Biomechanical Study Of The Effect Of Carotid Geometry On The In-stent Neointimal Hyperplasia

Carotid angioplasty and stenting(CAS)is emerging as a main treatment strategy for carotid stenosis.However,in-stent restenosis(ISR)remains a drawback of this treatment strategy.As an important stage of ISR,the development of neointimal hyperplasia(NIH)influences the formation of restenosis.Hence,it is of great clinical significance to predict neointimal hyperplasia and restenosis by exploring the risk factors of neointimal hyperplasia.In this thesis,computational fluid dynamics(CFD)was used to simulate the synthetic models and the patient-specific models respectively to evaluate the relationship among morphology,local hemodynamics and neointimal hyperplasia.First,twenty-five three-dimensional synthetic models of carotid bifurcation with different morphological parameters were established to investigate the impact of the geometric variations on carotid artery hemodynamic systematically.The geometric variations included internal carotid artery(ICA)/common carotid artery(CCA)diameter ratio,external carotid artery(ECA)/CCA diameter ratio,sinus/CCA diameter ratio,ICA angle,tortuosity and planarity angle.Time-average wall shear stress(TAWSS),oscillatory shear index(OSI)and time-average wall shear stress gradient(TAWSSG)were selected for further statistical analysis.Multiple linear regression analysis revealed that ECA/CCA diameter ratio,sinus/CCA diameter ratio and ICA angle were significantly correlated with the local hemodynamics.Among them,ICA angle had a significant negative correlation with all three hemodynamic parameters(P<0.001,P<0.001,P=0.001).Cases with simultaneous bilateral carotid artery stent placement(SBCAS)were collected to exclude the influence of interindividual differences,and to explore the morphological and hemodynamic factors leading to bilateral neointimal hyperplasia asymmetry.In the patientderived data,a low TAWSS and a high OSI were found at the location of neointima.Twentyfive patients were divided into two groups(13 asymmetric and 12 symmetric patients)due to its intraindividual difference of neointimal hyperplasia development.Significant differences were shown in OSI percentage area(10.56±20.798% vs.-5.87±18.259%,P=0.048)and ECA/CCA diameter ratio(5.64±12.751% vs.-3.59±8.697%,P=0.047).The changes of carotid bifurcation geometry can make apparent differences in hemodynamic distributions and lead to bilateral NIH asymmetry.It may therefore be reasonable to consider certain geometric and hemodynamic variations as potential local risk factors for neointimal hyperplasia.