Prediction of the Localization of High-Risk Coronary Atherosclerotic Plaques on the Basis of Low Endothelial Shear Stress

Identification of the haemodynamic environment permissive for plaque erosion

Endothelial erosion of atherosclerotic plaques is the underlying cause of approximately 30% of acute coronary syndromes (ACS). As the vascular endothelium is profoundly affected by the haemodynamic environment to which it is exposed, we employed computational fluid dynamic (CFD) analysis of the luminal geometry from 17 patients with optical coherence tomography (OCT)-defined plaque erosion, to determine the flow environment permissive for plaque erosion. Our results demonstrate that 15 of the 17 cases analysed occurred on stenotic plaques with median 31% diameter stenosis (interquartile range 28–52%), where all but one of the adherent thrombi located proximal to, or within the region of maximum stenosis. Consequently, all flow metrics related to elevated flow were significantly increased (time averaged wall shear stress, maximum wall shear stress, time averaged wall shear stress gradient) with a reduction in relative residence time, compared to a non-diseased reference segment. We also identified two cases that did not exhibit an elevation of flow, but occurred in a region exposed to elevated oscillatory flow. Our study demonstrates that the majority of OCT-defined erosions occur where the endothelium is exposed to elevated flow, a haemodynamic environment known to evoke a distinctive phenotypic response in endothelial cells.

The Impact of Coronary Artery Calcification on Long-Term Cardiovascular Outcomes

Decades of research and experimental studies have investigated various strategies to prevent acute coronary events. However, significantly efficient preventive methods have not been developed and still remains a challenge to determine if a coronary atherosclerotic plaque will become vulnerable and unstable. This review aims to assess the significance of plaque vulnerability markers, more precisely the role of spotty calcifications in the development of major cardiac events, given that coronary calcification is a hallmark of atherosclerosis. Recent studies have suggested that microcalcifications, spotty calcifications, and the presence of the napkin-ring sign are predictive vulnerable plaque features, and their presence may cause plaque instability.

Application of physics-based flow models in cardiovascular medicine: Current practices and challenges

Personalized physics-based flow models are becoming increasingly important in cardiovascular medicine. They are a powerful complement to traditional methods of clinical decision-making and offer a wealth of physiological information beyond conventional anatomic viewing using medical imaging data. These models have been used to identify key hemodynamic biomarkers, such as pressure gradient and wall shear stress, which are associated with determining the functional severity of cardiovascular diseases. Importantly, simulation-driven diagnostics can help researchers understand the complex interplay between geometric and fluid dynamic parameters, which can ultimately improve patient outcomes and treatment planning. The possibility to compute and predict diagnostic variables and hemodynamics biomarkers can therefore play a pivotal role in reducing adverse treatment outcomes and accelerate development of novel strategies for cardiovascular disease management.

Evaluation of Plaque Characteristics and Inflammation Using Magnetic Resonance Imaging

Atherosclerosis is an inflammatory disease of large and medium-sized arteries, characterized by the growth of atherosclerotic lesions (plaques). These plaques often develop at inner curvatures of arteries, branchpoints, and bifurcations, where the endothelial wall shear stress is low and oscillatory. In conjunction with other processes such as lipid deposition, biomechanical factors lead to local vascular inflammation and plaque growth. There is also evidence that low and oscillatory shear stress contribute to arterial remodeling, entailing a loss in arterial elasticity and, therefore, an increased pulse-wave velocity. Although altered shear stress profiles, elasticity and inflammation are closely intertwined and critical for plaque growth, preclinical and clinical investigations for atherosclerosis mostly focus on the investigation of one of these parameters only due to the experimental limitations. However, cardiovascular magnetic resonance imaging (MRI) has been demonstrated to be a potent tool which can be used to provide insights into a large range of biological parameters in one experimental session. It enables the evaluation of the dynamic process of atherosclerotic lesion formation without the need for harmful radiation. Flow-sensitive MRI provides the assessment of hemodynamic parameters such as wall shear stress and pulse wave velocity which may replace invasive and radiation-based techniques for imaging of the vascular function and the characterization of early plaque development. In combination with inflammation imaging, the analyses and correlations of these parameters could not only significantly advance basic preclinical investigations of atherosclerotic lesion formation and progression, but also the diagnostic clinical evaluation for early identification of high-risk plaques, which are prone to rupture. In this review, we summarize the key applications of magnetic resonance imaging for the evaluation of plaque characteristics through flow sensitive and morphological measurements. The simultaneous measurements of functional and structural parameters will further preclinical research on atherosclerosis and has the potential to fundamentally improve the detection of inflammation and vulnerable plaques in patients.

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.

Risk prediction of in-stent restenosis among patients with coronary drug-eluting stents: current clinical approaches and challenges

Introduction: In-stent restenosis (ISR) has been one of the biggest limitations to the success of percutaneous coronary intervention for the treatment of coronary artery disease (CAD). The introduction of drug-eluting stent (DES) was a revolution in the treatment of CAD because these devices drastically reduced ISR to very low levels (<5%). Subsequently, newer generation DES treatments have overcome the drawbacks of first-generation DES, i.e. delayed endothelialization, and late stent thrombosis. However, the issue of late ISR, including neoatherosclerosis after DES implantation especially in high-risk patients and complex lesions, still exists as a challenge to be overcome.Areas covered: We discuss the mechanisms of ISR development including neoatherosclerosis, past and current clinical status of ISR, and methods to predict and overcome this issue from pathological and clinical points of view.Expert opinion: The initial drawbacks of first-generation DES, such as delayed endothelial healing and subsequent risk of late stent thrombosis, have been improved upon by the current generation DES. To achieve better long-term clinical outcomes, further titration of drug-release and polymer degradation profile, strut thickness as well as material innovation are needed.

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.

