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: This article focuses on the transient behaviour of blood flow in stenotic arteries. Human blood is modelled as an incompressible non-Newtonian fluid. A numerical technique based on the finite element method is developed to simulate the blood flow taking into account of the transient periodic behaviour of the blood flow in cardiac cy-cles. The flow pattern, the distribution of pressure and the wall shear stresses, are computed. The results show that the pulsatile pressure and the time variation of wall shear rate have patterns similar to that for the pulsatile velocity during the cardiac cycles. On the back toe of the stenosis there exists a small recirculation region which causes the direction of the wall shear stress in some part to oscillate, likely lead-ing to atherosclerotic disease. The back toe is thus an ideal location for applying a clot dissolving drug.
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ABSTRACT: This study documents the superior hemodynamics of a novel coupled sequential anastomoses (SQA) graft design in comparison with the routine conventional end-to-side (ETS) anastomoses in coronary artery bypass grafts (CABG). The flow fields inside three polydimethylsiloxane (PDMS) models of coronary artery bypass grafts, including the coupled SQA graft design, a conventional ETS anastomosis, and a parallel side-to-side (STS) anastomosis, are investigated under pulsatile flow conditions using particle image velocimetry (PIV). The velocity field and distributions of wall shear stress (WSS) in the models are studied and compared with each other. The measurement results and WSS distributions, computed from the near wall velocity gradients reveal that the novel coupled SQA design provides: (i) a uniform and smooth flow at its ETS anastomosis, without any stagnation point on the artery bed and vortex formation in the heel region of the ETS anastomosis within the coronary artery; (ii) more favorable WSS distribution; and (iii) a spare route for the blood flow to the coronary artery, to avoid re-operation in case of re-stenosis in either of the anastomoses. This in vitro investigation complements the previous computational studies of blood flow in this coupled SQA design, and is another necessary step taken toward the clinical application of this novel design. At this point and prior to the clinical adoption of this novel design, in vivo animal trials are warranted, in order to investigate the biological effects and overall performance of this anastomotic configuration in vivo.Medical Engineering & Physics 08/2014; 36(10). DOI:10.1016/j.medengphy.2014.06.024 · 1.84 Impact Factor
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ABSTRACT: We investigate the behaviour of the pulsatile blood flow in a stenosed right coronary artery with a bypass graft. The human blood is as-sumed as a non-Newtonian fluid and its viscous behaviour is de-scribed by the Carreau model. The transient phenomena of blood flow through the stenosed region and the bypass graft are simulated for five cardiac cycles by solving the three dimensional unsteady Navier– Stokes equations coupled with the non-Newtonian model. Effects of the time variations of pulsatile velocity and pulse pressure are taken C278 into account. The influence of the bypass angle on the flow interaction between the jet flow from the native artery and the flow from the by-pass graft is investigated. Distributions of velocity, pressure and wall shear stresses are determined under various conditions. The results show that the blood pressure in the stenosed artery drops dramatically in the stenosis area and that high wall shear stresses occur around the stenosis site.