Hemodynamic changes for half cover Left subclavian artery ostium during thoracic endovascular aortic repair

Hemodynamic changes for half cover Left subclavian artery ostium during thoracic endovascular aortic repair | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Hemodynamic changes for half cover Left subclavian artery ostium during thoracic endovascular aortic repair Xiaowei Li, Zan Wen, Xiaoming Yuan, Wei Bi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4621144/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Some clinicians use endograft to cover half the left subclavian artery (LSA) ostium to cure some cases with insufficient landing area in thoracic endovascular aortic repair(TEVAR) treatment. So we used computational fluid dynamics (CFD) to study the hemodynamic changes on LSA, because they may cause acute thrombosis or arteriosclerosis of LSA. Methods The digital model of the aortic arch was established and named model A, which only included supraarch branch the LSA. By directly covering half of the LSA ostiumto simulate half cover LSA ostium as model B. All established models were imported into the Gambit grid division software for grid division and were subsequently imported into the Fluent software for hemodynamic numerical simulation and calculation. The related changes for hemodynamic parameters of LSA were analyzed and compared. Results Under the same aortic inlet flow, in model B, the local blood flow velocity of LSA ostium increased and whole blood flow velocity at the distal end decreased. The average wall shear stress(WSS) of the LSA was significantly decreased. Meanwhile there was an obvious turbulent flow in the LSA lumen, and the related blood flow state was disordered. Conclusion CFD research confirmed that the implantation of an endograft covering half the LSA ostium can cause obvious hemodynamic changes, which is likely to cause a long-term hardening or an acute thrombosis of the LSA, finally increased the risk of stroke. Once this operation is performed in some specific clinical cases for simplicityand economy, we should actively anticoagulate and follow up regularly. Health sciences/Cardiology Biological sciences/Computational biology and bioinformatics Biological sciences/Computational biology and bioinformatics/Computational models thoracic endovascular aortic repair endograft half coverage left subclavian artery computational fluid dynamics Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction Thoracic endovascular aortic repair (TEVAR), as a lowly invasive surgical technique, has been rapidly developed. The success of this technique made its associated mortality rate low. Currently, it has been optimized and applied for the treatment of descending aorta lesions[ 1 ]. A sufficient and intact proximal land zone is a necessary anatomical condition for the endovascular treatment and avoidance of a typeⅠendoleak. As such, according to routine requirements, the land zone should not be smaller than 15 mm[ 2 ]. Related research shows that, due to anatomical factors, the primary disease site of the descending aorta in about 40% patients is close to the LSA [ 3 ]. Due to the shape of the aortic arch, the distance between partial breaches is less than 15 mm [ 4 ]. In order to reach the effective anchorage distance, in this study, TEVAR has covered the left subclavian artery (LSA) ostium. Some scholars hypothesize that it is safe for some patients to cover the origin of the LSA without any revascularisation[ 5 ]. Nevertheless, completely covering the LSA does not affect the blood supply of the left upper limb and increases the risk of paraplegia for some patients, it also loses the compensation potential of the left vertebral artery and increases the incidence of a cerebral stroke. As such, most scholars actively recommend an LSA revascularisation[ 6 ]. Therefore, many approaches for the revascularisation of the LSA were developed. Clinicians should provide an individualized treatment, according to the characteristics of the patient. Importantly, each operation method has its own advantages and limitations[ 7 ]. However, regardless of the treatment method, it will change the morphological anatomy and hemodynamics of the LSA. For example, some scholars have previously studied the hemodynamics of chimney revascularisation, and proposed that different LSA stent placement positions and directions could produce different results[ 8 ]. Since hemodynamic factors are the key determinants of atherosclerosis [ 9 ], the long-term patency rate of the LSA in such operations has gradually become the focus of clinical attention. In the early stage of endovascular treatment, or under specific emergency conditions, clinicians extended the landing area, by partially covering the ostium of the LSA. At the same time, they reserved the blood supply of a part of the LSA and vertebral artery[ 10 ]. However, there are still few studies on the hemodynamic changes of the LSA using this surgical methods,the research is based on clinical follow-up, which is greatly influenced by the individual factors of patients (heart rate, blood pressure, basic diseases, etc.)[ 11 ]. With the rapid development of computational fluid dynamics (CFD), the parameters of intra-arterial hemodynamics can be quickly evaluated. These parameters become a reliable tool to understand hemodynamics, pathological vascular disease progress, and to predict the performance of medical equipment[ 12 ]. Moreover, they can avoid the drawbacks of limited prospective research in clinical trials, time-consuming procedures, high costs, and ethical problems[ 13 ]. Therefore, in the present work, we studied the hemodynamic changes of the LSA using an endograft covering half the ostium of the LSA. In order to provide valuable reference for clinical treatment, CFD was applied to analyze the changes in common indices, such as the blood flow field, the blood velocity distribution, and the blood pressure on the arterial wall in the LSA after implantation of endograft[ 14 ]. Materials and Methods Test software The Solidworks 2019 modeling software was adopted in this study. The meshing was divided into the Ansys19.2 Mesh module and the numerical simulation software was Fluent19.2. Establishment and grid division In the modeling process, we sought to use the personalized vascular model reconstructed by MIMICS; however, the stent was an ideal model and could not closely fit the wall of the aorta. In the later stage, this limitation affected the calculation of computational fluid dynamics. Because the main concern in our study was the influence of stent implantation on the blood flow of the LSA, we used modeling software to simulate the ideal model of the aorta and the LSA. This choice has the advantage of not only excluding specific errors caused by different individual factors, but also reducing the number of mesh generation steps(simple modeling requires fewer steps than simulating individual modeling by MIMICS). So a three-dimensional digital model including the aortic arch and an LSA branch was established, based on the data of the normal human aortic anatomy[ 15 ]. The diameter of the aortic arch was 35 mm, the length was 200 mm, and the radian was 180degrees. the diameter of the LSA branch was 12 mm. The aortic arch model diagram was named model A. Using the Solidworks software,the LSA ostium was directly blocked with a die with the same thickness of the vascular wall to simulate the digital model of the aorta implanted with the endograft as model B. Because the bare keel at the front end of the covered stent was thin and in a reduced number, it was disregarded. The flow channel of the blood vessel model was extracted and imported into Fluent For mesh generation.For grid division, the established model was imported into the Fluent Mesh software. The grid number of model A without support was 208 and the number of nodes was 195. The grid number of model B (after stent placement) was 92911 and the number of nodes was 262968. We shows the overall schematic diagrams of the grid division of model A and model B respectively(All process is shown in Fig. 1 ). Numerical simulation Governing equations and boundary conditions In this work, the following assumptions were made: the blood in the aorta behaves as an incompressible Newtonian viscous fluid, the blood flow is laminar according to the Reynolds number, the blood vessel wall is rigid and has no slip[ 16 ], the blood flow velocity at the wall surface is 0, the outlet of the LSA and descending aorta is defined as a free outflow, and the pressure is 0 Pa. The blood flow satisfies the Navier-Stokes equation, in which the blood density (ρ) is 1060 kg/m3 and the blood viscosity coefficient is µ. 0.0035 kg/ms, the number of iterations is 500, the time step is 0.001 s, and the maximum number of iterations is 50[ 17 ]. Numerical simulation Use FLUENT ENT19.2 computational fluid dynamics software to calculate the change of blood flow velocity. In this study, we assume that the arterial blood flow is turbulent, and the peak inlet velocity is 0.5 m/s. Two cardiac cycles, each of which is 0.5s, were calculated. When using Fluent to calculate transient step size, it is necessary to set appropriate time step size, boundary conditions and numerical solutions according to specific problems. The accuracy