Mechanical determinants of plaque modeling, remodeling and disruption

Non-Contrast and Contrast-Enhanced Cardiac Computed Tomography Imaging in the Diagnostic and Prognostic Evaluation of Coronary Artery Disease

In recent decades, cardiac computed tomography (CT) has emerged as a powerful non-invasive tool for risk stratification, as well as the detection and characterization of coronary artery disease (CAD), which remains the main cause of morbidity and mortality in the world. Advances in technology have favored the increasing use of cardiac CT by allowing better performance with lower radiation doses. Coronary artery calcium, as assessed by non-contrast CT, is considered to be the best marker of subclinical atherosclerosis, and its use is recommended for the refinement of risk assessment in low-to-intermediate risk individuals. In addition, coronary CT angiography (CCTA) has become a gate-keeper to invasive coronary angiography (ICA) and revascularization in patients with acute chest pain by allowing the assessment not only of the extent of lumen stenosis, but also of its hemodynamic significance if combined with the measurement of fractional flow reserve or perfusion imaging. Moreover, CCTA provides a unique incremental value over functional testing and ICA by imaging the vessel wall, thus allowing the assessment of plaque burden, composition, and instability features, in addition to perivascular adipose tissue attenuation, which is a marker of vascular inflammation. There exists the potential to identify the non-obstructive lesions at high risk of progression to plaque rupture by combining all of these measures.

Dilation of proximal internal carotid artery collapse due to severe distal stenosis after angioplasty for distal stenosis: A case report

Background

We report a case of proximal internal carotid artery (ICA) collapse due to severe distal stenosis that dilated after angioplasty for distal stenosis.

Case Description

A 69-year-old woman underwent thrombectomy for the left ICA occlusion due to stenosis of C3 portion and was discharged home with a modified Rankin Scale score of 0. One year later, she developed cerebral infarction due to progressive stenosis of the C3 portion of the left ICA with proximal ICA collapse and underwent emergency percutaneous transluminal angioplasty (PTA) for distal stenosis. Device guidance to the stenosis was difficult due to proximal ICA collapse. After PTA, blood flow in the left ICA increased, and proximal ICA collapse dilated over time. Due to severe residual stenosis, she underwent more aggressive PTA followed by Wingspan stenting. Device guidance to the residual stenosis was facilitated because proximal ICA collapse had already dilated. Six months later, proximal ICA collapse further dilated.

Conclusion

PTA for severe distal stenosis with proximal ICA collapse may result in dilation of proximal ICA collapse over time.

Imaging Identification and Prognosis of the Distal Internal Carotid Artery With Near and Complete Occlusion After Recanalization

Background and Purpose: Previous studies have mainly focused on treatment strategies and clinical outcomes for internal carotid artery near occlusion (ICANO) and internal carotid artery complete occlusion (ICACO). However, reports on the morphological changes of distal internal carotid artery (ICA) after recanalization are scarce. This study aimed at illustrating identifying features, assessing prognosis of the distal ICA after recanalization, and exploring best practices for treatment for ICANO and ICACO.

Materials and Methods: We retrospectively studied the clinical characteristics of 57 patients with ICANO or ICACO who underwent surgical recanalization. The clinical data, angiographic morphology, technical successful rate, perioperative complications, and the lumen changes of distal ICA before and after successful recanalization were analyzed.

Results: Fifty-two patients who achieved successfully recanalization were studied. Based on the postoperative lumen diameter changes in the distal ICA, 19 cases were classified as distal-dilatation and the remaining 33 as distal-narrowness. Patients in the distal-narrowness group mostly had ICACO (21.1 vs. 54.5%) and were men (68.4 vs. 93.9%). In the distal-narrowness group, the lumen of the distal ICA recovered to normal in 32 of the 33 patients during the follow-up period. Of the 32 patients reviewed, the ICA of 28 patients dilated back to normal after 1 week of surgery; the ICA of remaining patients 4 dilated 2 weeks postoperatively.

Conclusions: Narrowness of the distal ICA after hybrid recanalization was more prevalent in male patients with ICACO. Homogeneous stenosis of the whole course of the distal ICA is a low-perfusion narrowness which does not require intervention and will spontaneously recover after successful recanalization with an increase in the forward flow.

Photochemical Tissue Passivation of Arteriovenous Grafts Prevents Long-Term Development of Intimal Hyperplasia in a Swine Model

BACKGROUND

The autologous vein remains the standard conduit for lower extremity and coronary artery bypass grafting despite a 30%-50% 5-y failure rate, primarily attributable to intimal hyperplasia (IH) that develops in the midterm period (3-24 mo) of graft maturation. Our group discovered that externally strengthening vein grafts by cross-linking the adventitial collagen with photochemical tissue passivation (PTP) mitigates IH in an arteriovenous model at 4 wk. We now investigate whether this effect is retained in the midterm period follow-up.

