| Background:Acute Aortic Dissection(AAD)is a kind of cardiovascular disease with high mortality,which has the features of acute onset,rapid progression and complicated condition.The appearance of Endovascular aortic repair has solved the problem of proximal break,the majority of patients with acute AD survive and start with a chronic phase.The false lumen of some AD patients will increase gradually and become Aortic Dissecting Aneurysms.Because most of the visceral arteriesare involved,although there are endovascular techniques such as fenestrated stent-grafts,it is still very difficult to deal with.Under this background,the emergence of multilayer bare stents technique has overturned the traditional concept of treatment.Combining the changes of hydromechanics and the physiological coagulation function of human body,it induces thrombosis to form in the false lumen of dissection,and maintains the patency of branch artery,so as to achieve the purpose of treatment.Objective:To evaluate the safety and effectiveness of multilayer bare stents for aortic dissection aneurysms and explore its mechanism of action.Including evaluation of efficacy of the short-term and mid-term effects of the treatment for AD with multilayer bare stents in clinical research,and analyze the influence on blood hydrodynamic effect before and after the multilayer bare stents implantation from a hydrodynamic model based on the hydromechanics of multilayer bare stents has been constructed.Methods:Clinical Research All the cases of AD from 2013 to 2016 have been retrieved and the ones being treated with multilayer bare stents were included in the study.The Computed tomography angiography(CTA)data before the surgery and during the follow-up were collected for imaging measurement,including the diameters of true lumen and false lumen of dissection before and after the surgery,the sac thrombosis ratio(STR)in false lumen,the branch patency rate,etc.A comprehensive evaluation of the short-term and mid-term effects of multilayer bare stent was made.Hydrodynamics Research on the Formation of Thrombus Induced by Multilayer bare Stents.Firstly,The CTA images of dissecting aneurysms before and after the treatment of multilayer bare stents were stented and reorganized through materialise's interactive medical image control system in the study,and the three-dimensional models of the dissecting aneurysms were obtained.Secondly,the fluid-solid coupling simulation analysis on the models were made by the large-scale commercial finite element software ANSYS and CFX.Finally,the results were processed to analyze the stress changes of the aneurysm wall and the changes of blood flow field before and after the operation.Results:Clinical Findings:(1)Surgical Data: The technical success rate is 100%;the operation time is 90 ± 30mins;the intraoperative blood loss is 100 ± 20ml;the average number of implanted stents is 2.25;there is no complications such as aortic dissection rupture,and no death during the perioperative period.(2)Follow-up Results: The follow up period is 20-60 months(an average of 45 months),during which there is no death.In the 3 months of follow-up,5 cases(25%)are completely thrombogenic;in 6 months,8 cases(50%)are completely thrombogenic,in 12 months,11 cases(69%)are completely thrombogenic,in 18 months,13 cases(81%)are completely thrombogenic.The average maximum diameters of the thoracic aortic dissection and abdominal aortic dissection are respectively 48.7±7.9 mm and 36.4±6.5mm before the operation.The average maximum diameters of the thoracic aortic dissection are 43.5±6.1mm,43.3±5.7mm,43.6±5.8mm and 43.7±6.0mm(p?0.05)3 months,6 months,12 months and 18 months after the operation;The average maximum diameters of the abdominal aortic dissection are 41.3±5.9mm,41.1±5.2 mm,41.3±5.6mm and 41.5±5.4mm(p?0.05)3 months,6 months,12 months and 18 months after the operation;The diameter of true lumen of dissection is 17.9±5.1mm before the operation,and it changes into 24.8±3.6mm,26.1±3.5mm,26.5±3.3 mm and 27.1±4.3 mm(p<0.05)3 months,6 months,12 months and 18 months after the operation.The rupture of the aortic dissection aneurysm has not been observed.The branch arteries remains unobstructed during the follow-up.Findings of Hydrodynamics Research on the Formation of Thrombus Induced by Multilayer bare Stents:(1)The Change of Blood Flow Pattern before and after the Operation:The result shows that the blood streamline and blood flow velocity have decreased significantly after the multilayer bare stents surgery,and the velocity of blood flow has decreased significantly with the increase of the number of bare stents.There are more eddy flows after the multilayer bare stents surgery,which increase the stagnation time of blood flow,facilitate platelet activation,thereby promoting thrombosis and reducing the risk of dissection rupture.(2)The Change of Shear Force on the Wall: The overall characteristic of the WSS distribution is that the shear force at the dissection crevasse is the highest,and the WSS decreases with the increase of the number of metal bare stent layers.Conclusion:Multilayer bare stents technique provides a new method for intracavitary treatment of complicated aortic dissection involving the branches of artery.It has preliminarily confirmed the safety and effectiveness of multilayer bare stents technique in stabilizing aortic dissection and maintaining the patency of branch artery.The results of the study are positive in the short-term and mid-term effects,but further observation is still needed for the long-term effect.The hydrodynamic analysis on the models is carried out by fluid-solid coupling method.The results shows that the multilayer bare stents technique can induce thrombosis and reduce the shear force of the tube wall by altering the hemodynamic characteristics of the dissection false lumen,so as to prevent the rupture of the dissection.However,because of the relative hypothesis on the vessel wall and blood,the material properties of blood vessel wall and the non-Newtonian characteristic of blood will be considered in the future research. |
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