Low shear stress induced vascular endothelial cell pyroptosis by TET2/SDHB/ROS pathway

Vascular endothelial cell (VEC) inflammation induced by low shear stress plays key roles in the initiation and progression of atherosclerosis (As). Pyroptosis is a form of inflammatory programmed cell death that is critical for As. However, the effect of low shear stress on VEC pyroptosis and the underlying mechanisms were not clear. Here we show that low shear stress promoted VEC pyroptosis and reduced the expression of Ten-Eleven Translocation 2 (TET2) methylcytosine dioxygenase. Loss of TET2 resulted in the upregulation of the expression and activity of mitochondrial respiratory complex II subunit succinate dehydrogenase B (SDHB) by decreasing the recruitment of histone deacetylase 2, independent of DNA demethylation modification. The overexpression of SDHB mediated mitochondrial injury and increased the production of reactive oxygen species (ROS). The administration of ROS scavenger NAC alleviated VEC pyroptosis induced by SDHB overexpression and TET2 shRNA. These findings show that low shear stress induced endothelial cell pyroptosis through the TET2/SDHB/ROS pathway and offer new insights into As.

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.

Hemodynamic impacts of hematocrit level by two-way coupled FSI in the left coronary bifurcation

Cardiovascular disease is now under the influence of several factors that encourage researchers to investigate the flow of these vessels. Oscillation influences the blood circulation in the volume of red blood cells (RBC) strongly. Therefore, in this study, its effects have been considered on hemodynamic parameters in the elastic wall and coronary bifurcation. In this study, a 3D geometry of non-Newtonian and pulsatile blood circulation is considered in the left coronary artery bifurcation. The Casson model with various hematocrits is analyzed in elastic and rigid walls. The wall shear stress (WSS) cannot show the stenosis artery alone, therefore, the oscillatory shear index (OSI) is represented as a hemodynamic parameter of WSS individually of time. The results are determined using two-way fluid-structure interaction (FSI) coupling method using an arbitrary Lagrangian-Eulerian method. The most prominent difference in velocity happened in the bifurcation and at hematocrit 30 with yield stress 6.59E-04 Pa. The backflow and vortex flow in the LCx branch grown with increasing shear rates. The likelihood of plaque generation at the ending of the LM branch is observed in hematocrits 10 and 20, while the WSS magnitude is normal in the hematocrit 60 with the greatest yield stress in the bifurcation. The shear stress among the rigid and elastic models is the highest at the ending of the LM branch. The wall shear stress magnitude among the models decreased at most of 24.49% by dividing the flow. Time-independent results for models showed that there is the highest value of OSI at the bifurcation, which then quickly dropped.

Spherization of red blood cells and platelet margination in COPD patients

Red blood cells (RBCs) in pathological situations undergo biochemical and conformational changes, leading to alterations in rheology involved in cardiovascular events. The shape of RBCs in volunteers and stable and exacerbated chronic obstructive pulmonary disease (COPD) patients was analyzed. The effects of RBC spherization on platelet transport (displacement in the flow field caused by their interaction with RBCs) were studied in vitro and by numerical simulations. RBC spherization was observed in COPD patients compared with volunteers. In in vitro experiments at a shear rate of 100 s^-1 , treatment of RBCs with neuraminidase induced greater sphericity, which mainly affected platelet aggregates without changing aggregate size. At 400 s^-1 , neuraminidase treatment changes both the size of the aggregates and the number of platelet aggregates. Numerical simulations indicated that RBC spherization induces an increase of the platelet mean square displacement, which is traditionally linked to the platelet diffusion coefficient. RBCs of COPD patients are more spherical than healthy volunteers. Experimentally, RBC spherization induces increased platelet transport to the wall. Additional studies are needed to understand the link between the effect of RBCs on platelet transport and the increased cardiovascular events observed in COPD patients.

Relationship Between Coronary Fractional Flow Reserve and Computational Fluid Dynamics Analysis in Moderate Stenosis of the Coronary Artery

Background: Fractional flow reserve (FFR) is used to evaluate the need for percutaneous coronary intervention (PCI) in cases of moderate stenosis of the coronary artery. Recently, diagnostic imaging support with computational fluid dynamics (CFD) analysis has been garnering attention. This study defines the relationship between FFR conducted for cardiac catheterization and CFD analyses conducted using coronary computed tomography (CT) for moderate stenosis, in addition to considering whether wall pressure (WP) and wall shear stress (WSS) can be used to evaluate ischemia.

Methods and Results: Cases in which FFR was measured via coronary CT and cardiac catheterization was performed within 3 months were collected retrospectively. In the CFD analysis, WP and WSS were calculated and compared with FFR. Three groups were created to compare results of CFD analysis and FFR values according to the location of the stenosis: the right coronary artery, the left anterior descending artery, and the left circumflex artery. There was a correlation between FFR and WSS according to CFD analysis for moderate stenosis of the coronary artery, with a cut-off value for treatment able to be calculated.

Conclusions: The results of this study suggest that ischemia can be evaluated by conducting CFD analysis (WSS) using coronary CT.

Exploring wall shear stress spatiotemporal heterogeneity in coronary arteries combining correlation-based analysis and complex networks with computational hemodynamics

Atherosclerosis at the early stage in coronary arteries has been associated with low cycle-average wall shear stress magnitude. However, parallel to the identification of an established active role for low wall shear stress in the onset/progression of the atherosclerotic disease, a weak association between lesions localization and low/oscillatory wall shear stress has been observed. In the attempt to fully identify the wall shear stress phenotype triggering early atherosclerosis in coronary arteries, this exploratory study aims at enriching the characterization of wall shear stress emerging features combining correlation-based analysis and complex networks theory with computational hemodynamics. The final goal is the characterization of the spatiotemporal and topological heterogeneity of wall shear stress waveforms along the cardiac cycle. In detail, here time-histories of wall shear stress magnitude and wall shear stress projection along the main flow direction and orthogonal to it (a measure of wall shear stress multidirectionality) are analyzed in a representative dataset of 10 left anterior descending pig coronary artery computational hemodynamics models. Among the main findings, we report that the proposed analysis quantitatively demonstrates that the model-specific inlet flow-rate shapes wall shear stress time-histories. Moreover, it emerges that a combined effect of low wall shear stress magnitude and of the shape of the wall shear stress–based descriptors time-histories could trigger atherosclerosis at its earliest stage. The findings of this work suggest for new experiments to provide a clearer determination of the wall shear stress phenotype which is at the basis of the so-called arterial hemodynamic risk hypothesis in coronary arteries.

