Numerical and Experimental Investigation of the Hemodynamic Performance of Bifurcated Stent Grafts with Various Torsion Angles.

The "crossed limbs" strategy for bifurcated stent grafts (BSGs) is widely employed when abdominal aortic aneurysm (AAA) patients have unfavorable neck or highly splayed iliac arteries. Helical flow is regarded as a typical flow pattern within the human arterial system and is believed to have the positive physiological effects of inhibiting thrombosis formation and atherosclerosis. The "crossed limbs" strategy may induce helical flow and improve the stent graft outcome. To verify the performance of this strategy by considering hemodynamics, we constructed a series of idealized BSGs with various torsion angles and evaluated the hemodynamic performance, including the helical strength, time-averaged wall shear stress (TAWSS), oscillatory shear index, relative resident time (RRT), and displacement force. Our numerical results indicate that an increased torsion angle enhances the helicity strength at the iliac outlets. However, with increasing torsion angle, the TAWSS in the iliac graft decreases and the RRT increases. In addition, our numerical simulations and in vitro experiments reveal that the displacement force increases gradually with increasing torsion angle. In summary, the "crossed limbs" strategy may have benefits for AAA treatment in terms of helical flow, but because of the unfavorable hemodynamic performance verified by analyzing the hemodynamic indicators, the risk of stent graft migration increases with increasing torsion angle. Therefore, the "crossed limbs" strategy should be carefully employed in surgical AAA treatment.