Noninvasive Detection and Localization of Vulnerable Plaque and Arterial Thrombosis With Computed Tomography Angiography/Positron Emission Tomography

"Vascular inflammation and cardiovascular disease: review about the role of PET imaging"

Inflammation characterizes all stages of atherothrombosis and provides a critical pathophysiological link between plaque formation and its acute rupture, leading to coronary occlusion and heart attack. In the last 20 years the possibility of quantifying the degree of inflammation of atherosclerotic plaques and, therefore, also of vascular inflammation aroused much interest. ¹⁸Fluoro-deoxy-glucose photon-emissions-tomography (¹⁸F-FDG-PET) is widely used in oncology for staging and searching metastases; in cardiology, the absorption of ¹⁸F-FDG into the arterial wall was observed for the first time incidentally in the aorta of patients undergoing PET imaging for cancer staging. PET/CT imaging with ¹⁸F-FDG and ¹⁸F-sodium fluoride (¹⁸F-NaF) has been shown to assess atherosclerotic disease in its molecular phase, when the process may still be reversible. This approach has several limitations in the clinical practice, due to lack of prospective data to justify their use routinely, but it's desirable to develop further scientific evidence to confirm this technique to detect high-risk patients for cardiovascular events.

In vivo real-time red blood cell migration and microcirculation flow synergy imaging-surveyed thrombolytic therapy with iron-oxide complexes

Nanotherapeutics as a nascent method has attracted widely interest on the treatment of thrombosis. However, due to the limited temporal and spatial resolution of conventional imaging modalities, the dynamic visualization the thrombogenesis and evaluation of the effect of thrombolytic drugs are facing severely difficulties in vivo. In addition, the development of high targeting, short circulation time, and small size thrombolysis nanotherapeutics agents requires further research. Herein, we report a synergy imaging modality that combining a label-free capillary microscopy and laser speckle microcirculation imaging, which realized dynamic visualization of single red blood cell migration and large-field dynamic blood flow. In this work, we investigated the red blood cells migration and blood flow velocity response before and after treated through introducing a functional nano-thrombolytics, iron-oxide complexes coated urokinase (IPN@UK) on an orthotopic animal model in vivo. The functionalized IPN@UK nanocomposites exhibited outstanding thrombolysis effect. Significantly, whole-course changes, including red blood cell activity, complex thrombolytic therapeutics, were well surveilled and evaluated using dual-modality combining imaging strategy. These results show this synergy imaging strategy not only can achieve multiscale non-invasive visualization of dynamic thrombus events in real-time, but also can quantify hemodynamics information of thrombus. Our study demonstrates the potential of this synergy imaging method, which for early detection of thrombus, evaluation of the effect of drug thrombolysis, developing the thrombolytic drugs, and imaging-guide thrombolytic therapy in living systems.

18F-fluorodeoxyglucose positron emission tomography for the detection of inflammatory lesions of the arterial vessel walls in Wistar rats

The present study aimed to evaluate the use of ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) for detection of high-fat and high-salt diet-induced inflammatory lesions of the arterial vessel walls in Wistar rats. A total of 20 healthy, 8-week-old, male Wistar rats were randomly assigned to the high-fat diet group and the normal diet group. After 16 and 24 weeks of feeding, Wistar rats in the normal diet group and the high-fat diet group (five rats in each group) were injected with ¹⁸F-FDG through the tail vein at a dose of 1 mCi/kg after fasting for 12 h. After 1 h, the rats were anesthetized with 2% isoflurane, followed by micro-PET imaging with a 10-min image capture duration and immunohistochemical staining. The standardized uptake values (SUVs) of ¹⁸F-FDG were significantly higher in the iliac artery in the high-fat diet group compared with those in the normal diet group at 16 weeks (1.53±0.08 vs. 1.04±0.03; P<0.05) and at 24 weeks (1.96±0.17 vs. 1.12±0.07; P<0.05). The SUVs of ¹⁸F-FDG were also significantly greater in the abdominal aorta in the high-fat diet group compared with those in the normal diet group at 16 weeks (1.35±0.08 vs. 1.02±0.02; P<0.05) and at 24 weeks (1.54±0.09 vs. 1.04±0.02; P<0.05). In addition, the SUVs of ¹⁸F-FDG in the iliac artery and abdominal aorta were significantly higher at 24 weeks compared with those at 16 weeks in the high-fat diet group (P<0.05). As determined by immunohistochemistry, the percentage of CD68-positive cells in the total number of cells per unit area in each group was 3.20±1.80% in the 24-week normal diet group, 4.70±2.02% in the 16-week high-fat diet group and 6.94±2.02% in the 24-week high-fat diet group; the percentage of CD68-positive cells in the high-fat diet group at 24 weeks was significantly higher than that in the high-fat diet group at 16 weeks and in the normal diet group at 24 weeks (P<0.05). In conclusion, ¹⁸F-FDG PET is a noninvasive imaging tool that can continuously monitor inflammatory lesions of the arterial vessel walls in Wistar rats. Further improvement of the Wistar rat atherosclerosis model may provide data to support the early assessment of and intervention in atherosclerosis.

Antithrombotic Therapy in Carotid Artery Disease

The management of asymptomatic atherosclerotic carotid artery disease and the role of antithrombotic therapy is of increasing importance for stroke prevention. Non-invasive imaging of carotid plaques can identify high-risk plaque features that are associated with the risk of plaque rupture. Carotid plaque necrosis, hemorrhage, fibrous cap thinning, and the presence of foam cells have all been correlated with the risk of rupture and onset of neurological symptoms in patients with carotid stenosis. Antiplatelets are currently recommended for patients with a history of ischemic stroke and/or significant carotid artery stenosis, with aspirin and clopidogrel being the most widely used and studied agents. The role of dual antiplatelet therapy remains controversial. Moreover, there is scarce evidence on the role of newer anticoagulant agents in stable patients with carotid artery stenosis. In this review article, we discuss the pathophysiology of carotid atherosclerosis, the use of non-invasive imaging for detecting the vulnerable carotid plaque and summarize the existing clinical evidence on the use of antiplatelet and antithrombotic agents in carotid artery disease.

Current Advances in the Diagnostic Imaging of Atherosclerosis: Insights into the Pathophysiology of Vulnerable Plaque

Atherosclerosis is a lipoprotein-driven inflammatory disorder leading to a plaque formation at specific sites of the arterial tree. After decades of slow progression, atherosclerotic plaque rupture and formation of thrombi are the major factors responsible for the development of acute coronary syndromes (ACSs). In this regard, the detection of high-risk (vulnerable) plaques is an ultimate goal in the management of atherosclerosis and cardiovascular diseases (CVDs). Vulnerable plaques have specific morphological features that make their detection possible, hence allowing for identification of high-risk patients and the tailoring of therapy. Plaque ruptures predominantly occur amongst lesions characterized as thin-cap fibroatheromas (TCFA). Plaques without a rupture, such as plaque erosions, are also thrombi-forming lesions on the most frequent pathological intimal thickening or fibroatheromas. Many attempts to comprehensively identify vulnerable plaque constituents with different invasive and non-invasive imaging technologies have been made. In this review, advantages and limitations of invasive and non-invasive imaging modalities currently available for the identification of plaque components and morphologic features associated with plaque vulnerability, as well as their clinical diagnostic and prognostic value, were discussed.