Vertebral Artery Stenoses Contribute to the Development of Diffuse Plaques in the Basilar Artery

Vertebral artery (VA) stenosis is relevant to a high early risk of recurrent stroke and basilar artery (BA) is the most common intracranial site of atherosclerotic lesions. It is important to show predictive risk factors for transient ischemic attack (TIA) or posterior infarctions. The aim of the study is to investigate morphometry and hemodynamics in intracranial vertebral and basilar arteries of health and diseased patients to enhance the risk assessment. Based on the geometrical model reconstructed from CTA images in 343 patients, a transient three-dimensional computational model was used to determine the hemodynamics. Patients were classified in symmetric, asymmetric, hypoplastic, and stenotic groups while patients in the stenotic group were divided into unilateral, bilateral, bifurcation, and tandem stenotic sub-groups. Patients in bilateral, bifurcation, and tandem stenotic sub-groups had significantly lower basilar artery diameters than other groups. Patients in the stenotic group had significantly higher surface area ratio (SAR) of high time-averaged wall shear stress gradient (TAWSSG) and higher incidence of TIAs or posterior infarctions than other groups while patients in the tandem stenotic sub-group had the highest values (SAR-TAWSSG of 57 ± 22% and TIAs or posterior infarction incidence of 54%). The high SAR-TAWSSG is predisposed to induce TIAs or posterior infarction.

The improvement of the shear stress and oscillatory shear index of coronary arteries during Enhanced External Counterpulsation in patients with coronary heart disease

Background

Enhanced External Counterpulsation (EECP) can chronically relieve ischemic chest pain and improve the prognosis of coronary heart disease (CHD). Despite its role in mitigating heart complications, EECP and the mechanisms behind its therapeutic nature, such as its effects on blood flow hemodynamics, are still not fully understood. This study aims to elucidate the effect of EECP on significant hemodynamic parameters in the coronary arterial tree.

Methods

A finite volume method was used in conjunction with the inlet pressure wave (surrogated by the measured aortic pressure) before and during EECP and outlet flow resistance, assuming the blood as newtonian fluid. The time-average wall shear stress (TAWSS) and oscillatory shear index (OSI) were determined from the flow field.

Results

Regardless of the degree of vascular stenosis, hemodynamic conditions and flow patterns could be improved during EECP. In comparison with the original tree, the tree with a severe stenosis (75% area stenosis) demonstrated more significant improvement in hemodynamic conditions and flow patterns during EECP, with surface area ratio of TAWSS risk area (SAR-TAWSS) reduced from 12.3% to 6.7% (vs. SAR-TAWSS reduced from 7.2% to 5.6% in the original tree) and surface area ratio of OSI risk area (SAR-OSI) reduced from 6.8% to 2.5% (vs. SAR-OSI of both 0% before and during EECP in the original tree because of mild stenosis). Moreover, it was also shown that small ratio of diastolic pressure (D) and systolic pressure (S) (D/S) could only improve the hemodynamic condition mildly. The SAR-TAWSS reduction ratio significantly increased as D/S became larger.

Conclusions

A key finding of the study was that the improvement of hemodynamic conditions along the LMCA trees during EECP became more significant with the increase of D/S and the severity degree of stenoses at the bifurcation site. These findings have important implications on EECP as adjuvant therapy before or after percutaneous coronary intervention (PCI) in patients with diffuse atherosclerosis.

Histopathologic and physiologic effect of bifurcation stenting: current status and future prospects

Introduction: Coronary bifurcation lesions are involved in up to 20% of all percutaneous coronary interventions (PCI). However, bifurcation lesion intervention is associated with a high complication rate, and optimal treatment of coronary bifurcation is an ongoing debate.Areas covered: Both different stenting techniques and a variety of devices have been suggested for bifurcation treatment, including the use of conventional coronary stents, bioresorbable vascular scaffolds (BVS), drug-eluting balloons (DEB), and stents dedicated to bifurcations. This review will summarize different therapeutic approaches with their advantages and shortcomings, with special emphasis on histopathologic and physiologic effects of each treatment strategy.Expert opinion: Histopathology and clinical data have shown that a more simple treatment strategy is beneficial in bifurcation lesions, achieving superior results. Bifurcation interventions through balloon angioplasty or placement of stents can importantly alter the bifurcation's geometry and accordingly modify local flow conditions. Computational fluid dynamics (CFD) studies have shown that the outcome of bifurcation interventions is governed by local hemodynamic shear conditions. Minimizing detrimental flow conditions as much as possible should be the ultimate strategy to achieve long-term success of bifurcation interventions.

Sex/Gender-Specific Imbalance in CVD: Could Physical Activity Help to Improve Clinical Outcome Targeting CVD Molecular Mechanisms in Women?

In the last two decades, new insights have been gained regarding sex/gender-related differences in cardiovascular disease (CVD). CVD represents the leading cause of death worldwide in both men and women, accounting for at least one-third of all deaths in women and half of deaths in women over 50 years in developing countries. Important sex-related differences in prevalence, presentation, management, and outcomes of different CVDs have been recently discovered, demonstrating sex/gender-specific pathophysiologic features in the presentation and prognosis of CVD in men and women. A large amount of evidence has highlighted the role of sex hormones in protecting women from CVDs, providing an advantage over men that is lost when women reach the menopause stage. This hormonal-dependent shift of sex-related CVD risk consequently affects the overall CVD epidemiology, particularly in light of the increasing trend of population aging. The benefits of physical activity have been recognized for a long time as a powerful preventive approach for both CVD prevention and aging-related morbidity control. Exercise training is indeed a potent physiological stimulus, which reduces primary and secondary cardiovascular events. However, the underlying mechanisms of these positive effects, including from a sex/gender perspective, still need to be fully elucidated. The aim of this work is to provide a review of the evidence linking sex/gender-related differences in CVD, including sex/gender-specific molecular mediators, to explore whether sex- and gender-tailored physical activity may be used as an effective tool to prevent CVD and improve clinical outcomes in women.