of numerical simulation is affected by grid quality, grid number, time step size and other factors. The number of grids is small, the calculation is easy to converge, but sometimes the results are inaccurate, and the number of grids is large, which requires high computer configuration, long calculation time, and difficult to converge. In order to ensure the accuracy of the calculation results and save the time and cost, the model A without support is taken as an example to verify the grid independence, and the average outlet velocity and pressure on the aortic wall were taken as evaluation indexes to ensure that other boundary conditions remain unchanged. Three sets of simulations with the number of grids of 195,814, 297,143and 394,247 were set up to verify the grid independence. The analysis results are shown in Table 1 . Table 1 Verification of grid independence of model A in fluid domain Number of grids (units) Average exit velocity (m/s) Average exit velocity Error (%) Wall average Pressure value (MPa) Wall average Pressure value error (%) 195814 0.1902 0 6.866 0 297143 0.1899 0.17 6.691 2.56 394247 0.1898 0.17 6.645 3.23 The simulation results show that with the increase of the number of grids, the average velocity and the average pressure error of the outlet gradually increase, but the error growth trend gradually decreases, and the error values are less than 5%. It can be seen that the increase of the number of grids has little influence on the simulation results, and when the number of fluid grids is 195,814, the requirements for the number and quality of grids in simulation calculation can be met. Similarly, in order to eliminate the influence of time step on numerical calculation results, it is necessary to carry out step independence test. Taking the A model without support as an example, the total time of numerical calculation is set to 1.5s, and the time steps are set to 0.001s, 0.0005s and 0.0001s respectively. Taking the average outlet velocity and the average pressure on the main aortic wall as evaluation indexes, other boundary conditions are kept unchanged, and the final error is guaranteed to be within 5%, and the numerical model with the time step of 0.001s is selected for subsequent calculation. In the same way, the B model is verified by grid independence and step independence, and the simulation results are as follows( shown in Fig. 2 ). We iterate coupling in each time step until the residual of the coupling system is less than the specified residual[ 18 ].In this study, the residual was set to 10 − 6. Hemodynamic characteristics were studied, including the blood flow field distribution, the blood pressure distribution, and the shear stress distribution on the wall of the LSA under half coverage. What needs special emphasis is that this study uses CFD to simulate the hemodynamic changes after stent implantation, and the research object does not involve humans and animals, so ethical approval is not necessary. Results Velocity variation 1)Comparison of local blood flow velocity at the ostium of the LSA From the cross-sectional velocity nephogram of LSA, we intercept the peak time of aortic contraction to compare the local blood flow velocity at LSA ostium, and we can see that the local blood flow velocity in model B is faster than model A. In addition, in the velocity nephogram of the local section of LSA port, we can observe that Model A shows normal laminar flow, and the velocity in the central part is the fastest. However, due to the change of the blood flow direction of LSA branch, a small part of blood flow in the peripheral week became abnormal. However, in model B, most of the low-speed areas appear at the distal end of the stent covering the LSA ostium, while high-speed blood flow appears at the remaining ostium, and the local maximum blood-sucking flow velocity is significantly higher than that in model A(model A = 0.49 ± 0.12 vs model B = 0.76 ± 0.24 m/s,P < 0.05)(shown in Fig. 3) . Figure 3. Comparison of Velocity nephogram and local velocity nephogram between model A and model B. Meanwhile, the peak flow velocity changes in the whole cardiac cycle are also presented. of the LSA in model A and model B.The darker the color, the higher the flow rate. 2)Comparison of overall average velocity at the distal end of the LSA However, for the overall average velocity at the distal end of the LSA, there were opposing results. The results show that this hemodynamic characteristic in model B was smaller than model A. In model B, the LSA revealed the smallest range of high-speed blood flow at the distal end. In model A, the average velocity at the distal end was larger, because there was no stent interference (model A = 0.42 ± 0.16 vs model B = 0.29 ± 0.11 m/s,P < 0.05) (shown in Fig. 4 ). Wall shear stress of LSA Before stent implantation, the WSS of LSA in model A fluctuated regularly with the change of blood flow cardiac cycle, indicating this indicator was related to blood flow velocity. During the cardiac cycle after stent implantation, the WSS of model B decreased in systole, but did not change obviously in diastole, and showed a downward trend at the end of diastole. However, the average WSS is lower than that of Model A(1.13 ± 0.82 vs. 1.26 ± 0.92Pa,P < 0.05) (shown in Fig. 5 ). The pressure change of the LSA Compared with the systolic peak, the local high pressure area of model A (before stent implantation) is located on the concave side of LSA, that is, the apex of arterial blood flow bifurcation, and the low pressure area is located on the convex side of LSA(shown in Fig. 6 A). In model B, the high pressure area is located at the front end of the proximal stent graft, which is the area where the stent graft causes blood flow bifurcation. In model B, the overall flow rate and velocity of LSA decreased due to the siphon effect of eccentric high-speed blood flow and the occlusion of covered stent, which caused the total pressure of the stent-covered LSA in the far proximal range to decrease and the relative low-pressure area to increase, but the low-pressure area at the far end may be reduced due to the impact of high-speed blood flow (shown in Fig. 6 B). Changes of blood flow state in LSA cavity Compared with model A, we can observe that the normal laminar flow at the far end of LSA opening in model B becomes a low-speed vortex, and a large number of turbulent lines appear, which is due to the interference of the covered stent on the blood flow at the opening. This observation shows that in Model B after stent implantation, the flow pattern at the proximal end of LSA becomes disordered, especially a large area of low-speed blood flow retention area appears behind the stent film (shown in Fig. 7 ). Discussion TEVAR has developed rapidly. However, in order to obtain an effective proximal anchoring region, the injury of descending aorta near LSA leads to inevitable implantation in Z2 region. This position partially or completely blocks LSA, which leads to complications, such as claudication of the left upper arm and, in severe cases, a stroke[ 19 ]. Therefore, LSA revascularization in Z2 region after endovascular repair of thoracic aorta is very important. At present, there are many vascular reconstructions for LSA [ 20 ], including surgical bypass, chimney, fenestration technology, single stent technology and so on. Although different revascularization of LSA ensures good distal perfusion, it also changes its hemodynamics, as well as the occurrence and development of arteriosclerosis and thrombotic diseases (closely related to local hemodynamic changes) [ 21 ]. Therefore, we should be alert to the risk of acute thrombosis or long-term arteriosclerosis in LSA. However, observing the hemodynamic changes during the formation of atherosclerotic stenosis is limited, time-consuming, and involves ethical issues [ 22 ]. Therefore, it is very important to find an alternative, economical and effective method to study hemodynamic changes. At present, CFD is a research method of numerical simulation of hemodynamics with personalized or idealized model constructed by computer technology. CFD has the advantages of convenient operation, low costand short operation cycle. It can quantify hemodynamic indexes, such as pressure distribution, wall shear stress, and blood flow velocity. It can also simulate the development trend of vascular system diseases before and after treatment, and is also widely used in clinical research of these diseases [ 23 ]. Therefore, the focus of our research is to observe and compare the hemodynamic effects caused by the implantation of covered stent in Z2 area covering the ostium of LSA by CFD method, and to predict the long-term impact on LSA, so as to guide its clinical application. Firstly, according to the theory of fluid mechanics, it is likely that the low luminal flow rate and velocity of liquid will reduce the shear stress on the lumen wall. The results of this study confirm that the overall flow at the distal end of LSA in model B was reduced, due to the obstruction of the LSA ostium by the stent. This reduction leads to a decreased average flow rate, and the overall wall pressure was also reduced. WSS is a mechanical force exerted by the blood flow on the surface of endothelial cells in the tangential direction. It is considered to be the most relevant