Systemic atherosclerotic plaque vulnerability in patients with Coronary Artery Disease with a single Whole Body FDG PET-CT scan

OBJECTIVES

Cardiovascular disease is a leading cause of morbimortality with over half cardiovascular events occurring in the asymptomatic population by traditional risk stratification. This preliminary study aimed to evaluate systemic plaque vulnerability in patients with prior Coronary Artery Disease (CAD) with a single Whole Body [FDG] PET-CT scan in terms of plaque inflammation and calcifications.

METHODS

Twenty-two patients referred for oncological evaluation and with prior history of advanced CAD or age and gender matched controls without cardiovascular disease, underwent a Whole Body PET-CT scan 90 min after injection of 18F-FDG. A total of 975 transaxial PET images were retrospectively analysed to assess plaque inflammation using a standardized method of analysis with averaged Target-to-Background Ratios (TBRs) at different levels, in the thoracic and abdominal aorta, carotids, LAD, common iliac and femoral arteries, and were correlated with calcium scores from the CT images.

RESULTS

TBRs from the thoracic aorta were higher in male patients than controls (1.49±0.11, p<0.05) and a gradient was observed (ascending > descending > aortic arch), and were also higher in the carotids in female patients (1.43±0.07) versus controls (p<0.05). A tendency for higher levels of plaque inflammation in the abdominal aorta was noted in all groups, but no significant FDG uptake was found either in the iliac or femoral arteries in any group. Plaque inflammation was also higher in the LAD in males but with large variations. Higher levels of calcifications were noted in the LAD, infra-renal abdominal aorta and common iliac arteries, but without significant correlation with plaque inflammation except sporadic overlapping.

CONCLUSION

Patients with advanced CAD are at risk for vulnerable inflamed atheromas in other territories such as the thoracic aorta and carotid arteries, underpinning the systemic nature of the atherosclerotic disease. Coexistence with calcifications is rare, suggesting a different functional status of the plaques and different stages of the disease. Evaluation of subclinical systemic plaque vulnerability in CAD with a Whole Body [FDG] PET-CT scan is feasible and a potentially useful biomarker to assess subclinical vascular risk for risk stratification and treatment optimization, but further studies are needed.

Intracranial atherosclerotic disease

Intracranial atherosclerosis (ICAS) is a progressive pathological process that causes progressive stenosis and cerebral hypoperfusion and is a major cause of stroke occurrence and recurrence around the world. Multiple factors contribute to the development of ICAS. Angiography imaging techniques can improve the diagnosis of and the selection of appropriate treatment regimens for ICAS. Neither aggressive medication nor endovascular interventions can eradicate stroke recurrence in patients with ICAS. Non-pharmacological therapies such as remote ischemic conditioning and hypothermia are emerging. Comprehensive therapy with medication in combination with endovascular intervention and/or non-pharmacological treatment may be a potential strategy for ICAS treatment in the future. We summarized the epidemiology, pathophysiological mechanisms, risk factors, biomarkers, imaging and management of ICAS.

Target identification for the diagnosis and intervention of vulnerable atherosclerotic plaques beyond 18F-fluorodeoxyglucose positron emission tomography imaging: promising tracers on the horizon

Cardiovascular disease is the major cause of morbidity and mortality in developed countries and atherosclerosis is the major cause of cardiovascular disease. Atherosclerotic lesions obstruct blood flow in the arterial vessel wall and can rupture leading to the formation of occlusive thrombi. Conventional diagnostic tools are still of limited value for identifying the vulnerable arterial plaque and for predicting its risk of rupture and of releasing thromboembolic material. Knowledge of the molecular and biological processes implicated in the process of atherosclerosis will advance the development of imaging probes to differentiate the vulnerable plaque. The development of imaging probes with high sensitivity and specificity in identifying high-risk atherosclerotic vessel wall changes and plaques is crucial for improving knowledge-based decisions and tailored individual interventions. Arterial PET imaging with ¹⁸F-FDG has shown promising results in identifying inflammatory vessel wall changes in numerous studies and clinical trials. However, due to its limited specificity in general and its intense physiological uptake in the left ventricular myocardium that impair imaging of the coronary arteries, different PET tracers for the molecular imaging of atherosclerosis have been evaluated. This review describes biological, chemical and medical expertise supporting a translational approach that will enable the development of new or the evaluation of existing PET tracers for the identification of vulnerable atherosclerotic plaques for better risk prediction and benefit to patients.

Detection of thrombosis in microvessels with indocyanine green videoangiography

Atherosclerosis is a systemic condition that is responsible for many diseases, and becomes a problem in cases where plaques form at several sites. The formation of a thrombotic embolus may jeopardise vascular operations, including microvascular anastomoses in replantation procedures or free tissue transfers. A mobile imaging tool for the detection of thrombosis preoperatively or intraoperatively would be valuable. An intimal injury, simulating removal of atherosclerotic plaques, was made microsurgically in 60 rat aortas, and results were analysed macroscopically, histologically, and with intraoperative indocyanine green (ICG) videoangiography immediately postoperatively. The Spearman and Pearson correlation tests were used to compare the three techniques. The sensitivity and specificity of ICG videoangiography was calculated in relation to both macroscopic and histological results. Detection of thrombosis was possible in 25 cases, and in 18 cases no thrombosis was correctly diagnosed by all methods used. In 31 of 60 specimens formation of thrombus was detected histologically, and in 29 of 60 examinations it was detected clinically, which yielded a correlation of 93.5% between the two examinations. Macroscopic analysis correlated better with ICG videoangiography (sensitivity 86.2% and specificity 64.5%) than histological observations (sensitivity 80.6% and specificity 62.1%). There was a significant correlation among all comparisons (each p≤0.001) with correlation indexes of 0.94, 0.52, and 0.44 for macroscopic/histological, clinical/ICG videoangiographic, and ICG videoangiographic/histological results, respectively. Our results show that ICG videoangiography is an important method for the detection of formation of acute thrombi and may be an important tool in vascular procedures.

PET/CTA detection of muscle inflammation related to cholesterol crystal emboli without arterial obstruction

BACKGROUND

PET/CTA was used to evaluate the effect of cholesterol crystal emboli (CCE) on muscle injury. Cholesterol crystals (CCs) released during plaque rupture travel downstream and lodge in muscle triggering inflammation and tissue injury.

METHODS

Thigh muscles in three groups of rabbits (n = 22) were studied after intra-arterial injection of CCs, Group I (n = 10); polystyrene microspheres, Group II (n = 5); or normal saline, Group III (n = 7). After 48 hours, muscle inflammation and injury were measured by fluorodeoxy-glucose uptake using PET/CTA, serum tissue factor (TF), and creatinine phosphokinase (CPK). Macrophages were stained with RAM11 and CCs with Bodipy.

RESULTS

SUVmax of thigh muscles was greater for Group I vs Group II and III (0.40 ± 0.16 vs 0.21 ± 0.11, P = .038 and 0.23 ± 0.06, P = .036). CPK levels rose significantly in Group I vs Group II and III (6.7 ± 6.0 vs 0.6 ± 0.4, P = .007 and 0.9 ± 0.4 mg·dL-1, P = .023). No arterial thrombosis was detected by CTA or histology of embolized arteries and TF did not rise significantly. There were extensive macrophage infiltrates surrounding muscle necrosis in Group I only.

