Coronary thrombosis and platelet/fibrin microemboli in death associated with acute myocardial infarction

Qihuang Zhuyu formula alleviates coronary microthrombosis by inhibiting PI3K/Akt/αIIbβ3-mediated platelet activation

BACKGROUND

Coronary microembolism (CME) is commonly seen in the peri-procedural period of Percutaneous Coronary Intervention (PCI), where local platelet activation and endothelial cell inflammation crosstalk may lead to micro thrombus erosion and rupture, with serious consequences. Qihuang Zhuyu Formula (QHZYF) is a Chinese herbal compound with high efficacy against coronary artery disease, but its antiplatelet mechanism is unclear.

HYPOTHESIS/PURPOSE

This study aimed to elucidate the effects and mechanisms of QHZYF on sodium laurate-induced CME using network pharmacology and in vitro and in vivo experiments.

METHODS

We employed high-performance liquid chromatography mass spectrometry to identify the main components of QHZYF. Network pharmacology analysis, molecular docking and surface plasmon resonance (SPR) were utilized to predict the primary active components, potential therapeutic targets, and intervention pathways mediating the effects of QHZYF on platelet activation. Next, we pretreated a sodium laurate-induced minimally invasive CME rat model with QHZYF. In vivo experiments were performed to examine cardiac function in rats, to locate coronary arteries on heart sections to observe internal microthrombi, to extract rat Platelet-rich plasma (PRP) for adhesion assays and CD62p and PAC-1 (ITGB3/ITGA2B) flow assays, and to measure platelet-associated protein expression in PRP. In vitro clot retraction and Co-culture of HUVECs with PRP were performed and the gene pathway was validated through flow cytometry and immunofluorescence.

RESULTS

Combining UPLC-Q-TOF/MS technology and database mining, 78 compounds were finally screened as the putative and representative compounds of QHZYF, with 75 crossover genes associated with CME. QHZYF prevents CME mainly by regulating key pathways of the inflammation and platelets, including Lipid and atherosclerosis, Fluid shear stress, platelet activation, and PI3K-Akt signaling pathways. Five molecules including Calyson, Oroxin A, Protosappanin A,Kaempferol and Geniposide were screened and subjected to molecular docking and SPR validation in combination with Lipinski rules (Rule of 5, Ro5). In vivo experiments showed that QHZYF not only improved myocardial injury but also inhibited formation of coronary microthrombi. QHZYF inhibited platelet activation by downregulating expression of CD62p receptor and platelet membrane protein αIIbβ3 and reduced the release of von Willebrand Factor (vWF), Ca2+ particles and inflammatory factor IL-6. Further analysis revealed that QHZYF inhibited the activation of integrin αIIbβ3, via modulating the PI3K/Akt pathways. In in vitro experiments, QHZYF independently inhibited platelet clot retraction. Upon LPS induction, the activation of platelet membrane protein ITGB3 was inhibited via the PI3K/Akt pathway, revealing an important mechanism for attenuating coronary microthrombosis. We performed mechanistic validation using PI3K inhibitor LY294002 and Akt inhibitor MK-2206 to show that QHZYF inhibited platelet membrane protein activation and inflammation to improved coronary microvessel embolism by regulating PI3K/Akt/αIIbβ3 pathways, mainly by inhibiting PI3K and Akt phosphorylation.

CONCLUSION

QHZYF interferes with coronary microthrombosis through inhibition of platelet adhesion, activation and inflammatory crosstalk, thus has potential in clinical anti-platelet applications. Calyson, Oroxin A, Protosappanin A, Kaempferol and Geniposide may be the major active ingredient groups of QHZYF that alleviate coronary microthrombosis.

Relationship between the Fibrinogen/Albumin Ratio and Microvascular Perfusion in Patients Undergoing Primary Percutaneous Coronary Intervention for ST-Elevated Myocardial Infarction: A Prospective Study

BACKGROUND

Correct TIMI frame count (CTFC), myocardial blush grade (MBG), and ST-segment resolution (STR) are parameters used to evaluate reperfusion at the microvascular level in patients that have undergone primary percutaneous coronary intervention (pPCI). Fibrinogen-to-albumin ratio (FAR) has been associated with thrombotic events in patients with ST-elevation myocardial infarction (STEMI) and chronic venous insufficiency.

OBJECTIVES

To investigate the relationship of FAR with CTFC, MBG, and STR. Methods: The study included 167 consecutive patients who underwent successful pPCI for STEMI and achieved TIMI-3 flow. The cases were divided into two groups, high (>0.0765) and low FAR (≤0.0765), according to the cut-off value of this parameter in the receiver operator characteristic analysis (ROC). STR, CTFC, and MBG were used to evaluate myocardial reperfusion. P values<0.05 were considered statistically significant.

RESULTS

CTFC value, SYNTAX score, neutrophil/lymphocyte ratio, low-density lipoprotein, glucose, and peak cTnT were significantly higher, whereas STR, MBG, and LVEF were lower in the high FAR group. Spearman's correlation analysis revealed a significant relationship between the FAR and STR (r=-0.666, p<0.001), MBG (-0.523, p<0.001), and CTFC (r=0.731, p≤0.001). According to the logistic regression analysis, FAR, glucose, peak cTnT, and pain to balloon time were the most important independent predictors of MBG 0/1, CTFC>28, and STR<50%).ROC analysis revealed that the cut-off value of FAR≥0.0765 was a predictor of incomplete STR with a sensitivity of 71.9 % and a specificity of 69.8 %, MBG0/1 with a sensitivity of 72.6 % and a specificity of 68.6 %, and CTFC >28 with a sensitivity of 76 % and a specificity of 65.8 %.

CONCLUSIONS

FAR is an important independent predictor of microvascular perfusion in patients undergoing pPCI for STEMI.

Angiography-Derived and Sensor-Wire Methods to Assess Coronary Microvascular Dysfunction in Patients With Acute Myocardial Infarction

ST-segment elevation myocardial infarction (STEMI) treatment with primary percutaneous coronary intervention has dramatically impacted prognosis. However, despite satisfactory angiographic result, occurrence or persistence of coronary microvascular dysfunction after revascularization still affects long-term outcomes. The diagnostic and therapeutic value of understanding the status of coronary microcirculation is gaining attention in the cardiology community. However, current methods to assess microvascular function (namely, cardiac magnetic resonance and invasive wire-based coronary physiology) remain, at least in part, limited by technical and logistic aspects. On the other hand, angiography-based indices of microcirculatory resistance are emerging as valid and user-friendly tools with potential impact on prognostic stratification of patients with STEMI. This review provides an overview about conventional and novel methods to assess coronary microvascular dysfunction in patients with STEMI. The authors also provide a proposed procedural algorithm to facilitate optimal use of wire-based and angiography-based indices in the acute setting of STEMI.

