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Three-Dimensional Printing to Guide the Application of Modified Prefenestrated Stent Grafts to Treat Aortic Arch Disease
Three-Dimensional Printing to Guide the Application of Modified Prefenestrated Stent Grafts to Treat Aortic Arch Disease Yuanhao Tong, Yi Qin, Tong Yu, Min Zhou, Chen Liu, Changjian Liu, Xiaoqiang Li, and Zhao Liu, Nanjing, Jiangsu, China
Background: The aim of this study was to summarize the experience and outcomes of total endovascular repair of aortic arch disease using three-dimensional (3D) printing to guide the application of modified prefenestrated/branched stent grafts. Patients and methods: From April 2018 to March 2019, 17 patients with aortic arch disease were treated in our department. Five patients had an aortic arch aneurysm and 12 had undergone an aortic arch dissection. Thirteen men and 4 were women, with an average age of 57.82 ± 10.47 years. Preoperatively, a 3D-printed model of the aorta was made according to computed tomography data. Then, under the guidance of the 3D-printed aortic model, modified prefenestrated/branched stent grafts were prepared, and the diameter of the stent grafts was reduced intraoperatively by a physician for total endovascular repair. Aortic computed tomography angiography was performed 3 and 6 months after the surgery. Results: All procedures were completed in one stage with no conversions to sternotomy. Among all 17 patients, the operation was successful in 16. One patient was treated with a chimney graft and a stent graft fenestrated in situ because of distortion of the stent. The success rate of the technique was 94.18%. The average operation time was 4.18 ± 1.57 hr, and no patients died. No neurologic complications, such as cerebral infarction or paraplegia, were observed during the follow-up period. Conclusions: Three-Dimensional printing can be used to help guide the treatment of aortic arch disease using modified prefenestrated/branched stent grafts. This minimally invasive total treatment technique is accurate, allows quick recovery, and has a low complication rate. The short-term follow-up data show the safety and reliability of the method; however, further research and development are needed.
Y.T and Y.Q. authors contribute equally to this work. Funding: This work was supported by the National Science Foundation for Young Scientists (81600375); Jiangsu Provincial Medical Youth Talent (JQX17003); Fundamental Research Funds for the Central Universities (021414380342); Department of Science and Technology for Social Development of Jiangsu (BE2019604). Department of Vascular Surgery, Nanjing Drum-Tower Hospital, Affiliated to Nanjing University Medical School, Nanjing, Jiangsu, China. Correspondence to: Zhao Liu, Department of Vascular Surgery, Nanjing Drum-Tower Hospital, Affiliated to Nanjing University Medical School, Nanjing, Jiangsu 210008, China; E-mail: [email protected] Ann Vasc Surg 2020; 66: 152–159 https://doi.org/10.1016/j.avsg.2019.12.030 Ó 2020 Elsevier Inc. All rights reserved. Manuscript received: September 10, 2019; manuscript accepted: December 14, 2019; published online: 7 January 2020
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Since the US Food and Drug Administration approved the GoreÒ TAGÒ device (WL Gore & Associates, Flagstaff, AZ) for thoracic endovascular aortic repair (TEVAR) to treat descending aortic aneurysms in 2005,1 TEVAR surgery has been extensively developed in countries across the world and has become one of the preferred methods for the treatment of type B aortic dissections and descending aortic aneurysms. A large number of clinical studies have shown that the rates of early mortality and major complications of TEVAR surgery are superior to those of open surgery.2,3 However, operations on the aortic arch involving important branches of the aorta have high rates of mortality
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and complications, which are still the most difficult and serious challenges to be solved in clinical treatment. Currently, total endovascular techniques to treat aortic arch lesions mainly include the chimney stent graft technique for TEVAR, the branched stent graft technique for TEVAR, and the fenestrated stent graft technique for TEVAR, which are associated with certain technical difficulties. There are few relevant studies in the literature and reports on clinical experience with these techniques, and the safety and efficacy of these techniques remain controversial; the long-term survival rate and outcomes need to be further proven.4 From April 2018 to March 2019, 17 patients with aortic arch lesions were treated with F/B-TEVAR surgery using a modified prefenestrated stent graft guided by threedimensional (3D) printing in our department. Good outcomes were achieved, as reported in the upcomingyfollowing sections.
MATERIALS AND METHODS General Information There were 17 patients in this group, including 13 men and 4 women, aged from 38 to 73 years; 5 cases were aortic arch aneurysm and 12 cases had undergone aortic arch dissection, including 2 cases of retrograde dissection after TEVAR and 3 cases of postoperative endoleak involving the aortic arch, which need secondary surgeries. The main clinical features were as follows: chest pain in 9 cases; physical examination that revealed the condition with no symptoms in 8 cases; and hypertension in 15 cases. Computed tomography angiography (CTA) examination was performed to confirm the diagnosis (Table I). The study protocol was approved by the Institutional Review Board of Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University, and all participants provided written informed consent for the procedure and follow-up. Treatment Preoperative data collection and 3D-printed model preparation. The patients underwent thin-slice enhanced CTA (Brilliance CT6, Philips, Inc., Netherlands, or Discovery CT750 HD, GE, Inc., USA) of the aorta preoperatively (Figs. 1A and 2A). The original data were input into EndoSize software for 3D image reconstruction to measure several key points of the aorta: the aortic lesion (aortic aneurysm or true and false lumen), the proximal and distal side of the anchor zone, the vertical
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Table I. Clinical data of patients with thoracoabdominal aortic disease Characteristics of patients
Male/female Age (years) Risk factors Hypertension Diabetes Hyperlipidemia Coronary heart disease Cerebral infarction History of smoking Pathological classification Thoracic aortic aneurysm Mean diameter of aneurysm (mm) Thoracic aortic dissection Primary lesion Proximal retrograde dissection after TEVAR Endoleak after TEVAR
(n ¼ 17)
13/4 57.82 ± 10.47 15 (88.24%) 2 (11.76%) 6 (35.29%) 3 (17.65%) 2 (11.76%) 9 (52.94%) 5 58.37 ± 4.86 12 7 2 3
TEVAR, thoracic endovascular aortic repair.
