Low Endothelial Shear Stress Predicts Evolution to High-Risk Coronary Plaque Phenotype in the Future

Vulnerable or High-Risk Plaque: A JACC: Cardiovascular Imaging Position Statement

The concept of high-risk plaque emerged from pathologic and epidemiologic studies 3 decades ago that demonstrated plaque rupture with thrombosis as the predominant mechanism of acute coronary syndrome and sudden cardiac death. Thin-cap fibroatheroma, a plaque with a large lipidic core covered by a thin fibrous cap, is the prototype of the rupture-prone plaque and has been traditionally defined as "vulnerable plaque." Although knowledge on the pathophysiology of plaque instability continues to grow, the risk profile of our patients has shifted and the character of atherosclerotic disease has evolved, partly because of widespread use of lipid-lowering therapies and other preventive measures. In vivo intracoronary imaging studies indicate that superficial erosion causes up to 40% of acute coronary syndromes. This changing landscape calls for broader perspective, expanding the concept of high-risk plaque to the precursors of all major substrates of coronary thrombosis beyond plaque rupture. Other factors to take into consideration include dynamic changes in plaque composition, the importance of plaque burden, inflammatory activation (both local and systemic), healing mechanisms, regional hemodynamic pattern, properties of the fluid phase of blood, and the amount of myocardium at risk subtended by a lesion. Rather than the traditional focus limited to the thin-cap fibroatheroma, the authors advocate a more comprehensive approach that considers both morphologic features and biological activity of plaques and blood. This position paper highlights the challenges to the usual concept of high-risk plaque, proposes a broader definition, and analyzes its key morphologic features, the technological progress of plaque imaging (particularly using intracoronary imaging techniques), advances in pharmacologic therapies for plaque regression and stabilization, and the feasibility and efficacy of focal interventional treatments including preemptive plaque sealing.

Endothelial Shear Stress Metrics Associate With Proinflammatory Pathways at the Culprit Site of Coronary Erosion

Low endothelial shear stress (ESS) and associated adverse biomechanical features stimulate inflammation, contribute to atherogenesis, and predispose to coronary plaque disruption. The mechanistic links between adverse flow-related hemodynamics and inflammatory mediators implicated in plaque erosion, however, remain little explored. We investigated the relationship of high-risk ESS metrics to culprit lesion proinflammatory/proatherogenic cells and cytokines/chemokines implicated in coronary plaque erosion in patients with acute coronary syndromes. In eroded plaques, low ESS, high ESS gradient, and steepness of plaque topographical slope associated with increased numbers of local T cells and subsets (CD4+, CD8+, natural killer T cells) as well as inflammatory mediators (interleukin [IL]-6, macrophage inflammatory protein-1β, IL-1β, IL-2).

A Review Paper on Optical Coherence Tomography Evaluation of Coronary Calcification Pattern: Is It Relevant Today?

The process of coronary calcification represents one of the numerous pathophysiological mechanisms involved in the atherosclerosis continuum. Optical coherence tomography (OCT) represents an ideal imaging modality to assess plaque components, especially calcium. Different calcification patterns have been contemporarily described in both early stages and advanced atherosclerosis. Microcalcifications and spotty calcifications correlate positively with macrophage burden and inflammatory markers and are more frequently found in the superficial layers of ruptured plaques in acute coronary syndrome patients. More compact, extensive calcification may reflect a later stage of the disease and was traditionally associated with plaque stability. Nevertheless, a small number of culprit coronary lesions demonstrates the presence of dense calcified plaques. The purpose of the current paper is to review the most recent OCT data on coronary calcification and the interrelation between calcification pattern and plaque vulnerability. How different calcified plaques influence treatment strategies and associated prognostic implications is of great interest.

Angiography and optical coherence tomography derived shear stress: are they equivalent in my opinion?

Advances in image reconstruction using either single or multimodality imaging data provide increasingly accurate three-dimensional (3D) patient's arterial models for shear stress evaluation using computational fluid dynamics (CFD). We aim to evaluate the impacts on endothelial shear stress (ESS) derived from a simple image reconstruction using 3D-quantitative coronary angiography (3D-QCA) versus a multimodality reconstruction method using optical coherence tomography (OCT) in patients' vessels treated with bioresorbable scaffolds. Seven vessels at baseline and five-year follow-up of seven patients from a previous CFD investigation were retrospectively selected for a head-to-head comparison of angiography-derived versus OCT-derived ESS. 3D-QCA significantly underestimated the minimum stent area [MSA] (-2.38mm2) and the stent length (-1.46 mm) compared to OCT-fusion method reconstructions. After carefully co-registering the region of interest for all cases with a sophisticated statistical method, the difference in MSA measurements as well as the inability of angiography to visualise the strut footprint in the lumen surface have translated to higher angiography-derived ESS than OCT-derived ESS (1.76 Pa or 1.52 times for the overlapping segment). The difference in ESS widened with a more restricted region of interest (1.97 Pa or 1.63 times within the scaffold segment). Angiography and OCT offer two distinctive methods of ESS calculation. Angiography-derived ESS tends to overestimate the ESS compared to OCT-derived ESS. Further investigations into ESS analysis resolution play a vital role in adopting OCT-derived ESS.