CONCLUSIONS

Cholesterol crystal emboli triggered muscle inflammation and necrosis with an intact circulation. PET/CTA may help in the early detection of inflammation caused by CCs.

PET/CT evaluation of 18F-FDG uptake in pericoronary adipose tissue in patients with stable coronary artery disease: Independent predictor of atherosclerotic lesions' formation?

BACKGROUND

Inflammatory infiltrations in EAT which releases inflammatory cytokines correspond anatomically to the atheromatous plaques in underlying coronary vessels. However, it is unknown whether inflammatory activity of pericoronary adipose tissue (PCAT) promotes coronary atherosclerosis.

METHODS AND RESULTS

35 non-diabetic patients with confirmed CAD and 35 non-CAD controls matched for age and BMI underwent 18F-FDG-PET/CT. Maximal SUV normalized by LA blood activity was measured on the sections corresponding to the respective coronaries (RCA, LCX, LAD), as well, as in subcutaneous fat, visceral fat, and epicardial fat. Extent of CAD was determined by % stenosis in segments corresponding to 18F-FDG-PET/CT sections in coronarography using quantitative coronary analysis. PCAT SUV was significantly greater than SUV in other fat locations, as well as PCAT SUV in the controls. In CAD patients with BMI >25, PCAT SUV was positively related to % stenosis of a respective coronary artery (RCA: 0.43; P < .05; LCX 0.58; P < .05; LAD 0.65; P < .05). PCAT SUV was the only independent predictor of coronary stenosis of LAD and RCA.

CONCLUSIONS

Inflammatory activity of PCAT is greater than in other fat locations, in CAD is greater than in non-CAD controls, and is independently associated with coronary stenosis. In overweight patients, PCAT SUV correlates with the extent of CAD.

Cholesterol crystal embolization following plaque rupture: a systemic disease with unusual features

Cholesterol crystal embolic (CCE) syndrome is often a clinically challenging condition that has a poor prognostic implication. It is a result of plaque rupture with release of cholesterol crystals into the circulation that embolize into various tissue organs. Plaque rupture seems to be triggered by an expanding necrotic core during cholesterol crystallization forming sharp tipped crystals that perforate and tear the fibrous cap. Embolizing cholesterol crystals then initiate both local and systemic inflammation that eventually lead to vascular fibrosis and obstruction causing symptoms that can mimic other vasculitic conditions. In fact, animal studies have demonstrated that cholesterol crystals can trigger an inflammatory response via NLRP3 inflammasome similar to that seen with gout. The diagnosis of CCE syndrome often requires a high suspicion of the condition. Serum inflammation biomarkers including elevated sedimentation rate, abnormal renal function tests and eosinophilia are useful but non-specific. Common target organ involvement includes the skin, kidney, and brain. Various testing including fundoscopic eye examination and other non-invasive procedures such as trans-esophageal echocardiography and magnetic resonance imaging may be helpful in identifying the embolic source. Treatment includes aspirin and clopidogrel, high dose statin and possibly steroids. In rare cases, mechanical intervention using covered stents may help isolate the ruptured plaque. Anticoagulation with warfarin is not recommended and might even be harmful. Overall, CCE syndrome is usually a harbinger of extensive and unstable atherosclerotic disease that is often associated with acute cardiovascular events.

Plaque Rupture and Thrombosis: the Value of the Atherosclerotic Rabbit Model in Defining the Mechanism

Persistent inflammation and mechanical injury associated with cholesterol crystal accretion within atherosclerotic plaques typically precedes plaque disruption (rupture and/or erosion) and thrombosis--often the terminal events of atherosclerotic cardiovascular disease. To elucidate the mechanisms of these events, the atherosclerotic rabbit model provides a unique and powerful tool that facilitates studies of atherogenesis starting with plaque buildup to eventual disruption. Examination of human coronary arteries obtained from patients who died with myocardial infarction demonstrates evidence of cholesterol crystals perforating the plaque cap and intimal surface of the arterial wall that can lead to rupture. These observations were made possible by omitting ethanol, an avid lipid solvent, from the tissue processing steps. Importantly, the atherosclerotic rabbit model exhibits a similar pathology of cholesterol crystals perforating the intimal surface as seen in ruptured human plaques. Local and systemic inflammatory responses in the model are also similar to those observed in humans. The strong parallel between the rabbit and human pathology validates the atherosclerotic rabbit model as a predictor of human pathophysiology of atherosclerosis. Thus, the atherosclerotic rabbit model can be used with confidence to evaluate diagnostic imaging and efficacy of novel anti-atherosclerotic therapy.

Imaging High-Risk Atherosclerotic Plaques with PET

OPINION STATEMENT

Atherosclerotic disease, a primary cause of stroke and myocardial infarction, is the most common underlying cause of death worldwide. While atherosclerosis was formerly considered to be a relatively inert structural abnormality, decades of research have since shown that it is a biologically active process, driven by active inflammation. In concert with this conceptual shift, newer strategies to image vascular lesions have evolved. ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET) imaging has been validated as a non-invasive tool to characterize atherosclerotic inflammation. It is hypothesized that a combination of structural and biological (e.g., inflammatory) imaging may provide better means to assess clinical risk, to assess efficacy of therapy, and to identify new, effective treatments. Limitations remain, however, and further advances in technology and tracer development are required before FDG PET imaging will contribute a significant clinical impact at the level of the individual patient.

Comparison of Somatostatin Receptor 2-Targeting PET Tracers in the Detection of Mouse Atherosclerotic Plaques

PURPOSE

Rupture-prone atherosclerotic plaques are characterized by accumulation of macrophages, which have shown to express somatostatin type 2 receptors. We aimed to investigate whether somatostatin receptor-targeting positron emission tomography (PET) tracers, [(68)Ga]DOTANOC, [(18)F]FDR-NOC, and [(68)Ga]DOTATATE, can detect inflamed atherosclerotic plaques.

PROCEDURES

Atherosclerotic IGF-II/LDLR(-/-)ApoB(100/100) mice were studied in vivo and ex vivo for tracer uptake into atherosclerotic plaques. Furthermore, [(68)Ga]DOTANOC and [(68)Ga]DOTATATE were compared in a head-to-head setting for in vivo PET/X-ray computed tomography (CT) imaging characteristics.

RESULTS

Ex vivo uptake of [(68)Ga]DOTANOC and [(68)Ga]DOTATATE in the aorta was higher in atherosclerotic mice compared to control C57Bl/6N mice, while the aortic uptake of [(18)F]FDR-NOC showed no genotype difference. Unlike [(18)F]FDR-NOC, [(68)Ga]DOTANOC and [(68)Ga]DOTATATE showed preferential binding to atherosclerotic plaques with plaque-to-wall ratio of 1.7 ± 0.3 and 2.1 ± 0.5, respectively. However, the aortic uptake and aorta-to-blood ratio of [(68)Ga]DOTANOC were higher compared to [(68)Ga]DOTATATE in in vivo PET/CT imaging.

CONCLUSION

Our results demonstrate superior applicability for [(68)Ga]DOTANOC and [(68)Ga]DOTATATE in the detection of atherosclerotic plaques compared to [(18)F]FDR-NOC.

