Beneficial effects of intracoronary adenosine as an adjunct to primary angioplasty in acute myocardial infarction

No-reflow after recanalization in ischemic stroke: From pathomechanisms to therapeutic strategies

Endovascular reperfusion therapy is the primary strategy for acute ischemic stroke. No-reflow is a common phenomenon, which is defined as the failure of microcirculatory reperfusion despite clot removal by thrombolysis or mechanical embolization. It has been reported that up to 25% of ischemic strokes suffer from no-reflow, which strongly contributes to an increased risk of poor clinical outcomes. No-reflow is associated with functional and structural alterations of cerebrovascular microcirculation, and the injury to the microcirculation seriously hinders the neural functional recovery following macrovascular reperfusion. Accumulated evidence indicates that pathology of no-reflow is linked to adhesion, aggregation, and rolling of blood components along the endothelium, capillary stagnation with neutrophils, astrocytes end-feet, and endothelial cell edema, pericyte contraction, and vasoconstriction. Prevention or treatment strategies aim to alleviate or reverse these pathological changes, including targeted therapies such as cilostazol, adhesion molecule blocking antibodies, peroxisome proliferator-activated receptors (PPARs) activator, adenosine, pericyte regulators, as well as adjunctive therapies, such as extracorporeal counterpulsation, ischemic preconditioning, and alternative or complementary therapies. Herein, we provide an overview of pathomechanisms, predictive factors, diagnosis, and intervention strategies for no-reflow, and attempt to convey a new perspective on the clinical management of no-reflow post-ischemic stroke.

Coronary microvascular obstruction and dysfunction in patients with acute myocardial infarction

Despite prompt epicardial recanalization in patients presenting with ST-segment elevation myocardial infarction (STEMI), coronary microvascular obstruction and dysfunction (CMVO) is still fairly common and is associated with poor prognosis. Various pharmacological and mechanical strategies to treat CMVO have been proposed, but the positive results reported in preclinical and small proof-of-concept studies have not translated into benefits in large clinical trials conducted in the modern treatment setting of patients with STEMI. Therefore, the optimal management of these patients remains a topic of debate. In this Review, we appraise the pathophysiological mechanisms of CMVO, explore the evidence and provide future perspectives on strategies to be implemented to reduce the incidence of CMVO and improve prognosis in patients with STEMI.

Adenosine as adjunctive therapy in acute coronary syndrome: a meta-analysis of randomized controlled trials

AIMS

Adenosine has been tested in several randomized controlled trials (RCTs) to minimize the incidence of coronary microvascular obstruction (CMVO). The aim of this study was to pool all the RCTs comparing intracoronary or intravenous adenosine versus placebo in patients with acute coronary syndrome (ACS) undergoing myocardial revascularization.

METHODS AND RESULTS

PubMed and Scopus electronic databases were scanned for eligible studies up to 5th June 2022. A total of 26 RCTs with 5843 patients were included. Efficacy endpoints were major adverse cardiac events (MACE), all-cause death, non-fatal myocardial infarction, and heart failure. Atrioventricular blocks and ventricular fibrillation/sustained ventricular tachycardia (VF/SVT) were the safety endpoints. Myocardial blush grade, thrombolysis in myocardial infarction (TIMI) flow grade, left ventricular ejection fraction (LVEF), infarct size, and ST-segment resolution were also assessed. Adenosine administration was not associated with any clinical benefit in terms of MACE, all-cause death, non-fatal myocardial infarction, and heart failure. However, adenosine was associated with an increased rate of advanced atrioventricular blocks and of VF/SVT in studies with total mean ischaemic time >3 h, compared to placebo. Remarkably, among patients undergoing percutaneous coronary intervention, adenosine was associated with reduced myocardial blush grade 0-1 and TIMI flow grade 0-2, compared to placebo. Furthermore, adenosine did not show favourable effects on LVEF and infarct size.

CONCLUSION

Adenosine infusion, as adjunctive therapy in ACS, was associated with an increased risk of advanced atrioventricular blocks and increased rates of adenosine-triggered ventricular arrhythmias in patients with long ischaemic time, without providing any clinical benefit compared to placebo.

Mechanisms of the "No-Reflow" Phenomenon After Acute Myocardial Infarction: Potential Role of Pericytes

Pericytes contract during myocardial ischemia resulting in capillary constriction and no reflow. Reversing pericyte contraction pharmacologically reduces no reflow and infarct size. These findings open up an entire new venue of research aimed at altering pericyte function in myocardial ischemia and infarction.

Techniques to Treat Slow-Flow/No-Reflow During Primary Percutaneous Coronary Intervention

OBJECTIVE

The aim of this study was to compare TIMI flow after administering intracoronary (IC) medications through various routes for the treatment of slow flow/no-reflow during primary PCI.

METHODS

Two independent parallel cohorts of the patients who underwent primary PCI for STEMI and developed slow/no-reflow were recruited. Selection of cohort was based on the route of administration of IC medications as proximal or distal. Post administration TIMI follow was compared between the two cohorts.

RESULTS

A total of 100 patients were included in both, proximal and distal, cohort. Distribution of angiographic, clinical and demographic characteristics was not significant between the two cohorts except prevalence of hypertension, and diabetes mellitus. Frequency of hypertension, and diabetes mellitus were 45 % vs.70 %; p < 0.001 and 28 % vs. 44 %; p = 0.018 among patients in distal and proximal cohort respectively. Final TIMI III flow was achieved in significantly higher number of patients in distal cohort with the frequency of 88 % vs. 76 %; p = 0.027 as compared to proximal cohort.

CONCLUSION

Administration of IC medication via distal route is observed to be more effective for the treatment of slow flow/no-reflow during primary PCI. Distal route via export catheter or perforated balloon technique should be preferred wherever feasible.

Endless Journey of Adenosine Signaling in Cardioprotective Mechanism of Conditioning Techniques: Clinical Evidence

Myocardial ischemic injury is a primary cause of death among various cardiovascular disorders. The condition occurs due to an interrupted supply of blood and vital nutrients (necessary for normal cellular activities and viability) to the myocardium, eventually leading to damage. Restoration of blood supply to ischemic tissue is noted to cause even more lethal reperfusion injury. Various strategies, including some conditioning techniques, like preconditioning and postconditioning, have been developed to check the detrimental effects of reperfusion injury. Many endogenous substances have been proposed to act as initiators, mediators, and end effectors of these conditioning techniques. Substances, like adenosine, bradykinin, acetylcholine, angiotensin, norepinephrine, opioids, etc., have been reported to mediate cardioprotective activity. Among these agents, adenosine has been widely studied and suggested to have the most pronounced cardioprotective effects. The current review article highlights the role of adenosine signaling in the cardioprotective mechanism of conditioning techniques. The article also provides an insight into various clinical studies that substantiate the applicability of adenosine as a cardioprotective agent in myocardial reperfusion injury.

