Coronary thrombosis in pathogenesis of acute myocardial infarction. Histopathological study of coronary arteries in 108 necropsied cases using serial section

Do Patients with Myocardial Infarction with Non-Obstructive Coronary Arteries Have Similar Prognosis Compared to Ones with MI-CAD?

Acute myocardial infarction (AMI) is a leading cause of morbidity and mortality worldwide and it is primarily caused by acute plaque disruption and coronary occlusion. Recent studies suggest that myocardial infarction with non-obstructive coronary arteries (MINOCA) also occurs but the underlying mechanisms have not been fully understood until recently. The evidence also suggests that the clinical outcomes of patients presenting with MINOCA are similar to AMI patients with obstructive coronary artery disease (MI-CAD), including all-cause mortality and major adverse cardiovascular events. The present narrative review considers the risk factors, pathological changes, and outcomes associated with MINOCA and compares them with MI-CAD.

Interventional stroke treatment - Is it also safe for arteries? Looking at thrombectomy wall damage through clot histology

BACKGROUND AND PURPOSE

The aim of this study was to investigate whether morphological evidence of intracranial vascular injury can be found in the occluding thrombi of patients with ischemic stroke.

METHODS

From 2015 until 2018 specimens of thrombi from patients with large vessel occlusion treated either by stent-assisted aspiration thrombectomy (TE) or by aspiration thrombectomy were prospectively collected. Thrombus specimens were formalin-fixed, paraffin-embedded and stained. Architectural features, presence of parts of vessel wall or atheromatous material, organisation of the thrombi, technique and number of thrombectomy manoeuvers were evaluated.

RESULTS

Thrombus specimens from 302 patients were analyzed. 238 (80%) patients were treated with stent-assisted aspiration TE and 64 (20%) patients with aspiration TE only. 286 (95%) had fresh thrombi, 14 (4.6%) showed initial/complete thrombus organisation and multi-staged thrombi were found in 2 (<1%) patients. In 8 patients (2.6%) we found atypical thrombus content after a time interval longer 6 hours after onset and final thrombectomy manoeuvre: 4 with atheromatous material and 4 with parts of a vessel wall. In 1 patient with parts of vessel wall angiographically a dissection was detected. No parts of the vessel wall were found after sole aspiration thrombectomy.

CONCLUSIONS

The overall risk of arterial vessel wall injury aspiration thrombectomy was low in our study. Aspiration thrombectomy and the procedure related with a retrieving device together with an ischemia time longer than 6 hours may increase the risk of vessel injury through the thrombectomy procedure. Further investigations are necessary to elucidate the influence of the mentioned aspects.

Analytic Review: Thrombolytic Therapy in Acute Myocardial Infarction

The salvage of myocardium in the setting of acute myocardial infarction has long been a goal of physicians involved in the care of patients with coronary artery disease. Understanding the role of thrombosis in the pathogenesis of acute myocardial infarction has led the way to an entirely new approach to the treatment of this entity. Thrombolytic therapy has now become a widely used form of treatment with encouraging results. Both intravenous and intracoronary administration of thrombolytic agents have been shown to promote recanalization of acutely occluded coronary arteries. Results of studies using the clot-specific agent, tissue plasminogen activator, intravenously have been most encouraging; successful reperfusion has been obtained in approximately 70% of patients treated. In addition, a recent large-scale trial has shown a reduction in morbidity and mortality with the early use of thrombolytic agents.

Ongoing trials should help delineate the precise role and timing of these agents as the initial form of therapy for acute myocardial infarction. Other issues that remain unresolved are the frequency of restenosis and the role of percutaneous transluminal coronary angioplasty in addition to thrombolytic therapy in the treatment of acute myocardial infarction.

Arteriosclerosis: facts and fancy

Arterial vascular diseases comprise the leading cause of death in the industrialized world. Every physician learns about the pathology of these diseases in medical school. All pathologists evaluate arterial disease in surgical pathology and/or autopsy specimens. All clinicians encounter patients with clinical manifestations of these diseases. With such a common and clinically-important group of entities one would think there would be a general understanding of the "known" information that exists. That is, physicians and scientists should be able to separate what is fact and what is fancy. This review article is intended to generate thought in this regard.

An integrated backscatter ultrasound technique for the detection of coronary and carotid atherosclerotic lesions

The instability of carotid and coronary plaques has been reported to be associated with acute coronary syndrome, strokes and other cerebrovascular events. Therefore, recognition of the tissue characteristics of carotid and coronary plaques is important to understand and prevent coronary and cerebral artery disease. Recently, an ultrasound integrated backscatter (IB) technique has been developed. The ultrasound IB power ratio is a function of the difference in acoustic characteristic impedance between the medium and target tissue, and the acoustic characteristic impedance is determined by the density of tissue multiplied by the speed of sound. This concept allows for tissue characterization of carotid and coronary plaques for risk stratification of patients with coronary and cerebral artery disease. Two- and three-dimensional IB color-coded maps for the evaluation of tissue components consist of four major components: fibrous, dense fibrosis, lipid pool and calcification. Although several ultrasound techniques using special mathematical algorithms have been reported, a growing body of literature has shown the reliability and usefulness of the IB technique for the tissue characterization of carotid and coronary plaques. This review summarizes concepts, experimental procedures, image reliability and the application of the IB technique. Furthermore, the IB technique is compared with other techniques.

The physiology of cardiovascular disease and innovative liposomal platforms for therapy

Heart disease remains the major cause of death in males and females, emphasizing the need for novel strategies to improve patient treatment and survival. A therapeutic approach, still in its infancy, is the development of site-specific drug-delivery systems. Nanoparticle-based delivery systems, such as liposomes, have evolved into robust platforms for site-specific delivery of therapeutics. In this review, the clinical impact of cardiovascular disease and the pathophysiology of different subsets of the disease are described. Potential pathological targets for therapy are introduced, and promising advances in nanotherapeutic cardiovascular applications involving liposomal platforms are presented.

