Patterns of Coronary Artery Movement and the Development of Coronary Atherosclerosis

Considering the Influence of Coronary Motion on Artery-Specific Biomechanics Using Fluid-Structure Interaction Simulation

The endothelium in the coronary arteries is subject to wall shear stress and vessel wall strain, which influences the biology of the arterial wall. This study presents vessel-specific fluid-structure interaction (FSI) models of three coronary arteries, using directly measured experimental geometries and boundary conditions. FSI models are used to provide a more physiologically complete representation of vessel biomechanics, and have been extended to include coronary bending to investigate its effect on shear and strain. FSI both without- and with-bending resulted in significant changes in all computed shear stress metrics compared to CFD (p = 0.0001). Inclusion of bending within the FSI model produced highly significant changes in Time Averaged Wall Shear Stress (TAWSS) + 9.8% LAD, + 8.8% LCx, - 2.0% RCA; Oscillatory Shear Index (OSI) + 208% LAD, 0% LCx, + 2600% RCA; and transverse wall Shear Stress (tSS) + 180% LAD, + 150% LCx and + 200% RCA (all p < 0.0001). Vessel wall strain was homogenous in all directions without-bending but became highly anisotropic under bending. Changes in median cyclic strain magnitude were seen for all three vessels in every direction. Changes shown in the magnitude and distribution of shear stress and wall strain suggest that bending should be considered on a vessel-specific basis in analyses of coronary artery biomechanics.

Perivascular mechanical environment: A narrative review of the role of externally applied mechanical force in the pathogenesis of atherosclerosis

Atherosclerosis is promoted by systemic factors, such as dyslipidemia, hypertension, diabetes, and smoking, which cause atherosclerosis in blood vessels throughout the body. However, atherosclerotic lesions are characterized by their frequent occurrence in specific vessels and sites. Blood vessels are exposed to various mechanical forces related to blood pressure and flow. Although shear stress promotes the initiation and progression of atherosclerotic lesions, the pathogenesis of site specificity of atherosclerosis is not sufficiently explained by shear stress. We propose the concept of a perivascular mechanical environment (PVME). Compelling evidence suggests that site specificity in atherosclerotic lesions depends on a distinct local PVME. Atheroprone arteries, such as the coronary artery, are markedly affected by externally applied mechanical force (EMF), whereas atheroprotective arteries, such as the internal thoracic artery, are less affected. Recent studies have shown that the coronary artery is affected by cardiac muscle contraction, the carotid artery by the hyoid bone and the thyroid cartilage, and the abdominal aorta and lower extremity arteries by musculoskeletal motion. We speculate that the thoracic cage protects the internal thoracic artery from EMF owing to a favorable PVME. Furthermore, evidence suggests that plaque eccentricity is provided by EMF; plaques are frequently observed on an external force-applied side. In each vascular tree, site-specific characteristics of the PVME differ substantially, inducing individual atherogenicity. From the perspective of the mechanical environment, hemodynamic stress occurs in an inside-out manner, whereas EMF occurs in an outside-in manner. These inward and outward forces apply mechanical load individually, but interact synergistically. The concept of a PVME is a novel pathogenesis of atherosclerosis and also might be a pathogenesis of other arterial diseases.

The Effect of Mechanical Overloading on Surface Roughness of the Coronary Arteries

Background

Surface roughness can be used to identify disease within biological tissues. Quantifying surface roughness in the coronary arteries aids in developing treatments for coronary heart disease. This study investigates the effect of extreme physiological loading on surface roughness, for example, due to a rupture of an artery.

Methods

The porcine left anterior descending (LAD) coronary arteries were dissected ex vivo. Mechanical overloading was applied to the arteries in the longitudinal direction to simulate extreme physiological loading. Surface roughness was calculated from three-dimensional reconstructed images. Surface roughness was measured before and after damage and after chemical processing to dehydrate tissue specimens.

