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

The role of optical coherence tomography in vascular medicine

Optical coherence tomography (OCT) is an emerging imaging modality that provides high-resolution, microstructural information on atherosclerotic plaques in biological systems. Intracoronary OCT can identify thin-cap fibroatheroma and other vulnerable plaques that may be responsible for acute coronary events. These characteristics make OCT helpful in guiding coronary management and interventions, including stent apposition and early identification of procedure-related complications. OCT is being assessed for its potential role in carotid plaque characterization and in the diagnosis of peripheral arterial atherosclerosis. Its current use in studying carotid and cerebral vasculature and in the diagnosis of peripheral arterial diseases is limited and ill defined, but it is finding increasing application in these areas. Its performance can be further improved by increasing the signal to noise ratio and by using dynamic focus tracking techniques. It can potentially be used to monitor the progression and regression of atherosclerosis in the coronary, cerebral and peripheral vasculature. New indications for its use in vascular medicine are emerging as its technology continues to improve over time.

Quantification and characterization of obstructive coronary plaques using 64-slice computed tomography: a comparison with intravascular ultrasound

PURPOSE

The aim of this study was to determine the diagnostic accuracy of 64-slice computed tomography (CT) coronary angiography in the quantification and characterization of obstructive coronary plaques in comparison with intravascular ultrasound (IVUS).

MATERIALS AND METHODS

Thirty-nine patients were selected who underwent both CT coronary angiography (CTCA) and IVUS. For each stenotic site (n = 61), the maximum vessel cross-sectional area, lumen cross-sectional area, plaque area, and percentage of luminal obstruction were measured. Plaque composition was analyzed according to IVUS (plaque echogenicity and classified into several types: calcified, mixed, fibrous, and soft plaques) and CTCA criteria (Hounsfield units [HU]). The correlation between CTCA and IVUS measurements was determined using Pearson correlation coefficient. The statistical significance of differences in the CT densities of plaques among plaque types determined by IVUS was assessed using the Scheffe method.

RESULTS

The correlation coefficients for the measurements of the lumen, vessel, plaque area, and percentage of luminal obstruction were r = 0.712, r = 0.654, r = 0.753, and r = 0.799, respectively. The mean CT density values for soft (n = 10), fibrous (n = 11), mixed (n = 31), and calcified plaques (n = 9) were 54 +/- 13 HU, 82 +/- 17 HU, 162 +/- 57 HU, and 392 +/- 155 HU, respectively. Computed tomography density measurements were not significantly different between soft and fibrous plaques (P = 0.224).

CONCLUSIONS

Sixty-four-slice CTCA is a noninvasive modality that allows quantification of coronary artery plaques. However, reliable classification of noncalcified plaques as vulnerable or stable plaques based on CT density measurements is currently limited.

Non-invasive assessment of vulnerable plaque

BACKGROUND

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

OBJECTIVE

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

METHODS

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

CONCLUSION

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

Estimation of the transverse strain tensor in the arterial wall using IVUS image registration

Intravascular ultrasound (IVUS) elastography is an imaging technique that obtains the local mechanical properties of the artery wall and atherosclerotic plaques through strain measurements using IVUS. Knowledge of these mechanical properties may provide crucial information that can help in estimating plaque composition and its vulnerability. Here, we present a new method to estimate the transverse strain tensor of the arterial wall based on nonrigid image registration using IVUS images. This method registers a pair of images acquired at a vessel site under different levels of luminal pressure. The 2-D displacement field in the vessel cross-section is estimated from image registration; then the displacement field is used to calculate the 2-D local strain tensor. From the strain tensor, the strain in any direction in the cross-section can be obtained; here, the radial and circumferential strain distributions are presented. This strain estimation method has been validated with synthetic motion IVUS images and evaluated using the IVUS images of a polyvinyl alcohol cryogel phantom. The accuracy of the estimated strain and the ability of the method to overcome IVUS system noise are demonstrated.

A new method for assessment of plaque vulnerability based on vasa vasorum imaging, by using contrast-enhanced intravascular ultrasound and differential image analysis

BACKGROUND

Increased neovascularization in vasa vasorum and atherosclerotic plaques has recently been identified as a common feature of inflammation and plaque vulnerability. Microbubble contrast agents, which have been used for intravascular imaging, can be used to trace neovascularization. The aim of the study was to detect and evaluate the density of vasa vasorum in non-culprit coronary atherosclerotic plaques of patients with acute coronary syndrome.

METHODS

We have studied intravascular ultrasound (IVUS) signals before, during, and after intracoronary injection of microbubbles, proximal to non-culprit atherosclerotic plaques in 16 patients with acute coronary syndrome. Analyses were accomplished using a computational algorithm for the detection of contrast perfusion in such contrast-enhanced sequences. Perfusion density was evaluated by the mean enhancement in the region of interest provided by this difference-imaging technique.

RESULTS

Qualitative and quantitative analysis of the pre- and post-injection images showed a significant enhancement in the grey-scale intensity of intima-media and adventitia after injection (intima-media: from 6.0+/-2.5 to 7.9+/-3.3%, p=0.006 and adventitia: from 7.1+/-2.2 to 7.6+/-2.5%, p=0.035).

CONCLUSIONS

Contrast-enhanced intravascular imaging is a novel, yet clinically available, technique that has the potential to enhance IVUS-based characterization of atherosclerotic plaques. The technique introduces a new perspective to the detection of vulnerable plaques and warrants further investigations.

Emigration of monocyte-derived cells to lymph nodes during resolution of inflammation and its failure in atherosclerosis

PURPOSE OF REVIEW

This review compares the fate of monocyte-derived cells that enter atherosclerotic plaques with those that accumulate at other sites of inflammation.

RECENT FINDINGS

Resolution of inflammatory reactions involves emigration of monocyte-derived cells out of the inflamed site through nearby lymphatic vessels. However, this emigratory process associated with resolution is impaired in atherosclerosis. The mechanism for impeded emigration from plaques in vivo remains to be determined, but multiple factors are likely involved, including specialized properties of artery walls and a negative impact of lipid mediators on monocyte-derived cell migration.

