The thin-cap fibroatheroma: a type of vulnerable plaque: the major precursor lesion to acute coronary syndromes

Systemic tumor necrosis factor-related apoptosis-inducing ligand delivery shows antiatherosclerotic activity in apolipoprotein E-null diabetic mice

BACKGROUND

Although in vitro studies have suggested that tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) might be involved in vascular biology, its potential role in the pathogenesis and/or treatment of atherosclerosis has not been investigated.

METHODS AND RESULTS

Both recombinant human TRAIL and an adeno-associated virus vector expressing human TRAIL were used to deliver TRAIL in apolipoprotein E (apoE)-null mice in which diabetes mellitus was induced by destruction of islet cells with streptozotocin. Diabetes in apoE-null mice was associated with a significant increase in atherosclerotic plaque area and complexity in the aorta as assessed by a marked increase in interstitial collagen, cellular proliferation, and macrophage infiltration and a focal loss of endothelial coverage. Repeated intraperitoneal injections of recombinant human TRAIL and a single intravenous injection of adeno-associated virus-human TRAIL significantly attenuated the development of atherosclerotic plaques in apoE-null animals. TRAIL also markedly affected the cellular composition of plaque lesions by inducing apoptosis of infiltrating macrophages and increasing the vascular smooth muscle cell content. Moreover, TRAIL promoted the in vitro migration of cultured human aortic vascular smooth muscle cells but not of monocytes or macrophages. Conversely, TRAIL selectively induced apoptosis of human cultured macrophages but not of vascular smooth muscle cells.

CONCLUSIONS

Overall, data from the present study indicate that atherosclerosis in diabetic apoE-null mice is ameliorated by systemic TRAIL administration and that adeno-associated virus-mediated TRAIL gene delivery might represent an innovative method for the therapy of diabetic vascular diseases.

Intravascular ultrasound profile analysis of ruptured coronary plaques

Angiographic studies have shown that lesions preceding nonfatal acute events are usually not hemodynamically significant. This has led to the concept that plaque ruptures occur at minimal disease sites. We used intravascular ultrasound to create a prerupture "profile" of unstable (vulnerable) plaques. We analyzed 112 ruptured plaques detected by intravascular ultrasound. Reference and lesion external elastic membrane (EEM) and lumen areas were measured to calculate prerupture estimates of plaque area, plaque burden (plaque/EEM area), eccentricity, area stenosis, and remodeling. The narrowest coefficients of variance were for lesion EEM area, maximum plaque thickness, and plaque burden, reference lumen area, and remodeling index (coefficients of variance 0.29, 0.25, 0.12, 0.29, and 0.18, respectively); conversely, there was great variability in measurements of calcification and lumen compromise (minimum lumen area and area stenosis). When using the 5 variables with the narrowest coefficient of variance, we found that 67% of ruptured plaques fit all of following 10th or 90th percentile parameters (> 14.3 mm2 lesion EEM area, > 8.1 mm2 reference lumen area, > 1.6 mm maximum lesion plaque thickness, > 0.63 lesion plaque burden, and > 0.87 remodeling index). Further, 89% of ruptured plaques fit 4 of 5 parameters and 96% fit 3 of 5 parameters. In conclusion, plaque ruptures do not occur at minimal disease sites. Rather, vulnerable (rupture-prone) plaques predictably have significant plaque accumulation and remodeling and occur in larger arteries. It is only the degree of lumen compromise that is variable and often insignificant.

Smoking, diabetes, and blood cholesterol differ in their associations with subclinical atherosclerosis: The Multiethnic Study of Atherosclerosis (MESA)

Previous reports suggest that low-density lipoprotein cholesterol (LDLc) is associated with atherosclerosis plaque initiation while cigarette smoking is more associated with plaque progression. The role of diabetes in plaque initiation and progression is not clear. The aim of this study was to confirm and extend these findings. Among 6384 men and women aged 45-84 free of clinical cardiovascular disease, subclinical atherosclerosis severity was classified on the basis of ultrasound measures of carotid stenosis and thickness and the ankle-brachial blood pressure index of lower extremity arterial disease. Carotid plaques were classified as echolucent or echogenic. Distensibility was calculated from the change in carotid diameter over the cardiac cycle. The smoking association with minimal, moderate, and more severe disease was progressive, estimated as equivalent to LDLc effects of 40, 85 and 238 mg/dl respectively. LDLc was relatively more associated with echolucent plaques; smoking with echogenic plaques. Diabetes was associated with carotid stiffness, whereas smoking was associated with greater distensibility. The results, together with pathological literature, suggest that LDLc may be of key importance both in plaque initiation and vulnerability to rupture, whereas smoking may relate to plaque progression to thicker, more fibrous lesions. Diabetes contributes uniquely to arterial stiffness.

Near-infrared spectroscopy for the detection of vulnerable coronary artery plaques

This review describes efforts to use near-infrared (NIR) spectroscopy to identify chemical components of coronary artery plaques as a means to assess vulnerability. Near-infrared spectroscopy has been well-validated by the physical sciences as a method to characterize chemical composition of various bio-materials and could be ideal to detect vulnerable coronary plaques in patients. Recent studies in aortic and coronary artery autopsy specimens have confirmed the ability of the technique to identify lipid-rich thin-cap fibroatheromas through blood. A catheter-based system has been developed to address the challenges-of access to the coronary artery, blood, motion, and the need to scan-that must be overcome for use in patients. Initial clinical experience in six patients with stable angina demonstrates that high-quality NIR spectra can be safely obtained. Additional studies are planned to validate the ability of the technique to identify lipid-rich coronary artery plaques and ultimately link chemical characterization with subsequent occurrence of an acute coronary syndrome.

Pathology of the Vulnerable Plaque

The majority of patients with acute coronary syndromes (ACS) present with unstable angina, acute myocardial infarction, and sudden coronary death. The most common cause of coronary thrombosis is plaque rupture followed by plaque erosion, whereas calcified nodule is infrequent. If advances in coronary disease are to occur, it is important to recognize the precursor lesion of ACS. Of the three types of coronary thrombosis, a precursor lesion for acute rupture has been postulated. The non-thrombosed lesion that most resembles the acute plaque rupture is the thin cap fibroatheroma (TCFA), which is characterized by a necrotic core with an overlying fibrous cap measuring <65 microm, containing rare smooth muscle cells but numerous macrophages. Thin cap fibroatheromas are most frequently observed in patients dying with acute myocardial infarction and least common in plaque erosion. They are most frequently observed in proximal coronary arteries, followed by mid and distal major coronary arteries. Vessels demonstrating TCFA do not usually show severe narrowing but show positive remodeling. In TCFAs the necrotic core length is approximately 2 to 17 mm (mean 8 mm) and the underlying cross-sectional area narrowing in over 75% of cases is <75% (diameter stenosis <50%). The area of the necrotic core in at least 75% of cases is < or =3 mm2. These lesions have lesser degree of calcification than plaque ruptures. Thin cap fibroatheromas are common in patients with high total cholesterol (TC) and high TC/high-density lipoprotein cholesterol ratio, in women >50 years, and in those patients with elevated high levels of high sensitivity C-reactive protein. It has only recently been recognized that their identification in living patients might help reduce the incidence of sudden coronary death.

