Coronary artery wall shear stress is associated with progression and transformation of atherosclerotic plaque and arterial remodeling in patients with coronary artery disease

Influence of renal artery stenosis morphology on hemodynamics

OBJECTIVE

Currently, the clinical classification of the severity of renal artery stenosis (RAS) solely depends on the degree of stenosis. In addition, when the stenosis degree is between 50% and 70%, the clinical strategy is decided based on whether the RAS is hemodynamically significant. In this study, the influence of RAS morphological parameters on hemodynamics was numerically analyzed to provide a theoretical basis for clinical treatment.

METHODS

Idealized RAS models were established to investigate the hemodynamic effects of the stenosis length, asymmetric stenosis, and direction of the opening of the renal artery.

RESULTS

The longer the stenosis length, the greater is the ratio of the low time-averaged wall shear stress (WSS) and high oscillatory shear index (OSI) area distal stenosis (when the stenosis area is the same). In addition, asymmetric stenosis leads to a significant increase in the ratio of the renal artery peak systolic velocity (R-PSV) and the abdominal aorta peak systolic velocity (A-PSV) when the stenosis area is 60-70%. Furthermore, the fraction flow reserve (FFR) of the RAS model with 12 mm stenosis length, upward eccentricity and upward direction of renal artery opening was approximately equal to the cumulative value of the influence of different stenosis morphologies on FFR.

CONCLUSION

An assessment of the severity of RAS should consider the stenosis area and other morphological parameters, including the length and asymmetry of RAS as well as the direction of the opening of renal artery, particularly when the stenosis degree of RAS is between 50% and 70%.

Usability of Fantom Encore® scaffold in non-complex bifurcations-Analysis in bench models

OBJECTIVE

Present bench study aimed to evaluate whether technical characteristics of Fantom Encore® bioresorbable scaffold (BRS) allow to perform proximal optimization/side branch dilation/proximal optimization (POT-SB-POT) technique, as an adequate solution for bifurcation percutaneous coronary intervention.

METHODS

Two Fantom Encore® BRS platforms (small with 3.0 mm nominal diameter, n = 7; and large with 3.5 mm nominal diameter, n = 7) were evaluated in bench models, which were designed according to Finet-law and fitted to nominal scaffold diameter in the distal main branch (MB) and fitted to indicated maximal expansion capacity in the proximal main branch (MB). Results were evaluated by (a) fluoroscopy, (b) optical coherence tomography (OCT) and (c) micro-computed tomography (μCT).

RESULTS

All procedures were performed according to the protocol. Careful review of the fluoroscopic loops by an independent operator did not reveal any strut fracture or major deformation. By OCT the overall rate of perfectly apposed struts in the bifurcation area was 15 ± 6% after SB opening, that increased significantly but remained low with 22 ± 9% after final POT (p = .001). Compared to SB ballooning alone, significant benefit of final POT was found in rate of perfect apposition in the proximal MB (15 ± 12% vs. 26 ± 15%, respectively; p = .017) and at the abostial side of polygon of confluence (7 ± 9% vs. 16 ± 13%, respectively; p = .005). μCT analysis revealed a single strut fracture in one case with the small platform, while four cases showed single or multiple strut fractures with the large platform.

CONCLUSION

The mechanical characteristics of the device are not suitable for use of Conventional techniques for bifurcation PCI such as POT-SB-POT. The use of Fantom Encore® BRS for bifurcation PCI with relevant SB should not be encouraged.

Multidirectional wall shear stress promotes advanced coronary plaque development: comparing five shear stress metrics

Aims

Atherosclerotic plaque development has been associated with wall shear stress (WSS). However, the multidirectionality of blood flow, and thus of WSS, is rarely taken into account. The purpose of this study was to comprehensively compare five metrics that describe (multidirectional) WSS behaviour and assess how WSS multidirectionality affects coronary plaque initiation and progression.

Methods and results

Adult familial hypercholesterolaemic pigs (n = 10) that were fed a high-fat diet, underwent imaging of the three main coronary arteries at three-time points [3 (T₁), 9 (T₂), and 10–12 (T₃) months]. Three-dimensional geometry of the arterial lumen, in combination with local flow velocity measurements, was used to calculate WSS at T₁ and T₂. For analysis, arteries were divided into 3 mm/45° sectors (n = 3648). Changes in wall thickness and final plaque composition were assessed with near-infrared spectroscopy–intravascular ultrasound, optical coherence tomography imaging, and histology. Both in pigs with advanced and mild disease, the highest plaque progression rate was exclusively found at low time-averaged WSS (TAWSS) or high multidirectional WSS regions at both T₁ and T₂. However, the eventually largest plaque growth was located in regions with initial low TAWSS or high multidirectional WSS that, over time, became exposed to high TAWSS or low multidirectional WSS at T₂. Besides plaque size, also the presence of vulnerable plaque components at the last time point was related to low and multidirectional WSS. Almost all WSS metrics had good predictive values for the development of plaque (47–50%) and advanced fibrous cap atheroma (FCA) development (59–61%).

Conclusion

This study demonstrates that low and multidirectional WSS promote both initiation and progression of coronary atherosclerotic plaques. The high-predictive values of the multidirectional WSS metrics for FCA development indicate their potential as an additional clinical marker for the vulnerable disease.

High Coronary Wall Shear Stress Worsens Plaque Vulnerability: A Systematic Review and Meta-Analysis

Aim:

The aim of this meta-analysis is to assess the impact of wall shear stress (WSS) severity on arterial plaque vulnerability.

Methods:

We systematically searched electronic databases and selected studies which assessed the relationship between WSS measured by intravascular ultrasound and coronary artery plaque features. In 7 studies, a total of 615 patients with 28 276 arterial segments (median follow-up: 7.71 months) were identified. At follow-up, the pooled analysis showed high WSS to be associated with regression of plaque fibrous area, weighted mean difference (WMD) −0.11 (95% CI: −0.20 to −0.02, P = .02) and fibrofatty area, WMD −0.09 (95% CI: −0.17 to −0.01, P = .02), reduction in plaque total area, WMD −0.09 (95% CI: −0.14 to −0.04, P = .007) and increased necrotic core area, and WMD 0.04 (95% CI: 0.01-0.09, P = .03) compared with low WSS. Dense calcium deposits remained unchanged in high and low WSS (0.01 vs 0.02 mm²; P > .05). High WSS resulted in profound remodeling (40% vs 18%, P < .05) and with more constructive remodeling than low WSS (78% vs 40%, P < .01).

Conclusions:

High WSS in coronary arteries is associated with worsening plaque vulnerability and more profound arterial wall remodeling compared with low WSS.

Computational Modeling of Blood Flow Hemodynamics for Biomechanical Investigation of Cardiac Development and Disease

The heart is the first functional organ in a developing embryo. Cardiac development continues throughout developmental stages while the heart goes through a serious of drastic morphological changes. Previous animal experiments as well as clinical observations showed that disturbed hemodynamics interfere with the development of the heart and leads to the formation of a variety of defects in heart valves, heart chambers, and blood vessels, suggesting that hemodynamics is a governing factor for cardiogenesis, and disturbed hemodynamics is an important source of congenital heart defects. Therefore, there is an interest to image and quantify the flowing blood through a developing heart. Flow measurement in embryonic fetal heart can be performed using advanced techniques such as magnetic resonance imaging (MRI) or echocardiography. Computational fluid dynamics (CFD) modeling is another approach especially useful when the other imaging modalities are not available and in-depth flow assessment is needed. The approach is based on numerically solving relevant physical equations to approximate the flow hemodynamics and tissue behavior. This approach is becoming widely adapted to simulate cardiac flows during the embryonic development. While there are few studies for human fetal cardiac flows, many groups used zebrafish and chicken embryos as useful models for elucidating normal and diseased cardiogenesis. In this paper, we explain the major steps to generate CFD models for simulating cardiac hemodynamics in vivo and summarize the latest findings on chicken and zebrafish embryos as well as human fetal hearts.

Blood Flow Modeling in Coronary Arteries: A Review

Atherosclerosis is one of the main causes of cardiovascular events, namely, myocardium infarction and cerebral stroke, responsible for a great number of deaths every year worldwide. This pathology is caused by the progressive accumulation of low-density lipoproteins, cholesterol, and other substances on the arterial wall, narrowing its lumen. To date, many hemodynamic studies have been conducted experimentally and/or numerically; however, this disease is not yet fully understood. For this reason, the research of this pathology is still ongoing, mainly, resorting to computational methods. These have been increasingly used in biomedical research of atherosclerosis because of their high-performance hardware and software. Taking into account the attempts that have been made in computational techniques to simulate realistic conditions of blood flow in both diseased and healthy arteries, the present review aims to give an overview of the most recent numerical studies focused on coronary arteries, by addressing the blood viscosity models, and applied physiological flow conditions. In general, regardless of the boundary conditions, numerical studies have been contributed to a better understanding of the development of this disease, its diagnosis, and its treatment.