mechanical factor for arteriosclerosis, stenosis, and plaque rupture[ 24 ]. A low wall shear stress increases the permeability of endothelial cells and interferes with the connection of arterial endothelial cells. This process results in the weakening of the barrier crossed by macromolecules, thus causing the increase of lipid uptake in atherosclerosis. Wall shear force is also negatively correlated with the number of smooth muscle cells. however, the exposure to a normal laminar shear force environment does not affect the number of smooth muscle cells[ 25 ]. Half covering the LSA ostium could obviously reduce the blood flow at the distal end of the LSA and also lower the wall shear stress. As such, it may accelerate arteriosclerosis at the distal end of the LSA in many ways, this sis an aspect worthing of clinical investigation. Secondly, blood can be regarded as a non-Newtonian fluid. When its velocity in blood vessels is low, the fluid particles move only axially (without any lateral movement) and the surrounding fluids are not mixed with each other. This flow pattern is called laminar flow. From the velocity nephograms of the two models, it could be noted that, after the steady laminar flow in the aorta flowed into the LSA, the blood flow state sharply changed, turbulence appeared at the far side of the blood flow bifurcation and the convex side of the blood vessel bent, which made the fluid have longitudinal and lateral velocities. As a result, momentum transfer occurred in the adjacent liquid layer. On the other hand, in model B, the blood flow state significantly changed after the ostium was partially blocked. The local flow velocity also increased, and the laminar flow pattern began to be disrupted, resulting in a lateral movement perpendicular to the main flow direction, followed by multiple small eddies. Simultaneously, in fluid mechanics, it is considered that the three-dimensional spiral flow mode has a greater pressure on the tube wall than the laminar linear flow mode, which causes intima and media proliferation, thickens the tube wall, hinders the clearance of the endoplasm in the tube wall, and causes connective tissue proliferation[ 26 ]. Therefore, in our study, it could be observed that the half coverage of the LSA ostium by the endograft could cause a turbulent state of the blood at the opening and distal end. This state generated an additional longitudinal vascular pressure, which could make normal blood vessels expand more easily. This expansion could damage the vascular endothelium of the subclavian artery. At the same time, the blood flow velocity in the turbulent region was significantly slowed down, which is beneficial for the deposition of blood components, by reducing the tight connection between endothelial cells, leading to lipid infiltration in the wall of the tube, and triggering inflammatory reactions. It is suggested that this operation can accelerate the process of secondary arteriosclerosis after the change of blood flow mode of the LSA. Thirdly, when the blood flows through the stenosis and enters the anatomical expansion section, a downstream turbulent flow and low shear zone are formed. The movement, velocity, and pressure at all points in this space are extremely irregular, resulting in a disordered blood flow and an extremely slow local flow velocity. This low velocity prolongs the contact time between blood flow components and the interface, thus promoting the aggregation of platelets, lipoproteins, and other components against the wall, also strengthening the role of microthrombosis caused by platelet aggregation[ 27 ]. The volume fraction of red blood cells in the low-speed vortex region is also small, and local hypoxia is likely to occur. These alterations can result in lipid concentration, polarization, and macromolecular substance deposition, which leads to increased permeability of the blood vessel walls and intima damage. Consequently, the immune system is activated, leading to lipid substance deposition and intimal growth, thus easily inducing atherosclerotic plaque formation. In our study, we confirmed that the partial coverage LSA ostium model caused ostium stenosis, local flow velocity increases, distal flow velocity decreases, and large-scale turbulence. As such, the possibility of predicting long-term arteriosclerosis increased. On the other hand, the existence of turbulent and low velocity zones behind the stent membrane might induce an imbalance of the coagulation and fibrinolysis system in the blood flow, which may lead to acute thrombosis. Therefore, it is worthy of our consideration whether the patients undergoing this operation in the clinic should be routinely subjected to an anticoagulation procedure, because, even if a tiny thrombus is formed, once it is detached, it may cause a serious basilar artery embolism. Conclusion In the past, for some Z2 lesions, although some scholars have confirmed the feasibility of this operation in emergency or other special circumstances[ 28 ], there is still a lack of long-term follow-up data. Here, we used ANSYS software to simulate and calculate the changes of hemodynamic parameters of LSA before and after stent implantation. The results showed the graft stent half covered the ostium of LSA changed the hemodynamics greatly. Anticoagulant therapy can be actively applied after operation to prevent arterial thrombosis in patients with no obvious contraindications, avoid embolism complicationsand reduce the possibility of stroke. At the same time, routine lipid-lowering therapy is also of clinical significance to prevent slow down the process of arteriosclerosis. Once severe proximal LSA stenosis occurs, surgery may be needed to intervene subclavian steal syndrome. CFD method is convenient and simple, and is not limited by ethical issues or long-term follow-up time. Its related research results can provide reference and guidance for clinical treatment. Abbreviations LSA left subclavian artery TEVAR thoracic endovascular aortic repair CFD computational fluid dynamics WSS wall shear stress Declarations Author Contribution XL, XY, ZW and WB designed and coordinated the study, XL,ZW and carried out experiment and data process, and XL drafted the manuscript. All authors gave final approval for publication. Acknowledgements This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors. Data Availability The datasets analyzed during the current study are available from the corresponding author on reasonable request. References Tadros RO, Tang GHL, Barnes HJ, Mousavi I, Kovacic JC, Faries P, et al. Optimal Treatment of Uncomplicated Type B Aortic Dissection: JACC Review Topic of the Week. J Am Coll Cardiol. 2019;74:1494–1504. Queiroz AB, Lopes JB, Santos VP, Cruz PBAF, Fidelis RJR, Filho JSA,, et al. Physician-Modified Endovascular Grafts for Zone-2 Thoracic Endovascular Aortic Repair. Aorta (Stamford). 2022;10:13–19. Qiu P, Liu J, Chen Y, Zha B, Ye K, Qin J, et al. Changes in aortic arch geometry and the risk for Stanford B dissection. J Thorac Dis. 2020; 12:7193–7201. Kreibich M, Siepe M, Berger T, Kondov S, Morlock J, Pingpoh C, et al. Downstream thoracic endovascular aortic repair following zone 2, 100-mm stent graft frozen elephant trunk implantation. Interact Cardiovasc Thorac Surg.2022; 34:1141–1146. Sun M, Wang Y, Zhou T, Liu X, Jing Q, Liu H, et al. Safety of Left Subclavian Artery Selective Coverage without Revascularization in Thoracic Endovascular Aortic Repair for Type B Aortic Dissections. Ann Thorac Cardiovasc Surg. 2023; 29:70–77. Grigorian A, Lewis M, Wlodarczyk JR, Chien CY, Park T Demetriades D. Left subclavian artery coverage during endovascular repair of thoracic aorta injury in trauma and non-trauma patients. Eur J Trauma Emerg Surg. 2022;48:4425–4429. Xie W, Xue Y, Li S, Jin M, Zhou Q, Wang D. Left subclavian artery revascularization in thoracic endovascular aortic repair: single center's clinical experiences from 171 patients. J Cardiothorac Surg.2021;16:207. Tricarico R, Tran-Son-Tay R, Laquian L, Scali ST, Lee TC, Beck AW, et al. Haemodynamics of Different Configurations of a Left Subclavian Artery Stent Graft for Thoracic Endovascular Aortic Repair. Eur J Vasc Endovasc Surg.2020;59:7–15. Hoogendoorn A, Kok AM, Hartman EMJ, de Nisco G, Casadonte L, Chiastra C, et al. Multidirectional wall shear stress promotes advanced coronary plaque development: comparing five shear stress metrics. Cardiovasc Res.2020;116:1136–1146. Chait JD, Alsheekh A, Hingorani AP, Singh N, Marks NA, Ascher E. Partial subclavian artery coverage in TEVAR patients for acute type B aortic dissections: an alternative solution. J Cardiovasc Surg (Torino).2021; 62:230–233. Si Y, Fu W, Liu Z, Zuo C, Shi X, Wang Y, Guo D, Xu Q, Chen B, et al. Coverage of the left subclavian artery without revascularization during thoracic endovascular repair is feasible: a prospective study. Ann Vasc Surg.2014; 28:850–9. Berger T, Kreibich M. Computational fluid dynamics: a promising diagnostic tool. Eur J Cardiothorac Surg.2021; 60:392. Acuna A, Berman AG, Damen FW, Meyers BA, Adelsperger AR, Bayer KC, et al. Computational Fluid Dynamics of Vascular Disease in Animal Models. J Biomech Eng.2018; 140:0808011–08080114.. Obrist D, von Tengg-Kobligk H. Computational Fluid Dynamics (CFD) For Predicting Pathological Changes In The Aorta: Is It Ready