Coronary artery bypass grafting hemodynamics and anastomosis design: a biomedical engineering review

10.1186/1475-925X-12-129BioMedical Engineering Online121Article number 129, 28 page

Laser coronary revascularization: an evaluation of metal-capped optical fibres

Imperial Users onl

Computational fluid dynamics of a novel perfusion strategy using direct perfusion of a left carotid-subclavian bypass during hybrid thoracic aortic repair

To mitigate the risk of perioperative neurological complications during frozen elephant trunk procedures, we aimed to computationally evaluate the effects of direct cerebral perfusion strategy through a left carotid-subclavian bypass on hemodynamics in a patient-specific thoracic aorta model

Effect of Stenosis Severity on Wall Shear Stress Based Hemodynamic Descriptors using Multiphase Mixture Theory

A variety of wall shear stress (WSS) based hemodynamic descriptors have been defined over the years to study hemodynamic flow instabilities as potential indicators or prognosticators of endothelial wall dysfunction. Generally, these hemodynamic indicators have been calculated numerically using ‘single phase’ approach. In single phase models, the flow-dependent cell interactions and their transport are usually neglected by treating blood as a single phase non- Newtonian fluid. In the present investigation, a multiphase mixture-theory model is used to define the motion of red blood cells (RBCs) in blood plasma and interactions between these two-components. The multiphase mixture theory model exhibited good agreement with the experimental results and performed better than non-Newtonian single phase model. The mixture-theory model is then applied to simulate pulsatile blood flow through four idealized coronary artery models having different degrees of stenosis (DOS) severities viz., 30, 50, 70 and 85% diameter reduction stenosis. The maximum WSS is seen at the stenosis throat in all the cases and maximum oscillatory shear index (OSI) is seen in downstream region of the stenosis. Our findings suggest that for degree of coronary stenosis more than 50%, a more disturbed fluid dynamics is observed downstream of stenosis. This could lead to further progression of stenosis and may promote a higher risk of atherogenesis and plaque buildup in the flow-disturbed area. The potential atherosclerotic lesion sites were identified based on clinically relevant values of WSS, time-averaged WSS gradient (TAWSSG), time-averaged WSS (TAWSS), and OSI. Finally, the change in potential atherosclerotic lesion sites with respect to DOS has been quantified

Hemodynamic Features in Stenosed Coronary Arteries: CFD Analysis Based on Histological Images

Histological images from the longitudinal section of four diseased coronary arteries were used, for the first time, to study the pulsatile blood flow distribution within the lumen of the arteries by means of computational fluid dynamics (CFD). Results indicate a strong dependence of the hemodynamics on the morphology of atherosclerotic lesion. Distinctive flow patterns appear in different stenosed regions corresponding to the specific geometry of any artery. Results show that the stenosis affects the wall shear stress (WSS) locally along the diseased arterial wall as well as other adjacent walls. The maximum magnitude of WSS is observed in the throat of stenosis. Moreover, high oscillatory shear index (OSI) is observed along the stenosed wall and the high curvature regions. The present study is capable of providing information on the shear environment in the longitudinal section of the diseased coronary arteries, based on the models created from histological images. The computational method may be used as an effective way to predict plaque forming regions in healthy arterial walls

Development of a haemodynamic model for improving clinical treatment of vascular disease