Study on the association of wall shear stress and vessel structural stress with atherosclerosis: An experimental animal study

BACKGROUND AND AIMS

Artery is subject to wall shear stress (WSS) and vessel structural stress (VSS) simultaneously. This study is designed to explore the role of VSS in development of atherosclerosis.

METHODS

Silastic collars were deployed on the carotid to create two constrictions on 13 rabbits for a distinct mechanical environment at the constriction. MRI was performed to visualize arteries' configuration. Animals with high fat (n = 9; Model-group) and normal diet (n = 4; Control-group) were sacrificed after 16 weeks. 3D fluid-structure interaction analysis was performed to quantify WSS and VSS simultaneously.

RESULTS

Twenty plaques were found in Model-group and 3 in Control-group. In Model-group, 8 plaques located proximally to the first constriction (Region-1, close to the heart) and 7 distally to the second (Region-2, close to the head) and 5 plaques were found on the contralateral side of 3 rabbits. Plaques at Region-1 tended to be bigger than those at Region-2 and the macrophage density at these locations was comparable. Minimum time-averaged WSS (TAWSS) in Region-1 was significantly higher than that in Region-2, and both maximum oscillatory shear index (OSI) and particle relative residence time (RRT) were significantly lower. Peak and mean VSS in Region-1 were significantly higher than those in Region-2. Correlation analyses indicated that low TAWSS, high OSI and RRT were only associated with plaque in Region-2, while lesions in Region-1 were only associated with high VSS. Moreover, only VSS was associated with wall thickness of plaque-free regions in both regions.

CONCLUSIONS

VSS might contribute to the initialization and development of atherosclerosis solely or in combination with WSS.

Hemodynamics is associated with vessel wall remodeling in patients with middle cerebral artery stenosis

OBJECTIVES

To evaluate the relationship between hemodynamics and vessel wall remodeling patterns in middle cerebral artery (MCA) stenosis based on high-resolution magnetic resonance imaging and computational fluid dynamics (CFD).

METHODS

Forty consecutive patients with recent ischemic stroke or transient ischemic attack attributed to unilateral atherosclerotic MCA stenosis (50-99%) were prospectively recruited. All patients underwent a cross-sectional scan of the stenotic MCA vessel wall. The parameters of the vessel wall, the number of patients with acute infarction, translesional wall shear stress ratio (WSSR), wall shear stress in stenosis (WSSs), and translesional pressure ratio were obtained. The patients were divided into positive remodeling (PR) and negative remodeling (NR) groups. The differences in vessel wall parameters and hemodynamics were compared. Correlations between the parameters of the vessel wall and hemodynamics were calculated.

RESULTS

Of the 40 patients, 16 had PR, 19 had NR, and the other 5 displayed non-remodeling. The PR group had a smaller lumen area (p = 0.004), larger plaque area (p < 0.001), normal wall index (p = 0.004), and higher WSSR (p = 0.004) and WSSs (p = 0.023) at the most narrowed site. The PR group had more enhanced plaques (12 vs 6, p = 0.03). The number of patients with acute stroke in the PR group was more than that in the NR group (11 vs 4, p = 0.01). The remodeling index (r = 0.376, p = 0.026) and plaque area (r = 0.407, p = 0.015) showed a positive correlation with WSSR, respectively.

CONCLUSIONS

Hemodynamics plays a role in atherosclerotic plaques and vessel wall remodeling. Individuals with greater hemodynamic values might be more prone to stroke.

KEY POINTS

• Stenotic plaques in middle cerebral artery with positive remodeling have smaller lumen area and larger resp. higher plaque area, normal wall index, translesional wall shear stress ratio, and wall shear stress than negative remodeling. • The remodeling index and plaque area are positively correlated with translesional wall shear stress ratio. • Hemodynamic may help to understand the role of positive remodeling in the development of acute stroke.

Estimation of endothelial shear stress in atherosclerotic lesions detected by intravascular ultrasound using computational fluid dynamics from coronary CT scans with a pulsatile blood flow and an individualized blood viscosity

INTRODUCTION

Endothelial shear stress (ESS) is a local hemodynamic factor that is dependent on vessel geometry and influences the process of atherogenesis. As in vivo measurements of ESS are not possible, it must be calculated using computational fluid dynamics (CFD). In this feasibility study we explore CFD-models generated from coronary CT-angiography (CCTA) using an individualised blood viscosity and a pulsatile flow profile derived from in vivo measurements.

MATERIALS AND METHODS

We retrospectively recruited 25 consecutive patients who received a CCTA followed by a coronary angiography including intravascular ultrasound (IVUS) and generated 3D models of the coronary arteries from the CT-datasets. We then performed CFD-simulations on these models. Hemodynamically non-relevant stenosis were identified in IVUS. They were isolated in the CFD-model and separated longitudinally into a half with atherosclerotic lesion (AL) and one without (NAL). ESS was measured and compared for both halves.

RESULTS

After excluding vessels with no IVUS data or relevant stenosis we isolated 31 hemodynamically non-relevant excentric AL from a total of 14 vessels. AL segments showed consistently significantly lower ESS when compared to their corresponding NAL segments when regarding minimum (0.9 Pa, CI [0.6, 1.2] vs. 1.3 Pa, CI [0.9, 1.8]; p = 0.004), mean (5.0 Pa, CI [3.4, 6.0] vs. 6.7 Pa, CI [5.5, 8.4]; p = 0.008) and maximum ESS values (12.4 Pa, CI [8.6, 14.6] vs. 19.6 Pa, CI [12.4, 21.0]; p = 0.005). Qualitatively ESS was lower on the inside of bifurcations and curvatures.

CONCLUSION

CFD simulations of coronary arteries from CCTA with an individualised flow profile and blood viscosity are feasible and could provide further prognostic information and a better risk stratification in coronary artery disease. Further prospective studies are needed to investigate this claim.

Preemptive percutaneous coronary intervention for coronary artery disease: identification of the appropriate high-risk lesion

PURPOSE OF REVIEW

Management of patients with coronary artery disease (CAD) has been based on identification of a coronary obstruction causing ischemia and performing a revascularization procedure to reduce that ischemia, with the goal of thereby preventing subsequent major adverse cardiac events (MACEs) in that vascular territory. Recent investigations demonstrate that preemptive percutaneous coronary intervention (PCI) of nonculprit coronary lesions (NCLs) that may not cause ischemia in patients with ST-segment elevation myocardial infarction (STEMI) reduces MACE. In this review, we focus on preemptive PCI, discuss its mechanistic benefits and speculate on its potential value for other coronary syndromes.

RECENT FINDINGS

The COMPLETE trial in STEMI patients treated with primary PCI demonstrated that preemptive PCI of NCL obstructions, which may not cause ischemia, but often exhibit high-risk OCT plaque characteristics, reduced cardiovascular death or nonfatal myocardial infarction. Reduction in MACE from preemptive PCI of NCL was similar for lesions confirmed to cause ischemia (fractional flow reserve <0.80) and for lesions that were only visually assessed to have luminal obstruction at least 70%.The ISCHEMIA trial in patients with stable CAD and moderate/severe ischemia demonstrated that MACE risk increased progressively with more extensive atherosclerosis, but that performing PCI of ischemia-producing lesions did not reduce MACE. Adverse cardiac events likely originated in high-risk plaque areas not treated with PCI.

SUMMARY

In STEMI patients, preemptive PCI of high-risk NCL that may not cause ischemia improves long-term MACE. In stable CAD patients, MACE increases as the atherosclerotic burden increases, but PCI of the ischemia-producing lesion itself does not improve outcomes compared with optimal medical therapy. Adverse events likely originate in high-risk plaque areas that are distinct from ischemia-producing obstructions. Identification of highest-risk atherosclerotic lesions responsible for future MACE may provide an opportunity for preemptive PCI in patients with a variety of coronary syndromes.

Bioresorbable vascular scaffolds versus everolimus-eluting stents: a biomechanical analysis of the ABSORB III Imaging substudy

AIMS

The Absorb bioresorbable vascular scaffold (BVS) has high rates of target lesion failure (TLF) at three years. Low wall shear stress (WSS) promotes several mechanisms related to device TLF. We investigated the impact of BVS compared to XIENCE V (XV) on coronary WSS after device deployment.

METHODS AND RESULTS

In the prospective, randomised, controlled ABSORB III Imaging study (BVS [n=77] or XV [n=36]), computational fluid dynamics were performed on fused angiographic and intravascular ultrasound (IVUS) images of post-implanted vessels. Low WSS was defined as <1 Pa. There were no differences in demographics, clinical risks, angiographic reference vessel diameter or IVUS minimal lumen diameter between BVS and XV patients. A greater proportion of vessels treated with BVS compared to XV demonstrated low WSS across the whole device (BVS: 17/77 [22%] vs XV: 2/36 [6%], p<0.029). Compared to XV, BVS demonstrated lower median circumferential WSS (1.73 vs 2.21 Pa; p=0.036), outer curvature WSS (p=0.026), and inner curvature WSS (p=0.038). Similarly, BVS had lower proximal third WSS (p=0.024), middle third WSS (p=0.047) and distal third WSS (p=0.028) when compared to XV. In a univariable logistic regression analysis, patients who received BVS were 4.8 times more likely to demonstrate low WSS across the scaffold/stent when compared to XV patients. Importantly, in a multivariable linear regression model, hypertension (beta: 0.186, p=0.023), lower contrast frame count velocity (beta: -0.411, p<0.001), lower post-stent residual plaque burden (beta: -0.338, p<0.001), lower % underexpanded frames (beta: -0.170, p=0.033) and BVS deployment (beta: 0.251, p=0.002) remained independently associated with a greater percentage of stented coronary vessel areas exposed to low WSS.

