Accuracy of In Vivo Coronary Plaque Morphology Assessment

Lipid-Lowering Therapy With Ezetimibe Decreases Spontaneous Atherothrombotic Occlusions in a Rabbit Model of Plaque Erosion: A Role of Serum Oxysterols

OBJECTIVE

Plaque erosion is increasing its importance as one of the mechanisms of acute coronary syndromes in this statin era. However, the clinical efficacy of currently used lipid-lowering agents in the prevention of thrombotic complications associated with plaque erosion has not been clarified. Therefore, we examined the therapeutic effects of ezetimibe or rosuvastatin monotherapy on spontaneous atherothrombotic occlusion.

APPROACH AND RESULTS

Femoral arteries of Japanese white rabbits, fed a high-cholesterol diet, were injured by balloon catheter, and then angiotensin II was continuously administrated. In 94% of these arteries, spontaneous thrombotic occlusions were observed after 5 weeks (median) of balloon injury. Histochemical analyses indicated that the injured arteries had similar pathological features to human plaque erosions; (1) spontaneous thrombotic occlusion, (2) lack of endothelial cells, and (3) tissue factor expression in vascular smooth muscle cells. Ezetimibe (1.0 mg/kg per day), but not rosuvastatin (0.6 mg/kg per day), significantly decreased thrombotic occlusion of arteries accompanied with accelerated re-endothelialization and the decreases of serum oxysterols despite the comparable on-treatment serum cholesterol levels. The 7-ketocholesterol inhibited the migration of human umbilical vein endothelial cells. Both 7-ketocholesterol and 27-hydroxycholesterol increased tissue factor expression in cultured rat vascular smooth muscle cells. Tissue factor expression was also induced by serum from vehicle- or rosuvastatin-treated rabbits, but the induction was attenuated with serum from ezetimibe-treated rabbits.

CONCLUSIONS

We have established a novel rabbit model of spontaneous atherothromobotic occlusion without plaque rupture that is feasible to test the therapeutic effects of various pharmacotherapies. Ezetimibe may decrease atherothrombotic complications after superficial plaque erosion by reducing serum oxysterols.

Association of D-dimer with Plaque Characteristics and Plasma Biomarkers of Oxidation-Specific Epitopes in Stable Subjects with Coronary Artery Disease

D-dimer has emerged as a biomarker of cardiovascular event risk, yet pathophysiological factors associated with plasma D-dimer levels in stable coronary artery disease (CAD) subjects are poorly understood. In 106 stable CAD subjects undergoing intravascular ultrasound with virtual histology (IVUS-VH), we measured D-dimer, lipoprotein(a) (Lp(a)), plasminogen, biomarkers reflecting oxidation-specific epitopes (OSE) such as oxidized phospholipids on apolipoprotein B-100 (OxPL-apoB), OxPL on plasminogen (OxPL-PLG), and autoantibodies to phosphorylcholine-BSA [PC-BSA] and a malondialdehyde [MDA] mimotope. In univariate analysis, D-dimer was positively associated with Lp(a), OxPL-apoB, OxPL-PLG, and coronary artery calcium, and inversely associated with autoantibodies to OSE and plaque fibrosis. D-dimer levels > 500 ng/ml also showed positive association with plaque necrosis. After multivariate analysis, D-dimer remained significantly associated with Lp(a) and plaque calcium. While further studies are needed, results provide evidence that plasma D-dimer levels are associated with levels of OxPLs and IVUS-VH indices linked to plaque erosion and rupture.

Microcalcifications, Their Genesis, Growth, and Biomechanical Stability in Fibrous Cap Rupture

For many decades, cardiovascular calcification has been considered as a passive process, accompanying atheroma progression, correlated with plaque burden, and apparently without a major role on plaque vulnerability. Clinical and pathological analyses have previously focused on the total amount of calcification (calcified area in a whole atheroma cross section) and whether more calcification means higher risk of plaque rupture or not. However, this paradigm has been changing in the last decade or so. Recent research has focused on the presence of microcalcifications (μCalcs) in the atheroma and more importantly on whether clusters of μCalcs are located in the cap of the atheroma. While the vast majority of μCalcs are found in the lipid pool or necrotic core, they are inconsequential to vulnerable plaque. Nevertheless, it has been shown that μCalcs located within the fibrous cap could be numerous and that they behave as an intensifier of the background circumferential stress in the cap. It is now known that such intensifying effect depends on the size and shape of the μCalc as well as the proximity between two or more μCalcs. If μCalcs are located in caps with very low background stress, the increase in stress concentration may not be sufficient to reach the rupture threshold. However, the presence of μCalc(s) in the cap with a background stress of about one fifth to one half the rupture threshold (a stable plaque) will produce a significant increase in local stress, which may exceed the cap rupture threshold and thus transform a non-vulnerable plaque into a vulnerable one. Also, the classic view that treats cardiovascular calcification as a passive process has been challenged, and emerging data suggest that cardiovascular calcification may encompass both passive and active processes. The passive calcification process comprises biochemical factors, specifically circulating nucleating complexes, which would lead to calcification of the atheroma. The active mechanism of atherosclerotic calcification is a cell-mediated process via cell death of macrophages and smooth muscle cells (SMCs) and/or the release of matrix vesicles by SMCs.

