Fatigue Resistance of the Advanta V12/iCast and Viabahn Balloon-Expandable Stent-Graft as Bridging Stents in Experimental Fenestrated Endografting

Abstract

Purpose: Bridging stents undergo millions of cycles during respiratory movements of the kidneys throughout the patient’s life. Thus, understanding the response of fabric and endoskeleton of the stent to cyclic loading over the time is crucial. In this study, we compare the fatigue resistance of the Viabahn Balloon-Expandable stent-graft (VBX) with the widely used Advanta V12/iCast under prolonged stress induction. Materials and Methods: A polyester test sheet with 10 fenestrations was used simulating a fenestrated endograft. Five 6×59 mm VBX stent-grafts and five 6×58 mm Advanta stent-grafts were implanted into 6×6 mm fenestrations. The stents were flared with a 10×20 mm PTA (percutaneous transluminal angioplasty) catheter and connected with a fatigue stress machine. All stent-grafts were evaluated by microscopy and radiography at baseline and after regular intervals until 50,000,000 cycles were applied, simulating a life span of approximately 75 months. Freedom from fracture (FF), freedom from initial polytertafluoroethylene (PTFE) changes (FIC), and from PTFE breakpoint (FBP, all-layer defect) were calculated. Results: Digital radiographic images did not show any stent fracture in both groups after 50,000,000 cycles. The VBX stent-graft was free from any all-layer defects at the conclusion of 50,000,00 cycles resulting in a significant higher FBP compared with Advanta V12 (50,000,000 vs 33,400,000; p<0.01). All-layer defects were observed only in the Advanta group. Two of 5 Advanta stents showed early penetration of the nitinol ring causing a defect of PTFE. Regarding FIC, there was no significant difference between the stents (3,400,000 in VBX vs 3,200,000 in Advanta). Conclusions: In fatigue tests simulating respiration movements, VBX and Advanta V12 performed equally well in terms of fracture resistance and freedom from initial PTFE changes. VBX maintained freedom from PTFE breakpoint throughout the full 50,000,000 cycles. All-layers defects were detected only in Advanta and were mainly caused by penetration of the nitinol ring through the PTFE.

Systematic Review of the Current In Vitro Experience of the Endovascular Treatment of Juxtarenal Abdominal Aortic Aneurysms by Fenestrated and Parallel Endografting

“…Six out of 7 studies evaluated the Zenith fenestrated endograft highlighting the lack of in vitro evidence on other employed fenestrated endografts. Also, although Advanta V12 has been cited as the standard of care, 11,13 many other off-the-shelf SGs are employed in the everyday practice without any in vitro differentiation and characterization for their use as bridging stents, underlying the necessity of a dedicated SG.…”

“…Each test shall be repeated at least 3 times for inter-reader reproducibility. Although the evaluation of the testing was based on POF analysis in the majority of FEVAR tests and CT imaging in all PG testing, other modalities like the biplanar digital radiography to detect possible changes of the stent structure or SG fracture, microscopic evaluation of possible fabric or stent changes, [10][11][12][13] and ECG-gated CT to evaluate device changes with cardiac cycle need to be considered for more detailed evaluation of SG performance.…”

“…A total of 8 in vitro studies evaluated the fenestrated technology for the endovascular treatment of jAAA [7][8][9][10][11][12][13] (Table 1). The resistance to displacement and migration in FEVAR was studied by Scurr et al using a testing rig with two overlapping acrylic tubes with two sets of holes representing bilateral renal artery in their first study in 2008 9 and a tensile tester via plastic sealing plugs and pneumatic clamps in their second study in 2012.…”

“…22 Bridging stents' radial force, flareability, fatigue, and fracture resistance were studied in the four studies conducted by Torsello et al They used test sheets with two rows of 5 fenestrations with 5 or 10 mm diameter in all their studies. [10][11][12][13] They used water permeability test for the bridging stent when evaluating the GORE VIABAHN VBX Balloon Expandable Endoprosthesis (W.L. Gore and Associates, Flagstaff, AZ, USA) due to the increased translucency in the microscopic pretests.…”

“…Different in vitro tests have previously been performed to investigate the stability of fenestrated grafts or their components 7,8 to assess the specific properties of bridging stents 9,[10][11][12][13] or chimney grafts (CGs) 14,15 and to define the ideal graft position and configuration for the chimney technique [16][17][18] and the potential benefits of the use of gutter fillings 19 or EndoAnchors. 20 The cornerstone of every in vitro study is the used phantom.…”