, and impaired STR was defined as STR <50% on an electrocardiogram after PCI. Slow-flow/no-reflow was observed in 31 patients. In multivariate analysis, estimated glomerular filtration rate (eGFR; odds ratio [OR] 0.97; P=0.007), a history of cerebrovascular disease (OR 4.65, P=0.007), time to recanalization ≥4 h (OR 2.76, P=0.023), and systolic blood pressure ≤90 mmHg (OR 3.45, P=0.046) were independent predictors of slow-flow/no-reflow. Impaired STR was observed in 102 of 248 patients with TIMI Grade 3. In multivariate analysis, eGFR (OR 0.94, P<0.001) and occlusion of the left anterior descending artery (OR 4.48, P<0.001) were independent predictors of impaired STR; eGFR was the only independent predictor of both slow-flow/no-reflow and impaired STR.

CONCLUSIONS

Renal dysfunction may be related to coronary microvascular dysfunction and obstruction.

Acute Coronary Syndromes (ACS)-Unravelling Biology to Identify New Therapies-The Microcirculation as a Frontier for New Therapies in ACS

In acute coronary syndrome (ACS) patients, restoring epicardial culprit vessel patency and flow with percutaneous coronary intervention or coronary artery bypass grafting has been the mainstay of treatment for decades. However, there is an emerging understanding of the crucial role of coronary microcirculation in predicting infarct burden and subsequent left ventricular remodelling, and the prognostic significance of coronary microvascular obstruction (MVO) in mortality and morbidity. This review will elucidate the multifaceted and interconnected pathophysiological processes which underpin MVO in ACS, and the various diagnostic modalities as well as challenges, with a particular focus on the invasive but specific and reproducible index of microcirculatory resistance (IMR). Unfortunately, a multitude of purported therapeutic strategies to address this unmet need in cardiovascular care, outlined in this review, have so far been disappointing with conflicting results and a lack of hard clinical end-point benefit. There are however a number of exciting and novel future prospects in this field that will be evaluated over the coming years in large adequately powered clinical trials, and this review will briefly appraise these.

Long-term outcomes of ischemic post-conditioning primary PCI and conventional primary PCI in acute STEMI: a meta-analysis of randomized trials

BACKGROUND

Data regarding ischemic postconditioning during percutaneous coronary intervention (PCI) as compared conventional PCI alone has yielded conflicting results.

METHODS

Online databases comparing use of ischemic postconditioning percutaneous coronary intervention (ICP-PPCI) in STEMI patients with conventional PPCI were selected. Mortality, heart failure (HF), myocardial infarction (MI), and major adverse cardiac events (MACE) were evaluated. The primary outcome was composite of HF, MI, and mortality. Pooled risk ratio (RR) with 95% confidence interval (CI) were computed using random-effects model.

RESULTS

Eight studies consisting of 2,566 patients (ICP-PPCI n = 1,228; PPCI n = 1,278) were included. The mean age for PPCI group was 61.38 ± 7.86 years (51% men) and for PCI 59.83 ± 8.94 years (47% men). There were no differences in outcome between ICP-PPCI and PPCI in terms of HF (RR 0.87 95% CI0.51-1.48; p = 0.29), MI (RR 1.28, 95%CI0.74-2.20; p = 0.20), mortality (RR 0.93, 95%CI0.64-1.34; p = 0.58), and MACE (RR 0.89, 95%CI0.74-1.07; p = 0.22). The results for composite event for the ICP-PPCI and PPIC procedures, at ≥1 year follow-up duration, were comparable (RR 1.00 95%CI0.82-1.22; p = 1).

CONCLUSION

Ischemic postconditioning post percutaneous coronary intervention in STEMI patients has no long-term benefits over conventional PCI.

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.

Left ventricular reverse remodeling in patients with anterior wall ST-segment elevation acute myocardial infarction treated with primary percutaneous coronary intervention

Introduction

The study aimed to evaluate the prevalence and predictors of left ventricular (LV) reverse remodeling and its impact on long-term prognosis in patients with anterior ST-segment elevation myocardial infarction (STEMI).