Direct Thrombus Imaging in Stroke

There is an emergent need for imaging methods to better triage patients with acute stroke for tissue-plasminogen activator (tPA)-mediated thrombolysis or endovascular clot retrieval by directly visualizing the size and distribution of cerebral thromboemboli. Currently, magnetic resonance (MR) or computed tomography (CT) angiography visualizes the obstruction of blood flow within the vessel lumen rather than the thrombus itself. The present visualization method, which relies on observation of the dense artery sign (the appearance of cerebral thrombi on a non-enhanced CT), suffers from low sensitivity. When translated into the clinical setting, direct thrombus imaging is likely to enable individualized acute stroke therapy by allowing clinicians to detect the thrombus with high sensitivity, assess the size and nature of the thrombus more precisely, serially monitor the therapeutic effects of thrombolysis, and detect post-treatment recurrence. This review is intended to provide recent updates on stroke-related direct thrombus imaging using MR imaging, positron emission tomography, or CT.

Longitudinal imaging of the ageing mouse

Several non-invasive imaging techniques are used to investigate the effect of pathologies and treatments over time in mouse models. Each preclinical in vivo technique provides longitudinal and quantitative measurements of changes in tissues and organs, which are fundamental for the evaluation of alterations in phenotype due to pathologies, interventions and treatments. However, it is still unclear how these imaging modalities can be used to study ageing with mice models. Almost all age related pathologies in mice such as osteoporosis, arthritis, diabetes, cancer, thrombi, dementia, to name a few, can be imaged in vivo by at least one longitudinal imaging modality. These measurements are the basis for quantification of treatment effects in the development phase of a novel treatment prior to its clinical testing. Furthermore, the non-invasive nature of such investigations allows the assessment of different tissue and organ phenotypes in the same animal and over time, providing the opportunity to study the dysfunction of multiple tissues associated with the ageing process. This review paper aims to provide an overview of the applications of the most commonly used in vivo imaging modalities used in mouse studies: micro-computed-tomography, preclinical magnetic-resonance-imaging, preclinical positron-emission-tomography, preclinical single photon emission computed tomography, ultrasound, intravital microscopy, and whole body optical imaging.

Combined non-invasive assessment of endothelial shear stress and molecular imaging of inflammation for the prediction of inflamed plaque in hyperlipidaemic rabbit aortas

AIMS

To evaluate the incremental value of low endothelial shear stress (ESS) combined with high-resolution magnetic resonance imaging (MRI)- and computed tomography angiography (CTA)-based imaging for the prediction of inflamed plaque.

METHODS AND RESULTS

Twelve hereditary hyperlipidaemic rabbits underwent quantitative analysis of plaque in the thoracic aorta with 256-slice CTA and USPIO-enhanced (ultra-small superparamagnetic nanoparticles, P904) 1.5-T MRI at baseline and at 6-month follow-up. Computational fluid dynamics using CTA-based 3D reconstruction of thoracic aortas identified the ESS patterns in the convex and concave curvature subsegments of interest. Subsegments with low baseline ESS exhibited significant increase in wall thickness and plaque inflammation by MRI, in non-calcified plaque burden by CTA, and developed increased plaque size, lipid and inflammatory cell accumulation (high-risk plaque features) at follow-up by histopathology. Multiple regression analysis identified baseline ESS and inflammation by MRI to be independent predictors of plaque progression, while receiver operating curve analysis revealed baseline ESS alone or in combination with inflammation by MRI as the strongest predictor for augmented plaque burden and inflammation (low ESS at baseline: AUC = 0.84, P < 0.001; low ESS and inflammation by molecular MRI at baseline: AUC = 0.89, P < 0.001).

CONCLUSION

Low ESS predicts progression of plaque burden and inflammation as assessed by non-invasive USPIO-enhanced MRI. Combined non-invasive assessment of ESS and imaging of inflammation may serve to predict plaque with high-risk features.

Nuclear Molecular Imaging for Vulnerable Atherosclerotic Plaques

Atherosclerosis is an inflammatory disease as well as a lipid disorder. Atherosclerotic plaque formed in vessel walls may cause ischemia, and the rupture of vulnerable plaque may result in fatal events, like myocardial infarction or stroke. Because morphological imaging has limitations in diagnosing vulnerable plaque, molecular imaging has been developed, in particular, the use of nuclear imaging probes. Molecular imaging targets various aspects of vulnerable plaque, such as inflammatory cell accumulation, endothelial activation, proteolysis, neoangiogenesis, hypoxia, apoptosis, and calcification. Many preclinical and clinical studies have been conducted with various imaging probes and some of them have exhibited promising results. Despite some limitations in imaging technology, molecular imaging is expected to be used both in the research and clinical fields as imaging instruments become more advanced.

Pericoronary adipose tissue: a novel therapeutic target in obesity-related coronary atherosclerosis

Inflammation plays a crucial role in the development and destabilization of atherosclerotic plaques in coronary vessels. Adipose tissue is considered to act in paracrine manner, which modulates a number of physiological and pathophysiological processes. Perivascular adipose tissue has developed specific properties that distinguish it from the fat in other locations. Interestingly, its activity depends on several metabolic conditions associated with insulin resistance and weight gain. Particularly in obesity perivascular fat seems to change its character from a protective to a detrimental one. The present review analyzes literature in terms of the pathophysiology of atherosclerosis, with particular emphasis on inflammatory processes. Additionally, the authors summarize data about confirmed paracrine activity of visceral adipose tissue and especially about pericoronary fat influence on the vascular wall. The contribution of adiponectin, leptin and resistin is addressed. Experimental and clinical data supporting the thesis of outside-to-inside signaling in the pericoronary milieu are further outlined. Clinical implications of epicardial and pericoronary adipose tissue activity are also evaluated. The role of pericoronary adipose tissue in obesity-related atherosclerosis is highlighted. In conclusion, the authors discuss potential therapeutical implications of these novel phenomena, including adipokine imbalance in pericoronary adipose tissue in the setting of obesity, the influence of lifestyle and diet modification, pharmaceutical interventions and the growing role of microRNAs in adipogenesis, insulin resistance and obesity. Key teaching points: • adipose tissue as a source of inflammatory mediators • changes in the vascular wall as a result of outside-to-inside signaling • anatomy, physiology, and clinical implications of epicardial and pericoronary adipose tissue activity • adipokines and their role in obesity-related atherosclerosis • therapeutic perspectives and future directions.

Coronary plaque progression of non-culprit lesions after culprit percutaneous coronary intervention in patients with moderate to advanced chronic kidney disease: intravascular ultrasound and integrated backscatter intravascular ultrasound study

Previous studies have suggested that the deterioration of renal function increases the risk of major adverse clinical events not only in culprit lesions but also in non-culprit lesions (NCLs) after percutaneous coronary intervention (PCI). This study evaluated serial coronary plaque change of NCL in patients with different stages of chronic kidney disease (CKD) using intravascular ultrasound (IVUS) and integrated backscatter IVUS (IB-IVUS). In 113 patients (113 NCLs) underwent both IVUS-guided PCI and follow-up IVUS, volumetric IVUS analyses were performed at proximal reference NCLs in de novo target vessels post PCI and at 8-month follow-up. NCLs were divided into 4 groups based on baseline CKD stage: CKD-1, n = 18; CKD-2, n = 42; CKD-3, n = 29; and CKD4-5, n = 24. We compared serial changes of plaque burden and composition among groups under statin treatment. Plaque progression occurred in CKD-3 (+4.6 mm(3), p < 0.001) and CKD4-5 (+9.8 mm(3), p < 0.001) despite anti-atherosclerotic treatment, whereas plaque regression occurred in CKD-1 (-5.4 mm(3), p = 0.002) and CKD-2 (-3.2 mm(3), p = 0.001) mainly due to initiate statin treatment after PCI. Plaque volume change was correlated with eGFR (p < 0.0001). Multivariate analysis showed CKD stage 3-5 was an independent predictor of plaque progression. Regarding IB-IVUS analyses, lipid plaque increased in CKD-3 (+4.6 mm(3), p < 0.001) and CKD4-5 (+5.4 mm(3), p < 0.001), but decreased in CKD-2 (-2.7 mm(3), p < 0.05). Fibrotic plaque also increased in CKD4-5 (+3.4 mm(3), p < 0.001). Moderate to advanced CKD was associated with coronary plaque progression characterized by greater lipid and fibrotic plaque volumes in NCL under statin treatment after culprit PCI.