Intracoronary Administration of Drugs in Clinical Practice

Intracoronary administration of drugs allows to achieve the fastest possible effect in interventional cardiology. This allows to avoid all the biological filters of the body and achieve the required concentration of the active substance at the injection site. Also, given the local action, systemic side effects are nearly absent. The aim. To study the literature data of the leading countries of the world in the field of intracoronary drug administration. To analyze the experience of different centers on the use of various medications in the treatment of the phenomenon of distal microembolization. Results. One of the first drugs administered intracoronary was streptokinase for the treatment of acute myocardial infarction. After that, it became clear that this method of delivering drugs is possible and can be used. With the beginning of the treatment of acute coronary syndromes by stenting, one of the possible complications arose in the form of no-reflow. At the same time, realizing that this is a local problem, they began to use the possibility of intracoronary administration of drugs to treat this phenomenon. The main advantage of this method is quick response to drug administration. Today, the drugs of choice in the treatment of no-reflow are verapamil, adenosine, nitroprusside, adrenaline. On the other hand, probably the most common drug that is administered intracoronary is nitroglycerin. It is used as a vasodilator in the event of spasm of the coronary arteries. Subsequently, it has been recommended to deliver drugs via a microcatheter or aspiration catheter to achieve even more selective effect in the area of the affected vessel, and this also minimizes drug loss due to coronary reflux into the aortic sinuses while usinga guiding catheter. Work is also underway on the use of intracoronary insulin in acute coronary syndrome in order to reduce the area of damage in myocardial infarction. It is also very promising to study the introduction of stem cells directlyinto the myocardium through a microcatheter in order to regenerate the myocardium after a heart attack. Conclusions. Intracoronary administration of drugs allows to achieve the maximum effect in the shortest possible time. Today, many drugs can be used in this way, starting from the treatment of the phenomenon of distal microembolization and ending with myocardial regeneration after myocardial infarction.

Adenosine in Acute Myocardial Infarction-Associated Reperfusion Injury: Does it Still Have a Role?

The mainstay of acute myocardial infarction has long been timely reperfusion of the culprit obstruction. Reperfusion injury resulting from a multitude of pathophysiological processes has been demonstrated to negatively affect myocardial recovery and function post-infarction. Adenosine interacts directly with the sequential pathophysiological processes culminating in reperfusion injury by inhibiting them upstream. The evidence for adenosine’s benefit in acute myocardial infarction has produced mixed results with regards to myocardial salvage and long-term mortality. The heterogenous evidence with regards to benefits on clinical outcomes has resulted in modest uptake of adenosine in the clinical setting. However, it is critical to analyze the variability in study methodologies. The goal of this review is to evaluate how adenosine dose, route of administration, timing of administration, and site of administration play essential roles in the molecule’s efficacy. The benefits of adenosine, as highlighted in the following review, are clear and its role in the treatment of acute myocardial infarction should not be discounted

Comparison of angiographic results and clinical outcomes of no-reflow after stenting in left anterior descending (LAD) versus non-LAD culprit STEMI

Objectives:

No-reflow is a complication that frequently occurs after stenting during primary percutaneous coronary intervention. In this study, we focused on angiographic results and clinical outcomes after no-reflow in the left anterior descending (LAD) artery versus non–left anterior descending artery ST-elevation myocardial infarction (STEMI).

Methods:

In this prospective study, a total of 201 patients who had developed no-reflow during primary percutaneous coronary intervention were enrolled. The patients were divided into left anterior descending artery culprit and non-left anterior descending artery culprit groups. The primary endpoints were final thrombolysis in myocardial infarction flow, corrected thrombolysis in myocardial infarction frame count and final myocardial blush grade. Secondary endpoints were major adverse cardiovascular events in-hospital and at 1 month.

Results:

Out of the 201 patients, 60.19% had culprit left anterior descending artery. Pulse rate, baseline systolic and diastolic blood pressure, single-vessel disease, left ventricular ejection fraction <30%, baseline thrombolysis in myocardial infarction I flow and final thrombolysis in myocardial infarction II flow (24.8% vs 11.3%, p = .017), and thrombolysis in myocardial infarction frame count (28.17 ± 11.86 vs 24.38 ± 9.05, p = .016) were significantly higher in the left anterior descending artery group. In contrast, baseline Killip Class I, three-vessel disease, baseline thrombolysis in myocardial infarction II flow, final thrombolysis in myocardial infarction III flow (74.4% vs 87.5%, p = .024) and left ventricular ejection fraction >40% were significantly greater in the non–left anterior descending artery group. However, for both in-hospital and at 30 days, overall major adverse cardiovascular event was similar in the two groups. The demographics, clinical and medication profiles and the routes used to treat no-reflow were all comparable in both groups.

Conclusions:

No-reflow in left anterior descending artery ST-elevation myocardial infarction is associated with lower final thrombolysis in myocardial infarction III flow, higher thrombolysis in myocardial infarction frame count and relatively lower Grade III myocardial blush than non-left anterior descending artery ST-elevation myocardial infarction with subsequent lower left ventricular ejection fraction and a higher frequency of in-hospital heart failure and hospitalisation due to heart failure.

Complementary Pharmacotherapy for STEMI Undergoing Primary PCI: An Evidence-Based Clinical Approach

Antithrombotic therapy is the cornerstone of pharmacological treatment in patients undergoing primary percutaneous coronary intervention (PCI). However, the acute management of ST elevation myocardial infarction (STEMI) patients includes therapy for pain relief and potential additional strategies for cardioprotection. The safety and efficacy of some commonly used treatments have been questioned by recent evidence. Indeed a concern about morphine use is the interaction between opioids and oral P2Y₁₂ inhibitors; early beta-blocker treatment has shown conflicting results for the improvement of clinical outcomes; and supplemental oxygen therapy lacks benefit in patients without hypoxia and may be of potential harm. Other additional strategies remain disappointing; however, some treatments may be selectively used. Therefore, we intend to present a critical updated review of complementary pharmacotherapy for a modern treatment approach for STEMI patients undergoing primary PCI.

Comparison of Intracoronary Epinephrine and Adenosine for No-Reflow in Normotensive Patients With Acute Coronary Syndrome (COAR Trial)

Background:

Intracoronary epinephrine has been effectively used in treating refractory no-reflow, but there is a dearth of data on its use as a first-line drug in normotensive patients in comparison to the widely used adenosine.

Methods:

In this open-labeled randomized clinical trial, 201 patients with no-reflow were randomized 1:1 into intracoronary epinephrine as the treatment group and intracoronary adenosine as the control group and followed for 1 month. The primary end points were improvement in coronary flow, as assessed by TIMI (Thrombolysis in Myocardial Infarction) flow, frame counts, and myocardial blush. Secondary end points were in-hospital and short-term mortality and major adverse cardiac events.