Restoration of normal blood flow in atherosclerotic arteries promotes plaque stabilization

Blood flow is a key regulator of atherosclerosis. Disturbed blood flow promotes atherosclerotic plaque development, whereas normal blood flow protects against plaque development. We hypothesized that normal blood flow is also therapeutic, if it were able to be restored within atherosclerotic arteries. Apolipoprotein E-deficient (ApoE^-/-) mice were initially instrumented with a blood flow-modifying cuff to induce plaque development and then five weeks later the cuff was removed to allow restoration of normal blood flow. Plaques in decuffed mice exhibited compositional changes that indicated increased stability compared to plaques in mice with the cuff maintained. The therapeutic benefit of decuffing was comparable to atorvastatin and the combination had an additive effect. In addition, decuffing allowed restoration of lumen area, blood velocity, and wall shear stress to near baseline values, indicating restoration of normal blood flow. Our findings demonstrate that the mechanical effects of normal blood flow on atherosclerotic plaques promote stabilization.

Endothelial shear stress computed from coronary computed tomography angiography: A direct comparison to intravascular ultrasound

INTRODUCTION

Intravascular ultrasound (IVUS) studies have shown that biomechanical variables, particularly endothelial shear stress (ESS), add synergistic prognostic insight when combined with anatomic high-risk plaque features. Non-invasive risk assessment of coronary plaques with coronary computed tomography angiography (CCTA) would be helpful to enable broad population risk-screening.

AIM

To compare the accuracy of ESS computation of local ESS metrics by CCTA vs IVUS imaging.

METHODS

We analyzed 59 patients from a registry of patients who underwent both IVUS and CCTA for suspected CAD. CCTA images were acquired using either a 64- or 256-slice scanner. Lumen, vessel, and plaque areas were segmented from both IVUS and CCTA (59 arteries, 686 3-mm segments). Images were co-registered and used to generate a 3-D arterial reconstruction, and local ESS distribution was assessed by computational fluid dynamics (CFD) and reported in consecutive 3-mm segments.

RESULTS

Anatomical plaque characteristics (vessel, lumen, plaque area and minimal luminal area [MLA] per artery) were correlated when measured with IVUS and CCTA: 12.7 ​± ​4.3 vs 10.7 ​± ​4.5 ​mm2, r ​= ​0.63; 6.8 ​± ​2.7 vs 5.6 ​± ​2.7 ​mm2, r ​= ​0.43; 5.9 ​± ​2.9 vs 5.1 ​± ​3.2 ​mm2, r ​= ​0.52; 4.5 ​± ​1.3 vs 4.1 ​± ​1.5 ​mm2, r ​= ​0.67 respectively. ESS metrics of local minimal, maximal, and average ESS were also moderately correlated when measured with IVUS and CCTA (2.0 ​± ​1.4 vs 2.5 ​± ​2.6 ​Pa, r ​= ​0.28; 3.3 ​± ​1.6 vs 4.2 ​± ​3.6 ​Pa, r ​= ​0.42; 2.6 ​± ​1.5 vs 3.3 ​± ​3.0 ​Pa, r ​= ​0.35, respectively). CCTA-based computation accurately identified the spatial localization of local ESS heterogeneity compared to IVUS, with Bland-Altman analyses indicating that the absolute ESS differences between the two CCTA methods were pathobiologically minor.

CONCLUSION

Local ESS evaluation by CCTA is possible and similar to IVUS; and is useful for identifying local flow patterns that are relevant to plaque development, progression, and destabilization.

Wall shear stress and its role in atherosclerosis

Atherosclerosis (AS) is the major form of cardiovascular disease and the leading cause of morbidity and mortality in countries around the world. Atherosclerosis combines the interactions of systemic risk factors, haemodynamic factors, and biological factors, in which biomechanical and biochemical cues strongly regulate the process of atherosclerosis. The development of atherosclerosis is directly related to hemodynamic disorders and is the most important parameter in the biomechanics of atherosclerosis. The complex blood flow in arteries forms rich WSS vectorial features, including the newly proposed WSS topological skeleton to identify and classify the WSS fixed points and manifolds in complex vascular geometries. The onset of plaque usually occurs in the low WSS area, and the plaque development alters the local WSS topography. low WSS promotes atherosclerosis, while high WSS prevents atherosclerosis. Upon further progression of plaques, high WSS is associated with the formation of vulnerable plaque phenotype. Different types of shear stress can lead to focal differences in plaque composition and to spatial variations in the susceptibility to plaque rupture, atherosclerosis progression and thrombus formation. WSS can potentially gain insight into the initial lesions of AS and the vulnerable phenotype that gradually develops over time. The characteristics of WSS are studied through computational fluid dynamics (CFD) modeling. With the continuous improvement of computer performance-cost ratio, WSS as one of the effective parameters for early diagnosis of atherosclerosis has become a reality and will be worth actively promoting in clinical practice. The research on the pathogenesis of atherosclerosis based on WSS is gradually an academic consensus. This article will comprehensively review the systemic risk factors, hemodynamics and biological factors involved in the formation of atherosclerosis, and combine the application of CFD in hemodynamics, focusing on the mechanism of WSS and the complex interactions between WSS and plaque biological factors. It is expected to lay a foundation for revealing the pathophysiological mechanisms related to abnormal WSS in the progression and transformation of human atherosclerotic plaques.