Plaque quantification by coronary CT and intravascular ultrasound identifies a low CT density core as a marker of plaque instability in acute coronary syndromes

The purpose of this study was to demonstrate the relationship between the presence and amount of a low-density core (LDC) with a CT density < 30 Hounsfield units (HU) by coronary computed tomography angiography (CCTA) and IVUS-derived markers of vulnerability in the culprit lesions (CL) of patients with acute coronary syndromes (ACS).In 43 patients with ACS, 105 coronary plaques were scanned using CCTA and IVUS for the quantitative and qualitative assessment of vulnerability markers.The presence of a low attenuation plaque (LAP) was identified in 67.4% of the CL and 29.03% of the non-CL (P = 0.0001). The presence of a LDC > 6.0 mm(3) was significantly correlated with the percentage of the necrotic core (NC) (22.08% versus 7.97%, P = 0.001) and the fibro-fatty tissue by IVUS (18.68% versus 15.87%, P = 0.02). LDC volumes showed a good correlation with the percentage of the NC (r = 0.7303, P < 0.0001) and the fibro-fatty tissue in the CL (r = 0.4928, P < 0.0008). Quantitative plaque analysis revealed a significant difference in plaque composition between CL and non-CL in regards to the LDC (18.45 versus 6.5, P < 0.001), the percentage of NC (20.74 versus 18.74, P = 0.02), fibro-fatty tissue (17.77 versus 15.48, P = 0.002), and fibrotic tissue (51.68 versus 54.8, P = 0.01).VH-IVUS and CCTA plaque quantification showed that the presence of a low-density (< 30 HU) core within the CL of patients with ACS represents a marker of vulnerability and correlates well with other CCTA and IVUS-derived features of vulnerability, particularly the NC of the plaque.

Focal arterial inflammation precedes subsequent calcification in the same location: a longitudinal FDG-PET/CT study

BACKGROUND

Arterial calcium (Ca) deposition has been identified as an active inflammatory process. We sought to test the hypothesis that local vascular inflammation predisposes to subsequent arterial calcium deposition in humans.

METHODS AND RESULTS

From a hospital database, we identified 137 patients (age, 61 ± 13 years; 48.1% men) who underwent serial positron-emission tomography/computed tomography (1-5 years apart). Focal arterial inflammation was prospectively determined by measuring 18F-flourodeoxyglucose uptake (using baseline positron-emission tomography) within predetermined locations of the thoracic aortic wall and was reported as a standardized uptake value. A separate, blinded investigator evaluated calcium deposition (on the baseline and follow-up computed tomographic scans) along the same standardized sections of the aorta. New calcification was prospectively defined using square root-transformed difference of calcium volume score, with a cutoff value of 2.5. Accordingly, vascular segment was classified as either with or without subsequent calcification. Overall, 67 (9%) of aortic segments demonstrated subsequent calcification. Baseline median (interquartile range) standardized uptake value was higher in segments with versus without subsequent calcification (2.09 [1.84-2.44] versus 1.92 [1.72-2.20], P=0.002). This was also true in the subset of segments with Ca present at baseline (2.08 [1.81-2.40] versus 1.86 [1.66-2.09], P=0.02), as well as those without (2.17 [1.87-2.51] versus 1.93 [1.73-2.20], P=0.04). Furthermore, across all patients, subsequent Ca deposition was associated with the underlying 18F-flourodeoxyglucose uptake (inflammatory signal), measured as standardized uptake value (odds ratio [95% confidence interval]=2.94 [1.27-6.89], P=0.01) or target-to-background ratio (2.59 [1.18-5.70], =0.02), after adjusting for traditional cardiovascular risk factors.

CONCLUSIONS

Here, we provide first-in-man evidence that arterial inflammation precedes subsequent Ca deposition, a marker of plaque progression, within the underlying location in the artery wall.

Detection of vulnerable atherosclerotic plaque and prediction of thrombosis events in a rabbit model using 18F-FDG -PET/CT

BACKGROUND

Detection of vulnerable plaques could be clinically significant in the prevention of cardiovascular events. We aimed to compare Fluorine-18 fluorodeoxyglucose ((18)F-FDG) uptake in vulnerable and stable plaques, and investigate the feasibility of predicting thrombosis events using Positron Emission Tomography/Computed Tomography (PET/CT) angiography.

METHODS

Atherosclerosis was induced in 23 male New Zealand white rabbits. The rabbits underwent pharmacological triggering to induce thrombosis. A pre-triggered PET/CTA scan and a post-triggered PET/CTA scan were respectively performed. (18)F-FDG uptake by the aorta was expressed as maximal standardized uptake value (SUVmax) and mean SUV (SUVmean). SUVs were measured on serial 7.5 mm arterial segments.

RESULTS

Thrombosis was identified in 15 of 23 rabbits. The pre-triggered SUVmean and SUVmax were 0.768 ± 0.111 and 0.804 ± 0.120, respectively, in the arterial segments with stable plaque, and 1.097 ± 0.189 and 1.229 ± 0.290, respectively, in the arterial segments with vulnerable plaque (P<0.001, respectively). The post-triggered SUVmean and SUVmax were 0.849 ± 0.167 and 0.906 ± 0.191, respectively in the arterial segments without thrombosis, and 1.152 ± 0.258 and 1.294 ± 0.313, respectively in the arterial segments with thrombosis (P<0.001, respectively). The values of SUVmean in the pre-triggered arterial segments were used to plot a receiver operating characteristic curve (ROC) for predicting thrombosis events. Area under the curve (AUC) was 0.898. Maximal sensitivity and specificity (75.4% and 88.5%, respectively) were obtained when SUVmean was 0.882.

CONCLUSIONS

Vulnerable and stable plaques can be distinguished by quantitative analysis of (18)F-FDG uptake in the arterial segments in this rabbit model. PET/CT may be used for predicting thrombosis events and risk-stratification in patients with atherosclerotic disease.

Multislice computed tomographic coronary angiography for quantitative assessment of culprit lesions in acute coronary syndromes

BACKGROUND

We studied the characteristics of low-density plaque (LDP) burden in patients with acute coronary syndrome (ACS), using 64-slice computed tomography (CT) assessment. Though several CT plaque features such as positive remodelling, adjacent spotty calcification or the presence of LDP have been demonstrated to be associated with unstable plaques, it is still unknown whether their severity and extent present any differences between different types of ACS.