Prognostic Value of Myocardial Blush Grade in ST-elevation MI: A Systematic Review and Meta-analysis

Background: Ineffective myocardial perfusion despite angiographic success after angioplasty occurs frequently and is associated with an increased risk of mortality. Hence, this study determined whether myocardial perfusion measured by myocardial blush grade (MBG) identifies ST-elevation MI (STEMI) patients at high risk for poor outcomes after successful angioplasty. Methods: The search employed strategies designed for research databases. An article was eligible if it included adults who underwent coronary angioplasty for STEMI, post-angioplasty MBG was assessed, and mortality or major adverse cardiovascular events (MACE) were determined. Risk for bias was assessed using the Quality In Prognosis Studies tool and forest plots in a Mantel-Haenszel fixed effects model were created using RevMan5.4. Results/discussion: Eight observational studies with an overall low risk of bias were included, involving 8,044 patients. MBG 0/1 with no to poor myocardial perfusion had a negative prognostic value for mortality (OR 2.68; 95% CI [2.22–3.23]) and MACE (OR 1.20; 95% CI [1.01–1.41]). Furthermore, MBG 2 with moderate myocardial perfusion and MBG 3 with normal myocardial perfusion were associated with increased survival with a logHR of 0.47 (95% CI [0.43–0.52]) and 0.20 percutaneous coronary intervention (95% CI [0.18–0.23]). These results imply MBG is a useful prognostic marker for STEMI patients. Conclusion: MBG 0/1 after primary angioplasty is a strong negative prognostic marker for long-term all-cause mortality and MACE among STEMI patients, and a post-primary angioplasty MBG of 2 or 3 is a robust prognostic marker for long-term survival.

Pathophysiology and mechanisms of Acute Coronary Syndromes: athero-thrombosis, immune-inflammation and beyond

INTRODUCTION

The pathophysiology of atherosclerosis and its acute complications, such as the Acute Coronary Syndromes (ACS), is continuously under investigation. Immunity and inflammation seem to play a pivotal role in promoting formation and grow of atherosclerotic plaques. At the same time, plaque rupture followed by both platelets' activation and coagulation cascade induction lead to intracoronary thrombus formation. Although these phenomena might be considered responsible of about 90% of ACS, in up to 5-10% of acute syndromes a non-obstructive coronary artery disease (MINOCA) might be documented. This paper gives an overview on athero-thrombosis and immuno-inflammation processes involved in ACS pathophysiology also emphasizing the pathological mechanisms potentially involved in MINOCA.

AREAS COVERED

The relationship between immuno-inflammation and atherothrombosis is continuously updated by recent findings. At the same time, pathophysiology of MINOCA still remains a partially unexplored field, stimulating the research of potential links between these two aspects of ACS pathophysiology.

EXPERT OPINION

Pathophysyiology of ACS has been extensively investigated; however, several grey areas still remain. MINOCA represents one of these areas. At the same time, many aspects of immune-inflammation processes are still unknown. Thus, research should be continued to shed a brighter light on both these sides of "ACS" moon.

A fresh look at coronary microembolization

Mechanical stress from haemodynamic perturbations or interventional manipulation of epicardial coronary atherosclerotic plaques with inflammatory destabilization can release particulate debris, thrombotic material and soluble substances into the coronary circulation. The physical material obstructs the coronary microcirculation, whereas the soluble substances induce endothelial dysfunction and facilitate vasoconstriction. Coronary microvascular obstruction and dysfunction result in patchy microinfarcts accompanied by an inflammatory reaction, both of which contribute to progressive myocardial contractile dysfunction. In clinical studies, the benefit of protection devices to retrieve atherothrombotic debris during percutaneous coronary interventions has been modest, and the treatment of microembolization has mostly relied on antiplatelet and vasodilator agents. The past 25 years have witnessed a relative proportional increase in non-ST-segment elevation myocardial infarction in the presentation of acute coronary syndromes. An associated increase in the incidence of plaque erosion rather than rupture has also been recognized as a key mechanism in the past decade. We propose that coronary microembolization is a decisive link between plaque erosion at the culprit lesion and the manifestation of non-ST-segment elevation myocardial infarction. In this Review, we characterize the features and mechanisms of coronary microembolization and discuss the clinical trials of drugs and devices for prevention and treatment.

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.

Lancaster G, W. Zarich S. Invasive Evaluation of the Microvasculature in Acute Myocardial Infarction: Coronary Flow Reserve versus the Index of Microcirculatory Resistance

Acute myocardial infarction (AMI) is one of the most common causes of death in both the developed and developing world. It has high associated morbidity despite prompt institution of recommended therapy. The focus over the last few decades in ST-segment elevation AMI has been on timely reperfusion of the epicardial vessel. However, microvascular consequences after reperfusion, such as microvascular obstruction (MVO), are equally reliable predictors of outcome. The attention on the microcirculation has meant that traditional angiographic/anatomic methods are insufficient. We searched PubMed and the Cochrane database for English-language studies published between January 2000 and November 2019 that investigated the use of invasive physiologic tools in AMI. Based on these results, we provide a comprehensive review regarding the role for the invasive evaluation of the microcirculation in AMI, with specific emphasis on coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR).

Proteomics Analysis of Myocardial Tissues in a Mouse Model of Coronary Microembolization

Coronary microembolization (CME) is an important clinical problem, and it is related to poor outcome. The specific molecular mechanisms of CME are not fully understood. In the present study, we established a mice model of CME. Isobaric tags for relative and absolute quantitation (iTRAQ) and liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) technologies identified 249 differentially expressed proteins in the myocardial tissues of CME mice as compared with sham-operated mice. Bioinformatics analysis demonstrated that these differentially expressed proteins were enriched in several energy metabolism or cytoskeleton organization related processes or pathways. Quantitative PCR and Western blotting validation experiments revealed that succinate dehydrogenase (SDHA and SDHB) were upregulated, Rho GDP dissociation inhibitor α (RhoGDIα) and Filamin-A (FLNA) were downregulated significantly in CME mice. These findings indicated that the alternations of the cytoskeleton and energy metabolism pathways play important roles in the pathogenesis of CME, future studies are warranted to verify if targeting these molecules might be useful to alleviate CME injury or not.

[Comparative study of functional and structural changes produced in a porcine model of acute and chronic heart attack]

INTRODUCTION AND OBJECTIVES

Animal models are a useful tool for the evaluation of disease mechanisms and also for technologies for diagnosis and treatment. In this study we performed a descriptive analysis of the functional and structural cardiac changes occurred as a result of acute coronary occlusion in pigs and its evolution during 5 weeks.

METHODS

19-Large White pigs, weighing 20kg, randomized into 3-experimental series were used. After sternotomy, anterior descending coronary artery was occluded. Duration of occlusion: Series 1 (n=6) 60min; series 2 (n=8) 90min; series 3 (n=5) 60min followed for 5 weeks. The following parameters where then analyzed: global cardiac function (ECG, left ventricular and atrium pressures, aortic flow and cardiac echocardiography), regional contractility, troponin T and CK-MB levels, macroscopic and histological analyzes.

RESULTS

Coronary occlusion transiently altered the global cardiac function and produced increased cell damage markers, impaired regional contractility and produced histological changes. The increment of ischemic time (60 vs. 90min) increased infarct size (13.4±5.4% vs. 22.9±7.8 S1 S2%; P=.04). After 5 weeks, morphological remodelling changes were evident. In 79% of cases ischemia triggered ventricular fibrillation.

CONCLUSION

The porcine open chest model of acute myocardial infarction and reperfusion is valid for studying the pathophysiology of coronary ischemia, allows direct analysis of regional myocardial function and is easily retrievable in the event of serious arrhythmias.

Prognostic utility of myocardial blush grade after PCI in patients with NSTE-ACS: Analysis from the ACUITY trial

OBJECTIVE

We evaluated the ability of post-procedural myocardial blush grade (MBG) to stratify outcomes of patients undergoing percutaneous coronary intervention (PCI) for non-ST segment elevation acute coronary syndromes (NSTE-ACS).

