Histology and Electron Microscopy of Explanted Bifurcated Endovascular Aortic Grafts: Evidence of Early Incorporation and Healing

Midterm results following endovascular repair of blunt thoracic aortic injuries

OBJECTIVE

Previous studies have focused on early outcomes of thoracic endovascular repair (TEVAR) of blunt thoracic aortic injuries (BTAIs). Late results remain ill-defined. The purpose of this study is to review the midterm results of our experience with endovascular repair of BTAIs.

METHODS

A retrospective analysis was performed reviewing all endovascular repairs of BTAIs from 2002 to present. Preoperative, operative, and postoperative variables were recorded. Clinical end points included aortic-related mortality, stroke and paraplegia, hospital length of stay, procedure-related complications, endoleaks, and reinterventions. Computed tomography data sets were postprocessed for assessing integrity of stent grafts and late complications.

RESULTS

A total of 24 cases of BTAIs treated with TEVAR were identified. Thoracic endovascular repair was successful in treating BTAIs in all patients and there were no instances of procedure-related death, stroke, or paraplegia. One access complication occurred, requiring an iliofemoral bypass. Actuarial survival estimates and freedom from reintervention at 5 years were 88.7% and 95.8%, respectively. No late endoleaks, stent fractures, or device migration were identified. One patient required a secondary intervention 1 year following the initial repair to treat a pseudocoarctation syndrome caused by a diaphragm at the distal half of the stented aorta. This was treated successfully with repeated endografting.

CONCLUSIONS

Thoracic endovascular repair for BTAIs can be performed safely with low periprocedural mortality and morbidity. Midterm follow-up data presented in this report further support the therapeutic role of endoluminal approach for treating BTAIs in anatomically suitable patients.

Overview of success of EVAR: Progress to date

Endovascular aneurysm repair (EVAR) of abdominal aortic aneurysms has been challenged by a number of groups, and the shortcomings of this procedure have been documented in the scientific literature. However, patients and physicians continue to pursue this procedure as a viable means of treating abdominal aortic aneurysms. Both device evolution and advancement of technical skills have led to dramatic improvements in the outcomes of EVAR within the last decade. These improvements and accomplishments have also been chronicled in the literature. This review looks at the successes of EVAR, based on both US Food and Drug Administration trials and independent studies comparing conventional open repair and endovascular repair.

Failed AAA endograft exclusion due to type II endoleak: explant analysis

PURPOSE

To report the patient history and analysis of an explanted modular bifurcated endograft that was implanted to exclude an abdominal aortic aneurysm (AAA).

CASE REPORT

An 80-year-old man with a 6-cm AAA underwent uneventful endovascular implantation of a bifurcated AneuRx stent-graft. His postprocedural clinical course was uneventful, although persistent contrast enhancement of the aneurysm remained via the inferior mesenteric artery (IMA). By 6 months, an endoleak connecting to the lumbar and mesenteric arteries became apparent. Over the ensuing 12 months, the endoleak and aneurysm enlarged; branch artery embolization was attempted in 4 percutaneous procedures. Despite successful IMA occlusion, the aneurysm continued to increase in diameter and volume, necessitating conversion to a conventional bypass at 20 months. Analysis of the explanted specimen revealed an intact endograft with fibrous incorporation of the stent framework at the proximal and distal fixation sites only; no incorporation of the endograft was noted within the aneurysm. The feeding channel for the endoleak was not identified.

CONCLUSIONS

Serial imaging is a vital component of endograft surveillance, and persistent type II endoleaks that cannot be completely embolized endanger the longevity of the aneurysm exclusion. Explant analysis can play an important role in understanding the mechanisms of endograft failure.

First-generation aortic endografts: analysis of explanted Stentor devices from the EUROSTAR Registry

PURPOSE

To examine the structure and healing characteristics of chronically implanted Stentor endografts that were explanted due to migration, endoleak, thrombosis, or aneurysm expansion.

