Quantitative Analysis Of Blood Flow And Study Of Fluid Dynamics Mechanism In Endovascular Aortic Repai

Aortic disease,including aortic dissection,aortic aneurysm,aortic ulcer,is a kind of cardiovascular disease that seriously threatens human life,which has a rapid onset and progression.Once ruptured,it can lead to sudden death.Even if surgery is performed timely,the overall postoperative hospital mortality rate is still 23.9%to 29%.Complex aortic diseases with serious complications are more dangerous and seriously endanger people’s health,which has always been a hotspot and challenge in this field.Thoracic aortic endovascular repair(TEVAR)uses covered stents to minimally and invasively seal the aortic lesions,thereby reducing the risk of aortic rupture.It has become one of the mainstreams for thoracic aortic diseases,and continues to challenge complex lesions.Visceral malperfusion and insufficient proximal landing zone are important reasons that determine the success or failure of endovascular repair and clinical outcomes.These factors are closely related to hemodynamic changes during TEVAR.However,the current imaging techniques have shortcomings in the immediate real-time,quantification and repeatability of intraoperative evaluation of blood flow.Moreover,it is hard to explain the specific internal mechanism of the reconstruction effect of supra-arch branches and the changes of visceral perfusion in aortic dissection during endovascular repair.Hemodynamic analysis technology based on medical clinical images,as a new clinical diagnosis technology,brings functional evaluation criteria in hemodynamics for disease diagnosis.The clinical value of quantitative blood flow fraction(QFR)in the evaluation of coronary artery stenosis have been fully confirmed.However,quantitative blood flow analysis for functional diagnosis of aortic diseases is still lacking in further studies.As a color-coded quantitative analysis technique based on digital subtraction angiography,iFlow can automatically quantify the blood perfusion of target vessels and organs during operation,and provide hemodynamic basis for surgical decision-making and efficacy evaluation.Studies have reported its unique advantages in the evaluation of the diagnosis and treatment effect of interventional therapy for tumors and cerebrovascular diseases.With the application of computational fluid dynamics(CFD)in the field of aortic diseases,it provides new tools for the study of the hydrodynamic mechanism of aortic diseases and the evaluation of hemodynamic status during operation.On the one hand,the mathematical model established by CFD can rely on the morphological configuration and boundary conditions of real clinical cases to explore the hemodynamic mechanism and related risk factors in the pathogenesis of aortic diseases.On the other hand,fluid dynamics simulations of surgical strategies can be performed to provide hemodynamic evidence for optimizing device design and surgical decision-making.This paper consists of three parts,mainly focusing on iFlow color-coded quantitative analysis technique and CFD,to carry out the study of quantitative analysis of renal blood flow during TEVAR in type B aortic dissection,quantitative flow evaluation for different patterns of left subclavian artery management during TEVAR,and hemodynamics analysis of parallel stent graft for Zone 2 TEVAR.The summary of each part is introduced as follows:Part 1 Quantitative analysis of renal blood flow during thoracic endovascular aortic repair in type B aortic dissection using iFlowObjective The purpose of this study was to quantitatively analyze the hemodynamic changes in renal artery blood flow and perfusion before and after thoracic endovascular aortic repair(TEVAR)and to identify the correlation between hemodynamic parameters and renal function.Methods This study retrospectively evaluated 51 patients with type B aortic dissection undergoing TEVAR between April 2017 and September 2019.The pre-and post-procedural angiography images were postprocessed using iFlow.The average peak ratio(avg.Pr),average delayed time to peak(avg.dTTP),and average area under the curve ratio(avg.AUCr)of the renal arteries and renal cortex were analyzed.Wilcoxon signed-rank test was used to compare iFlow parameters before and after endovascular repair.Spearman correlation analyses were performed to study iFlow parameters and renal function parameters and the estimated glomerular filtration rate(eGFR)and blood urea nitrogen(BUN).Results A total of 102 images were successfully post-processed.Following TEVAR,iFlow showed a significant 33.0%increase in avg.Pr(P<0.001)and a significant 35.1%increase in avg.AUCr(P<0.001)in the renal artery.Additionally,there was a significant 12.2%decrease in