METHODS

In 45 subjects with ACS (22 unstable angina and 23 non-ST-elevation myocardial infarction [NSTEMI]), 118 coronary plaques were evaluated using a CT multislice 64 assessment including the burden with atheroma having a CT density below 30, 60, or 100 Hounsfield units (HU), remodelling index and spotty calcification.

RESULTS

Culprit lesions tend to be larger in volume (111.11 mm(3) vs 62.25 mm(3); P < 0.0001), have a higher remodelling index (1.27 vs 1.01; P < 0.0001), and present a significantly larger LDP with a density < 30 HU (23.3 mm(3) vs 7.6 mm(3); P < 0.0001) or < 60 HU (33.4 mm(3) vs 16.9 mm(3); P < 0.0001) than nonculprit lesions. The presence of a plaque more than 20 mm(3) in volume with a CT density < 30 HU (P = 0.0009) and the presence of all 3 markers of plaque vulnerability (LDP, spotty calcifications or positive remodelling) (P = 0.01) significantly correlated with the presence of an NSTEMI.

CONCLUSIONS

Culprit lesions demonstrated larger plaque volumes, a higher burden with low-density cores, and more intense remodelling than nonculprit lesions, whereas culprit lesions associated with NSTEMI showed a higher burden with lower density cores than those associated with unstable angina.

Arterial inflammation in patients with HIV

CONTEXT

Cardiovascular disease is increased in patients with human immunodeficiency virus (HIV), but the specific mechanisms are unknown.

OBJECTIVE

To assess arterial wall inflammation in HIV, using 18fluorine-2-deoxy-D-glucose positron emission tomography (18F-FDG-PET), in relationship to traditional and nontraditional risk markers, including soluble CD163 (sCD163), a marker of monocyte and macrophage activation.

DESIGN, SETTING, AND PARTICIPANTS

A cross-sectional study of 81 participants investigated between November 2009 and July 2011 at the Massachusetts General Hospital. Twenty-seven participants with HIV without known cardiac disease underwent cardiac 18F-FDG-PET for assessment of arterial wall inflammation and coronary computed tomography scanning for coronary artery calcium. The HIV group was compared with 2 separate non-HIV control groups. One control group (n = 27) was matched to the HIV group for age, sex, and Framingham risk score (FRS) and had no known atherosclerotic disease (non-HIV FRS-matched controls). The second control group (n = 27) was matched on sex and selected based on the presence of known atherosclerotic disease (non-HIV atherosclerotic controls).

MAIN OUTCOME MEASURE

Arterial inflammation was prospectively determined as the ratio of FDG uptake in the arterial wall of the ascending aorta to venous background as the target-to-background ratio (TBR).

RESULTS

Participants with HIV demonstrated well-controlled HIV disease (mean [SD] CD4 cell count, 641 [288] cells/μL; median [interquartile range] HIV-RNA level, <48 [<48 to <48] copies/mL). All were receiving antiretroviral therapy (mean [SD] duration, 12.3 [4.3] years). The mean FRS was low in both HIV and non-HIV FRS-matched control participants (6.4; 95% CI, 4.8-8.0 vs 6.6; 95% CI, 4.9-8.2; P = .87). Arterial inflammation in the aorta (aortic TBR) was higher in the HIV group vs the non-HIV FRS-matched control group (2.23; 95% CI, 2.07-2.40 vs 1.89; 95% CI, 1.80-1.97; P < .001), but was similar compared with the non-HIV atherosclerotic control group (2.23; 95% CI, 2.07-2.40 vs 2.13; 95% CI, 2.03-2.23; P = .29). Aortic TBR remained significantly higher in the HIV group vs the non-HIV FRS-matched control group after adjusting for traditional cardiovascular risk factors (P = .002) and in stratified analyses among participants with undetectable viral load, zero calcium, FRS of less than 10, a low-density lipoprotein cholesterol level of less than 100 mg/dL (<2.59 mmol/L), no statin use, and no smoking (all P ≤ .01). Aortic TBR was associated with sCD163 level (P = .04) but not with C-reactive protein (P = .65) or D-dimer (P = .08) among patients with HIV.

CONCLUSION

Participants infected with HIV vs noninfected control participants with similar cardiac risk factors had signs of increased arterial inflammation, which was associated with a circulating marker of monocyte and macrophage activation.

18FDG PET-CT imaging detects arterial inflammation and early atherosclerosis in HIV-infected adults with cardiovascular disease risk factors

BACKGROUND

Persistent vascular inflammation has been implicated as an important cause for a higher prevalence of cardiovascular disease (CVD) in HIV-infected adults. In several populations at high risk for CVD, vascular 18Fluorodeoxyglucose (18FDG) uptake quantified using 3D-positron emission-computed tomography (PET-CT) has been used as a molecular level biomarker for the presence of metabolically active proinflammatory macrophages in rupture-prone early atherosclerotic plaques. We hypothesized that 18FDG PET-CT imaging would detect arterial inflammation and early atherosclerosis in HIV-infected adults with modest CVD risk.

METHODS

We studied 9 HIV-infected participants with fully suppressed HIV viremia on antiretroviral therapy (8 men, median age 52 yrs, median BMI 29 kg/m2, median CD4 count 655 cells/μL, 33% current smokers) and 5 HIV-negative participants (4 men, median age 44 yrs, median BMI 25 kg/m2, no current smokers). Mean Framingham Risk Scores were higher for HIV-infected persons (9% vs. 2%, p < 0.01). 18FDG (370 MBq) was administered intravenously. 3D-PET-CT images were obtained 3.5 hrs later. 18FDG uptake into both carotid arteries and the aorta was compared between the two groups.

RESULTS

Right and left carotid 18FDG uptake was greater (P < 0.03) in the HIV group (1.77 ±0.26, 1.33 ±0.09 target to background ratio (TBR)) than the control group (1.05 ± 0.10, 1.03 ± 0.05 TBR). 18FDG uptake in the aorta was greater in HIV (1.50 ±0.16 TBR) vs control group (1.24 ± 0.05 TBR), but did not reach statistical significance (P = 0.18).

CONCLUSIONS

Carotid artery 18FDG PET-CT imaging detected differences in vascular inflammation and early atherosclerosis between HIV-infected adults with CVD risk factors and healthy HIV-seronegative controls. These findings confirm the utility of this molecular level imaging approach for detecting and quantifying glucose uptake into inflammatory macrophages present in metabolically active, rupture-prone atherosclerotic plaques in HIV infected adults; a population with increased CVD risk.

Relation between estimated glomerular filtration rate and composition of coronary arterial atherosclerotic plaques

It is well known that chronic kidney disease is a risk factor for atherosclerosis. The present study was conducted to identify any relation between the estimated glomerular filtration rate (eGFR) and coronary plaque characteristics using integrated backscatter intravascular ultrasound (IB-IVUS), which can detect coronary plaque composition. We performed IB-IVUS for 201 consecutive patients undergoing percutaneous coronary intervention, and they were divided into 3 groups according to the eGFR values (group 1 [n = 20], ≥90 ml/min/1.73 m(2); group 2 [n = 123], 60 to 90 ml/min/1.73 m(2); and group 3 [n = 58], <60 ml/min/1.73 m(2)). Coronary plaques in nonculprit lesions on 3-dimensional analysis were evaluated using IB-IVUS. The baseline characteristics were similar, except for older age and a greater prevalence of men in group 3. IB-IVUS showed a percentage of lipid volume of 44.7 ± 5.0% in group 1, 53.6 ± 6.2% in group 2, and 63.5 ± 6.2% in group 3 (p <0.01), with a corresponding percentage of fibrous volume of 53.9 ± 4.9%, 45.1 ± 6.0%, and 35.3 ± 6.1%, respectively (p <0.01). The eGFR correlated significantly with both parameters (r = -0.68, p <0.001 and r = 0.68, p <0.001, respectively). In conclusion, lower eGFR levels were associated with greater lipid and lower fibrous contents, contributing to coronary plaque vulnerability.