New Opportunities for Identification and Reduction of Coronary Risk

Advances in the understanding of the role of vulnerable plaque in the causation of coronary events, coupled with novel diagnostic and therapeutic approaches, create a new opportunity for progress against cardiovascular disease. The recognition that non-flow-limiting plaques often produce cardiac events has led to the development of invasive and non-invasive methods to identify such plaques prospectively. Treatments such as stenting, photodynamic therapy, and novel pharmaceutical agents are under consideration as methods to stabilize the vulnerable plaques and patients that might be detected, thereby enhancing both primary and secondary prevention. Despite the promise of the field, many issues remain to be resolved, including the focality versus systemic nature of the atherosclerotic process, the ability of detectors to identify the target for which they were developed and prove that such a target is linked to clinical events, and the efficacy of specific therapy. If vulnerable plaques and patients can be successfully identified and treated, there will be immense clinical benefits, accompanied by cost savings.

How critical is fibrous cap thickness to carotid plaque stability? A flow-plaque interaction model

BACKGROUND AND PURPOSE

Acute cerebral ischemic events are associated with rupture of vulnerable carotid atheroma and subsequent thrombosis. Factors such as luminal stenosis and fibrous cap thickness have been thought to be important risk factors for plaque rupture. We used a flow-structure interaction model to simulate the interaction between blood flow and atheromatous plaque to evaluate the effect of the degree of luminal stenosis and fibrous cap thickness on plaque vulnerability.

METHODS

A coupled nonlinear time-dependent model with a flow-plaque interaction simulation was used to perform flow and stress/strain analysis in a stenotic carotid artery model. The stress distribution within the plaque and the flow conditions within the vessel were calculated for every case when varying the fibrous cap thickness from 0.1 to 2 mm and the degree of luminal stenosis from 10% to 95%. A rupture stress of 300 kPa was chosen to indicate a high risk of plaque rupture. A 1-sample t test was used to compare plaque stresses with the rupture stress.

RESULTS

High stress concentrations were found in the plaques in arteries with >70% degree of stenosis. Plaque stresses in arteries with 30% to 70% stenosis increased exponentially as fibrous cap thickness decreased. A decrease of fibrous cap thickness from 0.4 to 0.2 mm resulted in an increase of plaque stress from 141 to 409 kPa in a 40% degree stenotic artery.

CONCLUSIONS

There is an increase in plaque stress in arteries with a thin fibrous cap. The presence of a moderate carotid stenosis (30% to 70%) with a thin fibrous cap indicates a high risk for plaque rupture. Patients in the future may be risk stratified by measuring both fibrous cap thickness and luminal stenosis.

Desensitization of platelet-derived growth factor receptor-beta by oxidized lipids in vascular cells and atherosclerotic lesions: prevention by aldehyde scavengers

The platelet-derived growth factor receptor-beta (PDGFRbeta) signaling pathway regulates smooth muscle cell (SMC) migration and proliferation and plays a role in the vascular wall response to injury. Oxidized low-density lipoprotein (oxLDL) in atherosclerotic lesions can activate the PDGFRbeta pathway, but the long-term effects of oxLDL on PDGFRbeta function are not well understood. We found that oxLDL induced a dual effect on PDGFRbeta signaling. Initial activation of the PDGFR was followed by desensitization of the receptor. PDGFRbeta desensitization was not attributable to PDGFRbeta degradation or changes in localization to the caveolae but instead resulted from decreased PDGF binding and inhibition of PDGFRbeta tyrosine kinase activity. This inhibition was associated with formation of (4HNE)- and acrolein-PDGFRbeta adducts and was mimicked by preincubation of cells with 4HNE. These PDGFRbeta adducts were also detected in aortae of apolipoprotein-deficient mice and hypercholesterolemic rabbits and in human carotid plaques. The aldehyde scavengers DNPH and Hydralazine prevented both oxLDL- and 4HNE-induced structural modification and PDGFRbeta signaling dysfunction in cells and in vivo. OxLDL inhibition of PDGF signaling may contribute to defective SMC proliferation and decrease the stability of a vulnerable plaque.

Optical coherence tomography for imaging the vulnerable plaque

While our understanding of vulnerable coronary plaque is still at an early stage, the concept that certain types of plaques predispose patients to developing an acute myocardial infarction continues to be at the forefront of cardiology research. Intracoronary optical coherence tomography (OCT) has been developed to both identify and study these lesions due to its distinct resolution advantage over other imaging modalities. We review clinical research conducted at the Massachusetts General Hospital over the past five years to develop, validate, and utilize this technology to improve our understanding of vulnerable plaque. Our results show that intracoronary OCT may be safely conducted in patients and that it provides abundant information regarding plaque microscopic morphology, which is essential to the identification and study of high-risk lesions. Even though many basic biological, clinical, and technological challenges must be addressed prior to widespread use of this technology, the unique capabilities of OCT ensure that it will have a prominent role in shaping the future of cardiology.

Nucleoprotein interactions governing cell type-dependent repression of the mouse smooth muscle alpha-actin promoter by single-stranded DNA-binding proteins Pur alpha and Pur beta

Pur alpha and Pur beta are structurally related single-stranded DNA/RNA-binding proteins implicated in the control of cell growth and differentiation. The goal of this study was to determine whether Pur alpha and Pur beta function in a redundant, distinct, or collaborative manner to suppress smooth muscle alpha-actin gene expression in cell types relevant to wound repair and vascular remodeling. RNA interference-mediated loss-of-function analyses revealed that, although Pur beta was the dominant repressor, the combined action of endogenous Pur alpha and Pur beta was necessary to fully repress the full-length smooth muscle alpha-actin promoter in cultured fibroblasts but to a lesser extent in vascular smooth muscle cells. The activity of a minimal core enhancer containing a truncated 5' Pur repressor binding site was unaffected by knockdown of Pur alpha and/or Pur beta in fibroblasts. Conversely, gain-of-function studies indicated that Pur alpha or Pur beta could each independently repress core smooth muscle alpha-actin enhancer activity albeit in a cell type-dependent fashion. Biochemical analyses indicated that purified recombinant Pur alpha and Pur beta were essentially identical in terms of their binding affinity and specificity for GGN repeat-containing strands of several cis-elements comprising the core enhancer. However, Pur alpha and Pur beta exhibited more distinctive protein interaction profiles when evaluated for binding to enhancer-associated transcription factors in extracts from fibroblasts and vascular smooth muscle cells. These findings support the hypothesis that Pur alpha and Pur beta repress smooth muscle alpha-actin gene transcription by means of DNA strand-selective cis-element binding and cell type-dependent protein-protein interactions.

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

INTRODUCTION

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

METHODS AND RESULTS

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

CONCLUSION

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

TRAIL-expressing T cells induce apoptosis of vascular smooth muscle cells in the atherosclerotic plaque

Acute coronary syndromes (ACS) are precipitated by a rupture of the atherosclerotic plaque, often at the site of T cell and macrophage infiltration. Here, we show that plaque-infiltrating CD4 T cells effectively kill vascular smooth muscle cells (VSMC). VSMCs sensitive to T cell-mediated killing express the death receptor DR5 (TNF-related apoptosis-inducing ligand [TRAIL] receptor 2), and anti-TRAIL and anti-DR5 antibodies block T cell-mediated apoptosis. CD4 T cells that express TRAIL upon stimulation are expanded in patients with ACS and more effectively induce VSMC apoptosis. Adoptive transfer of plaque-derived CD4 T cells into immunodeficient mice that are engrafted with human atherosclerotic plaque results in apoptosis of VSMCs, which was prevented by coadministration of anti-TRAIL antibody. These data identify that the death pathway is triggered by TRAIL-producing CD4 T cells as a direct mechanism of VSMC apoptosis, a process which may lead to plaque destabilization.