Antithrombotic Treatment in Coronary Artery Disease

Coronary artery disease exhibits growing mortality and morbidity worldwide despite the advances in pharmacotherapy and coronary intervention. Coronary artery disease is classified in the acute coronary syndromes and chronic coronary syndromes according to the most recent guidelines of the European Society of Cardiology. Antithrombotic treatment is the cornerstone of therapy in coronary artery disease due to the involvement of atherothrombosis in the pathophysiology of the disease. Administration of antiplatelet agents, anticoagulants and fibrinolytics reduce ischemic risk, which is amplified early post-acute coronary syndromes or post percutaneous coronary intervention; though, antithrombotic treatment increases the risk for bleeding. The balance between ischemic and bleeding risk is difficult to achieve and is affected by patient characteristics, procedural parameters, concomitant medications and pharmacologic characteristics of the antithrombotic agents. Several pharmacological strategies have been evaluated in patients with coronary artery disease, such as the effectiveness and safety of antithrombotic agents, optimal dual antiplatelet treatment schemes and duration, aspirin de-escalation strategies of dual antiplatelet regimens, dual inhibition pathway strategies as well as triple antithrombotic therapy. Future studies are needed in order to investigate the gaps in our knowledge, including special populations.

Coronary artery plaque rupture and erosion: Role of wall shear stress profiling and biological patterns in acute coronary syndromes

AIMS

Wall shear stress (WSS) is involved in coronary artery plaque pathological mechanisms and modulation of gene expression. This study aims to provide a comprehensive haemodynamic and biological description of unstable (intact-fibrous-cap, IFC, and ruptured-fibrous-cap, RFC) and stable (chronic coronary syndrome, CCS) plaques and investigate any correlation between WSS and molecular pathways.

METHODS AND RESULTS

We enrolled 24 CCS and 25 Non-ST Elevation Myocardial Infarction-ACS patients with IFC (n = 11) and RFC (n = 14) culprit lesions according to optical coherence tomography analysis. A real-time PCR primer array was performed on peripheral blood mononuclear cells for 17 different molecules whose expression is linked to WSS. Computational fluid dynamics simulations were performed in high-fidelity 3D-coronary artery anatomical models for three patients per group. A total of nine genes were significantly overexpressed in the unstable patients as compared to CCS patients, with no differences between IFC and RFC groups (GPX1, MMP1, MMP9, NOS3, PLA2G7, PI16, SOD1, TIMP1, and TFRC) while four displayed different levels between IFC and RFC groups (TNFα, ADAMTS13, EDN1, and LGALS8). A significantly higher WSS was observed in the RFC group (p < 0.001) compared to the two other groups. A significant correlation was observed between TNFα (p < 0.001), EDN1 (p = 0.036), and MMP9 (p = 0.005) and WSS values in the RFC group.

CONCLUSIONS

Our data demonstrate that IFC and RFC plaques are subject to different WSS conditions and gene expressions, suggesting that WSS profiling may play an essential role in the plaque instability characterization with relevant diagnostic and therapeutic implications in the era of precision medicine.

Wall shear stress-related plaque growth of lipid-rich plaques in human coronary arteries: an near-infrared spectroscopy and optical coherence tomography study

AIMS

Low wall shear stress (WSS) is acknowledged to play a role in plaque development through its influence on local endothelial function. Also, lipid-rich plaques (LRPs) are associated with endothelial dysfunction. However, little is known about the interplay between WSS and the presence of lipids with respect to plaque progression. Therefore, we aimed to study the differences in WSS-related plaque progression between LRPs, non-LRPs, or plaque-free regions in human coronary arteries.

METHODS AND RESULTS

In the present single-centre, prospective study, 40 patients who presented with an acute coronary syndrome successfully underwent near-infrared spectroscopy intravascular ultrasound (NIRS-IVUS) and optical coherence tomography (OCT) of at least one non-culprit vessel at baseline and completed a 1-year follow-up. WSS was computed applying computational fluid dynamics to a three-dimensional reconstruction of the coronary artery based on the fusion of the IVUS-segmented lumen with a CT-derived centreline, using invasive flow measurements as boundary conditions. For data analysis, each artery was divided into 1.5 mm/45° sectors. Plaque growth based on IVUS-derived percentage atheroma volume change was compared between LRPs, non-LRPs, and plaque-free wall segments, as assessed by both OCT and NIRS. Both NIRS- and OCT-detected lipid-rich sectors showed a significantly higher plaque progression than non-LRPs or plaque-free regions. Exposure to low WSS was associated with a higher plaque progression than exposure to mid or high WSS, even in the regions classified as a plaque-free wall. Furthermore, low WSS and the presence of lipids had a synergistic effect on plaque growth, resulting in the highest plaque progression in lipid-rich regions exposed to low shear stress.

CONCLUSION

This study demonstrates that NIRS- and OCT-detected lipid-rich regions exposed to low WSS are subject to enhanced plaque growth over a 1-year follow-up. The presence of lipids and low WSS proves to have a synergistic effect on plaque growth.