Update on acute coronary syndromes: the pathologists' view

Although mortality rates from coronary heart disease in the western countries have declined in the last few decades, morbidity caused by this disease is increasing and a substantial number of patients still suffer acute coronary syndrome (ACS) and sudden cardiac death. Acute coronary syndrome occurs as a result of myocardial ischaemia and its manifestations include acute myocardial infarction and unstable angina. Culprit plaque morphology in these patients varies from thrombosis with or without coronary occlusion to sudden narrowing of the lumen from intraplaque haemorrhage. The coronary artery plaque morphologies primarily responsible for thrombosis are plaque rupture, and plaque erosion, with plaque rupture being the most common cause of acute myocardial infarction, especially in men. Autopsy data demonstrate that women <50 years of age more frequently have erosion, whereas in older women, the frequency of rupture increases with each decade. Ruptured plaques are associated with positive (expansive) remodelling and characterized by a large necrotic core and a thin fibrous cap that is disrupted and infiltrated by foamy macrophages. Plaque erosion lesions are often negatively remodelled with the plaque itself being rich in smooth muscle cells and proteoglycans with minimal to absence of inflammation. Plaque haemorrhage may expand the plaque rapidly, leading to the development of unstable angina. Plaque haemorrhage may occur from plaque rupture (fissure) or from neovascularization (angiogenesis). Atherosclerosis is now recognized as an inflammatory disease with macrophages and T-lymphocytes playing a dominant role. Recently at least two subtypes of macrophages have been identified. M1 is a pro-inflammatory macrophage while M2 seems to play a role in dampening inflammation and promoting tissue repair. A third type of macrophage, termed by us as haemoglobin associated macrophage or M(Hb) which is observed at site of haemorrhage also can be demonstrated in human atherosclerosis. In order to further our understanding of the specific biological events which trigger plaque instability and as well as to monitor the effects of novel anti-atherosclerotic therapies newer imaging modalities in vivo are needed.

Compulsive Thrombus Management in STEMI Interventions

Thrombus is a fundamental concept in the pathophysiology of ST-elevated myocardial infarction (STEMI). Distal embolization and no reflow are associated with less angiographic success, reduced myocardial blush, less ST resolution after primary percutaneous coronary intervention, larger enzymatic infarct size, lower left ventricular ejection fraction at discharge, and higher long-term mortality. We believe that with the use of thrombectomy devices, these shortcomings can be minimized. Based on our experience from the Single Individual Community Experience Registry (SINCERE) database, we formulated a selective thrombus burden management strategy (the Mehta classification) for thrombus management.

Tissue characterization of coronary plaques and assessment of thickness of fibrous cap using integrated backscatter intravascular ultrasound. Comparison with histology and optical coherence tomography

BACKGROUND

The purpose of this study was to develop a new online integrated backscatter intravascular ultrasound (IB-IVUS) system and to validate its ability to measure fibrous cap thickness by comparing IB-IVUS images with those from optical coherence tomography (OCT).

METHODS AND RESULTS

Images were acquired from 125 segments of 26 coronary arteries obtained at autopsy from 11 cadavers. In the training study (n=30), 242 regions-of-interest on color-coded maps were compared with histology. In the validation study, 95 cross-sections were diagnosed by IB-IVUS and histology. In 24 patients with stable angina, 28 arterial cross-sections were imaged by IB-IVUS and OCT in vivo. In the training study, cutoff values of 39 decibels (dB) and 17dB were the optimal predictors of lipid pool/fibrosis and fibrosis/calcification, respectively, with 38-MHz mode; 42dB and 20dB, respectively, with 43-MHz mode. In the validation study, IB classified the fibrous, lipid-rich and fibrocalcific components with an accuracy of 92%, 91% and 95%, respectively. Agreement between the histological and IB-IVUS diagnoses was excellent (Cohen's κ=0.83). There was a correlation between the fibrous cap thickness measured by IB-IVUS and OCT (r=0.74, P<0.001).

CONCLUSIONS

The IB-IVUS system with improved resolution provides high diagnostic accuracy for the analysis of the tissue characteristics of coronary plaques, and enables estimation of the thickness of the fibrous cap in the clinical setting.

Inflammatory markers: linking unstable plaques to coronary event, an interventional perspective

Abundant data links inflammatory mechanisms to atheromatous plaque destabilization leading to plaque rupture and coronary events. The discovery of inflammatory cells and inflammatory mediators within atherosclerotic plaques prone to rupture led to a series of studies demonstrating an association between various markers of inflammation and future coronary events. Inflammatory markers have also been used in patients undergoing coronary angioplasty in an attempt to predict restenosis and risk for post-procedural coronary events. This review article provides an overview on the potential use of inflammatory markers in the context of coronary interventions.

Oral anticoagulation in the secondary prevention of myocardial infarction

Evidence in favour of oral anticoagulant therapy (OAT) in patients suffering from an acute myocardial infarction has been published in 1977 by Chalmers and co-workers (New Engl. J. Med. 297, 1091). For OAT after discharge an International Review Group (IRG) concluded in 1970 that "anticoagulant therapy probably prolongs survival at least over two years, but that benefit is as a rule restricted to patients with a history of angina or previous infarction" (The Lancet, 1, 203). Since the IRG finished their analysis, favourable results of four additional comparative studies have been published, three of which were double-blind and performed in the Netherlands. These four studies demonstrated a beneficial effect of adequate oral anticoagulation. The latest study was performed to assess benefits and untoward reactions of long-term OAT in the elderly. Results were published in November 1980 (The Lancet, 2,989). Mortality in the 738 patients who entered the trial, all of whom older than sixty years, having survived a transmural infarction, and having been on OAT for at least six months (mean: six years), was lower in patients on active treatment (p = 0.016), due to the important difference in recurrent myocardial infarction (RMI). Fifty-eight RMI's occurred in the placebo group as compared to only twenty in the AC group (p less than 0.01). Fatal cerebrovascular accidents were evenly distributed over the two groups, with a preponderance of haemorrhage in patients on active treatment. No fatal extracranial haemorrhage occurred. Incidence and severity of bleeding complications were in agreement with good patient compliance. No significant relationship was found between the recurrence of infarction and either the age of the patient or the length of treatment before entering trial. The steadiness of the widening gap between the mortality and RMI's observed in the two groups indicates that the efficacy of OAT persisted throughout the entire observation period of two years.

Non-invasive assessment of vulnerable plaque

BACKGROUND

Sudden cardiac death or unheralded acute coronary syndromes are common initial manifestations of coronary atherosclerosis and most such events occur at sites of non-flow limiting coronary atherosclerosis.

OBJECTIVE

Non-invasive detection of high-risk plaques might provide a means to improve risk stratification in primary and secondary prevention settings.

METHODS

This review is focused on the potential of multidetector computed tomography coronary angiography (MDCT-CA) to provide the opportunity to identify different aspects of plaque vulnerability throughout the coronary tree in an accurate, fast, safe and non-invasive manner.

CONCLUSION

Coronary artery calcium scoring, on top of established risk stratification, could potentially be a cost-effective strategy for primary prevention. MDCT-CA allows a non-invasive evaluation of several features commonly seen in vulnerable plaques and has demonstrated an independent prognostic value on a patient basis. The value of the technique itself might result, potentially, in a better estimation of the relative risk of an invidual plaque to rupture.