SUMMARY

Impaired egress would be expected to compound macrophage accumulation within plaques, contribute to build-up of necrotic pools, and explain in part the reticence of many plaques to regress, or resolve. Restoration of the capacity of monocyte-derived cells to leave plaques would, by contrast, be expected to facilitate regression, but it remains to be determined whether restoring egress may sometimes provoke unwanted outcomes as well.

Prominent lectin-like oxidized low density lipoprotein (LDL) receptor-1 (LOX-1) expression in atherosclerotic lesions is associated with tissue factor expression and apoptosis in hypercholesterolemic rabbits

BACKGROUND

Despite increasing in vitro evidence that lectin-like oxidized low density lipoprotein (LDL) receptor-1 (LOX-1), a cell-surface receptor for oxidized LDL, is implicated in the atherogenesis and thrombus formation, its in vivo participation to the atherosclerotic plaque destabilization, rupture and thrombus formation remains unclear. Here, we compared the in vivo expression of LOX-1, with tissue factor (TF) expression and cell apoptosis, in atherosclerotic lesions of myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbits.

METHODS AND RESULTS

We prepared sixty series of cross sections in the aortic arch and the thoracic aorta from four WHHLMI rabbits. LOX-1 and TF expression, as well as apoptotic events were determined by immunohistochemical staining and TUNEL methods, respectively. LOX-1 expression was mainly observed in the macrophage-rich lipid areas of vulnerable plaque-like atheromatous lesions where TF expression and apoptotic events were prominent. LOX-1 expression was positively correlated with TF expression (r=0.53, p<0.0001), apoptotic events (r=0.52, p<0.0001) and morphological vulnerability (r=0.63, p<0.0001).

CONCLUSIONS

LOX-1 expression appears to be closely associated with TF expression, apoptotic events and the morphological vulnerability, suggesting the in vivo involvement of LOX-1 in the destabilization and rupture of atherosclerotic lesions and the subsequent thrombus formation. The present findings in hypercholesterolemic rabbits should help advance our understanding of the pathophysiology of atherosclerosis.

Azimuthal registration of image sequences affected by nonuniform rotation distortion

Imaging modalities that use a mechanically rotated endoscopic probe to scan a tubular volume, such as an artery, often suffer from image degradation due to nonuniform rotation distortion (NURD). In this paper, we present a new method to align individual lines in a sequence of images. It is based on dynamic time warping, finding a continuous path through a cost matrix that measures the similarity between regions of two frames being aligned. The path represents the angular mismatch corresponding to the NURD. The prime advantage of this novel approach compared to earlier work is the line-to-line continuity, which accurately captures slow intraframe variations in rotational velocity of the probe. The algorithm is optimized using data from a clinically available intravascular optical coherence tomography (OCT) instrument in a realistic vessel phantom. Its efficacy is demonstrated on an in vivo recording, and compared with conventional global rotation block matching. Intravascular OCT is a particularly challenging modality for motion correction because, in clinical situations, the image is generally undersampled, and correlation between the speckle in different lines or frames is absent. The algorithm can be adapted to ingest data frame-by-frame, and can be implemented to work in real time.

Assessment of culprit and remote coronary narrowings using optical coherence tomography with long-term outcomes

Much currently known information about vulnerable plaque stems from postmortem studies that identified several characteristics making them prone to rupture, including the presence of a thin fibrous cap and a large lipid core. This study used optical coherence tomography (OCT) to assess culprit and remote coronary narrowings and investigate whether intracoronary OCT in living patients was able to visualize morphologic features associated with vulnerable plaque in postmortem studies. Twenty-three patients successfully underwent OCT before percutaneous coronary intervention. The culprit lesion and mild to moderate coronary narrowings remote from the target stenosis were investigated. Using OCT, the culprit lesion was found to be fibrous in 39.1%, fibrocalcific in 34.4%, and lipid rich in 26.1% of cases. Two patients met criteria for thin-cap fibroatheroma (TCFA; defined as the presence of a signal-rich fibrous cap covering a signal-poor lipid/necrotic core with cap thickness <0.2 mm). Most plaques at remote segments were proximal to the culprit lesion (73.9%) and predominantly fibrous and lipid rich. OCT identified 7 TCFA lesions in 6 patients with a mean cap thickness of 0.19 +/- 0.05 mm, extending for 103 degrees +/- 49 degrees of the total vessel circumference. At 24 months of clinical follow-up, the only event occurred in a patient with in-stent restenosis who underwent repeated percutaneous revascularization. There were no clinically apparent plaque rupture-related events in the 6 patients found to have remote TCFA. This study showed that OCT can be safely applied to image beyond the culprit lesion and can detect in vivo morphologic features associated with plaque vulnerability using retrospective pathologic examination. In conclusion, detection of TCFA, particularly in stable patients, is desirable and may principally allow for early intervention and prevention of adverse events.

Non-invasive assessment of plaque rupture by 64-slice multidetector computed tomography--comparison with intravascular ultrasound

BACKGROUND

Plaque rupture and secondary thrombus formation play key roles in the onset of acute coronary syndrome (ACS). Multidetector computed tomography (MDCT) allows the non-invasive assessment of coronary artery stenosis and plaque properties. In this study, we investigated whether 64-slice MDCT could non-invasively detect a plaque rupture in patients with de novo angina.

METHODS AND RESULTS

The study population comprised 67 patients with de novo angina. All patients underwent contrast-enhanced 64-slice MDCT and intravascular ultrasound (IVUS). Patients were divided into a plaque rupture group (n=27) and a non-rupture group (n=40) based on the IVUS. The 64-slice MDCT revealed that the prevalence of an ulcer-like enhancement space (37% vs 5%, p<0.01), a ring-like sign (41% vs 18%, p=0.04), in the plaque rupture group was higher than those in the non-rupture group. Maximum plaque thickness (2.1+/-0.9 mm vs 1.6+/-1.0 mm, p=0.04), outer vessel area (17.6+/-4.9 mm2 vs 13.4+/-5.0 mm2, p<0.01), percentage plaque area (82.3+/-9.1% vs 73.4+/-15.7%, p=0.01), and remodeling index (1.11+/-0.18 vs 1.01+/-0.15, p=0.04) of the plaque rupture group were all significantly larger than those of the non-rupture group.

