Morphological predictors of arterial remodeling in coronary atherosclerosis

Comparison of arterial remodeling and changes in plaque composition between patients with progression versus regression of coronary atherosclerosis during statin therapy (from the TRUTH study)

Statin therapy produces regression of coronary artery plaques and reduces the incidence of coronary artery disease. However, not all patients show regression of coronary atherosclerosis after statin therapy. The purpose of the present study was to identify differences in clinical characteristics, serum lipid profiles, arterial remodeling, and plaque composition between patients with progression and those with regression of coronary atherosclerosis during statin therapy. The effects of 8-month statin therapy on coronary atherosclerosis were evaluated in the Treatment With Statin on Atheroma Regression Evaluated by Intravascular Ultrasound With Virtual Histology (TRUTH) study using intravascular ultrasound-virtual histology. One hundred nineteen patients were divided into 2 groups according to atheroma volume increase (progressors) or decrease (regressors) during an 8-month follow-up period. Fifty-one patients (43%) were categorized as progressors and the remaining 68 (57%) as regressors. External elastic membrane volume increased, although not significantly (0.8%, p = 0.34), and luminal volume decreased significantly (-5.3%, p = 0.0003) in progressors, while external elastic membrane volume decreased significantly (-3.2%, p <0.0001) and luminal volume increased (2.2%, p = 0.13) in regressors. The fibrous component increased significantly in progressors, while this component decreased in regressors. A strong positive correlation was observed between change in atheroma volume and change in fibrous volume (r = 0.812, p <0.0001). In conclusion, coronary arteries showed negative remodeling during statin-induced plaque regression. The difference in plaque composition between patients with progression and those with regression of coronary atherosclerosis during statin therapy arose from the difference in the change in fibrous component.

Effect of hypertension on coronary remodeling patterns in angiographically normal or minimally atherosclerotic coronary arteries: an intravascular ultrasound study

Whether there is any particular role of hypertension in remodeling process has not been completely understood yet. The aim of this study was to assess the association between hypertension and remodeling patterns in normal or minimally atherosclerotic coronary arteries. Seventy-nine patients who were free of significant coronary atherosclerosis were divided into two groups according to the absence (n = 39) or presence (n = 40) of hypertension; and standard intravascular ultrasound examination was performed in 145 segments. To determine the remodeling pattern in early atherosclerotic process, patients were also analyzed according to the level of plaque burden at the lesion site after the analysis of remodeling patterns. Positive remodeling was more prevalent in the hypertensive group (52.5% vs. 12.8%; P < .001) whereas negative remodeling was more common in diabetic patients (53.6% vs. 27.4%; P = .03). Mean remodeling index was 1.04 for hypertensives and 0.96 for normotensives (P = .03). There were no correlations between remodeling patterns and other risk factors such as age, family history, and hypercholesterolemia. Early atherosclerotic lesions (< 30%) exhibited more negative remodeling characteristics while intermediate pattern was observed more frequently in patients with high plaque burden (P = .006 and .02, respectively). Positive remodeling showed no association in this context (P = .07). This study demonstrated that minimal atherosclerotic lesions in hypertensives had a tendency for compensatory arterial enlargement. Positive remodeling may result from local adaptive processes within vessel wall or hemodynamic effects of blood pressure itself.

Relationship of antihypertensive treatment to plasma markers of vascular inflammation and remodeling in the Comparison of Amlodipine versus Enalapril to Limit Occurrences of Thrombosis study

BACKGROUND

Antihypertensive agents lower the risk of cardiovascular events, but whether they affect pathways important in inflammation and plaque remodeling in atherosclerosis is uncertain. We assessed whether 2 commonly used antihypertensive agents affected plasma biomarkers reflecting specific inflammatory and remodeling processes over 2 years in the Comparison of Amlodipine versus Enalapril to Limit Occurrences of Thrombosis (CAMELOT) study.

METHODS

The study was a randomized controlled trial of 2 antihypertensives (amlodipine and enalapril) compared with placebo in patients with coronary artery disease and diastolic blood pressure less than 100 mm Hg. In 196 subjects who had baseline and 2-year intravascular coronary ultrasound examinations, we measured plasma interleukin 18, interleukin 1 receptor antagonist, matrix metalloproteinase 9, neopterin, and C-reactive protein. Results for both treatment groups were pooled and compared with placebo.