For Clinical Use? Arq Bras Cardio.2022;118:461–462. Rylski B, Schofer F, Beyersdorf F, Kondov S, Kreibich M, Schlett CL, et al. Aortic Arch Anatomy in Candidates for Aortic Arch Repair. Semin Thorac Cardiovasc Surg.2022;34:19–26. Marrocco-Trischitta MM, van Bakel TM, Romarowski RM, de Beaufort HW, Conti M, van Herwaarden JA, et al. The Modified Arch Landing Areas Nomenclature (MALAN) Improves Prediction of Stent Graft Displacement Forces: Proof of Concept by Computational Fluid Dynamics Modelling. Eur J Vasc Endovasc Surg.2018;55:584–592. Conti M, Romarowski RM, Ferrarini A, Stochino M, Auricchio F, Morganti S, et al. Patient-specific computational fluid dynamics analysis of transcatheter aortic root replacement with chimney coronary grafts. Interact Cardiovasc Thorac Surg.2021;32:408–416. Kanzaki T, Numata S, Yamazaki S, Ikemoto K, Hohri Y, Yaku H, et al. Computational fluid dynamics of internal mammary artery-left anterior descending artery anastomoses. Interact Cardiovasc Thorac Surg.2020;31:611–617. Upchurch GR Jr, Escobar GA, Azizzadeh A, Beck AW, Conrad MF, Matsumura JS, et al. Society for Vascular Surgery clinical practice guidelines of thoracic endovascular aortic repair for descending thoracic aortic aneurysms. J Vasc Surg.2021;73:55S-83S. Liebeskind DS, Hinman JD, Kaneko N, Kitajima H, Honda T, De Havenon AH, et al. Endothelial Shear Stress and Platelet FcγRIIa Expression in Intracranial Atherosclerotic Disease. Front Neurol.2021;12:646309. Pan Y, Jing J, Cai X, Jin Z, Wang S, Wang Y, et al. Prevalence and Vascular Distribution of Multiterritorial Atherosclerosis Among Community-Dwelling Adults in Southeast China. JAMA Netw Open.2022; 5:e2218307. Suzuki T. [Computational Fluid Dynamics(CFD)]. No Shinkei Geka.2021;49:425–431. Murayama Y, Fujimura S, Suzuki T, Takao H. Computational fluid dynamics as a risk assessment tool for aneurysm rupture. Neurosurg Focus.2019;47:E12. Chen S, Zhang H, Hou Q, Zhang Y, Qiao A. Multiscale Modeling of Vascular Remodeling Induced by Wall Shear Stress. Front Physiol.2022; 12:808999. Ene-Iordache B, Remuzzi A. Blood Flow in Idealized Vascular Access for Hemodialysis: A Review of Computational Studies. Cardiovasc Eng Techno.2017;8:295–312. Buck AKW, Groszek JJ, Colvin DC, Keller SB, Kensinger C, Forbes R, et al. Combined In Silico and In Vitro Approach Predicts Low Wall Shear Stress Regions in a Hemofilter that Correlate with Thrombus Formation In Vivo. ASAIO J.2018;64:211–217. Mesar T, Alie-Cusson FS, Rathore A, Dexter DJ, Stokes GK, Panneton JM. A more proximal landing zone is preferred for thoracic endovascular repair of acute type B aortic dissections. J Vasc Surg.2022;75:38–46. SultanS,KavanaghEP,DiethrichE,CostacheV,SultanM,JordanF,etal.A clinical review of early outcomes from contemporary flow modulation versus open, fenestrated and branch technologies in the management of thoracoabdominal aortic aneurysm.Vascular.2018;26:209–215. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4621144","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":323453364,"identity":"e780bd58-1743-415f-905b-54f508becaba","order_by":0,"name":"Xiaowei Li","email":"","orcid":"","institution":"Second Hospital of Hebei Medical University","correspondingAuthor":false,"prefix":"","firstName":"Xiaowei","middleName":"","lastName":"Li","suffix":""},{"id":323453365,"identity":"b8af7756-a09d-4c71-8bfd-4f278222c010","order_by":1,"name":"Zan Wen","email":"","orcid":"","institution":"Yanshan University","correspondingAuthor":false,"prefix":"","firstName":"Zan","middleName":"","lastName":"Wen","suffix":""},{"id":323453366,"identity":"2ae762a3-77ae-46ee-b10e-6ec092780117","order_by":2,"name":"Xiaoming Yuan","email":"","orcid":"","institution":"Yanshan University","correspondingAuthor":false,"prefix":"","firstName":"Xiaoming","middleName":"","lastName":"Yuan","suffix":""},{"id":323453367,"identity":"336cbbfa-3a2a-4095-98e0-3a88f2ab19ed","order_by":3,"name":"Wei Bi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAyElEQVRIiWNgGAWjYDCCA8wNDAwGEjz27Y2NDz4Qp4URqKXARs6A53Cz4QzitXxIMzaQSG+T5iBGB9/tg23SPAaHE7dLPmyQZmCwk9NtIKBF8lxiszFIy87ZiQ3GBQzJxmYHCGgxOMPY+DgHqKXhdmJD8gyGA4nbiNDScBis5ebBhsM8RGoB2QL0/g3GxmaitEieYWw2/mNgIyfZk9jMOMOACL/wnWE+JjnjjwQPP/vx5z8+VNjJEdSC7k7SlI+CUTAKRsEowAEAJuVIuR8J/HgAAAAASUVORK5CYII=","orcid":"","institution":"Second Hospital of Hebei Medical University","correspondingAuthor":true,"prefix":"","firstName":"Wei","middleName":"","lastName":"Bi","suffix":""}],"badges":[],"createdAt":"2024-06-22 09:18:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4621144/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4621144/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":60708062,"identity":"6f90fda2-c615-45c9-a572-dfe1f26d6b77","added_by":"auto","created_at":"2024-07-19 19:39:33","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":402221,"visible":true,"origin":"","legend":"\u003cp\u003eModel diagram of model Aand Model B(simulated the implantation of endograft stent in aorta covering half of the ostium of LSA). Diagram of grid division in model A and model B after runner extraction was shown in lower part.\u003c/p\u003e","description":"","filename":"Fig.1.png","url":"https://assets-eu.researchsquare.com/files/rs-4621144/v1/f6851040f98e2c5daec29255.png"},{"id":60707137,"identity":"77bb3902-1e12-4608-bdaa-2e969e91d5f7","added_by":"auto","created_at":"2024-07-19 19:31:33","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":32421,"visible":true,"origin":"","legend":"\u003cp\u003eThe simulation results were verified by grid independence and step independence between model A and model B.\u003c/p\u003e","description":"","filename":"Fig.2.png","url":"https://assets-eu.researchsquare.com/files/rs-4621144/v1/0f6264103f95728ecc3aa344.png"},{"id":60708063,"identity":"9bd0a1c3-e9f4-422e-abc2-b38f5fc47583","added_by":"auto","created_at":"2024-07-19 19:39:33","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":345922,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of Velocity nephogram and local velocity nephogram \u0026nbsp;between model A and model B. Meanwhile, the peak flow velocity changes in the whole cardiac cycle are also presented. of the LSA in model A and model B.The darker the color, the higher the flow rate.\u003c/p\u003e","description":"","filename":"Fig.3.png","url":"https://assets-eu.researchsquare.com/files/rs-4621144/v1/27a764f1877d90d4e5dddd81.png"},{"id":60707134,"identity":"da1c812c-af5f-4ede-b509-0414cbc741ea","added_by":"auto","created_at":"2024-07-19 19:31:33","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":398611,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of velocity nephogram of blood flow and local lumen of LSA distal end in LSA lumen, aslo, changes of blood flow velocity of LSA with cardiac cycle are showed between model A and model B.The darker the color, the higher the flow rate.\u003c/p\u003e","description":"","filename":"Fig.4.png","url":"https://assets-eu.researchsquare.com/files/rs-4621144/v1/89a9af67e5abdb0a31f435c4.png"},{"id":60705946,"identity":"3b83bee5-9155-4b0a-8040-c5bf84ddd42a","added_by":"auto","created_at":"2024-07-19 19:23:33","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":55144,"visible":true,"origin":"","legend":"\u003cp\u003eAverage wall shear stress of the LSA in model A and model B.\u003c/p\u003e","description":"","filename":"Fig.5.png","url":"https://assets-eu.researchsquare.com/files/rs-4621144/v1/e2b9652e129f174a1490ad40.png"},{"id":60705950,"identity":"aa8a5374-02b3-44c4-9055-0ed2581bb47b","added_by":"auto","created_at":"2024-07-19 19:23:33","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":417052,"visible":true,"origin":"","legend":"\u003cp\u003eComparison of pressure nephogram in longitudinal section ,proximal ostium and distal end section of LSAbetween model A and model B.The darker the color, the higher the pressure.\u003c/p\u003e","description":"","filename":"Fig.6.png","url":"https://assets-eu.researchsquare.com/files/rs-4621144/v1/1fb2f4496a7bec38dda6e844.png"},{"id":60705951,"identity":"c6089f52-ef09-4fea-88a0-4c88d417e0a7","added_by":"auto","created_at":"2024-07-19 19:23:33","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":34221,"visible":true,"origin":"","legend":"\u003cp\u003eStreamline diagram of the systolic peak of the LSA in model A and model B.\u003c/p\u003e","description":"","filename":"Fig.7.png","url":"https://assets-eu.researchsquare.com/files/rs-4621144/v1/4d166420623a9fd599d83886.png"},{"id":62600109,"identity":"26cc15ce-9345-490a-9a78-8b56ef44010d","added_by":"auto","created_at":"2024-08-16 09:45:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2409537,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4621144/v1/f53fd865-0de5-408a-b314-3c96639dd9be.