CONCLUSIONS

The 64-slice MDCT can identify differences in lesion morphologies between ruptured plaques and non-ruptured plaques. From our results, the 64-slice MDCT might provide a useful tool for the non-invasive detection of plaque rupture.

Necrotic core thickness and positive arterial remodeling index: emergent biomechanical factors for evaluating the risk of plaque rupture

Fibrous cap thickness is often considered as diagnostic of the degree of plaque instability. Necrotic core area (Core(area)) and the arterial remodeling index (Remod(index)), on the other hand, are difficult to use as clinical morphological indexes: literature data show a wide dispersion of Core(area) thresholds above which plaque becomes unstable. Although histopathology shows a strong correlation between Core(area) and Remod(index), it remains unclear how these interact and affect peak cap stress (Cap(stress)), a known predictor of rupture. The aim of this study was to investigate the change in plaque vulnerability as a function of necrotic core size and plaque morphology. Cap(stress) value was calculated on 5,500 idealized atherosclerotic vessel models that had the original feature of mimicking the positive arterial remodeling process described by Glagov. Twenty-four nonruptured plaques acquired by intravascular ultrasound on patients were used to test the performance of the associated idealized morphological models. Taking advantage of the extensive simulations, we investigated the effects of anatomical plaque features on Cap(stress). It was found that: 1) at the early stages of positive remodeling, lesions were more prone to rupture, which could explain the progression and growth of clinically silent plaques and 2) in addition to cap thickness, necrotic core thickness, rather than area, was critical in determining plaque stability. This study demonstrates that plaque instability is to be viewed not as a consequence of fibrous cap thickness alone but rather as a combination of cap thickness, necrotic core thickness, and the arterial remodeling index.

Applications of multislice coronary computed tomographic angiography to percutaneous coronary intervention: how did we ever do without it?

By providing data previously available only by intravascular ultrasound, 64-slice multidetector computed tomographic angiography (CTA) will impact percutaneous coronary intervention (PCI) in multiple areas: (1) pre-PCI patient selection; (2) identification of significant lesions; (3) in-stent restenosis; (4) procedure planning: stent sizing, choice of intervention, and equipment, chronic total occlusions, 3D-CTA in the catheterization laboratory; (5) plaque evaluation and identification of high-risk lesions; (6) postcatheterization decisions, and (7) structural heart disease. The likely outcome is transformation of the catheterization laboratory into a streamlined interventional suite, utilizing on-line CTA data in an interactive format.

Controlling cardiac transport and plaque formation

Macro-particles transported in the bloodstream, such as LDL particles and macrophages, are considered to be one of the initiating factors of atherosclerotic plaque development. LDL infiltration from the bloodstream into a blood vessel's wall, whether the coronary, peripheral, or carotid arteries, is considered a major inflammatory factor, recruiting macrophages from the blood flow and leading to the formation of vulnerable atherosclerotic plaques. Infiltration sites are influenced by patterns of blood flow, as regions of lower shear stresses and high oscillations may give rise to higher infiltration rates through the endothelium, exacerbating the growth of a plaque and its tendency to rupture. Previous studies demonstrated a high prevalence of rupture sites proximal to the minimum lumen area, which raised the question of whether the existence of two distinct adjacent plaques, in which the distal plaque is more severe, can give rise to hemodynamic forces that can push the non-stenotic plaque to rupture. Models of the coronary arteries with one and two eccentric and concentric stenotic narrowings were built into a closed flow loop. The single stenosis model had a 75% area reduction narrowing (representing the vunerable atherosclerotic plaque) with relevant elastic properties. The double stenosis model included an additional distal 84% area reduction narrowing. The flow in the area between the two stenoses was recorded and analyzed using continuous doppler particle image velocimetry (CDPIV), together with the hydrostatic pressure acting on the proximal plaque. Results indicated that the combined shear rates and pressure effects in a model with a significant distal stenosis can contribute to the increase in plaque instability by LDL and enhanced macrophage uptake. The highly oscillatory nature of the disturbed flow near the shoulder of the vulnerable atherosclerotic plaque enriches its lipid soft core, and the high hydrostatic pressures acting on the same lesion in this geometry induce high internal maximal stresses that can trigger the rupture of the plaque.

Diagnosis and treatment of coronary vulnerable plaques

Thin-capped fibroatheroma is the morphology that most resembles plaque rupture. Detection of these vulnerable plaques in vivo is essential to being able to study their natural history and evaluate potential treatment modalities and, therefore, may ultimately have an important impact on the prevention of acute myocardial infarction and death. Currently, conventional grayscale intravascular ultrasound, virtual histology and palpography data are being collected with the same catheter during the same pullback. A combination of this catheter with either thermography capability or additional imaging, such as optical coherence tomography or spectroscopy, would be an exciting development. Intravascular magnetic resonance imaging also holds much promise. To date, none of the techniques described above have been sufficiently validated and, most importantly, their predictive value for adverse cardiac events remains elusive. Very rigorous and well-designed studies are compelling for defining the role of each diagnostic modality. Until we are able to detect in vivo vulnerable plaques accurately, no specific treatment is warranted.

A three-vessel virtual histology intravascular ultrasound analysis of frequency and distribution of thin-cap fibroatheromas in patients with acute coronary syndrome or stable angina pectoris

The frequency and distribution of thin-cap fibroatheromas (TCFA) have important clinical implications. We evaluated the frequency and distribution of TCFA identified by virtual histology intravascular ultrasound (VH-IVUS) in acute coronary syndrome (ACS) and stable angina pectoris (SAP). Preintervention 3-vessel VH-IVUS was performed in 105 patients with ACS and 107 with SAP. The length of left anterior descending artery imaged was 72 +/- 16 mm-54 +/- 12 mm in the left circumflex and 92 +/- 19 mm in the right coronary. VH-IVUS-derived TCFA (VH-TCFA) had a necrotic core > or =10% of plaque area without overlying fibrous tissue in a plaque burden > or =40%. There were 76 ruptured plaques (55 in ACS and 21 in SAP) and 439 VH-TCFA (262 in ACS and 177 in SAP, 2.5 +/- 1.5 vs 1.7 +/- 1.1 TCFA per patient with ACS and with SAP, respectively; p <0.001). Twelve patients with ACS and 1 with SAP had multiple ruptured plaques (p <0.001); 76 patients with ACS and 58 with SAP had multiple VH-TCFA (p = 0.009). Presentation of ACS was the only independent predictor for multiple ruptured plaques (p = 0.013) or multiple VH-TCFA (p = 0.011). Eighty-three percent of VH-TCFA were located within 40 mm of the coronary: 111 < or =10 (25%), 110 from 11 to 20 (25%), 83 from 21 to 30 (19%), and 61 from 31 to 40 mm (14%). The axial distribution of VH-TCFA was similar in patients with ACS and those with SAP and was similar to the axial distribution of ruptured plaques. In conclusion, 3-vessel VH-IVUS imaging showed a higher frequency of VH-TCFA in primary and secondary lesions in patients with ACS compared with those with SAP, but showed a similar clustering of VH-TCFA in the proximal 40 mm of each coronary artery.