Results

Control specimens confirmed that dehydration alone results in an increase of surface roughness in the circumferential direction only. No variation was noted between the hydrated healthy and damaged specimens, in both the longitudinal (0.91 ± 0.26 and 1.05 ± 0.25 μm) and circumferential (1.46 ± 0.38 and 1.47 ± 0.39 μm) directions. After dehydration, an increase in surface roughness was noted for damaged specimens in both the longitudinal (1.28 ± 0.33 μm) and circumferential (1.95 ± 0.56 μm) directions.

Conclusions

Mechanical overloading applied in the longitudinal direction did not significantly affect surface roughness. However, when combined with chemical processing, a significant increase in surface roughness was noted in both the circumferential and longitudinal directions. Mechanical overloading causes damage to the internal constituents of the arteries, which is significantly noticeable after dehydration of tissue.

Dynamic Viscoelasticity and Surface Properties of Porcine Left Anterior Descending Coronary Arteries

The aim of this study was, for the first time, to measure and compare quantitatively the viscoelastic properties and surface roughness of coronary arteries. Porcine left anterior descending coronary arteries were dissected ex vivo. Viscoelastic properties were measured longitudinally using dynamic mechanical analysis, for a range of frequencies from 0.5 to 10 Hz. Surface roughness was calculated following three-dimensional reconstructed of surface images obtained using an optical microscope. Storage modulus ranged from 14.47 to 25.82 MPa, and was found to be frequency-dependent, decreasing as the frequency increased. Storage was greater than the loss modulus, with the latter found to be frequency-independent with a mean value of 2.10 ± 0.33 MPa. The circumferential surface roughness was significantly greater (p < 0.05) than the longitudinal surface roughness, ranging from 0.73 to 2.83 and 0.35 to 0.92 µm, respectively. However, if surface roughness values were corrected for shrinkage during processing, circumferential and longitudinal surface roughness were not significantly different (1.04 ± 0.47, 0.89 ± 0.27 µm, respectively; p > 0.05). No correlation was found between the viscoelastic properties and surface roughness. It is feasible to quantitatively measure the viscoelastic properties of coronary arteries and the roughness of their endothelial surface.

Localization of in-stent neoatherosclerosis in relation to curvatures and bifurcations after stenting

BACKGROUND

In-stent neoatherosclerosis (ISNA) is a final common pathway of late-stent failure. However, distribution of ISNA has been little reported. This study was to evaluate the localization of ISNA in relation to curvatures and bifurcations after stent implantation using optical coherence tomography (OCT).

METHODS

We retrospectively selected patients who underwent OCT examination ≥12 months after stent (sirolimus-eluting stents, SES) implantation. A stent curvature was defined if the angulation of the stent segment was >29°. Distribution of ISNA in relation to stent curvature and bifurcation was evaluated.

RESULTS

Totally, 331 patients were enrolled. The mean follow-up time was 15 months. Forty-one (12.3%) patients were found with ISNA. OCT results showed that stents with ISNA had thicker neointima (mean neointima thickness: 0.16 vs. 0.08 mm, P<0.001) compared to patients without ISNA. Segments with angulation >29° had a higher prevalence of ISNA compared with to angulation ≤29° [18 (18.4%) vs. 23 (9.9%), P=0.032]. ISNA was more frequently located at the "inner curvature" than the "outer curvature" (77.8% vs. 22.2%, P=0.018). If ISNA occurred in a branch, it was more often on the opposite side of the branch compared with the same side of the branch [21 (77.8%) vs. 6 (22.2%), P=0.004].

CONCLUSIONS

Localization of ISNA is related to vessel curvatures and bifurcations. ISNA occurs more often on the inner curvature and the opposite side of the branch.

Relationship between left coronary artery bifurcation angle and restenosis after stenting of the proximal left anterior descending artery

INTRODUCTION

Restenosis after a percutaneous coronary intervention for proximal left anterior descending (pLAD) coronary artery disease remains a clinical challenge. However, the relationship between the left main trunk (LMT)/LAD bifurcation angle and the pLAD artery restenosis is unclear. This study examined the relationship between the LMT-LAD bifurcation angle and restenosis after stent implantation for pLAD disease.