CONCLUSIONS

In this randomised controlled study, the Absorb BVS was 4.8 times more likely than the XV metallic stent to demonstrate low WSS. BVS implantation, lower blood velocity and lower residual post-stent plaque burden were independently associated with greater area of low WSS.

Relationship between high shear stress and OCT-verified thin-cap fibroatheroma in patients with coronary artery disease

High-risk coronary plaques have been considered predictive of adverse cardiac events. Both wall shear stress (WSS) in patients with hemodynamically significant lesions and optical coherence tomography (OCT) -verified thin-cap fibroatheroma (TCFA) are associated with plaque rupture, the most common underlying mechanism of acute coronary syndrome. The aim of the study was to test the hypothesis that invasive coronary angiography-based high WSS is associated with the presence of TCFA detected by OCT in obstructive lesions. From a prospective study of patients who underwent OCT examination for angiographically obstructive lesions (Yellow II), we selected patients who had two angiographic projections to create a 3-dimensional reconstruction model to allow assessment of WSS. The patients were divided into 2 groups according to the presence and absence of TCFA. Mean WSS was assessed in the whole lesion and in the proximal, middle and distal segments. Of 70 patients, TCFA was observed in 13 (19%) patients. WSS in the proximal segment (WSSproximal) (10.20 [5.01, 16.93Pa]) and the whole lesion (WSSlesion) (12.37 [6.36, 14.55Pa]) were significantly higher in lesions with TCFA compared to WSSproximal (5.84 [3.74, 8.29Pa], p = 0.02) and WSSlesion (6.95 [4.41, 11.60], p = 0.04) in lesions without TCFA. After multivariate analysis, WSSproximal was independently associated with the presence of TCFA (Odds ratio 1.105; 95%CI 1.007-1.213, p = 0.04). The optimal cutoff value of WSSproximal to predict TCFA was 6.79 Pa (AUC: 0.71; sensitivity: 0.77; specificity: 0.63 p = 0.02). Our results demonstrate that high WSS in the proximal segments of obstructive lesions is an independent predictor of OCT-verified TCFA.

Physiology and coronary artery disease: emerging insights from computed tomography imaging based computational modeling

Improvements in spatial and temporal resolution now permit robust high quality characterization of presence, morphology and composition of coronary atherosclerosis in computed tomography (CT). These characteristics include high risk features such as large plaque volume, low CT attenuation, napkin-ring sign, spotty calcification and positive remodeling. Because of the high image quality, principles of patient-specific computational fluid dynamics modeling of blood flow through the coronary arteries can now be applied to CT and allow the calculation of local lesion-specific hemodynamics such as endothelial shear stress, fractional flow reserve and axial plaque stress. This review examines recent advances in coronary CT image-based computational modeling and discusses the opportunity to identify lesions at risk for rupture much earlier than today through the combination of anatomic and hemodynamic information.

Outcomes and Associated Factors of Discrepant Coronary and Carotid Atherosclerosis

Some patients exhibit discrepancies in carotid and coronary artery atherosclerosis. This study aimed to define the characteristics and prognosis of these discrepant patients and determine the best strategy to detect pan-vascular atherosclerosis. A database of 5,022 consecutively registered patients who underwent both coronary angiography and carotid ultrasonography, along with clinical and blood laboratory tests, echocardiography, and pulse wave velocity (PWV), was analyzed. The development of cerebro-cardiovascular (CV) events during the follow-up period was also evaluated. A significant proportion of patients (n = 1,741, 35%) presented with a discrepancy between carotid artery plaque and coronary artery disease (CAD). In patients without carotid plaque, male sex (odds ratio [OR], 1.71; 95% confidence interval [CI], 1.20-2.41; P = 0.003), older age (OR, 1.03; 95% CI, 1.01-1.04; P = 0.002), smoking history (OR, 1.58; 95% CI, 1.13-2.20; P = 0.008), lower high-density lipoprotein (HDL) -cholesterol level (OR, 0.97; 95% CI, 0.96-0.98; P < 0.001), and lower common carotid artery end-diastolic velocity (CCA-EDV) (OR, 0.97; 95% CI, 0.95-0.99; P = 0.005) were independently related to the presence of CAD. In patients without CAD, increased PWV was independently related to the presence of carotid plaque. In survival analysis, patients with isolated CAD had a higher probability of composite CV events; those with isolated carotid plaque had a higher probability of heart failure (HF) and mortality than their counterpart groups (P < 0.05). Even in patients without carotid artery plaque, careful coronary evaluation is needed in older or male patients with smoking history, lower HDL-cholesterol level, or lower CCA-EDV. Carotid plaque may be a potential risk factor for HF.

Computational fluid dynamics of internal mammary artery-left anterior descending artery anastomoses

OBJECTIVES

The aim of this study was to elucidate the remodelling of the internal mammary artery (IMA)-left anterior descending artery anastomosis and compare 2 different anastomosis techniques (end-to-side versus side-to-side) using computational fluid dynamics.

METHODS

This study included 9 patients. Computed tomography (CT) angiography was performed immediately after coronary artery bypass grafting (CABG) and at 3-6 months later. The computational fluid dynamics models were made using the CT data. The pulsatile 3-dimensional blood flow was achieved with the finite volume method to evaluate the postoperative morphological and haemodynamic changes at the anastomosis in each patient. Flow velocity distribution, wall shear stress (WSS) and its fluctuation oscillatory shear index were measured.

RESULTS

No early or mid-term graft occlusion was observed in the study series. In the side-to-side anastomosis, pouch formation at the distal end of IMA caused a vortex flow with low WSS immediately after CABG. However, at 3-6 months after surgery, this pouch disappeared. As a result, the laminar straight flow with uniform WSS distribution was achieved inside the anastomosis. In the end-to-side anastomosis, the anastomosis shape was remodelled, resulting in a laminar flow pattern with uniform WSS distribution. A patchy high oscillatory shear index was detected at the IMA wall on the top of anastomosis in either anastomosis techniques immediately after the surgery, but it disappeared at 3-6 months after surgery.

CONCLUSIONS

Regardless of the anastomosis technique used, a successful remodelling of the IMA-left anterior descending artery anastomosis shape was achieved a few months after surgery, resulting in a straightforward flow streamline, with uniform WSS distribution and minimal oscillatory shear index.

Effects of different positions of intravascular stent implantation in stenosed vessels on in-stent restenosis: An experimental and numerical simulation study

Percutaneous coronary intervention (PCI) has been widely used in the treatment of atherosclerosis, while in-stent restenosis (ISR) has not been completely resolved. Studies have shown that changes in intravascular mechanical environment are related to ISR. Hence, an in-depth understanding of the effects of stent intervention on vascular mechanics is important for clinically optimizing stent implantation and relieving ISR. Nine rabbits with stenotic carotid artery were collected by balloon injury. Intravascular stents were implanted into different longitudinal positions (proximal, middle and distal relative to the stenotic area) of the stenotic vessels for numerical simulations. Optical coherence tomography (OCT) scanning was performed to reconstruct the three-dimensional configuration of the stented carotid artery and blood flow velocity waveforms were collected by Doppler ultrasound. The numerical simulations were performed through direct solution of Naiver-Stokes equation in ANSYS. Results showed that the distributions of time-averaged wall shear stress (TAWSS), oscillating shear index (OSI) and relative residual time (RRT) in near-end segment were distinctively different from other regions of the stent which considered to promote restenosis for all three models. Spearman rank-correlation analysis showed a significant correlation between hemodynamic descriptors and the stent longitudinal positions (r_TAWSS = -0.718, r_OSI = 0.898, r_RRT = 0.818, p < 0.01). Histology results of the near-end segment showed neointima thickening deepened with the longitudinal positions of stent which was consistent with the numerical simulations. The results suggest that stent implantation can promote restenosis at the near-end segment. As the stenting position moves to distal end, the impact on ISR is more significant.