Results:

In all, 101 patients received intracoronary epinephrine and 100 patients received adenosine. Epinephrine was generally well tolerated with no immediate table death or ventricular fibrillation. No-reflow was more effectively improved with epinephrine with final TIMI III flow (90.1% versus 78%, P=0.019) and final corrected TIMI frame count (24±8.43 versus 26.63±9.22, P=0.036). However, no significant difference was observed in final grade III myocardial blush (55.4% versus 45%, P=0.139), mean reduction of corrected TIMI frame count (−25.71±11.79 versus −26.08±11.71, P=0.825), in-hospital and short-term mortality, and major adverse cardiac events.

Conclusions:

Epinephrine is relatively safe to use in no-reflow in normotensive patients. A significantly higher frequency of post-treatment TIMI III flow grade and lower final corrected TIMI frame count with relatively better achievement of myocardial blush grade III translate into it displaying relatively better efficacy than adenosine.

Registration:

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04699110.

Mechanism and potential treatment of the "no reflow" phenomenon after acute myocardial infarction: role of pericytes and GPR39

The "no reflow" phenomenon, where the coronary artery is patent after treatment of acute myocardial infarction (AMI) but tissue perfusion is not restored, is associated with worse outcome. The mechanism of no reflow is unknown. We hypothesized that pericytes contraction, in an attempt to maintain a constant capillary hydrostatic pressure during reduced coronary perfusion pressure, causes capillary constriction leading to no reflow and that this effect is mediated through the orphan receptor, GPR39, present in pericytes. We created AMI (coronary occlusion followed by reperfusion) in GPR39 knock out mice and littermate controls. In a separate set of experiments, we treated wild-type mice undergoing coronary occlusion with vehicle or VC43, a specific inhibitor of GPR39, before reperfusion. We found that no reflow zones were significantly smaller in the GPR39 knockouts compared with controls. Both no reflow and infarct size were also markedly smaller in animals treated with VC43 compared with vehicle. Immunohistochemistry revealed greater capillary density and larger capillary diameter at pericyte locations in the GPR39-knockout and VC43-treated mice compared with controls. We conclude that GPR39-mediated pericyte contraction during reduced coronary perfusion pressure causes capillary constriction resulting in no reflow during AMI and that smaller no reflow zones in GPR39-knockout and VC43-treated animals are associated with smaller infarct sizes. These results elucidate the mechanism of no reflow in AMI, as well as providing a therapeutic pathway for the condition.NEW & NOTEWORTHY The mechanism of "no reflow" phenomenon, where the coronary artery is patent after treatment of acute myocardial infarction but tissue perfusion is not restored, is unknown. This condition is associated with worse outcome. Here, we show that GPR39-mediated pericyte contraction during reduced coronary perfusion pressure causes capillary constriction resulting in no reflow. Smaller no-reflow zones in GPR39-knockout animals and those treated with a GPR39 inhibitor are associated with smaller infarct size. These results could have important therapeutic implications.

Angiographic predictors of outcome in myocardial infarction patients presenting with cardiogenic shock: a CULPRIT-SHOCK angiographic substudy

AIMS

The aim of this study was to determine the prognostic impact of pre- and post-PCI TIMI flow grade and TIMI myocardial perfusion grade (TMPG) in a well-defined group of patients with cardiogenic shock due to acute myocardial infarction.

METHODS AND RESULTS

Patients with infarct-related cardiogenic shock randomised into the CULPRIT-SHOCK trial were included in the angiographic predictor analysis whenever their TIMI flow grade or TMPG was available in the core lab database (96.9% of cases). A multivariable logistic regression analysis, adjusted on non-angiographic covariates, was performed to investigate whether TIMI flow grade or TMPG was independently associated with all-cause mortality or renal replacement therapy up to one year. Pre-PCI TIMI flow grade and TMPG did not impact on mortality. When analysed in separate multivariable models, post-PCI TIMI 3 flow and TMPG grade 3 were both significantly associated with reduced risk of 30-day mortality: aOR 0.61 (95% CI: 0.38-0.97, p=0.037) and 0.46 (95% CI: 0.29-0.72, p<0.001), respectively. When considered in the same multivariable model, only TMPG was significantly associated with 30-day mortality (aOR 0.38 [0.20-0.71], p=0.002), the 30-day composite of all-cause mortality and renal replacement therapy (aOR 0.34 [0.18-0.66], p=0.001) and mortality at one-year follow-up (aOR 0.46 [0.24-0.88], p=0.02).

CONCLUSIONS

Post-PCI TIMI flow grade and TMPG are associated with mortality after PCI. TMPG is a better discriminator, supporting microcirculation rather than epicardial reperfusion for prognosis estimation.

High dose escalation of intracoronary adenosine in the assessment of fractional flow reserve: A retrospective cohort study

Maximal hyperaemia for fractional flow reserve (FFR) may not be achieved with the current recommended doses of intracoronary adenosine. Higher doses (up to 720 μg) have been reported to optimize hyperaemic stimuli in small dose-response studies. Real-world data from a large cohort of patients is needed to evaluate FFR results and the safety of high-dose escalation. This is a retrospective study aimed to evaluate the safety and frequency of FFR ≤0.8 after high-dose escalation of intracoronary adenosine. Data were extracted from the medical databases of two university hospitals. Increasing doses (100, 200, 400, 600, and 800 μg) of adenosine were administered as intracoronary boluses until FFR ≤0.8 was achieved or heart block developed. The percentage of FFR ≤0.8 after higher-dose escalation was compared with those at conventional doses, and the predictors for FFR ≤0.8 after higher doses were analysed. In the 1163 vessels of 878 patients, 402 vessels (34.6%) achieved FFR ≤0.8 at conventional doses and 623 vessels (53.6%) received high-dose escalation. An additional 84 vessels (13.5%) achieved FFR ≤0.8 after high-dose escalation. No major complications developed during high-dose escalation. Borderline FFR (0.81-0.85) at the conventional dose, stenosis >60%, and triple-vessel disease increased the likelihood of FFR ≤0.8 after high-dose escalation, but chronic kidney disease decreased it. For vessels of borderline FFR at conventional doses, 46% achieved FFR ≤0.8 after high-dose escalation. In conclusion, High-dose escalation of intracoronary adenosine increases the frequency of FFR ≤0.8 without major complications. It could be especially feasible for borderline FFR values near the 0.8 diagnostic threshold.

