Flow Patterns in Stented Arteries

Intravascular stents are rigid metallic devices designed to improve patency rates following balloon angioplasty. However, recent experience has shown that stented arteries are still subjected to restenosis. While the introduction of a stent may well restore a more uniform local geometry to a blood vessel and the distension of a stent will reduce the risk of stent migration, the inevitable mismatches in compliance and diameter between the stented segment and the host artery will, in turn, give rise to hemodynamic disturbances that will reduce its patency in the long term. The aims of this study are therefore twofold: (i) to investigate the local flow field around individual stent wires, and (ii) to understand the flow disturbances caused by the mismatches. To study the disturbances created by the protrusion of the stent wires into the flow, a numerical model of a two-dimensional channel is constructed which takes the stent geometry into account. Calculations are performed using a CFD package for pulsatile flow through the channel. The predicted results show that for larger filament diameter and smaller ratio of spacing between stent wires to uncovered height, vortices are formed between the stent wires. To incorporate the mismatches mentioned above, three numerical models are constructed for flow in the stented vessel (1) ideal stenting, (2) residual stenosis, and (3) residual expansion. In these models, the flow is considered as three-dimensional and pulsatile, the vessel wall being treated as compliant with the exception of the stented segment where the wall is assumed to be rigid. It has been found that localized recirculation regions exist immediately downstream of the stented segment in all three models. These become more pronounced in the last two cases.