and horizontal diameter of important branch arteries, and the length of the lesion. The thickness of the scans was 0.625 mm, which was as same as the 3D models. The surgical plan was made after confirming that the condition of the patient and range and anatomical structure of the lesion were suitable for F/B-TEVAR. First, the collected original data were input into Mimics software (Materialise’s interactive medical image control system, Materialise, Inc., Belgium) for 3D reconstruction of the vessels in the aortic arch area (proximal and distal side of the normal aorta, diseased aorta, and openings of aortic branches.) The 3D reconstruction data were input into design software (Geomagic Studio 2014, Geomagic, Inc., USA) for further preprocessing. Second, nonparametric surface reconstruction of the vessels was performed with reverse engineering technology to obtain a computer-aided design (Autodesk, Inc., USA) mathematical model. Geomagic Design Direct 2014 (Geomagic, Inc., USA) was used for simulation analysis of the model, and in combination with the predesigned surgical plan, the location of the holes of the main branch arteries of the aortic arch was determined. A guide plate was designed and delivered to the 3D printer (Eden260VS, Stratasys, Inc., USA) to complete the preparation of a hollow 3D aortic model similar to the diseased aorta of the patient. It took about 5 hr (1 hr for reconstruction, 3 hr for printing, and 1 hr for postprocessing), and all were performed by technicians. The 3D model was usually printed immediately after receiving the
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Fig. 1. Repair of aortic arch aneurysm with triple prefenestrated stent graft technique guided by 3D printing. (A) Preoperative 3D CT reconstruction; (B) design of the 3D-printed model; (C) release of stent in the model to determine the fenestrations; (D) reduced diameter of
proximal stent; (E) preoperative angiography of the aortic arch; (F) access of long sheath and system for conveying the fenestrated stent; (G) postoperative angiography of the aortic arch; (H) CT reconstruction at 3 months after the surgery. CT, computed tomography.
examination data. We could receive the model on the next day when the patient did CT examination, so it did not delay the treatment. For true aneurysms, the 3D printing models were made according to the actual size, with a wall thickness of about 1 mm. For the dissection aneurysms, we designed the enlargement of the true lumen by ellipse fitting, which was in accordance with the arc of true lumen cross-section and combined with the diameter of the stent graft. The long axis of ellipse took the dividing line of the true and false lumen as a reference. The 3D-printed model (Fig. 1B) was sterilized with ethylene oxide, sealed, and packaged in preparation to guide the surgeon in creating a physicianmodified stent graft (PMSG). Intraoperative PMSG. According to the measurement results of EndoSize software based on the
imaging data of the aortic arch lesion, a thoracic aortic stent (LifeTech Co., China; Medtronic Co., USA) and branch artery stents (Bard Co., USA; Abbot Co., USA) with a postrelease system of appropriate specifications were selected. Different combinations of the main and branch stent were made, and the corresponding guidewire, arterial sheath, and expanding balloon were prepared. According to the proximal anchor zone planned before surgery, the thoracic aortic stent was placed into the hollow 3D-printed model and completely released (Figs. 1C and 2B). Through the openings of the 3D model, the positions of fenestrations or branch stents were marked on the film of the aortic stent with a marker pen. After the stent was removed, the fenestrations were made using an electric pen (CIRX, Inc., China) for cautery on the film where
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Fig. 2. Treatment of type A aortic dissection with triple prefenestrated stent graft technique guided by 3D printing. (A) Preoperative 3D CT reconstruction and crosssectional image; (B) determination of the fenestrations using the model; (C) preoperative angiography of the
aortic arch; (D) in the state of a reduced diameter, the system for conveying the fenestrated stent; (E) postoperative angiography of the aortic arch; (F) CT reconstruction at 3 months after the surgery.
marked in prior. Then, we would trim the edge of the fenestration with microscissors. In principle, the diameter of a fenestration should be slightly smaller than the expected diameter of the implanted branch stent to achieve tight closure and prevent endoleak after implantation of the branch stent. The fenestration diameter was generally 5e7 mm; fenestrations in branch stents could be greater than 10 mm if there were no lacerations in the dissection of the aortic arch. For a large true aneurysm in the aortic arch, as estimated by a large gap
between the stent and the aneurysmal wall, sometimes a 10- to 20-mm-long branch stent sleeve should be sewn onto the fenestration to prevent endoleak at the junction in the late stage. The soft end of a snare guide wire (EV3 Co., USA) or a dehaired platinum spring coil (Cook Co., USA) was sewn up to the edge of the fenestration with 5e0 nonabsorbent sutures to strengthen it and serve as a marker during the operation. An X-rayeproof marker was sewn up to the top of the greater curvature side of the thoracic aortic stent to avoid
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fenestration positioning error caused by torsion during placement of the stent delivery sheath. In addition, 4e0 Prolene sutures and 0.018-inch guidewire were combined on the minor curvature side of the thoracic aortic stent, and a detachable suture method was used to reduce the diameter of the anterior segment of the thoracic aortic stent by 30e40%. The length of the stent, which was generally approximately 100 mm, was adjusted according to the position of the fenestrations (Fig. 1D). The reduced diameter stent could be fine-tuned after being placed to facilitate the intraoperative selection of the branch artery guidewire through the fenestrations and allow sufficient blood flow into the carotid artery, reducing the possibility of stroke. Although the stent graft partially constrained, fenestrations and branches can be released totally because the diameter-reducing wire was positioned on the opposite side of the graft. After being modified, the bare part of the graft was then reconstrained in the top cap, and the entire graft including branches were constained with a sterilized plastic hose and then reloaded into the original existing graft sheath carefully. Then, the graft system was introduced into the sheath with a diameter of 22F in the femoral artery. Placement of aortic and branch stents. The operation was divided into 2 groups. One group of surgeons prepared the PMSGs, whereas the other group prepared the surgical approach. The patient was placed in the supine position under general anesthesia. The right femoral artery, left brachial artery, and the left and right common carotid arteries were usually selected as access arteries via longitudinal incisions 30e50 mm in length. According to the preoperative CTA images, the angle of the digital subtraction angiography (DSA) machine was selected to perform DSA and positioning of the aorta (Figs. 1E and 2C). Heparin (1 mg/kg) was administered intravenously for wholebody heparinization. Via the right femoral artery, the aortic stent sheath was placed at the corresponding part of the aortic arch, and the anterior portion of the aortic stent with a reduced diameter was released. During release of the thoracic aortic stent, the angle of the DSA machine was perpendicular to the longitudinal axis of the aortic arch to ensure that the mark at the greater curvature of the stent was located at the top of the aortic arch. Puncturing was performed from the left and right carotid arteries and left brachial artery. With the stent in a state of a reduced diameter, catheters were placed into the fenestrations. Then, the appropriate long vascular sheath or stent delivery system was placed directly (Figs. 1F and 2D). The guidewire reducing the diameter of the stent was then pulled out, completely releasing the
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thoracic aortic stent. Finally, according to the lesion and the diameter of the branch arteries, the corresponding branch stents were placed. Typically, covered stents were implanted; however, bare stents were implanted in a few innominate arteries of patients. The corresponding balloon was expanded to prevent internal endoleak at the junction. Owing to the reduced diameter of the main stent and fenestrations, the blood supply to the brain was sufficient, and nFo additional bypass technique was required during the operation. Ascending aorta and aortic arch angiography were performed to confirm the patency of each branch artery and the presence of endoleak to ultimately complete the F/B-TEVAR surgery (Figs. 1G and 2E).