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hemodynamic changes for half cover Left subclavian artery ostium during thoracic endovascular aortic repair","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThoracic endovascular aortic repair (TEVAR), as a lowly invasive surgical technique, has been rapidly developed. The success of this technique made its associated mortality rate low. Currently, it has been optimized and applied for the treatment of descending aorta lesions[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. A sufficient and intact proximal land zone is a necessary anatomical condition for the endovascular treatment and avoidance of a typeⅠendoleak. As such, according to routine requirements, the land zone should not be smaller than 15 mm[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Related research shows that, due to anatomical factors, the primary disease site of the descending aorta in about 40% patients is close to the LSA [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Due to the shape of the aortic arch, the distance between partial breaches is less than 15 mm [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. In order to reach the effective anchorage distance, in this study, TEVAR has covered the left subclavian artery (LSA) ostium. Some scholars hypothesize that it is safe for some patients to cover the origin of the LSA without any revascularisation[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Nevertheless, completely covering the LSA does not affect the blood supply of the left upper limb and increases the risk of paraplegia for some patients, it also loses the compensation potential of the left vertebral artery and increases the incidence of a cerebral stroke. As such, most scholars actively recommend an LSA revascularisation[\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Therefore, many approaches for the revascularisation of the LSA were developed. Clinicians should provide an individualized treatment, according to the characteristics of the patient. Importantly, each operation method has its own advantages and limitations[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. However, regardless of the treatment method, it will change the morphological anatomy and hemodynamics of the LSA. For example, some scholars have previously studied the hemodynamics of chimney revascularisation, and proposed that different LSA stent placement positions and directions could produce different results[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Since hemodynamic factors are the key determinants of atherosclerosis [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], the long-term patency rate of the LSA in such operations has gradually become the focus of clinical attention.\u003c/p\u003e \u003cp\u003eIn the early stage of endovascular treatment, or under specific emergency conditions, clinicians extended the landing area, by partially covering the ostium of the LSA. At the same time, they reserved the blood supply of a part of the LSA and vertebral artery[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, there are still few studies on the hemodynamic changes of the LSA using this surgical methods,the research is based on clinical follow-up, which is greatly influenced by the individual factors of patients (heart rate, blood pressure, basic diseases, etc.)[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWith the rapid development of computational fluid dynamics (CFD), the parameters of intra-arterial hemodynamics can be quickly evaluated. These parameters become a reliable tool to understand hemodynamics, pathological vascular disease progress, and to predict the performance of medical equipment[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. Moreover, they can avoid the drawbacks of limited prospective research in clinical trials, time-consuming procedures, high costs, and ethical problems[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Therefore, in the present work, we studied the hemodynamic changes of the LSA using an endograft covering half the ostium of the LSA. In order to provide valuable reference for clinical treatment, CFD was applied to analyze the changes in common indices, such as the blood flow field, the blood velocity distribution, and the blood pressure on the arterial wall in the LSA after implantation of endograft[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e"},{"header":"Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n \u003ch2\u003eTest software\u003c/h2\u003e\n \u003cp\u003eThe Solidworks 2019 modeling software was adopted in this study. The meshing was divided into the Ansys19.2 Mesh module and the numerical simulation software was Fluent19.2.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n \u003ch2\u003eEstablishment and grid division\u003c/h2\u003e\n \u003cp\u003eIn the modeling process, we sought to use the personalized vascular model reconstructed by MIMICS; however, the stent was an ideal model and could not closely fit the wall of the aorta. In the later stage, this limitation affected the calculation of computational fluid dynamics. Because the main concern in our study was the influence of stent implantation on the blood flow of the LSA, we used modeling software to simulate the ideal model of the aorta and the LSA. This choice has the advantage of not only excluding specific errors caused by different individual factors, but also reducing the number of mesh generation steps(simple modeling requires fewer steps than simulating individual modeling by MIMICS). So a three-dimensional digital model including the aortic arch and an LSA branch was established, based on the data of the normal human aortic anatomy[\u003cspan class=\"CitationRef\"\u003e15\u003c/span\u003e]. The diameter of the aortic arch was 35 mm, the length was 200 mm, and the radian was 180degrees. the diameter of the LSA branch was 12 mm. The aortic arch model diagram was named model A. Using the Solidworks software,the LSA ostium was directly blocked with a die with the same thickness of the vascular wall to simulate the digital model of the aorta implanted with the endograft as model B. Because the bare keel at the front end of the covered stent was thin and in a reduced number, it was disregarded. The flow channel of the blood vessel model was extracted and imported into Fluent For mesh generation.For grid division, the established model was imported into the Fluent Mesh software. The grid number of model A without support was 208 and the number of nodes was 195. The grid number of model B (after stent placement) was 92911 and the number of nodes was 262968. We shows the overall schematic diagrams of the grid division of model A and model B respectively(All process is shown in Fig. \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\n \u003ch2\u003eNumerical simulation\u003c/h2\u003e\n \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n \u003ch2\u003eGoverning equations and boundary conditions\u003c/h2\u003e\n \u003cp\u003eIn this work, the following assumptions were made: the blood in the aorta behaves as an incompressible Newtonian viscous fluid, the blood flow is laminar according to the Reynolds number, the blood vessel wall is rigid and has no slip[\u003cspan class=\"CitationRef\"\u003e16\u003c/span\u003e], the blood flow velocity at the wall surface is 0, the outlet of the LSA and descending aorta is defined as a free outflow, and the pressure is 0 Pa. The blood flow satisfies the Navier-Stokes equation, in which the blood density (ρ) is 1060 kg/m3 and the blood viscosity coefficient is µ. 0.0035 kg/ms, the number of iterations is 500, the time step is 0.001 s, and the maximum number of iterations is 50[\u003cspan class=\"CitationRef\"\u003e17\u003c/span\u003e].\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\n \u003ch2\u003e\u003cimg src=\"data:image/png;base64,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\"\u003e\u003cbr\u003e\u003c/h2\u003e\n \u003cdiv id=\"Sec8\" class=\"Section3\"\u003e\n \u003cdiv id=\"Sec9\" class=\"Section4\"\u003e\n \u003ch2\u003eNumerical simulation\u003c/h2\u003e\n \u003cp\u003eUse FLUENT ENT19.2 computational fluid dynamics software to calculate the change of blood flow velocity. In this study, we assume that the arterial blood flow is turbulent, and the peak inlet velocity is 0.5 m/s. Two cardiac cycles, each of which is 0.5s, were calculated. When using Fluent to calculate transient step size, it is necessary to set appropriate time step size, boundary conditions and numerical solutions according to specific problems. The accuracy of numerical simulation is affected by grid quality, grid number, time step size and other factors. The number of grids is small, the calculation is easy to converge, but sometimes the results are inaccurate, and the number of grids is large, which requires high computer configuration, long calculation time, and difficult to converge. In order to ensure the accuracy of the calculation results and save the time and cost, the model A without support is taken as an example to verify the grid independence, and the average outlet velocity and pressure on the aortic wall were taken as evaluation indexes to ensure that other boundary conditions remain unchanged. Three sets of simulations with the number of grids of 195,814, 297,143and 394,247 were set up to verify the grid independence. The analysis results are shown in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eVerification of grid independence of model A in fluid domain\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"5\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNumber of grids (units)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAverage exit velocity (m/s)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAverage exit velocity\u003c/p\u003e\n \u003cp\u003eError (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWall average\u003c/p\u003e\n \u003cp\u003ePressure value (MPa)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eWall average\u003c/p\u003e\n \u003cp\u003ePressure value error (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e195814\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.1902\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.866\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e297143\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.1899\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.691\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.56\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e394247\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.1898\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.645\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eThe simulation results show that with the increase of the number of grids, the average velocity and the average pressure error of the outlet gradually increase, but the error growth trend gradually decreases, and the error values are less than 5%. It can be seen that the increase of the number of grids has little influence on the simulation results, and when the number of fluid grids is 195,814, the requirements for the number and quality of grids in simulation calculation can be met. Similarly, in order to eliminate the influence of time step on numerical calculation results, it is necessary to carry out step independence test. Taking the A model without support as an example, the total time of numerical calculation is set to 1.5s, and the time steps are set to 0.001s, 0.0005s and 0.0001s respectively. Taking the average outlet velocity and the average pressure on the main aortic wall as evaluation indexes, other boundary conditions are kept unchanged, and the final error is guaranteed to be within 5%, and the numerical model with the time step of 0.001s is selected for subsequent calculation. In the same way, the B model is verified by grid independence and step independence, and the simulation results are as follows( shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). We iterate coupling in each time step until the residual of the coupling system is less than the specified residual[\u003cspan class=\"CitationRef\"\u003e18\u003c/span\u003e].In this study, the residual was set to 10 − 6. Hemodynamic characteristics were studied, including the blood flow field distribution, the blood pressure distribution, and the shear stress distribution on the wall of the LSA under half coverage.\u003c/p\u003e\n \u003cp\u003eWhat needs special emphasis is that this study uses CFD to simulate the hemodynamic changes after stent implantation, and the research object does not involve humans and animals, so ethical approval is not necessary.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"Results","content":"\u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eVelocity variation\u003c/h2\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e1)Comparison of local blood flow velocity at the ostium of the LSA\u003c/h2\u003e \u003cp\u003eFrom the cross-sectional velocity nephogram of LSA, we intercept the peak time of aortic contraction to compare the local blood flow velocity at LSA ostium, and we can see that the local blood flow velocity in model B is faster than model A. In addition, in the velocity nephogram of the local section of LSA port, we can observe that Model A shows normal laminar flow, and the velocity in the central part is the fastest. However, due to the change of the blood flow direction of LSA branch, a small part of blood flow in the peripheral week became abnormal. However, in model B, most of the low-speed areas appear at the distal end of the stent covering the LSA ostium, while high-speed blood flow appears at the remaining ostium, and the local maximum blood-sucking flow velocity is significantly higher than that in model A(model A\u0026thinsp;=\u0026thinsp;0.49\u0026thinsp;\u0026plusmn;\u0026thinsp;0.12 vs model B\u0026thinsp;=\u0026thinsp;0.76\u0026thinsp;\u0026plusmn;\u0026thinsp;0.24 m/s,P\u0026thinsp;\u0026lt;\u0026thinsp;0.05)(shown in Fig.\u0026nbsp;3)\u003c/p\u003e \u003cp\u003e.\u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;3. Comparison of Velocity nephogram and local velocity nephogram between model A and model B. Meanwhile, the peak flow velocity changes in the whole cardiac cycle are also presented. of the LSA in model A and model B.The darker the color, the higher the flow rate.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003e2)Comparison of overall average velocity at the distal end of the LSA\u003c/h2\u003e \u003cp\u003eHowever, for the overall average velocity at the distal end of the LSA, there were opposing results. The results show that this hemodynamic characteristic in model B was smaller than model A. In model B, the LSA revealed the smallest range of high-speed blood flow at the distal end. In model A, the average velocity at the distal end was larger, because there was no stent interference (model A\u0026thinsp;=\u0026thinsp;0.42\u0026thinsp;\u0026plusmn;\u0026thinsp;0.16 vs model B\u0026thinsp;=\u0026thinsp;0.29\u0026thinsp;\u0026plusmn;\u0026thinsp;0.11 m/s,P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section2\"\u003e \u003ch2\u003eWall shear stress of LSA\u003c/h2\u003e \u003cp\u003eBefore stent implantation, the WSS of LSA in model A fluctuated regularly with the change of blood flow cardiac cycle, indicating this indicator was related to blood flow velocity. During the cardiac cycle after stent implantation, the WSS of model B decreased in systole, but did not change obviously in diastole, and showed a downward trend at the end of diastole. However, the average WSS is lower than that of Model A(1.13\u0026thinsp;\u0026plusmn;\u0026thinsp;0.82 vs. 1.26\u0026thinsp;\u0026plusmn;\u0026thinsp;0.92Pa,P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section2\"\u003e \u003ch2\u003eThe pressure change of the LSA\u003c/h2\u003e \u003cp\u003eCompared with the systolic peak, the local high pressure area of model A (before stent implantation) is located on the concave side of LSA, that is, the apex of arterial blood flow bifurcation, and the low pressure area is located on the convex side of LSA(shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003eA). In model B, the high pressure area is located at the front end of the proximal stent graft, which is the area where the stent graft causes blood flow bifurcation. In model B, the overall flow rate and velocity of LSA decreased due to the siphon effect of eccentric high-speed blood flow and the occlusion of covered stent, which caused the total pressure of the stent-covered LSA in the far proximal range to decrease and the relative low-pressure area to increase, but the low-pressure area at the far end may be reduced due to the impact of high-speed blood flow (shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e6\u003c/span\u003eB).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section2\"\u003e \u003ch2\u003eChanges of blood flow state in LSA cavity\u003c/h2\u003e \u003cp\u003eCompared with model A, we can observe that the normal laminar flow at the far end of LSA opening in model B becomes a low-speed vortex, and a large number of turbulent lines appear, which is due to the interference of the covered stent on the blood flow at the opening. This observation shows that in Model B after stent implantation, the flow pattern at the proximal end of LSA becomes disordered, especially a large area of low-speed blood flow retention area appears behind the stent film (shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e7\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eTEVAR has developed rapidly. However, in order to obtain an effective proximal anchoring region, the injury of descending aorta near LSA leads to inevitable implantation in Z2 region. This position partially or completely blocks LSA, which leads to complications, such as claudication of the left upper arm and, in severe cases, a stroke[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Therefore, LSA revascularization in Z2 region after endovascular repair of thoracic aorta is very important. At present, there are many vascular reconstructions for LSA [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e], including surgical bypass, chimney, fenestration technology, single stent technology and so on. Although different revascularization of LSA ensures good distal perfusion, it also changes its hemodynamics, as well as the occurrence and development of arteriosclerosis and thrombotic diseases (closely related to local hemodynamic changes) [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Therefore, we should be alert to the risk of acute thrombosis or long-term arteriosclerosis in LSA. However, observing the hemodynamic changes during the formation of atherosclerotic stenosis is limited, time-consuming, and involves ethical issues [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Therefore, it is very important to find an alternative, economical and effective method to study hemodynamic changes. At present, CFD is a research method of numerical simulation of hemodynamics with personalized or idealized model constructed by computer technology. CFD has the advantages of convenient operation, low costand short operation cycle. It can quantify hemodynamic indexes, such as pressure distribution, wall shear stress, and blood flow velocity. It can also simulate the development trend of vascular system diseases before and after treatment, and is also widely used in clinical research of these diseases [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Therefore, the focus of our research is to observe and compare the hemodynamic effects caused by the implantation of covered stent in Z2 area covering the ostium of LSA by CFD method, and to predict the long-term impact on LSA, so as to guide its clinical application.