First-generation aortic endografts: Analysis of explanted stenter devices from the EUROSTAR registry

Purpose: To examine the structure and healing characteristics of chronicall y implanted Stenter endografts that were explanted due to migration, endole ak, thrombosis, or aneurysm expansion. Methods: The devices were harvested following reoperation (n = 5) or autops y (n = 1) with implantation times ranging from 13 to 53 months. Structural modifications to the metal components were examined using radiography, endo scopy, and magnetic resonance imaging IM RI). Specimens taken from componen ts of the modular stent-g rafts were examined histologically and with scann ing electron microscopy (SEM) to assess healing behavior. Physical and chem ical stability of the nitinol wires and woven polyester graft material was evaluated using SEM and electron spectroscopy for chemical analysis. Results: Although the endografts were retrieved for a variety of reasons, t hey exhibited similar healing and structural modifications. The woven polye ster sleeve showed evidence of yam shifting and distortion, yarn damage, an d filament breakage leading to the formation of openings in the fabric. The luminal surface endografts showed incomplete healing characterized by a po orly organized, nonadherent thrombotic matrix of variable thickness. Radiog raphic and endoscopic observations indicated that structural failure of the grafts, particularly in the main aortic component, was related to severe c ompaction and dislocation of the metallic frame due to suture breaks. Corro sion marks were observed on some nitinol wires in all devices. Chemical ana lysis and ion bombardment of the nitinol wires revealed that the surface co ncentrations of titanium and nickel were not homogenous. The first layer wa s composed of carbon or organic elements, followed by a stratum of highly o xidized titanium with a low nickel concentration; the titanium-nickel alloy lay beneath these layers. Conclusions: Although the materials selected for construction of endovascul ar grafts appears judicious, the assembly of these biomaterials into variou s interrelated structures within the device requires further improvement.