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

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

Distance from the ostium as an independent determinant of coronary plaque composition in vivo: an intravascular ultrasound study based radiofrequency data analysis in humans

AIMS

Relative plaque composition, more than its morphology alone, is thought to play a pivotal role in determining propensity to vulnerability. Thus, we investigated in vivo whether the distance from coronary ostium to plaque location independently affects plaque composition in humans. This may help explaining the recently reported non-uniform distribution of culprit lesions along the vessel in acute coronary syndromes.

METHODS AND RESULTS

In 51 consecutive patients (45 men), aged 38-76 years (mean age: 58+/-10), a non-culprit vessel was investigated through spectral analysis of IVUS radiofrequency data (IVUS-Virtual Histology). The study vessel was the left anterior descending artery in 23 (45%) patients; the circumflex artery in nine (18%), and right coronary artery in 19 (37%). The overall length of the region of interest, subsequently divided into 10 mm segments, was 41.5+/-13 mm long (range: 30.2-78.4). No significant change was observed in terms of relative plaque composition along the vessel with respect to fibrous, fibrolipidic, and calcified tissue, whereas the percentage of lipid core resulted to be increased in the first (median: 8.75%; IQR: 5.7-18) vs. the third (median: 6.1%; IQR: 3.2-12) (P=0.036) and fourth (median: 4.5%; IQR: 2.4-7.9) (P=0.006) segment. At multivariable regression analysis, distance from the ostium resulted to be an independent predictor of relative lipid content [beta=-0.28 (95%CI: -0.15, -0.41)], together with older age, unstable presentation, no use of statin, and presence of diabetes mellitus.

CONCLUSION

Plaque distance from the coronary ostium, as an independent determinant of relative lipid content, is potentially associated to plaque vulnerability in humans.

Clinical imaging of the vulnerable plaque in the coronary arteries: new intracoronary diagnostic methods

Rupture of a vulnerable plaque is the main cause of acute coronary syndromes and myocardial infarction. The features of rupture-prone atherosclerotic plaques have been previously described by pathologists. However, identification of vulnerable plaques in vivo is essential to study their natural history and to evaluate potential treatment modalities. Coronary angiography is the gold standard for the diagnosis of coronary artery disease, but it is unable to distinguish between stable and unstable plaques and to accurately predict future cardiac events. This current perspective describes the recently developed invasive imaging techniques to detect atherosclerotic vulnerable plaques in the coronary tree.

In vivo intravascular ultrasound-derived thin-cap fibroatheroma detection using ultrasound radiofrequency data analysis

OBJECTIVES

The purpose of this study was to assess the prevalence of intravascular ultrasound (IVUS)-derived thin-cap fibroatheroma (IDTCFA) and its relationship with the clinical presentation using spectral analysis of IVUS radiofrequency data (IVUS-Virtual Histology [IVUS-VH]).

BACKGROUND

Thin-cap fibroatheroma lesions are the most prevalent substrate of plaque rupture.

METHODS

In 55 patients, a non-culprit, non-obstructive (<50%) lesion was investigated with IVUS-VH. We classified IDTCFA lesions as focal, necrotic core-rich (> or =10% of the cross-sectional area) plaques being in contact with the lumen; IDTCFA definition required a percent atheroma volume (PAV) > or =40%.

RESULTS

Acute coronary syndrome (ACS) (n = 23) patients presented a significantly higher prevalence of IDTCFA than stable (n = 32) patients (3.0 [interquartile range (IQR) 0.0 to 5.0] vs. 1.0 [IQR 0.0 to 2.8], p = 0.018). No relation was found between patient's characteristics such as gender (p = 0.917), diabetes (p = 0.217), smoking (p = 0.904), hypercholesterolemia (p = 0.663), hypertension (p = 0.251), or family history of coronary heart disease (p = 0.136) and the presence of IDTCFA. A clear clustering pattern was seen along the coronaries, with 35 (35.4%), 31 (31.3%), 19 (19.2%), and 14 (14.1%) IDTCFAs in the first 10 mm, 11 to 20 mm, 21 to 30 mm, and > or =31 mm segments, respectively, p = 0.008. Finally, we compared the severity (mean PAV 56.9 +/- 7.4 vs. 54.8 +/- 6.0, p = 0.343) and the composition (mean percent necrotic core 19.7 +/- 4.1 vs. 18.1 +/- 3.0, p = 0.205) of IDTCFAs between stable and ACS patients, and no significant differences were found.

CONCLUSIONS

In this in vivo study, IVUS-VH identified IDTCFA as a more prevalent finding in ACS than in stable angina patients.

Matrix metalloproteinase-13/collagenase-3 deletion promotes collagen accumulation and organization in mouse atherosclerotic plaques

BACKGROUND

Interstitial collagen plays a crucial structural role in arteries. Matrix metalloproteinases (MMPs), including MMP-13/collagenase-3, likely contribute to collagen catabolism in atherosclerotic plaques.

METHODS AND RESULTS

To test the hypothesis that a specific MMP-collagenase influences the development and structure of atherosclerotic plaques, this study used atherosclerosis-susceptible apolipoprotein E-deficient mice that lack MMP-13/collagenase-3 (Mmp-13(-/-)/apoE(-/-)) or express wild-type MMP-13/collagenase-3 (Mmp-13(+/+)/apoE(-/-)). Both groups consumed an atherogenic diet for 5 (n=8) or 10 weeks (n=9). Histological analyses of the aortic root of both groups revealed similar plaque size and accumulation of smooth muscle cells (a collagen-producing cell type) and macrophages (a major source of plaque collagenases) after 5 and 10 weeks of atherogenic diet. By 10 weeks, the plaques of Mmp-13(-/-)/apoE(-/-) mice contained significantly more interstitial collagen than those of Mmp-13(+/+)/apoE(-/-) mice (P<0.01). Furthermore, quantitative optical analyses revealed thinner and less aligned periluminal collagen fibers within the plaques of Mmp-13(+/+)/apoE(-/-) mice versus those from Mmp-13(-/-)/apoE(-/-) mice.

CONCLUSIONS

These data support the hypothesis that MMP-13/collagenase-3 plays a vital role in the regulation and organization of collagen in atherosclerotic plaques.

Localized measurement of optical attenuation coefficients of atherosclerotic plaque constituents by quantitative optical coherence tomography

Optical coherence tomography (OCT) is a novel, high-resolution diagnostic tool that is capable of imaging the arterial wall and plaques. The differentiation between different types of atherosclerotic plaque is based on qualitative differences in gray levels and structural appearance. We hypothesize that a quantitative data analysis of the OCT signal allows measurement of light attenuation by the local tissue components, which can facilitate quantitative spatial discrimination between plaque constituents. High-resolution OCT images (at 800 nm) of human atherosclerotic arterial segments obtained at autopsy were histologically validated. Using a new, simple analysis algorithm, which incorporates the confocal properties of the OCT system, the light attenuation coefficients for these constituents were determined: for diffuse intimal thickening (5.5 +/- 1.2 mm(-1)) and lipid-rich regions (3.2 +/- 1.1 mm(-1)), the attenuation differed significantly from media (9.9 +/- 1.8 mm(-1)), calcifications (11.1 +/- 4.9 mm(-1) ) and thrombi (11.2 +/- 2.3 mm(-1)) (p < 0.01). These proof of principle studies show that simple quantitative analysis of the OCT signals allows spatial determination of the intrinsic optical attenuation coefficient of atherosclerotic tissue components within regions of interest. Combining morphological imaging by OCT with the observed differences in optical attenuation coefficients of the various regions may enhance discrimination between various plaque types.