Aim

To assess the percentage of reverse remodeling and its prognostic factors in anterior STEMI patients.

Material and methods

This observational study included 40 patients with first ever STEMI of the anterior wall. LV reverse remodeling was defined as the reduction of left ventricular end-systolic volume (ΔLVESV) by ≥ 10% in 3D transthoracic echocardiography (3D-TTE) at 3-month follow-up. 3D-TTE and speckle tracking imaging were performed during index hospitalization, while 3D-TTE and cardiac magnetic resonance (CMR) were performed at 3 months following the procedure. Patients were followed up for a median time of 3.4 years in order to evaluate major adverse cardiovascular events.

Results

Left ventricular reverse remodeling at 3-month follow-up was confirmed in 15 (37.5%) patients. The presence of reverse remodeling was predicted by lower troponin levels (unit OR = 0.86, p = 0.02), lower sum of ST-segment elevations before (unit OR = 0.87, p = 0.03) and after PCI (unit OR = 0.40, p = 0.03), lower maximal ST-segment elevation after PCI (unit OR = 0.01, p = 0.03), lower wall motion score index (unit OR 0.40, p = 0.03) and more negative anterior wall global longitudinal strain (unit OR = 0.88, p = 0.045). Nine MACE were reported in the without reverse remodeling group only. Non-significantly better event-free survival in the reverse remodeling group was demonstrated (log-rank p = 0.07).

Conclusions

Development of reverse modeling in patients with optimal revascularization and tailored pharmacotherapy is relatively high. Further studies are warranted in order to adjudicate its prognostic role for the prediction of adverse events.

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.

Ischemic postconditioning influences electron transport chain protein turnover in Langendorff-perfused rat hearts

Ischemia postconditioning (IPo) is a promising strategy in reducing myocardial ischemia reperfusion (I/R) injury (MIRI), but its specific molecular mechanism is incompletely understood. Langendorff-perfused isolated rat hearts were subjected to global I/R and received IPo in the absence or presence of the mitochondrial ATP-sensitive potassium channel (mitoKATP) blocker 5-hydroxydecanoate (5-HD). Myocardial mitochondria were extracted and mitochondrial comparative proteomics was analyzed. IPo significantly reduces post-ischemic myocardial infarction and improved cardiac function in I/R rat hearts, while 5-HD basically cancelled IPo's myocardial protective effect. Joint application of two-dimensional polyacrylamide gel electrophoresis (2DE) and MALDI-TOF MS identified eight differentially expressed proteins between groups. Expression of cardiac succinate dehydrogenase (ubiquinone) flavoprotein subunit (SDHA) increased more than two-fold after I/R, while IPo led to overexpression of dihydrolipoyl dehydrogenase (DLD), NADH dehydrogenase (ubiquinone) flavoprotein 1 and isoform CRA_b (NDUFV1). When the mitoKATP was blocked, MICOS complex subunit Mic60 (IMMT) and Stress-70 protein (Grp75) were over expressed, while DLDH, ATPase subunit A (ATPA) and rCG44606 were decreased. Seven of the differential proteins belong to electron transport chain (ETC) or metabolism regulating proteins, and five of them were induced by closing mitoKATP in I/R hearts. We thus conclude that IPo's myocardial protective effect relies on energy homeostasis regulation. DLD, SDHA, NDUFV1, Grp75, ATPA and rCG44606 may contribute to IPo's cardial protective effect.

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.