Adenosine and Its Receptors: An Expected Tool for the Diagnosis and Treatment of Coronary Artery and Ischemic Heart Diseases

Adenosine is an endogenous nucleoside which strongly impacts the cardiovascular system. Adenosine is released mostly by endothelial cells and myocytes during ischemia or hypoxia and greatly regulates the cardiovascular system via four specific G-protein-coupled receptors named A₁R, A_2AR, A_2BR, and A₃R. Among them, A₂ subtypes are strongly expressed in coronary tissues, and their activation increases coronary blood flow via the production of cAMP in smooth muscle cells. A_2A receptor modulators are an opportunity for intense research by the pharmaceutical industry to develop new cardiovascular therapies. Most innovative therapies are mediated by the modulation of adenosine release and/or the activation of the A_2A receptor subtypes. This review aims to focus on the specific exploration of the adenosine plasma level and its relationship with the A_2A receptor, which seems a promising biomarker for a diagnostic and/or a therapeutic tool for the screening and management of coronary artery disease. Finally, a recent class of selective adenosine receptor ligands has emerged, and A_2A receptor agonists/antagonists are useful tools to improve the management of patients suffering from coronary artery disease.

Targeted pharmacotherapy for ischemia reperfusion injury in acute myocardial infarction

INTRODUCTION

Achieving reperfusion immediately after acute myocardial infarction improves outcomes; despite this, patients remain at a high risk for mortality and morbidity at least for the first year after the event. Ischemia-reperfusion injury (IRI) has a complex pathophysiology and plays an important role in myocardial tissue injury, repair, and remodeling.

AREAS COVERED

In this review, the authors discuss the various mechanisms and their pharmacological agents currently available for reducing myocardial ischemia-reperfusion injury (IRI). They review important original investigations and trials in various clinical databases for treatments targeting IRI.

EXPERT OPINION

Encouraging results observed in many preclinical studies failed to show similar success in attenuating myocardial IRI in large-scale clinical trials. Identification of critical risk factors for IRI and targeting them individually rather than one size fits all approach should be the major focus of future research. Various newer therapies like tocilizumab, anakinra, colchicine, revacept, and therapies targeting the reperfusion injury salvage kinase pathway, survivor activating factor enhancement, mitochondrial pathways, and angiopoietin-like peptide 4 hold promise for the future.

Postconditioning with Nitrates Protects Against Myocardial Reperfusion Injury: A New Use for an Old Pharmacological Agent

Early reperfusion remains the key therapy to salvage viable myocardium and must be applied as soon as possible following an acute myocardial infarction (AMI) to attenuate the ischemic insult. However, reperfusion injury may develop following reintroduction of blood and oxygen to vulnerable myocytes, which results in more severe cell death than in the preceding ischemic episode. Ischemic postconditioning (I-PostC) provides a cardioprotective effect in combination with pharmacological agents. Although nitrates have been tested in many experimental and clinical studies of acute AMI to evaluate the cardioprotective effect, few investigations have been focused on nitrates postconditioning in patients undergoing percutaneous coronary intervention (PCI). This review presents the manifestations of myocardial reperfusion injury (RI) and potential mechanisms underlying it, and provides the mechanisms involved in the cardioprotection of I-PostC. We also present a new therapeutic approach to attenuate RI by use of an ‘old’ agent – nitrates – in AMI patients.

2019 Canadian Cardiovascular Society/Canadian Association of Interventional Cardiology Guidelines on the Acute Management of ST-Elevation Myocardial Infarction: Focused Update on Regionalization and Reperfusion

Rapid reperfusion of the infarct-related artery is the cornerstone of therapy for the management of acute ST-elevation myocardial infarction (STEMI). Canada's geography presents unique challenges for timely delivery of reperfusion therapy for STEMI patients. The Canadian Cardiovascular Society/Canadian Association of Interventional Cardiology STEMI guideline was developed to provide advice regarding the optimal acute management of STEMI patients irrespective of where they are initially identified: in the field, at a non-percutaneous coronary intervention-capable centre or at a percutaneous coronary intervention-capable centre. We had also planned to evaluate and incorporate sex and gender considerations in the development of our recommendations. Unfortunately, inadequate enrollment of women in randomized trials, lack of publication of main outcomes stratified according to sex, and lack of inclusion of gender as a study variable in the available literature limited the feasibility of such an approach. The Grading Recommendations, Assessment, Development, and Evaluation system was used to develop specific evidence-based recommendations for the early identification of STEMI patients, practical aspects of patient transport, regional reperfusion decision-making, adjunctive prehospital interventions (oxygen, opioids, antiplatelet therapy), and procedural aspects of mechanical reperfusion (access site, thrombectomy, antithrombotic therapy, extent of revascularization). Emphasis is placed on integrating these recommendations as part of an organized regional network of STEMI care and the development of appropriate reperfusion and transportation pathways for any given region. It is anticipated that these guidelines will serve as a practical template to develop systems of care capable of providing optimal treatment for a wide range of STEMI patients.

Ischemia Reperfusion Injury: Mechanisms of Damage/Protection and Novel Strategies for Cardiac Recovery/Regeneration

Ischemic diseases in an aging population pose a heavy social encumbrance. Moreover, current therapeutic approaches, which aimed to prevent or minimize ischemia-induced damage, are associated with relevant costs for healthcare systems. Early reperfusion by primary percutaneous coronary intervention (PPCI) has undoubtedly improved patient's outcomes; however, the prevention of long-term complications is still an unmet need. To face these hurdles and improve patient's outcomes, novel pharmacological and interventional approaches, alone or in combination, reducing myocardium oxygen consumption or supplying blood flow via collateral vessels have been proposed. A number of clinical trials are ongoing to validate their efficacy on patient's outcomes. Alternative options, including stem cell-based therapies, have been evaluated to improve cardiac regeneration and prevent scar formation. However, due to the lack of long-term engraftment, more recently, great attention has been devoted to their paracrine mediators, including exosomes (Exo) and microvesicles (MV). Indeed, Exo and MV are both currently considered to be one of the most promising therapeutic strategies in regenerative medicine. As a matter of fact, MV and Exo that are released from stem cells of different origin have been evaluated for their healing properties in ischemia reperfusion (I/R) settings. Therefore, this review will first summarize mechanisms of cardiac damage and protection after I/R damage to track the paths through which more appropriate interventional and/or molecular-based targeted therapies should be addressed. Moreover, it will provide insights on novel non-invasive/invasive interventional strategies and on Exo-based therapies as a challenge for improving patient's long-term complications. Finally, approaches for improving Exo healing properties, and topics still unsolved to move towards Exo clinical application will be discussed.