METHODS

The devices were harvested following reoperation (n = 5) or autopsy (n = 1) with implantation times ranging from 13 to 53 months. Structural modifications to the metal components were examined using radiography, endoscopy, and magnetic resonance imaging (MRI). Specimens taken from components of the modular stent-grafts were examined histologically and with scanning electron microscopy (SEM) to assess healing behavior. Physical and chemical 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, they exhibited similar healing and structural modifications. The woven polyester sleeve showed evidence of yarn shifting and distortion, yarn damage, and filament breakage leading to the formation of openings in the fabric. The luminal surface endografts showed incomplete healing characterized by a poorly organized, nonadherent thrombotic matrix of variable thickness. Radiographic and endoscopic observations indicated that structural failure of the grafts, particularly in the main aortic component, was related to severe compaction and dislocation of the metallic frame due to suture breaks. Corrosion marks were observed on some nitinol wires in all devices. Chemical analysis and ion bombardment of the nitinol wires revealed that the surface concentrations of titanium and nickel were not homogenous. The first layer was composed of carbon or organic elements, followed by a stratum of highly oxidized titanium with a low nickel concentration; the titanium-nickel alloy lay beneath these layers.

CONCLUSIONS

Although the materials selected for construction of endovascular grafts appears judicious, the assembly of these biomaterials into various interrelated structures within the device requires further improvement.

First-generation aortic endografts: analysis of explanted Stentor devices from the EUROSTAR Registry

PURPOSE

To examine the structure and healing characteristics of chronically implanted Stentor endografts that were explanted due to migration, endoleak, thrombosis, or aneurysm expansion.

METHODS

The devices were harvested following reoperation (n = 5) or autopsy (n = 1) with implantation times ranging from 13 to 53 months. Structural modifications to the metal components were examined using radiography, endoscopy, and magnetic resonance imaging (MRI). Specimens taken from components of the modular stent-grafts were examined histologically and with scanning electron microscopy (SEM) to assess healing behavior. Physical and chemical 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, they exhibited similar healing and structural modifications. The woven polyester sleeve showed evidence of yarn shifting and distortion, yarn damage, and filament breakage leading to the formation of openings in the fabric. The luminal surface endografts showed incomplete healing characterized by a poorly organized, nonadherent thrombotic matrix of variable thickness. Radiographic and endoscopic observations indicated that structural failure of the grafts, particularly in the main aortic component, was related to severe compaction and dislocation of the metallic frame due to suture breaks. Corrosion marks were observed on some nitinol wires in all devices. Chemical analysis and ion bombardment of the nitinol wires revealed that the surface concentrations of titanium and nickel were not homogenous. The first layer was composed of carbon or organic elements, followed by a stratum of highly oxidized titanium with a low nickel concentration; the titanium-nickel alloy lay beneath these layers.

CONCLUSIONS

Although the materials selected for construction of endovascular grafts appears judicious, the assembly of these biomaterials into various interrelated structures within the device requires further improvement.

Endovascular repair of thoracic aortic aneurysm in dogs: evaluation of a nitinol-polyester self-expanding stent-graft

PURPOSE

To validate the ease of deployment and in vivo healing performance of a nitinol-polyester self-expanding stent-graft using a canine thoracic aortic aneurysm model.

METHODS

Arterial aneurysms were surgically created in 8 dogs by sewing a polyester patch onto the anterior side of the thoracic aorta. The nitinol-polyester self-expandable stent-grafts (Cragg EndoPro System 1) were implanted transluminally via the femoral route and deployed at the site of the thoracic aneurysm. Aneurysm exclusion and endograft patency were assessed by angiography after implantation and before animal sacrifice at scheduled periods ranging from 1 week to 3 months. The explanted specimens were examined with magnetic resonance imaging (MRI) to study the position of the stent-graft with respect to the aneurysmal sac. Histological analysis using light microscopy and scanning electron microscopy was performed to examine the inflammatory response and healing characteristics of the device.

RESULTS

Seven of 8 stent-grafts were implanted successfully; a bend occurred within the aneurysmal sac in 1 dog, which led to continued perfusion of side branches. This endoleak sealed spontaneously within 1 week, and complete exclusion of the aneurysms in all 8 animals continued throughout implantation. At the time of explantation, all devices were structurally intact and well positioned in the aneurysmal sac. At 1 week, the luminal surface displayed a thin layer of thrombotic matrix, which was gradually replaced by a collagenous internal capsule with endothelial-like cell coverage along both ends of the stent-grafts at 2 and 3 months. No exacerbated inflammatory reaction due to either the nitinol wires or the polyester sleeve was observed after 3 months of implantation.

CONCLUSIONS

This short-term in vivo study of a nitinol-polyester self-expanding endograft demonstrated the effective exclusion of thoracic aneurysms with a satisfactory healing response and no excessive tissue or inflammatory reactions.