RESULTS AND ANALYSIS In this study, under the guidance of 3D printing, 17 patients with aortic arch lesions were treated by total endovascular therapy with PMSGs, and 19 branches were added in cases where there was a gap to the aortic wall in total; 16 patients were successfully operated as planned, whereas 1 patient was treated with a chimney stent and in situ fenestration. The technical success rate was 94.18%, with no surgical deaths. The mean operation time was 4.18 ± 1.57 hr, including the mean duration required for custom stent preparation (1.25 ± 0.46 hr), and the mean endovascular operation time was (2.07 ± 0.54 hr). The mean intraoperative blood loss was 418.25 ± 157.64 mL, and the transfusion volume was 0e1,000 mL. The mean contrast agent volume was 225.45 ± 46.13 mL, and the mean radiation dose was 2,731.52 ± 550.62 mGy. The mean postoperative ICU monitoring time was 0.65 day (0e3 day), and the mean postoperative hospitalization duration was 8.72 ± 2.93 day (Table II). All 17 patients were followed up for 3 to 14 months, with a mean of 6 months. The occurrence rate of cerebral infarction, paraplegia, and other neurologic complications was zero. No deaths occurred. The aortic CTA follow-up examinations at 3 and 6 months after the surgery indicated that all 3 branches of the aortic arch were unobstructed, and thrombosis of the aneurysm cavity or dissection was observed without aneurysm enlargement or retrograde dissection. There was a small endoleak at the junction of the stent in one case, which was considered to be related to the implantation of a bare stent in the innominate artery; this patient was closely followed up. Typical follow-up CT images in this case are provided (Figs. 1H and 2F).
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Table II. Summary of operations Characteristics of patients
Average operation time (hr) Mean time for custom stent preparation (hr) Mean endovascular operation time (hr) Mean intraoperative blood loss volume (mL) Mean contrast agent volume (mL) Mean radiation dose (mGy) Mean postoperative ICU monitoring duration (day) Mean postoperative hospitalization duration (day) Average number of implanted aortic stents (n) Mean aortic lesion coverage length (cm) Triple prefenestrated stent graft Double prefenestrated stent graft + single in situ fenestrated stent graft Single prefenestrated stent graft + double in situ fenestrated stent graft
(n ¼ 17)
4.18 ± 1.57 1.25 ± 0.46 2.07 ± 0.54 418.25 ± 157.64 225.45 ± 46.13 2,731.52 ± 550.62 0.65 (0e3) 8.72 ± 2.93 1.62 (0e3) 22.54 ± 3.81 12 3
2
DISCUSSION As aortic arch lesions involve the ascending aorta and important branches of the aortic arch, conventional TEVAR cannot be used to treat them. Currently, the chimney technique is one of the most widely used techniques and consists of a simple operation with low technical difficulty. However, current research has shown that the 3-yr patency rate of the chimney stent technique is 88% and that the incidence of endoleak could reach 22%.5,6 The fenestrated or branch stent graft technique provides a physiologically based total endovascular repair method for the treatment of aortic arch lesions. The use of an in situ fenestrated stent graft technique can prevent the inaccurate positioning of prefenestrated stent grafts. However, the use of an in situ fenestrated stent graft technique for the 3 branches of the aortic arch requires temporary bypass to ensure a sufficient blood supply to the brain because all 3 branches are blocked at the same time. This operation is complicated and easily causes brain-related complications. With the traditional prefenestrated stent graft technique,7,8 the appropriate position of the fenestrations could be selected, and a good therapeutic effect could be achieved with accurate intraoperative positioning. Nonetheless, owing to the complex anatomical
structure of the aortic arch, improper positioning is likely to occur, and once an important artery of the aortic arch is lost, severe brain complications also become more likely to occur. 3D printing, also known as rapid prototyping, can transform a virtual digitized model into a physical 3D model of various materials.9,10 It has shown great potential and value for applications in many fields and has been increasingly applied in the medical field, especially in the clinical diagnosis and treatment of cardiovascular diseases in recent years, which has attracted the attention of many scholars. The original data for 3D printing can be obtained by CT or magnetic resonance imaging to yield an individualized 3D reconstruction based on the complex anatomy of cardiovascular lesions. This model helps doctors to understand the abnormal cardiovascular structure of various complex lesions more directly in comparison with 3D CTA images.11 Modified 3D-printed medical models can be used to help make a clinical diagnosis, select the best surgical method, predict intraoperative challenges and pitfalls, train young surgeons, make or improve grafts in vitro (e.g., stent or bone grafts), and determine the appropriate position in transplantation, among others.12 Owing to the complex anatomical structure of the aortic arch and the important artery branches, it is difficult to observe and measure the true 3D relationship between these structures and an aortic lesion using conventional CT images. Reconstructions and 3D-printed models can help doctors directly understand and determine the relationship of an aortic aneurysm or dissection with arterial branches to facilitate surgical planning and provide guidance during TEVAR for these life-threatening arterial conditions. Moreover, such models can be used to simulate the endovascular release of stents and the position of fenestrations to create a PMSG. It is very important that 3D-printed anatomical models of the aortic arch have high precision. Without high precision, surgeons cannot plan the operation confidently and accurately according to the model. Ho et al.13 compared the contrastenhanced CT results and 3D-printed models of patient arteries, and the error was less than 1 mm, which is clinically acceptable. The fenestrated or branched stent graft technique is currently the most ideal technique for the endovascular repair of aortic arch lesions.14,15 There are 2 ways to prepare a prefenestrated stent graft: (1) with manufacturer customization, the stent graft is modifiable according to the CT data of patients, which takes a long time (more than 6 weeks) and is expensive16; and (2) with intraoperative PMSG