Characterization of coronary plaque regions in intravascular ultrasound images using a hybrid ensemble classifier

BACKGROUND AND OBJECTIVES

The purpose of this study was to propose a hybrid ensemble classifier to characterize coronary plaque regions in intravascular ultrasound (IVUS) images.

METHODS

Pixels were allocated to one of four tissues (fibrous tissue (FT), fibro-fatty tissue (FFT), necrotic core (NC), and dense calcium (DC)) through processes of border segmentation, feature extraction, feature selection, and classification. Grayscale IVUS images and their corresponding virtual histology images were acquired from 11 patients with known or suspected coronary artery disease using 20 MHz catheter. A total of 102 hybrid textural features including first order statistics (FOS), gray level co-occurrence matrix (GLCM), extended gray level run-length matrix (GLRLM), Laws, local binary pattern (LBP), intensity, and discrete wavelet features (DWF) were extracted from IVUS images. To select optimal feature sets, genetic algorithm was implemented. A hybrid ensemble classifier based on histogram and texture information was then used for plaque characterization in this study. The optimal feature set was used as input of this ensemble classifier. After tissue characterization, parameters including sensitivity, specificity, and accuracy were calculated to validate the proposed approach. A ten-fold cross validation approach was used to determine the statistical significance of the proposed method.

RESULTS

Our experimental results showed that the proposed method had reliable performance for tissue characterization in IVUS images. The hybrid ensemble classification method outperformed other existing methods by achieving characterization accuracy of 81% for FFT and 75% for NC. In addition, this study showed that Laws features (SSV and SAV) were key indicators for coronary tissue characterization.

CONCLUSIONS

The proposed method had high clinical applicability for image-based tissue characterization.

Oscillatory wall shear stress is a dominant flow characteristic affecting lesion progression patterns and plaque vulnerability in patients with coronary artery disease

Although experimental studies suggest that low and oscillatory wall shear stress (WSS) promotes plaque transformation to a more vulnerable phenotype, this relationship has not been examined in human atherosclerosis progression. Thus, the aim of this investigation was to examine the association between oscillatory WSS, in combination with WSS magnitude, and coronary atherosclerosis progression. We hypothesized that regions of low and oscillatory WSS will demonstrate progression towards more vulnerable lesions, while regions exposed to low and non-oscillatory WSS will exhibit progression towards more stable lesions. Patients (n = 20) with non-flow-limiting coronary artery disease (CAD) underwent baseline and six-month follow-up angiography, Doppler velocity and radiofrequency intravascular ultrasound (VH-IVUS) acquisition. Computational fluid dynamics models were constructed to compute time-averaged WSS magnitude and oscillatory WSS. Changes in VH-IVUS-defined total plaque and constituent areas were quantified in focal regions (i.e. sectors; n = 14 235) and compared across haemodynamic categories. Compared with sectors exposed to low WSS magnitude, high WSS sectors demonstrated regression of total plaque area (p < 0.001) and fibrous tissue (p < 0.001), and similar progression of necrotic core. Sectors subjected to low and oscillatory WSS exhibited total plaque area regression, while low and non-oscillatory WSS sectors demonstrated total plaque progression (p < 0.001). Furthermore, compared with low and non-oscillatory WSS areas, sectors exposed to low and oscillatory WSS demonstrated regression of fibrous (p < 0.001) and fibrofatty (p < 0.001) tissue and similar progression of necrotic core (p = 0.82) and dense calcium (p = 0.40). Herein, we demonstrate that, in patients with non-obstructive CAD, sectors subjected to low and oscillatory WSS demonstrated regression of total plaque, fibrous and fibrofatty tissue, and progression of necrotic core and dense calcium, which suggest a transformation to a more vulnerable phenotype.

Analysis of Cardiovascular Tissue Components for the Diagnosis of Coronary Vulnerable Plaque from Intravascular Ultrasound Images

The purpose of this study was to characterize cardiovascular tissue components and analyze the different tissue properties for predicting coronary vulnerable plaque from intravascular ultrasound (IVUS) images. For this purpose, sequential IVUS image frames were obtained from human coronary arteries using 20 MHz catheters. The plaque regions between the intima and media-adventitial borders were manually segmented in all IVUS images. Tissue components of the plaque regions were classified into having fibrous tissue (FT), fibrofatty tissue (FFT), necrotic core (NC), or dense calcium (DC). The media area and lumen diameter were also estimated simultaneously. In addition, the external elastic membrane (EEM) was computed to predict the vulnerable plaque after the tissue characterization. The reliability of manual segmentation was validated in terms of inter- and intraobserver agreements. The quantitative results found that the FT and the media as well as the NC would be good indicators for predicting vulnerable plaques in IVUS images. In addition, the lumen was not suitable for early diagnosis of vulnerable plaque because of the low significance compared to the other vessel parameters. To predict vulnerable plaque rupture, future study should have additional experiments using various tissue components, such as the EEM, FT, NC, and media.

Does calcium burden impact culprit lesion morphology and clinical results? An ADAPT-DES IVUS substudy

BACKGROUND

Increasing coronary lesion calcification is thought to be associated with adverse percutaneous coronary intervention (PCI) and clinical outcomes. We investigated the effects of calcium burden on culprit lesion morphology and clinical events after intravascular ultrasound (IVUS)-guided PCI in the ADAPT-DES study.