Pathophysiology of Myocardial Infarction

Myocardial infarction is defined as sudden ischemic death of myocardial tissue. In the clinical context, myocardial infarction is usually due to thrombotic occlusion of a coronary vessel caused by rupture of a vulnerable plaque. Ischemia induces profound metabolic and ionic perturbations in the affected myocardium and causes rapid depression of systolic function. Prolonged myocardial ischemia activates a "wavefront" of cardiomyocyte death that extends from the subendocardium to the subepicardium. Mitochondrial alterations are prominently involved in apoptosis and necrosis of cardiomyocytes in the infarcted heart. The adult mammalian heart has negligible regenerative capacity, thus the infarcted myocardium heals through formation of a scar. Infarct healing is dependent on an inflammatory cascade, triggered by alarmins released by dying cells. Clearance of dead cells and matrix debris by infiltrating phagocytes activates anti-inflammatory pathways leading to suppression of cytokine and chemokine signaling. Activation of the renin-angiotensin-aldosterone system and release of transforming growth factor-β induce conversion of fibroblasts into myofibroblasts, promoting deposition of extracellular matrix proteins. Infarct healing is intertwined with geometric remodeling of the chamber, characterized by dilation, hypertrophy of viable segments, and progressive dysfunction. This review manuscript describes the molecular signals and cellular effectors implicated in injury, repair, and remodeling of the infarcted heart, the mechanistic basis of the most common complications associated with myocardial infarction, and the pathophysiologic effects of established treatment strategies. Moreover, we discuss the implications of pathophysiological insights in design and implementation of new promising therapeutic approaches for patients with myocardial infarction.

Coronary microvascular obstruction in acute myocardial infarction

The success of a primary percutaneous intervention (PCI) in the setting of ST elevation myocardial infarction depends on the functional and structural integrity of coronary microcirculation. Coronary microvascular dysfunction and obstruction (CMVO) occurs in up to half of patients submitted to apparently successful primary PCI and is associated to a much worse outcome. The current review summarizes the complex mechanisms responsible for CMVO, including pre-existing coronary microvascular dysfunction, and highlights the current limitations in the assessment of microvascular function. More importantly, at the light of the substantial failure of trials hitherto published on the treatment of CMVO, this review proposes a novel integrated therapeutic approach, which should overcome the limitations of previous studies.

Rationale and design of the Cyclosporine to ImpRove Clinical oUtcome in ST-elevation myocardial infarction patients (the CIRCUS trial)

BACKGROUND

Both acute myocardial ischemia and reperfusion contribute to cardiomyocyte death in ST-elevation myocardial infarction (STEMI). The final infarct size is the principal determinant of subsequent clinical outcome in STEMI patients. In a proof-of-concept phase II trial, the administration of cyclosporine prior to primary percutaneous coronary intervention (PPCI) has been associated with a reduction of infarct size in STEMI patients.

METHODS

CIRCUS is an international, prospective, multicenter, randomized, double-blinded, placebo-controlled trial. The study is designed to compare the efficacy and safety of cyclosporine versus placebo, in addition to revascularization by PPCI, in patients presenting with acute anterior myocardial infarction within 12 hours of symptoms onset and initial TIMI flow ≤1 in the culprit left anterior descending coronary artery. Patients are randomized in a 1:1 fashion to 2.5 mg/kg intravenous infusion of cyclosporine or matching placebo performed in the minutes preceding PCI. The primary efficacy end point of CIRCUS is a composite of 1-year all-cause mortality, rehospitalization for heart failure or heart failure worsening during initial hospitalization, and left ventricular adverse remodeling as determined by sequential transthoracic echochardiography. Secondary outcomes will be tested using a hierarchical sequence of left ventricular (LV) ejection fraction and absolute measurements of LV volumes. The composite of death and rehospitalization for heart failure or heart failure worsening during initial hospitalization will be further assessed at three years after the initial infarction.

RESULTS

Recruitment lasted from April 2011 to February 2014. The CIRCUS trial has recruited 975 patients with acute anterior myocardial infarction. The 12-months results are expected to be available in 2015.

CONCLUSIONS

The CIRCUS trial is testing the hypothesis that cyclosporine in addition to early revascularization with PPCI compared to placebo in patients with acute anterior myocardial infarction reduces the incidence of death, heart failure and adverse LV remodeling at one-year follow-up.