The Relationship between Coronary Artery Wall Shear Strain and Plaque Morphology: A Systematic Review and Meta-Analysis

Background and Aim: Arterial wall shear strain (WSS) has been proposed to impact the features of atherosclerotic plaques. The aim of this meta-analysis was to assess the impact of different types of WSS on plaque features in coronary artery disease (CAD). Methods: We systematically searched PubMed-Medline, EMBASE, Scopus, Google Scholar, and the Cochrane Central Registry, from 1989 up to January 2020 and selected clinical trials and observational studies which assessed the relationship between WSS, measured by intravascular ultrasound (IVUS), and plaque morphology in patients with CAD. Results: In four studies, a total of 72 patients with 13,098 coronary artery segments were recruited, with mean age 57.5 ± 9.5 years. The pooled analysis showed that low WSS was associated with larger baseline lumen area (WMD 2.55 [1.34 to 3.76, p < 0.001]), smaller plaque area (WMD −1.16 [−1.84 to −0.49, p = 0.0007]), lower plaque burden (WMD −12.7 [−21.4 to −4.01, p = 0.04]), and lower necrotic core area (WMD −0.32 [−0.78 to 0.14, p = 0.04]). Low WSS also had smaller fibrous area (WMD −0.79 [−1.88 to 0.30, p = 0.02]) and smaller fibro-fatty area (WMD −0.22 [−0.57 to 0.13, p = 0.02]), compared with high WSS, but the dense calcium score was similar between the two groups (WMD −0.17 [−0.47 to 0.13, p = 0.26]). No differences were found between intermediate and high WSS. Conclusions: High WSS is associated with signs of plaque instability such as higher necrotic core, higher calcium score, and higher plaque burden compared with low WSS. These findings highlight the role of IVUS in assessing plaque vulnerability.

Effect of Wall Elasticity on Hemodynamics and Wall Shear Stress in Patient-Specific Simulations in the Coronary Arteries

Wall shear stress (WSS) has been shown to be associated with myocardial infarction (MI) and progression of atherosclerosis. Wall elasticity is an important feature of hemodynamic modeling affecting WSS calculations. The objective of this study was to investigate the role of wall elasticity on WSS, and justify use of either rigid or elastic models in future studies. Digital anatomic models of the aorta and coronaries were created based on coronary computed tomography angiography (CCTA) in four patients. Hemodynamics was computed in rigid and elastic models using a finite element flow solver. WSS in five timepoints in the cardiac cycle and time averaged wall shear stress (TAWSS) were compared between the models at each 3 mm subsegment and 4 arcs in cross sections along the centerlines of coronaries. In the left main (LM), proximal left anterior descending (LAD), left circumflex (LCX), and proximal right coronary artery (RCA) of the elastic model, the mean percent radial increase 5.95 ± 1.25, 4.02 ± 0.97, 4.08 ± 0.94, and 4.84 ± 1.05%, respectively. WSS at each timepoint in the cardiac cycle had slightly different values; however, when averaged over the cardiac cycle, there were negligible differences between the models. In both the subsegments (n = 704) and subarc analysis, TAWSS in the two models were highly correlated (r = 0.99). In investigation on the effect of coronary wall elasticity on WSS in CCTA-based models, the results of this study show no significant differences in TAWSS justifying using rigid wall models for future larger studies.

A novel in vivo assessment of fluid dynamics on aortic valve leaflet using epi-aortic echocardiogram

BACKGROUND

Mechanical stress caused by blood flow, such as wall shear stress (WSS) and its related parameters, is key moderator of endothelial degeneration. However, an in vivo method to measure WSS on heart valves has not been developed.

METHODS

We developed a novel approach, based on vector flow mapping using intraoperative epi-aortic echocardiogram, to measure WSS and oscillatory shear index (OSI) on the aortic valve. We prospectively enrolled 15 patients with normal valves, who underwent coronary artery bypass graft.

RESULTS

Systolic WSS on the ventricularis (2.40 ± 0.44 Pa [1.45-3.00 Pa]) was higher than systolic WSS on the fibrosa (0.33 ± 0.08 Pa [0.14-0.47 Pa], P < .001) and diastolic WSS on the ventricularis (0.18 ± 0.07 Pa [0.04-0.28 Pa], P < .001). Oscillatory shear index on the fibrosa was higher than on the ventricularis (0.29 ± 0.04 [0.24-0.36] vs 0.05 ± 0.03 [0.01-0.12], P < .001). A pilot study involving two patients with severe aortic regurgitation showed significantly different values in fluid dynamics.

CONCLUSION

Vector flow mapping method using intraoperative epi-aortic echocardiogram is an effective way of measuring WSS and OSI on normal aortic leaflet in vivo, allowing for better understanding of the pathophysiology of aortic valve diseases.

Angiographic Restenosis in Coronary Bifurcations Treatment with Regular Drug Eluting Stents and Dedicated Bifurcation Drug-Eluting BiOSS Stents: Analysis Based on Randomized POLBOS I and POLBOS II Studies

Aim

The marked variation in bifurcation anatomy has brought about an ongoing search for stents specifically constructed for coronary bifurcations. This study aimed to analyze the angiographic restenosis prevalence and patterns and predictors of different patterns in dedicated bifurcation BiOSS® vs. current generation drug-eluting stents implanted in coronary bifurcation lesions based on data from two clinical trials POLBOS I and II.

Methods

Dedicated bifurcation BiOSS® stents were compared with drug-eluting stents (DES) in patients with stable coronary artery disease (CAD) or nonST elevation acute coronary syndrome (NSTE-ACS) (POLBOS I: paclitaxel eluting BiOSS® Expert vs. DES; POLBOS II: sirolimus eluting BiOSS® LIM vs. DES). Provisional T-stenting was the default treatment. Morphological pattern of in-stent restenosis according to the modified Mehran classification adopted for bifurcation lesions was assessed with bifurcation dedicated quantitative coronary angiographic software (CAAS 5.11, Pie Medical Imaging BV, the Netherlands).

Results

In total, 445 patients (222 patients in BiOSS group and 223 patients in DES group) were included into the analysis. In BiOSS group 24 cases of angiographic restenosis (10.8%) were recorded, and in DES group-17 cases (7.6%) at 12 months follow-up (angiographic control rate at follow-up-90.3%). In the BiOSS group most frequent medina classification in restenotic cases was 0.0.1 (25%), whereas in DES-0.0.1 and 0.1.1 (23.5% each). In multivariate regression analysis proximal optimization technique was associated with the lowest chance for restenosis (OR 0.15, 95% CI 0.06-0.33), whereas diabetes on insulin was associated with the highest risk of restenosis (OR 4.21, 95% CI 1.48-11.44).