Adenosine and the Cardiovascular System

Adenosine is an endogenous nucleoside with a short half-life that regulates many physiological functions involving the heart and cardiovascular system. Among the cardioprotective properties of adenosine are its ability to improve cholesterol homeostasis, impact platelet aggregation and inhibit the inflammatory response. Through modulation of forward and reverse cholesterol transport pathways, adenosine can improve cholesterol balance and thereby protect macrophages from lipid overload and foam cell transformation. The function of adenosine is controlled through four G-protein coupled receptors: A₁, A_2A, A_2B and A₃. Of these four, it is the A_2A receptor that is in a large part responsible for the anti-inflammatory effects of adenosine as well as defense against excess cholesterol accumulation. A_2A receptor agonists are the focus of efforts by the pharmaceutical industry to develop new cardiovascular therapies, and pharmacological actions of the atheroprotective and anti-inflammatory drug methotrexate are mediated via release of adenosine and activation of the A_2A receptor. Also relevant are anti-platelet agents that decrease platelet activation and adhesion and reduce thrombotic occlusion of atherosclerotic arteries by antagonizing adenosine diphosphate-mediated effects on the P2Y12 receptor. The purpose of this review is to discuss the effects of adenosine on cell types found in the arterial wall that are involved in atherosclerosis, to describe use of adenosine and its receptor ligands to limit excess cholesterol accumulation and to explore clinically applied anti-platelet effects. Its impact on electrophysiology and use as a clinical treatment for myocardial preservation during infarct will also be covered. Results of cell culture studies, animal experiments and human clinical trials are presented. Finally, we highlight future directions of research in the application of adenosine as an approach to improving outcomes in persons with cardiovascular disease.

Cardioprotection of PLGA/gelatine cardiac patches functionalised with adenosine in a large animal model of ischaemia and reperfusion injury: A feasibility study

The protection from ischaemia‐reperfusion‐associated myocardial infarction worsening remains a big challenge. We produced a bioartificial 3D cardiac patch with cardioinductive properties on stem cells. Its multilayer structure was functionalised with clinically relevant doses of adenosine. We report here the first study on the potential of these cardiac patches in the controlled delivery of adenosine into the in vivo ischaemic‐reperfused pig heart. A Fourier transform infrared chemical imaging approach allowed us to perform a characterisation, complementary to the histological and biochemical analyses on myocardial samples after in vivo patch implantation, increasing the number of investigations and results on the restricted number of pigs (n = 4) employed in this feasibility step. In vitro tests suggested that adenosine was completely released by a functionalised patch, a data that was confirmed in vivo after 24 hr from patch implantation. Moreover, the adenosine‐loaded patch enabled a targeted delivery of the drug to the ischaemic‐reperfused area of the heart, as highlighted by the activation of the pro‐survival signalling reperfusion injury salvage kinases pathway. At 3 months, though limited to one animal, the used methods provided a picture of a tissue in dynamic conditions, associated to the biosynthesis of new collagen and to a non‐fibrotic outcome of the healing process underway. The synergistic effect between the functionalised 3D cardiac patch and adenosine cardioprotection might represent a promising innovation in the treatment of reperfusion injury. As this is a feasibility study, the clinical implications of our findings will require further in vivo investigation on larger numbers of ischaemic‐reperfused pig hearts.

Outcomes Among Clopidogrel, Prasugrel, and Ticagrelor in ST-Elevation Myocardial Infarction Patients Who Underwent Primary Percutaneous Coronary Intervention From the TOTAL Trial

BACKGROUND

Robust comparisons between oral P2Y12 inhibitors (clopidogrel, prasugrel, ticagrelor) in ST-elevation myocardial infarction (STEMI) patients who undergo primary percutaneous coronary intervention are lacking. We sought to evaluate outcomes on the basis of P2Y12 inhibitor therapy in patients from the Thrombectomy With PCI Versus PCI Alone in Patients With STEMI Undergoing Primary PCI (TOTAL) trial.

METHODS

We grouped 9932 patients according to P2Y12 inhibitor at hospital discharge: clopidogrel (n = 6500; 65.5%), prasugrel (n = 1244; 12.5%), or ticagrelor (n = 2188; 22.0%). The primary composite end point of cardiovascular death, recurrent myocardial infarction, cardiogenic shock, or New York Heart Association class IV heart failure was examined at 1 year. Secondary efficacy and safety end points were also assessed. Cox proportional hazard ratios were determined and adjusted for confounders via propensity scoring.

RESULTS

Baseline characteristics differing between the 3 groups were mainly age 75 years or older, diabetes, and previous stroke. After adjustment, ticagrelor use was associated with a lower rate of the primary composite outcome compared with clopidogrel (adjusted hazard ratio [aHR], 0.72; 95% confidence interval [CI], 0.57-0.91; P < 0.02) and prasugrel (aHR, 0.65; 95% CI, 0.48-0.89; P = 0.02). Prasugrel use was not associated with a lower rate of the primary outcome compared with clopidogrel (aHR, 1.09; 95% CI, 0.86-1.39; P > 0.99). Neither prasugrel nor ticagrelor were associated with increased risk of stroke compared with clopidogrel. Compared with clopidogrel, ticagrelor was associated with significantly lower rates of major bleeding.

CONCLUSIONS

In this observational analysis of STEMI patients who underwent primary percutaneous coronary intervention, ticagrelor was associated with improved outcomes compared with clopidogrel and prasugrel. An appropriately powered randomized trial is needed to confirm these findings.

Assessing and managing coronary microcirculation dysfunction in acute ST-segment elevation myocardial infarction

INTRODUCTION

Microvascular dysfunction in the setting of acute ST-segment elevation myocardial infarction (STEMI) is an indicator of poor long-term prognosis. Prompt assessment and pharmacological or procedural therapy (prophylactic or post onset of dysfunction) may improve outcomes in STEMI post-primary percutaneous intervention. Areas covered: The aim of this review is to provide a comprehensive analysis of the evidence available about the assessment and management of coronary microcirculatory injury/dysfunction in STEMI. We also aim to elucidate the possible strategies that could be applied in clinical practice to support the application of already available or novel therapeutic strategies for the prevention and management of microvascular impairment. Expert commentary: There are multiple established methods in assessing microvascular dysfunction, both non-invasively and invasively. Invasive physiological measurements allow real-time assessment of microvascular dysfunction and have prognostic cut-off values. Multiple therapeutic modalities exist for both preventing and treating microvascular dysfunction. These can be either pharmacological or mechanical, and there is no algorithm to guide if, how and when to apply them. Future research into both procedural and pharmacological therapy guided by physiological measurements is needed, with the aim of recognizing high-risk patients who would benefit from therapy.

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.

Effect of intracoronary agents on the no-reflow phenomenon during primary percutaneous coronary intervention in patients with ST-elevation myocardial infarction: a network meta-analysis

Background

Despite the restoration of epicardial flow after primary percutaneous coronary intervention (PPCI), myocardial reperfusion remains impaired in a significant proportion of patients. We performed a network meta-analysis to assess the effect of 7 intracoronary agents (adenosine, anisodamine, diltiazem, nicorandil, nitroprusside, urapidil, and verapamil) on the no-reflow phenomenon in patients with ST-elevation myocardial infarction (STEMI) undergoing PPCI.