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preparation, which is simple, rapid, and less expensive. Such methods have been used for TEVAR in zones Z0 to Z2.17 It is required to mark the stent graft based on the CTA results to create the fenestrations and PMSG, but it is very difficult to position the fenestrations accurately according to the target lesions of the vessels and the spatial distribution of the branch arteries. In vivo release may result in dislocation of the fenestrations, especially in cases of severe twisting of the aortic arch and abnormal arterial structures. The use of a 3D-printed aortic template can improve the accuracy of fenestration positioning. Reducing the stent diameter creates a gap between the stent and aorta during the operation, which enables more flexible fenestration positioning without blocking the blood flow of important branches of the aorta. Currently, in China, Ankura (LifeTech Co., China) and Captivia (Medtronic Co., USA) are the major aortic stent graft systems that meet the requirements of creating a PMSG for the aortic arch. Both stents have a postrelease device, which can be completely released in vitro. After reconstruction and 3D printing, the stent can be transported into the sheath. The Ankura stent graft system has a reinforcing metal structure on the greater curvature, which can be used as a positioning marker such that the stent does not easily twist during the operation. However, its conveying sheath is relatively thick, which could cause certain difficulties if the access artery is diseased or the aorta is twisted. The Captivia stent graft system is designed without a reinforcing metal structure, and the conveying sheath is thin and soft, which helps to pass through the complex anatomical structures of the aorta. However, due to the lack of a marker on the greater curvature and because the stent can easily twist during adjustment, it is necessary to not only sew on a counterpoint marker but also take extra care to prevent the main body of the stent from folding during the operation. Although the 3D printing technique allows more precise fenestration positioning and a reduction in the stent diameter to facilitate placement, improper positioning of the fenestrations for the branch arteries could still occur during the operation. In this study, improper positioning occurred in one patient, who was the second patient to undergo treatment with the technique since it was developed in our department. This result is related to the learning curve of the technique and the anatomical distortion of the aortic arch in the patient. Therefore, materials for both the chimney stent graft technique and the in situ fenestrated stent graft technique should be prepared as supplementary measures if
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improper positioning occurs during the operation. If necessary, traditional open surgery of the aortic arch should be performed to save the life of the patient. Open surgery for aortic arch lesions (aortic dissection and aortic aneurysm) is complicated, takes a long time, and causes a great deal of intraoperative bleeding. The method requires extracorporeal circulation and hypothermia, causes major surgical trauma, and has high rates of complications and mortality. Despite the rapid development of TEVAR surgery in the treatment of aortic lesions in recent years, many problems remain to be solved. The prefenestrated stent graft technique guided by 3D printing to treat complex aortic arch lesions provides a new approach to solve these problems. The advantages of the new surgical method applied by the authors are as follows: (1) A PMSG could be prepared using an existing commercially available thoracic aortic stent with low cost, and preparation of the 3D-printed model could be completed in a short time, that is, 6 hr, which could even be applied in emergent cases.18 (2) The operation is relatively simple, and the learning curve is short, such that experienced vascular surgeons could master the operation quickly after a short training period. (3) The 3D-printed model greatly improved the accuracy of the in vitro prefenestrated stent graft technique for treating lesions of the complex anatomical structures of the aortic arch. (4) The operation is convenient and safe, with minor trauma, fast recovery, and reduced bleeding. Generally, blood transfusions, extracorporeal circulation, and hypothermic circulation arrest are not required. (5) Because a sufficient blood supply to the brain is maintained when the thoracic aortic stent with fenestrations and a reduced diameter is placed, the complicated procedure for in vitro bypass, which is performed for the in situ fenestrated stent graft technique, can be avoided, significantly reducing brain-related complications. Early postoperative follow-up data show no cases of mortality and a low rate of endoleak, but the medium- and longterm results need further research.
REFERENCES 1. Makaroun MS, Dillavou ED, Kee SD, et al. Endovas- cular treatment of thoracic aortic aneurysms: results of the phase II multicenter trial of the GORE TAG thoracic endoprosthesis. J Vasc Surg 2005;41:1e9. 2. Cheng D, Martin J, Shennib H, et al. Endovascular aortic repair versus open surgical repair for descending thoracic aortic disease a systematic review and meta-analysis of comparative studies. J Am Coll Cardiol 2010;55:986e1001.
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3. Bell D, Bassin L, Neale M, et al. A review of the endovascular management of thoracic aortic pathology. Heart Lung Circ 2015;24:1211e5. 4. Goodney PP, Travis L, Lucas FL, et al. Survival after open versus endovascular thoracic aortic aneurysm repair in an observational study of the medicare population. Circulation 2011;124:2661e9. 5. Ohrlander T, Sonesson B, Ivancev K, et al. The chimney graft: a technique for preserving or rescuing aortic branch vessels in stent-graft sealing zones. J Endovasc Ther 2008;15:427e32. 6. Scali ST, Feezor RJ, Chang CK, et al. Critical analysis of results after chimney endovascular aortic aneurysm repair raises cause for concern. J Vasc Surg 2014;60: 865e73. 7. Iwakoshi S, Ichihashi S, Itoh H, et al. Clinical outcomes of thoracic endovascular aneurysm repair using commercially available fenestrated stent graft (Najuta endograft). J Vasc Surg 2015;62:1473e8. 8. Tan GWL, Quek L, Tan BP, et al. Early experience and lessons learnt with customized fenestrated thoracic endovascular aortic reconstruction for aortic arch pathology in an Asian population. Cardiovasc Intervent Radiol 2018;41: 544e53. 9. Salloum C, Lim C, Fuentes L, et al. Fusion of information from 3D printing and surgical robot: an innovative minimally technique illustrated by the resection of a large celiac trunk aneurysm. World J Surg 2016;40:245e7.
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10. Bangeas P, Voulalas G, Ktenidis K. Rapid prototyping in aortic surgery. Interact Cardiovasc Thorac Surg 2016;22:513e4. 11. Shi D, Liu K, Zhang X, et al. Applications of threedimensional printing technology in the cardiovascular field. Intern Emerg Med 2015;10:769e80. 12. Youssef RF, Spradling K, Yoon R, et al. Applications of threedimensional printing technology in urological practice. BJU Int 2015;116:697e702. 13. Ho D, Squelch A, Sun Z. Modelling of aortic aneurysm and aortic dissection through 3D printing. J Med Radiat Sci 2017;64:10e7. 14. Joseph G, Premkumar P, Thomson V, et al. Externalized guidewires to facilitate fenestrated endograft deployment in the aortic arch. J Endovasc Ther 2016;23:160e71. 15. Barbante M, Sobocinski J, Maurel B, et al. Fenestrated endografting after bare metal dissection stent implantation. J Endovasc Ther 2015;22:207e11. 16. Michel M, Becquemin JP, Clement MC, et al. Editor’s choice - thirty day outcomes and costs of fenestrated and branched stent grafts versus open repair for complex aortic aneurysms. Eur J Vasc Endovasc Surg 2015;50:189e96. 17. Tsilimparis N, Heidemann F, Rohlffs F, et al. Outcome of surgeon-modified fenestrated/branched stent-grafts for symptomatic complex aortic pathologies or contained rupture. J Endovasc Ther 2017;24:825e32. 18. Huang J, Li G, Wang W, et al. 3D printing guiding stent graft fenestration: a novel technique for fenestration in endovascular aneurysm repair. Vascular 2017;25:442e6.