Percutaneous coronary intervention of bifurcation lesions

Bifurcation coronary artery disease is common as the development of atherosclerosis is facilitated by altered endothelial shear stress. Multiple anatomical and physiological factors need to be considered when treating bifurcation lesions. To achieve optimal results, various stenting techniques have been developed, each with benefits and limitations. In this state-of-the-art review we describe technically important characteristics of bifurcation lesions and summarise the evidence supporting contemporary bifurcation techniques.

Non-Newtonian Endothelial Shear Stress Simulation: Does It Matter?

Patient-specific coronary endothelial shear stress (ESS) calculations using Newtonian and non-Newtonian rheological models were performed to assess whether the common assumption of Newtonian blood behavior offers similar results to a more realistic but computationally expensive non-Newtonian model. 16 coronary arteries (from 16 patients) were reconstructed from optical coherence tomographic (OCT) imaging. Pulsatile CFD simulations using Newtonian and the Quemada non-Newtonian model were performed. Endothelial shear stress (ESS) and other indices were compared. Exploratory indices including local blood viscosity (LBV) were calculated from non-Newtonian simulation data. Compared to the Newtonian results, the non-Newtonian model estimates significantly higher time-averaged ESS (1.69 (IQR 1.36)Pa versus 1.28 (1.16)Pa, p < 0.001) and ESS gradient (0.90 (1.20)Pa/mm versus 0.74 (1.03)Pa/mm, p < 0.001) throughout the cardiac cycle, under-estimating the low ESS (<1Pa) area (37.20 ± 13.57% versus 50.43 ± 14.16%, 95% CI 11.28-15.18, p < 0.001). Similar results were also found in the idealized artery simulations with non-Newtonian median ESS being higher than the Newtonian median ESS (healthy segments: 0.8238Pa versus 0.6618Pa, p < 0.001 proximal; 0.8179Pa versus 0.6610Pa, p < 0.001 distal; stenotic segments: 0.8196Pa versus 0.6611Pa, p < 0.001 proximal; 0.2546Pa versus 0.2245Pa, p < 0.001 distal) On average, the non-Newtonian model has a LBV of 1.45 times above the Newtonian model with an average peak LBV of 40-fold. Non-Newtonian blood model estimates higher quantitative ESS values than the Newtonian model. Incorporation of non-Newtonian blood behavior may improve the accuracy of ESS measurements. The non-Newtonian model also allows calculation of exploratory viscosity-based hemodynamic indices, such as local blood viscosity, which may offer additional information to detect underlying atherosclerosis.

A Non-Canonical Link between Non-Coding RNAs and Cardiovascular Diseases

Cardiovascular diseases (CVDs) are among the top leading causes of mortality worldwide. Besides canonical environmental and genetic changes reported so far for CVDs, non-coding RNAs (ncRNAs) have emerged as key regulators of genetic and epigenetic mechanisms involved in CVD progression. High-throughput and sequencing data revealed that almost 80% of the total genome not only encodes for canonical ncRNAs, such as micro and long ncRNAs (miRNAs and lncRNAs), but also generates novel non-canonical sub-classes of ncRNAs, such as isomiRs and miRNA- and lncRNA-like RNAs. Moreover, recent studies reveal that canonical ncRNA sequences can influence the onset and evolution of CVD through novel “non-canonical” mechanisms. However, a debate exists over the real existence of these non-canonical ncRNAs and their concrete biochemical functions, with most of the dark genome being considered as “junk RNA”. In this review, we report on the ncRNAs with a scientifically validated canonical and non-canonical biogenesis. Moreover, we report on canonical ncRNAs that play a role in CVD through non-canonical mechanisms of action.

Consistency in Geometry Among Coronary Atherosclerotic Plaques Extracted From Computed Tomography Angiography

Background: The three-dimensional (3D) geometry of coronary atherosclerotic plaques is associated with plaque growth and the occurrence of coronary artery disease. However, there is a lack of studies on the 3D geometric properties of coronary plaques. We aim to investigate if coronary plaques of different sizes are consistent in geometric properties.

Methods: Nineteen cases with symptomatic stenosis caused by atherosclerotic plaques in the left coronary artery were included. Based on attenuation values on computed tomography angiography images, coronary atherosclerotic plaques and calcifications were identified, 3D reconstructed, and manually revised. Multidimensional geometric parameters were measured on the 3D models of plaques and calcifications. Linear and non-linear (i.e., power function) fittings were used to investigate the relationship between multidimensional geometric parameters (length, surface area, volume, etc.). Pearson correlation coefficient (r), R-squared, and p-values were used to evaluate the significance of the relationship. The analysis was performed based on cases and plaques, respectively. Significant linear relationship was defined as R-squared > 0.25 and p < 0.05.

Results: In total, 49 atherosclerotic plaques and 56 calcifications were extracted. In the case-based analysis, significant linear relationships were found between number of plaques and number of calcifications (r = 0.650, p = 0.003) as well as total volume of plaques (r = 0.538, p = 0.018), between number of calcifications and total volume of plaques (r = 0.703, p = 0.001) as well as total volume of calcification (r = 0.646, p = 0.003), and between the total volumes of plaques and calcifications (r = 0.872, p < 0.001). In plaque-based analysis, the power function showed higher R-squared values than the linear function in fitting the relationships of multidimensional geometric parameters. Two presumptions of plaque geometry in different growth stages were proposed with simplified geometric models developed. In the proposed models, the exponents in the power functions of geometric parameters were in accordance with the fitted values.

