Computational Fluid Dynamics Analysis Of Stanford Type B Aortic Dissection And Its Application In Endovascular Treatment

Objective:Aortic dissection(AD)is a serious cardiovascular disease and critical disease threatening human health,and its mortality can be as high as 36%to 71%within 48 hours,and 75%within 2 weeks.With the development of endovascular treatment,thoracic endovascular aortic repair(TEVAR)has become the main surgical approach in the treatment of Stanford Type B aortic dissection(TB AD).However,some problems of endovascular treatment of AD are still controversial or not well solved.Firstly,there are no effective methods to effective disease risk,so it is still a controversy about whether and when to carry out surgery for specific uncomplicated Stanford type B dissection(UTBAD)and the distal dissection left over after TEVAR surgery.Secondly,for the complex lesions of the aortic arch,there is an urgent clinical need for a rapid and accurate preoperative evaluation method,so as to master the anatomical characteristics and help surgeons to make the surgical plan.Thirdly,for the complex pathologies and high-risk patients with insufficient proximal landing zone(PLZ)who cannot be treated by open surgery or hybrid surgery,there is no effective endovascular method to carry out endovascular treatment of aortic lesions and reconstruct blood flow of supra-aortic branches(SAB),using existing conventional equipment.The purpose of this study:to explore the method to establish a 3D geometric model of AD through the principles and methods of computational fluid dynamics(CFD),and to make preoperative evaluation of complex aortic disease and surgical plans faster and more accurate;to quantitatively analyze hemodynamic characteristics and explore its influence for progession of AD,so as to provide theoretical basis for the clinical treatment of UTBAD and distal aortic dissection;to combine the results of CFD numerical simulation with the hemodynamic performance demonstrating in digital subtraction angiography(DSA),in order to conduct personalized endovascular treatment and explore the method of endovascular reconstruction of SAB blood flow.Methods:Computer aided three-dimensional(3D)model construction and its application in the endovascular treatment for thoracic aortic lesions with complicated anatomy.Based on individualized computed tomography angiography(CTA)of TBAD patients in Digital Image Communication standard format(Digital Image and Communication on Medicine,DICOM),to establish the 3D geometric model using the reverse engineering medical imaging software and to explore the methods of 3D model iptimization and meshing,in order to CFD analyze,observe the pathological feature and measure the operation related data,quickly grasp the anatomical characteristics of lesions,assist surgical treatment,and provide anatomical basis for surgery.Computational fluid dynamics analysis of UTBAD and its application in endovascular treatment.Based on 3D geometric model from the first part,and to calculate and analyze hemodynamic performance of AD and its inside Red Blood cell(RBC)mass flow respectively,to get hemodynamic characteristics and parameters of AD,such as velocity field,pressure field and wall shear stress(WSS),in order to provide theoretical basis for disease risk assessment and preoperative assessment;to observe the haemodynamic performance of DSA and to follow up the changes of CTA results,in order to verify the effectiveness of CFD numerical simulation and the feasibility of applying CFD results and methods to clinical applications;for the complicated lesions and distal aortic dissection,individualized endovascular treatment was explored according to the characteristics of lesions and hemodynamic manifestations,so as to reduce the risk of AD progression and improve the long-term prognosis of patients.Computational fluid dynamics analysis of complicated TBAD and its application in endovascular treatment to reconstruct blood flow of supra-aortic branches(SAB).According to the anatomic structure and hemodynamic characteristics,to explore a completely minimally invasive treatment,without affecting SAB blood flow under the premise of use of the existing conventional equipment,expanding the proximal anchoring zone,in order to treat aortic arch lesions,and to protect and reconstruct blood flow of SAB at the same time,and make its hemodynamic behavior as much as possible in accordance with normal anatomical condition hemodynamic performance.Results:Seven 3D geometric models of the different kind of typical cases were successfully