The unresolved issues with risk stratification and management of patients with coronary artery disease undergoing major vascular surgery

PURPOSE

The purpose of this article, with a specific focus on patients undergoing vascular surgery, is to review controversial issues related to mechanisms of perioperative myocardial infarction (MI), coronary artery disease detection, and strategies to reduce perioperative complications. We propose explanations for the many conflicting results that have recently emerged in the literature.Source documents: We searched MEDLINE and reviewed all relevant manuscripts and scientific statements regarding management of patients undergoing non-cardiac surgery.

PRINCIPAL FINDINGS

Identification and prevention of ischemia in patients undergoing vascular surgery remains controversial. While the identification of preoperative ischemia is a marker of a higher perioperative risk, the value of identifying such ischemia has been questioned. We believe this may be, at least in part, due to our limited understanding of perioperative MI. Appropriate management of patients, based on the results of such testing, is likely the key to improving outcomes, and deserves further investigation. Efforts aimed at reducing the ischemic consequences of severe coronary plaques (by revascularization or beta-blocker therapy) have yielded conflicting results. The use of high doses of preoperative beta-blocker therapy may be harmful. Some studies suggest a promising role for statin therapy. Benefits of acetylsalicylic acid must be weighted against the risk of bleeding.

CONCLUSION

Many questions remain unanswered about the impact of detecting inducible ischemia, and the role of revascularization or beta-blockers in patients undergoing vascular surgery. A better understanding of the pathophysiology of perioperative MI is critical, in order to identify the best approach to improve cardiac outcomes in these patients.

Tissue characterization of coronary plaques: comparison of integrated backscatter intravascular ultrasound with virtual histology intravascular ultrasound

BACKGROUND

Integrated backscatter (IB) intravascular ultrasound (IVUS) and IVUS Virtual Histology (VH) have been developed for tissue characterization, but have never been compared directly. The purpose of this study was to compare the overall agreement between IB-IVUS and IVUS-VH in the tissue characterization of plaques from the same coronary arterial cross-section.

METHODS AND RESULTS

Images were acquired from 46 coronary arteries from 25 cadavers. Of a total of 392 histology/IVUS image pairs, 152 pairs were diagnosed as Stary's type III, IV, Va, Vb and Vc, and compared for IB-IVUS, IVUS-VH and histology. In the qualitative comparison, the overall agreement between histological and IB-IVUS diagnoses was higher (kappa = 0.81, 95% confidence interval (CI): 0.74-0.89) than that of the IVUS-VH diagnoses (kappa = 0.66, 95%CI: 0.56-0.75). The % fibrosis area determined by IB-IVUS was significantly correlated with the relative area of fibrosis based on histology (r = 0.67, p < 0.001). In the quantitative comparison, the overall agreement between the histological and IB-IVUS diagnoses was higher (kappa = 0.83, 95% CI: 0.75-0.91) than that of the IVUS-VH diagnoses (kappa = 0.73, 95% CI: 0.63-0.83).

CONCLUSION

Based on histology as the gold standard, IB-IVUS provided higher diagnostic accuracy than IVUS-VH for tissue characterization of coronary plaques.

Development of integrated backscatter intravascular ultrasound for tissue characterization of coronary plaques

Tissue characterization of plaques of coronary arteries is important to clarify the process of acute coronary syndrome and prevent it. The purpose of this study is to develop an online integrated backscatter intravascular ultrasound (IB-IVUS) system and validate the diagnostic accuracy for the characterization of coronary plaques. A personal computer equipped with custom software was connected to an IVUS imaging system. Images were acquired from 242 segments of 46 coronary arteries from 25 cadavers obtained at autopsy. In the training study, a total of 724 regions-of-interests on color-coded maps were compared with histologic images. In the validation study, a total of 192 cross-sections of coronary arteries were evaluated. Receiver operating characteristic curve analysis showed that the cut-off points of -49 dB (area under curve = 0.98) and -29 dB (area under curve = 0.99) were the most reliable predictors of lipid pools, fibrosis and calcification. In the validation study, the analysis using IB values classified fibrous, lipid-rich and fibrocalcific plaque components with a high accuracy of 93%, 90% and 96%, respectively. The overall agreement between histologic and IB-IVUS diagnoses (n = 175) was high (Cohen's kappa = 0.81). The IB-IVUS system provides high diagnostic accuracy for analysis of tissue characteristics of coronary plaques.

Three-dimensional isotropic wavelets for post-acquisitional extraction of latent images of atherosclerotic plaque components from micro-computed tomography of human coronary arteries

RATIONALE AND OBJECTIVES

The capability of wavelet transforms to separate signals into frequency bands is the basis for its use in image compression and storage, data management and transmission, and, recently, extraction of latent images of tissue components from noisy medical images. Analysis of temporal variations of radiofrequency backscatter of intravascular ultrasound with one-dimensional wavelets can detect lipid-laden plaque in coronary arteries with a sensitivity and specificity of >80%. In this study we evaluate the capability of a novel, 3-dimensional isotropic wavelet analysis to perform high resolution, non-directionally biased, statistically reliable, non-invasive discrimination between components of human coronary atherosclerotic plaques in micro-CT.

MATERIALS AND METHODS

Coronary artery segments (5-15 mm) were excised at necropsy from 18 individuals with advanced coronary atherosclerosis. Specimens were imaged using a GE Locus SP ex vivo micro-CT scanner and processed for histological correlation (833 sections). The isotropic wavelet constructs were applied to the entire volume of CT data of each arterial segment to distinguish tissue textures of varying scales and intensities. Voxels were classified and plaque characterization achieved by comparing the relative magnitudes of these wavelet constituents to that of several reference plaque tissue components.

RESULTS

Processing of micro-CT images via these isotropic wavelet algorithms permitted 3-D, color-coded, high resolution, digital discrimination between lumen, calcific deposits, lipid-rich deposits, and fibromuscular tissue providing detail not possible with conventional thresholding based on Hounsfield intensity units. Using the isotropic wavelets (with histology as the gold standard), lipid-rich pools approaching the size of the filter for the isotropic wavelet algorithm (0.25 mm [250 microns] in length) were identified with 81% sensitivity and 86% specificity. Calcific deposits, fibromuscular tissue, and lumen equal to or larger than the wavelet filter size were detected without error (100% sensitivity and specificity).

CONCLUSION

Isotropic wavelet analysis permits high resolution, multi-dimensional identification of coronary atherosclerotic plaque components in micro-CT with sensitivity and specificity similar to that achieved with data obtained invasively (from IVUS in vivo) using one-dimensional wavelets. Further studies are necessary to test the applicability of this technology to clinical, multi-detector scanners.

Plaque stabilization: Can we turn theory into evidence?