A Cost-Effectiveness Analysis of a Hypothetical Catheter-Based Strategy for the Detection and Treatment of Vulnerable Coronary Plaques with Drug-Eluting Stents

AIM

Extensive efforts are underway to develop methods for the detection and treatment of vulnerable/high-risk coronary artery plaques. We utilized decision analysis to evaluate the hypothetical clinical benefits and cost-effectiveness of a catheter-based strategy.

METHODS AND RESULTS

Currently, stenotic coronary plaques are treated without regard to vulnerability. In a new strategy, vulnerable coronary plaques are detected with a catheter-based test and treated with a drug-eluting stent, regardless of degree of stenosis. A Markov-decision model was developed to compare the new strategy with current practice. Monte Carlo simulations were performed from a societal perspective, costs were converted to year 2003 U.S. dollars, and future costs and outcomes were discounted at 3%. Sensitivity analyses were performed to evaluate the effect of assumptions on variables such as the prevalence of vulnerable plaques and treatment effect. In 60-year-old male patients with coronary stenoses the new strategy would be less expensive and more effective than current practice (37,045 dollars vs 38,257 dollars and 10.23 vs 9.86 quality-adjusted life years (QALYs), respectively). The benefits of the new strategy were robust in sensitivity analyses (e.g., if the prevalence of vulnerable plaques in this patient group was 50% or more and the sensitivity and specificity of the new test were at least 0.80).

CONCLUSION

In selected patients with coronary artery stenosis, the detection of vulnerable plaques with a catheter-based test followed by their treatment with a drug-eluting stent could be a less expensive and more effective strategy than current practice. If applied to 1 million such patients in the United States undergoing catheterization, the new strategy would add 370,000 QALYs and save 1.2 billion dollars per year.

In vivo temperature heterogeneity is associated with plaque regions of increased MMP-9 activity

AIMS

Plaque rupture has been associated with a high matrix metalloproteinase (MMP) activity. Recently, regional temperature variations have been observed in atherosclerotic plaques in vivo and ascribed to the presence of macrophages. As macrophages are a major source of MMPs, we examined whether regional temperature changes are related to local MMP activity and macrophage accumulation.

METHODS AND RESULTS

Plaques were experimentally induced in rabbit (n=11) aortas, and at the day of sacrifice, a pull-back was performed with a thermography catheter. Hot (n=10), cold (n=10), and reference (n=11) regions were dissected and analysed for smooth muscle cell (SMC), lipids (L), collagen (COL), and macrophage (MPhi) cell densities (%); a vulnerability index (VI) was calculated as VI=MPhi+L/(SMC+COL). In addition, accumulation and activity of MMP-2 and MMP-9 were determined with zymography. Ten hot regions were identified with an average temperature of 0.40+/-0.03 degrees C (P<0.05 vs. reference) and 10 cold regions with 0.07+/-0.03 degrees C (P<0.05 vs. hot). In the hot regions, a higher macrophage density (173%), less SMC density (77%), and a higher VI (100%) were identified. In addition, MMP-9 (673%) activity was increased. A detailed regression analysis revealed that MMP-9 predicted hot regions better than macrophage accumulation alone.

CONCLUSION

In vivo temperature measurements enable to detect plaques that contain more macrophages, less SMCs, and a higher MMP-9 activity.

Methodological considerations and approach to cross-technique comparisons using in vivo coronary plaque characterization based on intravascular ultrasound radiofrequency data analysis: insights from the Integrated Biomarker and Imaging Study (IBIS)

Grey scale intravascular ultrasound (IVUS) is a valuable clinical tool to assess the extent and severity of coronary atheroma. However, it cannot reliably identify plaques with a high-risk of future clinical events. Serial IVUS studies to assess the progression and/or regression of atherosclerotic plaques demonstrated only modest effects, of pharmacological intervention on plaque burden, even when clinical efficacy is documented. Spectral analysis of radiofrequency ultrasound data (IVUS-virtual histology (IVUS-VH), Volcano Therapeutics, Rancho Cordova, CA) has the potential to characterize accurately plaque composition. The Integrated Biomarker and Imaging Study (IBIS) evaluated both invasive and non-invasive imaging techniques along with the assessment of novel biomarkers to characterize sub-clinical atherosclerosis. IVUS-VH was not included at the start of the IBIS protocol. The purpose of this paper is to describe the methodology we used to obtain and analyse IVUS-VH images and the approach to cross-correlations with the other techniques.

Rationale and methods of the integrated biomarker and imaging study (IBIS): combining invasive and non-invasive imaging with biomarkers to detect subclinical atherosclerosis and assess coronary lesion biology

Death or myocardial infarction, the most serious clinical consequences of atherosclerosis, often result from plaque rupture at non-flow limiting lesions. Current diagnostic imaging with coronary angiography only detects large plaques that already impinge on the lumen and cannot accurately identify those that have a propensity to cause unheralded events. Accurate evaluation of the composition or of the biomechanical characteristics of plaques with invasive or non-invasive methods, alone or in conjunction with assessment of circulating biomarkers, could help identify high-risk patients, thus providing the rationale for aggressive treatments in order to reduce future clinical events. The IBIS (Integrated Biomarker and Imaging Study) study is a prospective, single-center, non-randomized, observational study conducted in Rotterdam. The aim of the IBIS study is to evaluate both invasive (quantitative coronary angiography, intravascular ultrasound (IVUS) and palpography) and non-invasive (multislice spiral computed tomography) imaging techniques to characterize non-flow limiting coronary lesions. In addition, multiple classical and novel biomarkers will be measured and their levels correlated with the results of the different imaging techniques. A minimum of 85 patients up to a maximum of 120 patients will be included. This paper describes the study protocol and methodological solutions that have been devised for the purpose of comparisons among several imaging modalities. It outlines the analyses that will be performed to compare invasive and non-invasive imaging techniques in conjunction with multiple biomarkers to characterize non-flow limiting subclinical coronary lesions.

Altered expression balance of matrix metalloproteinases and their inhibitors in human carotid plaque disruption: results of quantitative tissue analysis using real-time RT-PCR method

BACKGROUND

The balance between degradation and synthesis of extracellular matrix determines its content in atherosclerotic tissue. To examine the role of expression balance of matrix metalloproteinases (MMPs) to their inhibitors, tissue inhibitors of metalloproteinases (TIMPs) and tissue factor pathway inhibitor-2 (TFPI-2) in the development and disruption of atherosclerotic plaque, these gene expressions in human carotid plaque were quantitatively determined by real-time reverse transcription (RT)-polymerase chain reaction (PCR) method.

METHODS

Total RNA for cDNA synthesis was extracted from tissues in 24 patients with carotid endarterectomy. The amounts of cDNAs for MMP-1, -2, -3 and -9, TFPI-2 and TIMP-1, -2 and -3 were determined by real-time RT-PCR method, and normalized with glutaraldehyde 3-dehydrogenase.

RESULTS

In plaques, the expression MMP-1 (1.53+/-0.25, mean+/-S.E.M.), MMP-3 (1.99+/-0.59) and MMP-9 (2.00+/-0.51) was augmented compared to those in the adjacent control regions (0.60+/-0.16, 0.46+/-0.18 and 0.58+/-0.21, respectively, p<0.05). The expression of TFPI-2 was lower in plaques (0.32+/-0.08) than in controls (0.94+/-0.23, p<0.01). Although the expression of TIMP-1 was higher in plaques (1.28+/-0.23) than in controls (0.81+/-0.10, p<0.05), the indices of MMP-1/TIMP-1, MMP-3/TIMP-3 and MMP-9/TIMP-1 were still significantly higher in plaques. Interestingly, MMP-9 and the resulting MMP-9/TIMP-1 balance in plaques with disruption were significantly higher (3.36+/-1.52 and 1.66+/-0.12, n=11) than those in non-disrupted plaques (1.11+/-0.52 and 0.76+/-0.12, n=13, p<0.05).