Conclusion: In patients with coronary artery disease, coronary plaques and calcifications are positively related in number and volume. Different coronary plaques are consistent in the relationship between geometry parameters in different dimensions.

Optical Coherence Tomography of Coronary Plaque Progression and Destabilization: JACC Focus Seminar Part 3/3

The development of optical coherence tomography (OCT) has revolutionized our understanding of coronary artery disease. In vivo OCT research has paralleled with advances in computational fluid dynamics, providing additional insights in the various hemodynamic factors influencing plaque growth and stability. Recent OCT studies introduced a new concept of plaque healing in relation to clinical presentation. In addition to known mechanisms of acute coronary syndromes such as plaque rupture and plaque erosion, a new classification of calcified plaque was recently reported. This review will focus on important new insights that OCT has provided in recent years into coronary plaque development, progression, and destabilization, with a focus on the role of local hemodynamics and endothelial shear stress, the layered plaque (signature of previous subclinical plaque destabilization and healing), and the calcified culprit plaque.

Characteristic findings of microvascular dysfunction on coronary computed tomography angiography in patients with intermediate coronary stenosis

OBJECTIVES

We aimed to assess the prevalence of coexistence of coronary microvascular dysfunction (CMD) in patients with intermediate epicardial stenosis and to explore coronary computed tomography angiography (CCTA)-derived lesion-, vessel-, and cardiac fat-related characteristic findings associated with CMD.

METHODS

A retrospective cross-sectional single-center study included a total of 177 patients with intermediate stenosis in the left anterior descending artery (LAD) who underwent CCTA and invasive physiological measurements. The 320-slice CCTA analysis included qualitative and quantitative assessments of plaque, vessel, epicardial fat volume (ECFV) and epicardial fat attenuation (ECFA), and pericoronary fat attenuation (FAI). CMD was defined by the index of microcirculatory resistance (IMR) ≥ 25.

RESULTS

In the entire cohort, median fractional flow reserve (FFR) and median IMR values were 0.77 (0.69-0.84) and 19.0 (13.7-27.7), respectively. The prevalence of CMD was 32.8 % (58/177) in the total cohort. The coexistence of CMD and functionally significant stenosis was 34.3 % (37/108), whereas CMD in nonsignificant intermediate stenosis was 30.4 % (21/69). CMD was significantly associated with greater lumen volume (p = 0.031), greater fibrofatty and necrotic component (FFNC) volume (p = 0.030), and greater ECFV (p = 0.030), but not with FAI (p = 0.832) and ECFA (p = 0.445). On multivariable logistic regression analysis, vessel volume, vessel lumen volume, lesion remodeling index, ECFV, and lesion FFNC volume were independent predictors of CMD.

CONCLUSIONS

The prevalence of CMD was about one-third in patients with intermediate stenosis in LAD regardless of the presence or absence of functional stenosis significance. The integrated CCTA assessment may help in the identification of CMD.

KEY POINTS

• The coexistence of coronary microvascular dysfunction (CMD) and functionally significant stenosis was 34.3 %, whereas CMD in nonsignificant intermediate stenosis was 30.4 %. • Coronary computed tomography angiography (CCTA)-derived CMD characteristics were vessel volume, vessel lumen volume, remodeling index, epicardial fat volume, and fibrofatty necrotic core volume. • Integrated CCTA assessment may help identify the coexistence of CMD and epicardial stenosis.

Exploring the causal inference of shear stress associated DNA methylation in carotid plaque on cardiovascular risk

BACKGROUND AND AIMS

Atherosclerosis is a lipid-driven inflammatory disease presumably initiated by endothelial activation. Low vascular shear stress is known for its ability to activate endothelial cells. Differential DNA methylation (DNAm) is a relatively unexplored player in atherosclerotic disease development and endothelial dysfunction. Previous studies showed that the expression of 11 genes was associated with differential DNAm due to low shear stress in murine endothelial cells. We hypothesized a causal relationship between DNAm of shear stress associated genes in human carotid plaque and increased risk of cardiovascular disease.

METHODS

Using Mendelian randomisation (MR) analysis, we explored the potential causal role of DNAm of shear stress associated genes on cardiovascular disease risk. We used data from the Athero-Expression Biobank Study for the discovery of methylation quantitative trait loci (mQTLs) in 442 advanced carotid plaques. Next, we performed MR analysis using these mQTLs and publicly available GWAS summary statistics of coronary artery disease (CAD) and ischemic stroke (IS).

RESULTS

We discovered 9 mQTLs in plaque in the promoters of shear stress associated genes. We found no significant effect of shear stress gene promoter methylation and increased risk of CAD and IS.

CONCLUSIONS

Differential methylation of shear stress associated genes in advanced atherosclerotic plaques in unlikely to increase cardiovascular risk in human.

