| Objective: To explore and improve the establishment method of the aortic dissection model of canine,and evaluate the effectiveness of multiple overlapping bare stent(MOBS)in the treatment of aortic dissection.Methods: A.Firstly,20 healthy and adult local mongrel dogs from Tianjin were selected,which were 36-48 months old and weighing 25-30 Kg.They were randomly assigned to the experimental group or the control group,with 10 in each group.Both the experimental group and the control group underwent open thoracic surgery and free thoracic aorta under general anesthesia with endotracheal intubation and mechanical ventilation.In the control group,the entire descending aorta was longitudinally dissected,and a nerve dissector was used to separate the layers at 2/3 and 1/3 of the media.1 cm of inner layer was removed and the remaining inner layer was longitudinally sutured.Then the outer layer was sutured.Otherwise,the experimental group was longitudinally incised to the boumdary between the inner 2/3 and the outer 1/3 of the media,and those two layers were dissected using a self-made separation tool,followed by a lateral transverse incision on the inner layer,and both sides of the intima were fixed to the lateral wall of the aortia,respectively.Both groups received intravenous epinephrine at a dose of 0.05 mg/kg to increase blood pressure after suture and hemostasis.The chest was closed if there's no abnormalities during a 1-hour observation.A contrast-enhanced ultrasound imaging was performed under general anesthesia 3 days after surgery.The experimental dogs were executed 7 days after surgery and gross specimens were obtained.Observation,measurement,and pathological examination were performed.If the experimental dogs died before day 7 after surgery,the specimens were obtained on the same day.The number of dissected models,the average length of the dissection ex vivo,and the number of models with dissection involving the visceral arteries were compared between the experimental group and the control group.B.Computed Tomography Angiography(CTA)data of an aortic dissection patient were imported into Mimics 17.0 software to construct a three-dimensional aortic model,and the computer model of multiple overlapping bare stent was constructed using Solidworks.The combination of the aforementioned 3D model of the aorta and the bare stent was integrated and imported into ANSYS ICEMCFD for meshing before calculation.Three surgical procedures were simulated,namely proximal and distal breaches sealed with covered stents and visceral arteries remain untreated(plan A)/visceral arteries treated with MOBS(plan B),and all-MOBS methed(plan C).The calculation and simulation of flow field distribution before and after surgical intervention were performed with ANSYS CFX software.The streamline,wall shear stress(WSS),postoperative blood pressure changes,and blood flow distribution after each intervention were compared to evaluate the effect of MOBS implantation..Results: A.1.There was no significant difference between the two groups in terms of age,gender,weight,etc.(P>0.05).2.In the experimental group,2 cases died during operation,and 3 died of severe dissection complications.In the control group,1 case died during the operation.Others shared a relevantly good commen state and recover of the incision.The postoperative survival rates were 80.0%(8/10)and 90.0%(9/10)in the two groups,respectively,with no significant difference(p>0.999).Postoperative overall survival was 50.0%(5/10).90.0%(9/10),the difference was not statistically significant(p=0.141);the incidence of postoperative dissection complications was 30%(3/10),0%(0/10),and there was no difference in statistics significance(p=0.211).3.The dissection incidence was 100%(10/10)in the experimental group and 70%(7/10)in the control group.The difference between the two groups was not statistically significant(p=0.211).The rates of visceral artery involvement were 30%(3/10)and 0%(0/10),respectively,and the difference was not statistically significant(p=0.211).There was a significant difference in the length of the dissection between two groups though,in which the experimental group was 11.41±2.98 cm and the control group was 2.84 ±0.71 cm(p<0.001).4.Negative results of contrast-enhanced ultrasound 5.The sections of the aorta stained with HE were all match the pathological changes of the aortic dissection.B.1.The area of fluid particles released from the entrance is more and more confined to the vicinity of the branch vessel with the increase of the number of layers of bare stents covering the branch vessels,and this area is highly coincident with the range of the false lumens of postoperative three-dimensional reconstruction.At the same time,the surgical intervention limits the number and flow rate of fluid particles that flow into the false lumen through the entry tear,and becomes more so as the number of bare stent layers increases.2.Similar with the results of the streamline diagram,compared with preoperative,each protocol generally reduced the WSS in the false lumen,and progressively decreased with the increase of the MOBS insertion layer covering the branch vessels.The high WSS area is mainly concentrated around the branch vessels.3.At the selected level,postoperative blood pressure increased by approximately 6%,and the blood pressure in the false lumen increased by approximately 7%.4.Changes in redistribution of blood flow at each outlet were not significant.Conclusion: 1.The improved establishment method of the aortic dissection model significantly prolonged the length of the aortic dissection compared to traditional mold making methods 2.Although the two groups have shown a separation trend in terms of the incidence of dissection and the rate of visceral artery involvement,but limited by the sample size,the difference is not yet statistically significant.Therefore,the sample size still needs to be further increased.3.Modeling methods still need to be further explored to further improve the survival rate after the success rate is increased,so as to meet the need of the evaluation of the subsequent effect of MOBS implantation.4.Contrast-enhanced ultrasound as a means of detection,it is difficult to identify thoracic aortic dissection,and the experimental animals must be transported and examined under general anesthesia,which increased the possibility of accidents.5.In theory,MOBS can be used to treat B-type dissections that involve the visceral arteries,and the effect is better than simply applying the covered stent-graft.6,Computer simulation is based on ideal physical model,and the reality may vary,and the representativeness of single case analysis is limited,the number of analysis is still needed to further increase.And if possible,we should perform personalized preoperative calculation for every patient to find the best plan for surgical intervention. |
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