Conclusions

The angiographic restenosis pattern and rate was similar between BiOSS stents and DES in coronary bifurcation lesions.

Coronary artery plaque growth: A two-way coupled shear stress-driven model

Atherosclerosis in coronary arteries can lead to plaque growth, stenosis formation, and blockage of the blood flow supplying the heart tissue. Several studies have shown that hemodynamics play an important role in the growth of coronary artery plaques. Specifically, low wall shear stress (WSS) appears to be the leading hemodynamic parameter promoting atherosclerotic plaque growth, which in turn influences the blood flow and WSS distribution. Therefore, a two-way coupled interaction exists between WSS and atherosclerosis growth. In this work, a computational framework was developed to study the coupling between WSS and plaque growth in coronary arteries. Computational fluid dynamics (CFD) was used to quantify WSS distribution. Surface mesh nodes were moved in the inward normal direction according to a growth model based on WSS. After each growth stage, the geometry was updated and the CFD simulation repeated to find updated WSS values for the next growth stage. One hundred twenty growth stages were simulated in an idealized tube and an image-based left anterior descending artery. An automated framework was developed using open-source software to couple CFD simulations with growth. Changes in plaque morphology and hemodynamic patterns during different growth stages are presented. The results show larger plaque growth towards the downstream segment of the plaque, agreeing with the reported clinical observations. The developed framework could be used to establish hemodynamic-driven growth models and study the interaction between these processes.

Endothelial responses to shear stress in atherosclerosis: a novel role for developmental genes

Flowing blood generates a frictional force called shear stress that has major effects on vascular function. Branches and bends of arteries are exposed to complex blood flow patterns that exert low or low oscillatory shear stress, a mechanical environment that promotes vascular dysfunction and atherosclerosis. Conversely, physiologically high shear stress is protective. Endothelial cells are critical sensors of shear stress but the mechanisms by which they decode complex shear stress environments to regulate physiological and pathophysiological responses remain incompletely understood. Several laboratories have advanced this field by integrating specialized shear-stress models with systems biology approaches, including transcriptome, methylome and proteome profiling and functional screening platforms, for unbiased identification of novel mechanosensitive signalling pathways in arteries. In this Review, we describe these studies, which reveal that shear stress regulates diverse processes and demonstrate that multiple pathways classically known to be involved in embryonic development, such as BMP-TGFβ, WNT, Notch, HIF1α, TWIST1 and HOX family genes, are regulated by shear stress in arteries in adults. We propose that mechanical activation of these pathways evolved to orchestrate vascular development but also drives atherosclerosis in low shear stress regions of adult arteries.

Variation in Coronary Atherosclerosis Severity Related to a Distinct LDL (Low-Density Lipoprotein) Profile: Findings From a Familial Hypercholesterolemia Pig Model

OBJECTIVE

In an adult porcine model of familial hypercholesterolemia (FH), coronary plaque development was characterized. To elucidate the underlying mechanisms of the observed inter-individual variation in disease severity, detailed lipoprotein profiles were determined. Approach and Results: FH pigs (3 years old, homozygous LDLR R84C mutation) received an atherogenic diet for 12 months. Coronary atherosclerosis development was monitored using serial invasive imaging and histology. A pronounced difference was observed between mildly diseased pigs which exclusively developed early lesions (maximal plaque burden, 25% [23%-34%]; n=5) and advanced-diseased pigs (n=5) which developed human-like, lumen intruding plaques (maximal plaque burden, 69% [57%-77%]) with large necrotic cores, intraplaque hemorrhage, and calcifications. Advanced-diseased pigs and mildly diseased pigs displayed no differences in conventional risk factors. Additional plasma lipoprotein profiling by size-exclusion chromatography revealed 2 different LDL (low-density lipoprotein) subtypes: regular and larger LDL. Cholesterol, sphingosine-1-phosphate, ceramide, and sphingomyelin levels were determined in these LDL-subfractions using standard laboratory techniques and high-pressure liquid chromatography mass-spectrometry analyses, respectively. At 3 months of diet, regular LDL of advanced-diseased pigs contained relatively more cholesterol (LDL-C; regular/larger LDL-C ratio 1.7 [1.3-1.9] versus 0.8 [0.6-0.9]; P=0.008) than mildly diseased pigs, while larger LDL contained more sphingosine-1-phosphate, ceramides, and sphingomyelins. Larger and regular LDL was also found in plasma of 3 patients with homozygous FH with varying LDL-C ratios.

CONCLUSIONS

In our adult FH pig model, inter-individual differences in atherosclerotic disease severity were directly related to the distribution of cholesterol and sphingolipids over a distinct LDL profile with regular and larger LDL shortly after the diet start. A similar LDL profile was detected in patients with homozygous FH.

[Hot issues in bifurcation lesions PCI in 2019]

Coronary bifurcations are involved in 15-20% of all percutaneous coronary interventions (PCI) and remain one of the most challenging lesions in interventional cardiology in terms of procedural success rate as well as long-term cardiac events. The optimal management of bifurcation lesions is still debated but involves careful assessment, planning and a sequential provisional approach. The preferential strategy for PCI of bifurcation lesions remains to use main vessel (MV) stenting with a proximal optimisation technique (POT) and provisional side branch (SB) stenting as a preferred approach. Final kissing balloon inflation is not recommended in all cases. In the minority of lesions where two stents are required, careful deployment and optimal expansion are essential to achieve a long-term result. Intracoronary imaging techniques (IVUS, OCT) and FFR are useful endovascular tools to achieve optimal results.