Spatial relationships among hemodynamic, anatomic, and biochemical plaque characteristics in patients with coronary artery disease

BACKGROUND AND AIMS

We aimed to characterize the spatial proximity of plaque destabilizing features local endothelial shear stress (ESS), minimal luminal area (MLA), plaque burden (PB), and near-infrared spectroscopy (NIRS) lipid signal in high- vs. low-risk plaques.

METHODS

Coronary arteries imaged with angiography and NIRS-intravascular ultrasound (IVUS) underwent 3D reconstruction and computational fluid dynamics calculations of local ESS. ESS, PB, MLA, and lipid core burden index (LCBI), for each 3-mm arterial segment were obtained in arteries with large lipid-rich plaque (LRP) vs. arteries with smaller LRP. The locations of the MLA, minimum ESS (minESS), maximum ESS (maxESS), maximum PB (maxPB), and maximum LCBI in a 4-mm segment (maxLCBI4mm) were determined along the length of each plaque.

RESULTS

The spatial distributions of minESS, maxESS, maxPB, and maxLCBI4mm, in reference to the MLA, were significantly heterogeneous within and between each variable. The location of maxLCBI4mm was spatially discordant from sites of the MLA (p<0.0001), minESS (p = 0.003), and maxESS (p = 0.003) in arteries with large LRP (maxLCBI4mm ≥ 400) and non-large LRP. Large LRP arteries had higher maxESS (9.31 ± 4.78 vs. 6.32 ± 5.54 Pa; p = 0.023), lower minESS (0.41 ± 0.16 vs. 0.61 ± 0.26 Pa; p = 0.007), smaller MLA (3.54 ± 1.22 vs. 5.14 ± 2.65 mm2; p = 0.002), and larger maxPB (70.64 ± 9.95% vs. 56.70 ± 13.34%, p<0.001) compared with non-large LRP arteries.

CONCLUSIONS

There is significant spatial heterogeneity of destabilizing plaque features along the course of both large and non-large LRPs. Large LRPs exhibit significantly more abnormal destabilizing plaque features than non-large LRPs. Prospective, longitudinal studies are required to determine which patterns of heterogeneous destabilizing features act synergistically to cause plaque destabilization.

Contribution of atherosclerotic plaque location and severity to the near-wall hemodynamics of the carotid bifurcation: an experimental study and FSI modeling

Atherosclerosis is initiated by endothelial injury that is related to abnormal values of hemodynamic parameters such as wall shear stress (WSS), oscillatory shear index (OSI) and stress phase angle (SPA), which are more common in arterial bifurcations due to the complex structure. An experimental model of human carotid bifurcation with accurate geometrical and mechanical features was set up, and using realistic pulsatile flow rates, the inlet and outlet pressure pulses were measured for normal and stenosed models with 40% and 80% severities at common carotid (CCA), internal carotid (ICA) and external carotid (ECA) arteries. Based on the obtained experimental data, fluid-structure models were developed to obtain WSS, OSI, and SPA and evaluate pathological consequences at different locations. Mild severity had minor impact, however, inducing severe 80% stenosis in each branch led to considerable localized changes of hemodynamic parameters both in the stenosis site and other locations. This included sharp increases in WSS values accompanied by very low values close to zero before and after the peaks. Severe stenosis not only caused significant changes in the local artery, but also in other branches. OSI and SPA were less sensitive to stenosis, although high peaks were observed on bifurcation site for the stenosis at ECA. The interconnection of arteries at carotid bifurcation results in altered pressure/flow patterns in all branches when a stenosis is applied in any site. Such effect confirms pathological findings that atherosclerotic plaques are observed simultaneously in different carotid branches, although with different degrees of plaque growth and severity.

High Wall Shear Stress Is Related to Atherosclerotic Plaque Rupture in the Aortic Arch of Patients with Cardiovascular Disease: A Study with Computational Fluid Dynamics Model and Non-Obstructive General Angioscopy

Aims: Wall shear stress (WSS) has been considered a major determinant of aortic atherosclerosis. Recently, non-obstructive general angioscopy (NOGA) was developed to visualize various atherosclerotic pathologies, including in vivo ruptured plaque (RP) in the aorta. However, the relationship between aortic RP and WSS distribution within the aortic wall is unclear. This study aimed to investigate the relationship between aortic NOGA-derived RP and the stereographic distribution of WSS by computational fluid dynamics (CFD) modeling using three-dimensional computed tomography (3D-CT) angiography.

Methods: We investigated 45 consecutive patients who underwent 3D-CT before coronary angiography and NOGA during coronary angiography. WSS in the aortic arch was measured by CFD analysis based on the finite element method using uniform inlet and outlet flow conditions. Aortic RP was detected by NOGA.

Results: Patients with a distinct RP showed a significantly higher maximum WSS value in the aortic arch than those without aortic RP (56.2±30.6 Pa vs 36.2±19.8 Pa, p =0.017), no significant difference was noted in the mean WSS between those with and without aortic RP. In a multivariate logistic regression analysis, the presence of a maximum WSS value more than a specific value was a significant predictor of aortic RP (odds ratio 7.21, 95% confidence interval 1.78-37.1, p =0.005).

