Establishment Of A Fluid Model Of Acute Type B Aortic Dissection And Analysis Of Fluid Dynamics Pre-and Post-TEVAR

BackgroundAortic dissection(AD)is a cardiovascular disease that poses a major threat to human health and has the characteristics of rapid onset and high mortality.The current guidelines recommend thoracic aortic endovascular repair(TEVAR)for the treatment of acute complex type B aortic dissection,effectively reducing the mortality of patients with dissection.However,the aortic stent only covers the upper thoracic aorta,the lower thoracic aorta and the abdominal aorta do not have stent coverage.The unrepaired false lumen and rupture are closely related to the higher secondary surgery and complication rate after TEVAR..Hemodynamics is closely related to the process of aortic dissection.The computational fluid dynamics(CFD)method was used to observe the changes of intravascular blood flow,and the hydrodynamic parameters of the aorta before and after TEVAR were compared.Changes provide new tools for assessing the efficacy of surgery in clinical.MethodThis article consists of two parts.Part I:Retrospective analysis of different outcomes of the type B aortic dissection model.The A model had multiple fractures in the thoracic and abdominal aorta.There were only two fractures in the B model.The blood vessels were modeled and analyzed after 6 months of follow-up.Part II:prospective inclusion of TEVAR in the treatment of aortic dissection of a total of 20 patients,including 16 males and 4 females,male to female ratio of 4:1,age range of 43 to 80 years,an average of 62.1±12.3 years.All the 20 patients in this study group had hypertension,including 7 cases of diabetes.There were 3 cases of mild serum creatinine elevation before operation,2 cases of I b type endoleak after operation,no type Ⅱ,type Ⅲ,Type Ⅳ endoleak.No serious complications occurred after surgery.The aortic CTA raw data of patients before surgery and after TEVAR were collected.Based on the individualized aortic image,the three-dimensional vascular model was reconstructed inversely,and the fluid domain was meshed.After setting the boundary conditions,it was imported into ANSYS CFX software to analyze the flow rate,pressure and shear force.Statistical analysis was performed using SPSS 22.0 for statistical analysis.The test method used a paired sample t test,and the statistical test used a two-sided probability test.P<0.05 considered the difference to be statistically significant.Result1.The area where the shear stress is high and the blood flow field is obviously disordered before surgery,and the secondary fracture occurs after operation.In the unclosed area of the false lumen after surgery,a long time vortex can be seen throughout the cardiac cycle.In the high-viscosity area observed after surgery,further thrombosis was observed in the corresponding area during follow-up.2.The pressure of each point of interest in the 20 patients observed was significantly higher than before,and the difference was statistically significant(P<0.001).The pressure difference between the true and false lumens of the abdominal aorta was significantly increased after TEVAR.By comparing the pressure difference between the true and false lumens of different levels,it increased from 142.03±91.22 and 266.80±176.74 before surgery to 1984.76±647.43,1607.69±657.84,the difference was statistically significant(P<0.001).The postoperative true lumen flow was significantly increased(118.42±19.03 vs66.93±10.95,P<0.001),and the false lumen flow was significantly lower than that before surgery(32.22±13.46 vs 111.35±20.61,P<0.001).Compared with preoperative,the wall shear stress of the aortic arch and thoracic aortic segment after TEVAR decreased compared with that before surgery,and the abdominal aortic segment still had higher shear stress value than the preoperative increase(40.21±25.26 vs 31.79± 26.69,P<0.001).Conclusion1.Acute Stanford type B aortic dissection with TEVAR,the overall flow of the true lumen of the blood vessel is significantly improved compared with preoperative,which is beneficial to correct the ischemic state of each organ.The pressure difference between the true and false cavities is significantly higher than that before surgery,which is beneficial to the repair of the endometrium and affirms the efficacy of TEVAR.After the operation of the true cavity,the blood flow in the thoracic aorta was more stable than before.The shear stress of the thoracic aortic wall was significantly lower than that before the operation,which reduced the risk of further damage of the vessel wall.The shear stress of the abdominal aortic segment increased potential risk of rupture.2.Modeling of fluid mechanics modeling to analyze hemodynamic status before and after aortic dissection TEVAR is feasible.Computational fluid dynamics can simulate blood flow,help us understand blood flow,analyze the postoperative outcomes of patients,and help us to identify potential lesions or thrombotic areas of blood vessels,evaluate the prognosis of patients and choose the appropriate treatment for the situation.