BACKGROUND

MBG strongly correlates with survival after reperfusion therapy in patients with ST-segment elevation myocardial infarction (STEMI).

METHODS

Of 13,819 NSTE-ACS patients randomized in the ACUITY trial, 3,115 patients underwent PCI and had MBG analyzed by an independent angiographic core laboratory. We examined net adverse clinical events (NACE; composite ischemia or bleeding), composite ischemia (death, MI or ischemia-driven revascularization) and non-CABG major bleeding according to final MBG.

RESULTS

At 30 days, patients with MBG-0/1 had higher rates of NACE (25.1% vs. 13.9%, P = 0.002) and composite ischemia (19.1% vs. 9.4%, P = 0.002) than patients with MBG-2/3. At 1-year follow-up, MBG-0/1 patients had significantly higher rates of composite ischemia compared to other patients (27.8% vs. 19.8%, P = 0.02). By multivariable analysis, MBG-0/1 was an independent predictor of 30-day ischemia-driven revascularization (OR 5.74 [2.63, 12.54], P < 0.0001) in the total population and among patients with normal post-PCI epicardial TIMI-3 flow (OR 6.39 [2.06, 19.78], P = 0.001). However, 1-year outcomes were similar between patients with and without normal myocardial perfusion.

CONCLUSIONS

In conclusion, MBG is a predictor of 30-day revascularization in the overall population and in patients with normal epicardial flow but fails to stratify 1-year outcomes. Thus, unlike in STEMI patients, the prognostic value of MBG in NSTE-ACS patients appears to be limited to the short-term. © 2015 Wiley Periodicals, Inc.

MRI quantification of left ventricular function in microinfarct versus large infarct in swine model

To quantify, using MRI, the acute impacts of defined volume and sizes of coronary microemboli on myocardial viability and left ventricular (LV) function and to use LAD occlusion/reperfusion, as a reference. A total of 28 farm pigs were used in this study. Eight animals were used as controls. Successful coronary interventions were performed under X-ray fluoroscopy in 16 pigs to induce microinfarct (delivery of 16 mm(3) of 40-120 μm) and large infarct (90 min LAD occlusion/reperfusion). On day 3, animals were imaged using contrast enhanced (in beating and non-beating hearts) and cine MRI for evaluating LV viability and function, respectively. Microscopy and cardiac injury enzymes were used to confirm the presence of necrosis. Myocardial damage was smaller after microembolization than occlusion/reperfusion (6.5 ± 0.6%LV mass vs. 12.6 ± 1.2%, P < 0.001). The increase in LV end-systolic volume and decreases in ejection fraction, cardiac output and regional systolic wall thickening, however, were comparable between groups, but significantly differed from controls. MRI also demonstrated microvascular obstruction after microembolization and occlusion/reperfusion as hyperenhanced and hypoenhanced regions, respectively. Microscopic examination revealed patchy necrosis, inflammatory cell infiltration, but no intramyocardial hemorrhage after microembolization and extensive intramyocardial hemorrhage and transmural damage in the occlusion/reperfusion group. Cardiac injury enzymes confirmed presence of myocardial damage in animals with interventions. Coronary microemboli have acute impact on LV function compared to control animals. Despite the difference in myocardial damage, global and regional LV dysfunction after microembolization was comparable to occlusion/reperfusion. This MR study suggests that the pattern of myocardial damage plays a role in LV dysfunction.

Large deforming buoyant embolus passing through a stenotic common carotid artery: a computational simulation

Arterial embolism is responsible for the death of lots of people who suffers from heart diseases. The major risk of embolism in upper limbs is that the ruptured particles are brought into the brain, thus stimulating neurological symptoms or causing the stroke. We presented a computational model using fluid-structure interactions (FSI) to investigate the physical motion of a blood clot inside the human common carotid artery. We simulated transportation of a buoyant embolus in an unsteady flow within a finite length tube having stenosis. Effects of stenosis severity and embolus size on arterial hemodynamics were investigated. To fulfill realistic nonlinear property of a blood clot, a rubber/foam model was used. The arbitrary Lagrangian-Eulerian formulation (ALE) and adaptive mesh method were used inside fluid domain to capture the large structural interfacial movements. The problem was solved by simultaneous solution of the fluid and the structure equations. Stress distribution and deformation of the clot were analyzed and hence, the regions of the embolus prone to lysis were localized. The maximum magnitude of arterial wall shear stress during embolism occurred at a short distance proximal to the throat of the stenosis. Through embolism, arterial maximum wall shear stress is more sensitive to stenosis severity than the embolus size whereas role of embolus size is more significant than the effect of stenosis severity on spatial and temporal gradients of wall shear stress downstream of the stenosis and on probability of clot lysis due to clot stresses while passing through the stenosis.

Platelets and cardiac arrhythmia

Sudden cardiac death (SCD) remains one of the most prevalent modes of death in industrialized countries, and myocardial ischemia due to thrombotic coronary occlusion is its primary cause. The role of platelets in the occurrence of SCD extends beyond coronary flow impairment by clot formation. Here we review the substances released by platelets during clot formation and their arrhythmic properties. Platelet products are released from three types of platelet granules: dense core granules, alpha-granules, and platelet lysosomes. The physiologic properties of dense granule products are of special interest as a potential source of arrhythmic substances. They are released readily upon activation and contain high concentrations of serotonin, histamine, purines, pyrimidines, and ions such as calcium and magnesium. Potential arrhythmic mechanisms of these substances, e.g., serotonin and high energy phosphates, include induction of coronary constriction, calcium overloading, and induction of delayed after-depolarizations. Alpha-granules produce thromboxanes and other arachidonic-acid products with many potential arrhythmic effects mediated by interference with cardiac sodium, calcium, and potassium channels. Alpha-granules also contain hundreds of proteins that could potentially serve as ligands to receptors on cardiomyocytes. Lysosomal products probably do not have an important arrhythmic effect. Platelet products and ischemia can induce coronary permeability, thereby enhancing interaction with surrounding cardiomyocytes. Antiplatelet therapy is known to improve survival after myocardial infarction. Although an important part of this effect results from prevention of coronary clot formation, there is evidence to suggest that antiplatelet therapy also induces anti-arrhythmic effects during ischemia by preventing the release of platelet activation products.

Microvascular obstruction: underlying pathophysiology and clinical diagnosis

Successful restoration of epicardial coronary artery patency after prolonged occlusion might result in microvascular obstruction (MVO) and is observed both experimentally as well as clinically. In reperfused myocardium, myocytes appear edematous and swollen from osmotic overload. Endothelial cell changes usually accompany the alterations seen in myocytes but lag behind myocardial cell injury. Endothelial cells become voluminous, with large intraluminal endothelial protrusions into the vascular lumen, and together with swollen surrounding myocytes occlude capillaries. The infiltration and activation of neutrophils and platelets and the deposition of fibrin also play an important role in reperfusion-induced microvascular damage and obstruction. In addition to these ischemia-reperfusion-related events, coronary microembolization of atherosclerotic debris after percutaneous coronary intervention is responsible for a substantial part of clinically observed MVO. Microvascular flow after reperfusion is spatially and temporally complex. Regions of hyperemia, impaired vasodilatory flow reserve and very low flow coexist and these perfusion patterns vary over time as a result of reperfusion injury. The MVO first appears centrally in the infarct core extending toward the epicardium over time. Accurate detection of MVO is crucial, because it is independently associated with adverse ventricular remodeling and patient prognosis. Several techniques (coronary angiography, myocardial contrast echocardiography, cardiovascular magnetic resonance imaging, electrocardiography) measuring slightly different biological and functional parameters are used clinically and experimentally. Currently there is no consensus as to how and when MVO should be evaluated after acute myocardial infarction.