Characterization of atherosclerotic plaques in human coronary arteries with 16-slice multidetector row computed tomography by analysis of attenuation profiles

RATIONALE AND OBJECTIVES

We investigated if 16-slice multidetector row computed tomography (MDCT) allows correct classification of coronary plaques into calcified or noncalcified and further subclassification of noncalcified plaques into either lipid-rich with a necrotic core or fibrous.

MATERIALS AND METHODS

Coronary arteries of 30 isolated hearts were filled postmortem with a contrast medium and scanned with a 16-slice MDCT imager (Light Speed 16 pro, GEMS, Milwaukee, WI). Imaging parameters: collimation 16 x 0.625 mm, pitch 0.325, tube voltage 120 kV, tube current 250 mA, and gantry rotation time 500 milliseconds. The images were reformatted perpendicular to the axis of the coronary arteries (AW 4.2 software, GEMS) and analyzed by establishing attenuation profiles of the coronary cross sections (ImageJ 1.33n software, NIH, Bethesda, MD). Results were compared with the correlating histopathologic sections of the arteries.

RESULTS

Analysis of 195 CT cross-sections showed a sensitivity and specificity for the correct classification of calcified plaques of 100% and 97.3% and for noncalcified plaques of 80.8% and 95.1%, respectively. The attenuation of epicardial fat ranged from -119 Hounsfield units (HU) to 23 HU (median -71 HU), and from 93 HU to 625 HU (308 HU) for the contrast medium. Calcified plaques showed an attenuation between 333 HU and 1944 HU (1,089 HU), noncalcified plaques between 26 HU and 124 HU (52 HU). Further subclassification of noncalcified plaques showed attenuation values between 26 HU and 67 HU (median 44 HU) for lipid-rich plaques with a necrotic core and from 37 HU to 124 HU (median 67 HU) for fibrous plaques.

CONCLUSIONS

Coronary atherosclerotic plaques can be reliably identified and classified as either calcified or noncalcified by 16-slice MDCT in postmortem studies. Further differentiation of noncalcified plaques in either lipid-rich or fibrous is not reliably feasible because of substantial overlap of the attenuation.

Matrix vesicles in the fibrous cap of atherosclerotic plaque: possible contribution to plaque rupture

Plaque rupture is the most common type of plaque complication and leads to acute ischaemic events such as myocardial infarction and stroke. Calcification has been suggested as a possible indicator of plaque instability. Although the role of matrix vesicles in the initial stages of arterial calcification has been recognized, no studies have yet been carried out to examine a possible role of matrix vesicles in plaque destabilization. Tissue specimens selected for the present study represented carotid specimens obtained from patients undergoing carotid endarterectomy. Serial frozen cross-sections of the tissue specimens were cut and mounted on glass slides. The thickness of the fibrous cap (FCT) in each advanced atherosclerotic lesion, containing a well developed lipid/necrotic core, was measured at its narrowest sites in sets of serial sections. According to established criteria, atherosclerotic plaque specimens were histologically subdivided into two groups: vulnerable plaques with thin fibrous caps (FCT <100 μm) and presumably stable plaques, in which fibrous caps were thicker than 100 μm. Twenty-four carotid plaques (12 vulnerable and 12 presumably stable plaques) were collected for the present analysis of matrix vesicles in fibrous caps. In order to provide a sufficient number of representative areas from each plaque, laser capture microdissection (LCM) was carried out. The quantification of matrix vesicles in ultrathin sections of vulnerable and stable plaques revealed that the numbers of matrix vesicles were significantly higher in fibrous caps of vulnerable plaques than those in stable plaques (8.908±0.544 versus 6.208±0.467 matrix vesicles per 1.92 μm² standard area; P= 0.0002). Electron microscopy combined with X-ray elemental microanalysis showed that some matrix vesicles in atherosclerotic plaques were undergoing calcification and were characterized by a high content of calcium and phosphorus. The percentage of calcified matrix vesicles/microcalcifications was significantly higher in fibrous caps in vulnerable plaques compared with that in stable plaques (6.705±0.436 versus 5.322±0A94; P= 0.0474). The findings reinforce a view that the texture of the extracellular matrix in the thinning fibrous cap of atherosclerotic plaque is altered and this might contribute to plaque destabilization.

Comprehensive evaluation of noncalcified coronary plaque characteristics detected using 64-slice computed tomography in patients with proven or suspected coronary artery disease

BACKGROUND

Multislice computed tomography has recently been shown to have the potential to characterize noncalcified coronary atherosclerotic lesions (NCALs). We evaluated the relationship among computed tomography (CT) density, arterial remodeling, and the adherent calcium morphology of NCALs detected using 64-slice CT.

METHODS

We studied 138 patients with proven or suspected coronary artery disease who underwent contrast-enhanced 64-slice CT examination. For each NCAL detected within the vessel wall, we determined the minimum CT density, remodeling index (RI = lesion/reference vessel area), and the presence or absence of coronary calcium in or adjacent to each NCAL and its morphology. Intravascular ultrasound (IVUS) was additionally performed in a subset of 21 patients.