METHODS

ADAPT-DES was a prospective, multicenter registry of 8582 consecutive patients undergoing successful PCI using DES. A pre-specified virtual histology (VH)-IVUS substudy of 638 culprit lesions (638 patients) had both pre- and post-PCI VH-IVUS. We divided lesions into tertiles according to pre-PCI percent dense calcium volume (DCV%=dense calcium/plaque volume×100).

RESULTS

Compared with low and intermediate DCV% tertiles, patients in the high DCV% tertile had the largest arc of superficial calcium, highest percentage of necrotic core volume, and smallest remodeling index; they were also more likely to have advanced lesion morphology such as attenuated plaque and VH thin-cap fibroatheromas. In the high DCV% tertile IVUS guidance was associated with a minimum stent area that was smaller than tertiles with less calcium (p=0.01), but acceptable range, and similar stent expansion (73.8±16.8% vs. 74.0±19.2% vs. 72.4±17.3%, p=0.62) after more frequent use of rotational atherectomy and higher maximum inflation pressure. There was no significant association between pre-PCI DCV% and 2-year target lesion revascularization or major adverse cardiac events (cardiac death, myocardial infarction, or stent thrombosis).

CONCLUSIONS

Increasing coronary artery calcification burden was associated with more advanced, complex VH-IVUS lesion morphology, but not with adverse clinical outcomes, perhaps due to more aggressive PCI techniques that optimized stent expansion.

Early Detection and Treatment of the Vulnerable Coronary Plaque

Early identification and treatment of the vulnerable plaque, that is, a coronary artery lesion with a high likelihood of rupture leading to an acute coronary syndrome, have gained great interest in the cardiovascular research field. Postmortem studies have identified clear morphological characteristics associated with plaque rupture. Recent advances in invasive and noninvasive coronary imaging techniques have empowered the clinician to identify suspected vulnerable plaques in vivo and paved the way for the evaluation of therapeutic agents targeted at reducing plaque vulnerability. Local treatment of vulnerable plaques by percutaneous coronary intervention and systemic treatment with anti-inflammatory and low-density lipoprotein–lowering drugs are currently being investigated in large randomized clinical trials to assess their therapeutic potential for reducing adverse coronary events. Results from these studies may enable a more patient-tailored strategy for the treatment of coronary artery disease.

New developments for the detection and treatment of cardiac vasculopathy

PURPOSE OF REVIEW

Cardiac allograft vasculopathy (CAV) is a major limitation to long-term survival after heart transplantation. Innovative new techniques to diagnose CAV have been applied to detect disease. This review will examine the current diagnostic and treatment options available to clinicians for CAV.

RECENT FINDINGS

Diagnostic modalities addressing the pathophysiology underlying CAV (arterial wall thickening and decreased coronary blood flow) improve diagnostic sensitivity when compared to traditional (angiography and dobutamine stress echocardiography) techniques.

SUMMARY

Limited options are available to prevent and treat CAV; however, progress has been made in making an earlier and more accurate diagnosis. Future research is needed to identify the optimal time to modify immunosuppression and investigate novel treatments for CAV.

Fibrinogen in relation to degree and composition of coronary plaque on intravascular ultrasound in patients undergoing coronary angiography

OBJECTIVE

The aim of this study was to provide additional insight into the role of fibrinogen in coronary artery disease by investigating the associations between plasma fibrinogen with both degree and composition of coronary atherosclerosis as determined by virtual histology-intravascular ultrasound.

PATIENTS AND METHODS

In 581 patients undergoing coronary angiography for acute coronary syndrome (ACS) or stable angina pectoris, preprocedural blood samples were drawn for fibrinogen, C-reactive protein (CRP), interleukin-6, and plasminogen activator inhibitor-1 measurements, and virtual histology-intravascular ultrasound of a nonculprit coronary artery was performed. The degree [plaque volume, plaque burden (PB), and lesions with PB≥70%] and the composition of coronary atherosclerotic plaque (fibrous, fibrofatty, dense calcium, necrotic core tissue, and thin-cap fibroatheroma lesions) were assessed.

RESULTS

Fibrinogen showed a tendency toward a positive association with PB [β (95% CI): 2.55 (-0.52-5.61) increase in PB per ln(g/l) fibrinogen, P=0.09], which was driven significantly by an association in the ACS subgroup [β (95% CI): 4.11 (0.01-8.21) increase in PB per ln(g/l) fibrinogen, P=0.049]. Fibrinogen was also related to the presence of lesions with PB 70% or more in both the full cohort [OR (95% CI): 2.27 (1.17-4.43), P=0.016] and ACS patients [OR (95% CI): 2.92 (1.17-7.29), P=0.022]. All associations were independent of established cardiovascular risk factors, but not CRP. Interleukin-6 and plasminogen activator inhibitor-1 did not provide incremental value to fibrinogen when examining the associations with degree of atherosclerosis. Substantial associations with plaque composition were absent.

CONCLUSION

Fibrinogen is associated with degree of coronary atherosclerosis, especially in ACS patients. However, whether this association is independent of CRP might be questioned and needs further investigation.