Symptomatic and asymptomatic carotid artery plaque

Carotid atherosclerotic plaques represent both stable and unstable atheromatous lesions. Atherosclerotic plaques that are prone to rupture owing to their intrinsic composition such as a large lipid core, thin fibrous cap and intraplaque hemorrhage are associated with subsequent thromboembolic ischemic events. At least 15-20% of all ischemic strokes are attributable to carotid artery atherosclerosis. Characterization of plaques may enhance the understanding of natural history and ultimately the treatment of atherosclerotic disease. MRI of carotid plaque and embolic signals during transcranial Doppler have identified features beyond luminal stenosis that are predictive of future transient ischemic attacks and stroke. The value of specific therapies to prevent stroke in symptomatic and asymptomatic patients with severe carotid artery stenosis are the subject of current research and analysis of recently published clinical trials that are discussed in this article.

Plaque Rupture and Thrombosis Are Reduced by Lowering Cholesterol Levels and Crystallization With Ezetimibe and Are Correlated With Fluorodeoxyglucose Positron Emission Tomography

Objective—

This study evaluated effects of lipid lowering with ezetimibe on plaque burden and associated cholesterol crystallization and inflammation in a rabbit model of plaque disruption and thrombosis.

Methods and Results—

Atherosclerotic rabbits (Group I, n=10 without; Group II, n=12 with ezetimibe, 1 mg/kg per day) were pharmacologically triggered for plaque disruption. Fluorodeoxyglucose positron emission tomography, RAM 11 macrophage staining, and serum inflammatory markers detected arterial inflammation. Serum and aortic wall cholesterol levels were measured, and thrombus area was planimetered. Cholesterol crystal density on aortic surface was scored (0 to +3) by scanning electron microscopy. Serum and aortic wall cholesterol, plaque area, and thrombosis area were significantly lower in Group II versus Group I (83.4±106.4 versus 608±386 mg/dL, P =0.002; 3.12±1.40 versus 9.39±5.60 mg/g, P =0.003; 10.84±1.6 versus 17.48±1.8 mm 2 , P <0.001; and 0.05±0.15 versus 0.72±0.58 mm 2 , P =0.01, respectively). There were significant correlations between crystal density and plaque area ( r =0.75, P <0.003) and between crystal density and RAM 11 ( r =0.82, P <0.001). Scanning electron microscopy demonstrated that there were fewer crystals in Group II versus Group I (+1.2±0.61 versus +2.4±0.63, P <0.001) and less inflammation detected by fluorodeoxyglucose positron emission tomography and RAM 11 ( P <0.004 and P <0.04, respectively).

Conclusion—

Lowering cholesterol levels with ezetimibe reduced plaque burden, crystallization, and inflammation, preventing plaque disruption and thrombosis.

Vascular imaging with positron emission tomography

Atherosclerosis is an inflammatory disease that causes most myocardial infarctions, strokes and acute coronary syndromes. Despite the identification of multiple risk factors and widespread use of drug therapies, it still remains a global health concern with associated costs. Although angiography is established as the gold standard means of detecting coronary artery stenosis, it does not image the vessel wall itself, reporting only on its consequences such as luminal narrowing and obstruction. MRI and computed tomography provide more information about the plaque structure, but recently positron emission tomography (PET) imaging using [(18) F]-fluorodeoxyglucose (FDG) has been advocated as a means of measuring arterial inflammation. This results from the ability of FDG-PET to highlight areas of high glucose metabolism, a feature of macrophages within atherosclerosis, particularly in high-risk plaques. It is suggested that the degree of FDG accumulation in the vessel wall reflects underlying inflammation levels and that tracking any changes in FDG uptake over time or with drug therapy might be a way of getting an early efficacy readout for novel anti-atherosclerotic drugs. Early reports also demonstrate that FDG uptake is correlated with the number of cardiovascular risk factors and possibly even the risk of future cardiovascular events. This review will outline the evidence base, shortcomings and emerging applications for FDG-PET in vascular imaging. Alternative PET tracers and other candidate imaging modalities for measuring vascular inflammation will also be discussed.

Systemic and vascular inflammation in patients with moderate to severe psoriasis as measured by [18F]-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT): a pilot study

OBJECTIVE

To evaluate the feasibility of using [18F]-fluorodeoxyglucose positron emission tomography-computed tomography (FDG-PET/CT) to detect and quantify systemic inflammation in patients with psoriasis.

DESIGN

Case series with a nested case-control study.

SETTING

Referral dermatology and preventive cardiology practices.

PARTICIPANTS

Six patients with psoriasis affecting more than 10% of their body surface area and 4 controls age and sex matched to 4 of the patients with psoriasis for a nested case-control study.

MAIN OUTCOME MEASURES

The FDG uptake in the liver, musculoskeletal structures, and aorta measured by mean standardized uptake value, a measure of FDG tracer uptake by macrophages and other inflammatory cells.

RESULTS

FDG-PET/CT identified numerous foci of inflammation in 6 patients with psoriasis within the skin, liver, joints, tendons, and aorta. Inflammation in the joints was observed in a patient with psoriatic arthritis as well as in 1 patient with no history of joint disease or joint symptoms. In a nested case-control study, FDG-PET/CT imaging demonstrated increased vascular inflammation in multiple segments of the aorta compared with controls. These findings persisted after adjustment for traditional cardiovascular risk factors in multivariate analysis (mean β = 0.33; P < .001). Patients with psoriasis further demonstrated increased hepatic inflammation after adjusting for cardiovascular risk factors (β = 0.18; P < .001), but the association was no longer significant when adjusted for alcohol intake (β = -0.25; P = .07).

CONCLUSION

FDG-PET/CT is a sensitive tool for identifying inflammation and can be used to identify clinically observed inflammation in the skin and subclinical inflammation in the blood vessels, joints, and liver of patients with psoriasis.

Prevalence of coronary artery calcium scores and silent myocardial ischaemia was similar in Indian Asians and European whites in a cross-sectional study of asymptomatic subjects from a U.K. population (LOLIPOP-IPC)

BACKGROUND

Coronary heart disease (CHD) mortality is 70% higher among Indian Asians (IA) than European whites (EW), the reasons for this excess remain unexplained. Coronary artery calcification (CAC) is highly correlated with coronary plaque burden and silent myocardial ischaemia in EW; but fails to identify excess risk in IA. We hypothesised that IA have a higher prevalence of silent myocardial ischaemia compared to EW, despite similar CAC, and this may explain their excess CHD mortality.

METHODS

CAC was measured for 2,369 asymptomatic men and women, aged 35 to 75 years, as part of the London Life Sciences Population (LOLIPOP) study. 518 subjects had CAC scores >100 Agatston units and of these 256 (49%) patients underwent myocardial perfusion scintigraphy (MPS).