Background: The aim of this study was to summarize the experience and outcomes of total endovascular repair of aortic arch disease using three-dimensional (3D) printing to guide the application of modified prefenestrated/branched stent grafts. Patients and methods: From April 2018 to March 2019, 17 patients with aortic arch disease were treated in our department. Five patients had an aortic arch aneurysm and 12 had undergone an aortic arch dissection. Thirteen men and 4 were women, with an average age of 57.82 ± 10.47 years. Preoperatively, a 3D-printed model of the aorta was made according to computed tomography data. Then, under the guidance of the 3D-printed aortic model, modified prefenestrated/branched stent grafts were prepared, and the diameter of the stent grafts was reduced intraoperatively by a physician for total endovascular repair. Aortic computed tomography angiography was performed 3 and 6 months after the surgery. Results: All procedures were completed in one stage with no conversions to sternotomy. Among all 17 patients, the operation was successful in 16. One patient was treated with a chimney graft and a stent graft fenestrated in situ because of distortion of the stent. The success rate of the technique was 94.18%. The average operation time was 4.18 ± 1.57 hr, and no patients died. No neurologic complications, such as cerebral infarction or paraplegia, were observed during the follow-up period. Conclusions: Three-Dimensional printing can be used to help guide the treatment of aortic arch disease using modified prefenestrated/branched stent grafts. This minimally invasive total treatment technique is accurate, allows quick recovery, and has a low complication rate. The short-term follow-up data show the safety and reliability of the method; however, further research and development are needed.
Y.T and Y.Q. authors contribute equally to this work. Funding: This work was supported by the National Science Foundation for Young Scientists (81600375); Jiangsu Provincial Medical Youth Talent (JQX17003); Fundamental Research Funds for the Central Universities (021414380342); Department of Science and Technology for Social Development of Jiangsu (BE2019604). Department of Vascular Surgery, Nanjing Drum-Tower Hospital, Affiliated to Nanjing University Medical School, Nanjing, Jiangsu, China. Correspondence to: Zhao Liu, Department of Vascular Surgery, Nanjing Drum-Tower Hospital, Affiliated to Nanjing University Medical School, Nanjing, Jiangsu 210008, China; E-mail: [email protected] Ann Vasc Surg 2020; 66: 152–159 https://doi.org/10.1016/j.avsg.2019.12.030 Ó 2020 Elsevier Inc. All rights reserved. Manuscript received: September 10, 2019; manuscript accepted: December 14, 2019; published online: 7 January 2020
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Since the US Food and Drug Administration approved the GoreÒ TAGÒ device (WL Gore & Associates, Flagstaff, AZ) for thoracic endovascular aortic repair (TEVAR) to treat descending aortic aneurysms in 2005,1 TEVAR surgery has been extensively developed in countries across the world and has become one of the preferred methods for the treatment of type B aortic dissections and descending aortic aneurysms. A large number of clinical studies have shown that the rates of early mortality and major complications of TEVAR surgery are superior to those of open surgery.2,3 However, operations on the aortic arch involving important branches of the aorta have high rates of mortality
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and complications, which are still the most difficult and serious challenges to be solved in clinical treatment. Currently, total endovascular techniques to treat aortic arch lesions mainly include the chimney stent graft technique for TEVAR, the branched stent graft technique for TEVAR, and the fenestrated stent graft technique for TEVAR, which are associated with certain technical difficulties. There are few relevant studies in the literature and reports on clinical experience with these techniques, and the safety and efficacy of these techniques remain controversial; the long-term survival rate and outcomes need to be further proven.4 From April 2018 to March 2019, 17 patients with aortic arch lesions were treated with F/B-TEVAR surgery using a modified prefenestrated stent graft guided by threedimensional (3D) printing in our department. Good outcomes were achieved, as reported in the upcomingyfollowing sections.
MATERIALS AND METHODS General Information There were 17 patients in this group, including 13 men and 4 women, aged from 38 to 73 years; 5 cases were aortic arch aneurysm and 12 cases had undergone aortic arch dissection, including 2 cases of retrograde dissection after TEVAR and 3 cases of postoperative endoleak involving the aortic arch, which need secondary surgeries. The main clinical features were as follows: chest pain in 9 cases; physical examination that revealed the condition with no symptoms in 8 cases; and hypertension in 15 cases. Computed tomography angiography (CTA) examination was performed to confirm the diagnosis (Table I). The study protocol was approved by the Institutional Review Board of Nanjing Drum Tower Hospital, The Affiliated Hospital of Nanjing University, and all participants provided written informed consent for the procedure and follow-up. Treatment Preoperative data collection and 3D-printed model preparation. The patients underwent thin-slice enhanced CTA (Brilliance CT6, Philips, Inc., Netherlands, or Discovery CT750 HD, GE, Inc., USA) of the aorta preoperatively (Figs. 1A and 2A). The original data were input into EndoSize software for 3D image reconstruction to measure several key points of the aorta: the aortic lesion (aortic aneurysm or true and false lumen), the proximal and distal side of the anchor zone, the vertical
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Table I. Clinical data of patients with thoracoabdominal aortic disease Characteristics of patients
Male/female Age (years) Risk factors Hypertension Diabetes Hyperlipidemia Coronary heart disease Cerebral infarction History of smoking Pathological classification Thoracic aortic aneurysm Mean diameter of aneurysm (mm) Thoracic aortic dissection Primary lesion Proximal retrograde dissection after TEVAR Endoleak after TEVAR
(n ¼ 17)
13/4 57.82 ± 10.47 15 (88.24%) 2 (11.76%) 6 (35.29%) 3 (17.65%) 2 (11.76%) 9 (52.94%) 5 58.37 ± 4.86 12 7 2 3
TEVAR, thoracic endovascular aortic repair.