Coronary events often result from thrombi that form because of physical disruption of the atherosclerotic plaque. The dynamic nature of the plaque offers the opportunity to intervene to modify plaque biology with lifestyle changes and, if needed, pharmacologic measures. Inhibitors of 3-hydroxy-3-methylglutaryl coenzyme A reductase (statins) reduce levels of serum cholesterol and decrease the incidence of coronary events, but some of the benefits of statins may not depend on their effects on circulating lipids. Indeed, increasing evidence suggests that statins may also enhance plaque stability. Such evidence includes results of preclinical studies with experimental atherosclerosis as well as imaging data and analyses of proinflammatory and prothrombotic mediators in clinical trials. Currently, however, no studies have demonstrated conclusively the mechanisms underlying the unexpected magnitude and rapidity of statin benefits. This article reviews the evolution of the concept of plaque stabilization and reexamines the evidence for the role of statins in that process.

Diagnostic Accuracy of Optical Coherence Tomography and Integrated Backscatter Intravascular Ultrasound Images for Tissue Characterization of Human Coronary Plaques

OBJECTIVES

The purpose of the present study was to validate the diagnostic accuracy of optical coherence tomography (OCT), integrated backscatter intravascular ultrasound (IB-IVUS), and conventional intravascular ultrasound (C-IVUS) for tissue characterization of coronary plaques and to evaluate the advantages and limitations of each of these modalities.

BACKGROUND

The diagnostic accuracy of OCT for characterizing tissue types is well established. However, comparisons among OCT, C-IVUS, and IB-IVUS have not been done.

METHODS

We examined 128 coronary arterial sites (42 coronary arteries) from 17 cadavers; IVUS and OCT images were acquired on the same slice as histology. Ultrasound signals were obtained using an IVUS system with a 40-MHz catheter and digitized at 1 GHz with 8-bit resolution. The IB values of the ultrasound signals were calculated with a fast Fourier transform.

RESULTS

Using histological images as a gold standard, the sensitivity of OCT for characterizing calcification, fibrosis, and lipid pool was 100%, 98%, and 95%, respectively. The specificity of OCT was 100%, 94%, and 98%, respectively (Cohen's kappa = 0.92). The sensitivity of IB-IVUS was 100%, 94%, and 84%, respectively. The specificity of IB-IVUS was 99%, 84%, and 97%, respectively (Cohen's kappa = 0.80). The sensitivity of C-IVUS was 100%, 93%, and 67%, respectively. The specificity of C-IVUS was 99%, 61%, and 95%, respectively (Cohen's kappa = 0.59).

CONCLUSIONS

Within the penetration depth of OCT, OCT has a best potential for tissue characterization of coronary plaques. Integrated backscatter IVUS has a better potential for characterizing fibrous lesions and lipid pools than C-IVUS.

Assessment of coronary plaque collagen with polarization sensitive optical coherence tomography (PS-OCT)

INTRODUCTION

Current evidence indicates that most plaques classified as vulnerable or ruptured plaque do not lead to unstable angina or myocardial infarction. Improved methods are needed to risk stratify plaques to identify those which lead to most acute coronary syndromes. Collagen depletion in the intima overlying lipid collections appears to be a critical component of unstable plaques. In this study, we use polarization sensitive optical coherence tomography (PS-OCT) for the assessment of coronary plaque collagen. Collagen is birefringent, meaning that different polarization states travel through it at different velocities.

METHODS AND RESULTS

Changes in PS-OCT images are a measure of tissue birefringence. Twenty-two coronary artery segments were imaged with PS-OCT and analyzed by picrosirius staining (a measure of collagen intensity and fiber size) and trichrome blue. The regression plot between PS-OCT changes and measured collagen yielded a correlation coefficient value of 0.475 (p<0.002). The predictive value of a PS-OCT measurement of negligible birefringence (less than 33% change) for minimal collagen was 93% while the predictive value of high birefringence (greater than 66% change) for high collagen concentrations was 89%. The effect of fiber type (chemical composition) was minimal relative to the effect due to fiber concentration.

CONCLUSION

The capability of PS-OCT to assess plaque collagen content, in addition to its ability to generate high resolution structural assessments, make it a potentially powerful technology for identifying high risk plaques.

Usefulness of multidetector computed tomography for noninvasive evaluation of coronary arteries in asymptomatic patients

This editorial addresses the capabilities, limitations, and potential of multidetector computed tomography (MDCT) for the noninvasive evaluation of coronary arteries in asymptomatic patients. The quantification of coronary calcium with MDCT correlates highly with that obtained by electron-beam computed tomography, but to date, neither has the capability of assessing the distribution of various morphologic patterns of calcium and their relation to other "soft" plaque components. Although MDCT can assess the thickness of the atherosclerotic wall and can readily identify calcific deposits, further plaque characterization (e.g., lipid pools and fibrous tissue), a prerequisite for the identification of most vulnerable lesions, is not yet a workable reality, even with the 64-slice machines in their current configuration. The noninvasive identification by MDCT of plaque components subtending vulnerable lesions will require additional improvement in the primary instrumentation, the use of hybrid constructs (e.g., with positron emission tomography and magnetic resonance imaging), the development of novel methods of post-acquisitional analysis to extract latent images of plaque components (e.g., signal analysis based on 3-dimensional wavelets), or the adaptation of molecular imaging techniques at the cell and gene levels to computed tomography. Such unique approaches may soon contribute a long list of additional parameters that could be evaluated on a noninvasive basis as predictors of acute coronary syndromes and overall patient vulnerability.

Perioperative cardiac events in patients undergoing noncardiac surgery: a review of the magnitude of the problem, the pathophysiology of the events and methods to estimate and communicate risk

This is the first of 2 articles evaluating cardiac events in patients undergoing noncardiac surgery. In this article, we review the magnitude of the problem, the pathophysiology of these events, approaches to risk assessment and communication of risk. The number of patients undergoing noncardiac surgery worldwide is growing, and annually 500,000 to 900,000 of these patients experience perioperative cardiac death, nonfatal myocardial infarction (MI) or nonfatal cardiac arrest. Although the evidence is limited, a substantial proportion of fatal perioperative MIs may not share the same pathophysiology as nonoperative MIs. A clearer understanding of the pathophysiology is needed to direct future research evaluating prophylactic, acute and long-term interventions. Researchers have developed tools to facilitate the estimation of perioperative cardiac risk. Studies suggest that the Lee index is the most accurate generic perioperative cardiac risk index. The limitations of the studies evaluating the ability of noninvasive cardiac tests to predict perioperative cardiac risk reveals considerable uncertainty as to the role of these popular tests. Similarly, there is uncertainty as to the predictive accuracy of the American College of Cardiology/American Heart Association algorithm for cardiac risk assessment. Patients are likely to benefit from improved estimation and communication of cardiac risk because the majority of noncardiac surgeries are elective and accurate risk estimation is important to allow informed patient and physician decision-making.

