Background: The left internal mammary artery (LIMA) is the most selected vessel in coronary artery bypass graft, because of its long-term patency. But the influence of flow coming from incomplete stenosis of native coronary artery which is called competitive flow is an important factor for graft failure. There are many factors that affect the competitive flow such as the stenosis severity, the amount of myocardial tissue subtended by the stenosis, the length of lesion, as well as the afterload etc. This article is aimed to discuss the hemodynamic influence of different length of intermediate lesion to competitive flow.

Materials and Methods: A patient-special 3-dimensional model with internal mammary artery graft was constructed. The research made a 50% stenosis of six different lengths in the left anterior descending (LAD), including 3mm, 5mm,10mm,15mm,20mm,25mm. Geometric multiscale analysis method which couples the lumped parameter model(LPM) and three-dimensional (3D) model was used in the numerical simulations.

Results: From the results of numerical simulation, graft flow, coronary flow, wall shear stress(WSS) and the oscillatory shear index(OSI) of graft were extracted. With the increase of the lesion length, the mean graft flow and graft WSS increased, in addition, the coronary flow and graft OSI decreased, but when the stenosis reached 15 mm, these variables were stable and almost had no change.

Conclusion: Apart from the stenosis rate, competitive flow is also affected by the length of lesion. Because of the presence of competitive flow, it should be put more attention to choose bypass surgery for moderate stenosis. But below 15mm, with the increase of the length of stenosis, the hemodynamic environment in bypass surgery is becoming better. In summary, for moderate stenosis, stenosis length is a very important factor in the choice of treatment options.