Research On The Hemodynamics Of Calcified Aortic Valve Disease And Aortic Valve Replacement

Calcific aortic stenosis is one of the most common aortic valve diseases that is mainly treatment of surgical aortic valve replacement（SAVR）and transcatheter aortic valve replacement（TAVR）in clinically.The hemodynamics of the aortic root after valve replacement is affected by differences in the degree of aortic valve calcification,individualized aortic root differences,and aortic valve replacement methods,which is easy to cause secondary valve diseases.In this dissertation,a three-dimension reconstruction of aortic root geometric model is established based on medical CT imaging data,the influence of the degree of aortic valve calcification,implantation depth and valve replacement method on the hemodynamics of the aortic root and aortic sinus was studied by particle image velocimetry（PIV）technology and fluid dynamics numerical simulation.The purpose is to reveal the mechanism of secondary valve disease caused by aortic valve replacement implantation location and replacement method,and provide theoretical basis and technical reference for clinical calcified aortic valve disease treatment and aortic valve replacement surgery.（1）The influence of the degree of aortic valve calcification on the hemodynamics of the aortic root.The hemodynamics of the aortic root during calcific aortic stenosis were studied by fluid dynamics simulation,and the influence of the degree of calcification on aortic root velocity,pressure,transvalvuar pressure gradients and wall shear stress was analyzed.Calcific aortic stenosis due to the limited opening of the valve leaflets,resulting in a decrease in the diameter of the valve opening and an increase in blood flow velocity.The left ventricle needs to generate greater pressure to maintain the valve opening and closing function when the aortic valve is calcified in order to maintain the normal blood flow,which leads to an increase in the transvalvuar pressure gradients and load imparted to the myocardium of the calcified aortic valve,and an increased risk of left ventricular hypertrophy.The downstream vortex center of the valve leaflet gradually moves away from the sinotubular junction and increases to size of the degree of calcification increases,which makes the ascending aorta bears the shear stress to overload with the location that is prone to expansion,and provides the basis for the calcified aortic valve to easily cause the ascending aorta to expand.（2）The effect of aortic valve implantation depth on the hemodynamics downstream of the valve leaflet.The hemodynamics of the aortic root and aortic sinus at different aortic valve implantation depths were studied through the PIV experiment,and the effects of the implantation depth on aortic root velocity,viscous shear stress,and aortic sinus vorticity and viscous shear stress were analyzed.Compared with D=0mm,the starting position of the systolic jet is near the middle of the aortic sinus,the systolic jet at the valve orifice gradually approaches the position of the physiological valve annulus when implanted valve deviates from the position of the valve annulus,resulting in the full development of the right coronary sinus blood flow and the flow velocity increases,and the high viscous shear stress increases in the distribution area of the right coronary sinus,which easily damages the endothelial cells of the aortic sinus wall.The vorticity value and vorticity fluctuation and distribution area increase in the right coronary sinus with the implantation depth increases,high viscous shear stress begins to appear in the accelerating and continues to the late systolic,which may lead to blood damage and cell hemolysis.（3）The hemodynamic study of valve thrombosis caused by transcatheter aortic valve replacement.The hemodynamics of the aortic root and region of interest（ROI）near the valve leaflets during different aortic valve replacement methods was studied by PIV,and analysis of the aortic root velocity and vorticity distribution,velocity and viscous shear stress of the ROI near the valve distributed.The blood flow characteristics in the aortic root during the valve opening and closing process of the two replacement methods are similar,but the TAV central jet has a larger diameter and exhibits an unsteady behavior at the peak systole.Compare with the parallel distribution of the SAV aortic root shear layer,shear layer in TAV tends to dissipate exhibiting an unsteady behavior with quicker vorticity fluctuations,and the peak systole vorticity value is greater than the physiological shear rate threshold,increasing the risk of platelet hemolysis.The ROI blood flow velocity and viscous shear stress near the TAV aortic valve are reduced,and blood flow is stagnated in the early systole and late diastole,which provides favorable conditions for valve thrombosis.