METHODS

We analysed the data of 177 consecutive patients who underwent stent implantation for pLAD disease, followed by coronary angiography between December 2008 and September 2013. The LMT-LAD bifurcation angle was measured in the left or the right anterior oblique caudal (CAU) angiographic view.

RESULTS AND DISCUSSION

Out of 177 patients, 12 developed in-stent restenosis and 21 developed in-segment restenosis. The mean angle in patients with in-stent restenosis (52.2°±14.5°) in the left anterior oblique CAU view was significantly larger than that in patients without restenosis (32.0°±18.1°; P<0.001). The LMT-LAD angle in the right anterior oblique CAU view was significantly larger in patients with in-segment restenosis (27.3°±14.3°) than in patients without restenosis (17.5°±10.1°; P<0.001). Moreover, by multivariate analysis, the LMT-LAD angle was an independent predictor of in-stent and in-segment restenosis, after adjustment for significant confounders such as diabetes, hypertension, dyslipidaemia, final minimum lesion diameter and lesion length.

CONCLUSION

This study suggests that a wide LMT-LAD angle is a predictor of restenosis after stent implantation for pLAD artery disease.

The Relationship between Coronary Artery Movement Type andStenosis Severity with Acute Myocardial Infarction

INTRODUCTION

The severity of coronary artery stenosis which leads to myocardial infarction (MI) has been a matter of controversy. Historical data are in favor of mild luminal stenosis (<50% diameter stenosis) while recent studies suggest hemodynamically-significant coronary stenosis as the main substrate for subsequent MI. Also, mechanical stress resulted from coronary artery movement (CAM) may be responsible for plaques rupture. In this study, we evaluated the severity of plaques leading to MI and common CAM patterns in the involved coronary segments.

METHODS

In a cross-sectional descriptive-analytical study, on patients with acute ST-segment myocardial infarction (STEMI) undergoing coronary angiography, the relationship between coronary artery movement type and stenosis severity with acute MI was evaluated. Lesions with stenosis diameter greater than 50 percent were defined as moderate and those equal or higher than 70% were defined as severe stenosis. Three different patterns of coronary artery motion including compression, bending and displacement types were evaluated in segments with culprit lesion.

RESULTS

One hundred and sixty two patients were enrolled. Ninety patients (55.6%) were male and 72 (44.4%) were female. Mean age of the patients was 60.56±13.43 years. In terms of Infarct related lesions (IRLs), 86% of the cases had at least moderate stenosis and in 67%, severe stenosis was present. More than 50% stenosis was found in all patients with anterior STEMI involving LAD. Among three types of coronary motion patterns, compression pattern was significantly higher in LAD (P<0.001), RCA (P<0.001), Diagonal artery (P<0.001) and OM branch (P=0.044), but not in proper LCX (P=0.307).

CONCLUSION

Most of the lesions leading to myocardial infarction have a diameter stenosis of at least 50% and mainly are located in the coronary segments with compression movement pattern.

The compression type of coronary artery motion in patients with ST-segment elevation acute myocardial infarction and normal controls: a case-control study

Background

Prediction of the location of culprit lesions responsible for ST-segment elevation myocardial infarctions may allow for prevention of these events. A retrospective analysis of coronary artery motion (CAM) was performed on coronary angiograms of 20 patients who subsequently had ST-segment elevation myocardial infarction treated by primary or rescue angioplasty and an equal number of age and sex matched controls with normal angiograms.

Findings

There was no statistically significant difference between the frequency of CAM types of the ST-segment elevation acute myocardial infarction and control patients (p = 0.97). The compression type of CAM is more frequent in the proximal and mid segments of all three coronary arteries. No statistically significant difference was found when the frequency of the compression type of CAM was compared between the ST-segment elevation acute myocardial infarction and control patients for the individual coronary artery segments (p = 0.59).