and horizontal diameter of important branch arteries, and the length of the lesion. The thickness of the scans was 0.625 mm, which was as same as the 3D models. The surgical plan was made after confirming that the condition of the patient and range and anatomical structure of the lesion were suitable for F/B-TEVAR. First, the collected original data were input into Mimics software (Materialise’s interactive medical image control system, Materialise, Inc., Belgium) for 3D reconstruction of the vessels in the aortic arch area (proximal and distal side of the normal aorta, diseased aorta, and openings of aortic branches.) The 3D reconstruction data were input into design software (Geomagic Studio 2014, Geomagic, Inc., USA) for further preprocessing. Second, nonparametric surface reconstruction of the vessels was performed with reverse engineering technology to obtain a computer-aided design (Autodesk, Inc., USA) mathematical model. Geomagic Design Direct 2014 (Geomagic, Inc., USA) was used for simulation analysis of the model, and in combination with the predesigned surgical plan, the location of the holes of the main branch arteries of the aortic arch was determined. A guide plate was designed and delivered to the 3D printer (Eden260VS, Stratasys, Inc., USA) to complete the preparation of a hollow 3D aortic model similar to the diseased aorta of the patient. It took about 5 hr (1 hr for reconstruction, 3 hr for printing, and 1 hr for postprocessing), and all were performed by technicians. The 3D model was usually printed immediately after receiving the
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Fig. 1. Repair of aortic arch aneurysm with triple prefenestrated stent graft technique guided by 3D printing. (A) Preoperative 3D CT reconstruction; (B) design of the 3D-printed model; (C) release of stent in the model to determine the fenestrations; (D) reduced diameter of
proximal stent; (E) preoperative angiography of the aortic arch; (F) access of long sheath and system for conveying the fenestrated stent; (G) postoperative angiography of the aortic arch; (H) CT reconstruction at 3 months after the surgery. CT, computed tomography.
examination data. We could receive the model on the next day when the patient did CT examination, so it did not delay the treatment. For true aneurysms, the 3D printing models were made according to the actual size, with a wall thickness of about 1 mm. For the dissection aneurysms, we designed the enlargement of the true lumen by ellipse fitting, which was in accordance with the arc of true lumen cross-section and combined with the diameter of the stent graft. The long axis of ellipse took the dividing line of the true and false lumen as a reference. The 3D-printed model (Fig. 1B) was sterilized with ethylene oxide, sealed, and packaged in preparation to guide the surgeon in creating a physicianmodified stent graft (PMSG). Intraoperative PMSG. According to the measurement results of EndoSize software based on the
imaging data of the aortic arch lesion, a thoracic aortic stent (LifeTech Co., China; Medtronic Co., USA) and branch artery stents (Bard Co., USA; Abbot Co., USA) with a postrelease system of appropriate specifications were selected. Different combinations of the main and branch stent were made, and the corresponding guidewire, arterial sheath, and expanding balloon were prepared. According to the proximal anchor zone planned before surgery, the thoracic aortic stent was placed into the hollow 3D-printed model and completely released (Figs. 1C and 2B). Through the openings of the 3D model, the positions of fenestrations or branch stents were marked on the film of the aortic stent with a marker pen. After the stent was removed, the fenestrations were made using an electric pen (CIRX, Inc., China) for cautery on the film where
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Fig. 2. Treatment of type A aortic dissection with triple prefenestrated stent graft technique guided by 3D printing. (A) Preoperative 3D CT reconstruction and crosssectional image; (B) determination of the fenestrations using the model; (C) preoperative angiography of the
aortic arch; (D) in the state of a reduced diameter, the system for conveying the fenestrated stent; (E) postoperative angiography of the aortic arch; (F) CT reconstruction at 3 months after the surgery.
marked in prior. Then, we would trim the edge of the fenestration with microscissors. In principle, the diameter of a fenestration should be slightly smaller than the expected diameter of the implanted branch stent to achieve tight closure and prevent endoleak after implantation of the branch stent. The fenestration diameter was generally 5e7 mm; fenestrations in branch stents could be greater than 10 mm if there were no lacerations in the dissection of the aortic arch. For a large true aneurysm in the aortic arch, as estimated by a large gap
between the stent and the aneurysmal wall, sometimes a 10- to 20-mm-long branch stent sleeve should be sewn onto the fenestration to prevent endoleak at the junction in the late stage. The soft end of a snare guide wire (EV3 Co., USA) or a dehaired platinum spring coil (Cook Co., USA) was sewn up to the edge of the fenestration with 5e0 nonabsorbent sutures to strengthen it and serve as a marker during the operation. An X-rayeproof marker was sewn up to the top of the greater curvature side of the thoracic aortic stent to avoid
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fenestration positioning error caused by torsion during placement of the stent delivery sheath. In addition, 4e0 Prolene sutures and 0.018-inch guidewire were combined on the minor curvature side of the thoracic aortic stent, and a detachable suture method was used to reduce the diameter of the anterior segment of the thoracic aortic stent by 30e40%. The length of the stent, which was generally approximately 100 mm, was adjusted according to the position of the fenestrations (Fig. 1D). The reduced diameter stent could be fine-tuned after being placed to facilitate the intraoperative selection of the branch artery guidewire through the fenestrations and allow sufficient blood flow into the carotid artery, reducing the possibility of stroke. Although the stent graft partially constrained, fenestrations and branches can be released totally because the diameter-reducing wire was positioned on the opposite side of the graft. After being modified, the bare part of the graft was then reconstrained in the top cap, and the entire graft including branches were constained with a sterilized plastic hose and then reloaded into the original existing graft sheath carefully. Then, the graft system was introduced into the sheath with a diameter of 22F in the femoral artery. Placement of aortic and branch stents. The operation was divided into 2 groups. One group of surgeons prepared the PMSGs, whereas the other group prepared the surgical approach. The patient was placed in the supine position under general anesthesia. The right femoral artery, left brachial artery, and the left and right common carotid arteries were usually selected as access arteries via longitudinal incisions 30e50 mm in length. According to the preoperative CTA images, the angle of the digital subtraction angiography (DSA) machine was selected to perform DSA and positioning of the aorta (Figs. 1E and 2C). Heparin (1 mg/kg) was administered intravenously for wholebody heparinization. Via the right femoral artery, the aortic stent sheath was placed at the corresponding part of the aortic arch, and the anterior portion of the aortic stent with a reduced diameter was released. During release of the thoracic aortic stent, the angle of the DSA machine was perpendicular to the longitudinal axis of the aortic arch to ensure that the mark at the greater curvature of the stent was located at the top of the aortic arch. Puncturing was performed from the left and right carotid arteries and left brachial artery. With the stent in a state of a reduced diameter, catheters were placed into the fenestrations. Then, the appropriate long vascular sheath or stent delivery system was placed directly (Figs. 1F and 2D). The guidewire reducing the diameter of the stent was then pulled out, completely releasing the
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thoracic aortic stent. Finally, according to the lesion and the diameter of the branch arteries, the corresponding branch stents were placed. Typically, covered stents were implanted; however, bare stents were implanted in a few innominate arteries of patients. The corresponding balloon was expanded to prevent internal endoleak at the junction. Owing to the reduced diameter of the main stent and fenestrations, the blood supply to the brain was sufficient, and nFo additional bypass technique was required during the operation. Ascending aorta and aortic arch angiography were performed to confirm the patency of each branch artery and the presence of endoleak to ultimately complete the F/B-TEVAR surgery (Figs. 1G and 2E).