METHODS

Six Hanford miniature pigs received bilateral carotid artery interposition vein grafts. In each animal, the external surface of one graft was treated with PTP before grafting, whereas the opposite side served as the untreated control. The grafts were harvested after 3 mo. Ultrasound evaluation of all vein grafts was performed at the time of grafting and harvest. The grafts were also evaluated histomorphometrically and immunohistologically for markers of IH.

RESULTS

All vein grafts were patent at 3 mo except one graft in the PTP-treated group because of early technical failure. The control vein grafts had significantly greater IH than PTP-treated grafts at 3 mo, as evidenced by the intimal area (2.6 ± 1.0 mm²versus 1.4 ± 1.5 mm², respectively, P = 0.045) and medial area (5.1 ± 1.9 mm²versus 2.7 ± 2.4 mm², respectively, P = 0.048). The control grafts had an increased presence and proliferation of mural myofibroblasts with greater smooth muscle actin and proliferating cell nuclear antigen staining.

CONCLUSIONS

PTP treatment to the external surface of the vein grafts decreases IH at 3 mo after arteriovenous grafting and may prevent future graft failure.

Association of Plasma Marker of Oxidized Lipid with Histologic Plaque Instability in Patients with Peripheral Artery Disease

BACKGROUND

The association between oxidized low-density lipoprotein (OxLDL) and plaque instability in coronary and carotid artery disease is well established. However, the association between OxLDL and the histologic changes of plaque in peripheral artery disease has not been clearly elucidated. This study aims to investigate the association between plasma OxLDL and histologic plaque instability in patients with peripheral artery disease.

METHODS

Prospectively obtained plaques from 48 patients who underwent endovascular atherectomy (n = 20), surgical endarterectomy (n = 9), or bypass surgery (n = 19) for treatment of atherosclerotic femoropopliteal artery disease were evaluated for histologic fibrosis, sclerosis, calcification, necrosis, cholesterol cleft, and foamy macrophages using hematoxylin and eosin, oil red O, and immunohistochemical staining. Unstable plaques were defined as plaques that were positive for foamy macrophages and with lipid content of more than 10% of the total plaque area. Plasma OxLDL levels were measured using an enzyme-linked immunosorbent assay (Mercodia AB, Uppsala, Sweden).

RESULTS

Of the 48 patients, 26 (54%) had unstable plaques. The unstable plaque group was younger, had fewer angiographic total occlusions, less calcification, and more CD68-positive and LOX-1-positive cells than the stable plaque group. Plasma OxLDL levels were significantly higher in the unstable plaque group than in the stable plaque group (57.4 ± 13.9 vs. 47.2 ± 13.6 U/L, P = 0.014). Multivariate analysis revealed that plasma OxLDL level, smoking, angiographic nontotal occlusion, and statin nonuse were independent predictors of unstable plaque.

CONCLUSIONS

Among patients with peripheral artery disease, the histologic instability of femoropopliteal plaque was independently associated with high plasma OxLDL, smoking, nontotal occlusion, and statin nonuse. Further large-scale studies are necessary to evaluate the role of noninvasive OxLDL measurement for predicting plaque instability and future adverse vascular event.

Orthogonal B-Mode Evaluation of Common Carotid Artery Plaques Reveals the Absence of Outward Remodeling

To properly assess morphologic and dynamic parameters of arteries and plaques, we propose the concept of orthogonal distance measurements, that is, measurements made perpendicular to the local lumen axis rather than along the ultrasound beam (vertical direction for a linear array). The aim of this study was to compare orthogonal and vertical artery and lumen diameters at the site of a plaque in the common carotid artery (CCA). Moreover, we investigated the interrelationship of orthogonal diameters and plaque size and the association of artery parameters with plaque echogenicity. In 29 patients, we acquired a longitudinal B-mode ultrasound recording of plaques at the posterior CCA wall. After semi-automatic segmentation of end-diastolic frames, diameters were extracted orthogonally along the lumen axis. To establish inter-observer variability of diameters obtained at the location of maximal plaque thickness, a second observer repeated the analysis (subset N = 21). Orthogonal adventitia-adventitia and lumen diameters could be determined with good precision (coefficient of variation: 1%-5%. However, the precision of the change in lumen diameter from diastole to systole (distension) at the site of the plaque was poor (21%-50%). The orthogonal lumen diameter was significantly smaller than the vertical lumen diameter (p <0.001). Surprisingly, the plaques did not cause outward remodeling, that is, a local increase in adventitia-adventitia distance at the site of the plaque. The intra- and inter-observer precision of diastolic-systolic plaque compression was poor and of the same order as the standard deviation of plaque compression. The orthogonal relative lumen distension was significantly lower for echogenic plaques, indicating a higher stiffness, than for echolucent plaques (p <0.01). In conclusion, we illustrated the feasibility of extracting orthogonal CCA and plaque dimensions, albeit that the proposed approach is inadequate to quantify plaque compression.