Vulnerable Plaque Imaging

The concept of vulnerable plaque is well established with increasing evidence from clinical and basic research. The paradigm has shifted from focusing exclusively on the hemodynamic effects of plaque (ie, resulting lumenal stenosis alone as a predictor of stroke risk) to assessment of the structure and composition of plaque (eg, denuded endothelium with inflammatory elements as a nidus for platelet-fibrin clumping). It is increasingly evident that methods to detect and characterize vulnerable plaque must be developed and optimized. Although MR imaging, CT, and ultrasound provide data regarding single lesions, future investigations relying heavily on nuclear medicine techniques may offer functional assessment of the entire cardiovascular system.

Diagnosis and treatment of non-hemodynamically significant coronary heart disease: where to start?

In the U.S. and all industrialized countries, more deaths result from heart attack and stroke than from any other cause. Increasingly it is proposed that many cardiac events occur following the rupture of minor, non-hemodynamically significant atherosclerotic plaque. Indeed many policy makers and some physicians have questioned the importance of traditional screening and treatment strategies for hemodynamically significant coronary artery lesions. As an alternative, it has been suggested that screening and treatment approaches should be guided by emerging data that support the predictive value of measures of inflammation, such as high sensitivity C-reactive protein, or of genetic markers. Our goal is review the biology of acute coronary events and the results of population-based studies and, in this light, consider the usefulness of the current "state-of-the-art" methods for diagnosing coronary heart disease.

Finding Vulnerable Atherosclerotic Plaques

Techniques to identify and treat vulnerable plaques are the focus of enormous research. Some have questioned the benefit of locating individual vulnerable plaque in a multifocal disease. On autopsy, it is found that most deaths are caused by thrombotic occlusion of a single plaque; simultaneous occurrence of 2 occlusive thrombi is rare, but a second vulnerable plaque is common, particularly in acute myocardial infarction (MI). Angiographic progression is poorly predicted by risk factors, and angiographic progression is a weak predictor of MI or death. Intravascular ultrasonography (intravascular ultrasound [IVUS]) studies find plaque rupture in most MI patients and in approximately half with unstable angina, but in only a minority of patients with stable angina. IVUS identifies a second vulnerable plaque in many patients with unstable angina, and in most MI patients. Angioscopy reveals a very low incidence of a second vulnerable plaque compared with angiography and IVUS, but identifies additional yellow plaques in many patients with stable angina and in most patients with unstable angina or MI. Using thermography catheters and a temperature cutoff of 0.1 degrees C, approximately half the patients with stable angina have >1 hot lesion; however, if the cutoff is 0.2 degrees C, only approximately 15% have a second hot lesion. New imaging techniques may detect additional characteristics of plaques and new predictive models may assess the risk of vulnerable plaques and patients. This approach enables physicians to "buy time" by application of local therapies until systemic therapies stabilize plaques. This may also reduce the risk in subjects in whom systemic therapies do not work.

Angiographic aspects of ruptured plaque in patients with acute myocardial infarction: correlation with clinical and laboratory variables

In patients with acute myocardial infarction (AMI), little is known about the correlation between prognostic variables and aspects of ruptured plaque at the coronary angiography. Five hundred patients with acute myocardial infarction were studied in a consecutive and prospective manner; of these, 264 patients were excluded mainly because of the presence of an occluded culprit coronary artery. The remaining 236 patients were divided according to the presence (113, 52%) or absence (126, 48%) of angiographic aspects suggestive of ruptured plaque, and correlated with 49 clinical, electrocardiographic, in-hospital complications, procedures, and other angiographic prognostic variables. The variables that correlated significantly and independently with angiographic aspects of ruptured plaque were: presence of thrombi and higher degree of residual stenosis at the culprit coronary artery, as well as white ethnic group.

Atheromatous plaque cap thickness can be determined by quantitative color analysis during angioscopy: implications for identifying the vulnerable plaque

BACKGROUND

Coronary angioscopy in acute myocardial infarction has frequently revealed disrupted yellow lesions. Furthermore, postmortem studies have demonstrated that these lesions have thin collagenous caps with underlying lipid-rich cores.

HYPOTHESIS

We hypothesized that the yellow color is due to visualization of reflected light from the lipid-rich yellow core through a thin fibrous cap. Thus, quantification of yellow color saturation may estimate plaque cap thickness and identify vulnerable plaques.

METHODS

To test this hypothesis, the feasibility of detecting cap thickness was tested using both a model of lipid-rich plaque and human atherosclerotic plaque. The model was constructed by injecting a yellow beta-carotene-lipid emulsion subendothelially into normal bovine aorta. Human plaque was obtained from cadaver aorta. Digitized images were obtained by angioscopy, and percent yellow saturation was analyzed using a custom computer program. Plaque cap thickness was measured by planimetry of digitized images on stained tissue sections. Percent yellow saturation was then correlated with plaque cap thickness.

RESULTS

In the bovine model, plaque cap thickness and percent yellow saturation correlated inversely (r2 = 0.91; p = 0.0001). In human plaques, yellow saturation was significantly greater in atheromatous than in white plaques (p < 0.0004). Also, there was a high correlation between plaque cap thickness and yellow saturation at various angles of view between 40 degrees and 90 degrees, the greatest between 50 degrees and 80 degrees (r2 = 0.75 to 0.88).

CONCLUSION

Plaque cap thickness is a determinant of plaque color, and this can be assessed by quantitative colorimetry. Thus, plaque color by angioscopy may be useful for detecting vulnerable plaques.

Coronary arterial remodeling in differing clinical presentations of unstable angina pectoris--an intravascular ultrasound study

BACKGROUND

Coronary arterial remodeling influences the clinical presentation of ischemic heart disease; however, there is little information on the relationship between coronary arterial remodeling and the type of angina pectoris that patients manifest.

HYPOTHESIS

The study was undertaken to determine the difference of coronary arterial remodeling in patients with different types of angina pectoris.

METHODS

We analyzed 100 patients with ischemic heart disease using intravascular ultrasound (IVUS). Intracoronary IVUS images of proximal reference (PR), distal reference (DR), and target lesion were recorded, and intraluminal area (LA) and external elastic membrane (EEM) were measured. We defined a remodeling index as 100 x (lesion EEM - [PR-EEM + DR-EEM]/2) / ([PR-EEM + DR-EEM]/2). Cases were classified into three groups according to the clinical history (Group 1a: de novo unstable angina pectoris, Group 1b: accelerating unstable angina pectoris, and Group 2; stable angina pectoris).

RESULTS

The remodeling index in Group 1a was significantly larger than that in Groups 1b and 2 (18.6 +/- 28.5 vs. 5.3 +/- 27.1 and 18.6 +/- 28.5 vs. -2.7 +/- 17.6, p = 0.0347 and p = 0.0005, respectively), but there was no statistical difference in remodeling index between Groups 1b and 2.