The effect of the degree and location of coronary stenosis on the hemodynamic status of a coronary vessel

The ongoing advances in the field of cardiovascular modelling during the past years have allowed for the creation of accurate three-dimensional models of the major coronary arteries. The aforementioned 3D models can accurately mimic the human coronary vasculature if they are combined with sophisticated computational fluid dynamics algorithms and shed light to non-trivial issues that concern the clinicians. One of these issues is to define whether a coronary lesion is more dangerous to present with ischemia if it is at a proximal or a distal part of the vessel. In this work, we aim to investigate the aforementioned issue by reconstructing in 3D a coronary arterial model from a healthy subject using Computed Tomography Coronary Angiography images and by editing it to create eight diseased arterial models that contain one or two lesions of different severities. After carrying out the appropriate blood flow simulations using the finite element method, we observed that the distal lesions are more dangerous than the proximal ones in terms of hemodynamic significance. Moreover, the distal severe stenosis (i.e. 70% diameter reduction) present with the highest peak Wall Shear Stress (WSS) values in comparison to the proximal ones.

Validation of Wall Shear Stress Assessment in Non-invasive Coronary CTA versus Invasive Imaging: A Patient-Specific Computational Study

Endothelial shear stress (ESS) identifies coronary plaques at high risk for progression and/or rupture leading to a future acute coronary syndrome. In this study an optimized methodology was developed to derive ESS, pressure drop and oscillatory shear index using computational fluid dynamics (CFD) in 3D models of coronary arteries derived from non-invasive coronary computed tomography angiography (CTA). These CTA-based ESS calculations were compared to the ESS calculations using the gold standard with fusion of invasive imaging and CTA. In 14 patients paired patient-specific CFD models based on invasive and non-invasive imaging of the left anterior descending (LAD) coronary arteries were created. Ten patients were used to optimize the methodology, and four patients to test this methodology. Time-averaged ESS (TAESS) was calculated for both coronary models applying patient-specific physiological data available at the time of imaging. For data analysis, each 3D reconstructed coronary artery was divided into 2 mm segments and each segment was subdivided into 8 arcs (45°).TAESS and other hemodynamic parameters were averaged per segment as well as per arc. Furthermore, the paired segment- and arc-averaged TAESS were categorized into patient-specific tertiles (low, medium and high). In the ten LADs, used for optimization of the methodology, we found high correlations between invasively-derived and non-invasively-derived TAESS averaged over segments (n = 263, r = 0.86) as well as arcs (n = 2104, r = 0.85, p < 0.001). The correlation was also strong in the four testing-patients with r = 0.95 (n = 117 segments, p = 0.001) and r = 0.93 (n = 936 arcs, p = 0.001).There was an overall high concordance of 78% of the three TAESS categories comparing both methodologies using the segment- and 76% for the arc-averages in the first ten patients. This concordance was lower in the four testing patients (64 and 64% in segment- and arc-averaged TAESS). Although the correlation and concordance were high for both patient groups, the absolute TAESS values averaged per segment and arc were overestimated using non-invasive vs. invasive imaging [testing patients: TAESS segment: 30.1(17.1-83.8) vs. 15.8(8.8-63.4) and TAESS arc: 29.4(16.2-74.7) vs 15.0(8.9-57.4) p < 0.001]. We showed that our methodology can accurately assess the TAESS distribution non-invasively from CTA and demonstrated a good correlation with TAESS calculated using IVUS/OCT 3D reconstructed models.

Patient-Specific Hemodynamics of New Coronary Artery Bypass Configurations

PURPOSE

This study aims to quantify the patient-specific hemodynamics of complex conduit routing configurations of coronary artery bypass grafting (CABG) operation which are specifically suitable for off-pump surgeries. Coronary perfusion efficacy and local hemodynamics of multiple left internal mammary artery (LIMA) with sequential and end-to-side anastomosis are investigated. Using a full anatomical model comprised of aortic arch and coronary artery branches the optimum perfusion configuration in multi-vessel coronary artery stenosis is desired.

METHODOLOGY

Two clinically relevant CABG configurations are created using a virtual surgical planning tool where for each configuration set, the stenosis level, anastomosis distance and angle were varied. A non-Newtonian computational fluid dynamics solver in OpenFOAM incorporated with resistance boundary conditions representing the coronary perfusion physiology was developed. The numerical accuracy is verified and results agreed well with a validated commercial cardiovascular flow solver and experiments. For segmental performance analysis, new coronary perfusion indices to quantify deviation from the healthy scenario were introduced.

RESULTS

The first simulation configuration set;-a CABG targeting two stenos sites on the left anterior descending artery (LAD), the LIMA graft was capable of 31 mL/min blood supply for all the parametric cases and uphold the healthy LAD perfusion in agreement with the clinical experience. In the second end-to-side anastomosed graft configuration set;-the radial artery graft anastomosed to LIMA, a maximum of 64 mL/min flow rate in LIMA was observed. However, except LAD, the obtuse marginal (OM) and second marginal artery (m2) suffered poor perfusion. In the first set, average wall shear stress (WSS) were in the range of 4 to 35 dyns/cm² for in LAD. Nevertheless, for second configuration sets the WSS values were higher as the LIMA could not supply enough blood to OM and m2.

CONCLUSION

The virtual surgical configurations have the potential to improve the quality of operation by providing quantitative surgical insight. The degree of stenosis is a critical factor in terms of coronary perfusion and WSS. The sequential anastomosis can be done safely if the anastomosis angle is less than 90 degrees regardless of degree of stenosis. The smaller proposed perfusion index value, O(0.04 - 0) × 10², enable us to quantify the post-op hemodynamic performance by comparing with the ideal healthy physiological flow.

Double-kissing culotte technique for coronary bifurcation stenting

AIMS

The aim of this study was to assess whether the culotte technique could be improved by an additional kissing dilation prior to main branch (MB) stenting.

METHODS AND RESULTS

Double-kissing (DK) culotte was compared to the culotte and DK-crush techniques in a bench model (n=24). Results were evaluated for stent apposition, luminal opening and flow dynamics. The total procedure duration of DK-culotte was 18.3±3.4 minutes, significantly lower than for DK-crush (24.3±5.7 min; p=0.015), but similar to culotte (21.6±5.9 min, p=0.104). In DK-culotte the overall rate of moderate (200-500 µm) and significant (>500 µm) malapposition was 2.1±1.9% and 0.4±0.2%, similar as compared to culotte (3.7±3.8%, p=0.459 and 1.0±1.0%, p=0.517, respectively), and lower as compared to DK-crush (8.1±2.5%, p<0.001 and 3.7±5.3%, p=0.002, respectively). The lower malapposition rate of DK-culotte as compared to DK-crush was due to less moderate and significant malapposition in the proximal MB (0.0±0.0% vs 14.0±7.6%, p<0.001 and 0.0±0.0% vs 4.2±9.1%, p=0.026, respectively). Micro-computed tomography did not show a difference in luminal opening at the proximal MB, distal MB or SB. There was no difference either in the maximum shear rate or in areas of high shear or recirculation.

CONCLUSIONS

Bench test data suggest that the DK approach facilitates the culotte technique. The clinical validity and relevance remain to be confirmed in a larger in vivo population.

Inflammatory Cytokines and Atherosclerotic Plaque Progression. Therapeutic Implications

PURPOSE OF THE REVIEW

Inflammatory cytokines play a major role in atherosclerotic plaque progression. This review summarizes the rationale for personalized anti-inflammatory therapy.

RECENT FINDINGS

Systemic inflammatory parameters may be used to follow the clinical outcome in primary and secondary prevention. Medical therapy, both in patients with stable cardiovascular disease, or with acute events, may be tailored taking into consideration the level and course of systemic inflammatory mediators. There is significant space for improvement in primary prevention and in the treatment of patients who have suffered from severe cardiovascular events, paying attention to not only blood pressure and cholesterol levels but also including inflammatory parameters in our clinical analysis. The potential exists to alter the course of atherosclerosis with anti-inflammatory drugs. With increased understanding of the specific mechanisms that regulate the relationship between inflammation and atherosclerosis, new, more effective and specific anti-inflammatory treatment may become available.

Regional High Wall Shear Stress Associated With Stenosis Regression in Symptomatic Intracranial Atherosclerotic Disease

Background and Purpose:

Understanding the mechanisms underlying progression/regression of symptomatic intracranial atherosclerotic stenosis (sICAS) will inform secondary prevention of the patients. Focal wall shear stress (WSS) may play an important role, which, however, had seldom been investigated.

Methods:

Patients with acute ischemic stroke or transient ischemic attack (TIA) attributed to 50% to 99% intracranial atherosclerotic stenosis were recruited. All patients underwent cerebral computed tomography angiography at baseline, and a computational fluid dynamics model was built based on computed tomography angiography to simulate blood flow and quantify WSS in the vicinity of the sICAS lesion. All patients received optimal medical treatment and a second computed tomography angiography at 1 year. The change in the luminal stenosis from baseline to 1 year in sICAS was defined as progression (increased >10%), quiescence (±10%), or regression (decreased >10%). Associations between baseline WSS metrics and sICAS regression were analyzed.

Results:

Among 39 patients (median age 62 years; 27 males), sICAS luminal stenosis progressed, remained quiescent and regressed in 6 (15.4%), 15 (38.5%), and 18 (46.2%) cases, respectively. A higher maximum WSS and larger high-WSS area, throughout the sICAS lesion or obtained separately in the proximal and distal parts of the lesion, were independently associated with regression of luminal stenosis in sICAS over 1 year.

