| ObjectiveEndovascular aneurysm repair(EVAR)has been a first-line treatment for abdominal aortic aneurysms(AAA).However,there is a high incidence of complication and reintervention during mid-term and long-term follow-up following EVAR.Recently,several studies demonstrated that intraluminal thrombus of AAA was related to the clinical outcome following EVAR,and also revealed that type Ⅱendoleak was correlated with preoperative intraluminal thrombus of AAA,however,there is still controversy among the studies.Computational fluid dynamics(CFD)method was used to accurately simulate and explore the mechanism of AAA and the complications following EVAR.At present,there is no hemodynamics study reported about the relationship between intraluminal thrombus of AAA and type Ⅱ endoleak following EVAR.Thus,the aim of the study is to explore the influence of pre-operative intraluminal thrombus of AAA on early and mid-long term clinical outcomes following EVAR,and to determine the impact of pre-operative intraluminal thrombus volume of AAA on the incidence of type Ⅱ endoleak and to build the prediction model of type Ⅱ endoleak,and to explore the influence of intraluminal thrombus of AAA on type Ⅱ endoleak through hemodynamics analysis.Materials and MethodsThe clinical study was a single-center,retrospective study,and patients with AAA who underwent EVAR were enrolled in the study.Perioperative complications,complications during the period of follow-up and patients’ survival status were monitored and recorded.The baseline information,preoperative comorbidities and anatomical parameters of AAA were obtained.The parameters related to intraluminal thrombus volume of AAA were measured through three-dimensional reconstruction of AAA.Firstly,in order to explore the impact of intraluminal thrombus of AAA on early and mid-long term clinical outcomes following EVAR,according to median of continuous variable,the proportion of intraluminal thrombus volume,patients were divided into two groups,low proportion of intraluminal thrombus volume(LILT)group and high proportion of intraluminal thrombus volume(HILT)group.The clinical outcomes were compared between two groups.Secondly,according to the presence of type II endoleak,patients were divided into two groups,endoleak group and non-endoleak group.In order to identify the independent predictor of type II endoleak,preoperative baseline information and anatomic parameters between the two groups were compared by univariate and multivariate logistics regression analysis.And the prediction model was constructed by using the ROC analysis.Finally,the study designed 16 idealized three-dimensional digital models of type II endoleak with different proportion of intraluminal thrombus volume(0%,10%,30%,50%)and different diameter of backflow blood vessel(2mm,3mm,4mm,5mm).All hemodynamics analysis were performed using Ansys Fluent software(V20.1,Fluent Inc.,USA)by selecting unsteady simulation analysis with the SIMPLEC algorithm.The hemodynamics data,including pressure,oscillation shear index(OSI),relative retention time(RRT),time-averaged wall shear stress(Tawss)and Transverse wall shear stress(TransWSS),were analyzed.Results1.Influence of Intraluminal Thrombus of Abdominal Aortic Aneurysms on Clinical Outcomes Following Endovascular Aneurysm RepairA total of 700 patients with AAA following EVAR were enrolled in this analysis,and there were 347 patients in LILT group and 353 patients in HILT group.Compared with the LILT group,the maximum diameter of aneurysm in the HILT group was larger(53.30±13.60 mm vs.55.45±13.47 mm,P=0.04),and the proportion of general anesthesia was lower(30.84%vs.22.10%,P=0.009),while other baseline parameters were not statistically different.As for short-term outcomes,there were no statistically significant differences in short-term outcomes between the two groups by univariate analysis and GEE regression analysis.As for mid-long term outcomes,the results by multivariate Cox regression analysis revealed that,compared with the LILT group,HILT group had a lower rate of type II endoleak(HR 0.41,95%CI 0.25-0.67,P<0.001)and higher rate of limb occlusion(HR 3.25,95%CI 1.05-10.08,P=0.04),while in other outcomes,there were no statistical difference between two groups.2.Preoperative Intraluminal Thrombus Volume of Abdominal Aortic Aneurysm Predicts Type Ⅱ Endoleak Following Endovascular Aneurysm RepairA total of 506 patients with AAA following EVAR were enrolled in this analysis,including 88 in endoleak group and 418 in non-endoleak group.The results by multivariate logistics regression analysis showed that the independent predictors of type Ⅱ endoleak were the proportion of intraluminal thrombus volume of AAA(OR 0.97,95%CI 0.96-0.99,P<0.001),the number of effective lumbar arteries(OR 1.41,95%CI 1.14-1.75,P=0.002)and the diameter of inferior mesenteric artery(OR 1.78,95%CI 1.26-2.52,P=0.001).Through the ROC analysis,the ideal