RESULTS

A total of 202 NCALs were detected in 97 patients. The mean CT density of 98 lesions with positive remodeling (PR) (RI >1.05) was significantly lower than that of 104 lesions without PR (25 +/- 23 vs 56 +/- 28 Hounsfield units, P < .001); and spotty calcium was more frequently observed with the PR lesions than non-PR lesions (59% vs 22%, P < .001). The mean CT density of the PR lesions with spotty calcium (n = 58) was substantially lower than that of the non-PR lesions without adherent calcium (n = 45) (20 +/- 20 vs 67 +/- 24 Hounsfield units, P < .001). Evaluation of the components, RI, and adherent calcium morphology of 38 NCALs by 64-slice CT was in close agreement with the IVUS findings.

CONCLUSIONS

Lower CT density, PR, and adherent spotty calcium, which may indicate plaque vulnerability, are intimately co-related in NCALs detected using 64-slice CT; these findings are consistent with those of IVUS.

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

RATIONALE AND OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

Lectin-like oxidized LDL receptor-1 (LOX-1) expression is associated with atherosclerotic plaque instability—analysis in hypercholesterolemic rabbits

Lectin-like oxidized LDL receptor-1 (LOX-1), a cell-surface receptor for oxidized LDL (Ox-LDL), has been implicated in vascular cell dysfunction related to atherosclerotic plaque instability, according to cell culture experiments. In the present study, we investigated the relationship between LOX-1 expression and plaque instability in hypercholesterolemic rabbits by immunohistological analyses in vivo. We prepared thirty series of cross sections of the thoracic aorta from six myocardial infarction-prone Watanabe heritable hyperlipidemic (WHHLMI) rabbits (12-24 months), in which seventy atherosclerotic plaques were observed. LOX-1, matrix metalloproteinase-9 (MMP-9), monocyte chemoattractant protein-1 (MCP-1) expression, apoptotic events, plaque instability index (an index of the morphological destabilization of atherosclerotic plaques) and fibromuscular cap thickness in each atherosclerotic plaque were determined by immunohistochemical staining, TUNEL staining and Azan-Mallory staining. LOX-1 expression was positively correlated with the plaque instability index and MMP-9 expression. LOX-1 expression was more prominent in atherosclerotic plaques with thinner fibromuscular cap (<100 microm). Furthermore, LOX-1 expression was shown in the macrophage-rich lipid core area where MCP-1 expression and apoptotic events were prominent. These results indicate that enhanced LOX-1 expression was associated with histologically unstable atherosclerotic plaques in hypercholesterolemic rabbits, suggesting the involvement of LOX-1 in the destabilization of atherosclerotic plaques in vivo.

Cardiovascular molecular imaging of apoptosis

Introduction

Molecular imaging strives to visualise processes at the molecular and cellular level in vivo. Understanding these processes supports diagnosis and evaluation of therapeutic efficacy on an individual basis and thereby makes personalised medicine possible.

Apoptosis and molecular imaging

Apoptosis is a well-organised mode of cell suicide that plays a role in cardiovascular diseases (CVD). Apoptosis is associated with loss of cardiomyocytes following myocardial infarction, atherosclerotic plaque instability, congestive heart failure and allograft rejection of the transplanted heart. Thus, apoptosis constitutes an attractive target for molecular imaging of CVD. Our current knowledge about the molecular players and mechanisms underlying apoptosis offers a rich palette of potential molecular targets for molecular imaging. However, only a few have been successfully developed so far.

Aims

This review highlights aspects of the molecular machinery and biochemistry of apoptosis relevant to the development of molecular imaging probes. It surveys the role of apoptosis in four major areas of CVD and portrays the importance and future perspectives of apoptosis imaging. The annexin A5 imaging protocol is emphasised since it is the most advanced protocol to measure apoptosis in both preclinical and clinical studies.

Contrast-enhanced intravascular ultrasound: combining morphology with activity-based assessment of plaque vulnerability

Acute coronary syndromes are the result of coronary plaque rupture in the majority of cases. Available diagnostic techniques that focus on the early detection of plaques that are prone to rupture are still limited. Increased neovascularization in the vasa vasorum of the atherosclerotic plaque has been identified recently as a common feature of inflammation and plaque vulnerability. Microbubbles, which have been used for ultrasound imaging, can be used to trace neovascularization. We present recent advances in contrast agents and contrast-enhanced intravascular ultrasound that may be used for the detection of vasa vasorum, including fundamental and harmonic contrast imaging. Identification of vasa vasorum proliferation in atherosclerotic plaques presents important clinical implications; in particular it could provide a means to detect vulnerability in vivo, thereby guiding targeted treatments.

Perioperative antiplatelet therapy: the case for continuing therapy in patients at risk of myocardial infarction

Recent clinical data show that the risk of coronary thrombosis after antiplatelet drugs withdrawal is much higher than that of surgical bleeding if they are continued. In secondary prevention, aspirin is a lifelong therapy and should never be stopped. Clopidogrel is regarded as mandatory until the coronary stents are fully endothelialized, which takes 3 months for bare metal stents, but up to 1 yr for drug-eluting stents. Therefore, interruption of antiplatelet therapy 10 days before surgery should be revised. After reviewing the data on the use of antiplatelet drugs in cardiology and in surgery, we propose an algorithm for the management of patients, based on the risk of myocardial ischaemia and death compared with that of bleeding, for different types of surgery. Even if large prospective studies with a high degree of evidence are still lacking on different antiplatelet regimens during non-cardiac surgery, we propose that, apart from low coronary risk situations, patients on antiplatelet drugs should continue their treatment throughout surgery, except when bleeding might occur in a closed space. A therapeutic bridge with shorter-acting antiplatelet drugs may be considered.

Applications of optical coherence tomography to cardiac and musculoskeletal diseases: bench to bedside?

Selected historical aspects of the transition of optical coherence tomography (OCT) research from the bench to bedside are focused on. The primary function of the National Institutes of Health (NIH) is to improve the diagnosis and treatment of human pathologies. Therefore, research funded by the NIH should have a direct envisioned pathway for transitioning bench work to the bedside. Ultimately, to be successful, this work must be accepted by physicians and by the general science community. This typically requires robustly validated hypothesis-driven research. Work that is not appropriately compared to the current gold standard or does not address a specific pathology is unlikely to achieve widespread acceptance. I outline OCT research in the musculoskeletal and cardiovascular systems, examining the rapid transition from bench to bedside and look at initial validated hypothesis-driven research data that suggested clinical utility, which drove technology development toward specific clinical scenarios. I also consider the time of initial funding compared to when it was applied in patients with clinical pathologies. Finally, ongoing bench work being performed in parallel with clinical studies is examined. The specific applications examined here are identifying unstable coronary plaque and the early detection of osteoarthritis, the former was brought to the bedside primarily through a commercial route while the latter through NIH-funded research.