Methods

Database searches were conducted to identify randomized controlled trials (RCTs) comparing the 7 agents with each other or with standard PPCI. Outcome measures included thrombolysis in myocardial infarction flow grade (TFG), ST-segment resolution (STR), left ventricular ejection fraction (LVEF), major adverse cardiovascular events (MACEs), and adverse events.

Results

Forty-one RCTs involving 4069 patients were analyzed. The addition of anisodamine to standard PPCI for STEMI was associated with improved post-procedural TFG, more occurrences of STR, and improvement of LVEF. The cardioprotective effect of anisodamine conferred a MACE-free survival benefit. Additionally, nitroprusside was regarded as efficient in improving coronary flow and clinical outcomes. Compared with standard care, adenosine, nicorandil, and verapamil improved coronary flow but had no corresponding benefits regarding cardiac function and clinical outcomes. The ranking probability for the 7 treatment drugs showed that anisodamine consistently ranked the highest in efficacy outcomes (TFG < 3, STR, LVEF, and MACEs). No severe adverse events, such as hypotension and malignant arrhythmia, were observed in patients treated with anisodamine. Network meta-regression analysis showed that age, the time to reperfusion, and study follow-up did not affect the treatment effects.

Conclusions

The intracoronary administration of anisodamine appears to improve myocardial reperfusion, cardiac function, and clinical outcomes in patients with STEMI undergoing PPCI. Given the limited quality and quantity of the included studies, more rigorous RCTs are needed to verify the role of this inexpensive and well-tolerated regimen.

Electronic supplementary material

The online version of this article (10.1186/s12872-017-0722-z) contains supplementary material, which is available to authorized users.

A Randomized Controlled Trial of Intra-Aortic Adenosine Infusion Before Release of the Aortic Cross-Clamp During Coronary Artery Bypass Surgery

OBJECTIVES

To assess the feasibility, safety, and potential useful effect of adenosine as a postconditioning agent in patients undergoing coronary artery bypass grafting surgeries.

DESIGN

Prospective randomized controlled study.

SETTING

University hospital.

PARTICIPANTS

The study comprised 60 patients scheduled for coronary artery bypass grafting surgery.

INTERVENTIONS

Adenosine (postconditioning group) or placebo (control group). Adenosine infusion (150 µg/kg/min) for 10 minutes via a cardioplegia needle into the aortic root was started 10 minutes before aortic cross-clamp removal.

MEASUREMENTS AND MAIN RESULTS

Compared with the control group, ejection fraction, fractional shortening, cardiac index (2.9 ± 0.3 v 2.2 ± 0.3 L/min/m², p = 0.032 at 60 min postbypass) and diastolic function indices were significantly better in the postconditioning group at most time points in the postbypass period. Cardiac troponin I and creatine kinase-MB release and the inotropic score were significantly lower in the postconditioning group at most time points in the postoperative period. The need for intra-aortic balloon and epicardial pacing were comparable in both groups, whereas incidence of arrhythmia, duration of postoperative mechanical ventilation, and intensive care unit and total hospital stays were significantly lower in the postconditioning group.

CONCLUSIONS

Adenosine postconditioning provided cardiac protection as evidenced by a favorable outcome on systolic and diastolic function indices, less cardiac troponin I and creatine kinase-MB release, lower incidence of arrhythmia, lower inotropic score, and shorter duration of postoperative mechanical ventilation and intensive care unit stay.

Current State of the Art in Approaches to Saphenous Vein Graft Interventions

Saphenous vein grafts (SVGs), used during coronary artery bypass graft surgery for severe coronary artery disease, are prone to degeneration and occlusion, leading to poor long-term patency compared with arterial grafts. Interventions used to treat SVG disease are susceptible to high rates of periprocedural MI and no-reflow. To minimise complications seen with these interventions, proper stents, embolic protection devices (EPDs) and pharmacological selection are crucial. Regarding stent selection, evidence has demonstrated superiority of drug-eluting stents over bare-metal stents in SVG intervention. The ACCF/AHA/SCA American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Society for Cardiovascular Angiography and Interventions guidelines recommend the use of EPDs during SVG intervention to decrease the risk of periprocedural MI, distal embolisation and no-reflow. The optimal pharmacological treatment for slow or no-reflow remains unclear, but various vasodilators show promise.

MethotrexaTE THerapy in ST-Segment Elevation MYocardial InfarctionS

Purpose:

Methotrexate is an anti-inflammatory drug that has been shown to have anti-ischemic effects. Our aim was to evaluate if methotrexate could reduce infarct size in patients with ST-segment elevation myocardial infarction (STEMI).

Methods:

We randomly assigned patients with STEMI to receive either methotrexate or placebo. Primary outcome was infarct size determined by calculating the area under the curve (AUC) for creatine kinase (CK) release. Secondary outcomes were AUC of CK MB (CK-MB) and AUC of troponin I; peak CK, peak CK-MB, and troponin I; B-type natriuretic peptide (BNP) level, high-sensitivity C-reactive protein (hsCRP) result, and erythrocyte sedimentation rate (ESR); left ventricular ejection fraction (LVEF); thrombolysis in myocardial infarction (TIMI) frame count; Killip score; mortality and reinfarction incidence; and incidence of adverse reactions.

Results:

We included 84 patients. Median AUC of CK was 78 861.0 in the methotrexate group and 68 088.0 in the placebo group ( P = .10). Patients given methotrexate and placebo exhibited, respectively, median AUC for CK-MB of 9803.4 and 8037.0 ( P = .42); median AUC for troponin of 3691.1 and 2132.6 ( P = .09); peak CK of 2806.0 and 2147.0 ( P = .05); peak CK-MB of 516.0 and 462.3 ( P = .25); and peak troponin of 121.0 and 85.1 ( P = .06). At 3 months, LVEF was lower in patients who received methotrexate (49.0% ± 14.1%) than in patients given placebo (56.4% ± 10.0%; P = .01). There were no differences in hsCRP, ESR, BNP, Killip scores, TIMI frame count, reinfarction, and mortality rates. There was a higher median serum glutamic–pyruvic transaminase levels in the methotrexate group.

Conclusion:

Methotrexate did not reduce infarction size and worsened LVEF at 3 months ( Clinicaltrials.gov identifier NCT01741558).

A review of strategies for infarct size reduction during acute myocardial infarction

Advances in medical and interventional therapy over the last few decades have revolutionized the treatment of acute myocardial infarction. Despite the ability to restore epicardial coronary artery patency promptly through percutaneous coronary intervention, tissue level damage may continue. The reported 30-day mortality after all acute coronary syndromes is 2 to 3%, and around 5% following myocardial infarction. Post-infarct complications such as heart failure continue to be a major contributor to cardiovascular morbidity and mortality. Inadequate microvascular reperfusion leads to worse clinical outcomes and potentially strategies to reduce infarct size during periods of ischemia-reperfusion can improve outcomes. Many strategies have been tested, but no single strategy alone has shown a consistent result or benefit in large scale randomised clinical trials. Herein, we review the historical efforts, current strategies, and potential novel concepts that may improve myocardial protection and reduce infarct size.