CONCLUSION

With the decreased expression of TFPI-2, upregulation of MMPs in atherosclerotic plaque was disproportional to that of TIMPs, suggesting that imbalanced degradation and synthesis of extracellular matrix persists in advanced lesions, particularly in plaques with disruption.

Atherosclerotic plaque progression and vulnerability to rupture: angiogenesis as a source of intraplaque hemorrhage

Observational studies of necrotic core progression identify intraplaque hemorrhage as a critical factor in atherosclerotic plaque growth and destabilization. The rapid accumulation of erythrocyte membranes causes an abrupt change in plaque substrate characterized by increased free cholesterol within the lipid core and excessive macrophage infiltration. Neoangiogenesis is associated closely with plaque progression, and microvascular incompetence is a likely source of intraplaque hemorrhage. Intimal neovascularization is predominantly thought to arise from the adventitia, where there are a plethora of pre-existing vasa vasorum. In lesions that have early necrotic cores, the majority of vessels invading from the adventitia occur at specific sites of medial wall disruption. A breech in the medial wall likely facilitates the rapid in-growth of microvessels from the adventitia, and exposure to an atherosclerotic environment stimulates abnormal vascular development characterized by disorganized branching and immature endothelial tubes with "leaky" imperfect linings. This network of immature blood vessels is a viable source of intraplaque hemorrhage providing erythrocyte-derived phospholipids and free cholesterol. The rapid change in plaque substrate caused by the excessive accumulation of erythrocytes may promote the transition from a stable to an unstable lesion. This review discusses the potential role of intraplaque vasa vasorum in lesion instability as it relates to plaque rupture.

Quantitative optical coherence tomography of arterial wall components

Optical coherence tomography (OCT) can be used to visualize the arterial wall and atherosclerotic plaques with high resolution. In this study, we verified the application of OCT to the quantitative analysis of plaque structural dimensions and optical attenuation coefficients of the components. We assessed the effect of balloon dilation on the OCT signal from the medial layer of porcine carotid artery ex vivo. Imaging of human autopsy samples was performed from the luminal side with a high (3.5 microm axial and 7 microm lateral) resolution OCT system (approximately 800 nm) or a regular (15-20 microm axial and 20 microm lateral resolution) OCT system (approximately 1,300 nm). For each sample, dimensions were measured by histomorphometry and OCT, and the optical attenuation was measured. In a tissue culture set-up, porcine carotid arteries were dilated and the attenuation coefficients of the dilated segments were compared to a control segment for 4 h. Quantitative analysis showed a strong and significant correlation between OCT and histology cap thickness measurements for both OCT systems. For both systems, the measured attenuation coefficients for diffuse intimal thickening and lipid-rich regions differed significantly from that of calcified tissue. Balloon dilation induced a time-dependent increase in the attenuation coefficient, which may be attributed to the induction of apoptosis. In conclusion both the high and regular resolution OCT systems can image the atherosclerotic plaques precisely. Quantitative analysis of the OCT signals allowed in situ determination of the intrinsic optical attenuation coefficient for atherosclerotic tissue components within regions of interest, which can help to discriminate between plaque and arterial wall components.

Noninvasive in vivo measurement of vascular inflammation with F-18 fluorodeoxyglucose positron emission tomography

BACKGROUND

Fluorine 18 fluorodeoxyglucose (FDG) has been shown to accumulate in inflamed tissues. However, it is not known whether vascular inflammation can be measured noninvasively. The aim of this study was to test the hypothesis that vascular inflammation can be measured noninvasively by use of positron emission tomography (PET) with FDG.

METHODS AND RESULTS

Inflamed atherosclerotic lesions were induced in 9 male New Zealand white rabbits via balloon injury of the aortoiliac arterial segment and exposure to a high cholesterol diet. Ten rabbits fed standard chow served as controls. Three to six months after balloon injury, the rabbits were injected with FDG (1 mCi/kg), after which aortic uptake of FDG was assessed (3 hours after injection). Biodistribution of FDG activity within aortic segments was obtained by use of standard well gamma counting. FDG uptake was also determined noninvasively in a subset of 6 live atherosclerotic rabbits and 5 normal rabbits, via PET imaging and measurement of standardized uptake values over the abdominal aorta. Plaque macrophage density and smooth muscle cell density were determined by planimetric analysis of RAM-11 and smooth muscle actin staining, respectively. Biodistribution of FDG within nontarget organs was similar between atherosclerotic and control rabbits. However, well counter measurements of FDG uptake were significantly higher within atherosclerotic aortas compared with control aortas (P < .001). Within the upper abdominal aorta of the atherosclerotic group (area of greatest plaque formation), there was an approximately 19-fold increase in FDG uptake compared with controls (108.9 +/- 55.6 percent injected dose [%ID]/g x 10(3) vs 5.7 +/- 1.2 %ID/g x 10(3) [mean +/- SEM], P < .001). In parallel with these findings, FDG uptake, as determined by PET, was higher in atherosclerotic aortas (standardized uptake value for atherosclerotic aortas vs control aortas, 0.68 +/- 0.06 vs 0.13 +/- 0.01; P < .001). Moreover, macrophage density, assessed histologically, correlated with noninvasive (PET) measurements of FDG uptake (r = 0.93, P < .0001). In contrast to this finding, FDG uptake did not correlate with either aortic wall thickness or smooth muscle cell staining of the specimens.

CONCLUSION

These data show that FDG accumulates in macrophage-rich atherosclerotic plaques and demonstrate that vascular macrophage activity can be quantified noninvasively with FDG-PET. As such, measurement of vascular FDG uptake with PET holds promise for the noninvasive characterization of vascular inflammation.

Cell Cycle-mediated Regulation of Smooth Muscle α-Actin Gene Transcription in Fibroblasts and Vascular Smooth Muscle Cells Involves Multiple Adenovirus E1A-interacting Cofactors

Expression of smooth muscle alpha-actin in growth factor-induced myofibroblasts and in differentiated vascular smooth muscle cells is transcriptionally controlled by multiple positive or negative trans-acting factors interacting with distinct cis-elements in the 5'-flanking region of the gene. Because none of the transcriptional regulators reported to date is smooth muscle cell- or myofibroblast-specific per se, the dynamic interplay among many factors interacting at specific sites along the promoter appears to be a signature feature of smooth muscle alpha-actin gene regulation in these cell types. Herein, the ability of the adenovirus E1A 12 S protein to bind and functionally inactivate specific cell regulatory factors has been exploited to identify several previously unknown coactivators of the mouse smooth muscle alpha-actin promoter in rodent fibroblasts and vascular smooth muscle cells. In transient cotransfection assays, ectopic expression of wild type E1A suppressed promoter activity in a dose- and cis-element-dependent manner. In asynchronous cells, N-terminal E1A mutants defective in CREB-binding protein (CBP) and p300 binding capacity exhibited markedly reduced inhibitory activity toward a smooth muscle alpha-actin promoter driven by a composite TEF-1-, SRF-, and Sp1/3-regulated enhancer. In synchronized cells, however, a more complex mutant E1A inhibitory pattern indicated that collaboration between CBP/p300 and the retinoblastoma family of pocket proteins was required to produce a fully functional enhancer. Cotransfection experiments conducted with Rb(-/-) fibroblasts demonstrated the necessity of pRB in augmenting smooth muscle alpha-actin enhancer/promoter activity. Physical interaction studies with the use of purified wild type and mutant E1A proteins confirmed that CBP, p300, and pRB were targets of E1A binding in nuclear extracts of vascular smooth muscle cells and/or fibroblasts. Collectively, these results suggest that a repertoire of E1A-interacting proteins, namely CBP/p300 and pRB, serve to integrate the activities of multiple trans-acting factors to control smooth muscle alpha-actin gene transcription in a cell type- and cell cycle-dependent manner.