Conclusion

The proportion of the compression type of coronary artery motion for individual artery segments is not different between patients who have subsequent ST-segment elevation myocardial infarctions and normal controls.

The relationship between coronary stenosis severity and compression type coronary artery movement in acute myocardial infarction

BACKGROUND

Acute myocardial infarction is thought to occur at sites of minor coronary stenosis. Recent data challenge this and also propose a role for coronary artery movement (CAM) in plaque instability. We examined the relationship between coronary stenosis severity, CAM pattern, and infarct-related lesions (IRLs) in acute myocardial infarction.

METHODS

We investigated 203 consecutive patients with ST-segment elevation myocardial infarction after successful fibrinolysis. Quantitative coronary angiography, CAM pattern, and extent score (atheroma burden) analysis was performed for each coronary artery segment.

RESULTS

The IRL stenosis was at least moderate (>50%) and severe (>70%) in 78% and 31% of patients, respectively. Culprit arteries were associated with higher atheroma extent scores (25.2 vs 21.6, P < .001). Analysis of 2,228 coronary segments showed that stenosis severity and IRLs were highly correlated, such that the likelihood of being a culprit segment progressively increased with worsening stenosis (odds ratio [OR] 30.0, 95% confidence interval [CI] 19.0-47.6, P < .001, for >70% vs <30% stenosis). Compression CAM was also strongly associated with culprit segments (OR 3.4, 95% CI 2.6-4.5, P < .001). In addition, compression CAM and stenosis severity were strongly correlated, with the likelihood of a coronary segment having compression CAM progressively increasing with worsening stenosis (OR 56.4, 95% CI 37.9-83.8, P < .001, for >70% vs <30% stenosis).

CONCLUSIONS

In patients with ST-segment elevation myocardial infarction, there is a strong relationship between stenosis severity and IRLs. Our study also raises the hypothesis that compression CAM may accelerate atherosclerosis and predispose to plaque vulnerability.

Biomechanics of coronary artery and bypass graft disease: potential new approaches

The contribution of biomechanical factors to the incidence and distribution of coronary artery and bypass graft disease is underrecognized. This review examined the literature to determine which factors were relevant and the evidence for their importance. It identified two primary biomechanical factors that predispose to disease: (1) low-wall shear stress and (2) high-wall mechanical stress or strain. A range of secondary biomechanical factors have also been identified and include: vessel geometry; vessel movement; vessel wall characteristics and the presence of reflection waves. Potential surgical approaches for minimizing these effects are discussed.

The Stretch–Compression Type of Coronary Artery Movement Predicts the Location of Culprit Lesions Responsible for ST-Segment Elevation Myocardial Infarctions

BACKGROUND

Prediction of the location of culprit lesions responsible for ST-segment elevation myocardial infarctions may allow for prevention of these events by safe and easily deliverable local therapies.

METHODS

A retrospective analysis of coronary movement was performed on coronary angiograms of patients who subsequently represented with ST-segment elevation myocardial infarction treated by primary or rescue angioplasty at a single institution.

RESULTS

Twenty patients were identified. The stretch-compression type of coronary artery movement (CAM) was a statistically significant independent predictor of the segment containing the culprit lesion (odds ratio 6.10, p-value 0.005).

CONCLUSIONS

The stretch-compression type of coronary artery movement is an independent predictor of the location of culprit lesions responsible for ST-segment elevation myocardial infarctions.

Stress-driven collagen fiber remodeling in arterial walls

A stress-driven model for the relation between the collagen morphology and the loading conditions in arterial walls is proposed. We assume that the two families of collagen fibers in arterial walls are aligned along preferred directions, located between the directions of the two maximal principal stresses. For the determination of these directions an iterative finite element based procedure is developed. As an example the remodeling of a section of a human common carotid artery is simulated. We find that the predicted fiber morphology correlates well with experimental observations. Interesting outcomes of the model including local shear minimization and the possibility of axial compressions due to high blood pressure are revealed and discussed.