The Role of Virtual Histology Intravascular Ultrasound in the Identification of Coronary Artery Plaque Vulnerability in Acute Coronary Syndromes

Markers of coronary plaque vulnerability, such as a high lipid burden, increased inflammatory activity, and a thin fibrous cap, have been identified in histological studies. In vivo, grayscale intravascular ultrasound (IVUS) provides more in-depth information on coronary artery plaque burden than conventional angiography but is unable to accurately distinguish between noncalcific tissue types within the plaque. An analysis of IVUS radiofrequency backscatter based on spectral pattern recognition, such as virtual histology IVUS, allows detailed scrutiny of plaque composition and classification of coronary lesions. This review discusses the virtual histology IVUS technology and its accuracy in identifying vulnerable plaque features, focusing on its use in predicting patient outcomes after acute coronary syndrome, and its limitations in clinical practice.

Tissue characterization and phenotype classification in patients presenting with acute myocardial infarction: Insights from the iWonder study

OBJECTIVES

We sought to assess a new modality of radiofrequency intravascular ultrasound (IVUS) called iMAP-IVUS (Boston Scientific, Santa Clara, California) during the evaluation of patients presenting with high-risk acute coronary syndromes.

BACKGROUND

There are limited data on plaque tissue characterization and phenotype classification using iMAP-IVUS.

METHODS

In the iWonder study patients presenting with ST-elevation myocardial infarction (STEMI) or non-STEMI underwent three-vessel grayscale IVUS and iMAP-IVUS tissue characterization prior to percutaneous intervention. In total 385 lesions from 100 patients were divided into culprit (n = 100) and nonculprit (n = 285) lesions. Lesion phenotype was classified as (i) thin-cap fibroatheroma (iMAP-derived TCFA); (ii) thick-cap fibroatheroma; (iii) pathological intimal thickening; (iv) fibrotic plaque; and (v) fibrocalcific plaque.

RESULTS

Culprit lesions had smaller minimum lumen cross-sectional area (MLA) with greater plaque burden compared to non-culprit lesions. Volumetric analysis showed that culprit lesions had longer length and larger vessel and plaque volumes compared to non-culprit lesions. iMAP-IVUS revealed that culprit lesions presented more NC and fibrofatty volume, both at lesion level and at the MLA site (all P < 0.001). Any fibroatheroma was more frequently identified in culprit lesions compared with non-culprit lesions (93% vs. 78.9%, P = 0.001), anywhere within the lesion 19.0%, P < 0.001) as well as at the MLA site (18.0% vs. 9.5%, P = 0.07).

CONCLUSIONS

Three-vessel radiofrequency iMAP-IVUS demonstrated a greater plaque burden and higher prevalence of any fibroatheroma as well as iMAP-derived TCFAs in culprit versus non-culprit lesions in patients presenting with STEMI or non-STEMI undergoing percutaneous coronary intervention. © 2017 Wiley Periodicals, Inc.

High wall shear stress and high-risk plaque: an emerging concept

In recent years, there has been a significant effort to identify high-risk plaques in vivo prior to acute events. While number of imaging modalities have been developed to identify morphologic characteristics of high-risk plaques, prospective natural-history observational studies suggest that vulnerability is not solely dependent on plaque morphology and likely involves additional contributing mechanisms. High wall shear stress (WSS) has recently been proposed as one possible causative factor, promoting the development of high-risk plaques. High WSS has been shown to induce specific changes in endothelial cell behavior, exacerbating inflammation and stimulating progression of the atherosclerotic lipid core. In line with experimental and autopsy studies, several human studies have shown associations between high WSS and known morphological features of high-risk plaques. However, despite increasing evidence, there is still no longitudinal data linking high WSS to clinical events. As the interplay between atherosclerotic plaque, artery, and WSS is highly dynamic, large natural history studies of atherosclerosis that include WSS measurements are now warranted. This review will summarize the available clinical evidence on high WSS as a possible etiological mechanism underlying high-risk plaque development.

Numerical study to indicate the vulnerability of plaques using an idealized 2D plaque model based on plaque classification in the human coronary artery

Atherosclerosis is one of the leading causes of death in the world. In this study, an idealized 2D plaque model based on plaque classification in the coronary artery is developed. When creating the idealized 2D model for each plaque type (fibrocalcic, FC; fibrofatty, FT; calcified fibroatheroma, CaFA; fibroatheroma, FA; calcified thin-cap fibroatheroma, CaTCFA; thin-cap fibroatheroma, TCFA), the cap thickness and stenosis by diameter were set as variables. In order to establish the correlation between each plaque type and plaque rupture, a numerical simulation was performed and the stress and stress gradient were reviewed to analyze the mechanical behavior. Results show that both the TCFA and CaTCFA plaque types, which have the smallest cap thicknesses of the different types of plaque, showed relatively high stress values in the thin membrane when compared with the FT type. The FT type is considered to be relatively stable since it does not have necrotic core or a thin membrane. With a stenosis rate of 50% and a cap thickness of 60 μm, the TCFA and CaTCFA types showed approximately 11 and 110% higher stress values, respectively, and 679 and 1568% higher negative stress gradient values, respectively. In other words, the plaque types with thin caps, which have weak load-bearing capacities, showed high stress values and high negative stress gradients in the radial direction. It is understood that this result could indicate the possibility of plaque rupture.