Frequency and Distribution of Thin-Cap Fibroatheroma and Ruptured Plaques in Human Coronary Arteries

OBJECTIVES

Our purpose was to quantify the frequency and distribution of suspected vulnerable lesions, defined as thin-capped fibroatheroma (TCFA) and ruptured plaque, in human coronary artery autopsy specimens.

BACKGROUND

Most acute coronary events and sudden death are believed to arise from rupture of a TCFA followed by thrombosis. Although there is general agreement that clinical events are usually caused by focal lesions, there is considerable debate over the relative importance of focal versus systemic factors in the pathogenesis of atherosclerosis.

METHODS

We longitudinally sectioned coronary arteries from 50 whole hearts taken from patients (mean age 73 years, 64% men) dying of cardiovascular (n = 33), noncardiovascular (n = 13), and unknown (n = 4) causes. A total of 3,639 longitudinal segments of length 3 mm were sectioned from 148 arteries, accounting for 10.9 m of total tissue length. Specimens were classified on the basis of histology and computer-aided morphometry.

RESULTS

Twenty-three TCFA and 19 ruptured plaques were found (mean +/- SD: 0.46 +/- 0.95 and 0.38 +/- 0.70 per heart, respectively), and these lesions accounted for only 1.6% and 1.2%, respectively, of the total length of the coronary tree examined in patients dying of cardiovascular causes. The majority of TCFA and ruptured plaque localized in the proximal third of the major coronary arteries, and in 92% of cases these lesions clustered within 2 or fewer nonoverlapping 20-mm segments.

CONCLUSIONS

The suspected precursors of rupture-mediated thrombosis occur in a limited, focal distribution in the coronary arteries.

Increased endoplasmic reticulum stress in atherosclerotic plaques associated with acute coronary syndrome

BACKGROUND

The endoplasmic reticulum (ER) responds to various stresses by upregulation of ER chaperones, but prolonged ER stress eventually causes apoptosis. Although apoptosis is considered to be essential for the progression and rupture of atherosclerotic plaques, the influence of ER stress and apoptosis on rupture of unstable coronary plaques remains unclear.

METHODS AND RESULTS

Coronary artery segments were obtained at autopsy from 71 patients, and atherectomy specimens were obtained from 40 patients. Smooth muscle cells and macrophages in the fibrous caps of thin-cap atheroma and ruptured plaques, but not in the fibrous caps of thick-cap atheroma and fibrous plaques, showed a marked increase of ER chaperone expression and apoptotic cells. ER chaperones also showed higher expression in atherectomy specimens from patients with unstable angina pectoris than in specimens from those with stable angina. Expression of 7-ketocholesterol was increased in the fibrous caps of thin-cap atheroma compared with thick-cap atheroma. Treatment of cultured coronary artery smooth muscle cells or THP-1 cells with 7-ketocholesterol induced upregulation of ER chaperones and apoptosis, whereas these changes were prevented by antioxidants. We also investigated possible signaling pathways for ER-initiated apoptosis and found that the CHOP (a transcription factor induced by ER stress)-dependent pathway was activated in unstable plaques. In addition, knockdown of CHOP expression by small interfering RNA decreased ER stress-dependent death of cultured coronary artery smooth muscle cells and THP-1 cells.

CONCLUSIONS

Increased ER stress occurs in unstable plaques. Our findings suggest that ER stress-induced apoptosis of smooth muscle cells and macrophages may contribute to plaque vulnerability.

Imaging techniques for the vulnerable coronary plaque

The goal of this article is to illustrate the main invasive and noninvasive diagnostic modalities to image the vulnerable coronary plaque, which is responsible for acute coronary syndrome. The main epidemiologic and histological issues are briefly discussed in order to provide an adequate background. Comprehensive coronary atherosclerosis imaging should involve visualization of the entire coronary artery tree and plaque characterization, including three-dimensional morphology, relationship with the lumen, composition, vascular remodelling and presence of inflammation. No single technique provides such a comprehensive description, and no available modality extensively identifies the vulnerable plaque. In particular, we describe multislice computed tomography, which at present seems to be the most promising noninvasive tool for an exhaustive image-based quantification of coronary atherosclerosis.

Imaging Collagen in Intact Viable Healthy and Atherosclerotic Arteries Using Fluorescently Labeled CNA35 and Two-Photon Laser Scanning Microscopy

We evaluated CNA35 as a collagen marker in healthy and atherosclerotic arteries of mice after both ex vivo and in vivo administration and as a molecular imaging agent for the detection of atherosclerosis. CNA35 conjugated with fluorescent Oregon Green 488 (CNA35/OG488) was administered ex vivo to mounted viable muscular (uterine), elastic (carotid), and atherosclerotic (carotid) arteries and fresh arterial rings. Two-photon microscopy was used for imaging. CNA35/OG488 labeling in healthy elastic arteries was compared with collagen type I, III, and IV antibody labeling in histologic sections. For in vivo labeling experiments, CNA35/OG488 was injected intravenously in C57BL6/J and apolipoprotein E−/− mice. Ex vivo CNA35/OG488 strongly labeled collagen in the tunica adventitia, media, and intima of muscular arteries. In healthy elastic arteries, tunica adventitia was strongly labeled, but labeling in tunica media and intima was prevented by endothelium and elastic laminae. Histology confirmed the affinity of CNA35 for type I, III, and IV collagen in arteries. Strong CNA35/OG488 labeling was found in atherosclerotic plaques. In vivo applied CNA35/OG488 minimally labeled the tunica intima of healthy carotid arteries. Atherosclerotic plaques in apolipoprotein E−/− mice exhibited large uptake. CNA35/OG488 imaging in organs revealed endothelium as a limiting barrier for in vivo uptake. CNA35/OG488 is a good molecular imaging agent for atherosclerosis.