Conclusions:

A majority of sICAS lesions regress or stay quiescent in the luminal stenosis over 1 year after stroke under optimal medical treatment, when higher focal WSS may facilitate stenosis regression. Further studies of the effects of hemodynamics including WSS in altering plaque vulnerability and stroke risks are needed.

Numerical simulation of magnetic nano drug targeting to atherosclerosis: Effect of plaque morphology (stenosis degree and shoulder length)

BACKGROUND AND OBJECTIVE

Nanoparticle-mediated targeted drug delivery is a promising option for treatment of atherosclerosis. However, the drug targeting may be affected by multiple factors. Considerable attentions have been focused on the influences of external factors, e.g., magnetic field, drug-loaded particle, but internal factors, e.g., plaque morphology (stenosis degree and shoulder length), have not received any attention yet. Therefore, we investigate the impact of plaque morphology on magnetic nanoparticles targeting under the action of an external field.

METHOD

Numerical simulation, based on Eulerian-Lagrangian coupled Fluid-Solid Interaction, is performed in ANSYS Workbench platform. Blood flow is solved by Navier-Stokes equation, particles are tracked by discrete phase model, and the incorporated effect is obtained by two-way method. Plaques with varying stenosis degrees and shoulder lengths are acquired by manually modifying the geometry of patient-specific. The quantified variables include targeted delivery efficiency (deposition+adhesive strength) of particles and plaque injury characterized by temporal-spatial averaged shear stress (TAWSS¯) during the process of drug transport, in which the critical deposition velocity is determined by plaques and particles, the DEFINE_DPM_BC and User Defined Memory are employed to evaluate whether the particles are deposited, and to store the total number and the adhesive strength of particles deposited on the plaque.

RESULTS

Results signify that, with an increment of plaque stenosis degree, the deposition of particle and the adhesive strength between particle and plaque decrease, while the TAWSS¯ increases. Furthermore, for the same stenosis degree, with the increase of plaque shoulder length, the deposition and the adhesive strength of particle increase, and the TAWSS¯ decreases.

CONCLUSIONS

Results demonstrates that the plaque with smaller stenosis degree or longer shoulder length may achieve a better treatment effect in view of the higher targeted delivery efficiency of particles and the lighter shear damage to plaque itself during the process of drug transport.

Endothelial shear stress and vascular remodeling in bioresorbable scaffold and metallic stent

BACKGROUND AND AIMS

The impact of endothelial shear stress (ESS) on vessel remodeling in vessels implanted with bioresorbable scaffold (BRS) as compared to metallic drug-eluting stent (DES) remains elusive. The aim of this study was to determine whether the relationship between ESS and remodeling patterns differs in BRS from those seen in metallic DES at 3-year follow-up.

METHODS

In the ABSORB II randomized trial, lesions were investigated by serial coronary angiography and intravascular ultrasound (IVUS). Three-dimensional reconstructions of coronary arteries post-procedure and at 3 years were performed. ESS was quantified using non-Newtonian steady flow simulation. IVUS cross-sections in device segment were matched using identical landmarks.

RESULTS

Paired ESS calculations post-procedure and at 3 years were feasible in 57 lesions in 56 patients. Post-procedure, median ESS at frame level was higher in BRS than in DES, with marginal statistical significance (0.97 ± 0.48 vs. 0.75 ± 0.39 Pa, p = 0.063). In the BRS arm, vessel area and lumen area showed larger increases in the highest tercile of median ESS post-procedure as compared to the lowest tercile. In contrast, in DES, no significant relationship between median ESS post-procedure and remodeling was observed. In multivariate analysis, smaller vessel area, larger lumen area, higher plaque burden post-procedure, and higher median ESS post-procedure were independently associated with expansive remodeling in matched frames. Only in BRS, younger age was an additional significant predictor of expansive remodeling.

CONCLUSIONS

In a subset of lesions with large plaque burden, shear stress could be associated with expansive remodeling and late lumen enlargement in BRS, while ESS had no impact on vessel dimension in metallic DES.

Balloon Deflation Strategy during Primary Percutaneous Coronary Intervention in Acute ST-Segment Elevation Myocardial Infarction: A Randomized Controlled Clinical Trial and Numerical Simulation-Based Analysis

Background

Primary percutaneous coronary intervention (PCI) is the best available reperfusion strategy in patients with acute ST-segment elevation myocardial infarction (STEMI). However, PCI is associated with a serious problem known as no-reflow phenomenon, resulting in poor clinical and functional outcomes. This study aimed to compare the influences of different balloon deflation velocity on coronary flow and cardiovascular events during primary PCI in STEM as well as transient hemodynamic changes in in vitro experiments. Method and Results. 211 STEMI patients were randomly assigned to either a rapid or a slow balloon deflation group during stent deployment. The primary end point was coronary flow at the end of PCI procedure, and secondary end points included myocardial infarct size. Transient hemodynamic changes were evaluated through an in vitro experimental apparatus and a computer model. In clinical practice, the level of corrected TIMI frame count (cTFC) in slow balloon deflation after primary PCI was significantly lower than that of rapid balloon deflation, which was associated with smaller infarct size. Numerical simulations revealed that the rapid deflation led to a sharp acceleration of flow in the balloon-vessel gap and a concomitant abnormal rise in wall shear stress (WSS).

Conclusion

This randomized study demonstrated that the slow balloon deflation during stent implantation improved coronary flow and reduced infarct size in reperfused STEMI. The change of flow in the balloon-vessel gap and WSS resulted from different balloon deflation velocity might be partly accounted for this results.

Numerical simulations of patient-specific models with multiple plaques in human peripheral artery: a fluid-structure interaction analysis

Atherosclerotic plaque in the femoral is the leading cause of peripheral artery disease (PAD), the worse consequence of which may lead to ulceration and gangrene of the feet. Numerical studies on fluid-structure interactions (FSI) of atherosclerotic femoral arteries enable quantitative analysis of biomechanical features in arteries. This study aims to investigate the hemodynamic performance and its interaction with femoral arterial wall based on the patient-specific model with multiple plaques (calcified and lipid plaques). Three types of models, calcification-only, lipid-only and calcification-lipid models, are established. Hyperelastic material coefficients of the human femoral arteries obtained from experimental studies are employed for all simulations. Oscillation of WSS is observed in the healthy downstream region in the lipid-only model. The pressure around the plaques in the two-plaque model is lower than that in the corresponding one-plaque models due to the reduction of blood flow domain, which consequently diminishes the loading forces on both plaques. Therefore, we found that stress acting on the plaques in the two-plaque model is lower than that in the corresponding one-plaque models. This finding implies that the lipid plaque, accompanied by the calcified plaque around, might reduce its risk of rupture due to the reduced the stress acting on it.

Coronary Computed Tomography Angiography From Clinical Uses to Emerging Technologies: JACC State-of-the-Art Review

Evaluation of coronary artery disease (CAD) using coronary computed tomography angiography (CCTA) has seen a paradigm shift in the last decade. Evidence increasingly supports the clinical utility of CCTA across various stages of CAD, from the detection of early subclinical disease to the assessment of acute chest pain. Additionally, CCTA can be used to noninvasively quantify plaque burden and identify high-risk plaque, aiding in diagnosis, prognosis, and treatment. This is especially important in the evaluation of CAD in immune-driven conditions with increased cardiovascular disease prevalence. Emerging applications of CCTA based on hemodynamic indices and plaque characterization may provide personalized risk assessment, affect disease detection, and further guide therapy. This review provides an update on the evidence, clinical applications, and emerging technologies surrounding CCTA as highlighted at the 2019 National Heart, Lung and Blood Institute CCTA Summit.

Coronary Microvascular Dysfunction

Many patients with chest pain undergoing coronary angiography do not show significant obstructive coronary lesions. A substantial proportion of these patients have abnormalities in the function and structure of coronary microcirculation due to endothelial and smooth muscle cell dysfunction. The coronary microcirculation has a fundamental role in the regulation of coronary blood flow in response to cardiac oxygen requirements. Impairment of this mechanism, defined as coronary microvascular dysfunction (CMD), carries an increased risk of adverse cardiovascular clinical outcomes. Coronary endothelial dysfunction accounts for approximately two-thirds of clinical conditions presenting with symptoms and signs of myocardial ischemia without obstructive coronary disease, termed "ischemia with non-obstructive coronary artery disease" (INOCA) and for a small proportion of "myocardial infarction with non-obstructive coronary artery disease" (MINOCA). More frequently, the clinical presentation of INOCA is microvascular angina due to CMD, while some patients present vasospastic angina due to epicardial spasm, and mixed epicardial and microvascular forms. CMD may be associated with focal and diffuse epicardial coronary atherosclerosis, which may reinforce each other. Both INOCA and MINOCA are more common in females. Clinical classification of CMD includes the association with conditions in which atherosclerosis has limited relevance, with non-obstructive atherosclerosis, and with obstructive atherosclerosis. Several studies already exist which support the evidence that CMD is part of systemic microvascular disease involving multiple organs, such as brain and kidney. Moreover, CMD is strongly associated with the development of heart failure with preserved ejection fraction (HFpEF), diabetes, hypertensive heart disease, and also chronic inflammatory and autoimmune diseases. Since coronary microcirculation is not visible on invasive angiography or computed tomographic coronary angiography (CTCA), the diagnosis of CMD is usually based on functional assessment of microcirculation, which can be performed by both invasive and non-invasive methods, including the assessment of delayed flow of contrast during angiography, measurement of coronary flow reserve (CFR) and index of microvascular resistance (IMR), evaluation of angina induced by intracoronary acetylcholine infusion, and assessment of myocardial perfusion by positron emission tomography (PET) and magnetic resonance (CMR).

