Biomechanical study for thoracic stent grafts in different aortic aneurysm neck morphologies

  • 江 政賢

Student thesis: Doctoral Thesis

Abstract

Serious descending aortic aneurysm is often treated by open surgery or endovascular aortic repair (EVAR) The latter results in effective short-term outcomes Patients receiving EVAR require lifelong monitoring due to potential risk of endo-leak stent graft migration or the implant failure Patients are eligible for EVAR only when they have favorable morphologies of aortic neck which is in the proximal site of an aneurysm As physicians are becoming more skillful in endograft techniques and advancing stent graft designs standard stent grafts have been implanted for shorter wider or highly angulated aortic necks However initial pullout tests of stent grafts were mostly performed in a straight section of animal or cadaveric aortas or in an idealized aortic neck of a silicone abdominal aortic aneurysm model Stent graft fixation in unfavorable aortic necks was seldom investigated The purpose of the first part of this study is to provide an apparatus for comparison of dislodgement forces for various thoracic stent grafts at varying neck angulations and oversizing conditions The purpose of the second part is to investigate the radial stress and shear of employing double stent grafts for an extremely enlarged aortic neck in a laboratory setting The results are compared with fixation characteristics of single stent grafts for clinical reference and application Three commercial stent grafts with sizes commonly used in Taiwan (Valiant: 34 36 38 and 40 mm; Zenith TX2: 34 36 38 and 40 mm; and TAG: 34 37 and 40 mm) were employed for pullout test in angulated silicone tubes (0° 45° 90° and 135° with a 32-mm inner diameter) in a temperature-controlled chamber (37 ± 2 ℃) Zenith TX2 endografts of sizes 34–42 mm were used for the fixation study of single stent graft and double stent grafts formation in the extremely enlarged aortic necks Results of pullout test in the varying neck angulation settings show mean dislodgement force of Valiant Zenith TX2 and TAG devices repectively decrease by 46 % 38 % and 50 % as the neck angulation increases from 0° to 135° Regression analysis shows that neck angulation was a significant factor for both the Valiant and Zenith TX2 devices Dislodgement force of the 3 different commercial stent grafts were studied and compared The different performances of the mean dislodgment forces may reflect the different framework designs of the 3 commercial stent grafts Our findings indicate that aortic neck angulation has a negative correlation with stent graft fixation Results of stent graft fixation in extremely enlarged aortic necks show that the double stent graft formation provides higher radial stress and shear to secure fixation for endovascular aortic repair The radial stress of the double stent graft formation is 15–25% higher than that of a single stent graft under normal 10–20 % oversizing condition Shear of the double stent grafts formation is comparable to that of a single stent graft with 25–35 % oversizing condition In addition results fixation of single stent graft show that radial stress and shear of a single Zenith TX2 stent graft decrease with increasing endograft diameters This characteristic makes it more difficult to have secure fixation in an enlarged aortic neck In conclusion aortic neck angulation does have negative correlation with stent graft fixation For patients with angulated aortic morphologies having longer contact fixation length and cautiously selected higher endograft oversizing is recommended Double stent graft formation provides higher fixation than a single stent graft in an enlarged aortic lumen For patients receiving double-barreled cannon aortic repair continuously follow up and observation of the disease progression is needed
Date of Award2018 Aug 16
LanguageEnglish
SupervisorMing-Long Yeh (Supervisor)

Cite this

Biomechanical study for thoracic stent grafts in different aortic aneurysm neck morphologies
政賢, 江. (Author). 2018 Aug 16

Student thesis: Doctoral Thesis