RESULTS

Antihypertensive treatment with either agent significantly lowered diastolic blood pressure (-4.7 vs placebo 1.3 mm Hg, P = .002) and progression of coronary atheroma (Δ percent atheroma volume 0.6 vs placebo 2.1, P = .031). Antihypertensive therapy did not affect plasma biomarkers of inflammation or plaque remodeling in the 135 subjects with baseline and 2-year biomarker samples. Progression in percent atheroma volume was significantly less in subjects taking statins at baseline (-2.5%, P = .0008).

CONCLUSIONS

In patients with coronary artery disease and well-controlled risk factors, antihypertensive therapy lowered blood pressure and progression of coronary atherosclerosis but did not affect plasma biomarkers of inflammation and remodeling. Antihypertensives may decrease atheroma progression by mechanisms other than those reflected by these plasma biomarkers.

Is Stenting an Appropriate Therapy in Women Presenting with Acute Coronary Syndrome? A Pathologist's Perspective

It has been more than 3 decades since the introduction of percutaneous transluminal coronary angioplasty for the treatment of coronary artery disease, and the introduction of bare metal stents and drug-eluting stents (DES) has significantly improved clinical outcomes by decreasing rates of acute vessel closure and restenosis. This article reviews pathologic findings from male and female patients who had received coronary stents for acute coronary syndrome and died suddenly with or without complications of stent implantation, at early (<30 days) and late (>30 days) time points after DES implantation.

The maximum necrotic core area is most often located proximally to the site of most severe narrowing: a virtual histology intravascular ultrasound study

Previous angiographic studies have shown that almost two-thirds of vulnerable plaques are located in non-obstructive lesions. Possibly, the maximum necrotic core (Max NC) area is not always identical to the site of most severe stenosis. Therefore, the purpose of this study was to evaluate the potential difference in location between the maximum necrotic core area and the site of most severe narrowing as assessed by virtual histology intravascular ultrasound (VH IVUS). Overall, 77 patients (139 vessels) underwent VH IVUS. The Max NC site was defined as the cross section with the largest necrotic core area per vessel. The site of most severe narrowing was defined as the minimum lumen area (MLA). Per vessel, the distance from both the Max NC site and MLA site to the origo of the coronary artery was evaluated. In addition, the presence of a virtual histology-thin cap fibroatheroma (VH-TCFA) was assessed. The mean difference (mm) between the MLA site and Max NC site was 10.8 ± 20.6 mm (p < 0.001). Interestingly, the Max NC site was located at the MLA site in seven vessels (5%) and proximally to the MLA site in 92 vessels (66%). Importantly, a higher percentage of VH-TCFA was demonstrated at the Max NC site as compared to the MLA site (24 vs. 9%, p < 0.001). In conclusion, the present findings demonstrate that the Max NC area is rarely at the site of most severe narrowing. Most often, the Max NC area is located proximal to the site of most severe narrowing.

Effect of calcification on the mechanical stability of plaque based on a three-dimensional carotid bifurcation model

Background

This study characterizes the distribution and components of plaque structure by presenting a three-dimensional blood-vessel modelling with the aim of determining mechanical properties due to the effect of lipid core and calcification within a plaque. Numerical simulation has been used to answer how cap thickness and calcium distribution in lipids influence the biomechanical stress on the plaque.

Method

Modelling atherosclerotic plaque based on structural analysis confirms the rationale for plaque mechanical examination and the feasibility of our simulation model. Meaningful validation of predictions from modelled atherosclerotic plaque model typically requires examination of bona fide atherosclerotic lesions. To analyze a more accurate plaque rupture, fluid-structure interaction is applied to three-dimensional blood-vessel carotid bifurcation modelling. A patient-specific pressure variation is applied onto the plaque to influence its vulnerability.

Results

Modelling of the human atherosclerotic artery with varying degrees of lipid core elasticity, fibrous cap thickness and calcification gap, which is defined as the distance between the fibrous cap and calcification agglomerate, form the basis of our rupture analysis. Finite element analysis shows that the calcification gap should be conservatively smaller than its threshold to maintain plaque stability. The results add new mechanistic insights and methodologically sound data to investigate plaque rupture mechanics.