Intracoronary Imaging in the Detection of Vulnerable Plaques

Coronary artery disease is the result of atherosclerotic changes to the coronary arterial wall, comprising endothelial dysfunction, vascular inflammation and deposition of lipid-rich macrophage foam cells. Certain high-risk atherosclerotic plaques are vulnerable to disruption, leading to rupture, thrombosis and the clinical sequelae of acute coronary syndrome. Though recognised as the gold standard for evaluating the presence, distribution and severity of atherosclerotic lesions, invasive coronary angiography is incapable of identifying non-stenotic, vulnerable plaques that are responsible for adverse cardiovascular events. The recognition of such limitations has impelled the development of intracoronary imaging technologies, including intravascular ultrasound, optical coherence tomography and near-infrared spectroscopy, which enable the detailed evaluation of the coronary wall and atherosclerotic plaques in clinical practice. This review discusses the present status of invasive imaging technologies; summarises up-to-date, evidence-based clinical guidelines; and addresses questions that remain unanswered with regard to the future of intracoronary plaque imaging.

A Review of Intravascular Ultrasound-based Multimodal Intravascular Imaging: The Synergistic Approach to Characterizing Vulnerable Plaques

Catheter-based intravascular imaging modalities are being developed to visualize pathologies in coronary arteries, such as high-risk vulnerable atherosclerotic plaques known as thin-cap fibroatheroma, to guide therapeutic strategy at preventing heart attacks. Mounting evidences have shown three distinctive histopathological features-the presence of a thin fibrous cap, a lipid-rich necrotic core, and numerous infiltrating macrophages-are key markers of increased vulnerability in atherosclerotic plaques. To visualize these changes, the majority of catheter-based imaging modalities used intravascular ultrasound (IVUS) as the technical foundation and integrated emerging intravascular imaging techniques to enhance the characterization of vulnerable plaques. However, no current imaging technology is the unequivocal "gold standard" for the diagnosis of vulnerable atherosclerotic plaques. Each intravascular imaging technology possesses its own unique features that yield valuable information although encumbered by inherent limitations not seen in other modalities. In this context, the aim of this review is to discuss current scientific innovations, technical challenges, and prospective strategies in the development of IVUS-based multi-modality intravascular imaging systems aimed at assessing atherosclerotic plaque vulnerability.

Microstructure-based biomechanics of coronary arteries in health and disease

Coronary atherosclerosis is the major cause of mortality and disability in developed nations. A deeper understanding of mechanical properties of coronary arteries and hence their mechanical response to stress is significant for clinical prevention and treatment. Microstructure-based models of blood vessels can provide predictions of arterial mechanical response at the macro- and micro-mechanical level for each constituent structure. Such models must be based on quantitative data of structural parameters (constituent content, orientation angle and dimension) and mechanical properties of individual adventitia and media layers of normal arteries as well as change of structural and mechanical properties of atherosclerotic arteries. The microstructural constitutive models of healthy coronary arteries consist of three major mechanical components: collagen, elastin, and smooth muscle cells, while the models of atherosclerotic arteries should account for additional constituents including intima, fibrous plaque, lipid, calcification, etc. This review surveys the literature on morphology, mechanical properties, and microstructural constitutive models of normal and atherosclerotic coronary arteries. It also provides an overview of current gaps in knowledge that must be filed in order to advance this important area of research for understanding initiation, progression and clinical treatment of vascular disease. Patient-specific structural models are highlighted to provide diagnosis, virtual planning of therapy and prognosis when realistic patient-specific geometries and material properties of diseased vessels can be acquired by advanced imaging techniques.

Characterization of coronary atherosclerosis by intravascular imaging modalities

Coronary artery disease (CAD) is highly prevalent in Western countries and is associated with morbidity, mortality, and a significant economic burden. Despite the development of anti-atherosclerotic medical therapies, many patients still continue to suffer from coronary events. This residual risk indicates the need for better risk stratification and additional therapies to achieve more reductions in cardiovascular risk. Recent advances in imaging modalities have contributed to visualizing atherosclerotic plaques and defining lesion characteristics in vivo. This innovation has been applied to refining revascularization procedure, assessment of anti-atherosclerotic drug efficacy and the detection of high-risk plaques. As such, intravascular imaging plays an important role in further improvement of cardiovascular outcomes in patients with CAD. The current article reviews available intravascular imaging modalities with regard to its method, advantage and disadvantage.

Ultrasound Imaging Techniques for Spatiotemporal Characterization of Composition, Microstructure, and Mechanical Properties in Tissue Engineering

Ultrasound techniques are increasingly being used to quantitatively characterize both native and engineered tissues. This review provides an overview and selected examples of the main techniques used in these applications. Grayscale imaging has been used to characterize extracellular matrix deposition, and quantitative ultrasound imaging based on the integrated backscatter coefficient has been applied to estimating cell concentrations and matrix morphology in tissue engineering. Spectral analysis has been employed to characterize the concentration and spatial distribution of mineral particles in a construct, as well as to monitor mineral deposition by cells over time. Ultrasound techniques have also been used to measure the mechanical properties of native and engineered tissues. Conventional ultrasound elasticity imaging and acoustic radiation force imaging have been applied to detect regions of altered stiffness within tissues. Sonorheometry and monitoring of steady-state excitation and recovery have been used to characterize viscoelastic properties of tissue using a single transducer to both deform and image the sample. Dual-mode ultrasound elastography uses separate ultrasound transducers to produce a more potent deformation force to microscale characterization of viscoelasticity of hydrogel constructs. These ultrasound-based techniques have high potential to impact the field of tissue engineering as they are further developed and their range of applications expands.

