Promoting Suitable Hemodynamic Conditions for Thrombus Formation in Abdominal Aortic Aneurysms With Multilayer Stents

Abstract

Multilayer stents or flow modulators are novel devices used for endovascular repair of abdominal aortic aneurysms (AAAs) in patients with unsuitable or complex endovascular geometries. The use of this device is still controversial due to insufficient patient follow-up data and the lack of CFD studies addressing the problem. In this work, we present a methodology to design the flow resistance characteristics needed from multilayer stents to induce suitable hemodynamic conditions inside the aneurysm sac. A hypothetical AAA geometry with and without the device is employed to study the impact on hemodynamic factors of interest such as: the shear stress and pressure distribution on the aneurysm wall, their maximum and average values, and the flow fields inside the aneurysm sac. To model the stent, the porosity and the flow resistance values are used to scale the mass and the Naviers’Stokes equations, including the contribution of the flow resistance on the momentum source term. Through a sensitivity study, the magnitude of the porosity is systematically varied to find the resistance profile that promotes suitable hemodynamic conditions inside the AAA, consistent with the goal of promoting intraluminal thrombus formation. Our results have important implications for designing the layer structures of the multilayer stent to reduce the risks of aneurysm rupture.

Optimization of porous stents for endovascular repair of abdominal aortic aneurysms

“…To generate the data required to uniquely determine Equation (2), a set of CFD simulations was performed by considering that each pore of the stent is shaped as a rhombus, consistent with our assumption that the pores are formed by extending the overlapping cylindrical surfaces of the stent wires onto a plane, as shown in Figure 1 26 . Using symmetry and periodicity arguments, we only consider in our simulations a small, periodic unit of the stent, containing 1/4 of a pore.…”

“…To generate the data required to uniquely determine Equation ( 2), a set of CFD simulations was performed by considering that each pore of the stent is shaped as a rhombus, consistent with our assumption that the pores are formed by extending the overlapping cylindrical surfaces of the stent wires onto a plane, as shown in Figure 1. 26 Using symmetry and periodicity arguments, we only consider in our simulations a small, periodic unit of the stent, containing 1/4 of a pore. This allows us to parameterize the geometry of the stent using only one parameter, the mid-angle of the rhombic element or wide-screen angle α, which defines both the aspect ratio of the rhombic pores and the porosity ϕ of the stent.…”

“…Pressure distribution on the AAA wall at peak systole with and without stent F I G U R E 5 Average pressure on the AAA wall during one cardiac cycle26 …”