Microemboli and microvascular obstruction in acute coronary thrombosis and sudden coronary death: relation to epicardial plaque histopathology

OBJECTIVES

This study examined myocardial microvascular emboli and obstruction, and related these to plaque in the epicardial coronary arteries supplying the affected microvessels.

BACKGROUND

Epicardial coronary thrombosis often causes microemboli and microvascular obstruction. The consequences of myocardial microvessel obstruction and myocyte necrosis are substantial, yet histopathologic characterization of epicardial coronary artery plaque has been incompletely characterized. This study examined myocardial microvascular emboli, and related these to plaque in the coronary arteries supplying the microvessels.

METHODS

Hearts from sudden coronary death patients underwent examination for coronary artery plaque type and cardiac microemboli.

RESULTS

Forty-four hearts were available for evaluation. Mean age at death was 51 +/- 15 years. Coronary artery analysis found 26 plaque ruptures and 21 erosions, and a mean of 4.5 microemboli per heart. Microemboli and microvascular obstruction occurred most often from eroded plaques. Microemboli and occluded intramyocardial vessels were most common in the left anterior descending coronary artery, and all vessels contained fibrin and platelets. Mean stenoses of the culprit lesion was 74% in those with emboli and 75% in those without (p = NS). Intramyocardial microemboli were more common in plaque erosion than in rupture. Microvessels <200 mum were most often those that were occluded.

CONCLUSIONS

Microemboli and microvascular obstruction are common in patients dying of acute coronary thrombosis. Plaque erosion is more likely to cause emboli in vessels <200 mum. These emboli and microvessel obstruction have a prominent clinical role since myonecrosis is often associated with these findings.

Coronary microembolization: from bedside to bench and back to bedside

Coronary microembolization from the erosion or rupture of a vulnerable atherosclerotic plaque occurs spontaneously in acute coronary syndromes and iatrogenically during percutaneous coronary interventions. Typical consequences of coronary microembolization are microinfarcts with an inflammatory response, contractile dysfunction, and reduced coronary reserve. Apart from transient elevations of creatine kinase and troponin, microemboli can be visualized by intracoronary Doppler and the resulting microinfarcts by late-enhancement nuclear magnetic resonance. Statins, antiplatelet agents, and coronary vasodilators protect against microembolization and microinfarction when started before percutaneous coronary interventions. Distal protection devices can retrieve atherothrombotic debris and prevent its embolization into the microcirculation, but their effect on clinical outcome has been disappointing so far, except for saphenous vein bypass grafts. Devices for aspiration of thrombi and thrombus-derived vasoconstrictor, thrombogenic, and inflammatory substances, however, reduce thrombus burden, improve perfusion, and provide protection in patients with acute myocardial infarction.

Efficacy of clopidrogel on reperfusion and high-sensitivity C-reactive protein in patients with acute myocardial infarction

We investigated the effects of clopidogrel on reperfusion and inflammatory process in STEMI. A total of 175 STEMI patients with similar clinical characteristics were included to this study. One was the standard pharmacological reperfusion therapy group (group 1, n : 90), who received 300 mg aspirin, 70 U/kg bolus, and 12 U/kg/hr continuous infusion of unfractioned heparin and accelerated t-PA. Clopidogrel 450 mg loading and 75 mg/d thereafter was added to standard reperfusion therapy in the other group (group 2, n : 85). The ST-segment resolution, CK-MB, and high-sensitive CRP (hs-CRP) parameters were measured. Complete ST resolution was observed in 32 patients (36.8%) in group 1 and 53 patients (63.8%) in group 2 (P < .001). Also in the first 24 hours, the CK-MB levels of patients in group 1 were significantly higher than those of group 2 (P = .001). The hs-CRP values were greater in group 1 than group 2 at 48th hour (gruop 1: 9.4 ± 0.1 mg/L, group 2: 3.7 ± 1.4 mg/L; P = .000). We concluded that adding clopidogrel to standard treatment in STEMI patients provided early reperfusion and suppression of inflammatory response.

Pathophysiology of acute myocardial infarction

More than 80% of acute myocardial infarcts are the result of coronary atherosclerosis with superimposed luminal thrombus. Uncommon causes of myocardial infarction include coronary spasm, coronary embolism, and thrombosis in nonatherosclerotic normal vessels. Additionally, concentric subendocardial necrosis may result from global ischemia and reperfusion in cases of prolonged cardiac arrest with resuscitation. Myocardial ischemia shares features with other types of myocyte necrosis, such as that caused by inflammation, but specific changes result from myocyte hypoxia that vary based on length of occlusion of the vessel, duration between occlusion and reperfusion, and presence of collateral circulation.

Intracoronary streptokinase after primary percutaneous coronary intervention

BACKGROUND

Microvascular perfusion is often impaired after primary percutaneous coronary intervention (PCI). We proposed that in situ thrombosis might contribute to poor myocardial perfusion in this setting. To test this hypothesis, we evaluated the effect of low-dose intracoronary streptokinase administered immediately after primary PCI.

METHODS

Forty-one patients undergoing primary PCI were randomly assigned to receive intracoronary streptokinase (250 kU) or no additional therapy. Two days later, cardiac catheterization was repeated, and coronary hemodynamic end points were measured with the use of a guidewire tipped with pressure and temperature sensors. In patients with anterior myocardial infarction, the deceleration time of coronary diastolic flow was measured with transthoracic echocardiography. At 6 months, angiography, echocardiography, and technetium-99m single-photon-emission computed tomography were performed.

RESULTS

Two days after PCI, all measures of microvascular function (means +/-SD) were significantly better in the streptokinase group than in the control group, including coronary flow reserve (2.01+/-0.57 vs. 1.39+/-0.31), the index of microvascular resistance (16.29+/-5.06 U vs. 32.49+/-11.04 U), the collateral-flow index (0.08+/-0.05 vs. 0.17+/-0.07), mean coronary wedge pressure (10.81+/-5.46 mm Hg vs. 17.20+/-7.93 mm Hg), systolic coronary wedge pressure (18.24+/-6.07 mm Hg vs. 33.80+/-11.00 mm Hg), and diastolic deceleration time (828+/-258 msec vs. 360+/-292 msec). The administration of intracoronary streptokinase was also associated with a significantly lower corrected Thrombolysis in Myocardial Infarction frame count (the number of cine frames required for dye to travel from the ostium of a coronary artery to a standardized distal coronary landmark) at 2 days. At 6 months, however, there was no evidence of a difference between the two study groups in left ventricular size or function.

CONCLUSIONS

In our pilot trial, the administration of low-dose intracoronary streptokinase immediately after primary PCI improved myocardial reperfusion but not long-term left ventricular size or function. These findings require clarification in a larger trial. (ClinicalTrials.gov number, NCT00302419.)