The importance of side branches in modeling 3D hemodynamics from angiograms for patients with coronary artery disease

Genesis of atherosclerotic lesions in the human arterial system is critically influenced by the fluid mechanics. Applying computational fluid dynamic tools based on accurate coronary physiology derived from conventional biplane angiogram data may be useful in guiding percutaneous coronary interventions. The primary objective of this study is to build and validate a computational framework for accurate personalized 3-dimensional hemodynamic simulation across the complete coronary arterial tree and demonstrate the influence of side branches on coronary hemodynamics by comparing shear stress between coronary models with and without these included. The proposed novel computational framework based on biplane angiography enables significant arterial circulation analysis. This study shows that models that take into account flow through all side branches are required for precise computation of shear stress and pressure gradient whereas models that have only a subset of side branches are inadequate for biomechanical studies as they may overestimate volumetric outflow and shear stress. This study extends the ongoing computational efforts and demonstrates that models based on accurate coronary physiology can improve overall fidelity of biomechanical studies to compute hemodynamic risk-factors.

PolNet: A Tool to Quantify Network-Level Cell Polarity and Blood Flow in Vascular Remodeling

In this article, we present PolNet, an open-source software tool for the study of blood flow and cell-level biological activity during vessel morphogenesis. We provide an image acquisition, segmentation, and analysis protocol to quantify endothelial cell polarity in entire in vivo vascular networks. In combination, we use computational fluid dynamics to characterize the hemodynamics of the vascular networks under study. The tool enables, to our knowledge for the first time, a network-level analysis of polarity and flow for individual endothelial cells. To date, PolNet has proven invaluable for the study of endothelial cell polarization and migration during vascular patterning, as demonstrated by two recent publications. Additionally, the tool can be easily extended to correlate blood flow with other experimental observations at the cellular/molecular level. We release the source code of our tool under the Lesser General Public License.

Impact of coronary lumen reconstruction on the estimation of endothelial shear stress: in vivo comparison of three-dimensional quantitative coronary angiography and three-dimensional fusion combining optical coherent tomography

Aims

It is not clearly elucidated how the fusion technique improves the accuracy of endothelial shear stress (ESS) prediction, in comparison with that of three-dimensional (3D) quantitative coronary angiography (QCA) alone. We aimed to evaluate the difference in geometric measurements and haemodynamic estimation between 3D QCA and a 3D fusion model combining 3D QCA and optical coherence tomography (OCT).

Methods and results

Computational fluid dynamics was assessed in the coronary models of 20 patients. In the plane-per-plane comparison, the difference and agreement were assessed using a generalized linear mixed model and concordance correlation coefficient (CCC), respectively. The haemodynamic feature around minimum-lumen-diameter (MLD) was characterized using CCC values calculated for 1-mm segments. In comparison with the 3D fusion model, 3D QCA showed a shorter maximum lumen diameter (2.54 ± 0.67 mm vs. 2.78 ± 0.73 mm, P < 0.001) and smaller lumen area (4.81 ± 2.56 mm2 vs. 5.66 ± 2.97 mm2, P < 0.001), resulting in a significantly higher ESS (4.64 Pa vs. 3.78 Pa, p = 0.029). A more asymmetric lumen shape of the 3D fusion model was more likely associated with under- and over-estimation of the maximum and minimum lumen diameters in the 3D QCA model, respectively. The circumferential ESS variations, which were blunted by 3D QCA, showed the worst concordance near the MLD site (CCC = 0.370) on segment-based comparison.

Conclusion

The 3D fusion technique may be a more relevant tool for the haemodynamic simulation of coronary arteries through providing more accurate lumen characterization than 3D QCA.

Density and morphology of coronary artery calcium for the prediction of cardiovascular events: insights from the Framingham Heart Study

OBJECTIVES

To investigate the association between directly measured density and morphology of coronary artery calcium (CAC) with cardiovascular disease (CVD) events, using computed tomography (CT).

METHODS

Framingham Heart Study (FHS) participants with CAC in noncontrast cardiac CT (2002-2005) were included and followed until 2016. Participants with known CVD or uninterpretable CT scans were excluded. We assessed and correlated (Spearman) CAC density, CAC volume, and the number of calcified segments. Moreover, we counted morphology features including shape (cylindrical, spherical, semi-tubular, and spotty), location (bifurcation, facing pericardium, or facing myocardium), and boundary regularity. In multivariate Cox regression analyses, we associated all CAC characteristics with CVD events (CVD-death, myocardial infarction, stroke).

RESULTS

Among 1330 included participants (57.8 ± 11.7 years; 63% male), 73 (5.5%) experienced CVD events in a median follow-up of 9.1 (7.8-10.1) years. CAC density correlated strongly with CAC volume (Spearman's ρ = 0.75; p < 0.001) and lower number of calcified segments (ρ = - 0.86; p < 0.001; controlled for CAC volume). In the survival analysis, CAC density was associated with CVD events independent of Framingham risk score (HR (per SD) = 2.09; 95%CI, 1.30-3.34; p = 0.002) but not after adjustment for CAC volume (p = 0.648). The extent of spherically shaped and pericardially sided calcifications was associated with fewer CVD events accounting for the number of calcified segments (HR (per count) = 0.55; 95%CI, 0.31-0.98; p = 0.042 and HR = 0.66; 95%CI, 0.45-0.98; p = 0.039, respectively).

CONCLUSIONS

Directly measured CAC density does not predict CVD events due to the strong correlation with CAC volume. The spherical shape and pericardial-sided location of CAC are associated with fewer CVD events and may represent morphological features related to stable coronary plaques.

KEY POINTS

• Coronary calcium density may not be independently associated with cardiovascular events. • Coronary calcium density correlates strongly with calcium volume. • Spherical shape and pericardial-sided location of CAC are associated with fewer CVD events.

Straight Channel Microfluidic Chips for the Study of Platelet Adhesion under Flow

Microfluidic devices have become an integral method of cardiovascular research as they enable the study of shear force in biological processes, such as platelet function and thrombus formation. Furthermore, microfluidic chips offer the benefits of ex vivo testing of platelet adhesion using small amounts of blood or purified platelets. Microfluidic chips comprise flow channels of varying dimensions and geometries which are connected to a syringe pump. The pump draws blood or platelet suspensions through the channel(s) allowing for imaging of platelet adhesion and thrombus formation by fluorescence microscopy. The chips can be fabricated from various blood-compatible materials. The current protocol uses commercial plastic or in-house polydimethylsiloxane (PDMS) chips. Commercial biochips offer the advantage of standardization whereas in-house chips offer the advantage of decreased cost and flexibility in design. Microfluidic devices are a powerful tool to study the biorheology of platelets and other cell types with the potential of a diagnostic and monitoring tool for cardiovascular diseases.