the avg.dTTP(P=0.001),a significant 24.5%increase in avg.Pr(P=0.004),and a significant 38.3%increase in avg.AUCr(P=0.009)in the renal cortex.Spearman correlation analysis showed that after TEVAR there was a significant correlation between the avg.Pr of the renal artery and eGFR(r=0.30;P=0.0349),the avg.Pr of the renal cortex and eGFR(r=0.30;P=0.0300),and the avg.AUCr of the renal cortex and BUN(r=0.31:P=0.0289).Conclusions iFlow provided a novel quantitative method for evaluating renal hemodynamic changes in patients with type B aortic dissection undergoing endovascular treatment.Time-intensity curve parameters may facilitate the intraprocedural evaluation of renal blood flow and perfusion to complement the color-coded map.Part 2 Quantitative flow evaluation for different patterns of left subclavian artery management during thoracic endovascular aortic repairObjective The aim of this study was to quantitatively analyze the hemodynamic parameters of blood flow based on different patterns of left subclavian artery(LSA)management during thoracic endovascular aortic repair(TEVAR)and to identify hemodynamic predictors associated with patency.Methods This study retrospectively evaluated 94 patients who received TEVAR without LSA intervention(n=16),with LSA revascularization(n=78)or LSA coverage(n=16).Digital subtraction angiography(DSA)images before and after the procedure were postprocessed using iFlow.Differential in delayed time to peak(diff.dTTP)and peak ratio(diff.Pr)in proximal(P),middle(M)and distal(D)areas of LSA were calculated and compared between two groups.LSA patency was revealed by follow-up computed tomography angiography(CTA).Hemodynamic predictors for LSA patency were identified using Cox regression analysis.Results During TEVAR,patients in LSA coverage group exhibited a higher hemodynamic delay of diff.dTTPs than LSA revascularization group(diffdTTP.P:P=0.009;diff,dTTPM:P=0.002;diff.dTTP.D:P=0.004).The similar trend was observed between non-LSA intervention and LSA coverage groups(diffdTTP.M:P=0.009;diff.dTTP.D:P=0.019).While,among the three groups of diff.Pr did not see the above changes.The median CTA follow-up duration was 1242 days.The LSA patency rate was 100%in the non-LSA intervention group,96.2%in the LSA revascularization group and 75.0%in the LSA coverage group(P=0.016).The diff.dTTPs were independent predictors of midterm LSA occlusion(diffdTTP.P:hazard ratio[HR]:30.0,95%confidence interval[Cl]:5.2-170.0,P<0.001;diff.dTTP.M:HR:6.1,95%CI:2.2-17.0,P<0.001;diff.dTTP.D:HR:5.1,95%CI:2.0-13.0,P<0.001).Conclusion iFlow provides real-time quantitative references for evaluating hemodynamic changes in TEVAR with LSA management.The dTTP may facilitate the evaluation of LSA blood flow and predict the prognosis of midterm patency.Part 3 Computational fluid dynamics based hemodynamics analysis of parallel stent graft for Zone 2 thoracic endovascular aortic repairObjective The purpose of this study was to evaluate the hemodynamic consequences of the left subclavian artery(LSA)and adjacent aorta induced by the geometric variations of the parallel stent graft during Zone 2 thoracic endovascular aortic repair(TEVAR).Methods Based on the patient-specific three-dimensional aortic geometry undergoing parallel graft technique,fifteen models in total for five kinds of LSA branched stent graft configurations(Forward,Backward,Extended,Elliptical and Periscopic)were designed virtually,and the hemodynamic discrepancies between them were analyzed by computational fluid dynamics(CFD).Results In this study,hemodynamic analysis demonstrated that the extension length of chimney stent graft has little influence on the energy loss and wall shear stress(WSS)related parameters.Meanwhile,all the parameters based on WSS of Forwardl5 are closer to those of Forward0,and the difference is within 6.45%,which suggested that antegrade curvature of less than 15 degrees may have a better hemodynamic status.Furthermore,the flatter chimney stent graft induces more aggressive hemodynamic forces,among which the difference of the maximum WSS between the flatter stent graft and nearly round stent graft reaches 65.56%,leading to the greater risk of endoleak and branch obstruction.Compared with chimney technique,the blood flow of patients undergoing periscope technique reduces by half,suggesting that periscope stent graft may cause more serious flow obstruction to LSA.Conclusion This study systematically investigated hemodynamic performances of different LSA branched stent graft configurations using CFD,so as to predict the potential risk of various complications after parallel graft technique.Results obtained might provide suggestions for physicians to formulate appropriate parallel graft technique schemes in TEVAR.