Vascular Adaptation: Pattern Formation and Cross Validation between an Agent Based Model and a Dynamical System

Myocardial infarction is the global leading cause of mortality (Go et al., 2014). Coronary artery occlusion is its main etiology and it is commonly treated by Coronary Artery Bypass Graft (CABG) surgery (Wilson et al, 2007). The long-term outcome remains unsatisfactory (Benedetto, 2016) as the graft faces the phenomenon of restenosis during the post-surgery, which consists of re-occlusion of the lumen and usually requires secondary intervention even within one year after the initial surgery (Harskamp, 2013). In this work, we propose an extensive study of the restenosis phenomenon by implementing two mathematical models previously developed by our group: a heuristic Dynamical System (DS) (Garbey and Berceli, 2013), and a stochastic Agent Based Model (ABM) (Garbey et al., 2015). With an extensive use of the ABM, we retrieved the pattern formations of the cellular events that mainly lead the restenosis, especially focusing on mitosis in intima, caused by alteration in shear stress, and mitosis in media, fostered by alteration in wall tension. A deep understanding of the elements at the base of the restenosis is indeed crucial in order to improve the final outcome of vein graft bypass. We also turned the ABM closer to the physiological reality by abating its original assumption of circumferential symmetry. This allowed us to finely replicate the trigger event of the restenosis, i.e. the loss of the endothelium in the early stage of the post-surgical follow up (Roubos et al., 1995) and to simulate the encroachment of the lumen in a fashion aligned with histological evidences (Owens et al., 2015). Finally, we cross-validated the two models by creating an accurate matching procedure. In this way we added the degree of accuracy given by the ABM to a simplified model (DS) that can serve as powerful predictive tool for the clinic.

Angiographic Characteristics of Pseudo-occlusion of the Internal Carotid Artery Before and After Stenting

BACKGROUND

Various definitions of pseudo-occlusion and clinical outcomes after various treatments have been reported, but reports discussing the stenotic characteristics of pseudo-occlusion are rare.

OBJECTIVE

To analyze the angiographic characteristics of pseudo-occlusion of the internal carotid artery (ICA) before and after carotid artery stenting (CAS).

METHODS

We retrospectively reviewed the angiographic characteristics of 56 patients with pseudo-occlusion of the ICA treated with CAS. Angiographic changes were evaluated from digital subtraction angiography in terms of lesion characteristics of the stenosis and the diameter changes in the distal ICA before and after CAS.

RESULTS

Fifty-six patients were successfully treated. Based on angiographic findings of ICA stenosis, 33 and 23 patients were classified into the single-channel and multiple-channel group, respectively. Regarding the diameter changes in the distal ICA after CAS, 31 cases were classified as immediate dilatation and the other 25 as restricted dilatation. Immediate dilatation of the distal ICA beyond the stent and that at a follow-up examination were observed significantly less frequently in the multiple-channel group than in the single-channel group. The use of multiple stents and stent occlusion at a follow-up examination were significantly more prevalent in the multiple-channel group than in the single-channel group.

CONCLUSION

Stenotic lesions of pseudo-occlusion of the ICA were classified as single channel and multiple channel. Restricted dilatation of the distal ICA after CAS was more prevalent in the multiple-channel group. Because adverse events tended to be more frequent in the multiple-channel group than in the single-channel group, the indications for CAS should be determined carefully in multiple-channel patients.

ABBREVIATIONS

CAS, carotid artery stentingICA, internal carotid artery.

Pathobiology of Ischemic Heart Disease: Past, Present and Future

This review provides a perspective on knowledge of ischemic heart disease (IHD) obtained from the contemporary era of research which began in the 1960s and has continued to the present day. Important discoveries have been made by basic and translational scientists and clinicians. Pathologists have contributed significantly to insights obtained from experimental studies and clinicopathological studies in humans. The review also provides a perspective for future directions in research in IHD aimed at increasing basic knowledge and developing additional therapeutic options for patients with IHD.