Coronary microembolization

Atherosclerotic plaque rupture is the key event in the pathogenesis of acute coronary syndromes and it also occurs during coronary interventions. Atherosclerotic plaque rupture does not always result in complete thrombotic occlusion of the epicardial coronary artery with subsequent impending myocardial infarction, but may in milder forms result in the embolization of atherosclerotic and thrombotic debris into the coronary microcirculation. This review summarizes the present experimental pathophysiology of coronary microembolization in animal models of acute coronary syndromes and highlights the main consequences of coronary microembolization--reduced coronary reserve, microinfarction, inflammation and oxidative modification of contractile proteins, contractile dysfunction and perfusion-contraction mismatch.Furthermore, the review presents the available clinical evidence for coronary microembolization in patients and compares the clinical observations with observations in the experimental model.

Recovery of global systolic function after primary angioplasty. Influence of coronary flow velocity reserve measured by transthoracic echocardiography

BACKGROUND

Our objective were to know whether coronary flow velocity reserve measured by transthoracic Doppler echocardiography, as marker of microvascular integrity, affects the recovery of global systolic function. Secondly, we intended to define the best cut-off point of coronary flow velocity reserve to predict recovery of global systolic function.

METHODS

We studied 57 patients with coronary flow recorded by transthoracic Doppler echocardiography, after suffering a first anterior acute myocardial infarction and undergoing a successful primary percutaneous coronary intervention (TIMI 3 flow). We measured, at discharge and at 1 month: ejection fraction, volume indexes and anterior wall motion score index. Coronary flow in left anterior descending artery was detected by transthoracic Doppler echocardiography and coronary flow velocity reserve was calculated.

RESULTS

After applying ROC curves, 1.54 was the best cut-off value of coronary flow velocity reserve for detection of recovery of global systolic function. Ejection fraction only increased significantly in patients with normal coronary flow velocity reserve. Only end-systolic volume index increased significantly at 1 month in patients with impaired coronary flow velocity reserve.

CONCLUSION

We showed that coronary flow velocity reserve, measured by transthoracic Doppler echocardiography, influence the recovery of global systolic function, mainly by ventricular dilation. Furthermore, a quite lower value of coronary flow velocity reserve than that used for diagnostic purpose should be used to predict improvement of systolic function.

Distal protection in cardiovascular medicine: current status

Iatrogenic and spontaneous downstream microembolization of atheromatous material is increasingly recognized as a source of cardiovascular morbidity and mortality. Devising ways of reducing this distal embolization using a variety of mechanical means--distal protection--is currently under intense and diverse investigation. This review therefore summarizes the present status of distal protection. It examines the problem of distal embolization, describes the available distal protection devices, reviews those areas of cardiovascular medicine where distal protection devices are being investigated, and discusses potential future developments.

Microvascular obstruction after successful fibrinolytic therapy in acute myocardial infarction. Comparison of reteplase vs reteplase+abciximab: A cardiovascular magnetic resonance study

BACKGROUND.: About one third of patients with TIMI 3 after reperfusion have evidence of microvascular obstruction (MO) which represents an independent predictor of myocardial wall rupture. This explains all efforts made to prevent MO. Magnetic resonance imaging (MRI) has proved to be particularly useful in detecting MO. The aim of this study was to evaluate with MRI if different fibrinolytic regimens in acute myocardial infarction display different effects on left ventricle (LV) volumes and ejection fraction (EF), as well as on myocardial infarct size (MIsz) and MO. METHODS.: Twenty male patients, mean age 58 years, affected by acute myocardial infarction, ten anterior and ten inferior, were treated with: full dose reteplase in ten, and half dose reteplase plus full dose abciximab (R+Abcx) in the other ten patients. In the fourth day after hospital admission, MRI STIR T2 images were used to quantify MIsz, while 2dflash cineloops were used after the injection of gadolinium, to quantify LV volumes, EF and to detect MO. RESULTS.: LV EF was higher in R+Abcx 51±10 than in reteplase 41±8. MIsz was similar in both treatment groups: however a close relationship was present between MIsz and EF in the reteplase group indicating that the greater the MIsz the lower the EF. In R+Abcx this relationship was no longer present, suggesting a protective effect of the drug on microcirculation. In fact extensive MO was present in 25% of all cases, 80% of which in the reteplase group while only 20% in R+Abcx. CONCLUSION.: R+Abcx prevents MO: compared to traditional fibrinolytic therapy it allows better LV function and most likely improved long term survival.

Increased Vascular Wall Thrombogenicity Combined With Reduced Blood Flow Promotes Occlusive Thrombus Formation in Rabbit Femoral Artery

OBJECTIVE

Plaque disruption does not always result in complete thrombotic occlusion. The mechanism of arterial thrombus propagation remains unclear.

METHODS AND RESULTS

We studied how vascular wall thrombogenicity and blood flow reduction affect thrombus propagation using a rabbit model of single and repeated balloon injury. After balloon injury of the normal femoral artery, the blood flow was reduced to 50%, 25%, or 10% (n=5). Small mural thrombi composed of aggregated platelets were produced, but no occlusive thrombi developed in any flow reduction. Three weeks after the first balloon injury, neointima with tissue factor expression and increased procoagulant activity was developed. Balloon injury of the neointima with the same blood flow reduction (n=5) induced fibrin-rich thrombus formation. Additionally, injury with flow reduced to 25% and 10% promoted thrombus propagation resulting in vessel occlusion within 160+/-18 and 71+/-17 seconds, respectively. An injection of anti-von Willebrand factor (vWF) monoclonal antibody (AJW200; 1.0 mg/kg) prevented occlusive thrombus formation.

CONCLUSIONS

Increased vascular wall thrombogenicity together with a substantial blood flow reduction is crucial for occlusive thrombus formation, and vWF plays an important role in thrombus propagation. Reduced blood flow at plaque disruption sites might contribute to thrombus propagation leading to acute coronary syndromes.

Effect of clopidogrel pretreatment on periprocedural rise in C-reactive protein after percutaneous coronary intervention

This study sought to determine the effect of clopidogrel pretreatment on the increase in C-reactive protein (CRP) after percutaneous coronary intervention. Clopidogrel pretreatment attenuated the periprocedural increase in CRP by 65% and was independently associated with an attenuation in the CRP increase in a multivariate model.

Effectiveness of thrombectomy before stent implantation in acute myocardial infarction

Percutaneous coronary intervention (PCI) in patients with acute myocardial infarction (AMI) may cause distal embolization, with deterioration of distal flow and further extension of the infarct. The purpose of the present study was to evaluate the effectiveness of pretreatment by thrombectomy on myocardial salvage after stent implantation in patients with AMI. From January 2000 to July 2002, 209 consecutive patients with AMI successfully underwent emergency stent implantation. They were divided into 2 groups: those treated in the year before the introduction of the thrombectomy device (Group A; n=109), and those treated the year after introduction of the device (Group B; n=100). Follow-up quantitative coronary angiography (QCA) and left ventriculography were carried out 6 months after PCI. Microvascular circulation after revascularization was assessed by Thrombolysis in myocardial infarction (TIMI) flow grade analysis, the maximum creatine kinase concentration was recorded, and the follow-up left ventricular ejection fraction and ST segment score were assessed on the 12-lead electrocardiography just before revascularization and on return to the coronary care unit. The QCA data, rate of restenosis (% restenosis) and rate of target lesion revascularization were also compared between the 2 groups. The results demonstrated that the introduction of thrombectomy had increased the number of patients who displayed blush-3 after primary angioplasty, which suggests that thrombectomy before stent implantation has the potential to minimize myocardial ischemic insult, presumably by protecting the coronary microvasculature.