CONCLUSIONS

Our results indicate that positive coronary arterial remodeling is more prevalent in patients with new onset of angina pectoris. The specific type of coronary arterial remodeling may affect the clinical presentation of patients with coronary artery disease.

BM-573, a dual thromboxane synthase inhibitor and thromboxane receptor antagonist, prevents pig myocardial infarction induced by coronary thrombosis

The aim of this study was to characterize the effects of BM-573 [N-terbutyl-N'-[2-(4'-methylphenylamino)-5-nitro-benzenesulfonyl] urea], a novel dual thromboxane A2 receptor antagonist and thromboxane synthase inhibitor, on myocardial infarction induced by topical ferric chloride (FeCl3) application to the left anterior descending (LAD) coronary artery in anesthetized pigs. All control animals (n = 6) developed an occlusive thrombus in the LAD coronary artery. The mean infarct size, revealed by triphenyl tetrazolium chloride (TTC), and the area at risk, evidenced by Evans blue, corresponded to 35.3 +/- 2.2 and 36.9 +/- 2.1% of the left ventricular mass, respectively. In the BM-573-treated group (n = 6), a drug infusion (10 mg. kg-1. h-1) started 30 min before FeCl3 application and continued throughout the experimentation. Among the BM-573-treated group, four pigs did not develop coronary artery thrombus and their myocardium appeared healthy. Histopathological examination of FeCl3-injured coronary artery revealed an occlusive and adherent thrombus in control group, while pretreatment with BM-573 prevented thrombus formation. In infarcted zones, lack of desmin staining and muscle structure disorganization were obvious. Depletion of myocardial ATP content was observed in the myocardial necrotic region of the control group, but not in myocardial samples of BM-573-treated pigs that did not develop myocardial infarction. When BM-573 prevented LAD artery occlusion, the area under the curve of plasmatic troponin T was reduced by 77% over 6 h. These data suggest that BM-573 could be useful for the prevention of myocardial infarction.

Intravascular ultrasound imaging of myocardial-infarction-related arteries after percutaneous transluminal coronary angioplasty reveals significant plaque burden and compensatory enlargement

We studied patients with acute myocardial infarction (MI) by intravascular ultrasound (IVUS) to elucidate the controversy as to the amount and severity of the atherosclerotic disease at the culprit lesion site in acute MI, as discrepancies exist between angiographic and pathological reports. Twenty-five consecutive patients (age 56 3 10.5 years), with acute MI, underwent IVUS study of the MI-related artery immediately following successful PTCA to the culprit lesion. The IVUS images were analyzed quantitatively and qualitatively and were compared with the angiography of the same arteries. At the PTCA site, 64% of the lesions had an area stenosis of 50-70% and the plaque cross-sectional area (CSA) averaged 0.5 3 0.18 of the arterial CSA. IVUS-defined atherosclerosis was found also in 72% of the segments proximal and distal to the culprit lesion with a plaque/artery CSA ratio of 0.25 3 0.2. The angiogram revealed only 30% of these segments to be abnormal (P 3 0.001). Sixty-nine per cent of all the plaques were defined as 'soft' (low echo-genecity) versus 31% 'hard' (high echo-genecity). The hard plaques were larger than the soft plaques (0.5 3 1.6 versus 0.37 3 0.19 CSA index, respectively, P 3 0.01). With the increase in plaque area there was a significant increase in arterial cross-sectional area. This was demonstrated for all the diseased segments with a correlation coefficient of 0.49 (P 3 0.0001) and for the diseased reference sites a similar correlation coefficient of 0.49 (P 3 0.003) was found. Contrary to coronary angiographic-based reports, this IVUS study revealed a significant atheromatous plaque burden at the culprit lesion of MI-related arteries as well as diffuse atherosclerosis in the reference segments proximal and distal to the lesion. The detection of compensatory enlargement may explain the discrepancies between the histopathological and the angiographic studies.

Warfarin, aspirin, or both after myocardial infarction

BACKGROUND

The role of antithrombotic therapy in secondary prevention after myocardial infarction is well established. Although the available literature suggests that warfarin is superior to aspirin, aspirin is currently the more widely used drug. We studied the efficacy and safety of warfarin, aspirin, or both after myocardial infarction.

METHODS

In a randomized, multicenter trial in 3630 patients, 1216 received warfarin (in a dose intended to achieve an international normalized ratio [INR] of 2.8 to 4.2), 1206 received aspirin (160 mg daily), and 1208 received aspirin (75 mg daily) combined with warfarin (in a dose intended to achieve an INR of 2.0 to 2.5). The mean duration of observation was four years.

RESULTS

The primary outcome, a composite of death, nonfatal reinfarction, or thromboembolic cerebral stroke, occurred in 241 of 1206 patients receiving aspirin (20.0 percent), 203 of 1216 receiving warfarin (16.7 percent; rate ratio as compared with aspirin, 0.81; 95 percent confidence interval, 0.69 to 0.95; P=0.03), and 181 of 1208 receiving warfarin and aspirin (15.0 percent; rate ratio as compared with aspirin, 0.71; 95 percent confidence interval, 0.60 to 0.83; P=0.001). The difference between the two groups receiving warfarin was not statistically significant. Episodes of major, nonfatal bleeding were observed in 0.62 percent of patients per treatment-year in both groups receiving warfarin and in 0.17 percent of patients receiving aspirin (P<0.001).

CONCLUSIONS

Warfarin, in combination with aspirin or given alone, was superior to aspirin alone in reducing the incidence of composite events after an acute myocardial infarction but was associated with a higher risk of bleeding.

Multifocal coronary plaque instability

Recent observations document that many patients with acute coronary syndromes harbor multiple complex plaques by angiography, which correlate with multiple plaque ruptures and clots at necropsy. Multifocal plaque instability is evident not only in coronary vessels but also in peripheral vessels where peripheral and coronary plaque instability may exist concomitantly. These observations support the concept that plaque instability is not merely a local vascular accident but instead reflects more systemic pathophysiological processes with potential to destabilize atherosclerotic plaques throughout the cardiovascular system.

Histopathologic evaluation of coronary artery thrombi obtained by directional coronary atherectomy in patients with restenosis-induced unstable angina pectoris

The pathogenesis of unstable angina pectoris (UAP) following percutaneous transluminal coronary angioplasty (PTCA) or directional coronary atherectomy (DCA) has not been adequately investigated, so the present study aimed to determine whether thrombi are present in restenotic lesions. The study group comprised 14 patients (16 arterial branches) with angina pectoris in whom either PTCA or DCA was performed and who had developed UAP associated with restenosis, and who then underwent DCA of the restenosed lesion (R-UAP group). The control groups comprised individuals with UAP undergoing DCA with no prior history of PTCA or DCA (P-UAP group; n=29, 29 branches), patients with acute myocardial infarction (AMI group; n=34, 34 branches), and patients with stable angina pectoris (SAP group; n=31, 33 branches). The presence of thrombi was determined by light microscopy of histologic specimens. Thrombus was present in only 1 of the 16 (6.3%) branches in the R-UAP group. 21 of the 29 (72.4%) branches in the P-UAP group, and in 25 of the 34 (73.5%) in the AMI group. In the SAP group, it was detected in only 2 of the 33 (7.1%) branches. The incidence of thrombus was significantly lower in the R-UAP group than in the P-UAP group. In conclusion, the role of thrombus is limited in causing post-interventional UAP at restenosed sites.