Visualising noncalcified coronary plaques by CT

Due to a rapid improvement of the new generation submillimetre multislice CT-technology noninvasive tomographic imaging of the coronary vessel wall has become reality. First clinical studies have shown the ability in particular of 16-slice CT to determine plaque burden, plaque composition and compensatory vessel-wall remodelling. These novel findings already constitute an important step forward to assess coronary atherosclerosis noninvasively in a detailed manner which opens promising new opportunities for a better understanding and riskstratification of coronary atherosclerosis. Current limitations, mainly the insufficient accuracy to detect small lesions in distal coronary segments, might be overcome by improved spatial and temporal resolution of the new generation scanners operating with 64 and more detectors.

Terrein: a new melanogenesis inhibitor and its mechanism

Terrein is a bioactive fungal metabolite whose effects are almost unknown. In this study, we found for the first time that terrein has a strong hypopigmentary effect in a spontaneously immortalized mouse melanocyte cell line, Mel-Ab. Treatment of Mel-Ab cells with terrein (10-100 microM) for 4 days significantly reduced melanin levels in a dose-dependent manner. In addition, terrein at the same concentration also reduced tyrosinase activity. We then investigated whether terrein influences the extracellular signal-regulated protein kinase (ERK) pathway and the expression of microphthalmia-associated transcription factor (MITF), which is required for tyrosinase expression. Terrein was found to induce sustained ERK activation and MITF down-regulation, and luciferase assays showed that terrein inhibits MITF promoter activity in a dose-dependent manner. To elucidate the correlation between ERK pathway activation and a decreased MITF transcriptional level, PD98059, a specific inhibitor of the ERK pathway, was applied before terrein treatment and found to abrogate the terrein-induced MITF attenuation. Terrein also reduced the tyrosinase protein level for at least 72 h. These results suggest that terrein reduces melanin synthesis by reducing tyrosinase production via ERK activation, and that this is followed by MITF down-regulation.

"Vulnerable plaques" — ticking of the time bomb

Atherosclerosis and its sequelae are one of the leading causes of morbidity and mortality, especially in the developed nations. Over the years, treatment protocols have changed with the changing understanding of the disease process. Inflammatory mechanisms have emerged as key players in the formation of the atherosclerotic plaque. For the majority of its life span, the plaque develops silently and only some exhibit overt clinical manifestations. The purpose of this review is to examine the inherent properties of some of these "vulnerable" or symptomatic plaques. Rupture of the plaque is related to the thickness of the fibrous cap overlying the necrotic lipid core. A thin cap is more likely to lead to rupture. Multiple factors broadly grouped as the "determinants of vulnerability" are responsible for directly or indirectly influencing the plaque dynamics. Apoptosis is considered an important underlying mechanism that contributes to plaque instability. Inflammatory reactions within the plaque trigger apoptosis by cell–cell contact and intra cellular death signaling. Once started, the apoptotic process affects all of the components that make up the plaque, including vascular smooth muscle cells, endothelial cells, and macrophages. Extensive research has identified many of the key cellular and molecular regulators that play a part in apoptosis within the atherosclerotic lesion. This information will help us to gain a better understanding of the underlying mechanisms at the cellular and molecular level and enable us to formulate better therapeutic strategies to combat this disease.Key words: apoptosis, atherosclerosis, inflammation, plaque stability, vulnerable plaques.

CT of coronary artery disease

The socioeconomic importance of heart disease provides considerable motivation for development of radiologic tools for noninvasive imaging of the coronary arteries. Current computed tomographic (CT) techniques combine high speed and spatial resolution with sophisticated electrocardiographic synchronization and robustness of use. Application of these modalities for evaluation of coronary artery disease is a topic of active current research. Coronary artery calcium measurements with different CT techniques have been used for determining the risk of coronary events, but the exact role of this marker for cardiac risk stratification remains unclear pending results of population-based studies. Contrast material-enhanced CT coronary angiography has become an established clinical indication for some scenarios (eg, coronary artery anomalies, bypass patency, surgical planning). With current technology, the accuracy of CT coronary angiography for detection of coronary artery stenoses appears promising enough to warrant pursuit of this application, but sensitivity is still not high enough for routine diagnostic needs. The high negative predictive value of a normal CT coronary angiogram, however, may be useful for reliable exclusion of coronary artery stenosis. The cross-sectional nature of CT may allow noninvasive assessment of the coronary artery wall. Use of contrast-enhanced CT coronary angiography for detection, characterization, and quantification of atherosclerotic changes and total disease burden in coronary arteries as a potential tool for cardiac risk stratification is currently being investigated.

Coronary artery spatial distribution of acute myocardial infarction occlusions

BACKGROUND

Acute coronary occlusions leading to ST-segment elevation myocardial infarctions (STEMIs) are due primarily to rupture of atherosclerotic plaques. Present "vulnerable plaque" detection technology focuses on identifying individual plaques with no clear therapeutic plan beyond conventional risk factor reduction. We developed a spatial map of the distribution of acute coronary occlusions to test our hypothesis that plaque ruptures do not occur uniformly throughout the coronary tree.

METHODS AND RESULTS

We analyzed 208 consecutive patients who presented to the Brigham and Women's Hospital with STEMI and mapped the location of the acute coronary occlusion. These occlusions were not uniformly distributed throughout each of the major epicardial coronary arteries but tended to cluster within the proximal third of each of the vessels (right coronary artery, P=0.001; left anterior descending artery, P=0.003; left circumflex artery, P=0.001). Furthermore, Poisson regression showed that for each 10-mm increase in distance from the ostium, the risk of an acute coronary occlusion was significantly decreased by 13% in the right coronary artery, 30% in the left anterior descending artery, and 26% in the left circumflex artery.

CONCLUSIONS

Acute coronary occlusions leading to STEMI tend to cluster in predictable "hot spots" within the proximal third of the coronary arteries. Identification of these high-risk zones for acute coronary occlusions will lead to future advances in vulnerable plaque detection technology and potentially locally directed preventive strategies.

Participation of macrophages in atherosclerotic lesion morphology in LDLr-/- mice

Lystbeige (beige) mice crossed with LDL receptor-deficient (LDLr-/-) mice had a distinct atherosclerotic lesion morphology that was not observed in LDLr-/- mice. This morphology is often associated with a stable plaque phenotype. We hypothesized that macrophage expression of the beige mutation accounted for this distinct morphology. Cultured bone marrow-derived macrophages from LDLr-/- and beige,LDLr-/- mice were compared for their ability to accumulate cholesterol, efflux cholesterol, migrate in response to chemotactic stimuli through Matrigel-coated membranes, and express matrix metalloproteinase 9 (MMP9). No differences in cholesterol metabolism were identified. Beige,LDLr-/- macrophage invasion in vitro appeared to be less than LDLr-/- macrophage invasion but did not achieve significance. Nevertheless, tumor necrosis factor-alpha-induced MMP9 expression, secretion, and enzymatic activity of beige,LDLr-/- macrophages were all significantly decreased compared with those of LDLr-/- macrophages (P < 0.05). For in vivo analyses of macrophage function, bone marrow transplantation (BMT) studies were performed. LDLr-/- mice and beige,LDLr-/- mice were irradiated and reconstituted with wild-type or beige bone marrow from mice expressing green fluorescent protein (GFP). Identification of GFP cells provided for direct identification of donor-derived cells within lesions. Only expression of the beige mutation in the BMT recipients altered the macrophage location and collagen content of the lesions. These results suggested that impaired macrophage function by itself did not account for the stable lesion morphology of beige,LDLr-/- double-mutant mice.