Clinical effect of postconditioning in ST-elevation myocardial infarction patients treated with primary percutaneous coronary intervention: a meta-analysis of randomized controlled trials

OBJECTIVE

To evaluate the clinical effect of postconditioning on patients with ST-elevation myocardial infarction (STEMI) treated with primary percutaneous coronary intervention (PCI).

METHODS

Randomized controlled trials were identified by searching relevant databases published up to April 2nd, 2014. A meta-analysis of eligible studies was performed by Stata 12.0 and Review Manager 5.2 with a fixed-effect model.

RESULTS

Ten studies providing adverse cardiac events in a total of 1346 STEMI patients treated with primary PCI were identified. The occurrence of heart failure was significantly reduced in patients treated with postconditioning compared with usual care (risk ratio (RR) 0.533; 95% confidence intervals (CI) 0.368-0.770), whereas non-fatal reinfarction slightly increased in the postconditioning group (RR 2.746; 95% CI 1.007-7.488). No significant difference in total major adverse cardiac events (MACEs) was observed between the two groups (RR 0.876; 95% CI 0.671-1.144).

CONCLUSIONS

Postconditioning in STEMI patients undergoing primary PCI significantly reduces the risk of heart failure, but fails to decrease the incidence of total MACEs and the risk of non-fatal reinfarction.

What is Wrong With Cardiac Conditioning? We May be Shooting at Moving Targets

Early recanalization of the occluded culprit coronary artery clearly reduces infarct size in both animal models and patients and improves clinical outcomes. Unfortunately, reperfusion can seldom be accomplished before some myocardium infarcts. As a result there has been an intensive search for interventions that will make the heart resistant to infarction so that reperfusion could salvage more myocardium. A number of interventions have been identified in animal models, foremost being ischemic preconditioning. It protects by activating signaling pathways that prevent lethal permeability transition pores from forming in the heart’s mitochondria at reperfusion. Such conditioning can be accomplished in a clinically relevant manner either by staccato reperfusion (ischemic postconditioning) or by pharmacological activation of the conditioning signaling pathways prior to reperfusion. Unfortunately, clinical trials of ischemic postconditioning and pharmacologic conditioning have been largely disappointing. We suggest that this may be caused by inappropriate use as models intended to mimic the clinical scenario of young healthy animals that receive none of the many drugs currently given to our patients. Patients may be resistant to some forms of conditioning because of comorbidities, for example, diabetes, or they may already be conditioned by adjunct medications, for example, P2Y12 inhibitors or opioids. Incremental technological improvements in patient care may render some approaches to cardioprotection redundant, and thus the clinical target may be continually changing, while our animal models have not kept pace. In remote conditioning, a limb is subjected to ischemia/reperfusion prior to or during coronary reperfusion. Its mechanism is not as well understood as that of ischemic preconditioning, but the results have been very encouraging. In the present article, we will review ischemic, remote, and pharmacologic conditioning and possible confounders that could interfere with their efficacy in clinical trials in 2 settings of myocardial ischemia: (1) primary angioplasty in acute myocardial infarction and (2) elective angioplasty.

Ischaemic postconditioning reduces infarct size: systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Infarct size (IS) is a major determinant of patient outcome after acute ST-segment elevation myocardial infarction (STEMI). Interventions aimed at reducing reperfusion injury, such as cardiac ischaemic postconditioning (IPost), may reduce IS and improve clinical outcomes. IPost has been shown to be feasible in patients with STEMI treated by primary percutaneous coronary intervention (PPCI).

AIMS

To provide an updated summary of the efficacy of IPost, assessed by analysing accurate surrogate markers of IS.

METHODS

We performed a meta-analysis of randomized controlled trials that evaluated the efficacy of IPost in STEMI patients undergoing PPCI. The main outcome was area under the curve of serum creatine kinase release (CK-AUC). Secondary outcomes were other surrogate biomarkers of IS, complete ST-segment resolution, direct measurement of IS by single-photon emission computed tomography and estimation of IS by cardiac magnetic resonance (CMR-IS).