Conclusion

Structural analysis using a three-dimensional calcified model represents a more realistic simulation of late-stage atherosclerotic plaque. We also demonstrate that increases of calcium content that is coupled with a decrease in lipid core volume can stabilize plaque structurally.

Statin treatment for coronary artery plaque composition based on intravascular ultrasound radiofrequency data analysis

BACKGROUND

Systemic therapy with statin has been shown to lower the risk of coronary events; however, the in vivo effects of statin therapy on plaque volume and composition are less understood.

METHODS

We conducted a prospective, open-labeled, randomized, multicenter study in 11 centers in Japan. A total of 164 patients were randomized to receive either 4 mg/d of pitavastatin (intensive lipid-lowering therapy) or 20 mg/d of pravastatin (moderate lipid-lowering therapy). Analyzable intravascular ultrasound data were obtained for 119 patients at baseline and at 8-month follow-up. The primary end point was the difference of volume changes in each of the 4 main plaque components (fibrosis, fibrofatty, calcium, and necrosis), assessed by virtual histology intravascular ultrasound, between the 2 groups.

RESULTS

The mean low-density lipoprotein cholesterol level at follow-up was significantly lower in the pitavastatin than in the pravastatin group (74 vs 95 mg/dL, P < .0001). During the 8-month follow-up period, statin therapy reduced the absolute and relative amount of fibrofatty component (pitavastatin: from 1.09 to 0.81 mm(3)/mm, P = .001; pravastatin: from 1.05 to 0.83 mm(3)/mm, P = .0008) and increased in the amount of calcium (pitavastatin: from 0.42 to 0.55 mm(3)/mm, P < .0001; pravastatin: from 0.44 to 0.55 mm(3)/mm, P = .005), whereas volume changes in both plaque components were not statistically different between the 2 groups.

CONCLUSIONS

Both pitavastatin and pravastatin altered coronary artery plaque composition by significantly decreasing the fibrofatty plaque component and increasing the calcified plaque component.

Genetic inactivation of IL-1 signaling enhances atherosclerotic plaque instability and reduces outward vessel remodeling in advanced atherosclerosis in mice

Clinical complications of atherosclerosis arise primarily as a result of luminal obstruction due to atherosclerotic plaque growth, with inadequate outward vessel remodeling and plaque destabilization leading to rupture. IL-1 is a proinflammatory cytokine that promotes atherogenesis in animal models, but its role in plaque destabilization and outward vessel remodeling is unclear. The studies presented herein show that advanced atherosclerotic plaques in mice lacking both IL-1 receptor type I and apolipoprotein E (Il1r1⁻/⁻Apoe⁻/⁻ mice) unexpectedly exhibited multiple features of plaque instability as compared with those of Il1r1⁺/⁺Apoe⁻/⁻ mice. These features included reduced plaque SMC content and coverage, reduced plaque collagen content, and increased intraplaque hemorrhage. In addition, the brachiocephalic arteries of Il1r1⁻/⁻Apoe⁻/⁻ mice exhibited no difference in plaque size, but reduced vessel area and lumen size relative to controls, demonstrating a reduction in outward vessel remodeling. Interestingly, expression of MMP3 was dramatically reduced within the plaque and vessel wall of Il1r1⁻/⁻Apoe⁻/⁻ mice, and Mmp3⁻/⁻Apoe⁻/⁻ mice showed defective outward vessel remodeling compared with controls. In addition, MMP3 was required for IL-1-induced SMC invasion of Matrigel in vitro. Taken together, these results show that IL-1 signaling plays a surprising dual protective role in advanced atherosclerosis by promoting outward vessel remodeling and enhancing features of plaque stability, at least in part through MMP3-dependent mechanisms.