established,including UTBAD,Retrograde Type A Aortic Dissection(RAAD),aortic intramural hematoma(IMH),penetrating ulcer(PAU)and one case of complicated TBAD with dissection of aberrant right subclavian artery(aRSA),one case of complicated RAAD with tear locating at the origin of LSA,and one case of chronic TBAD with pseudoaneurysm at ascending aorta.The anatomy of thoracic aortic lesions was complex,the 3D geometric models were built,anatomical structure was observed,measurement and 3D printing model were performed to assiste surgery,and personalized endovascular treatment was successfully implemented,which not only effectively repaired thoracic aortic lesions,but also protected SAB blood flow.The outcome of the operation was satisfactory and prognosis are good within the followed-up so far.Meanwhile,the optimized and meshed 3D models of the other two patients were successfully used for CFD numerical simulation.The hemodynamic features and the mass flow of RBC in dissected aorta of a patient with UTBAD and a patient with RAAD were successfully numerically calculated and analyzed.The results showed that:(1)the WSS at the proximal tear was significantly higher than WSS at the distal incision and other parts of the aorta,suggesting that active repair of proximal lesions could reduce the risk of disease progression;(2)the blood flow at the proximal end of the false lumen was complex,with such hemodynamic behaviors as vortices and RBC movement trajectory winding,suggesting that it may be beneficial to promote the thrombosis at the proximal end of the false lumen;(3)the continuous presence of distal tears and false lumen lead continuous low-speed blood flow between the true and false lumen,indicating a high risk of poor distal aortic perfusion;(4)there was reverse blood flow toward the proximal end in the distal false lumen,which was not conducive to thrombosis and postoperative reconstruction,and the distal lesion was at risk of progression.Through the observation of postoperative hemodynamic performance and the follow-up of the changes of CTA results,it was found that the CFD numerical simulation results of Case No.1 had good consistency with DSA hemodynamic performance.Through the follow-up of the distal dissection,individualized endovascular treatment according to the anatomical characteristics and hemodynamic performance can reduce the risk of the distal dissection progression and improve the prognosis of the patients.In the third part,14 patients with aortic arch lesions(mean age 52.86±14.46,range 27-79 years old)were successfully treated by looping-chimney technique combined with TEVAR,blood flow of IA and LCCA was successfully rebuilt through retrograde right brachial artery access.There were 8 cases of TBAD,1 case of PAU,one RAAD,2 cases of thoracic aortic aneurysms(TAA),and 2 case of thoracic aorta pseudoaneurysms(PSA).The mean follow-up time was 9.77±6.64 months(0-24 months).Except 1 dead case,all the rest of the 13 patients survived,and follow-up CTA showed that stents implanted in SAB(including:1 case of IA stents,13 cases LCCA stents and 5 cases of LSA)maintained a good location,no stent displacement,deformation,fracture,compression stenosis and thrombosis,and aortic arch lesions were well repair,and the false lumen or aneurysm was not displayed any more,with patent blood flow.Conclusions:1.The methods and results of computational fluid dynamics analysis of aorta can provide important theoretical basis for clinical diagnosis and treatment,and clinical application can help improve diagnosis and treatment of aortic dissection.2.Based on CTA images of patients with aortic dissection,the reverse engineering technology can rapidly and efficiently create three-dimensional geometric models for preoperative evaluation,surgical assistance and computational fluid dynamics numerical simulation.3.Computational fluid dynamics numerical simulation of aortic dissection has good consistency with the hemodynamic performance of digital subtraction angiography,which can provide important anatomical and hemodynamic basis for the risk assessment,preoperative evaluation and endovascular treatment of aortic dissection.4.Looping-chimney technique combined with thoracic endovascular aortic repair is a safe and effective method to reconstruct blood flow of supra-sortic branches.Postoperative angiography showed good hemodynamic performance whish was close to the normal anatomical and physiological state.Short-term and mid-term follow-up results were satisfactory,and the long-term safety and reliability needed further study and follow-up.