RESULTS

Eleven studies were retrieved, including 1313 STEMI patients undergoing PPCI with or without IPost. Compared with controls, we observed a significant reduction in CK-AUC (standard mean difference [SMD] -2.84 IU/L, 95% CI -5.43 to -0.25 IU/L; P=0.03). Other surrogate markers, such as CMR-IS (SMD -0.36, 95% CI -0.88 to 0.15; P=0.16), showed a non-significant IS reduction in the IPost group.

CONCLUSIONS

This meta-analysis, dealing with accurate surrogate markers of IS, suggests that IPost reduces IS. However, results should be interpreted cautiously because of limited sample sizes and significant heterogeneity. Whether this translates into improvements in cardiac function and patient prognosis still needs to be demonstrated in larger prospective randomized controlled studies that are powered sufficiently.

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.

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.

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.

Current state of clinical translation of cardioprotective agents for acute myocardial infarction

There is continued interest in the concept of limiting myocardial infarct size with adjunctive agents administered along with reperfusion injury; however, there remains considerable controversy in the literature. The purpose of this article is to review the medical literature on clinical trials performed during the past 3 years that have attempted to reduce myocardial infarct size by administration of adjunctive therapies along with reperfusion therapy. A PubMed-driven literature search revealed a host of clinical trials focusing on the following prominent types of therapies: endogenous conditioning (postconditioning and remote ischemic conditioning); rapid cooling; pharmacological therapy (cyclosporine, abciximab, clopidogrel, tirofiban, erythropoietin, thrombus aspiration, adenosine, glucose-insulin-potassium, statins, antidiabetic agents, FX06, iron chelation, and ranolazine). Although there remains some controversy, quite a few of these studies showed that adjunctive therapy further reduced myocardial infarct size when coupled with reperfusion. Antiplatelet agents are emerging as some of the newest agents that seem to have cardioprotective capabilities. Postconditioning has become a bit more controversial in the clinical literature; remote conditioning, early and rapid cooling, adenosine, and ranolazine are intriguing therapies deserving of larger studies. Certain agents and maneuvers, such as erythropoietin, protein kinase C δ inhibitors, iron chelation, and intra-aortic balloon counterpulsation, perhaps should be retired. The correct adjunctive therapy administered along with reperfusion has the capability of further reducing myocardial injury during ST-segment-elevation myocardial infarction.

Myocardial ischemia reperfusion injury: from basic science to clinical bedside

Myocardial ischemia reperfusion injury contributes to adverse cardiovascular outcomes after myocardial ischemia, cardiac surgery or circulatory arrest. Primarily, no blood flow to the heart causes an imbalance between oxygen demand and supply, named ischemia (from the Greek isch, restriction; and haema, blood), resulting in damage or dysfunction of the cardiac tissue. Instinctively, early and fast restoration of blood flow has been established to be the treatment of choice to prevent further tissue injury. Indeed, the use of thrombolytic therapy or primary percutaneous coronary intervention is the most effective strategy for reducing the size of a myocardial infarct and improving the clinical outcome. Unfortunately, restoring blood flow to the ischemic myocardium, named reperfusion, can also induce injury. This phenomenon was therefore termed myocardial ischemia reperfusion injury. Subsequent studies in animal models of acute myocardial infarction suggest that myocardial ischemia reperfusion injury accounts for up to 50% of the final size of a myocardial infarct. Consequently, many researchers aim to understand the underlying molecular mechanism of myocardial ischemia reperfusion injury to find therapeutic strategies ultimately reducing the final infarct size. Despite the identification of numerous therapeutic strategies at the bench, many of them are just in the process of being translated to bedside. The current review discusses the most striking basic science findings made during the past decades that are currently under clinical evaluation, with the ultimate goal to treat patients who are suffering from myocardial ischemia reperfusion-associated tissue injury.