Enhanced P2X7 activity in human fibroblasts from diabetic patients: a possible pathogenetic mechanism for vascular damage in diabetes

OBJECTIVE

We have investigated expression and function of the P2X7 receptor in fibroblasts from healthy subjects and patients with type 2 diabetes.

METHODS AND RESULTS

Fibroblasts were isolated from skin biopsies. P2X7 receptor expression in both cell populations was measured by functional assays, RT-PCR, fluorescence-activated cell sorter, and immunoblotting. We found that fibroblasts from diabetic subjects are characterized by enhanced P2X7-mediated responses as indicated by increased shape changes, microvesiculation, enhanced fibronectin and interleukin 6 secretion, and accelerated apoptosis. These responses were blocked by preincubation with the P2X blockers KN-62, oxidized ATP, or pyridoxal phosphate-6-azo(benzene-2,4-disulfonic acid). Furthermore, we also found a higher level of spontaneous fibronectin secretion and of apoptosis in fibroblasts from diabetic compared with healthy subjects. Both higher basal level of fibronectin secretion and spontaneous rate of apoptosis were likely attributable to the increased pericellular concentration of ATP because fibroblasts from diabetic subjects released 3x as much ATP into the supernatants compared with fibroblasts from healthy subjects.

CONCLUSIONS

We conclude that fibroblasts from type 2 diabetes patients are characterized by a hyperactive purinergic loop based either on a higher level of ATP release or on increased P2X7 reactivity.

Development of radiocontrast agents for vascular imaging: progress to date

The revolution in molecular imaging techniques is profoundly changing the understanding of the pathophysiology and treatment of atherosclerosis. With these rapid changes there is an increasing demand for development of sensitive and well tolerated novel imaging agents that can be rapidly translated from small animal models into patients with atherosclerosis. Nuclear medicine and positron emission tomography techniques have the ability to detect and serially monitor a variety of biologic and pathophysiologic processes usually with tracer quantities of radiolabeled peptides, drugs, and other molecules at dosages free of pharmacologic adverse effects unlike the current generation of intravenous agents required for magnetic resonance imaging (MRI) and computed axial tomography (CT) scanning. A representative sampling of the wide array of radiopharmaceuticals developed specifically for radionuclide imaging of atherosclerosis, that have been approved for clinical use and those in pre-clinical trials, have been reviewed in this article. The presence of an inflammatory stimulus increases expression of CC (cysteine-cysteine motif) chemokine receptor (CCR)-2 on monocytes and macrophages, and somatostatin receptors on T lymphocytes. Radiolabeled monocyte chemoattractant protein (MCP)-1 binds with high affinity to CCR-2 and can be used to detect subacute and chronic inflammatory lesions. Similarly, radiolabeled octreotide or depreotide can be used to detect activated T lymphocytes which may identify the vulnerable plaque. Animal models indicate that (99m)Tc-annexin V, (125)I-MCP-1 and [(18)F]-fluoro-2-deoxyglucose are effective in identifying apoptotic cell death, macrophage infiltration and metabolic activity in atheromatous lesions, respectively. Expression of alpha(v)beta(3) integrin is increased in activated endothelial cells and vascular smooth muscle cells after vascular injury, and alpha(v)beta(3) integrin is minimally expressed on smooth muscle cells and is not expressed on quiescent epithelial cells. Radiolabeled high-affinity peptides can be used to target the alpha(v)beta(3) integrin and visualize areas of vascular damage. Advances in technology such as the micro-single photon emission computed tomography (microSPECT) have the potential to overcome the drawbacks of older CT and MRI methodologies, such as lack of biologically relevant ligands and compatible blood pool contrast agents for imaging. Despite these advances in imaging technology, the small size of atheromatous lesions makes it difficult to detect using external imaging techniques. Therefore, recently there has been renewed interest in the use of intravascular catheter-based radiation detectors.

Accuracy of multidetector spiral computed tomography in identifying and differentiating the composition of coronary atherosclerotic plaques

OBJECTIVES

We evaluated the accuracy of contrast-enhanced multidetector spiral computed tomography (MDCT) for the noninvasive detection and classification of coronary plaques and compared it with intracoronary ultrasound (ICUS).

BACKGROUND

Noninvasive determination of plaque composition and plaque burden may be important to improve risk stratification and to monitor progression of coronary atherosclerosis.

METHODS

We included 46 consecutive patients with a distinctive risk profile, who were investigated by ICUS (Goldvision, 20 MHz, Jomed Inc., Rancho Cordova, California). Due to the inability to slow the heart rate below 65 beats/min (n = 7) and due to renal insufficiency (n = 2), nine of 46 consecutive patients could not be studied by MDCT (Sensation 16, Siemens, Forchheim, Germany).

RESULTS

In the remaining 37 patients, 68 vessels were investigated by ICUS, and 58 of these vessels were visualized by MDCT with image quality sufficient for analysis. In these vessels that were divided in 3-mm sections, MDCT correctly classified 62 of 80 (78%) sections containing hypoechoic plaque areas, 87 of 112 (78%) sections containing hyperechoic plaque areas, and 150 of 158 (95%) sections containing calcified plaque tissue. In 484 of 525 (92%) sections, atherosclerotic lesions were correctly excluded. The MDCT-derived density measurements within coronary lesions revealed significantly different values for hypoechoic (49 HU [Hounsfield Units] +/- 22), hyperechoic (91 HU +/- 22), and calcified plaques (391 HU +/- 156, p < 0.02).

CONCLUSIONS

This study demonstrates that, in the case of diagnostic image quality, contrast-enhanced MDCT permits an accurate identification of coronary plaques and that computed tomography density values measured within plaques reflect echogenity and plaque composition.

From vulnerable plaque to vulnerable patient: a call for new definitions and risk assessment strategies: Part I

Atherosclerotic cardiovascular disease results in >19 million deaths annually, and coronary heart disease accounts for the majority of this toll. Despite major advances in treatment of coronary heart disease patients, a large number of victims of the disease who are apparently healthy die suddenly without prior symptoms. Available screening and diagnostic methods are insufficient to identify the victims before the event occurs. The recognition of the role of the vulnerable plaque has opened new avenues of opportunity in the field of cardiovascular medicine. This consensus document concludes the following. (1) Rupture-prone plaques are not the only vulnerable plaques. All types of atherosclerotic plaques with high likelihood of thrombotic complications and rapid progression should be considered as vulnerable plaques. We propose a classification for clinical as well as pathological evaluation of vulnerable plaques. (2) Vulnerable plaques are not the only culprit factors for the development of acute coronary syndromes, myocardial infarction, and sudden cardiac death. Vulnerable blood (prone to thrombosis) and vulnerable myocardium (prone to fatal arrhythmia) play an important role in the outcome. Therefore, the term "vulnerable patient" may be more appropriate and is proposed now for the identification of subjects with high likelihood of developing cardiac events in the near future. (3) A quantitative method for cumulative risk assessment of vulnerable patients needs to be developed that may include variables based on plaque, blood, and myocardial vulnerability. In Part I of this consensus document, we cover the new definition of vulnerable plaque and its relationship with vulnerable patients. Part II of this consensus document focuses on vulnerable blood and vulnerable myocardium and provide an outline of overall risk assessment of vulnerable patients. Parts I and II are meant to provide a general consensus and overviews the new field of vulnerable patient. Recently developed assays (eg, C-reactive protein), imaging techniques (eg, CT and MRI), noninvasive electrophysiological tests (for vulnerable myocardium), and emerging catheters (to localize and characterize vulnerable plaque) in combination with future genomic and proteomic techniques will guide us in the search for vulnerable patients. It will also lead to the development and deployment of new therapies and ultimately to reduce the incidence of acute coronary syndromes and sudden cardiac death. We encourage healthcare policy makers to promote translational research for screening and treatment of vulnerable patients.