Coronary microembolization

Atherosclerotic plaque rupture is a key event in the pathogenesis of acute coronary syndromes and during coronary interventions. However, it does not always result in complete thrombotic occlusion of the entire epicardial coronary artery with subsequent acute myocardial infarction; in milder forms the result can be embolization of atherosclerotic and thrombotic debris into the coronary microcirculation. This review summarizes the available morphological evidence for coronary microembolization in patients who died from coronary artery disease, most notably from sudden death, and then goes on to address the experimental pathophysiology of coronary microembolization in animal models of acute coronary syndromes and heart failure. Finally, the review presents the available clinical evidence for coronary microembolization in patients, highlights its key features (ie, arrhythmias, contractile dysfunction, infarctlets and reduced coronary reserve) and addresses its prevention by mechanical protection devices and glycoprotein IIb/IIIa antagonism.

Association of platelet-derived microparticles with C-C chemokines on vascular complication in patients with acute myocardial infarction

The levels of platelet-derived microparticles (PDMPs), platelet activation markers (P-selectin, CD63, and PAC-1 on activated platelets), and C-C chemokines (monocyte chemotactic peptide [MCP]-1 and regulated on activation normally T-cell expressed and secreted [RANTES] were measured and compared in patients with acute myocardial infarction (AMI) or stable pectoris angina. These substances are thought to paricipate in the development of complications in patients with AMI. The percentage binding of anti-P-selectin, CD63, and PAC-1 antibody to platelets, and the levels of PDMPs (per 10(4) platelets) were higher in the patients with AMI than in those with stable pectoris angina (P-selectin, 23.1% +/- 2.1% vs. 10.3% +/- 1.2%, p < 0.001; CD63, 24.6% +/- 3.3% vs. 11.2% +/- 3.1%, p < 0.01; PAC-1, 14.1% +/- 1.7% vs. 9.3% +/- 2.1%, p < 0.05; PDMPs, 613 +/- 71 vs. 413 +/- 55, p < 0.01). There were no differences in platelet levels of GPIIb/IIIa and GPIb between groups. Levels of MCP-1 and RANTES were higher in the patients with AMI than in patients with stable pectoris angina (MCP-1, 430 +/- 35 vs. 265 +/- 23, p<0.01; RANTES, 175 +/- 32 vs. 88 +/- 29, p<0.001). The effects of percutaneous transluminal coronary angioplasty (PTCA) on the levels of these agents in patients with AMI were studied. Platelet activation markers were significantly decreased in patients with AMI after PTCA. RANTES level was also significantly decreased after treatment, but MCP-1 level was not changed. In addition, this tendency was clearer in STENT patients. These findings suggest that in patients with AMI PTCA, particularly STENT, may prevent the development of complications in which activated platelet and RANTES participate.

Administration of glycoprotein IIb-IIIa inhibitors in patients with ST-segment elevation myocardial infarction

Patients with ST-segment elevation acute myocardial infarction require immediate reperfusion therapy. Reperfusion therapy can be provided by either pharmacologic or mechanical means. Pharmacologic reperfusion therapy consists of administering fibrinolytics, whereas mechanical reperfusion consists of performing percutaneous intervention, usually with stent placement. Each approach has been shown to decrease mortality, but each has disadvantages in establishing flow in the infarct-related artery. Regardless of the approach, during an acute myocardial infarction, activation and externalization of glycoprotein (GP) IIb-IIIa receptors occur on the surface of platelets. The GP IIb-IIIa inhibitors block the binding of fibrinogen to these platelet receptors. These inhibitors have been investigated in combination with both reperfusion strategies. The goal of adding GP IIb-IIIa inhibitor therapy to either reperfusion approach is to obtain better early, complete, and sustained reperfusion. Subsequently, this should lead to better clinical outcomes for patients with ST-segment elevation acute myocardial infarction. Although no mortality benefit has been seen with the addition of GP IIb-IIIa inhibitor therapy, ischemic complications have been reduced significantly.

Fluid mechanics of vascular systems, diseases, and thrombosis

The cardiovascular system is an internal flow loop with multiple branches circulating a complex liquid. The hallmarks of blood flow in arteries are pulsatility and branches, which cause wall stresses to be cyclical and nonuniform. Normal arterial flow is laminar, with secondary flows generated at curves and branches. Arteries can adapt to and modify hemodynamic conditions, and unusual hemodynamic conditions may cause an abnormal biological response. Velocity profile skewing can create pockets in which the wall shear stress is low and oscillates in direction. Atherosclerosis tends to localize to these sites and creates a narrowing of the artery lumen--a stenosis. Plaque rupture or endothelial injury can stimulate thrombosis, which can block blood flow to heart or brain tissues, causing a heart attack or stroke. This small lumen and elevated shear rate in a stenosis create conditions that accelerate platelet accumulation and occlusion. The relationship between thrombosis and fluid mechanics is complex, especially in the post-stenotic flow field. New convection models have been developed to predict clinical from platelet thrombosis in diseased arteries. Future hemodynamic studies should address the complex mechanics of flow-induced, large-scale wall motion and convection of semisolid particles and cells in flowing blood.

Experimental rupture of atherosclerotic lesions increases distal vascular resistance: a limiting factor to the success of infarct angioplasty

Rupture of atherosclerotic lesions, resulting in localized thrombi and marked falls in distal blood flow, is a pivotal event in unstable coronary syndromes. We tested the hypothesis that after lesion rupture, vasoconstrictor mechanisms are major contributors to a marked rise in distal microvascular resistance, which is responsible for much of the interruption in blood flow. Cholesterol-fed rabbits underwent endothelial denudation of their left iliac arteries to induce angiographically severe, fatty, American Heart Association type IV-like atherosclerotic lesions. After lesion disruption with a stiff wire, we measured distal blood flow and pressure, capillary patency in the distal vascular bed, and the response to the vasodilators adenosine, nitroprusside, and glyceryl trinitrate. Morphology of the lesions and of the associated thrombi was also examined to assess lumen restriction at the site of rupture. Disruption of atherosclerotic lesions reduced mean flow from 5.04+/-1.21 to 1.23+/-0.37 mL/min (P<0.005), and calculated distal vascular resistance rose rapidly, from 17.5+/-2.9 to 37.9+/-6.4 mm Hg. min/mL (P<0.005). Lesion rupture did not significantly affect capillary patency in the distal muscle vascular bed, and although nonocclusive thrombi were present at the site of nearly all ruptured lesions, embolized thrombi were rare in capillaries (<1%). The early rise in distal microvascular resistance could be normalized with intra-arterially administered adenosine or the NO donor nitroprusside, but not glyceryl trinitrate, an organonitrate possessing large muscular artery-selective vasodilator characteristics. Thus, rupture of atherosclerotic lesions induces rapid and marked increases in distal vascular resistance, which is the consequence of severe microvascular vasoconstriction. Therapeutic targeting of the microvasculature should improve reperfusion in acute coronary syndromes.