Physiologic assessment of coronary artery disease by cardiac computed tomography

Coronary artery disease (CAD) remains the leading cause of death and morbidity worldwide. To date, diagnostic evaluation of patients with suspected CAD has relied upon the use of physiologic non-invasive testing by stress electrocardiography, echocardiography, myocardial perfusion imaging (MPI) and magnetic resonance imaging. Indeed, the importance of physiologic evaluation of CAD has been highlighted by large-scale randomized trials that demonstrate the propitious benefit of an integrated anatomic-physiologic evaluation method by performing lesion-specific ischemia assessment by fractional flow reserve (FFR)-widely considered the "gold" standard for ischemia assessment-at the time of invasive angiography. Coronary CT angiography (CCTA) has emerged as an attractive non-invasive test for anatomic illustration of the coronary arteries and atherosclerotic plaque. In a series of prospective multicenter trials, CCTA has been proven as having high diagnostic performance for stenosis detection as compared to invasive angiography. Nevertheless, CCTA evaluation of obstructive stenoses is prone to overestimation of severity and further, detection of stenoses by CCTA does not reliably determine the hemodynamic significance of the visualized lesions. Recently, a series of technological innovations have advanced the possibility of CCTA to enable physiologic evaluation of CAD, thereby creating the potential of this test to provide an integrated anatomic-physiologic assessment of CAD. These advances include rest-stress MPI by CCTA as well as the use of computational fluid dynamics to non-invasively calculate FFR from a typically acquired CCTA. The purpose of this review is to summarize the most recent data addressing these 2 physiologic methods of CAD evaluation by CCTA.

A dynamical system that describes vein graft adaptation and failure

Adaptation of vein bypass grafts to the mechanical stresses imposed by the arterial circulation is thought to be the primary determinant for lesion development, yet an understanding of how the various forces dictate local wall remodeling is lacking. We develop a dynamical system that summarizes the complex interplay between the mechanical environment and cell/matrix kinetics, ultimately dictating changes in the vein graft architecture. Based on a systematic mapping of the parameter space, three general remodeling response patterns are observed: (1) shear stabilized intimal thickening, (2) tension induced wall thinning and lumen expansion, and (3) tension stabilized wall thickening. Notable is our observation that the integration of multiple feedback mechanisms leads to a variety of non-linear responses that would be unanticipated by an analysis of each system component independently. This dynamic analysis supports the clinical observation that the majority of vein grafts proceed along an adaptive trajectory, where grafts dilate and mildly thicken in response to the increased tension and shear, but a small portion of the grafts demonstrate a maladaptive phenotype, where progressive inward remodeling and accentuated wall thickening lead to graft failure.

CORRELATION OF MECHANICAL BEHAVIOR AND MMP-1 PRESENCE IN HUMAN ATHEROSCLEROTIC PLAQUE

Regions of matrix metalloproteinase (MMP) activity potentially increase the susceptibility of the atherosclerotic lesion to complications associated with plaque rupture. Assessing the risk posed by this mechanism requires investigating the stress-strain environment associated with matrix metalloproteinase production in heterogeneous plaque. To this end, an experimental-computational technique was developed to perform mechanical analysis of physiologically loaded, diseased human aorta in vitro and to investigate relationships between vascular mechanics, histology, and histochemistry. Mechanical data and specimen histology were coupled through a heterogeneous finite element model, and tissue constituent material properties were determined by an optimization method. The cross-sectional distribution of MMP-1 was quantified using immunohistochemical techniques. Results show stresses and strains are strongly influenced by lesion structure and composition, and MMP-1 presence is correlated with histology and lesion mechanics. Interactions between lipid presence, mechanical stimuli, and extracellular matrix metabolism-catabolism likely affect arterial plaque remodeling, progression, and the risk of disruption and clinical symptoms.

The Relation Between the Arterial Stress and Restenosis Rate After Coronary Stenting

Two commercially available stents (the Palmaz–Schatz (PS) and S670 stents) with reported high and low restenosis rates, respectively, have been investigated in this paper. Finite element models simulating the stent, plaque, and artery interactions in 3 mm stenosed right coronary arteries were developed. These models were used to determine the stress field in artery walls after stent implantation. The material properties of porcine arteries were measured and implemented in the numerical models. The stress concentration induced in the artery by the PS stent was found to be more than double that of the S670 stent. It demonstrated a good correlation with the reported restenosis rate. The effects of stent structures, compliance mismatch, plaque geometry, and level of stenosis were studied. Results suggested that stent designs and tissue properties cause alterations in vascular anatomy that adversely affect arterial stress distributions within the wall, which impact vessel responses such as restenosis. Appropriate modeling of stent, plaque, and artery interactions provided insights for evaluating alterations to the arterial mechanical environment, as well as biomechanical factors leading to restenosis.