Predictors of no- reflow during primary angioplasty for acute myocardial infarction, from Medical College Hospital, Trivandrum

Background

Primary angioplasty (PCI) for acute myocardial infarction is associated with no-reflow phenomenon, in about 5–25% of cases. Here we analysed the factors predicting no reflow .

Methods

This was a case control study of consecutive patients with acute myocardial infarction who underwent Primary PCI from August 2014 to February 2015.

Results

Of 181 patients who underwent primary PCI, 47 (25.9%) showed an angiographic no-reflow phenomenon. The mean age was 59.19 ± 10.25 years and females were 11%.

Univariate predictors of no reflow were age >60 years (OR = 6.146, 95%CI 2.937–12.86, P = 0<0.001), reperfusion time >6 h (OR = 21.94, 95%CI 9.402–51.2, P = < 0.001), low initial TIMI flow (≤1) (OR = 12.12, 95%CI 4.117–35.65, P < 0.001), low initial TMPG flow (≤1) (OR = 36.19, 95%CI 4.847–270.2, P < 0.001) a high thrombus burden (OR = 11.04,95%CI 5.124–23.8, P < 0.001), a long target lesion (OR = 8.54, 95%CI 3.794–19.23, P < 0.001), Killip Class III/IV(OR = 2.937,95%CI 1.112–7.756,P = 0.025) and overlap stenting(OR = 3.733,95%CI 1.186–11.75,P = 0.017).

Multiple stepwise logistic regression analysis predictors were: longer reperfusion time > 6 h (OR = 13.844, 95%CI 3.214–59.636, P = <0.001), age >60 years (OR = 8.886, 95%CI 2.145–36.80, P = 0.003), a long target lesion (OR = 8.637, 95%CI 1.975–37.768, P = 0.004), low initial TIMI flow (≤1) (OR = 20.861, 95%CI 1.739–250.290, P = 0.017).

Conclusions

It is important to minimize trauma to the vessel, avoid repetitive balloon dilatations use direct stenting and use the shortest stent if possible.

Evaluation of Short- and Long-Term Efficacy of Combined Intracoronary Administration of High-Dose Adenosine and Tirofiban during Primary Percutaneous Coronary Intervention

BACKGROUND

To assess the influence of combined intracoronary application of high-dose adenosine and tirofiban in primary percutaneous coronary intervention (PCI) on clinical events and cardiac function.

METHODS

Our study evaluated consecutive patients with acute ST-segment elevation myocardial infarction undergoing primary PCI, who were randomly divided into adenosine group (n = 130) and control group (n = 128). Combined with thrombus aspiration and then intracoronary tirofiban, the adenosine group received intracoronary adenosine (2 mg) through the aspiration catheter 2 times. After thrombus aspiration and stenting of the infarct- related artery, the control group received placebo. The primary endpoint of our investigation was major adverse cardiac events (MACE) at the 1-year and 3-year marks. The secondary endpoint comprised left ventricular remodeling (LVR) at 6 months, myocardial blush grade (MBG), thrombolysis in myocardial infarction (TIMI) flow grade and corrected TIMI frame count (CTFC) after PCI.

RESULTS

Our study found that TIMI flow grade post-PCI did not differ significantly between the 2 groups, while CTFC favored the adenosine-treated patients (21.6 ± 6.5 vs. 25.1 ± 7.8, p = 0.001). Although the adenosine group achieved a higher rate of MBG 3 (45.1% vs. 32.0%, p = 0.035) and MBG 2-3 (76.2% vs. 62.3%, p = 0.018) than the control group, the incidences of MACE at 1 year (20.0% vs. 25.0%, p = 0.373) and 3 years (26.9% vs. 32.0%, p = 0.413) were comparable. LVR occurred in 23.1% (27/117) of adenosine-treated patients and in 29.8% (43/114) of the controls (p = 0.296).

CONCLUSIONS

Intracoronary administration of high-dose adenosine combined with intracoronary tirofiban and thrombus aspiration may further improve myocardial perfusion after primary PCI.

Mitochondrial Membrane Permeability Inhibitors in Acute Myocardial Infarction: Still Awaiting Translation

Despite therapeutic advances, acute myocardial infarction (AMI) remains a leading cause of morbidity and mortality worldwide. One potential limitation of the current treatment paradigm is the lack of effective therapies to optimize reperfusion after ischemia and prevent reperfusion-mediated injury. Experimental studies indicate that this process accounts for up to 50% of the final infarct size, lending it importance as a potential target for cardioprotection. However, multiple therapeutic approaches have shown potential in pre-clinical and early phase trials but a paucity of clear clinical benefit when expanded to larger studies. Here we explore this history of trials and errors of the studies of cyclosporine A and other mitochondrial membrane permeability inhibitors, agents that appeared to have a promising pre-clinical record yet provided disappointing results in phase III clinical trials.

Limitation of Infarct Size and No-Reflow by Intracoronary Adenosine Depends Critically on Dose and Duration

OBJECTIVES

In the absence of effective clinical pharmacotherapy for prevention of reperfusion-mediated injury, this study re-evaluated the effects of intracoronary adenosine on infarct size and no-reflow in a porcine model of acute myocardial infarction using clinical bolus and experimental high-dose infusion regimens.

BACKGROUND

Despite the clear cardioprotective effects of adenosine, when administered prior to ischemia, studies on cardioprotection by adenosine when administered at reperfusion have yielded contradictory results in both pre-clinical and clinical settings.

METHODS

Swine (54 ± 1 kg) were subjected to a 45-min mid-left anterior descending artery occlusion followed by 2 h of reperfusion. In protocol A, an intracoronary bolus of 3 mg adenosine injected over 1 min (n = 5) or saline (n = 10) was administered at reperfusion. In protocol B, an intracoronary infusion of 50 μg/kg/min adenosine (n = 15) or saline (n = 21) was administered starting 5 min prior to reperfusion and continued throughout the 2-h reperfusion period.

RESULTS

In protocol A, area-at-risk, infarct size, and no-reflow were similar between groups. In protocol B, risk zones were similar, but administration of adenosine resulted in significant reductions in infarct size from 59 ± 3% of the area-at-risk in control swine to 46 ± 4% (p = 0.02), and no-reflow from 49 ± 6% of the infarct area to 26 ± 6% (p = 0.03).

CONCLUSIONS

During reperfusion, intracoronary adenosine can limit infarct size and no-reflow in a porcine model of acute myocardial infarction. However, protection was only observed when adenosine was administered via prolonged high-dose infusion, and not via short-acting bolus injection. These findings warrant reconsideration of adenosine as an adjuvant therapy during early reperfusion.