Function and clinical significance of platelet-derived microparticles

Microparticles released from platelets (PMPs) may play a role in the normal hemostatic response to vascular injury because they demonstrate prothrombinase activity. PMPs were first observed as released vesicles from platelets following adhesion to vessel walls, and flow cytometry is now the most widely used method for studying PMPs. PMPs are thought to play a role in clinical disease because they express phospholipids that function as procoagulants. High shear stress can initiate both platelet aggregation and shedding of procoagulant-containing PMP, suggesting that PMP generation by high shear stress occurs in small diseased arteries and arterioles under various clinical conditions. In addition, the possibility that PMPs evoke cellular responses in their immediate microenvironments has recently been suggested. Despite many interesting findings, the significance of PMPs in various clinical conditions remains controversial. For example, it is not known whether PMPs found in peripheral blood vessels cause thrombosis, or if they are the results of thrombosis. There has been some question about whether the PMPs found in thromboses are consumed locally, meaning that PMPs circulating in the peripheral blood are not functionally important. Currently, the number of clinical disorders associated with elevated PMPs is increasing.

Coronary microembolization

Atherosclerotic plaque rupture is a key event in the pathogenesis of acute coronary syndromes and during coronary interventions. Atherosclerotic plaque rupture does not always result in complete thrombotic occlusion of the entire epicardial coronary artery with subsequent acute myocardial infarction; however, in milder forms it may result in the embolization of atherosclerotic and thrombotic debris into the coronary microcirculation. The present report summarizes the available morphologic evidence for coronary microembolization in patients who died of coronary artery disease, especially sudden death. The report then goes on to address the experimental pathophysiology of coronary microembolization in animal models of acute coronary syndromes and heart failure. Finally, the report presents the available clinical evidence for coronary microembolization, highlights its key features--arrhythmias, contractile dysfunction, infarctlets and reduced coronary reserve--and addresses prevention by mechanical protection devices and glycoprotein IIb/IIIa antagonism.

Importance of microembolization and inflammation in atherosclerotic heart disease

Considerable evidence now exists that inflammation is a central component of events that initiate and propagate an acute coronary syndrome. This process evokes the potential for embolization, which occurs more often than previously suspected, and imparts poor cardiovascular prognosis. Recent development of techniques to detect inflammation and embolization represents an important advance. In addition, therapies that diminish occurrence of these phenomena such as aspirin, statins, angiotensin converting enzyme (ACE) inhibitors, and IIb/IIIa receptor antagonists have been shown to improve outlook.

Isosorbide dinitrate inhibits platelet adhesion and aggregation in nonthrombolyzed patients with acute myocardial infarction

BACKGROUND

Apart from their vasodilatatory properties, nitrates have been shown to inhibit platelet aggregation. The effects of nitrates on platelet adhesion have not been studied. Nonselected patients with acute myocardial infarction (AMI) have been suggested to gain no benefit from administration of nitrates. However, the importance of nitrates may be greater in a subgroup of nonthrombolyzed patients with AMI.

HYPOTHESIS

Isosorbide dinitrate (ISDN) decreases platelet adhesion and aggregation in nonthrombolyzed patients with AMI.

METHODS

Consecutive 48 men with AMI, not eligible for thrombolytic therapy because of late presentation (> 12 h), were prospectively randomized 2:1 to double-blind ISDN (mean dose 2.4 +/- 0.9 mg/h) (n = 33) or placebo (0.9% sodium chloride) (n = 15) infusion. All patients received aspirin. Blood samples were taken at baseline (no study medication) and 3 h into ISDN or placebo infusion. Platelet adhesion to collagen was measured in the ethylene diamine tetraacetic acid (EDTA)-platelet rich plasma by recording changes in light transmission with an optical aggregometer. Platelet aggregation was measured using the Born's method.

RESULTS

Isosorbide dinitrate significantly decreased both platelet adhesion and aggregation. No effect was seen in the placebo group.

CONCLUSIONS

In patients with AMI who do not receive thrombolytic therapy, ISDN effectively inhibits platelet adhesion and aggregation. These effects of nitrates may be of therapeutic and prognostic significance in this group of patients.

Coronary microembolization--its role in acute coronary syndromes and interventions

The diagnosis coronary artery disease is classically based on patient's symptoms and morphology, as analyzed by angiography. The importance of risk factors for the development of coronary atherosclerosis and disturbance of coronary vasomotion is clearly established. However, microembolization of the coronary circulation has also to be taken into account. Microembolization may occur as a single or as multiple, repetitive events, and it may induce inflammatory responses. Spontaneous microembolization may occur, when the fibrous cap of an atheroma or fibroatheroma (Stary i.v. and Va) ruptures and the lipid pool with or without additional thrombus formation is washed out of the atheroma into the microcirculation. Such events with progressive thrombus formation are known as cyclic flow variations. Plaque rupture occurs more frequently than previously assumed, i.e. in 9% of patients without known heart disease suffering a traffic accident and in 22% of patients with hypertension and diabetes. Also, in patients dying from sudden death microembolization is frequently found. Patients with stable and unstable angina show not only signs of coronary plaque rupture and thrombus formation, but also microemboli and microinfarcts, the only difference between those with stable and unstable angina being the number of events. Appreciation of microembolization may help to better understand the pathogenesis of ischemic cardiomyopathy, diabetic cardiomyopathy and acute coronary syndromes, in particular in patients with normal coronary angiograms, but plaque rupture detected by intravascular ultrasound. Also, the benefit from glycoprotein IIb/IIIa receptor antagonist is better understood, when not only the prevention of thrombus formation in the epicardial atherosclerotic plaque, but also that of microemboli is taken into account. Microembolization also occurs during PTCA, inducing elevations of troponin T and I and elevations of the ST segment in the EKG. Elevated baseline coronary blood flow velocity, as a potential consequence of reactive hyperemia in myocardium surrounding areas of microembolization, is more frequent in patients with high frequency rotablation than in patients with stenting and in patients with PTCA. The hypothesis of iafrogenic microembolization during coronary interventions is now supported by the use of aspiration and filtration devices, where particles with a size of up to 700 microns have been retrieved. In the experiment, microembolization is characterized by perfusion-contraction mismatch, as the proportionate reduction of flow and function seen with an epicardial stenosis is lost and replaced by contractile dysfunction in the absence of reduced flow. The analysis of the coronary microcirculation, in addition to that of the morphology and function of epicardial coronary arteries, and in particular appreciation of the concept of microembolization will further improve the understanding of the pathophysiology and clinical symptoms of coronary artery disease.

Abciximab in primary coronary angioplasty for acute myocardial infarction improves short- and medium-term outcomes

OBJECTIVES

The purpose of this study was to compare the outcome of primary percutaneous transluminal coronary angioplasty for acute myocardial infarction (MI) when performed with or without the platelet glycoprotein IIb/IIIa antibody, abciximab.

BACKGROUND

Abciximab improves the outcome of angioplasty but the effect of abciximab in primary angioplasty has not been investigated.

METHODS

Data were collected from a computerized database. Follow-up was by telephone or review of outpatient or hospital readmission records.