A novel semiautomated atherosclerotic plaque characterization method using grayscale intravascular ultrasound images: comparison with virtual histology

Intravascular ultrasound (IVUS) virtual histology (VH-IVUS) is a new technique, which provides automated plaque characterization in IVUS frames, using the ultrasound backscattered RF-signals. However, its computation can only be performed once per cardiac cycle (ECG-gated technique), which significantly decreases the number of characterized IVUS frames. Also atherosclerotic plaques in images that have been acquired by machines, which are not equipped with the VH software, cannot be characterized. To address these limitations, we have developed a plaque characterization technique that can be applied in grayscale IVUS images. Our semiautomated method is based on a three-step approach. In the first step, the plaque area [region of interest (ROI)] is detected semiautomatically. In the second step, a set of features is extracted for each pixel of the ROI and in the third step, a random forest classifier is used to classify these pixels into four classes: dense calcium, necrotic core, fibrotic tissue, and fibro-fatty tissue. In order to train and validate our method, we used 300 IVUS frames acquired from virtual histology examinations from ten patients. The overall accuracy of the proposed method was 85.65% suggesting that our approach is reliable and may be further investigated in the clinical and research arena.

Association of coronary plaque composition and arterial remodelling: a optical coherence tomography study

BACKGROUND

Conflicting data have been reported about the association between plaque composition and remodelling index (RI). The aim of this study is to evaluate the relationship between plaque morphology obtained by optical coherence tomography (OCT) and arterial remodelling.

METHODS AND RESULTS

OCT and intravascular ultrasound imaging pull back was performed at corresponding sites on 94 lesions in 47 patients. OCT plaque characteristics for lipid content, fibrous cap thickness, thin-cap fibroatheroma (TCFA), plaque rupture, thrombus, calcification and erosion were derived using validated criteria. Compared with intermediate/negative remodelling (RI<1.0), positive remodelling (RI>1.0) was associated with presence of higher lipid pool (2.86 ± 0.42 vs. 2.20 ± 0.78; p<0.001), thin fibrous cap (47.86 ± 25.43 μm vs. 74.41 ± 32.41 μm; p<0.001), TCFA>3mm (82.1% vs. 22.7%; p<0.0001), plaque rupture and thrombus (42.8% vs. 19.7%; p = 0.024), and higher plaque burden (73.70 vs. 70.70; p = 0.048). No difference was observed in the presence of calcification and plaque erosions.

CONCLUSIONS

Coronary lesions with positive remodelling show higher incidences of vulnerable plaque and plaque rupture across the lesion length. This potentially explains the correlation between unstable coronary syndromes and positive remodelling.

[Intravascular ultrasound for recognition of atherosclerotic plaques and plaque composition. Current state of the diagnostic value]

Coronary atherosclerosis including acute coronary syndrome (ACS) is the leading cause of death in the western world and in the majority of patients is caused by plaque rupture in flow-limiting and non-flow-limiting angiographically intermediate stenoses. Histopathologic analyses have shown the relationship of plaque composition to acute clinical events and therefore to the vulnerability of coronary lesions. Knowledge of remodeling processes of the coronary artery has focused interest on non-flow-limiting lesions of the coronary tree. Intravascular ultrasound (IVUS) can demonstrate discrepancies between the extent of coronary atherosclerosis and angiographic imaging by in vivo plaque imaging. In addition the spectral analysis of IVUS-derived radiofrequency (RF) data enables more precise analysis of the plaque composition and plaque type.As IVUS is best able to assess stent underexpansion and malapposition the guidance of catheter-based coronary interventions plays a major role in angiographically unclear lesions even in the drug-eluting stent era. In the field of percutaneous coronary interventions (PCI) IVUS can influence the therapy and therefore optimize the stratification of patients.In terms of secondary prevention it is of great clinical importance to detect progression of coronary artery disease and moreover to predict coronary lesions with significant progression up to ACS. Coronary angiography and clinical parameters are poor surrogates to predict future events in a broad cohort of patients after PCI. In addition non-invasive imaging fails to identify coronary plaques with potential rupture and subsequent ACS. This highlights the need to identify potentially high risk lesions. However, prospective studies with IVUS-RF imaging to detect lesions that are considered to be prone to rupture showed no evidence for catheter-based invasive treatment of a non-flow-limiting high risk plaque.In the future the integrated combination of multiple technologies (e.g. IVUS-RF and optical coherence tomography) can further improve the accuracy of the analysis of high risk lesions.

In-vivo assessment of the natural history of coronary atherosclerosis: vascular remodeling and endothelial shear stress determine the complexity of atherosclerotic disease progression

PURPOSE OF REVIEW

Atherosclerotic disease progression is determined by localized plaque growth, which is induced by systemic and local hemodynamic factors, and the nature of the wall remodeling response. The purpose of this review is to summarize the processes underlying the heterogeneity of coronary atherosclerosis progression in relation to the local hemodynamic and arterial remodeling environment.