Elevated Levels of Serum Fibrin and Fibrinogen Degradation Products Are Independent Predictors of Larger Coronary Plaques and Greater Plaque Necrotic Core

BACKGROUND

Co-existence of vulnerable plaque and pro-thrombotic state may provoke acute coronary events. It was hypothesized that elevated serum levels of fibrin and fibrinogen degradation products (FDP) are associated with larger total plaque and necrotic core (NC) areas.

METHODS AND RESULTS

Seventy-five patients presenting with stable anginal symptoms (69%) or stabilized acute coronary syndrome (ACS; 31%), and found to have non-obstructive coronary artery disease (CAD) with a fractional flow reserve >0.8, were studied. Invasive virtual histology intravascular ultrasound (VH-IVUS) was performed in 68 LAD arteries, 6 circumflex arteries, and 1 right coronary artery. Serum FDP levels were measured using ELISA technique. Plaque volumetrics and composition were assessed in each VH-IVUS frame and averaged. The median age of patients was 56 (47-63) years; 52% were men and 23% had diabetes. The average length of coronary artery studied was 62 mm. After adjustment for systemic risk factors, medications, CRP levels and ACS, male gender (P<0.001) and serum FDP levels (P=0.02) were independent predictors of a larger NC area. Older age (P<0.001), male gender (P<0.0001) and increased serum FDP level (P=0.03) were associated with a larger plaque area.

CONCLUSIONS

In patients with CAD, a higher serum level of FDP is independently associated with larger plaques and greater plaque NC.

Changes of coronary plaque composition correlate with C-reactive protein levels in patients with ST-elevation myocardial infarction following high-intensity statin therapy

OBJECTIVES

Levels of inflammatory biomarkers associate with changes of coronary atheroma burden in statin-treated patients with stable coronary artery disease. This study sought to determine changes of plaque composition in vivo in relation to high-sensitivity C-reactive protein (hs-CRP) levels in patients with ST-elevation myocardial infarction (STEMI) receiving high-intensity statin therapy.

METHODS

The IBIS-4 study performed serial (baseline and 13-month), 2-vessel intravascular ultrasound (IVUS) and radiofrequency-IVUS of the non-infarct-related arteries in patients with STEMI treated with high-intensity statin therapy. The present analysis included 44 patients (80 arteries) with serial measurements of hs-CRP.

RESULTS

At follow-up, median low-density lipoprotein cholesterol (LDL-C) levels decreased from 126 to 77 mg/dl, HDL-C increased from 44 to 47 mg/dl, and hs-CRP decreased from 1.6 to 0.7 mg/L. Regression of percent atheroma volume (-0.99%, 95% CI -1.84 to -0.14, p = 0.024) was accompanied by reduction of percent fibro-fatty (p = 0.04) and fibrous tissue (p < 0.001), and increase in percent necrotic core (p = 0.006) and dense calcium (p < 0.001). Follow-up levels of hs-CRP, but not LDL-C, correlated with changes in percent necrotic core (p = 0.001) and inversely with percent fibrous tissue volume (p = 0.008). Similarly, baseline-to-follow-up change of hs-CRP correlated with the change in percent necrotic core volume (p = 0.02).

CONCLUSIONS

In STEMI patients receiving high-intensity statin therapy, stabilization of VH-IVUS-defined necrotic core was confined to patients with lowest on-treatment levels and greatest reduction of hs-CRP. Elevated CRP levels at follow-up may identify progression of high-risk coronary plaque composition despite intensive statin therapy and overall regression of atheroma volume.

Circulating Microparticles and Coronary Plaque Components Assessed by Virtual Histology Intravascular Ultrasound of the Target Lesion in Patients with Stable Angina

High levels of microparticles (MPs) circulate in the blood of patients with atherosclerotic diseases where they can serve as potential biomarkers of vascular injury and cardiovascular outcome. We used virtual histology intravascular ultrasound (VH-IVUS) to evaluate the relationship between the levels of circulating MPs and the coronary plaque composition in patients with stable angina. We included 35 patients with stable angina (22 men, age 64 ± 9 years) and a de novo target lesion. Preintervention gray-scale and VH-IVUS analysis was performed across the target lesion. Volumetric analysis was performed over a 10-mm-long segment centered at the minimum luminal site. Blood samples were obtained from the femoral artery before coronary angioplasty. MPs were measured using a solid-phase capture assay from a commercial kit. We divided participants into either a low MPs group or high MPs group based on the median value of MPs. There was no significant difference in baseline characteristics between the groups. The plaque burden and remodeling index were similar between the groups. The presence of VH-IVUS-derived thin-cap fibroatheroma was not different between the groups. The percentage of the necrotic core (NC) was significantly higher in the high MPs group than in the low MPs group, both in planar (17.0 ± 8.8% vs. 24.1 ± 6.9%, p = 0.012) and volumetric analyses (17.0 ± 4.8% vs. 22.1 ± 4.3%, p = 0.002). Circulating MPs were positively correlated with the percentage of the NC area at the minimal luminal site (r = 0.491, p = 0.003) and the percentage of the NC volume (r = 0.496, p = 0.002). Elevated levels of circulating MPs were associated with the amount of NC in the target lesion in those with stable angina, suggesting a potential role of circulating MPs as a biomarker for detecting unstable plaque in patients with stable angina.