Role of plaque rupture in acute coronary syndromes

Acute coronary syndromes are caused by plaque rupture. The conventional strategy of prevention of plaque rupture has been driven by the "lipid hypothesis"--if lipid levels are optimized to target levels, the risk of coronary events is decreased. Indeed, the hypothesis has been validated by the dramatic success of statin therapy. However, further major reductions in cardiac events is a realistic goal; various mechanistic and small clinical studies show that statins have beneficial effects in addition to their lipid-lowering properties. One of these beneficial effects is stabilization of plaque. Despite billions of dollars spent on randomized clinical trials, optimal therapy for coronary artery disease is yet to be tested. This therapy might include various combinations of the Mediterranean or low-fat diet, endothelial passivation, lipid-lowering drugs, antioxidants, antiplatelet agents and anti-inflammatory agents.

The vulnerable coronary plaque

Vulnerable coronary plaques are asymptomatic atherosclerotic lesions with the tendency to rupture. Plaque rupture is the initiating event in most acute coronary syndromes including sudden cardiac death, acute myocardial infarction, and unstable angina. Vulnerable plaques are commonly found in coronary arteries at autopsy but are virtually undetectable by standard diagnostic techniques such as stress testing and coronary angiography. Using new imaging techniques, in particular intravascular ultrasound and magnetic resonance imaging (MRI), scientists are now able to identify these plaques in vivo. A better understanding of the pathophysiology of plaque vulnerability and rupture will eventually lead to the therapeutic goal of plaque stabilization in the prevention of acute coronary syndromes. This article reviews the role of plaque vulnerability in coronary artery disease. The anatomy and pathophysiology of vulnerable plaques as well as diagnostic and therapeutic implication will be described.

Compensatory enlargement of the coronary artery in acute myocardial infarction

Compensatory enlargement occurred in 71% of lesions in patients with acute myocardial infarction and was more common in these patients than in patients with stable effort angina pectoris. These results suggest that compensatory enlargement may be associated with plaque rupture and subsequent acute myocardial infarction.

Extent and direction of arterial remodeling in stable versus unstable coronary syndromes : an intravascular ultrasound study

BACKGROUND

The morphological characteristics of coronary plaques in patients with stable versus unstable coronary syndromes have been described in vivo with intravascular ultrasound, but the relationship between arterial remodeling and clinical presentation is not well known.

METHODS AND RESULTS

We studied 85 patients with unstable and 46 patients with stable coronary syndromes using intravascular ultrasound before coronary intervention. The lesion site and a proximal reference site were analyzed. The remodeling ratio (RR) was defined as the ratio of the external elastic membrane (EEM) area at the lesion to that at the proximal reference site. Positive remodeling was defined as an RR >1.05 and negative remodeling as an RR <0.95. Plaque area (13.9+/-5.5 versus 11.1+/-4.8 mm(2); P=0.005), EEM area (16.1+/-6.2 versus 13.0+/-4.8 mm(2); P=0. 004), and the RR (1.06+/-0.2 versus 0.94+/-0.2; P=0.008) were significantly greater at target lesions in patients with unstable syndromes than in patients with stable syndromes. Positive remodeling was more frequent in unstable than in stable lesions (51. 8% versus 19.6%), whereas negative remodeling was more frequent in stable lesions (56.5% versus 31.8%) (P=0.001).

CONCLUSIONS

Positive remodeling and larger plaque areas were associated with unstable clinical presentation, whereas negative remodeling was more common in patients with stable clinical presentation. This association between the extent of remodeling and clinical presentation may reflect a greater tendency of plaques with positive remodeling to cause unstable coronary syndromes.

Is preinfarction angina related to the presence or absence of coronary plaque rupture?

OBJECTIVE

To analyse the prodrome of acute myocardial infarction in relation to the plaque morphology underlying the infarct.

DESIGN

A retrospective investigation of the relation between rupture and erosion of coronary atheromatous plaques and the clinical characteristics of acute myocardial infarction. The coronary arteries of 100 patients who died from acute myocardial infarction were cut transversely at 3 mm intervals. Segments with a stenosis were examined microscopically at 5 micrometer intervals. The clinical features of the infarction were obtained from the medical records.

RESULTS

A deep intimal rupture was encountered in 81 plaques, whereas 19 had superficial erosions only. There were no differences in the location of infarction, the incidence of hypertension, diabetes mellitus, or hyperlipidaemia, diameter stenosis of the infarcted related artery, Killip class, Forrester's haemodynamic subset, or peak creatine kinase between plaque rupture and plaque erosion groups. The presence of plaque rupture was associated with significantly greater incidences of leucocytosis, current smoking, and sudden or unstable onset of acute coronary syndrome. In patients with unstable preinfarction angina, new onset rest angina rather than worsening angina tended to develop more often in the plaque rupture group than in the plaque erosion group (p = 0.08).

CONCLUSIONS

Plaque rupture causes the sudden onset of acute myocardial infarction or unstable preinfarction angina, which may be aggravated by smoking and inflammation.

Coronary artery disease: arterial remodelling and clinical presentation

OBJECTIVE

To investigate the hypothesis that in coronary artery disease large plaques in compensatorily enlarged segments are associated with acute coronary syndromes, whereas smaller plaques in shrunken segments are associated with stable angina pectoris.

METHODS

Patients selected for percutaneous transluminal coronary angioplasty (PTCA) were divided into two groups, one with stable angina pectoris (stable group, n = 37) and one with unstable angina or postmyocardial infarction angina of the infarct related artery (unstable group, n = 32). In both groups, remodelling at the culprit lesion site was determined by intravascular ultrasound before the intervention. Remodelling was calculated as relative vessel area: [vessel area culprit lesion site / mean vessel area of both proximal and distal reference sites] x 100%. Compensatory enlargement was defined as remodelling of >/= 105%, whereas shrinkage was defined as remodelling of </= 95%.