Tensile and compressive properties of fresh human carotid atherosclerotic plaques

Accurate characterisation of the mechanical properties of human atherosclerotic plaque is important for our understanding of the role of vascular mechanics in the development and treatment of atherosclerosis. The majority of previous studies investigating the mechanical properties of human plaque are based on tests of plaque tissue removed following autopsy. This study aims to characterise the mechanical behaviour of fresh human carotid plaques removed during endarterectomy and tested within 2h. A total of 50 radial compressive and 17 circumferential tensile uniaxial tests were performed on samples taken from 14 carotid plaques. The clinical classification of each plaque, as determined by duplex ultrasound is also reported. Plaques were classified as calcified, mixed or echolucent. Experimental data indicated that plaques were highly inhomogeneous; with variations seen in the mechanical properties of plaque obtained from individual donors and between donors. The mean behaviour of samples for each classification indicated that calcified plaques had the stiffest response, while echolucent plaques were the least stiff. Results also indicated that there may be a difference in behaviour of samples taken from different anatomical locations (common, internal and external carotid), however the large variability indicates that more testing is needed to reach significant conclusions. This work represents a step towards a better understanding of the in vivo mechanical behaviour of human atherosclerotic plaque.

Characterizing intramural stress and inflammation in hypertensive arterial bifurcations

A histology-based methodology was developed and used to determine whether intramural stress and combined monocyte/macrophage density positively correlate within hypertensive bifurcations. Hypertension was induced in Sprague-Dawley rats using Angiotensin II pumps. Analysis focused on mesenteric bifurcations harvested 7 days (n = 4) post implant, but also included normotensive (n = 2) and 21-day hypertensive (n = 1) samples. Mesentery was processed in a manner that preserves morphology, corrects for histology-related distortions and results in reconstructions suitable for finite element analysis. Peaks in intramural stress and monocyte/macrophage density occurred near bifurcations after the onset of hypertension. Cell density peaks occurred in regions where surface curvature is complex and tends to heighten intramural stress. Also, a strong positive correlation between mean stress and mean cell density suggests that they are related phenomena. A point-by-point comparison of stress and cell density throughout each bifurcation did not exhibit a consistent pattern. We offer reasons why this most stringent test did not corroborate our other findings that high intramural stress is correlated with increased inflammation near the center of the bifurcation.

Cerebral Haemodynamic Disturbances in Patients with Moderate Carotid Artery Stenosis

OBJECTIVE

Dynamic MR perfusion imaging can detect cerebral perfusion deficits resulting from severe internal carotid artery (ICA) stenosis. It is unknown, however, whether moderate ICA stenosis (50-69%) also causes haemodynamic disturbance. We investigated whether cerebral perfusion deficits were detectable in patients with moderate ICA stenosis.

METHODS

Eighteen patients underwent T2* weighted cerebral MR perfusion imaging with a gadolinium based contrast agent. Differences in mean time to peak (mTTP) and relative cerebral blood volume (rCBV) between cerebral hemispheres were calculated for middle cerebral artery territory regions by a reader blinded to the angiographic and clinical findings.

RESULTS

There were significant differences in mTTP between cerebral hemispheres in 15 patients with a mean inter-hemispheric delay in mTTP of 0.49 s (95% confidence intervals, 0.25 and 0.72 s) which was statistically significant ( p <0.001). In 1 patient with bilateral moderate stenosis there was no difference in mTTP.

CONCLUSIONS

Moderate ICA stenosis results in significant ipsilateral cerebral perfusion delays detectable by dynamic susceptibility MRI. Follow-up studies might reveal whether these delays improve following carotid endarterectomy.

Increase in Collagen Turnover But Not in Collagen Fiber Content Is Associated with Flow-Induced Arterial Remodeling

BACKGROUND

Degradation and synthesis of collagen are common features in arterial geometrical remodeling. Previous studies described an association between arterial remodeling and an increase in collagen fiber content after balloon injury. However, this does not exclude that the association between collagen content and remodeling depends on arterial injury since the association of collagen fiber content and arterial remodeling, without arterial injury, has not been investigated. The aim of the present study was to study the relation between flow-induced arterial geometrical remodeling, without arterial injury, and collagen synthesis and degradation, collagen fiber content and cell-migration-associated moesin levels.

METHODS AND RESULTS

In 23 New Zealand White rabbits an arteriovenous shunt (AV shunt) was created in the carotid and femoral artery to induce a structural diameter increase or a partial ligation (n = 27 rabbits) to induce a diameter decrease. In both models, arterial remodeling was accompanied by increased procollagen synthesis, reflected by increased procollagen mRNA or Hsp47 protein levels. In both models, however, no changes were detected in collagen fiber content. Active MMP-2 and moesin levels were increased after AV shunting.

CONCLUSIONS

Collagen synthesis and MMP-2 activation were associated with arterial remodeling. However, a change in collagen fiber content was not observed. These results suggest that, during flow-induced geometrical arterial remodeling, increases in collagen synthesis are used for matrix collagen turnover and cell migration but not to augment collagen fiber content.

