Hemodynamic Analysis And Stent Implantation Planning In Multi-stenosed Tapered Vessels

In-stent restenosis is a common complication after stent intervention,which affects the long-term effect of stent intervention.Appropriate implantation planning will effectively reduce the incidence of in-stent restenosis,while the complex intravascular environment of multi-stenosed tapered vessels poses a higher challenge to stent intervention.Therefore,this dissertation starts from the study of hemodynamics of multi-stenosed tapered vessels,analyzes the hemodynamics before stent implantation,and explore the hemodynamic mechanism of multiple stenosis in tapered vessels.Then the stent implantation scheme of tapered vessels with multiple stenosis was planned.The expansibility during stent implantation and hemodynamics after stent implantation were analyzed,so as to provide a theoretical basis for the selection of clinical stent implantation planning.The main research contents and achievements are as follows:To study the hemodynamics of multi-stenosed tapered vessels before stent implantation.The effect of plaque stenosis rate on hemodynamic environment was studied.The results showed that the area between two plaques was in the low velocity recirculation zone,which is easy to cause a new plaque formation and increase the length of stenotic lesions.The low velocity recirculation zone downstream of distal plaque decreases with the increase of proximal plaque stenosis rate,while the increase of distal plaque stenosis rate will lead to the increase of low velocity recirculation zone downstream.The increase of stenosis rate will increase the risk of plaque rupture,and the plaque with higher stenosis rate is more likely to rupture.When the stenosis rate of proximal plaques in multi-stenosed tapered vessels increases,the areas of low TAWSS and high OSI decrease,while when the stenosis rate of distal plaque increases,the area of low TAWSS increases and the area of high OSI decreases.The increase of stenosis rate will lead to the decrease of FFR.The stress and deformation of blood vessels will gradually increase with the increase of stenosis rate.To study the effect of stent implantation planning on stent expansibility.Firstly,the effects of two different balloon shapes,the cylindrical balloon and tapered balloon,on the expansibility of cylindrical stent were compared.The results showed that the use of tapered balloons to expand can achieve a smaller axial shortening rate,while causing less vascular stress.Secondly,in the case of using tapered balloon expansion,the effect of two different stent shapes,the cylindrical and tapered stents,on expansibility were compared.The results showed that the tapered stent can produce smaller axial shortening rate and radial rebound rate,and cause less damage to blood vessels.Then,the effect of the expansion ratio of tapered stents on the expansibility was studied.The results showed that when the expansion ratio of the tapered stent increases,the stress of the stent,the axial shortening rate and the radial rebound rate are all increasing,and the vascular stress is also increasing.Finally,in multistenosed tapered vessels,two cylindrical balloons of different length were used to expand the cylindrical stents successively,and the effects of different expansion reference on the expansibility of the stents were compared.The vascular injury was the least in the implantation planning that the long balloon was used for the initial expansion based on the vascular diameter at the distal end of the distal plaque,and the short balloon was used for the over-dilation based on the vascular diameter at the distal end of the proximal plaque.In addition,compared with the stent shape,the influence of balloon shape on vascular injury is more sensitive.The expansion ratio of tapered stent and the expansion reference used when two cylindrical balloon expand the cylindrical stent have a great impact on vascular injury.To study the effect of stent implantation planning on hemodynamics.Firstly,the models after stent implantation were retrograde reconstructed in the study of stent expansibility,and then the hemodynamics was analyzed.The results showed that when the cylindrical stent is expanded with a cylindrical balloon and a tapered balloon respectively,the tapered balloon expansion can produce smaller low velocity and low TAWSS areas.When the tapered balloon was used to expand the cylindrical stent and the tapered stent,the cylindrical stent could produce a smaller region of low velocity and low TAWSS.The poor hemodynamic environment caused by tapered stent implantation will become worse with the increase of expansion ratio,which increases the risk of in-stent restenosis.When the cylindrical stent was expanded successively with two cylindrical balloons of different length,the hemodynamic environment generated by the implantation planning that the long balloon was used for the initial expansion based on the vascular diameter at the distal end of the distal plaque,and the short balloon was used for the over-dilation based on the vascular diameter at the proximal end of the proximal plaque can reduce the risk of ISR.In addition,the stent and balloon shape had little effect on the low velocity zone after stent implantation.TAWSS was sensitive to the stent shape and the expansion ratio of tapered stent.While FFR was almost not affected by the implantation planning.