Comprehensive Assessment of Coronary Plaque Progression With Advanced Intravascular Imaging, Physiological Measures, and Wall Shear Stress: A Pilot Double-Blinded Randomized Controlled Clinical Trial of Nebivolol Versus Atenolol in Nonobstructive Coronary Artery Disease

Background

We hypothesized that nebivolol, a β‐blocker with nitric oxide–mediated activity, compared with atenolol, a β‐blocker without such activity, would decrease oxidative stress and improve the effects of endothelial dysfunction and wall shear stress (WSS), thereby reducing atherosclerosis progression and vulnerability in patients with nonobstructive coronary artery disease.

Methods and Results

In this pilot double‐blinded randomized controlled trial, 24 patients treated for 1 year with nebivolol 10 mg versus atenolol 100 mg plus standard medical therapy underwent baseline and follow‐up coronary angiography with assessments of inflammatory and oxidative stress biomarkers, microvascular function, endothelial function, and virtual histology intravascular ultrasound. WSS was calculated from computational fluid dynamics. Virtual histology intravascular ultrasound segments were assessed for vessel volumetrics and remodeling. There was a trend toward more low‐WSS segments in the nebivolol cohort (P=0.06). Low‐WSS regions were associated with greater plaque progression (P<0.0001) and constrictive remodeling (P=0.04); conversely, high‐WSS segments demonstrated plaque regression and excessive expansive remodeling. Nebivolol patients had decreased lumen and vessel areas along with increased plaque area, resulting in more constrictive remodeling (P=0.002). There were no significant differences in biomarker levels, microvascular function, endothelial function, or number of thin‐capped fibroatheromas per vessel. Importantly, after adjusting for β‐blocker, low‐WSS segments remained significantly associated with lumen loss and plaque progression.

Conclusion

Nebivolol, compared with atenolol, was associated with greater plaque progression and constrictive remodeling, likely driven by more low‐WSS segments in the nebivolol arm. Both β‐blockers had similar effects on oxidative stress, microvascular function, and endothelial function.

Clinical Trial Registration

URL: https://clinicaltrials.gov/. Unique identifier: NCT01230892.

Enhanced characterization of calcified areas in intravascular ultrasound virtual histology images by quantification of the acoustic shadow: validation against computed tomography coronary angiography

We enhance intravascular ultrasound virtual histology (VH) tissue characterization by fully automatic quantification of the acoustic shadow behind calcified plaque. VH is unable to characterize atherosclerosis located behind calcifications. In this study, the quantified acoustic shadows are considered calcified to approximate the real dense calcium (DC) plaque volume. In total, 57 patients with 108 coronary lesions were included. A novel post-processing step is applied on the VH images to quantify the acoustic shadow and enhance the VH results. The VH and enhanced VH results are compared to quantitative computed tomography angiography (QTA) plaque characterization as reference standard. The correlation of the plaque types between enhanced VH and QTA differs significantly from the correlation with unenhanced VH. For DC, the correlation improved from 0.733 to 0.818. Instead of an underestimation of DC in VH with a bias of 8.5 mm(3), there was a smaller overestimation of 1.1 mm(3) in the enhanced VH. Although tissue characterization within the acoustic shadow in VH is difficult, the novel algorithm improved the DC tissue characterization. This algorithm contributes to accurate assessment of calcium on VH and could be applied in clinical studies.

Impact of Coronary Plaque Characteristics on Late Stent Malapposition after Drug-Eluting Stent Implantation

PURPOSE

To evaluate the impact of pre-procedural coronary plaque composition assessed by virtual histology intravascular ultrasound (VH-IVUS) on late stent malapposition assessed by optical coherence tomography (OCT) following drug-eluting stent (DES) implantation.

MATERIALS AND METHODS

The study population consisted of 121 patients (121 lesions) who underwent both pre-procedural VH-IVUS and follow-up OCT after DES implantation. The association between pre-procedural plaque composition [necrotic core (NC), dense calcium (DC), fibrotic (FT), and fibro-fatty (FF) volumes] assessed by VH-IVUS and late stent malapposition (percent malapposed struts) or strut coverage (percent uncovered struts) assessed by follow-up OCT was evaluated.

RESULTS

Pre-procedural absolute total NC, DC, FT, and FF plaque volumes were 22.9±19.0, 7.9±9.6, 63.8±33.8, and 16.5±12.4 mm³, respectively. At 6.3±3.1 months post-intervention, percent malapposed and uncovered struts were 0.8±2.5% and 15.3±16.7%, respectively. Pre-procedural absolute total NC and DC plaque volumes were positively correlated with percent malapposed struts (r=0.44, p<0.001 and r=0.45, p<0.001, respectively), while pre-procedural absolute total FT plaque volume was weakly associated with percent malapposed struts (r=0.220, p=0.015). Pre-procedural absolute total DC plaque volume was the only independent predictor of late stent malapposition on multivariate analysis (β=1.12, p=0.002). There were no significant correlations between pre-intervention plaque composition and percent uncovered struts.

CONCLUSION

Pre-procedural plaque composition was associated with late stent malapposition but not strut coverage after DES implantation. Larger pre-procedural absolute total DC plaque volumes were associated with greater late stent malapposition.

