A numerical methodology to fully elucidate the altered wall shear stress in a stented coronary artery

Arterial restenosis after coronary stenting is caused by excessive tissue growth which is stimulated by arterial injury and alterations to the hemodynamic wall shear stress (WSS). Recent numerical studies have predicted only minor differences in the altered WSS between different stent designs using a commonly employed threshold assessment technique. While it is possible that there are only minor differences, it is more likely that this assessment technique is incapable of fully elucidating the alterations to the WSS created by stent implantation. This paper proposes a methodology that involves a more complete investigation into the stent-induced alterations of WSS by incorporating the full suite of WSS-based variables: WSS, WSS gradient (WSSG), WSS angle gradient (WSSAG) and oscillatory shear index (OSI). The four variables are analyzed quantitatively and qualitatively to assess the effect of the stent implantation. The methodology is applied to three stents with contrasting designs: the Palmaz Schatz (PS), Gianturco Roubin II (GR-II) and Bx-Velocity (Bx) stents. For WSS the methodology ranks the stents (best to worst) as follows: PS, GR-II, Bx (Cohen's d: -0.01, -0.613), for WSSG: PS, Bx, GR-II (d: 0.159, 0.764), for WSSAG: PS GR-II Bx (d: 0.213, 0.082), and for OSI: PS, GR-II, Bx (d: 0.315, 0.380). The suggested quantitative and qualitative assessment of the WSS-based variables is shown to improve upon, and highlight the weakness of, the previously used threshold assessment technique. The proposed methodology could be utilized to minimize WSS alterations at the design stage of future coronary stents.