Macrophage accumulation within coronary arterial wall in diabetic patients with acute coronary syndrome: a study with in-vivo intravascular imaging modalities

Background and aims

Macrophage accumulation in arteriosclerotic plaque of coronary arteries is involved in plaque destabilization. Atherosclerosis has been known to be progressive in patients with type 2 diabetes mellitus (DM). This study compared the features of 3-dimensional (3D) spatial distribution of macrophage accumulation within coronary artery wall between acute coronary syndrome (ACS) patients with DM (n = 20) and those without (non-DM, n = 20) by using intravascular ultrasound (IVUS) and optical coherence tomography (OCT).

Methods

The OCT-derived macrophage accumulation was measured within the proximal left anterior-descending artery. This measurement was performed for the whole vessel segment of interest, higher shear stress region (flow divider side) and lower shear stress region (the opposite side).

Results

Normalized macrophage accumulation per unit length of the whole segment of interest was significantly larger in ACS patients with DM than without. In non-DM patients, macrophage density per IVUS-derived plaque volume was significantly higher in high shear stress region compared to low shear stress region, however, there was no significant difference between the two regions in DM patients. The macrophage density in the low shear stress region was significantly higher in the DM group than in the non-DM group. A multivariate analysis showed that the presence of DM was a major determinant for macrophage distribution.

Conclusions

Macrophage accumulation was more abundant and homogeneous within coronary arterial wall in DM patients with ACS compared to non-DM patients, suggesting that plaque destabilization may occur more widely throughout coronary wall in DM patients.

Blood flow simulations in patient-specific geometries of the carotid artery: A systematic review

Computational Fluid Dynamics (CFD) and Fluid-Structure Interaction (FSI) are currently widely applied in the study of blood flow parameters and their alterations under pathological conditions, which are important indicators for diagnosis of atherosclerosis. In this manuscript, a systematic review of the published literature was conducted, according to the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses, on the simulation studies of blood flow in patient-specific geometries of the carotid artery bifurcation. Scopus, PubMed and ScienceDirect databases were used in the literature search, which was completed on the 3rd of August 2020. Forty-nine articles were included after the selection process and were organized in two distinct categories: the CFD studies (36/49 articles), which comprise only the fluid analysis and the FSI studies (13/49 articles), which includes both fluid and Fluid-Structure domain in the analysis. The data of the research works was structured in different categories (Geometry, Viscosity models, Type of Flow, Boundary Conditions, Flow Parameters, Type of Solver and Validation). The aim of this systematic review is to demonstrate the methodology in the modelling, simulation and analysis of carotid blood flow and also identify potential gaps and challenges in this research field.

The Interplay between Features of Plaque Vulnerability and Hemodynamic Relevance of Coronary Artery Stenoses

Fractional flow reserve (FFR) may not be immune from hemodynamic perturbations caused by both vessel and lesion related factors. The aim of this study was to investigate the impact of plaque- and vessel wall-related features of vulnerability on the hemodynamic effect of intermediate coronary stenoses. Methods and Results: In this cross-sectional study, patients referred to catheterization laboratory for clinically indicated coronary angiography were prospectively screened for angiographically intermediate stenosis (50-80%). Seventy lesions from 60 patients were evaluated. Mean angiographic stenosis was 62.1 ± 16.3%. After having performed FFR assessment, intravascular ultrasound (IVUS) was performed over the FFR wire. Virtual histology IVUS was used to identify the plaque components and thin cap fibroatheroma (TCFA). TCFA was significantly more frequent (65 vs. 38%, p = 0.026), and necrotic core volume (26.15 ± 14.22 vs. 16.21 ± 8.93 mm3, p = 0.04) was significantly larger in the positively remodeled than non-remodeled vessels. Remodeling index correlated with necrotic core volume (r = 0.396, p = 0.001) and with FFR (r = -0. 419, p = 0.001). With respect to plaque components, only necrotic core area (r = -0.262, p = 0.038) and necrotic core volume (r = -0.272, p = 0.024) were independently associated with FFR. In the multivariable model, presence of TCFA was independently associated with significantly lower mean FFR value as compared to absence of TCFA (adjusted, 0.71 vs. 0.78, p = 0.034). Conclusion: The current study demonstrated that for a given stenosis geometry, features of plaque vulnerability such as necrotic core volume, TCFA, and positive remodeling may influence the hemodynamic relevance of intermediate coronary stenoses.

High spatial endothelial shear stress gradient independently predicts site of acute coronary plaque rupture and erosion

AIMS

To investigate local haemodynamics in the setting of acute coronary plaque rupture and erosion.

METHODS AND RESULTS

Intracoronary optical coherence tomography performed in 37 patients with acute coronary syndromes caused by plaque rupture (n = 19) or plaque erosion (n = 18) was used for three-dimensional reconstruction and computational fluid dynamics simulation. Endothelial shear stress (ESS), spatial ESS gradient (ESSG), and oscillatory shear index (OSI) were compared between plaque rupture and erosion through mixed-effects logistic regression. Lipid, calcium, macrophages, layered plaque, and cholesterol crystals were also analysed. By multivariable analysis, only high ESSG [odds ratio (OR) 5.29, 95% confidence interval (CI) 2.57-10.89, P < 0.001], lipid (OR 12.98, 95% CI 6.57-25.67, P < 0.001), and layered plaque (OR 3.17, 95% CI 1.82-5.50, P < 0.001) were independently associated with plaque rupture. High ESSG (OR 13.28, 95% CI 6.88-25.64, P < 0.001), ESS (OR 2.70, 95% CI 1.34-5.42, P = 0.005), and OSI (OR 2.18, 95% CI 1.33-3.54, P = 0.002) independently associated with plaque erosion. ESSG was higher at rupture sites than erosion sites [median (interquartile range): 5.78 (2.47-21.15) vs. 2.62 (1.44-6.18) Pa/mm, P = 0.009], OSI was higher at erosion sites than rupture sites [1.04 × 10-2 (2.3 × 10-3-4.74 × 10-2) vs. 1.29 × 10-3 (9.39 × 10-5-3.0 × 10-2), P < 0.001], but ESS was similar (P = 0.29).

CONCLUSIONS

High ESSG is independently associated with plaque rupture while high ESSG, ESS, and OSI associate with plaque erosion. While ESSG is higher at rupture sites than erosion sites, OSI is higher at erosion sites and ESS was similar. These results suggest that ESSG and OSI may play critical roles in acute plaque rupture and erosion, respectively.

Late-onset hypogonadism: Reductio ad absurdum of the cardiovascular risk-benefit of testosterone replacement therapy

BACKGROUND

Low testosterone (T) level is considered a marker of poor cardiovascular health. Ten years ago, the Testosterone in Older Men with Mobility Limitations (TOM) trial was discontinued due to a higher number of adverse events in men receiving T compared with placebo. Since then, several studies have investigated the risks of T replacement therapy (TRT) in late-onset hypogonadism (LOH).

OBJECTIVE

To review the mechanism by which TRT could damage the cardiovascular system.

MATERIALS AND METHODS

Comprehensive literature search of recent clinical and experimental studies.

RESULTS

The mechanisms of T-mediated coronary vasodilation were reviewed with emphasis on calcium-activated and ATP-sensitive potassium ion channels. We showed how T regulates endothelial nitric oxide synthase (eNOS) and phosphoinositide 3-kinase/protein kinase B/eNOS signaling pathways in vessel walls and its direct effects on cardiomyocytes via β1-adrenergic and ryanodine receptors and provided data on myocardial infarction and heart failure. Vascular smooth muscle senescence could be explained by the modulation of growth factors, matrix metalloproteinase-2, and angiotensin II by T. Furthermore, leukocyte trafficking, facilitated by changes in TNF-α, could explain some of the effects of T on atheromatous plaques. Conflicting data on prothrombotic risk linked to platelet aggregation inhibition via NO-triggered arachidonate synthesis or increased aggregability due to enhanced thromboxane A in human platelets provide evidence regarding the hypotheses on plaque maturation and rupture risk. The effects of T on cardiac electrophysiology and oxygen delivery were also reviewed.

DISCUSSION

The effects of TRT on the cardiovascular system are complex. Although molecular studies suggest a potential benefit, several clinical observations reveal neutral or occasionally detrimental effects, mostly due to confounding factors.