RESULTS

In the unstable group, the vessel area at the culprit lesion site was larger than in the stable group, at mean (SD) 18.1 (5.3) v 14.6 (5.4) mm(2) (p = 0.008). Lumen areas were similar. Consequently, plaque area and percentage remodelling were larger in the unstable group than in the stable group: mean (SD) 14.8 (4.8) v 11.6 (4.9) mm(2) (p = 0.009) and 112 (31)% v 95 (17)% (p = 0.005), respectively. Significantly more culprit lesion sites were classified as shrunken in the stable group (21/37) than in the unstable group (8/32; p = 0.014). On the other hand, more lesion sites were classified as enlarged in the unstable group (16/23) than in the stable group (8/37; p = 0.022).

CONCLUSIONS

In patients selected for PTCA, the mode of remodelling is related to clinical presentation.

Characterization of the unstable lesion by angiography, angioscopy, and intravascular ultrasound

Acute coronary syndromes are a spectrum of clinical presentations with various pathophysiologic substrates. As such, there is not one single type of lesion responsible for stable or unstable angina, acute myocardial infarction, and sudden cardiac death. Most of the information regarding the characteristics of culprit lesions derives from histopathologic studies, whether postmortem or from atherectomy samples, and from studies using angiography, angioscopy, and intravascular ultrasound. Characterization of the unstable coronary lesion is key to understanding the pathophysiology of coronary artery disease, this knowledge will allow clinicians to individualize treatment according to specific lesion types, and more importantly, will lead to strategies to identify atherosclerotic lesions in their early stages and implement preventive therapies.

Histological analysis of coronary artery lesions in fatal postoperative myocardial infarction

We sought to evaluate the underlying coronary pathology of fatal postoperative myocardial infarction (MI). It has been hypothesized that most MIs following noncardiac surgery occur in the setting of increased oxygen demand that exceeds coronary blood supply. However, most MIs not associated with surgery are caused by plaque rupture and intracoronary thrombosis. In a retrospective cohort study, we reviewed 1841 consecutive autopsy records from 1981 to 1995 at two institutions and identified 26 cases of postoperative MI with coronary arteries available. Plaque rupture was present in 12 cases (46%, 95% confidence interval [CI] 27%-67%). Of the 9 (35%) patients with intracoronary thrombus, 5 (56%; 19% of entire group) had total occlusion. Thrombus occurred on a >50% stenosis (by cross-sectional area) in a total of 33% (95% CI 16%-55%) of patients. The only statistically significant difference in clinical variables between patients with and without plaque rupture was longer interval from surgery to death in patients with plaque rupture (7.8+/-4.4 days versus 4.4+/-4.8 days; p = 0.047). In this autopsy series, coronary plaque rupture was associated with almost half of fatal postoperative MI cases. Strategies aimed at reducing triggers of plaque rupture with coronary occlusion might reduce postoperative MI fatality.

Coronary atherosclerosis and interventions: pathological sequences and restenosis

The primary cause of cardiac morbidity and mortality in developed countries is ischemic (coronary) heart disease. The incidence of this disease is virtually all due to atherosclerosis, and ischemic heart disease is also the most prevalent disease in the industrialized world, causing over 40% of all deaths in the United States and Western Europe. In Japan, the incidence of ischemic heart disease due to coronary atherosclerosis is gradually increasing as well. Compared with the classical nomenclature of atherosclerosis; that is, fatty streak, fibrous plaque and complicated lesions, the term Stary's classification has been universally accepted because it reflects the more recently acquired knowledge about the morphological and biochemical details of the processes in coronary atherosclerosis, which have been obtained by new strategies such as angioscopy, intravascular ultrasound and molecular biological methods. The term Stary's classification has been applied for the coronary atherosclerosis of patients with acute coronary syndrome at the National Cardiovascular Center, for the analysis of predisposing atherosclerosis of these patients. The recent findings regarding acute coronary syndrome resulting from a rupture of coronary atherosclerotic plaques indicate that this syndrome is probably the most important mechanism underlying the sudden onset. It has been found that the risk of plaque rupture may depend more on plaque composition than on plaque size. Plaques rich in soft extracellular lipids and macrophages are possibly more vulnerable to plaque rupture. Two of the goals of the present review are to clarify how plaque disruption occurs and to elucidate the relationship between plaque disruption and coronary risk factors in elderly Japanese patients with acute coronary syndrome. Coronary stents have been shown to be efficacious in the treatment of acute and threatened closure complicating percutaneous transluminal coronary angioplasty (PTCA) and have produced encouraging initial results in the prevention of restenosis. In the autopsy study of restenosis after PTCA, it was observed that dense caps of collagen fibers in the adventitia in the vicinity of the disrupted internal elastic laminae were present in all of the remodeling lesions. It is suggested that remodeling, which resulted in adventitial scarring, is one of the major causative factors of restenosis after PTCA. The long-term success of stenting, however, remains limited by the occurrence of late in-stent restenosis, with an incidence of 20-42% depending on the stent design and the patient population studied. Another aim of the present review is to describe the pathological mechanism of restenosis after PTCA and/or stent replacement and, consequently, the vascular remodeling that occurs around adventitial tissue after PTCA and intimal hyperplasia that is chronically irritated by a foreign body granulomatous reaction after stenting. Finally, the results of the investigation of the effect of a tissue factor pathway inhibitor on the prevention of interventional restenosis is described.

Intracoronary aspiration thrombectomy for acute myocardial infarction

To investigate the pathogenesis of acute myocardial infarction (AMI) and values of intracoronary aspiration thrombectomy (ICAT), we applied ICAT to reperfusion therapy using generally available intracoronary catheters to aspirate intracoronary occlusive tissues. We assigned ICAT or primary percutaneous transluminal coronary angioplasty (PTCA) to patients with evolving AMI (Thrombolysis In Myocardial Infarction (TIMI) trial grade 0), and investigated primary histopathologic, clinical, and angiographic outcomes in 43 patients treated with ICAT alone or followed by PTCA, and compared the outcomes with those in 48 patients treated with primary PTCA. No major complications (procedural death, emergent bypass graft surgery) occurred. Reconalization (TIMI grade 3 and 2) was achieved in 25 patients (58%) with ICAT alone and in 39 patients (91%) with ICAT alone or followed by PTCA. Aspirated thrombi were defined as recent thrombi in 21 cases (49%), atheroma in 6 (14%), no thrombi in 13 (30%), and organized thrombi in 1 case. In cases of recent thrombi, ICAT alone provided recanalization more frequently than in those of atheroma or no thrombi (18 of 21 [86%], 3 of 6 [50%], 4 of 13 [31%], respectively; p < 0.05; recent thrombi vs atheroma or no thrombi). There were no significant differences in primary recanalization rate (ICAT alone or followed by PTCA vs primary PTCA; 91% vs 92%) or incidence of complications between the 2 strategies. These results indicate that although the pathogenesis of AMI is heterogeneous in each individual case, intracoronary thrombus contributes little to the pathogenesis of average AMI, and therefore mechanical approaches may be feasible to maximize reperfusion therapies for AMI.