Non-invasive and Non-destructive Characterization of Tissue Engineered Constructs Using Ultrasound Imaging Technologies: A Review

With the rapid expansion of biomaterial development and coupled efforts to translate such advances toward the clinic, non-invasive and non-destructive imaging tools to evaluate implants in situ in a timely manner are critically needed. The required multi-level information is comprehensive, including structural, mechanical, and biological changes such as scaffold degradation, mechanical strength, cell infiltration, extracellular matrix formation and vascularization to name a few. With its inherent advantages of non-invasiveness and non-destructiveness, ultrasound imaging can be an ideal tool for both preclinical and clinical uses. In this review, currently available ultrasound imaging technologies that have been applied in vitro and in vivo for tissue engineering and regenerative medicine are discussed and some new emerging ultrasound technologies and multi-modality approaches utilizing ultrasound are introduced.

Coronary artery calcium: 0.5 mm slice-thickness reconstruction with adjusted attenuation threshold outperforms 3.0 mm by validating against spatially registered intravascular ultrasound with radiofrequency backscatter

RATIONALE AND OBJECTIVES

Coronary artery calcium (CAC) images can be reconstructed with thinner slice thickness on some modern multidetector-row computed tomography scanners without additional radiation. We hypothesized that the isotropic 0.5-mm CAC reconstruction outperforms the conventional 3.0-mm reconstruction in detecting and quantifying coronary calcium, and we proposed to compare them by validating against spatially registered intravascular ultrasound with radiofrequency backscatter-virtual histology (IVUS-VH).

MATERIALS AND METHODS

Twenty-seven patients were enrolled, and 5976 mm of coronary arteries were analyzed. A semiautomatic software was developed to coregister CAC and IVUS-VH on a detailed slice-by-slice basis. Calcium detection and calcium volume quantification were evaluated and compared using varying calcium attenuation thresholds. Algorithms for deriving individualized optimal threshold and comparable Agatston score on the 0.5-mm reconstruction were developed.

RESULTS

The isotropic 0.5-mm reconstruction achieved significantly higher area under receiver-operating curve than the conventional 3.0-mm reconstruction (0.9 vs. 0.74, P < .001). Using the optimal threshold, the 0.5-mm reconstruction had higher sensitivity (0.79 vs. 0.65), specificity (0.85 vs. 0.77), positive predictive value (0.42 vs. 0.29), and negative predictive value (0.97 vs. 0.94) than the 3.0 mm. Individualized optimal threshold was significantly correlated with the image noise (r = 0.66, P < .001) in the 0.5-mm reconstruction.

CONCLUSIONS

By optimizing the calcium threshold, the 0.5-mm reconstruction is superior to the conventional 3.0-mm in detecting and quantifying calcium, which may improve the clinical value of CAC without additional radiation.

Construction and validation of a plaque discrimination score from the anatomical and histological differences in coronary atherosclerosis: the Liverpool IVUS-V-HEART (Intra Vascular UltraSound-Virtual-Histology Evaluation of Atherosclerosis Requiring Treatment) study

AIMS

New markers to help stratify coronary atherosclerosis are needed. Although attempts have been made to differentiate active lesions from those that are stable, none of these has ever been formalised into a discriminatory score. The aim of this study was to analyse the differences between culprit ACS lesions and culprit stable angina lesions with intravascular ultrasound-derived virtual histology and to construct and validate a plaque score.

METHODS AND RESULTS

Prior to percutaneous coronary intervention (PCI), we performed volumetric, intravascular ultrasound-derived virtual histology (IVUS-VH) analysis in acute coronary syndrome (ACS) culprit lesions (AC - n=70) and stable angina culprit lesions (SC - n=35). A direct statistical comparison of IVUS-VH data and multiple logistic regression analysis was undertaken. Four main factors were found to be associated (p<0.05) with an AC lesion phenotype: necrotic core/dense calcium (NC/DC) ratio; minimum lumen area <4 mm2 (MLA <4); remodelling index @MLA >1.05 and VH-TCFA presence. Calculation of each logistic regression coefficient and the equation produces an active plaque discrimination score with an AUC of 0.96 on receiver operating characteristics (ROC) analysis. Validation of the score in 50 independent plaques from the Thoraxcenter in Rotterdam revealed an AUC of 0.71, confirming continued diagnostic ability.

CONCLUSIONS

We have found four features on IVUS and VH that can predict and discriminate ACS culprit lesion phenotypes from those that are clinically stable. Subsequently, we have constructed and validated the Liverpool Active Plaque Score based upon these features. It is hoped this score may help diagnose active coronary plaques, in the future, to help prevent major adverse cardiac events.

CTO pathophysiology: how does this affect management?

Chronic total occlusion (CTO) pathophysiology has been described in a few, small studies using post mortem histology, and more recently, in vivo intravascular ultrasound (IVUS) to analyse the constituents of occluded segments. Recent improvements in equipment and techniques have revealed new insights into physical characteristics of occluded coronaries, which in turn enable predictable procedural success. The purpose of this review is to consider the published evidence describing CTO pathophysiology from the perspective of the hybrid algorithm approach to CTO PCI.

Methods: Literature searches using “Chronic Occlusion”, “angioplasty”, and” pathology” as keywords. Further searches on “coronary” “collateral”, “Viability”. Bibliographies were scrutinised for further key publications in an iterative process. Papers describing animal models were excluded.