CONCLUSIONS

Attempts to demonstrate that TRT damages the cardiovascular system via systematic analysis of the putative mechanisms led to the contradiction of the initial hypothesis. Current evidence indicates that TRT is safe once other comorbidities are addressed.

The effects of clinically-derived parametric data uncertainty in patient-specific coronary simulations with deformable walls

Cardiovascular simulations are increasingly used for noninvasive diagnosis of cardiovascular disease, to guide treatment decisions, and in the design of medical devices. Quantitative assessment of the variability of simulation outputs due to input uncertainty is a key step toward further integration of cardiovascular simulations in the clinical workflow. In this study, we present uncertainty quantification in computational models of the coronary circulation to investigate the effect of uncertain parameters, including coronary pressure waveform, intramyocardial pressure, morphometry exponent, and the vascular wall Young's modulus. We employ a left coronary artery model with deformable vessel walls, simulated via an Arbitrary-Lagrangian-Eulerian framework for fluid-structure interaction, with a prescribed inlet pressure and open-loop lumped parameter network outlet boundary conditions. Stochastic modeling of the uncertain inputs is determined from intra-coronary catheterization data or gathered from the literature. Uncertainty propagation is performed using several approaches including Monte Carlo, Quasi Monte Carlo sampling, stochastic collocation, and multi-wavelet stochastic expansion. Variabilities in the quantities of interest, including branch pressure, flow, wall shear stress, and wall deformation are assessed. We find that uncertainty in inlet pressures and intramyocardial pressures significantly affect all resulting QoIs, while uncertainty in elastic modulus only affects the mechanical response of the vascular wall. Variability in the morphometry exponent used to distribute the total downstream vascular resistance to the single outlets, has little effect on coronary hemodynamics or wall mechanics. Finally, we compare convergence behaviors of statistics of QoIs using several uncertainty propagation methods on three model benchmark problems and the left coronary simulations. From the simulation results, we conclude that the multi-wavelet stochastic expansion shows superior accuracy and performance against Quasi Monte Carlo and stochastic collocation methods.

Using intravascular ultrasound image-based fluid-structure interaction models and machine learning methods to predict human coronary plaque vulnerability change

Plaque vulnerability prediction is of great importance in cardiovascular research. In vivo follow-up intravascular ultrasound (IVUS) coronary plaque data were acquired from nine patients to construct fluid-structure interaction models to obtain plaque biomechanical conditions. Morphological plaque vulnerability index (MPVI) was defined to measure plaque vulnerability. The generalized linear mixed regression model (GLMM), support vector machine (SVM) and random forest (RF) were introduced to predict MPVI change (ΔMPVI = MPVI_follow-up‒MPVI_baseline) using ten risk factors at baseline. The combination of mean wall thickness, lumen area, plaque area, critical plaque wall stress, and MPVI was the best predictor using RF with the highest prediction accuracy 91.47%, compared to 90.78% from SVM, and 85.56% from GLMM. Machine learning method (RF) improved the prediction accuracy by 5.91% over that from GLMM. MPVI was the best single risk factor using both GLMM (82.09%) and RF (78.53%) while plaque area was the best using SVM (81.29%).

Does the inflow velocity profile influence physiologically relevant flow patterns in computational hemodynamic models of left anterior descending coronary artery?

Patient-specific computational fluid dynamics is a powerful tool for investigating the hemodynamic risk in coronary arteries. Proper setting of flow boundary conditions in computational hemodynamic models of coronary arteries is one of the sources of uncertainty weakening the findings of in silico experiments, in consequence of the challenging task of obtaining in vivo 3D flow measurements within the clinical framework. Accordingly, in this study we evaluated the influence of assumptions on inflow velocity profile shape on coronary artery hemodynamics. To do that, (1) ten left anterior descending coronary artery (LAD) geometries were reconstructed from clinical angiography, and (2) eleven velocity profiles with realistic 3D features such as eccentricity and differently shaped (single- and double-vortex) secondary flows were generated analytically and imposed as inflow boundary conditions. Wall shear stress and helicity-based descriptors obtained prescribing the commonly used parabolic velocity profile were compared with those obtained with the other velocity profiles. Our findings indicated that the imposition of idealized velocity profiles as inflow boundary condition is acceptable as long the results of the proximal vessel segment are not considered, in LAD coronary arteries. As a pragmatic rule of thumb, a conservative estimation of the length of influence of the shape of the inflow velocity profile on LAD local hemodynamics can be given by the theoretical entrance length for cylindrical conduits in laminar flow conditions.

Carotid artery plaque composition and distribution: near-infrared spectroscopy and intravascular ultrasound analysis

Most atherosclerotic plaques (APs) form in typical predilection areas of low endothelial shear stress (ESS). On the contrary, previous data hinted that plaques rupture in their proximal parts where accelerated blood flow causes high ESS. It was postulated that high ESS plays an important role in the latter stages of AP formation and in its destabilization. Here, we used near-infrared spectroscopy (NIRS) to analyse the distribution of lipid core based on the presumed exposure to ESS. A total of 117 carotid arteries were evaluated using NIRS and intravascular ultrasound (IVUS) prior to carotid artery stenting. The point of minimal luminal area (MLA) was determined using IVUS. A stepwise analysis of the presence of lipid core was then performed using NIRS. The lipid core presence was quantified as the lipid core burden index (LCBI) within 2 mm wide segments both proximally and distally to the MLA. The analysed vessel was then divided into three 20 mm long thirds (proximal, middle, and distal) for further analysis. The maximal value of LCBI (231.9 ± 245.7) was noted in the segment localized just 2 mm proximally to MLA. The mean LCBI in the middle third was significantly higher than both the proximal (121.4 ± 185.6 vs. 47.0 ± 96.5, P < 0.01) and distal regions (121.4 ± 185.6 vs. 32.4 ± 89.6, P < 0.01). Lipid core was more common in the proximal region when compared with the distal region (mean LCBI 47.0 ± 96.5 vs. 32.4 ± 89.6, P < 0.01).

Accelerating massively parallel hemodynamic models of coarctation of the aorta using neural networks

Comorbidities such as anemia or hypertension and physiological factors related to exertion can influence a patient’s hemodynamics and increase the severity of many cardiovascular diseases. Observing and quantifying associations between these factors and hemodynamics can be difficult due to the multitude of co-existing conditions and blood flow parameters in real patient data. Machine learning-driven, physics-based simulations provide a means to understand how potentially correlated conditions may affect a particular patient. Here, we use a combination of machine learning and massively parallel computing to predict the effects of physiological factors on hemodynamics in patients with coarctation of the aorta. We first validated blood flow simulations against in vitro measurements in 3D-printed phantoms representing the patient’s vasculature. We then investigated the effects of varying the degree of stenosis, blood flow rate, and viscosity on two diagnostic metrics – pressure gradient across the stenosis (ΔP) and wall shear stress (WSS) - by performing the largest simulation study to date of coarctation of the aorta (over 70 million compute hours). Using machine learning models trained on data from the simulations and validated on two independent datasets, we developed a framework to identify the minimal training set required to build a predictive model on a per-patient basis. We then used this model to accurately predict ΔP (mean absolute error within 1.18 mmHg) and WSS (mean absolute error within 0.99 Pa) for patients with this disease.

Exploring the relationship between biomechanical stresses and coronary atherosclerosis

The pathophysiology of coronary atherosclerosis is multifaceted. Plaque initiation and progression are governed by a complex interplay between genetic and environmental factors acting through processes such as lipid accumulation, altered haemodynamics and inflammation. There is increasing recognition that biomechanical stresses play an important role in atherogenesis, and integration of these metrics with clinical imaging has potential to significantly improve cardiovascular risk prediction. In this review, we present the calculation of coronary biomechanical stresses from first principles and computational methods, including endothelial shear stress (ESS), plaque structural stress (PSS) and axial plaque stress (APS). We discuss the current experimental and human data linking these stresses to the natural history of coronary artery disease and explore the future potential for refining treatment options and predicting future ischaemic events.

Homeobox B9 integrates bone morphogenic protein 4 with inflammation at atheroprone sites

AIMS

Atherosclerosis develops near branches and bends of arteries that are exposed to disturbed blood flow which exerts low wall shear stress (WSS). These mechanical conditions alter endothelial cells (EC) by priming them for inflammation and by inducing turnover. Homeobox (Hox) genes are developmental genes involved in the patterning of embryos along their anterior-posterior and proximal-distal axes. Here we identified Hox genes that are regulated by WSS and investigated their functions in adult arteries.

