Flow simulations and measurements of a novel coronary arterial bypass graft design of sequential anastomoses

Coronary artery bypass grafting (CABG), the primary treatment for high-risk coronary artery disease patients, has a limited long-term patency mainly due to anastomotic intimal hyperplasia (IH). It is well proven that hemodynamic factors are implicated in the initiation and progression of IH. Therefore, in order to further improve the hemodynamics at the downstream anastomosis and alleviate the drawbacks of the available CABG anastomosis designs so as to attain higher patency rates in bypass grafts, a novel coupled sequential anastomoses (SQA) configuration design is developed in the present study, based on the beneficial flow characteristics and higher patency rates observed in the side-to-side (STS) anastomosis of sequential bypass grafts, as compared to the ETS anastomosis. In this distal SQA design, there is initially a STS anastomosis, located distal to the stenosis, and then the graft end is anastomosed to the same coronary artery further downstream in an ETS fashion. Firstly, the flow fields and distributions of various WSS parameters are studied in this CABG design, and compared to those of the conventional distal ETS anastomosis, by means of computational fluid dynamics (CFD) simulations of pulsatile Newtonian blood flow, assuming the blood vessels as rigid tubes. The simulation results demonstrate that the new SQA model provides: (i) a more uniform and smooth flow at the 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) 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; and (iii) improved distribution of HPs at the coronary artery bed and in the heel region of the ETS anastomosis, with more moderate shear stress indices. These advantages of the SQA design over the conventional ETS anastomosis are influenced by the occlusion ratio of the native coronary artery, and are most prominent when the proximal segment of the coronary artery is fully occluded. Upon varying the design parameters of the anastomotic angle and distance between the two anastomoses within a physiological range, the superior coupled STS-ETS anastomoses design is found to have the anastomotic angle of 30° and 30mm distance between the two (STS and ETS) components. Subsequently, the beneficial flow-simulation results of the novel SQA design are validated in vitro by experimental flow measurements, utilizing Particle Image Velocimetry (PIV) technique. Finally, the effects of wall compliance and non-Newtonian rheology on the local flow field and HPs distribution are investigated by a two-way coupled fluid–structure interaction (FSI) analysis in conjunction with the shear thinning property of blood. The time-averaged wall shear stress (TAWSS) is reduced up to 32% while the oscillatory nature of the flow is somewhat increased in the compliant model. The effect of non-Newtonian rheology on the HPs is found to be heterogeneous. In conclusion, although the coupled SQA design does involve one additional anastomosis, it brings about some positive features and provides distinct advantages in the flow field and distribution of HPs, which motivates the use of this design instead of the conventional ETS configuration. However, prior to clinical adoption of this novel SQA design, it is necessary to conduct animal studies, in order to find out the biological response and consequences of the employment of this suggested design in vivo.DOCTOR OF PHILOSOPHY (MAE