Endogenous cardioprotection by ischaemic postconditioning and remote conditioning

Persistent myocardial ischaemia causes cell death if not rescued by early reperfusion. Millions of years in nature's laboratory have evolved protective responses that 'condition' the heart (and other tissues) to adapt to stressors, and these responses are applicable to the relatively new societal stress of myocardial ischaemia and reperfusion injury. Conditioning can be applied before (preconditioning), during (perconditioning), or after (postconditioning) the ischaemic stressor by imposing short periods of non-lethal ischaemia separated by brief periods of reperfusion. This conditioning protects multiple cell types and induces or rebalances a number of physiological and molecular pathways that ultimately attenuate necrosis and apoptosis. The seemingly disparate pathways may converge directly or indirectly on the mitochondria as a final effector, but other pathways not affecting mitochondria broaden the mechanisms of cardioprotection. The potential downsides of imposing even brief ischaemia directly on the heart somewhat tempered the enthusiasm for applying conditioning stimuli to the heart, but this hurdle was surmounted by applying ischaemia to remote organs and tissues in pre-, per-, and postconditioning. Although the clinical translation of remote per- and postconditioning has been rapid compared with classical preconditioning, there are numerous basic questions that require further investigation, and wider adoption awaits large-scale randomized clinical trials. Pharmacological mimetics may provide another important therapeutic approach by which to treat evolving myocardial infarction.

Protective conditioning of the brain: expressway or roadblock?

The brain responds to noxious stimulation with protective signalling. Over the last decades, a number of experimental strategies have been established to study endogenous brain protection. Pre-, per-, post- and remote 'conditioning' are now widely used to unravel the underlying mechanisms of endogenous neuroprotection. Some of these strategies are currently being tested in clinical trials to protect the human brain against anticipated damage or to boost protective responses during or after injury. Here we summarize the principles of 'conditioning' research and current efforts to translate this knowledge into effective treatment of patients. Conditioning to induce protected brain states provides an experimental window into endogenous brain protection and can lead to the discovery of drugs mimicking the effects of conditioning. Mechanisms of endogenous brain tolerance can be activated through a wide variety of stimuli that signal 'danger' to the brain. These danger signals lead to the induction of regulator and effector mechanisms, which suppress death and induce survival pathways, decrease metabolism, as well as increase substrate delivery. We conclude that preclinical research on endogenous brain protection has greatly benefited from conditioning strategies, but that clinical applications are challenging, and that we should not prematurely rush into ill-designed and underpowered clinical trials.

Interrupted reperfusion reduces the activation of NADPH oxidase after cerebral I/R injury

Interrupted reperfusion reduces ischemia/reperfusion (I/R) injury. This study was designed to determine whether NADPH oxidase participates in the neural protection against global I/R injury after interrupted reperfusion. Mice were randomly divided into five groups: sham (sham-operated), I/R (20-min global I/R), RR (I/R+interrupted reperfusion), Apo (I/R+apocynin administration), and RR+Apo. Behavioral tests (pole test, beam walking, and Morris water maze) and Nissl staining were undertaken in all five groups; superoxide levels, expression of gp91(phox) and p47(phox), p47(phox) translocation, and Rac1 activation were measured in the sham, I/R, and RR groups. The motor coordination, bradykinesia, and spatial learning and memory, as well as the neuron survival rates, were better in the RR, Apo, and RR+Apo groups than in the I/R group. The NADPH oxidase-dependent superoxide levels, p47(phox) and gp91(phox) expression, p47(phox) translocation, and Rac1 activation were lower in the RR group than in the I/R group. In conclusion, the neural protective effect of interrupted reperfusion is at least partly mediated by decreasing the expression and assembly of NADPH oxidase and the levels of NADPH oxidase-derived superoxide. The most striking reduction Rac1-GTP in the RR group suggests that interrupted reperfusion also acts on the activation of assembled NADPH oxidase by reducing the availability of Rac1-GTP.