RESULTS AND ANALYSIS In this study, under the guidance of 3D printing, 17 patients with aortic arch lesions were treated by total endovascular therapy with PMSGs, and 19 branches were added in cases where there was a gap to the aortic wall in total; 16 patients were successfully operated as planned, whereas 1 patient was treated with a chimney stent and in situ fenestration. The technical success rate was 94.18%, with no surgical deaths. The mean operation time was 4.18 ± 1.57 hr, including the mean duration required for custom stent preparation (1.25 ± 0.46 hr), and the mean endovascular operation time was (2.07 ± 0.54 hr). The mean intraoperative blood loss was 418.25 ± 157.64 mL, and the transfusion volume was 0e1,000 mL. The mean contrast agent volume was 225.45 ± 46.13 mL, and the mean radiation dose was 2,731.52 ± 550.62 mGy. The mean postoperative ICU monitoring time was 0.65 day (0e3 day), and the mean postoperative hospitalization duration was 8.72 ± 2.93 day (Table II). All 17 patients were followed up for 3 to 14 months, with a mean of 6 months. The occurrence rate of cerebral infarction, paraplegia, and other neurologic complications was zero. No deaths occurred. The aortic CTA follow-up examinations at 3 and 6 months after the surgery indicated that all 3 branches of the aortic arch were unobstructed, and thrombosis of the aneurysm cavity or dissection was observed without aneurysm enlargement or retrograde dissection. There was a small endoleak at the junction of the stent in one case, which was considered to be related to the implantation of a bare stent in the innominate artery; this patient was closely followed up. Typical follow-up CT images in this case are provided (Figs. 1H and 2F).
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Table II. Summary of operations Characteristics of patients
Average operation time (hr) Mean time for custom stent preparation (hr) Mean endovascular operation time (hr) Mean intraoperative blood loss volume (mL) Mean contrast agent volume (mL) Mean radiation dose (mGy) Mean postoperative ICU monitoring duration (day) Mean postoperative hospitalization duration (day) Average number of implanted aortic stents (n) Mean aortic lesion coverage length (cm) Triple prefenestrated stent graft Double prefenestrated stent graft + single in situ fenestrated stent graft Single prefenestrated stent graft + double in situ fenestrated stent graft
(n ¼ 17)
4.18 ± 1.57 1.25 ± 0.46 2.07 ± 0.54 418.25 ± 157.64 225.45 ± 46.13 2,731.52 ± 550.62 0.65 (0e3) 8.72 ± 2.93 1.62 (0e3) 22.54 ± 3.81 12 3
2
DISCUSSION As aortic arch lesions involve the ascending aorta and important branches of the aortic arch, conventional TEVAR cannot be used to treat them. Currently, the chimney technique is one of the most widely used techniques and consists of a simple operation with low technical difficulty. However, current research has shown that the 3-yr patency rate of the chimney stent technique is 88% and that the incidence of endoleak could reach 22%.5,6 The fenestrated or branch stent graft technique provides a physiologically based total endovascular repair method for the treatment of aortic arch lesions. The use of an in situ fenestrated stent graft technique can prevent the inaccurate positioning of prefenestrated stent grafts. However, the use of an in situ fenestrated stent graft technique for the 3 branches of the aortic arch requires temporary bypass to ensure a sufficient blood supply to the brain because all 3 branches are blocked at the same time. This operation is complicated and easily causes brain-related complications. With the traditional prefenestrated stent graft technique,7,8 the appropriate position of the fenestrations could be selected, and a good therapeutic effect could be achieved with accurate intraoperative positioning. Nonetheless, owing to the complex anatomical
structure of the aortic arch, improper positioning is likely to occur, and once an important artery of the aortic arch is lost, severe brain complications also become more likely to occur. 3D printing, also known as rapid prototyping, can transform a virtual digitized model into a physical 3D model of various materials.9,10 It has shown great potential and value for applications in many fields and has been increasingly applied in the medical field, especially in the clinical diagnosis and treatment of cardiovascular diseases in recent years, which has attracted the attention of many scholars. The original data for 3D printing can be obtained by CT or magnetic resonance imaging to yield an individualized 3D reconstruction based on the complex anatomy of cardiovascular lesions. This model helps doctors to understand the abnormal cardiovascular structure of various complex lesions more directly in comparison with 3D CTA images.11 Modified 3D-printed medical models can be used to help make a clinical diagnosis, select the best surgical method, predict intraoperative challenges and pitfalls, train young surgeons, make or improve grafts in vitro (e.g., stent or bone grafts), and determine the appropriate position in transplantation, among others.12 Owing to the complex anatomical structure of the aortic arch and the important artery branches, it is difficult to observe and measure the true 3D relationship between these structures and an aortic lesion using conventional CT images. Reconstructions and 3D-printed models can help doctors directly understand and determine the relationship of an aortic aneurysm or dissection with arterial branches to facilitate surgical planning and provide guidance during TEVAR for these life-threatening arterial conditions. Moreover, such models can be used to simulate the endovascular release of stents and the position of fenestrations to create a PMSG. It is very important that 3D-printed anatomical models of the aortic arch have high precision. Without high precision, surgeons cannot plan the operation confidently and accurately according to the model. Ho et al.13 compared the contrastenhanced CT results and 3D-printed models of patient arteries, and the error was less than 1 mm, which is clinically acceptable. The fenestrated or branched stent graft technique is currently the most ideal technique for the endovascular repair of aortic arch lesions.14,15 There are 2 ways to prepare a prefenestrated stent graft: (1) with manufacturer customization, the stent graft is modifiable according to the CT data of patients, which takes a long time (more than 6 weeks) and is expensive16; and (2) with intraoperative PMSG