Uniaxial strain upregulates matrix-degrading enzymes produced by human vascular smooth muscle cells

Arteries remodel in response to environmental changes. We investigated whether mechanical strain modulates production of matrix metalloproteinase (MMP)-2 and -9 by cultured vascular smooth muscle cells (SMC). MMP-2 and MMP-9 expression were tested using human saphenous vein SMC cultured on silicone membranes at rest or subjected to physiological levels (5%) of stationary or cyclical (1 Hz) uniaxial strain. Compared with control, stationary strain significantly increased MMP-2 mRNA levels at all time points, whereas cyclic strain decreased it after 48 h. Both secreted and cell-associated pro-MMP-2 levels were increased by stationary strain at all times (P < 0.01), whereas cyclic strain decreased secreted levels after 48 h (P < 0.02). MMP-9 mRNA levels and pro-MMP-9 protein were increased after 48 h of stationary stretch (P < 0.01) compared with both no strain and cyclic strain. Our study indicates that vascular SMC show a selective response to different types of strain. We suggest that local increases in stationary mechanical strain resulting from stenting, hypertension, or atherosclerosis may lead to enhanced matrix degradation by SMC.

A new method for characterizing carotid plaque: multiple cross-sectional view echomorphology

PURPOSE

This study compares the ability of computer-derived B-mode ultrasound gray-scale measurements from a single longitudinal view (SLV) versus multiple cross-sectional views (MCSV) to differentiate symptomatic from asymptomatic carotid plaque causing more than 70% stenosis.

METHOD

Seventy-four internal carotid artery (ICA) stenoses (70%-99%; 33 asymptomatic, 41 symptomatic within 3 months) were imaged to obtain the "best" SLV and five to eight MCSV images at 5 mm intervals from the carotid bifurcation. Digitized sonograms were computerized and normalized to the gray scale median (GSM) of blood (0) and vessel adventitia (200). Plaque GSM was determined for each frame (image analysis, MATLAB 5.3). General risk factors for stroke and plaque echogenicity (SLV GSM; minimum MCSV GSM; cross-sectional axial heterogeneity (highest minus lowest MCSV GSM) were determined for each group.

RESULTS

Risk factors for stroke were similar in both groups, as was mean SLV GSM: symptomatic, 34 (95% confidence interval [CI], 24.8-43.0), asymptomatic, 43 (CI, 32.6-53.2); P =.1. Minimum MCSV GSM was lower for symptomatic plaque: 7 (CI, 4.2-9.8] vs 18.3 (CI, 12.2-24.5); P =.002. Greater axial GSM heterogeneity was present in symptomatic plaque: 34.5 (CI, 27.2-41.9) vs 16 (CI, 11.0-20.8); P =.0001.

CONCLUSIONS

MCSV cross-sectional imaging that enables objective assessment of regional plaque echolucency and heterogeneity is more sensitive than SLV sonography for differentiating symptomatic from asymptomatic plaque.

Biochemical characterization of atherosclerotic plaque constituents using FTIR spectroscopy and histology

The behavior of vulnerable atherosclerotic plaques is believed to be closely related to plaque composition. There is a need for an effective in vivo technique for examining plaque constituent properties. In this study, Fourier transform infrared spectroscopy using attenuated total reflectance (FTIR-ATR) was used to assess and analyze the biochemical properties of human atherosclerotic plaques. FTIR spectra clearly revealed prominent spectral features corresponding to plaque constituents of interest: the 2930 cm(-1) and 2850 cm(-1) peaks (indicating the presence of lipids), the 1730 cm(-1) peak (lipid esters), the 1550 cm(-1) and 1650 cm(-1) peaks (fibrous tissues), and the 1100-1000 cm(-1) broad phosphate peak (calcification). Spectral data examined on a qualitative basis correlated well with both gross tissue anatomy and histologic features. Gross spatial mappings of tissue sections of both lipidic and calcified plaques were performed. Spectra from various regions of the plaques demonstrated the evolution of lipid peaks, fibrous tissue peaks, and the phosphate calcification band within the plaques. Histologic analysis corroborated the spectral findings in this study.

Left ventricular muscle mass and elevated heart rate are associated with coronary plaque disruption

BACKGROUND

Plaque disruption is the central pathophysiological mechanism underlying acute coronary syndromes and the progression of coronary atherosclerosis. There exists only scant information about the factors that are associated with its development. The aim of the current study was to analyze the contribution of hemodynamic forces in the pathogenesis of plaque disruption. Plaque disruption was diagnosed by coronary angiography of stenosed but not completely occluded coronary arteries.