Atherosclerosis is a chronic artery disease that leads to heart attack and stroke; affecting millions of people worldwide. It tends to develop in locations where disturbed flow patterns occur, such as the carotid artery, left coronary artery and abdominal aorta. The causative factors leading to atherosclerosis still remain relatively poorly understood. Conventional diagnosis of arterial disease relies on a combination of history, clinical examination and clinical imaging derived from CT, MRI, etc. To address some of the important factors related to arterial haemodynamics, Computational Fluid Dynamics (CFD) studies were performed on in-vitro models using physiologically relevant conditions. The flow disturbances in terms of wall shear stress and oscillatory shear index were examined. Based on the current research, new insights from a haemodynamics point of view were provided. This study aims to enrich and complement the current arterial disease research, and contribute to promoting the diagnosis accuracy and efficiency in the future. This thesis is composed by six parts of work. Firstly, a comprehensive literature review was performed to identify the research gaps between the current relevant numerical studies with real clinical application. Secondly, the proposed CFD model was validated with published experimental work using particle image velocimetry (PIV) approach. A downstream impedance model was then developed to improve numerical simulation accuracy for image-based artery bifurcations. The numerical results were correlated with a clinical indicator to provide relevant findings for treating physicians. Lastly, a fully fluid-structure interaction (FSI) modelling over left coronary artery models with different bifurcation angles was conducted. The relationship between the mechanical force (first principle stress), the hemodynamic force (wall shear stress), and the bifurcation angle was analysed. In summary, this thesis developed a new downstream artery impedance model, and converted the numerical simulation results into clinical indicators, which can improve the current simulation accuracy and contribute more meaningful results to assist a better clinical diagnosis. A FSI simulation was performed over left coronary artery bifurcation models. The bifurcation angle influence on atherosclerosis progression was addressed. The left circumflex side bifurcation shoulder was found to be more vulnerable in developing atherosclerosis

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

Coronary Angiography

In the intervening 10 years tremendous advances in the field of cardiac computed tomography have occurred. We now can legitimately claim that computed tomography angiography (CTA) of the coronary arteries is available. In the evaluation of patients with suspected coronary artery disease (CAD), many guidelines today consider CTA an alternative to stress testing. The use of CTA in primary prevention patients is more controversial in considering diagnostic test interpretation in populations with a low prevalence to disease. However the nuclear technique most frequently used by cardiologists is myocardial perfusion imaging (MPI). The combination of a nuclear camera with CTA allows for the attainment of coronary anatomic, cardiac function and MPI from one piece of equipment. PET/SPECT cameras can now assess perfusion, function, and metabolism. Assessing cardiac viability is now fairly routine with these enhancements to cardiac imaging. This issue is full of important information that every cardiologist needs to now

Numerical Prediction of the Haemodynamic Impact of Coronary Stent Implantation

Arterial restenosis limits the effectiveness of coronary stenting. Restenosis is caused by excessive tissue growth which is stimulated by arterial injury and alterations to the arterial WSS. The altered WSS results from stent-induced disturbances to the natural haelnodynamics of the artery. Recent numerical studies have predcted only minor digerences in altered WSS between different stent designs using a commonly employed threshold assessment technique. While it is possible that there are only minor differences, it is more likely that the assessment technique is incapable of fully elucidating the altered WSS created by stent implantation. This thesis proposes a methodology that involves a more complete level of investigation into the stentinduced alterations to the WSS by incorporating the full suite of WSS-based variables: WSS, WSS gradient (WSSG), WSS angle gradient (WSSAG) and oscillatory shear index (OSI). Each of these variables highlights a different type of alteration to the arterial WSS that could lead to excessive tissue growth. The four variables are analysed quantitatively and qualitatively using statistical methods to assess the effect of the stent implantation. The methodology is applied to three stents with contrasting designs: the Palinaz-Schatz (PS), the Gianturco-Roubin II (GR-11) and the Bx-Velocity (Bx) stents. From the results, the sients are ranked (best to worst) for WSS: GR-11, PS, Bx (Cohen\u27s d: -0.01, -0.6131, for WSSG: PS, Bx, GR-I1 (d: 0.159,0.764), for WSSAG: PS GR-I1 Bx (d: 0.213, 0.082), and for OSI: PS, GR- 11, Bx (d: 0.3 15, 0.380). The proposed method of analysis is shown to elucidate the alterations to the WSS created by the stents to a far greater level than with the previously used threshold technique. This method of stent assessment could be utilised to minimise WSS alterations at the design stage of future bare metal, as well as permanent and bioabsorbable drug-eluting coronary stents

Atherogenesis

This monograph will bring out the state-of-the-art advances in the dynamics of cholesterol transport and will address several important issues that pertain to oxidative stress and inflammation. The book is divided into three major sections. The book will offer insights into the roles of specific cytokines, inflammation, and oxidative stress in atherosclerosis and is intended for new researchers who are curious about atherosclerosis as well as for established senior researchers and clinicians who would be interested in novel findings that may link various aspects of the disease