Towards understanding acute destabilization of vulnerable atherosclerotic plaques

BACKGROUND

The current wisdom is that destabilization of human atheromatous fibroinflammatory plaques may result in thrombosis and is responsible for most acute ischemic syndromes. This paradigm has led to vigorous research to understand the pathogenesis of plaque vulnerability and subsequent rupture, to find reliable systemic serological markers and to identify imaging techniques in order to determine vulnerability of individual plaques.

METHODS

Research examining the pathobiology of the vulnerable plaque and its subsequent destabilization is described. Investigations are based on the current understanding of vascular cell and molecular biology and clinical paradigms of acute coronary syndromes.

RESULTS

It is apparent that there are three steps that need to be considered. These are transformation of a stable plaque into a vulnerable plaque, destabilization of a vulnerable plaque and regulation of the complications following destabilization, the most serious being acute occlusive thrombosis. In vitro cell and molecular vascular biology studies, and animal model studies that alter specific gene(s) expression, have provided new knowledge on putative mechanisms leading to plaque vulnerability and on subsequent destabilization of the plaque. These studies show that several local and systemic factors, including inflammation, matrix disruption, lipid deposition, cell necrosis and apoptosis are likely to play a role in vulnerability, destabilization and clinical syndromes.

CONCLUSION

Plaque vulnerability and destabilization is of multifactoral etiology with inflammation, cap matrix and necrotic lipid core remodeling being important pathobiological processes associated with vulnerability and destabilization. Identifying gene-environment interactions, improving imaging techniques and improving our understanding of the mechanisms underlining plaque pathogenesis via animal models are essential elements for understanding human plaque vulnerability and destabilization.

Pathology of the thin-cap fibroatheroma: a type of vulnerable plaque

Thin cap atheroma is the precursor of plaque rupture, which accounts for a majority of coronary thrombi. The morphologic features of thin cap atheromas that predict rupture are unknown, but we know from studies of ruptured plaques that large necrotic cores, fibrous cap < 65 microns and numerous macrophages within the cap likely indicate instability. There is some evidence that a speckled pattern of calcification is associated with vulnerability to rupture. There are usually multiple thin cap atheroma in the hearts of patients dying with acute plaque rupture, as well as multiple fibroatheromas with intraplaque hemorrhage. Targeted therapy for the purpose of stabilizing coronary lesions that are prone to rupture is a major future goal of the interventionist.

Detecting vulnerable plaque using peripheral blood: inflammatory and cellular markers

The concept of the vulnerable patient has arrived. Enhanced diagnostic methods will eventually permit accurately finding and treating these patients and their disease. Clinical Cardiologists now recognize that coronary atherosclerosis is two pathophysiologically distinct syndromes: stable and unstable. Stable coronary syndromes result from fixed, severe stenoses limiting blood flow and causing secondary myocardial ischemia. The unstable acute coronary syndromes are frequently catastrophic and are pathophysiologically distinct. They result from different cell subsets causing vascular inflammatory syndromes rather than gradual lumen constriction by plaque. Though pathophysiologically distinct, they may show common pathophysiology when a ruptured plaque heals and progressively becomes a critical stenosis. For the present hs-CRP measurement is the strongest correlative factor for future clinical events due to arterial inflammation: myocardial infarction, unstable angina, stroke, and peripheral vascular disease in both diseased and apparently healthy, asymptomatic patients. The CRP plasma level also is the best risk assessment in patients with either stable or unstable angina, long term after myocardial infarction, and in patients undergoing revascularization therapies. One study showed the only independent cardiovascular risk indicators using multivariate, age adjusted and traditional risk analysis were CRP and Total/HDL cholesterol ratio. If CRP, IL-6, and ICAM-1 levels are added to lipid levels, risk assessment can be improved over lipids alone. The prevalence of high-risk subjects in the general population is low, amplifying diagnostic problems for vulnerable plaque. Since no test yet has high sensitivity or specificity, diagnostic errors are high, with many false positives and negatives. Sensitivity or specificity must be increased by developing a risk marker panel, or by simultaneously finding other markers that themselves are highly sensitive and specific for vulnerable plaque.

Vascular MRI in the diagnosis and therapy of the high risk atherosclerotic plaque

Disruption of a high risk plaque is known as the primary cause of cardiovascular events. Characterization of arterial wall components has become an essential adjunct in the identification of patients with plaques prone to rupture. Magnetic Resonance Imaging (MRI) has been revealed as one of the noninvasive tools possibly capable of identifying and characterizing high risk atherosclerotic plaque. MRI may facilitate diagnosis, and guide and serially monitor interventional and pharmacological treatment of atherosclerotic disease. In addition, it permits the simultaneous assessment of the anatomy, morphology, and hemodynamics for the study of flow-induced atherogenesis. It possibly will identify asymptomatic patients with subclinical atherosclerosis. This has potential significance for the improvement of strategies in primary and secondary prevention.

Coronary calcification compared in patients with acute versus in those with chronic coronary events by using dual-sector spiral CT

PURPOSE

To compare underlying calcific atherosclerotic lesions in acute versus chronic coronary events in patients with hypertension by using dual-sector spiral computed tomography (CT).

MATERIALS AND METHODS

Eight hundred eighty-four calcific lesions were analyzed in a cohort of 50 patients (39 men, 11 women; age range, 55-79 years; mean age, 66 years +/- 6 [SD]) with hypertension who sustained a coronary event during 3-year follow-up. All underwent dual-sector spiral CT within 12 months before the event. Twenty-nine patients had an acute event (acute group): acute myocardial infarction, 20; unstable angina pectoris, six; acute ischemia, two; sudden death, one. Twenty-one patients had chronic manifestations of obstructive coronary disease (chronic group): severe stable angina, five; angiographically identified disease, 12; disease requiring angioplasty, two; and disease requiring bypass surgery, two. To examine differences between the two study groups, the chi(2) or Fisher exact test was applied to categorical parameters and the two-sample t test or Wilcoxon rank sum test to quantitative parameters.

RESULTS

High prevalence of coronary calcium (total coronary calcium score [TCS] >0) was observed in both groups: 93% (27 of 29) in the acute and 95% (20 of 21) in the chronic group. There were 518 lesions in the chronic and 366 in the acute group, with a median number of 35 and nine lesions per patient, respectively (P <.001). The median TCS was 906 for the chronic and 63 for the acute group (P <.01).

CONCLUSION

A mild degree of calcification characterizes patients with acute coronary events, while diffuse high-attenuation calcific plaques are associated with chronic coronary events.