METHODS AND RESULTS

EC were isolated from inner (low WSS) and outer (high WSS) regions of the porcine aorta and the expression of Hox genes was analysed by quantitative real-time PCR. Several Hox genes (HoxA10, HoxB4, HoxB7, HoxB9, HoxD8, HoxD9) were significantly enriched at the low WSS compared to the high WSS region. Similarly, studies of cultured human umbilical vein EC (HUVEC) or porcine aortic EC revealed that the expression of multiple Hox genes (HoxA10, HoxB9, HoxD8, HoxD9) was enhanced under low (4 dyn/cm2) compared to high (13 dyn/cm2) WSS conditions. Gene silencing studies identified Hox genes (HoxB9, HoxD8, HoxD9) that are positive regulators of inflammatory molecule expression in EC exposed to low WSS, and others (HoxB9, HoxB7, HoxB4) that regulated EC turnover. We subsequently focused on HoxB9 because it was strongly up-regulated by low WSS and, uniquely, was a driver of both inflammation and proliferation. At a mechanistic level, we demonstrate using cultured EC and murine models that bone morphogenic protein 4 (BMP4) is an upstream regulator of HoxB9 which elicits inflammation via induction of numerous inflammatory mediators including TNF and downstream NF-κB activation. Moreover, the BMP4-HoxB9-TNF pathway was potentiated by hypercholesterolaemic conditions.

CONCLUSIONS

Low WSS induces multiple Hox genes that control the activation state and turnover of EC. Notably, low WSS activates a BMP4-HoxB9-TNF signalling pathway to initiate focal arterial inflammation, thereby demonstrating integration of the BMP and Hox systems in vascular pathophysiology.

CD4+/CD8+ ratio positively correlates with coronary plaque instability in unstable angina pectoris patients but fails to predict major adverse cardiovascular events

Background:

The association between CD4+/CD8+ ratio and coronary plaque instability in patients with unstable angina pectoris (UAP) has not been investigated. We sought to elucidate the correlation between CD4+/CD8+ ratio and plaque instability in this patient population.

Methods:

We enrolled 266 UAP patients who underwent pre-intervention optical coherence tomography (OCT) examination and percutaneous coronary intervention in our center from January 2016 to January 2018. Features of coronary plaques in the culprit arteries were classified as unstable plaque and stable plaque. Primary endpoint was occurrence of a major adverse cardiovascular event (MACE). Receiver operating characteristic (ROC) analyses were used to determine the predictive efficacy of the CD4+/CD8+ ratio for a group of unstable plaque patients, and binary logistic regression analysis was performed to evaluate potential independent predictors of plaque instability. All-cause mortality and MACE between the two groups were analyzed.

Results:

UAP patients with unstable plaque had a higher CD4/CD8 ratio compared with stable plaque patients (p < 0.05). Results of binary logistic regression analyses showed that CD4+/CD8+ ratio ⩾1.725 and prior stroke were predictors and risk factors of plaque instability (p < 0.05). ROC analyses showed that CD4+/CD8+ ratio ⩾1.725 was predictive of plaque instability in UAP patients. However, the Kaplan–Meier estimate for MACE and all-cause mortality showed no statistical significance.

Conclusions:

Higher CD4+/CD8+ ratio is associated with higher risk of plaque instability in our cohort of UAP patients. However, CD4+/CD8+ ratio was not an independent predictor of 1-year MACE or all-cause mortality.

Current Advances in the Diagnostic Imaging of Atherosclerosis: Insights into the Pathophysiology of Vulnerable Plaque

Atherosclerosis is a lipoprotein-driven inflammatory disorder leading to a plaque formation at specific sites of the arterial tree. After decades of slow progression, atherosclerotic plaque rupture and formation of thrombi are the major factors responsible for the development of acute coronary syndromes (ACSs). In this regard, the detection of high-risk (vulnerable) plaques is an ultimate goal in the management of atherosclerosis and cardiovascular diseases (CVDs). Vulnerable plaques have specific morphological features that make their detection possible, hence allowing for identification of high-risk patients and the tailoring of therapy. Plaque ruptures predominantly occur amongst lesions characterized as thin-cap fibroatheromas (TCFA). Plaques without a rupture, such as plaque erosions, are also thrombi-forming lesions on the most frequent pathological intimal thickening or fibroatheromas. Many attempts to comprehensively identify vulnerable plaque constituents with different invasive and non-invasive imaging technologies have been made. In this review, advantages and limitations of invasive and non-invasive imaging modalities currently available for the identification of plaque components and morphologic features associated with plaque vulnerability, as well as their clinical diagnostic and prognostic value, were discussed.

The Evolution of Data Fusion Methodologies Developed to Reconstruct Coronary Artery Geometry From Intravascular Imaging and Coronary Angiography Data: A Comprehensive Review

Understanding the mechanisms that regulate atherosclerotic plaque formation and evolution is a crucial step for developing treatment strategies that will prevent plaque progression and reduce cardiovascular events. Advances in signal processing and the miniaturization of medical devices have enabled the design of multimodality intravascular imaging catheters that allow complete and detailed assessment of plaque morphology and biology. However, a significant limitation of these novel imaging catheters is that they provide two-dimensional (2D) visualization of the lumen and vessel wall and thus they cannot portray vessel geometry and 3D lesion architecture. To address this limitation computer-based methodologies and user-friendly software have been developed. These are able to off-line process and fuse intravascular imaging data with X-ray or computed tomography coronary angiography (CTCA) to reconstruct coronary artery anatomy. The aim of this review article is to summarize the evolution in the field of coronary artery modeling; we thus present the first methodologies that were developed to model vessel geometry, highlight the modifications introduced in revised methods to overcome the limitations of the first approaches and discuss the challenges that need to be addressed, so these techniques can have broad application in clinical practice and research.

Computational fluid dynamic study of multiple sequential coronary artery bypass anastomoses in a native coronary stenosis model

BACKGROUND

The objective of this study was to evaluate the hemodynamic characteristics of multiple sequential coronary artery bypass grafting using a computational fluid dynamics study.

METHODS

First anastomosis was configured into parallel and diamond anastomoses, and the second anastomosis was set as end-side anastomosis. The anastomosis incision lengths were fixed at 2 mm. Various combinations of the degree of first and second stenoses were studied. The diameter of both the native and graft vessels was set at 2 mm. The inlet boundary condition was set by a sample of the transient time flow measurement, which was measured intraoperatively.

RESULTS

Both swirl and stagnation were observed at the outlets of the stenosis and the anastomosis sites. When the severity of the second stenosis was larger than that of the first, the flow at the outlet of the second stenosis was more unstable. Higher wall shear stress and larger oscillatory shear index regions were observed when the severe stenosis was bypassed by the first anastomosis, especially with diamond anastomoses. Less energy loss and higher energy efficiency were present when the vessel with more severe stenosis was bypassed as the second anastomosis. Energy loss was lower and energy efficiency was higher with parallel anastomosis than diamond anastomosis when the severity of the two stenoses was the same.

CONCLUSIONS

It is ideal to bypass the less severe stenosis vessel first with a parallel anastomosis method when employing multiple sequential bypass grafting. This improves hemodynamic stability and energy efficiency, according to a computational fluid dynamics model.

Utility of Multimodality Intravascular Imaging and the Local Hemodynamic Forces to Predict Atherosclerotic Disease Progression

OBJECTIVES

This study sought to examine the utility of multimodality intravascular imaging and of the endothelial shear stress (ESS) distribution to predict atherosclerotic evolution.

BACKGROUND

There is robust evidence that intravascular ultrasound (IVUS)-derived plaque characteristics and ESS distribution can predict, with however limited accuracy, atherosclerotic evolution; nevertheless, it is yet unclear whether multimodality imaging and ESS mapping enable more accurate prediction of coronary plaque progression.

METHODS

A total of 44 patients admitted with a myocardial infarction that had successful revascularization and 3-vessel IVUS and optical coherence tomography (OCT) imaging at baseline and 13-month follow-up were included in the study. The IVUS data acquired at baseline in the nonculprit vessels were fused with x-ray angiography to reconstruct coronary anatomy and in the obtained models blood flow simulation was performed and the ESS was estimated. The baseline plaque characteristics and ESS distribution were used to identify predictors of disease progression: defined as a lumen reduction and an increase in plaque burden at follow-up.

RESULTS

Seventy-three vessels were included in the final analysis. Baseline ESS and the IVUS-derived but not the OCT-derived plaque characteristics were independently associated with a decrease in lumen area and an increase in plaque burden. Low ESS (odds ratio: 0.45; 95% confidence interval: 0.28 to 0.71; p < 0.001) and plaque burden (odds ratio: 0.73; 95% confidence interval: 0.54 to 0.97; p = 0.030) were the only independent predictors of disease progression at follow-up. The accuracy of the IVUS-derived plaque characteristics in predicting disease progression did not improve when ESS (AUC: 0.824 vs. 0.847; p = 0.127) or when OCT variables and ESS (AUC: 0.842; p = 0.611) were added into the model.

CONCLUSIONS

ESS and OCT-derived variables did not improve the efficacy of IVUS in predicting disease progression. Further research is required to investigate whether multimodality imaging combined with ESS mapping will allow more reliable vulnerable plaque detection. (Comparison of Biomatrix Versus Gazelle in ST-Elevation Myocardial Infarction [STEMI] [COMFORTABLE]; NCT00962416).