RESULTS

A total of 182 consecutive patients were included; 103 received abciximab and 79 did not. The procedural success rate was 95% in the two groups. At 30-day follow-up, the composite event rate of unstable angina, reinfarction, target vessel revascularization and death from all causes was 13.5% in the group of patients who did not receive abciximab, 4% (p < 0.05) in the abciximab group and 2.4% (p < 0.05) in the subgroup of patients (n = 87) who completed the 12-h abciximab infusion. At the end of follow-up (mean 7+/-4 months), the composite event rate was 32.4%, 17% (p < 0.05) and 13.1% (p < 0.01) in these three categories respectively. Abciximab bolus followed by a 12-h infusion was an independent predictor of event-free survival, in a Cox proportional hazards model (relative risk 0.49; 95% confidence interval 0.24 to 0.99; p < 0.05).

CONCLUSIONS

Abciximab given at the time of primary angioplasty may improve the short- and medium-term outcome of patients with acute MI, especially when a 12-h infusion is completed.

Platelet aggregation in acute coronary syndromes: use of a new aggregometer with laser light scattering to assess platelet aggregability

OBJECTIVE

Platelet aggregation has been implicated in the pathogenesis of acute coronary syndromes. Small aggregates consisting of < or = 100 platelets cannot be quantified with a conventional aggregometer employing optical density. Using a recently developed aggregometer based on laser light scattering, we studied platelet aggregability in patients with acute coronary syndromes.

METHODS

Peripheral blood samples were obtained from 39 patients with acute myocardial infarction or unstable angina who had received no prior antiplatelet or anticoagulant therapy, to be assayed immediately using a PA-100 platelet aggregometer. Blood samples from 14 healthy volunteers were used as controls.

RESULTS

Spontaneous formation of platelet aggregates was observed only in patients with acute coronary syndromes. The size of these aggregates was small, consisting of < or = 100 platelets (primary aggregation). Agonist-induced aggregation consisted of two phases. In the first few minutes, the number of small aggregates increased markedly (primary aggregation), followed by an increase in larger aggregates (secondary aggregation). The EC50 of epinephrine for primary aggregation was nearly 50 times lower in acute coronary patients than in controls (P < 0.001), while the EC50 for secondary aggregation was only 2 times lower (P < 0.001).

CONCLUSIONS

Aggregometry using light scattering suggests that platelet hyperaggregability and hypersensitivity in acute coronary syndromes may occur in primary but not secondary aggregation.

Unmet therapeutic needs in the management of acute ischemia

Unstable angina and myocardial infarction (MI) continue to present a major challenge in clinical management. These acute ischemic coronary syndromes (AICS) are a spectrum of clinical presentations of the same pathophysiologic mechanism: thrombus formation superimposed on atherosclerotic plaque disruption or erosion. Current approaches to the management of AICS, which include both interventional and pharmacologic therapy, have been introduced to clinical practice during the past 20 years, and most of them have demonstrated efficacy in clinical studies. A common inadequacy of current therapies, however, is the lack of significant inhibition of platelet aggregation--the crucial event in the formation of coronary thrombi and the pathogenesis of AICS. The final common pathway to platelet aggregation is the activation of the platelet glycoprotein (GP) IIb-IIIa receptor, which allows the cross-linking of adjacent platelets by the adhesive plasma proteins fibrinogen and von Willebrand's factor. The emergence of the GP IIb-IIIa receptor as a potential treatment target has led to the development of several inhibitors of its function. The inhibitors most advanced in clinical development are the chimeric monoclonal antibody abciximab (ReoPro) and the cyclic peptide eptifibatide (INTEGRILIN). In phase III clinical trials, both abciximab and eptifibatide have been shown to reduce the incidence of cardiac events in patients at risk for abrupt vessel closure after coronary angioplasty. Inhibition of the GP IIb-IIIa receptor is the most promising novel approach to the treatment of unstable angina and MI, and it may soon be an indispensable component of the management of patients with AICS.

Effects of platelet glycoprotein IIb/IIIa receptor blockade by a chimeric monoclonal antibody (abciximab) on acute and six-month outcomes after percutaneous transluminal coronary angioplasty for acute myocardial infarction. EPIC investigators

Percutaneous transluminal coronary angioplasty (PTCA) for acute myocardial infarction is an attractive alternative to thrombolysis, but is still limited by recurrent ischemia and restenosis. We determined whether adjunctive platelet glycoprotein IIb/IIIa receptor blockade improved outcomes in patients undergoing direct and rescue PTCA in the Evaluation of c7E3 for Prevention of Ischemic Complications (EPIC) trial. Of the 2,099 patients undergoing percutaneous intervention who randomly received chimeric 7E3 Fab (c7E3) as a bolus, a bolus and 12-hour infusion, or placebo, 42 underwent direct PTCA for acute myocardial infarction and 22 patients had rescue PTCA after failed thrombolysis. The primary composite end point comprised death, reinfarction, repeat intervention, or bypass surgery. Outcomes were assessed at 30 days and 6 months. Baseline characteristics were similar in direct and rescue PTCA patients. Pooling the 2 groups, c7E3 bolus and infusion reduced the primary composite end point by 83% (26.1% placebo vs 4.5% c7E3 bolus and infusion, p = 0.06). No reinfarctions or repeat urgent interventions occurred in c7E3 bolus and infusion patients at 30 days, although there was a trend toward more deaths in c7E3-treated patients. Major bleeding was increased with c7E3 (24% vs 13%, p = 0.28). At 6 months, ischemic events were reduced from 47.8% with placebo to 4.5% with c7E3 bolus and infusion (p = 0.002), particularly reinfarction (p = 0.05) and repeat revascularization (p = 0.002). We conclude that adjunctive c7E3 therapy during direct and rescue PTCA decreased acute ischemic events and clinical restenosis in the EPIC trial. These data provide initial evidence of benefit for glycoprotein IIb/IIIa receptor blockade during PTCA for acute myocardial infarction.

Platelet function in acute myocardial infarction treated with direct angioplasty

BACKGROUND

In acute myocardial infarction (AMI), platelets play a key role in thrombotic processes that limit the patency of the recanalized, infarct-related coronary artery and contribute to reperfusion injury. Platelet function in the course of AMI treated by direct percutaneous transluminal coronary angioplasty (PTCA) has not been evaluated.

METHODS AND RESULTS

In 15 patients with anterior AMI, peripheral venous blood samples were obtained before and 4, 8, 24, and 48 hours after recanalization of the occluded artery by PTCA. Fifteen patients who had stable coronary heart disease and were undergoing elective balloon angioplasty served as control subjects. Fibrinogen receptor function and surface expression of P-selectin on platelets were determined by flow cytometry. In addition, we evaluated generation of platelet-derived microparticles and the effect of systemic plasma from patients with AMI on normal platelet function and on platelet adhesion to human endothelial cells in culture. We found fibrinogen receptor activity and P-selectin expression on circulating platelets 8 hours after direct PTCA are decreased (P < .01). This coincided with a decrease in peripheral platelet count (P < .05) and an increase in generation of microparticles (P < .002). Twenty-four to 48 hours after PTCA, fibrinogen receptor activity and P-selectin expression increased again. Systemic plasma obtained before and after direct PTCA sensitized normal platelets to hyperaggregate in vitro (P < .001) and stimulated platelet adhesion to endothelial cells in culture (P < .01). None of the changes found in AMI were detectable in the control group.

CONCLUSIONS

After transient apparent deactivation of circulating platelet, probably caused by sequestration of hyperactive platelets, the level of platelet activation increases in patients with AMI treated by direct PTCA. These findings underscore the need for novel antiplatelet strategies in AMI.