METHODS AND RESULTS

This study retrospectively analyzed 106 patients who underwent 2 coronary angiography procedures within 6 months. We investigated 53 patients with initially smooth stenoses who developed plaque disruption by the time of the second coronary angiogram and compared these patients with 53 age- and sex-matched individuals with smooth stenoses without angiographic signs of plaque disruption. The 2 groups were compared by analyzing central hemodynamics, echocardiographic measurements, and cardiovascular medication use. Logistic regression analysis identified positive associations between plaque disruption, left ventricular muscle mass >270 g, and a mean heart rate >80 bpm and a negative association with the use of beta-blockers.

CONCLUSIONS

The associations documented by our investigation indicate that hemodynamic forces may play a crucial role in the pathogenesis of plaque disruption. These findings may help to identify patients who are at an increased risk of plaque disruption and who might gain benefit from pharmacological interventions aimed at reducing heart rate, for example, by the use of beta-blockers, or a reduction of left ventricular hypertrophy.

Compressive stress-relaxation of human atherosclerotic plaque

Knowledge of the mechanical properties of human atherosclerotic plaque is fundamental to understanding atherosclerosis and its treatment. Data are scant, however, particularly with respect to the time-dependent nature of plaque behavior. Previous experiments in our lab showed that human plaques do not exhibit the traditional preconditioning behavior common to most soft tissues. In particular, the behaviors of three classes of plaques differed fundamentally in response to multiple, successive, cyclic compression protocols. In this report, we demonstrate that plaques exhibit different responses to successive relaxation tests in uniaxial compression. Not only is there significant relaxation, but there are composition-dependent differences in the general character of the relaxation responses. Such information on the time-dependent behavior is important for the design of clinical protocols such as stenting or angioplasty wherein the atherosclerotic vessel is subjected to persistent or multiple short duration loadings. This study presents a step toward a better understanding of the biomechanical behavior of atherosclerotic plaques; however, the need for much more data remains.

Blood flow and vessel mechanics in a physiologically realistic model of a human carotid arterial bifurcation

The pulsatile flow in an anatomically realistic compliant human carotid bifurcation was simulated numerically. Pressure and mass flow waveforms in the carotid arteries were obtained from an individual subject using non-invasive techniques. The geometry of the computational model was reconstructed from magnetic resonance angiograms. Maps of time-average wall shear stress, contours of velocity in the flow field as well as wall movement and tensile stress on the arterial wall are all presented. Inconsistent with previous findings from idealised geometry models, flow in the carotid sinus is dominated by a strong helical flow accompanied by a single secondary vortex motion. This type of flow is induced primarily by the asymmetry and curvature of the in vivo geometry. Flow simulations have been carried out under the rigid wall assumption and for the compliant wall, respectively. Comparison of the results demonstrates the quantitative influence of the vessel wall motion. Generally there is a reduction in the magnitude of wall shear stress, with its degree depending on location and phase of the cardiac cycle. The region of slow or reversed flow was greater, in both spatial and temporal terms in the compliant model, but the global characteristics of the flow and stress patterns remain unchanged. The analysis of mechanical stresses on the vessel surface shows a complicated stress field. Stress concentration occurs at both the anterior and posterior aspects of the proximal internal bulb. These are also regions of low wall shear stress. The comparison of computed and measured wall movement generally shows good agreement.

Prevention of mechanical stretch-induced endothelial and smooth muscle cell injury in experimental vein grafts

Vein grafts are subject to increased tensile stress due to exposure to arterial blood pressure, which has been hypothesized to induce endothelial cell (EC) and smooth muscle cell (SMC) injury. This study was designed to verify this hypothesis and to develop a tissue engineering approach that can be used to prevent these pathological events. Two experimental models were created in rats to achieve these goals: (1) a nonengineered vein graft with increased tensile stress, which was created by grafting a jugular vein into the abdominal aorta using a conventional end-to-end anastomotic technique; and (2) an engineered vein graft with reduced tensile stress, which was created by restricting a vein graft into a cylindrical sheath constructed using a polytetrafluoroethylene membrane. The integrity of ECs in these models was examined by using a silver nitrate staining method, and the integrity of SMCs was assessed by using a fluorescein phalloidin-labeling technique. It was found that nonengineered vein grafts were associated with early EC denudation with a change in EC coverage from 100 percent in normal jugular veins to 36 +/- 10, 28 +/- 12, 18 +/- 9, 44 +/- 15, 80 +/- 13, and 97 +/- 6 percent at 1 and 6 hours and 1, 5, 10, and 30 days, respectively. Similarly, rapid SMC actin filament degradation was found during the early period with a change in SMC coverage from approximately 94 percent in normal jugular veins to 80 +/- 10, 41 +/- 17, 25 +/- 9, 51 +/- 15, 79 +/- 15, 98 +/- 2 percent at 1 and 6 hours and 1, 5, 10, and 30 days, respectively, in nonengineered vein grafts. In engineered vein grafts with reduced tensile stress, EC denudation and SMC actin filament degradation were prevented significantly. These results suggested that mechanical stretch due to increased tensile stress contributed to EC and SMC injury in experimental vein grafts, and these pathological events could be partially prevented when tensile stress was reduced by using a biomechanical engineering approach.

