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2.3 MECHANICAL ENGINEERING, 3. MEDICAL AND HEALTH SCIENCES
Arterial restenosis limits the effectiveness of coronary stenting. Restenosis is caused by excessive tissue growth which is stimulated by arterial injury and alterations to the arterial WSS. The altered WSS results from stent-induced disturbances to the natural haelnodynamics of the artery. Recent numerical studies have predcted only minor digerences in 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 the assessment technique is incapable of fully elucidating the altered WSS created by stent implantation. This thesis proposes a methodology that involves a more complete level of investigation into the stentinduced alterations to the WSS by incorporating the full suite of WSS-based variables: WSS, WSS gradient (WSSG), WSS angle gradient (WSSAG) and oscillatory shear index (OSI). Each of these variables highlights a different type of alteration to the arterial WSS that could lead to excessive tissue growth. The four variables are analysed quantitatively and qualitatively using statistical methods to assess the effect of the stent implantation. The methodology is applied to three stents with contrasting designs: the Palinaz-Schatz (PS), the Gianturco-Roubin II (GR-11) and the Bx-Velocity (Bx) stents. From the results, the sients are ranked (best to worst) for WSS: GR-11, PS, Bx (Cohen's d: -0.01, -0.6131, for WSSG: PS, Bx, GR-I1 (d: 0.159,0.764), for WSSAG: PS GR-I1 Bx (d: 0.213, 0.082), and for OSI: PS, GR- 11, Bx (d: 0.3 15, 0.380). The proposed method of analysis is shown to elucidate the alterations to the WSS created by the stents to a far greater level than with the previously used threshold technique. This method of stent assessment could be utilised to minimise WSS alterations at the design stage of future bare metal, as well as permanent and bioabsorbable drug-eluting coronary stents.
Murphy, J.: Numerical Prediction of the Haemodynamic Impact of Coronary Stent Implantation. Doctoral Thesis. Dublin Institute of Technology, 2011.