RECENT FINDINGS

Multiple competing biological processes in the extracellular matrix define the extent of vascular remodeling and disease progression. The remodeling phenomenon is not consistent but is characterized by great phenotypical heterogeneity which reflects the complex effect of systemic, genetic and hemodynamic factors on the arterial wall response to plaque formation and progression. The exaggeration of expansive remodeling (i.e., excessive expansive remodeling) likely contributes to the transformation of an initially favorable action into an excessive course of vessel expansion, continued disease progression and plaque instability. Extremely low endothelial shear stress and excessive expansive remodeling establish a vicious cycle which leads to the formation of severe plaques with high-risk characteristics.

SUMMARY

The dynamic interplay between the local hemodynamic environment and the wall remodeling behavior determines the complexity of the natural history of atherosclerosis and explains the development of localized plaque vulnerability.

The vulnerable plaque: the real villain in acute coronary syndromes

The term "vulnerable plaque" refers to a vascular lesion that is prone to rupture and may result in life-threatening events which include myocardial infarction. It consists of thin-cap fibroatheroma and a large lipid core which is highly thrombogenic. Acute coronary syndromes often result from rupture of vulnerable plaques which frequently are only moderately stenosed and not visible by conventional angiography. Several invasive and non-invasive strategies have been developed to assess the burden of vulnerable plaques. Intravascular ultrasound provides a two-dimensional cross-sectional image of the arterial wall and can help assess the plaque burden and composition. Optical coherent tomography offers superior resolution over intravascular ultrasound. High-resolution magnetic resonance imaging provides non-invasive imaging for visualizing fibrous cap thickness and rupture in plaques. In addition, it may be of value in assessing the effects of treatments, such as lipid-lowering therapy. Technical issues however limit its clinical applicability. The role of multi-slice computed tomography, a well established screening tool for coronary artery disease, remains to be determined. Fractional flow reserve (FFR) may provide physiological functional assessment of plaque vulnerability; however, its role in the management of vulnerable plaque requires further studies. Treatment of the vulnerable patient may involve systemic therapy which currently include statins, ACE inhibitors, beta-blockers, aspirin, and calcium-channel blockers and in the future local therapeutic options such as drug-eluting stents or photodynamic therapy.

Comparison of in vivo assessment of vulnerable plaque by 64-slice multislice computed tomography versus optical coherence tomography

The aim of this study was to investigate the possibility of 64-slice multislice computed tomography (MSCT) to detect vulnerable plaque derived by optical coherence tomography. From September 2007 through December 2009, 122 lesions in 81 patients were evaluated by 64-slice MSCT and optical coherence tomography. Based on optical coherence tomographic findings, lesions were classified as thin-capped fibroatheroma (TCFA; n=37) and non-TCFA (n=85). Mean computed tomographic density value of the lesion was lower and remodeling index was larger in the TCFA group (44.9 ± 19.2 vs 78.7 ± 25.0 HU, p <0.0001; 1.14 ± 0.20 vs 0.95 ± 0.16, p<0.0001, respectively). Mean computed tomographic density value was correlated and remodeling index was inversely correlated with fibrous cap thickness (r=0.605, p<0.0001; r=-0.591, p<0.0001, respectively). Optimal threshold of mean computed tomographic value and remodeling index identified by receiver operating characteristic curve were 62.4 HU and 1.08 (area under the curve 0.859 and 0.781). Signet ringlike appearance was observed more frequently in the TCFA group (65% vs 16%, p<0.0001). In multivariate analysis, independent predictors of TCFA were mean computed tomographic density value ≤62.4 HU (odds ratio 8.20, 95% confidential interval 2.49 to 27.0, p=0.0005), remodeling index ≥1.08 (odds ratio 6.10, 95% confidential interval 2.04 to 18.2, p=0.0012), and signet ringlike appearance (odds ratio 6.33, 95% confidential interval 2.03 to 19.7, p=0.0014). In conclusion, based on comparisons with optical coherence tomographic findings, 64-slice MSCT may have the potential to detect vulnerable plaque.