\u003c/p\u003e \u003cp\u003eFirstly, according to the theory of fluid mechanics, it is likely that the low luminal flow rate and velocity of liquid will reduce the shear stress on the lumen wall. The results of this study confirm that the overall flow at the distal end of LSA in model B was reduced, due to the obstruction of the LSA ostium by the stent. This reduction leads to a decreased average flow rate, and the overall wall pressure was also reduced. WSS is a mechanical force exerted by the blood flow on the surface of endothelial cells in the tangential direction. It is considered to be the most relevant mechanical factor for arteriosclerosis, stenosis, and plaque rupture[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. A low wall shear stress increases the permeability of endothelial cells and interferes with the connection of arterial endothelial cells. This process results in the weakening of the barrier crossed by macromolecules, thus causing the increase of lipid uptake in atherosclerosis. Wall shear force is also negatively correlated with the number of smooth muscle cells. however, the exposure to a normal laminar shear force environment does not affect the number of smooth muscle cells[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Half covering the LSA ostium could obviously reduce the blood flow at the distal end of the LSA and also lower the wall shear stress. As such, it may accelerate arteriosclerosis at the distal end of the LSA in many ways, this sis an aspect worthing of clinical investigation.\u003c/p\u003e \u003cp\u003eSecondly, blood can be regarded as a non-Newtonian fluid. When its velocity in blood vessels is low, the fluid particles move only axially (without any lateral movement) and the surrounding fluids are not mixed with each other. This flow pattern is called laminar flow. From the velocity nephograms of the two models, it could be noted that, after the steady laminar flow in the aorta flowed into the LSA, the blood flow state sharply changed, turbulence appeared at the far side of the blood flow bifurcation and the convex side of the blood vessel bent, which made the fluid have longitudinal and lateral velocities. As a result, momentum transfer occurred in the adjacent liquid layer. On the other hand, in model B, the blood flow state significantly changed after the ostium was partially blocked. The local flow velocity also increased, and the laminar flow pattern began to be disrupted, resulting in a lateral movement perpendicular to the main flow direction, followed by multiple small eddies. Simultaneously, in fluid mechanics, it is considered that the three-dimensional spiral flow mode has a greater pressure on the tube wall than the laminar linear flow mode, which causes intima and media proliferation, thickens the tube wall, hinders the clearance of the endoplasm in the tube wall, and causes connective tissue proliferation[\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Therefore, in our study, it could be observed that the half coverage of the LSA ostium by the endograft could cause a turbulent state of the blood at the opening and distal end. This state generated an additional longitudinal vascular pressure, which could make normal blood vessels expand more easily. This expansion could damage the vascular endothelium of the subclavian artery. At the same time, the blood flow velocity in the turbulent region was significantly slowed down, which is beneficial for the deposition of blood components, by reducing the tight connection between endothelial cells, leading to lipid infiltration in the wall of the tube, and triggering inflammatory reactions. It is suggested that this operation can accelerate the process of secondary arteriosclerosis after the change of blood flow mode of the LSA.\u003c/p\u003e \u003cp\u003eThirdly, when the blood flows through the stenosis and enters the anatomical expansion section, a downstream turbulent flow and low shear zone are formed. The movement, velocity, and pressure at all points in this space are extremely irregular, resulting in a disordered blood flow and an extremely slow local flow velocity. This low velocity prolongs the contact time between blood flow components and the interface, thus promoting the aggregation of platelets, lipoproteins, and other components against the wall, also strengthening the role of microthrombosis caused by platelet aggregation[\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. The volume fraction of red blood cells in the low-speed vortex region is also small, and local hypoxia is likely to occur. These alterations can result in lipid concentration, polarization, and macromolecular substance deposition, which leads to increased permeability of the blood vessel walls and intima damage. Consequently, the immune system is activated, leading to lipid substance deposition and intimal growth, thus easily inducing atherosclerotic plaque formation. In our study, we confirmed that the partial coverage LSA ostium model caused ostium stenosis, local flow velocity increases, distal flow velocity decreases, and large-scale turbulence. As such, the possibility of predicting long-term arteriosclerosis increased. On the other hand, the existence of turbulent and low velocity zones behind the stent membrane might induce an imbalance of the coagulation and fibrinolysis system in the blood flow, which may lead to acute thrombosis. Therefore, it is worthy of our consideration whether the patients undergoing this operation in the clinic should be routinely subjected to an anticoagulation procedure, because, even if a tiny thrombus is formed, once it is detached, it may cause a serious basilar artery embolism.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn the past, for some Z2 lesions, although some scholars have confirmed the feasibility of this operation in emergency or other special circumstances[\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e], there is still a lack of long-term follow-up data. Here, we used ANSYS software to simulate and calculate the changes of hemodynamic parameters of LSA before and after stent implantation. The results showed the graft stent half covered the ostium of LSA changed the hemodynamics greatly. Anticoagulant therapy can be actively applied after operation to prevent arterial thrombosis in patients with no obvious contraindications, avoid embolism complicationsand reduce the possibility of stroke. At the same time, routine lipid-lowering therapy is also of clinical significance to prevent slow down the process of arteriosclerosis. Once severe proximal LSA stenosis occurs, surgery may be needed to intervene subclavian steal syndrome. CFD method is convenient and simple, and is not limited by ethical issues or long-term follow-up time. Its related research results can provide reference and guidance for clinical treatment.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eLSA \u0026nbsp; \u0026nbsp;left subclavian artery\u003c/p\u003e\n\u003cp\u003eTEVAR \u0026nbsp; thoracic endovascular aortic repair\u003c/p\u003e\n\u003cp\u003eCFD \u0026nbsp; \u0026nbsp; computational fluid dynamics\u003c/p\u003e\n\u003cp\u003eWSS \u0026nbsp; \u0026nbsp;wall shear stress\u0026nbsp;\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eXL, XY, ZW and WB designed and coordinated the study, XL,ZW and carried out experiment and data process, and XL drafted the manuscript. All authors gave final approval for publication.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eThis research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe datasets analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eTadros RO, Tang GHL, Barnes HJ, Mousavi I, Kovacic JC, Faries P, et al. Optimal Treatment of Uncomplicated Type B Aortic Dissection: JACC Review Topic of the Week. J Am Coll Cardiol. 2019;74:1494\u0026ndash;1504.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQueiroz AB, Lopes JB, Santos VP, Cruz PBAF, Fidelis RJR, Filho JSA,, et al. Physician-Modified Endovascular Grafts for Zone-2 Thoracic Endovascular Aortic Repair. Aorta (Stamford). 2022;10:13\u0026ndash;19.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQiu P, Liu J, Chen Y, Zha B, Ye K, Qin J, et al. Changes in aortic arch geometry and the risk for Stanford B dissection. J Thorac Dis. 2020; 12:7193\u0026ndash;7201.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKreibich M, Siepe M, Berger T, Kondov S, Morlock J, Pingpoh C, et al. Downstream thoracic endovascular aortic repair following zone 2, 100-mm stent graft frozen elephant trunk implantation. Interact Cardiovasc Thorac Surg.2022; 34:1141\u0026ndash;1146.