Real-world use of fractional flow reserve in Germany: results of the prospective ALKK coronary angiography and PCI registry

BACKGROUND

There is growing evidence for beneficial prognostic and economic effects of FFR-guided treatment of stable coronary artery disease. We sought to evaluate the real-world use of FFR measurements in patients undergoing elective coronary angiography.

METHODS AND RESULTS

We analyzed the data of the prospective ALKK coronary angiography and PCI registry including data of 38 hospitals from January 2010 to December 2013. A total of 100,977 patients undergoing coronary angiography were included. In 3240 patients (3.2 %) intracoronary pressure measurement was performed. There was a wide range of use of FFR measurement in the different analyzed ALKK hospitals from 0.1 to 8.8 % in elective patients with suspected or known coronary artery disease (median 2.7 %, quartiles 0.9 and 5.3 %), with a successive increase of use over time during the study period. Overall, it was performed in 3.2 % of coronary angiographies. Use in patients with three-vessel disease (2.5 %) and recommendation for bypass surgery (1.6 %) was less frequent. In procedures without PCI, dose area product was higher in the FFR group (2641 cGy × cm² vs. 2368 cGy × cm², p < 0.001), while it was lower in procedures with ad hoc PCI (4676 cGy × cm² vs. 5143 cGy × cm², p < 0.001). The performing center turned out to be the strongest predictor.

CONCLUSIONS

The use of FFR measurement was very heterogeneous between different hospitals and in general relatively low, in particular in patients with multivessel disease or recommendation for bypass surgery, but there was a positive trend during the study period. Technically, FFR measurement was not associated with an increased periprocedural complication rate.

Effect of Thrombus Composition and Viscosity on Sonoreperfusion Efficacy in a Model of Micro-Vascular Obstruction

Distal embolization of micro-thrombi during stenting for myocardial infarction causes micro-vascular obstruction (MVO). We have previously shown that sonoreperfusion (SRP), a microbubble (MB)-mediated ultrasound (US) therapy, resolves MVO from venous micro-thrombi in vitro in saline. However, blood is more viscous than saline, and arterial thrombi that embolize during stenting are mechanically distinct from venous clot. Therefore, we tested the hypothesis that MVO created with arterial micro-thrombi are more resistant to SRP therapy compared with venous micro-thrombi, and higher viscosity further increases the US requirement for effective SRP in an in vitro model of MVO. Lipid MBs suspended in plasma with adjusted viscosity (1.1 cP or 4.0 cP) were passed through tubing bearing a mesh with 40-μm pores to simulate a micro-vascular cross-section; upstream pressure reflected thrombus burden. To simulate MVO, the mesh was occluded with either arterial or venous micro-thrombi to increase upstream pressure to 40 mmHg ± 5 mmHg. Therapeutic long-tone-burst US was delivered to the occluded area for 20 min. MB activity was recorded with a passive cavitation detector. MVO caused by arterial micro-thrombi at either blood or plasma viscosity resulted in less effective SRP therapy compared to venous thrombi. Higher viscosity further reduced the effectiveness of SRP therapy. The passive cavitation detector showed a decrease in inertial cavitation when viscosity was increased, while stable cavitation was affected in a more complex manner. Overall, these data suggest that arterial thrombi may require higher acoustic pressure US than venous thrombi to achieve similar SRP efficacy; increased viscosity decreases SRP efficacy; and both inertial and stable cavitation are implicated in observed SRP efficacy.

Percutaneous Mechanical Reperfusion During Acute Myocardial Infarction

The treatment of acute myocardial infarction has progressed from bedrest to mechanical, catheter-based reperfusion. The authors review the use of percutaneous coronary intervention (PCI) as a primary treatment for acute myocardial infarction and the use of adjunctive agents. The most recent American College of Cardiology/ American Heart Association (ACC/AHA) guidelines for the use of PCI in ST segment elevation myocardial infarction (MI) advocate the use of PCI as primary therapy at those centers in which the procedure can be performed within accepted standards. Because a majority of hospitals (80%) do not have the capability of performing primary PCI, most patients are treated with thrombolytic therapy. PCI should be considered in those patients treated with thrombolytic therapy who have persistent or recurrent ischemia and/or cardiogenic shock. For patients with non-ST elevation MI, the use of an invasive strategy (early angiography and PCI if needed) has recently shown to be beneficial. Although revascularization is the basis of the acute therapy of MI, additional pharmacologic therapy in the acute setting is now recognized as a key to favorable long-term outcome.

Microvascular Alterations After Temporary Coronary Artery Occlusion: The No-Reflow Phenomenon

In experimental models of temporary coronary artery occlusion, tissue perfusion at the microvascular level remains incomplete even after patency of the infarct-related epicardial coronary artery is established, and distinct perfusion defects develop within the risk zone. This no-reflow phenomenon can be regarded as a basic cardiac response to ischemia-reperfusion. Perfusion defects observed in the clinical realm after reperfusion therapy for myocardial infarction may substantially be related to this mechanism in addition to microembolization and activation of platelets, as suggested in several recent studies. A major determinant of the amount of no-reflow seems to be infarct size itself. Reperfusion-related expansion of noreflow zones occurs within the first hours after the reopening of the coronary artery with a parallel reduction of regional myocardial flow, resulting in a potential therapeutic window. With various cardioprotective interventions, a close correlation between the size of the anatomic no-reflow and necrosis is a reproducible feature, which suggests a causal link between both entities of ischemic cardiac damage. Although vasodilating interventions failed to uncouple no-reflow zones from necrosis, the steps in the causal chain between microvascular and myocardial damage remain to be identified. On a long-term basis, tissue perfusion after ischemia-reperfusion remains markedly compromised for at least 4 weeks. Recent morphometric cardiac analyses suggested that the level of tissue perfusion after 4 weeks is a significant predictor of various indices of infarct healing, such as scar thickness, and infarct expansion index. As a consequence, improving tissue perfusion might concomitantly improve the healing process, which may provide the pathoanatomic basis for prognostic implications of no-reflow.

Management of Complications

Percutaneous coronary intervention (PCI) has matured rapidly to tackle increasingly complex coronary disease. Operators must be aware of the incidence of the basic risks involved with coronary angiography and PCI to appropriately inform patients and obtain procedural consent. Even before a wire enters a coronary artery, specific risks, including vascular access complications, renal injury, allergic reaction, and radiation injury, are constantly present. With initiation of PCI, new risks to the coronary circulation arise. A fundamental knowledge of the presentation of these complications and expert ability to emergently manage them are of the utmost importance to the successful completion of PCI.

A Practical Method for No-Reflow Treatment

No-reflow is an undesirable result of percutaneous coronary interventions. Vasoactive drug administration at the distal part of the coronary artery is suggested as a therapeutic option for no-reflow treatment. Here, we represent two cases of successful no-reflow management with previously used monorail balloon at the same procedure as a hand-made distal infusion catheter.