RESULTS

CAC scores were similar among IA and EW, after adjustment for conventional risk factors. MPS abnormalities were seen in 56 (22%) subjects. Presence of diabetes (P = .03) and increasing CAC (P < .001) were independent predictors for severity of silent myocardial ischaemia. Ethnicity did not influence the prevalence or the extent of silent myocardial ischaemia.

CONCLUSION

MPS did not identify greater ischaemia among IA compared with EW. This appears incongruent with almost 2-fold higher risk of CHD mortality observed in IA.

In vivo MR imaging of plaque disruption and thrombus formation in an atherosclerotic rabbit model

Our aim is to introduce an atherosclerotic rabbit model for inducing atherosclerosis lesions in rabbits, and to validate the model in vivo with 3T high resolution magnetic resonance imaging of the thrombosis followed a pharmacologically triggered plaque disruption. Twenty male New Zealand White rabbits were randomly allocated into an experimental group (n = 16) and a control group (n = 4). The aortic wall injuries were induced by an intravascular balloon in the experimental group rabbits after feeding them with a high cholesterol diet for 2 weeks. The pharmacological triggering with Russell's viper venom and histamine was performed after totally 16 weeks of intermittent cholesterol feeding. All of the animals underwent both the pre-trigger and post-trigger MR examinations including TOF, T1WI, T2WI and post contrast T1WI. Euthanasia was performed in all rabbits; gross anatomy and histological specimen of aorta were obtained. MR images were analyzed and compared with histological results. Compared with the control group rabbits, the aorta of the experimental group rabbits in the pre-triggered MR images showed an increased vessel wall thickening, luminal narrowing, and vessel wall enhancement. Fourteen rabbits survived the triggering, and 8 of them developed thrombosis (58.1%). No thrombus was found in the control group. The accuracy of the multi-sequences MR including TOF, T1WI, T2WI and post contrast T1WI was 87.1% (27/31) for detecting thrombus. MR data significantly correlated with the histopathology data for both thrombus length (r = 0.94, P < 0.01) and thrombus location (r = 0.85, P < 0.01), respectively. The study demonstrated that MR reliably determined the plaque disruption and thrombus formation in the atherosclerotic rabbit model.

Pregnancy-associated plasma protein A values in patients with stable cardiovascular disease: use of a new monoclonal antibody-based assay

BACKGROUND

PAPP-A is promising in improving risk stratification and invasive treatment decisions in stable cardiovascular patients. We evaluated the prognostic value of pregnancy-associated plasma protein A (PAPP-A) measured by a novel assay in stable cardiovascular patients.

METHODS

We investigated 228 stable cardiovascular outpatients. Blood was drawn for PAPP-A measurement after echocardiography and ergometry prior to heart catheterization. Angiographically we determined severity as well as qualitative characteristics suspect for vulnerability of coronary lesions. After 1108±297 days, follow-up information was obtained by questionnaire mailings and interviews by phone.

RESULTS

104 patients had coronary stenosis≥70%, 75 had B-type lesions≥50%, 46 showed complex lesions, and 68 were suspected to have vulnerable lesions. Median PAPP-A was 1.76 (interquartile range 1.21, 2.63) μIU/ml in the entire cohort. PAPP-A concentrations did not differ in dependence on coronary artery findings. A cutpoint of 2.7 μIU/ml was derived from receiver-operator characteristics for outcome measures. For this cutoff, Cox proportional hazard models with 19 further clinical variables showed that PAPP-A was predictive for all-cause death (HR 4.73, 95% CI 1.46-15.31, p=0.01), all-cause death or nonfatal infarction (HR 4.01, 95% CI 1.58-10.13, p=0.003) and all-cause death, nonfatal myocardial infarction or hospitalization (HR 1.96, 95% CI 1.03-3.70, p=0.04). The predictive value of PAPP-A did not change substantially after correction for values of cardiac troponin, using a highly sensitive cardiac troponin I research assay.

CONCLUSIONS

PAPP-A, measured by a new, monoclonal antibody-based assay is a promising prognostic marker in patients with stable cardiovascular disease and an indication for heart catheterization.

A rabbit model of thrombosis on atherosclerotic lesions

Thrombus formation on a disrupted atherosclerotic plaque is a key event that leads to atherothrombosis. Because thrombus is induced by chemical or physical injury of normal arteries in most animal models of thrombosis, the mechanisms of thrombogenesis and thrombus growth in atherosclerotic vessels should be investigated in diseased arteries of appropriate models. Pathological findings of human atherothrombosis suggest that tissue factor, an initiator of the coagulation cascade, significantly affects enhanced platelet aggregation and fibrin formation after plaque disruption. We established a rabbit model of atherothrombosis based on human pathology in which differences in thrombus formation between normal and atherosclerotic arteries, factors contributing to thrombus growth, and mechanisms of plaque erosion can be investigated. Emerging transgenic and stem cell technologies should also provide an invaluable rabbit experimental model in the near future.

Noninvasive Positron Emission Tomography Imaging of Coronary Arterial Inflammation

The importance of inflammation to atherothrombosis has led to the pursuit of noninvasive imaging methods to measure inflammation within the arterial wall. There is substantial evidence supporting the use of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) imaging for evaluation of atherosclerotic plaque inflammation. However, coronary imaging with this technique has been limited, due to several technical hurdles. Nonetheless, early experiences in coronary FDG-PET imaging have been encouraging. This review outlines the development of vascular PET imaging and its potential use for evaluation of coronary artery disease.

Imaging Atherosclerosis in the Carotid Arteries with F-18-Fluoro-2-deoxy-D-glucose Positron Emission Tomography: Effect of Imaging Time after Injection on Quantitative Measurement

PURPOSE

To compare F-18-fluoro-2-deoxy-D-glucose (F-18 FDG) positron emission tomography/computed tomography (PET/CT) imaging at two different circulation times after injection of F-18 FDG in order to measure atherosclerosis in carotid arteries.

METHODS

We assessed 12 patients with recent symptomatic plaques in the carotid arteries. F-18 FDG PET/CT carotid plaque imaging was performed for 20 min at 2 h after F-18 FDG injection in five patients and at 3 h in seven patients. We measured vessel wall uptake using the maximal standardized uptake value (SUV), and the mean and maximal blood target-to-background ratios (TBR) of the symptomatic carotid arteries. Blood pool activity (BPA) was measured as the mean SUV of the superior vena cava (SVC) and jugular vein of these 12 patients, and in 14 age- and gender-matched patients who underwent whole-body F-18 FDG PET/CT examinations 1 h after injection.

RESULTS

F-18 FDG PET/CT revealed visible F-18 FDG uptake in all patients with symptomatic carotid plaques. Maximal SUV did not differ between groups evaluated at 2 h and 3 h (2.62 ± 0.45 vs 3.00 ± 0.85, p = 0.335). However, mean (2.04 ± 0.22 vs 3.54 ± 0.62, p < 0.05) and maximal (1.65 ± 0.15 vs 2.70 ± 0.42, p < 0.05) TBR values that were normalized to BPA in the SVC differ significantly.

CONCLUSIONS

Symptomatic carotid plaques are visualized for a relatively short period of imaging time on ≥1-h PET/CT images. Quantitative parameters of atherosclerotic carotid arteries are preserved or even increased over time, whereas those of blood pools are decreased.