Imaging and molecular biomarkers of vulnerable atheromatous plaques

Rupture of a vulnerable atherosclerotic plaque is the main cause of acute coronary syndromes, myocardial infarction and death. Identification of biomarkers that accurately predict the risk of plaque rupture may be a means to establish and monitor response to therapeutic intervention. This review focuses on recent advances for the use of circulating molecular biomarkers and imaging modalities to assess atherosclerotic vulnerable plaques in both preclinical models and clinical conditions.

Relationship between a systemic inflammatory marker, plaque inflammation, and plaque characteristics determined by intravascular optical coherence tomography

OBJECTIVE

The purpose of this study was to evaluate the relationships between the peripheral white blood cell (WBC) count, local plaque fibrous cap macrophage density, and the morphological features and presence of thin-cap fibroatheromas (TCFA) identified by optical coherence tomography (OCT).

METHODS AND RESULTS

OCT was performed in patients undergoing catheterization. Images were analyzed using validated criteria for plaque characteristics. Baseline WBC count correlated with macrophage density (r=0.483, P<0.001). Both parameters were associated with lipid-rich plaque and correlated inversely with plaque fibrous cap thickness (r=-0.547 for macrophage density and -0.423 for WBC count, P<0.015). Plaques classified as TCFA had a higher median macrophage density than non-TCFA plaques (7.4 versus 4.99, P<0.001). Patients with TCFA had a higher WBC count compared with those without TCFA (11.0 versus 7.9, P=0.007). Receiver operator curves for WBC count, macrophage density, and these combined parameters for prediction of TCFA showed the area under the curves were 0.88, 0.91, and 0.97 (P<0.001), respectively.

CONCLUSION

This study provides the first in vivo data linking the peripheral WBC count, plaque fibrous cap macrophage density, and the characteristics and presence of TCFA. Macrophage density correlated with the WBC count, and both parameters independently and particularly in combination predict the presence of TCFA.

Methylglyoxal induces advanced glycation end product (AGEs) formation and dysfunction of PDGF receptor‐β: implications for diabetic atherosclerosis

PURPOSE

Low molecular weight carbonyl compounds, such as the alpha-ketoaldehydes methylglyoxal (MGO) and glyoxal (GO), are formed under hyperglycemic conditions and behave as advanced glycation end product (AGE) precursors. They form adducts on proteins, thereby inducing cellular dysfunctions involved in chronic complications of diabetes.

METHODS AND MAIN FINDINGS

Nontoxic concentrations of GO or MGO altered the PDGF-induced PDGFRbeta-phosphorylation, ERK1/2-activation, and nuclear translocation, and the subsequent proliferation of mesenchymal cells (smooth muscle cells and skin fibroblasts). This resulted mainly from inhibition of the intrinsic tyrosine kinase of PDGFRbeta and in part from altered PDGF-BB binding to PDGFRbeta. Concomitantly, the formation of AGE adducts (N(epsilon)carboxymethyl-lysine and N(epsilon)carboxyethyl-lysine) was observed on immunoprecipitated PDGFRbeta. Arginine and aminoguanidine, used as carbonyl scavengers, reversed the inhibitory effect and the formation of AGE adducts on PDGFRbeta. AGE-PDGFRbeta adducts were also detected by anti-AGE antibodies in PDGFRbeta immunopurified from aortas of diabetic (streptozotocin-treated) compared to nondiabetic apolipoprotein E-null mice. Mass spectrometry analysis of aortas demonstrated increased AGE formation in diabetic specimens.

CONCLUSIONS

These data indicate that MGO and GO induce desensitization of PDGFRbeta that helps to reduce mesenchymal cell proliferation.

Hemodynamic factors and atheromatic plaque rupture in the coronary arteries: from vulnerable plaque to vulnerable coronary segment

Coronary plaque disruption with superimposed thrombosis is the underlying pathology in the acute coronary syndromes and sudden death. Coronary plaques are constantly stressed by a variety of mechanical and hemodynamic forces that may precipitate or 'trigger' disruption of vulnerable or, at extreme conditions, even stable plaques. This paper reviews the exciting new evidence on the hemodynamic factors that may play a role in this process and provides the rationale for the introduction of the concept of the vulnerable coronary segment in the study of acute coronary syndromes.

Elimination of Neoangiogenesis for Plaque Stabilization

Emerging data suggest that intraplaque hemorrhage is critical in promoting atherosclerotic lesion instability. Because red blood cell membranes are a rich source of free cholesterol and accumulated red blood cells within plaques promote inflammation, intraplaque hemorrhage is associated with expansion of the necrotic core. Plaque hemorrhage results from the development of immature neointimal vasa vasorum. Therefore, it is proposed that molecular therapies designed to eliminate pathologic neovascularization within developing lesions will interrupt the process of hemorrhage and decrease the rate of necrotic core expansion. The elimination of intraplaque neovascularization would involve targeting of pre-existing and new vessel development. The concept of vascular regression has met some success in other neovascular-dependent diseases, including macular degeneration and malignancies. The efficacy of this novel approach is dependent on gaining critical knowledge of the environment required to support development and maturation of the vasa vasorum within varying plaque types. A multitargeted approach involving selective local antiangiogenic agents should contribute to prevention of plaque progression and its clinical consequences.

Robust intravascular optical coherence elastography by line correlations

We present a new method for intravascular optical coherence elastography, which is robust against motion artefacts. It employs the correlation between adjacent lines, instead of subsequent frames. Pressure to deform the tissue is applied synchronously with the line scan rate of the optical coherence tomography (OCT) instrument. The viability of the method is demonstrated with a simulation study. We find that the root mean square (rms) error of the displacement estimate is 0.55 microm, and the rms error of the strain is 0.6%. It is shown that high-strain spots in the vessel wall, such as observed at the sites of vulnerable atherosclerotic lesions, can be detected with the technique.