Numerical investigation of hemodynamic performance of a stent in the main branch of a coronary artery bifurcation

Introduction: The effect of a bare-metal stent on the hemodynamics in the main branch of a coronary artery bifurcation with a particular type of stenosis was numerically investigated by the computational fluid dynamics (CFD). Methods: Three-dimensional idealized geometry of bifurcation was constructed in Catia modelling commercial software package. The Newtonian blood flow was assumed to be incompressible and laminar. CFD was utilized to calculate the shear stress and blood pressure distributions on the wall of main branch. In order to do the numerical simulations, a commercial software package named as COMSOL Multiphysics 5.3 was employed. Two types of stent , namely, one-part stent and two-part stent were applied to prevent the build-up and progression of the atherosclerotic plaques in the main branch. Results: A particular type of stenosis in the main branch was considered in this research. It occurred before and after the side branch. Moreover, it was found that the main branch with an inserted one-part stent had the smallest region with the wall shear stress (WSS) below 0.5 Pa which was the minimum WSS in the main branch without the stenosis. Conclusion: The use of a one-part stent in the main branch of a coronary artery bifurcation for the aforementioned type of stenosis is recommended.

Understanding Vulnerable Plaques: Current Status and Future Directions

The main cause of acute myocardial infarction is plaque rupture accompanied by superimposed coronary thrombosis. Thin-cap fibroatheromas (TCFAs) have been suggested as a type of lesion with a vulnerability that can cause plaque rupture. However, not only the existence of a TCFA but also the fine and complex interactions of other anatomical and hemodynamic factors, such as microcalcification in the fibrous cap, cholesterol crystal-induced inflammasome activation, the apoptosis of intraplaque macrophages, and endothelial shear stress distribution should precede a clinical event caused by plaque rupture. Recent studies are being conducted to identify these mechanisms through molecular imaging and hemodynamic assessment using computational fluid dynamics, which will result in better clinical results through selective coronary interventions.

A Fully Discrete Open Source Framework for the Simulation of Vascular Remodelling

In this paper we present a novel computational framework for the theoretical study of the interaction between haemodynamics and vessel biology, with particular applications to the study of vascular remodelling. We introduce the mathematical formulation, validate the numerical method against an analytical solution derived for a simplified case, and present a case study of tissue remodelling in response to flow.

Clinical usefulness of the angle between left main coronary artery and left anterior descending coronary artery for the evaluation of obstructive coronary artery disease

Background

A wider angle between the left anterior descending coronary artery (LAD) and left circumflex coronary artery (LCX) has been suggested to induce plaque formation in the arterial system via changes in shear stress. However, the relationship between the left main coronary artery (LM)-LAD angle and LAD stenosis has not been investigated. Therefore, we aimed to evaluate the associations between the LM-LAD and LAD-LCX angles and LAD stenosis.

Methods

Coronary computed tomography angiographies (CTAs) of 201 patients with suspected coronary artery disease were analyzed. Angle measurements were performed twice by experts using CTA images, and the values were averaged. The patients were divided into two groups, based on the presence of significant LAD stenosis (luminal diameter narrowing ≥50%) on CTA.

Results

The mean LM-LAD and LAD-LCX angles were 37.46° and 63.04°, respectively. The LM-LAD and LAD-LCX angles of the group with significant LAD stenosis were significantly wider than that of the group with nonsignificant LAD stenosis (P<0.001; P = 0.020, respectively). In a multivariate analysis, an LAD-LCX angle greater than 60° showed a trend toward predicting significant LAD stenosis (HR, 3.14; 95% CI: 0.96–1026; P = 0.058). In contrast, an LM-LAD angle greater than 40° was a significant predictor of significant LAD stenosis (HR, 12.2; 95% CI: 2.60–56.52; P = 0.001).

Conclusions

The results of the present study may suggest that a wider LM-LAD angle could be used to identify patients at higher risk for coronary artery disease (CAD). Thus, close follow–up and preventive management of other risk factors may be needed in such cases.

Numerical analysis of the impact of flow rate, heart rate, vessel geometry, and degree of stenosis on coronary hemodynamic indices

Background

The stenosis of the coronary arteries is usually caused by atherosclerosis. Hemodynamic significance of patient-specific coronary stenoses and the risk of its progression may be assessed by comparing the hemodynamic effects induced by flow disorders. The present study shows how stenosis degree and variable flow conditions in coronary artery affect the oscillating shear index, residence time index, pressure drop coefficient and fractional flow reserve. We assume that changes in the hemodynamic indices in relation to variable flow conditions and geometries evaluated using the computational fluid dynamics may be an additional factor for a non-invasive assessment of the coronary stenosis detected on multi-slice computed tomography.

Methods

The local-parametrised models of basic shapes of the vessels, such as straight section, bend, and bifurcation as well as the global-patient-specific models of left coronary artery were used for numerical simulation of flow in virtually reconstructed stenotic vessels. Calculations were carried out for vessels both without stenosis, and vessels of 10 to 95% stenosis. The flow rate varied within the range of 20 to 1000 ml/min, and heart rate frequency within the range of 30 to 210 cycles/min.

The computational fluid dynamics based on the finite elements method verified by the experimental measurements of the velocity profiles was used to analyse blood flow in the coronary arteries.

Results

The results confirm our preliminary assumptions. There is significant variation in the coronary hemodynamic indices value caused by disturbed flow through stenosis in relation to variable flow conditions and geometry of vessels.

Conclusion

Variations of selected hemodynamic indexes induced by change of flow rate, heart rate and vessel geometry, obtained during a non-invasive study, may assist in evaluating the risk of stenosis progression and in carrying out the assessment of the hemodynamic significance of coronary stenosis. However, for a more accurate assessment of the variability of indices and coronary stenosis severity both local (near the narrowing) and global (in side branches) studies should be used.