Hemispheric symptoms and carotid plaque echomorphology

PURPOSE

In patients with carotid bifurcation disease, the risk of stroke mainly depends on the severity of the stenosis, the presenting hemispheric symptom, and, as recently suggested, on plaque echodensity. We tested the hypothesis that asymptomatic carotid plaques and plaques of patients who present with different hemispheric symptoms are related to different plaque structure in terms of echodensity and the degree of stenosis.

METHODS

Two hundred sixty-four patients with 295 carotid bifurcation plaques (146 symptomatic, 149 asymptomatic) causing more than 50% stenosis were examined with duplex scanning. Thirty-six plaques were associated with amaurosis fugax (AF), 68 plaques were associated with transient ischemic attacks (TIAs), and 42 plaques were associated with stroke. B-mode images were digitized and normalized using linear scaling and two reference points, blood and adventitia. The gray scale median (GSM) of blood was set to 0, and the GSM of the adventitia was set to 190 (gray scale range, black = 0; white = 255). The GSM of the plaque in the normalized image was used as the objective measurement of echodensity.

RESULTS

The mean GSM and the mean degree of stenosis, with 95% confidence intervals, for plaques associated with hemispheric symptoms were 13.3 (10.6 to 16) and 80.5 (78.3 to 82.7), respectively; and for asymptomatic plaques, the mean GSM and the mean degree of stenosis were 30.5 (26.2 to 34.7) and 72. 2 (69.8 to 74.5), respectively. Furthermore, in plaques related to AF, the mean GSM and the mean degree of stenosis were 7.4 (1.9 to 12. 9) and 85.6 (82 to 89.2), respectively; in those related to TIA, the mean GSM and the mean degree of stenosis were 14.9 (11.2 to 18.6) and 79.3 (76.1 to 82.4), respectively; and in those related to stroke, the mean GSM and the mean degree of stenosis were 15.8 (10.2 to 21.3) and 78.1 (73.4 to 82.8), respectively.

CONCLUSION

Plaques associated with hemispheric symptoms are more hypoechoic and more stenotic than those associated with no symptoms. Plaques associated with AF are more hypoechoic and more stenotic than those associated with TIA or stroke or those without symptoms. Plaques causing TIA and stroke have the same echodensity and the same degree of stenosis. These findings confirm previous suggestions that hypoechoic plaques are more likely to be symptomatic than hyperechoic ones. They support the hypothesis that the pathophysiologic mechanism for AF is different from that for TIA and stroke.

Haemodynamics, wall mechanics and atheroma: a clinician's perspective

Atherosclerosis, leading to myocardial infarction and stroke, is the major cause of death and morbidity in Western societies. Atheromatous lesions characteristically occur in regions of branching and marked curvature. Low shear stress and increased mural tensile stress may be major determinants underlying atheroma formation at these sites. Furthermore, the distribution of circumferential tensile stresses may play a critical role in where, why and when advanced atheromatous plaques rupture, leading to catastrophic ischaemic events. Recent advances in the application of computational modelling to in vivo vascular ultrasound and magnetic resonance imaging data should further elucidate the roles of haemodynamic factors and vessel wall mechanics in atherosclerosis. In future this is likely to lead to better use of currently available anti-atherosclerosis strategies. It may also facilitate the discovery, evaluation and development of novel treatments.

Mechanical analysis of heterogeneous, atherosclerotic human aorta

An experimental technique was developed to determine the finite strain field in heterogeneous, diseased human aortic cross sections at physiologic pressures in vitro. Also, the distributions within the cross sections of four histologic features (disease-free zones, lipid accumulations, fibrous intimal tissue, and regions of calcification) were quantified using light microscopic morphometry. A model incorporating heterogeneous, plane stress finite elements coupled the experimental and histologic data. Tissue constituent mechanical properties were determined through an optimization strategy, and the distributions of stress and strain energy in the diseased vascular wall were calculated. Results show that the constituents of atherosclerotic lesions exhibit large differences in their bilinear mechanical properties. The distributions of stress and strain energy in the diseased vascular wall are strongly influenced by both lesion structure and composition. These results suggest that accounting for heterogeneities in the mechanical analysis of atherosclerotic arterial tissue is critical to establishing links between lesion morphology and the susceptibility of plaque to mechanical disruption in vivo.