Acute coronary syndromes: an emphasis shift from treatment to prevention; and the enduring challenge of vulnerable plaque detection in the cardiac catheterization laboratory

Rupture of vulnerable plaques is the main cause of acute coronary syndromes and myocardial infarctions. Identification of these vulnerable plaques is therefore essential to enable the development of treatment modalities to stabilize them. Several intravascular technologies, investigating coronary areas that will be responsible for future events, are highlighted in this review. The ideal technique would provide morphological, mechanical and biochemical information. Although several imaging techniques are currently under development, none of them alone provides such an all-embracing assessment. Optical coherence tomography has the advantage of high resolution, thermography has the potential to measure metabolism, and Raman spectroscopy obtains information on chemical components. Intravascular coronary ultrasound (IVUS) and IVUS-palpography are easy to perform and assess morphology and mechanical instability. Shear stress is an important mechanical parameter deeply influencing vascular biology. Nevertheless, all these techniques are still under investigation and, at present, none of them can unequivocally and comprehensively identify a vulnerable plaque and, most importantly, predict its further development. From a clinical point of view, most techniques currently assess only one feature of the vulnerable plaque. Thus, a combination of several modalities will be important in the future to ensure a high sensitivity and specificity in detecting vulnerable plaques.

Effect of particle size on hydroxyapatite crystal-induced tumor necrosis factor alpha secretion by macrophages

Macrophages may promote a vicious cycle of inflammation and calcification in the vessel wall by ingesting neointimal calcific deposits (predominantly hydroxyapatite) and secreting tumor necrosis factor (TNF)alpha, itself a vascular calcifying agent. Here we have investigated whether particle size affects the proinflammatory potential of hydroxyapatite crystals in vitro and whether the nuclear factor (NF)-kappaB pathway plays a role in the macrophage TNFalpha response. The particle size and nano-topography of nine different crystal preparations was analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy and gas sorbtion analysis. Macrophage TNFalpha secretion was inversely related to hydroxyapatite particle size (P=0.011, Spearman rank correlation test) and surface pore size (P=0.014). A necessary role for the NF-kappaB pathway was demonstrated by time-dependent I kappaB alpha degradation and sensitivity to inhibitors of I kappaB alpha degradation. To test whether smaller particles were intrinsically more bioactive, their mitogenic activity on fibroblast proliferation was examined. This showed close correlation between TNFalpha secretion and crystal-induced fibroblast proliferation (P=0.007). In conclusion, the ability of hydroxyapatite crystals to stimulate macrophage TNFalpha secretion depends on NF-kappaB activation and is inversely related to particle and pore size, with crystals of 1-2 microm diameter and pore size of 10-50 A the most bioactive. Microscopic calcific deposits in early stages of atherosclerosis may therefore pose a greater inflammatory risk to the plaque than macroscopically or radiologically visible deposits in more advanced lesions.

CT of Coronary Artery Disease

The clinical relevance of coronary artery disease has considerably driven the recent development of radiologic tools for noninvasive cardiac imaging. Modern multidetector row computed tomographic (MDCT) systems combine high temporal and spatial resolution, electrocardiographic synchronization, and ease of use. In cardiac imaging, MDCT has not only replaced electron-beam CT, but also challenges competing methods such as magnetic resonance imaging, echocardiography, or even coronary catheterization. Noncontrast material-enhanced assessment of atherosclerotic plaques (CT calcium scoring) seems useful for the cardiac risk stratification in asymptomatic patients and monitoring of medical (statin) therapy. Contrast material-enhanced CT coronary angiography has become established as a valuable method for several clinical indications such as evaluation of coronary artery anomalies, bypass patency, or preoperative planning. Particularly, the high negative predictive value of a normal CT coronary angiogram allows reliable exclusion of coronary artery stenosis. Plaque characterization is another promising area of research in MDCT cardiac imaging. However, with current technology a reliable distinction between atheroma and fibroatheroma is impaired by restrictions in spatial resolution. Recent studies indicate that CT angiography may also be suited for other clinical applications such as triage of patients with acute coronary syndrome and inconclusive clinical presentation, patients with symptomatic chest pain, and intermediate risk profile or cardiac risk stratification in asymptomatic patients.

Imaging of vulnerable coronary artery plaques

Advances in the identification of vulnerable plaque can be an important step in preventing myocardial infarction and sudden cardiac death. 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. This review will present the use of noninvasive imaging modalities for identifying vulnerable plaque such as computed tomography and magnetic resonance imaging. We will also review the different invasive modalities such as intravascular magnetic resonance imaging, intravascular ultrasound, coronary angioscopy, coronary thermography, optical coherence tomography, near-infrared spectroscopy, and palpography.

Plaque Composition in the Left Main Stem Mimics the Distal But Not the Proximal Tract of the Left Coronary Artery

OBJECTIVES

We sought to investigate whether plaques located in the left main stem (LMS) differ in terms of necrotic core content from those sited in the proximal tract of the left coronary artery.

BACKGROUND

Plaque composition, favoring propensity to vulnerability, might be nonuniformly distributed along the vessel, which might explain the greater likelihood for plaque erosion or rupture to occur in the proximal but not in the distal tracts of the coronary artery or in LMS.

METHODS

A total of 72 patients were included prospectively; 48 (32 men; mean age 57 +/- 11 years; 25 with stable angina and 23 affected by acute coronary syndromes) underwent a satisfactory nonculprit vessel investigation through spectral analysis of intravascular ultrasound radiofrequency data (IVUS-Virtual Histology, Volcano Corp., Rancho Cordova, California). The region of interest was subsequently divided into LMS and LMS carina, followed by 6 consecutive nonoverlapping 6-mm segments in left anterior descending artery in 34 patients or in circumflex artery in 14 patients.

RESULTS

Necrotic core content (%): 1) was minimal in LMS (median [interquartile range]: 4.6 [2 to 7]), peaked in the first 6-mm coronary segment (11.8 [8 to 16]; p < 0.01), and then progressively decreased distally; 2) was overall greater in patients with acute coronary syndromes (11.4 [5.5 to 19.8]) than stable angina (7.3 [3.2 to 12.9]; p < 0.001); 3) was largely independent from plaque size; and 4) did not correlate to systemic levels of C-reactive protein or lipid profile.

CONCLUSIONS

Plaques located in the LMS carry minimal necrotic content. Thus, they mimic the distal but not the proximal tract of the left coronary artery, where plaque rupture or vessel occlusion occurs more frequently.