Biomechanical stress in coronary atherosclerosis: emerging insights from computational modelling

Coronary plaque rupture is the most common cause of vessel thrombosis and acute coronary syndrome. The accurate early detection of plaques prone to rupture may allow prospective, preventative treatment; however, current diagnostic methods remain inadequate to detect these lesions. Established imaging features indicating vulnerability do not confer adequate specificity for symptomatic rupture. Similarly, even though experimental and computational studies have underscored the importance of endothelial shear stress in progressive atherosclerosis, the ability of shear stress to predict plaque progression remains incremental. This review examines recent advances in image-based computational modelling that have elucidated possible mechanisms of plaque progression and rupture, and potentially novel features of plaques most prone to symptomatic rupture. With further study and clinical validation, these markers and techniques may improve the specificity of future culprit plaque detection.

Validation of Patient-Specific Cerebral Blood Flow Simulation Using Transcranial Doppler Measurements

We present a validation study comparing results from a patient-specific lattice-Boltzmann simulation to transcranial Doppler (TCD) velocity measurements in four different planes of the middle cerebral artery (MCA). As part of the study, we compared simulations using a Newtonian and a Carreau-Yasuda rheology model. We also investigated the viability of using downscaled velocities to reduce the required resolution. Simulations with unscaled velocities predict the maximum flow velocity with an error of less than 9%, independent of the rheology model chosen. The accuracy of the simulation predictions worsens considerably when simulations are run at reduced velocity, as is for example the case when inflow velocities from healthy individuals are used on a vascular model of a stroke patient. Our results demonstrate the importance of using directly measured and patient-specific inflow velocities when simulating blood flow in MCAs. We conclude that localized TCD measurements together with predictive simulations can be used to obtain flow estimates with high fidelity over a larger region, and reduce the need for more invasive flow measurement procedures.

Dependence of leukocyte capture on instantaneous pulsatile flow

Atherosclerosis, an artery disease, is currently the leading cause of death in the United States in both men and women. The first step in the development of atherosclerosis involves leukocyte adhesion to the arterial endothelium. It is broadly accepted that blood flow, more specifically wall shear stress (WSS), plays an important role in leukocyte capture and subsequent development of an atherosclerotic plaque. What is less known is how instantaneous WSS, which can vary by up to 5 Pa over one cardiac cycle, influences leukocyte capture. In this paper we use direct numerical simulations (DNS), performed using an in-house code, to illustrate that leukocyte capture is different whether as a function of instantaneous or time-averaged blood flow. Specifically, a stenotic plaque is modeled using a computational fluid dynamics (CFD) solver through fully three-dimensional Navier-Stokes equations and the immersed boundary method. Pulsatile triphasic inflow is used to simulate the cardiac cycle. The CFD is coupled with an agent-based leukocyte capture model to assess the impact of instantaneous hemodynamics on stenosis growth. The computed wall shear stress agrees well with the results obtained with a commercial software, as well as with theoretical results in the healthy region of the artery. The analysis emphasizes the importance of the instantaneous flow conditions in evaluating the leukocyte rate of capture. That is, the capture rate computed from mean flow field is generally underpredicted compared to the actual rate of capture. Thus, in order to obtain a reliable estimate, the flow unsteadiness during a cardiac cycle should be taken into account.

Evolving understanding of the heterogeneous natural history of individual coronary artery plaques and the role of local endothelial shear stress

PURPOSE OF REVIEW

Anatomic and morphologic features of high-risk coronary plaque have been identified by novel imaging modalities, but it has been less clear which ostensibly high-risk plaques will actually destabilize and cause a new cardiac event. Different plaques with different morphologies coexist within the same artery, but the impact of this heterogeneity on the natural history of coronary artery disease has not been extensively investigated.

RECENT FINDINGS

Coronary plaques exhibit remarkable heterogeneity of local morphological and blood-flow patterns, including endothelial shear stress (ESS), along their longitudinal axis, with important implications for the heterogeneous natural history of coronary disease. The natural history of individual plaques is considerably divergent, with most plaques, even ostensibly high-risk plaques, becoming quiescent and only a minority progressing to destabilize and precipitate a new clinical event. Local areas of proinflammatory low ESS appear to be an important condition for plaque destabilization.

SUMMARY

Characterization of an individual atherosclerotic plaque based on a snapshot of morphological features at a specific location, such as the minimal lumen diameter, may not be sufficiently comprehensive to accurately reflect the risk associated with that plaque. A detailed assessment of both anatomical and functional pathobiologic characteristics in the longitudinal plaque dimension may enhance our understanding of atherosclerosis progression and improve the management of individual patients with coronary artery disease.

Local Flow Patterns After Implantation of Bioresorbable Vascular Scaffold in Coronary Bifurcations - Novel Findings by Computational Fluid Dynamics

BACKGROUND

Development of methods for accurate reconstruction of bioresorbable scaffolds (BRS) and assessing local hemodynamics is crucial for investigation of vascular healing after BRS implantation.

METHODS AND RESULTS

Patients with BRS that crossed over in a coronary bifurcation were included for analysis. Reconstructions of the coronary lumen and BRS were performed by fusion of optical coherence tomography and coronary angiography generating a tree model (TM) and a hybrid model with BRS (TM-BRS). A virtual BRS model with thinner struts was created and all 3 models were analyzed using computational fluid dynamics to derive: (1) time-average shear stress (TASS), (2) TASS gradient (TASSG), which represents SS heterogeneity, and (3) fractional flow reserve (FFR). Reconstruction of the BRS was successful in all 10 patients. TASS and TASSG were both higher by TM-BRS than by TM in main vessels (difference 0.27±4.30 Pa and 10.18±27.28 Pa/mm, P<0.001), with a remarkable difference at side branch ostia (difference 13.51±17.40 Pa and 81.65±105.19 Pa/mm, P<0.001). With thinner struts, TASS was lower on the strut surface but higher at the inter-strut zones, whereas TASSG was lower in both regions (P<0.001 for all). Computational FFR was lower by TM-BRS than by TM for both main vessels and side branches (P<0.001).

CONCLUSIONS

Neglecting BRS reconstruction leads to significantly lower SS and SS heterogeneity, which is most pronounced at side branch ostia. Thinner struts can marginally reduce SS heterogeneity.