Conclusions: Aortic RP detected by NOGA was strongly associated with a higher maximum WSS in the aortic arch derived by CFD using 3D-CT. The maximum WSS value may have an important role in the underlying mechanism of not only aortic atherosclerosis, but also aortic RP.

Relationship between arterial remodelling and serial changes in coronary atherosclerosis by intravascular ultrasound: an analysis of the IBIS-4 study

AIMS

Arterial remodelling is an important determinant of coronary atherosclerosis. Assessment of the remodelling index, comparing a lesion to a local reference site, is a suboptimal correlate of serial vascular changes. We assessed a novel approach which, unlike the local-reference approach, uses the entire artery's global remodelling as reference.

METHODS AND RESULTS

Serial (baseline and 13 months) intravascular ultrasound was performed in 146 non-infarct-related arteries of 82 patients treated with high-intensity statin. Arteries were divided into 3-mm segments (n = 1479), and focal remodelling was characterized in individual segments at both timepoints applying the global arterial reference approach. First, we compared preceding vascular changes in relation to follow-up remodelling. Second, we examined whether baseline remodelling predicts subsequent plaque progression/regression. At follow-up, segments with constrictive vs. compensatory or expansive remodelling had greater preceding reduction of vessel area (-0.67 vs. -0.38 vs. -0.002 mm2; P < 0.001) and lumen area (-0.82 vs. -0.09 vs. 0.40 mm2; P < 0.001). Overall, we found significant regression in percent atheroma volume (PAV) [-0.80% (-1.41 to -0.19)]. Segments with constrictive remodelling at baseline had greater subsequent PAV regression vs. modest regression in the compensatory, and PAV progression in the expansive remodelling group (-6.14% vs. -0.71% vs. 2.26%; P < 0.001). Lesion-level analyses (n = 118) showed no differences when remodelling was defined by the local reference approach at baseline or follow-up.

CONCLUSION

Remodelling assessment using a global arterial reference approach, but not the commonly used, local reference site approach, correlated reasonably well with serial changes in arterial dimensions and identified arterial segments with subsequent PAV progression despite intensive statin treatment and overall atheroma regression.

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.

Advances in IVUS/OCT and Future Clinical Perspective of Novel Hybrid Catheter System in Coronary Imaging

Intravascular ultrasound (IVUS) and optical coherence tomography (OCT) have been developed and improved as both diagnostic and guidance tools for interventional procedures over the past three decades. IVUS has a resolution of 100 μm with a high tissue penetration and capability of assessing the entire structure of a coronary artery including the external elastic membrane, whereas OCT has a higher resolution of 10–20 μm to assess endoluminal structures with a limited tissue penetration compared to IVUS. Recently, two companies, CONAVI and TERUMO, integrated IVUS and OCT into a single catheter system. With their inherent strength and limitations, the combined IVUS and OCT probes are complementary and work synergistically to enable a comprehensive depiction of coronary artery. In this review, we summarize the performance of the two intracoronary imaging modalities—IVUS and OCT—and discuss the expected potential of the novel hybrid IVUS–OCT catheter system in the clinical field.

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.

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).

Spatial Distribution of Vulnerable Plaques: Comprehensive In Vivo Coronary Plaque Mapping

OBJECTIVES

The authors performed a comprehensive analysis on the distribution of coronary plaques with different phenotypes from our 3-vessel optical coherence tomography (OCT) database.

BACKGROUND

Previous pathology studies demonstrated that thin-cap fibroatheroma (TCFA) is localized in specific segments of the epicardial coronary arteries. A detailed description of in vivo coronary plaques of various phenotypes has not been reported.

METHODS

OCT images of all 3 coronary arteries in 131 patients were analyzed every 1 mm to assess plaque phenotype and features of vulnerability. In addition, plaques were divided into tertiles according to percent area stenosis (%AS).

RESULTS

Among 534 plaques identified in 393 coronary arteries, 27.0% were fibrous plaques, 13.3% were fibrocalcific plaques, 40.8% were thick-cap fibroatheromas, and 18.9% were TCFAs. TCFAs showed clustering in the proximal segment, particularly in the left anterior descending artery. On the other hand, fibrous plaques were relatively evenly distributed throughout the entire length of the coronary arteries. In patients with acute coronary syndromes (ACS), TCFAs showed stronger proximal clustering in the left anterior descending, 2 clustering peaks in the right coronary artery, and 1 clustering peak in the circumflex artery. The pattern of TCFA distribution was less obvious in patients without ACS. The prevalence of TCFA was higher in the highest %AS tertile, compared with the lowest %AS tertile (30% vs. 9%; p < 0.001).

CONCLUSIONS

The present 3-vessel OCT study showed that TCFAs cluster at specific locations in the epicardial coronary arteries, especially in patients with ACS. TCFA was more prevalent in segments with tight stenosis. (The Massachusetts General Hospital Optical Coherence Tomography Registry; NCT01110538).