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSun M, Wang Y, Zhou T, Liu X, Jing Q, Liu H, et al. Safety of Left Subclavian Artery Selective Coverage without Revascularization in Thoracic Endovascular Aortic Repair for Type B Aortic Dissections. Ann Thorac Cardiovasc Surg. 2023; 29:70\u0026ndash;77.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGrigorian A, Lewis M, Wlodarczyk JR, Chien CY, Park T Demetriades D. Left subclavian artery coverage during endovascular repair of thoracic aorta injury in trauma and non-trauma patients. Eur J Trauma Emerg Surg. 2022;48:4425\u0026ndash;4429.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXie W, Xue Y, Li S, Jin M, Zhou Q, Wang D. Left subclavian artery revascularization in thoracic endovascular aortic repair: single center's clinical experiences from 171 patients. J Cardiothorac Surg.2021;16:207.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTricarico R, Tran-Son-Tay R, Laquian L, Scali ST, Lee TC, Beck AW, et al. Haemodynamics of Different Configurations of a Left Subclavian Artery Stent Graft for Thoracic Endovascular Aortic Repair. Eur J Vasc Endovasc Surg.2020;59:7\u0026ndash;15.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHoogendoorn A, Kok AM, Hartman EMJ, de Nisco G, Casadonte L, Chiastra C, et al. Multidirectional wall shear stress promotes advanced coronary plaque development: comparing five shear stress metrics. Cardiovasc Res.2020;116:1136\u0026ndash;1146.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChait JD, Alsheekh A, Hingorani AP, Singh N, Marks NA, Ascher E. Partial subclavian artery coverage in TEVAR patients for acute type B aortic dissections: an alternative solution. J Cardiovasc Surg (Torino).2021; 62:230\u0026ndash;233.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSi Y, Fu W, Liu Z, Zuo C, Shi X, Wang Y, Guo D, Xu Q, Chen B, et al. Coverage of the left subclavian artery without revascularization during thoracic endovascular repair is feasible: a prospective study. Ann Vasc Surg.2014; 28:850\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBerger T, Kreibich M. Computational fluid dynamics: a promising diagnostic tool. Eur J Cardiothorac Surg.2021; 60:392.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAcuna A, Berman AG, Damen FW, Meyers BA, Adelsperger AR, Bayer KC, et al. Computational Fluid Dynamics of Vascular Disease in Animal Models. J Biomech Eng.2018; 140:0808011\u0026ndash;08080114..\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eObrist D, von Tengg-Kobligk H. Computational Fluid Dynamics (CFD) For Predicting Pathological Changes In The Aorta: Is It Ready For Clinical Use? Arq Bras Cardio.2022;118:461\u0026ndash;462.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRylski B, Schofer F, Beyersdorf F, Kondov S, Kreibich M, Schlett CL, et al. Aortic Arch Anatomy in Candidates for Aortic Arch Repair. Semin Thorac Cardiovasc Surg.2022;34:19\u0026ndash;26.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMarrocco-Trischitta MM, van Bakel TM, Romarowski RM, de Beaufort HW, Conti M, van Herwaarden JA, et al. The Modified Arch Landing Areas Nomenclature (MALAN) Improves Prediction of Stent Graft Displacement Forces: Proof of Concept by Computational Fluid Dynamics Modelling. Eur J Vasc Endovasc Surg.2018;55:584\u0026ndash;592.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eConti M, Romarowski RM, Ferrarini A, Stochino M, Auricchio F, Morganti S, et al. Patient-specific computational fluid dynamics analysis of transcatheter aortic root replacement with chimney coronary grafts. Interact Cardiovasc Thorac Surg.2021;32:408\u0026ndash;416.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKanzaki T, Numata S, Yamazaki S, Ikemoto K, Hohri Y, Yaku H, et al. Computational fluid dynamics of internal mammary artery-left anterior descending artery anastomoses. Interact Cardiovasc Thorac Surg.2020;31:611\u0026ndash;617.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eUpchurch GR Jr, Escobar GA, Azizzadeh A, Beck AW, Conrad MF, Matsumura JS, et al. Society for Vascular Surgery clinical practice guidelines of thoracic endovascular aortic repair for descending thoracic aortic aneurysms. J Vasc Surg.2021;73:55S-83S.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiebeskind DS, Hinman JD, Kaneko N, Kitajima H, Honda T, De Havenon AH, et al. Endothelial Shear Stress and Platelet FcγRIIa Expression in Intracranial Atherosclerotic Disease. Front Neurol.2021;12:646309.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePan Y, Jing J, Cai X, Jin Z, Wang S, Wang Y, et al. Prevalence and Vascular Distribution of Multiterritorial Atherosclerosis Among Community-Dwelling Adults in Southeast China. JAMA Netw Open.2022; 5:e2218307.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSuzuki T. [Computational Fluid Dynamics(CFD)]. No Shinkei Geka.2021;49:425\u0026ndash;431.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMurayama Y, Fujimura S, Suzuki T, Takao H. Computational fluid dynamics as a risk assessment tool for aneurysm rupture. Neurosurg Focus.2019;47:E12.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen S, Zhang H, Hou Q, Zhang Y, Qiao A. Multiscale Modeling of Vascular Remodeling Induced by Wall Shear Stress. Front Physiol.2022; 12:808999.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEne-Iordache B, Remuzzi A. Blood Flow in Idealized Vascular Access for Hemodialysis: A Review of Computational Studies. Cardiovasc Eng Techno.2017;8:295\u0026ndash;312.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBuck AKW, Groszek JJ, Colvin DC, Keller SB, Kensinger C, Forbes R, et al. Combined In Silico and In Vitro Approach Predicts Low Wall Shear Stress Regions in a Hemofilter that Correlate with Thrombus Formation In Vivo. ASAIO J.2018;64:211\u0026ndash;217.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMesar T, Alie-Cusson FS, Rathore A, Dexter DJ, Stokes GK, Panneton JM. A more proximal landing zone is preferred for thoracic endovascular repair of acute type B aortic dissections. J Vasc Surg.2022;75:38\u0026ndash;46.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSultanS,KavanaghEP,DiethrichE,CostacheV,SultanM,JordanF,etal.A clinical review of early outcomes from contemporary flow modulation versus open, fenestrated and branch technologies in the management of thoracoabdominal aortic aneurysm.Vascular.2018;26:209\u0026ndash;215.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"thoracic endovascular aortic repair, endograft, half coverage, left subclavian artery, computational fluid dynamics","lastPublishedDoi":"10.21203/rs.3.rs-4621144/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4621144/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSome clinicians use endograft to cover half the left subclavian artery (LSA) ostium to cure some cases with insufficient landing area in thoracic endovascular aortic repair(TEVAR) treatment. So we used computational fluid dynamics (CFD) to study the hemodynamic changes on LSA, because they may cause acute thrombosis or arteriosclerosis of LSA.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe digital model of the aortic arch was established and named model A, which only included supraarch branch the LSA. By directly covering half of the LSA ostiumto simulate half cover LSA ostium as model B. All established models were imported into the Gambit grid division software for grid division and were subsequently imported into the Fluent software for hemodynamic numerical simulation and calculation. The related changes for hemodynamic parameters of LSA were analyzed and compared.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eUnder the same aortic inlet flow, in model B, the local blood flow velocity of LSA ostium increased and whole blood flow velocity at the distal end decreased. The average wall shear stress(WSS) of the LSA was significantly decreased. Meanwhile there was an obvious turbulent flow in the LSA lumen, and the related blood flow state was disordered.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCFD research confirmed that the implantation of an endograft covering half the LSA ostium can cause obvious hemodynamic changes, which is likely to cause a long-term hardening or an acute thrombosis of the LSA, finally increased the risk of stroke. Once this operation is performed in some specific clinical cases for simplicityand economy, we should actively anticoagulate and follow up regularly.\u003c/p\u003e","manuscriptTitle":"Hemodynamic changes for half cover Left subclavian artery ostium during thoracic endovascular aortic repair","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-19 19:23:28","doi":"10.21203/rs.3.rs-4621144/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c0c09359-26da-4df3-a4a4-fe5af1f3544e","owner":[],"postedDate":"July 19th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":34209349,"name":"Health sciences/Cardiology"},{"id":34209350,"name":"Biological sciences/Computational biology and bioinformatics"},{"id":34209351,"name":"Biological sciences/Computational biology and bioinformatics/Computational models"}],"tags":[],"updatedAt":"2024-08-16T09:37:46+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-19 19:23:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4621144","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4621144","identity":"rs-4621144","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}