cutoff value of independent factors for predicting type Ⅱ endoleak was identified,and multivariate logistics regression analysis showed that the proportion of intraluminal thrombus volume of AAA less than 27.1%increased risk of type Ⅱ endoleak 5-fold(OR 6.00,95%CI 3.32-10.82,P<0.001),the number of effective lumbar artery number more than six increased about 2 times risk of type Ⅱ endoleak(OR 3.01,95%CI 1.62-5.58,P=0.001),and the diameter of inferior mesenteric artery more than 2.9 mm increased risk of type Ⅱ endoleak 1.5 times(OR 2.58,95%CI 1.50-4.44,P=0.001).The prediction model of type Ⅱ endoleak was constructed based on the proportion of intraluminal thrombus volume,the number of effective lumbar artery number and the diameter of inferior mesenteric artery,and the formula of the prediction model was:In(OR)=3.78998-0.03591 × proportion of intraluminal thrombus volume+0.33571 ×number of effective lumbar artery number+0.56221 × diameter of inferior mesenteric artery.3.Influence of Intraluminal Thrombus of Abdominal Aortic Aneurysm on type ⅡEndoleak Following Endovascular Aneurysm Repair:A Hemodynamic AnalysisAll 16 idealized three-dimensional digital models of type Ⅱ endoleak with different proportion of intraluminal thrombus volume of AAA and diameter of backflow blood vessel were constructed successfully.The hemodynamic analysis showed that the mean pressure of aneurysm sac and stent in the increasing flow phase(0.1s),the peak flow phase(0.25s)and the decreasing flow phase(0.5s),was not changed significantly under the conditions of different proportion of intraluminal thrombus volume.However,the mean pressure increased gradually with increasing diameter of backflow blood vessel in three phases.Moreover,the mean OSI and the minimum and maximum RRT were increased significantly with increasing proportion of intraluminal thrombus volume.However,OSI and RRT were not associated with diameter of backflow blood vessel.As for Tawss,in different proportion of intraluminal thrombus volume(0%,10%,30%,50%),the results showed that the mean Tawss was gradually decrease with increasing proportion of intraluminal thrombus volume(P=0.03),but under the conditions of different backflow blood vessel diameter,the mean Tawss did not change significantly(P=0.11).As for TransWSS,the mean TransWSS was not changed significantly with different proportion of intraluminal thrombus volume(P=0.38)under the different diameter of backflow blood vessel.However,the mean TransWSS gradually decrease with increasing diameter of backflow blood vessel(P=0.01).Conclusion1.The preoperative intraluminal thrombus volume proportion of AAA was associated with type Ⅱ endoleak and limb occlusion following EVAR during mid-long term follow-up.Higher proportion of intraluminal thrombus volume of AAA reduced the risk of type Ⅱ endoleak,however,increased the risk of limb occlusion.2.The proportion of intraluminal thrombus volume of AAA,the number of effective lumbar artery number and the diameter of inferior mesenteric artery were independent predictors of type Ⅱ endoleak following EVAR.And the prediction model was constructed based on the three independent predictors,and the model could guide the risk stratification of patients for prophylactic branch artery embolization.Moreover,the study revealed the cutoff value of predictors,and demonstrated that the proportion of intraluminal thrombus volume less than 27.1%,the number of effective lumbar artery number more than 6,and the diameter of inferior mesenteric artery more than 2.9 mm,were significantly increased the risk of type Ⅱ endoleak after EVAR.3.The idealized three-dimensional digital model of type Ⅱ endoleak was successful reconstructed,and this method could be used for the further study on type Ⅱ endoleak.Hemodynamics analysis demonstrated that higher proportion of intraluminal thrombus volume of AAA could increase OSI and RRT,and it suggested that higher proportion of intraluminal thrombus volume contributed to thrombosis in the sac after EVAR,and decreased the risk of type Ⅱ endoleak.Larger diameter of backflow artery increased the pressure of aneurysm wall and covered stent,and it suggested that type Ⅱ endoleak with large blood vessel of backflow might have a high risk of sac enlargement,and even aneurysm rupture.Both clinical and hemodynamic data have found that the higher proportion of intraluminal thrombus volume,reduced the risk of type Ⅱendoleak following EVAR,which suggested that prophylactic embolization of aneurysm sac could promote lumen thrombosis to reduce the risk of type Ⅱ endoleak.Larger diameter of backflow artery increased the risk of type Ⅱ endoleak,and might lead to sac enlargement,and even aneurysm rupture,and this suggested that prophylactic embolization of larger branch artery of abdominal aorta and intervening type Ⅱ endoleak with larger backflow artery early. |
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