Coronary Artery Disease and Endothelial Dysfunction: Novel Diagnostic and Therapeutic Approaches

Coronary artery disease is the leading cause of morbidity and mortality worldwide. The most common pathophysiologic substrate is atherosclerosis which is an inflammatory procedure that starts at childhood and develops throughout life. Endothelial dysfunction is associated with the initiation and progression of atherosclerosis and is characterized by the impaired production of nitric oxide. In general, endothelial dysfunction is linked to poor cardiovascular prognosis and different methods, both invasive and non-invasive, have been developed for its evaluation. Ultrasound evaluation of flow mediated dilatation of the branchial artery is the most commonly used method to assessed endothelial function while intracoronary administration of vasoactive agents may be also be used to test directly endothelial properties of the coronary vasculature. Endothelial dysfunction has also been the subject of therapeutic interventions. This review article summarizes the knowledge about evaluation of endothelial function in acute coronary syndromes and stable coronary artery disease and demonstrates the current therapeutic approaches against endothelial dysfunction.

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.

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.

Three-Dimensional Fibrous Cap Structure of Coronary Lipid Plaque - ST-Elevation Myocardial Infarction vs. Stable Angina

BACKGROUND

Fibrous cap thickness (FCT) is one of the key features of coronary vulnerable plaque. FCT is measured at an arbitrary point, determined on visual assessment of 2-D cross-sectional imaging. This method has poor reproducibility. The aim of this study was to compare the 3-D structure of FC in non-culprit lipid plaques between patients with ST-elevation myocardial infarction (STEMI) and with stable angina (SA) on optical coherence tomography.

METHODS AND RESULTS

A total of 54 non-culprit plaques from 23 STEMI and 23 SA patients were evaluated. Thin cap fibroatheroma (TCFA), defined as lipid plaque with FCT <80 µm, was identified using a novel algorithm. The number of TCFA, surface area of each TCFA, and the sum total area of TCFA in the target vessel were measured. Patients with STEMI had a greater median number of TCFA (9, IQR 1-17 vs. 2, IQR 0-5; P=0.002), the largest median single TCFA area (0.40, IQR 0.14-0.69 vs. 0.08, IQR 0.04-0.16 mm2; P<0.001) and median sum total area of TCFA (1.04, IQR 0.41-1.95 vs. 0.24, IQR 0.08-0.48 mm2, P<0.004).

CONCLUSIONS

Patients with STEMI, as compared with those with SA, have greater vulnerability to non-culprit plaque.

Implications of the local haemodynamic forces on the phenotype of coronary plaques

AIM

To examine the effect of endothelial shear stress (ESS) on the dynamic changes in plaque phenotype.

METHODS

Patients with myocardial infarction that had intravascular ultrasound-virtual histology (IVUS-VH) and optical coherence tomography (OCT) at baseline and 13-month follow-up were studied. The IVUS-VH data were used to reconstruct the nonculprit vessels, and in the obtained models the ESS was estimated in 3 mm segments. Plaque morphology was derived in each segment from IVUS-VH and OCT. Disease progression was defined as the presence of ≥2 out of the following criteria: reduction in lumen area, increase in plaque burden and change of plaque morphology to a more vulnerable phenotype. Linear mixed effects models were used to assess the effect of ESS in different phenotypes.

RESULTS

Sixty-eight vessels were included in the analysis. Low ESS was associated with plaque progression in all phenotypes. The effect of ESS on plaque burden (p for interaction=0.467) and phenotype (p for interaction=0.188) was similar in all plaque types, whereas the effect of ESS on the changes in lumen dimensions was more prominent in disease-free (β=0.70, p<0.001) than fibrotic/fibrocalcific (β=0.28, p<0.001) or lipid-rich plaques (β=0.15, p=0.015). Standalone IVUS-VH misclassified plaque morphology in one-third of the cases leading to erroneous estimations about the effect of ESS on plaque evolution in different phenotypes.

CONCLUSIONS

The effect of ESS on plaque progression is similar in all phenotypes and cannot be accurately assessed by standalone IVUS-VH which often misclassifies plaque morphology. Therefore, multimodality imaging should be considered to examine the implications of ESS on plaque evolution.

CLINICAL TRIAL REGISTRATION

NCT00962416; Post-results.

A Framework for Comparing Vascular Hemodynamics at Different Points in Time

Computational simulations of blood flow contribute to our understanding of the interplay between vascular geometry and hemodynamics. With an improved understanding of this interplay from computational fluid dynamics (CFD), there is potential to improve basic research and the targeting of clinical care. One avenue for further analysis concerns the influence of time on the vascular geometries used in CFD simulations. The shape of blood vessels changes frequently, as in deformation within the cardiac cycle, and over long periods of time, such as the development of a stenotic plaque or an aneurysm. These changes in the vascular geometry will, in turn, influence flow within these blood vessels. By performing CFD simulations in geometries representing the blood vessels at different points in time, the interplay of these geometric changes with hemodynamics can be quantified. However, performing CFD simulations on different discrete grids leads to an additional challenge: how does one directly and quantitatively compare simulation results from different vascular geometries? In a previous study, we began to address this problem by proposing a method for the simplified case where the two geometries share a common centerline. In this companion paper, we generalize this method to address geometric changes which alter the vessel centerline. We demonstrate applications of this method to the study of wall shear stress in the left coronary artery. First, we compute the difference in wall shear stress between simulations using vascular geometries derived from patient imaging data at two points in the cardiac cycle. Second, we evaluate the relationship between changes in wall shear stress and the progressive development of a coronary aneurysm or stenosis.