An S-type bypass can improve the hemodynamics in the bypassed arteries and suppress intimal hyperplasia along the host artery floor.

The development of distal end-to-side anastomotic intimal hyperplasia (IH) has been attributed to the flow disturbance and abnormal wall shear stress (WSS) distribution there. The geometry of the bypass has a strong influence on the flow pattern and WSS distribution. Using a canine model of end-to-side anastomosis, a 45 degrees S-type bypass was compared with 60 degrees , 45 degrees and 30 degrees conventional bypasses in the term of IH along the host artery floor. Numerical blood flow simulations were also carried out to characterize the flow patterns at the distal parts of the bypassed arteries for the 4 models. The results showed that the averaged intima thicknesses of the host artery floors for the 4 bypass models were 119.50+/-10.30 microm (60 degrees ), 65.56+/-6.53 microm (45 degrees ), 45.26+/-5.99 microm (30 degrees ) and 47.64+/-4.85 microm (S-type), respectively, vs. 9.81+/-1.88 microm in the control group (without bypass surgery). Compared with the control group, neointima thickness in all 4 bypass models was significantly increased, but the neointima thickness of the 45 degrees S-type bypass was apparently much better than its 45 degrees conventional counterpart, and was as good as the 30 degrees conventional bypass. The numerical simulation revealed an apparent swirling flow pattern in the S-type bypass, which was very different than the flow patterns in the 3 conventional bypass models. This swirling flow altered the overall flow pattern in the distal part of the bypassed artery and eliminated the low WSS zone along the host artery floor. The improvement in the term of IH for the S-type bypass is most likely due to the alteration of the overall flow pattern and WSS distribution by the geometrical configuration of the S-type bypass.