A numerical study of blood flow in coronary artery bypass graft side-to-side anastomoses.
ABSTRACT When sequential grafts are used in multivessel coronary artery bypass grafting, the graft first supplies blood to one or more coronary arteries via a side-to-side anastomosis. We studied hemodynamics in idealized models of "parallel" and "diamond" side-to-side anastomoses, identifying features that might promote restenosis.
Blood flow was computed in three representative anastomosis configurations: parallel side-to-side, diamond side-to-side, and end-to-side. We compared configurations and the effect of host-graft diameter ratio.
Hemodynamic patterns depended strongly on anastomosis geometry and graft/host diameter ratio. In the distal graft, the diamond configuration had large areas of low wall shear stress (WSS) and high spatial WSS gradients. In the proximal graft the unfavorable WSS patterns were comparable for all models, while the distal portion of the host artery the diamond model was best. Models with smaller host arteries had smaller regions of low WSS.
The parallel configuration was preferred over the diamond for maintaining graft patency, while the diamond configuration appeared best for maintaining host artery patency. Since graft patency is critical, parallel configurations seem hemodynamically advantageous. Larger graft/host ratios have better hemodynamic performance than smaller ones.
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ABSTRACT: The sequential bypass grafting technique has many advantages over coronary artery bypass grafting with single grafts. The aim of this study was to evaluate the consequences of sequential bypass graft failure. Between 1 January 1984 and 31 December 1996, 3846 patients underwent primary coronary artery bypass vein grafting. A total of 3490 patients received sequential vein bypass grafts and 356 patients received single vein bypass grafts (9%). There were 6177 sequential bypass grafts (3490 postero-lateral grafts (56%) and 2687 in the antero-lateral position (44%)) and 1468 single grafts (972 vein grafts and 496 internal thoracic artery grafts). Overall, there were 80 hospital deaths (2.1%). Mortality in relation to type of grafts used was: 13 deaths in 356 patients with only single graft (3.7%) and 67 deaths in 3490 patients who received sequential vein grafts (1.9%). Of 3766 hospital survivors, 3731 were followed for an average of 76 months. During follow-up, 85 patients died (2.3%), 15 patients (0.4%) underwent cardiac transplantation and 52 (1.4%) had re-do coronary artery bypass vein grafting. Graft-percutaneous transluminal coronary angioplasty was performed in 56 patients (1.5%), 37/1390 single bypass grafts (2.7%) and 19/6023 sequential bypass grafts (0.3%). There were 272/6023 symptomatic sequential graft occlusions (4.5%) (182 were in postero-lateral position and 90 in the antero-lateral position). There were 66/667 single vein graft occlusions (9.9%) and 15 symptomatic internal thoracic artery graft occlusions (2.1%) during follow-up. In 97% of patients, presenting symptoms of postero-lateral sequential bypass graft occlusion took the form of a renewed angina with a myocardial infarction rate of 3% and a mortality rate of 7%. Corresponding figures for antero-lateral sequential bypass grafts were 22, 78 and 68%, and anterior single vein bypass grafts were 70, 30 and 15%, respectively. The overall 10-year survival rate in patients with sequential bypass grafts was 81.2% and the cumulative patency rate (1464 angio-controls of 2576 sequential vein grafts) was 72.2%. A symptomatic occlusion of a postero-lateral sequential vein bypass results in a low incidence of myocardial infarction with low mortality, when the terminal anastomosis is connected to a high flow vessel. An antero-lateral sequential vein bypass graft has better long-term patency than single vein bypass, but should occlusion occur, it would usually be associated with a higher myocardial infarction and mortality rates than a single vein graft. The highest risk for failure of a sequential graft in the antero-lateral position occurs when the left anterior descending artery (LAD) is small or severely diseased. In this situation the single graft technique with internal thoracic artery appears to be safer.Cardiovascular Surgery - CARDIOVASC SURG. 01/1998; 6(4):389-397.
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ABSTRACT: Atherosclerosis, the leading cause of death in the developed world and nearly the leading cause in the developing world, is associated with systemic risk factors including hypertension, smoking, hyperlipidemia, and diabetes mellitus, among others. Nonetheless, atherosclerosis remains a geometrically focal disease, preferentially affecting the outer edges of vessel bifurcations. In these predisposed areas, hemodynamic shear stress, the frictional force acting on the endothelial cell surface as a result of blood flow, is weaker than in protected regions. Studies have identified hemodynamic shear stress as an important determinant of endothelial function and phenotype. Arterial-level shear stress (>15 dyne/cm2) induces endothelial quiescence and an atheroprotective gene expression profile, while low shear stress (<4 dyne/cm2), which is prevalent at atherosclerosis-prone sites, stimulates an atherogenic phenotype. The functional regulation of the endothelium by local hemodynamic shear stress provides a model for understanding the focal propensity of atherosclerosis in the setting of systemic factors and may help guide future therapeutic strategies.JAMA The Journal of the American Medical Association 01/2000; 282(21):2035-42. · 29.98 Impact Factor
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ABSTRACT: To investigate the effect of the distensible artery wall on the local flow field and to determine the mechanical stresses in the artery wall, a numerical model for the blood flow in the human carotid artery bifurcation has been developed. The wall displacement and stress analysis use geometrically non-linear shell theory where incrementally linearly elastic wall behavior is assumed. The flow analysis applies the time-dependent, three-dimensional, incompressible Navier-Stokes equations for non-Newtonian inelastic fluids. In an iteratively coupled approach the equations of the fluid motion and the transient shell equations are numerically solved using the finite element method. The study shows the occurring characteristics in carotid artery bifurcation flow, such as strongly skewed axial velocity in the carotid sinus with high velocity gradients at the internal divider wall and with flow separation at the outer common-internal carotid wall and at the bifurcation side wall. Flow separation results in locally low oscillating wall shear stress. Further strong secondary motion in the sinus is found. The comparison of the results for a rigid and a distensible wall model demonstrates quantitative influence of the vessel wall motion. With respect to the quantities of main interest, it can be seen, that flow separation and recirculation slightly decrease in the sinus and somewhat increase in the bifurcation side region, and the wall shear stress magnitude decreases by 25% in the distensible model. The global structure of the flow and stress patterns remains unchanged. The deformation analysis shows that the tangential displacements are generally lower by one order of magnitude than the normal directed displacements. The maximum deformation is about 16% of the vessel radius and occurs at the side wall region of the intersection of the two branches. The analysis of the maximum principal stresses at the inner vessel surface shows a complicated stress field with locally high gradients and indicates a stress concentration factor of 6.3 in the apex region.Journal of Biomechanics 08/1995; 28(7):845-56. · 2.72 Impact Factor