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preparation, which is simple, rapid, and less expensive. Such methods have been used for TEVAR in zones Z0 to Z2.17 It is required to mark the stent graft based on the CTA results to create the fenestrations and PMSG, but it is very difficult to position the fenestrations accurately according to the target lesions of the vessels and the spatial distribution of the branch arteries. In vivo release may result in dislocation of the fenestrations, especially in cases of severe twisting of the aortic arch and abnormal arterial structures. The use of a 3D-printed aortic template can improve the accuracy of fenestration positioning. Reducing the stent diameter creates a gap between the stent and aorta during the operation, which enables more flexible fenestration positioning without blocking the blood flow of important branches of the aorta. Currently, in China, Ankura (LifeTech Co., China) and Captivia (Medtronic Co., USA) are the major aortic stent graft systems that meet the requirements of creating a PMSG for the aortic arch. Both stents have a postrelease device, which can be completely released in vitro. After reconstruction and 3D printing, the stent can be transported into the sheath. The Ankura stent graft system has a reinforcing metal structure on the greater curvature, which can be used as a positioning marker such that the stent does not easily twist during the operation. However, its conveying sheath is relatively thick, which could cause certain difficulties if the access artery is diseased or the aorta is twisted. The Captivia stent graft system is designed without a reinforcing metal structure, and the conveying sheath is thin and soft, which helps to pass through the complex anatomical structures of the aorta. However, due to the lack of a marker on the greater curvature and because the stent can easily twist during adjustment, it is necessary to not only sew on a counterpoint marker but also take extra care to prevent the main body of the stent from folding during the operation. Although the 3D printing technique allows more precise fenestration positioning and a reduction in the stent diameter to facilitate placement, improper positioning of the fenestrations for the branch arteries could still occur during the operation. In this study, improper positioning occurred in one patient, who was the second patient to undergo treatment with the technique since it was developed in our department. This result is related to the learning curve of the technique and the anatomical distortion of the aortic arch in the patient. Therefore, materials for both the chimney stent graft technique and the in situ fenestrated stent graft technique should be prepared as supplementary measures if
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improper positioning occurs during the operation. If necessary, traditional open surgery of the aortic arch should be performed to save the life of the patient. Open surgery for aortic arch lesions (aortic dissection and aortic aneurysm) is complicated, takes a long time, and causes a great deal of intraoperative bleeding. The method requires extracorporeal circulation and hypothermia, causes major surgical trauma, and has high rates of complications and mortality. Despite the rapid development of TEVAR surgery in the treatment of aortic lesions in recent years, many problems remain to be solved. The prefenestrated stent graft technique guided by 3D printing to treat complex aortic arch lesions provides a new approach to solve these problems. The advantages of the new surgical method applied by the authors are as follows: (1) A PMSG could be prepared using an existing commercially available thoracic aortic stent with low cost, and preparation of the 3D-printed model could be completed in a short time, that is, 6 hr, which could even be applied in emergent cases.18 (2) The operation is relatively simple, and the learning curve is short, such that experienced vascular surgeons could master the operation quickly after a short training period. (3) The 3D-printed model greatly improved the accuracy of the in vitro prefenestrated stent graft technique for treating lesions of the complex anatomical structures of the aortic arch. (4) The operation is convenient and safe, with minor trauma, fast recovery, and reduced bleeding. Generally, blood transfusions, extracorporeal circulation, and hypothermic circulation arrest are not required. (5) Because a sufficient blood supply to the brain is maintained when the thoracic aortic stent with fenestrations and a reduced diameter is placed, the complicated procedure for in vitro bypass, which is performed for the in situ fenestrated stent graft technique, can be avoided, significantly reducing brain-related complications. Early postoperative follow-up data show no cases of mortality and a low rate of endoleak, but the medium- and longterm results need further research.
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3. Bell D, Bassin L, Neale M, et al. A review of the endovascular management of thoracic aortic pathology. Heart Lung Circ 2015;24:1211e5. 4. Goodney PP, Travis L, Lucas FL, et al. Survival after open versus endovascular thoracic aortic aneurysm repair in an observational study of the medicare population. Circulation 2011;124:2661e9. 5. Ohrlander T, Sonesson B, Ivancev K, et al. The chimney graft: a technique for preserving or rescuing aortic branch vessels in stent-graft sealing zones. J Endovasc Ther 2008;15:427e32. 6. Scali ST, Feezor RJ, Chang CK, et al. Critical analysis of results after chimney endovascular aortic aneurysm repair raises cause for concern. J Vasc Surg 2014;60: 865e73. 7. Iwakoshi S, Ichihashi S, Itoh H, et al. Clinical outcomes of thoracic endovascular aneurysm repair using commercially available fenestrated stent graft (Najuta endograft). J Vasc Surg 2015;62:1473e8. 8. Tan GWL, Quek L, Tan BP, et al. Early experience and lessons learnt with customized fenestrated thoracic endovascular aortic reconstruction for aortic arch pathology in an Asian population. Cardiovasc Intervent Radiol 2018;41: 544e53. 9. Salloum C, Lim C, Fuentes L, et al. Fusion of information from 3D printing and surgical robot: an innovative minimally technique illustrated by the resection of a large celiac trunk aneurysm. World J Surg 2016;40:245e7.
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10. Bangeas P, Voulalas G, Ktenidis K. Rapid prototyping in aortic surgery. Interact Cardiovasc Thorac Surg 2016;22:513e4. 11. Shi D, Liu K, Zhang X, et al. Applications of threedimensional printing technology in the cardiovascular field. Intern Emerg Med 2015;10:769e80. 12. Youssef RF, Spradling K, Yoon R, et al. Applications of threedimensional printing technology in urological practice. BJU Int 2015;116:697e702. 13. Ho D, Squelch A, Sun Z. Modelling of aortic aneurysm and aortic dissection through 3D printing. J Med Radiat Sci 2017;64:10e7. 14. Joseph G, Premkumar P, Thomson V, et al. Externalized guidewires to facilitate fenestrated endograft deployment in the aortic arch. J Endovasc Ther 2016;23:160e71. 15. Barbante M, Sobocinski J, Maurel B, et al. Fenestrated endografting after bare metal dissection stent implantation. J Endovasc Ther 2015;22:207e11. 16. Michel M, Becquemin JP, Clement MC, et al. Editor’s choice - thirty day outcomes and costs of fenestrated and branched stent grafts versus open repair for complex aortic aneurysms. Eur J Vasc Endovasc Surg 2015;50:189e96. 17. Tsilimparis N, Heidemann F, Rohlffs F, et al. Outcome of surgeon-modified fenestrated/branched stent-grafts for symptomatic complex aortic pathologies or contained rupture. J Endovasc Ther 2017;24:825e32. 18. Huang J, Li G, Wang W, et al. 3D printing guiding stent graft fenestration: a novel technique for fenestration in endovascular aneurysm repair. Vascular 2017;25:442e6.