Deployment technique and histopathological evaluation of an endoluminal vascular prosthesis used to repair an iliac artery aneurysm

Fatores envolvidos na migração das endopróteses em pacientes submetidos ao tratamento endovascular do aneurisma da aorta abdominal

A migração da endoprótese é complicação do tratamento endovascular definida como deslocamento da ancoragem inicial. Para avaliação da migração, verifica-se a posição da endoprótese em relação a determinada região anatômica. Considerando o aneurisma da aorta abdominal infrarrenal, a área proximal de referência consiste na origem da artéria renal mais baixa e, na região distal, situa-se nas artérias ilíacas internas. Os pacientes deverão ser monitorizados por longos períodos, a fim de serem identificadas migrações, visto que estas ocorrem normalmente após 2 anos de implante. Para evitar migrações, forças mecânicas que propiciam fixação, determinadas por características dos dispositivos e incorporação da endoprótese, devem predominar sobre forças gravitacionais e hemodinâmicas que tendem a arrastar a prótese no sentido caudal. Angulação, extensão e diâmetro do colo, além da medida transversa do saco aneurismático, são importantes aspectos morfológicos do aneurisma relacionados à migração. Com relação à técnica, não se recomenda implante de endopróteses com sobredimensionamento excessivo (> 30%), por provocar dilatação do colo do aneurisma, além de dobras e vazamentos proximais que também contribuem para a migração. Por outro lado, endopróteses com mecanismos adicionais de fixação (ganchos, farpas e fixação suprarrenal) parecem apresentar menos migrações. O processo de incorporação das endopróteses ocorre parcialmente e parece não ser suficiente para impedir migrações tardias. Nesse sentido, estudos experimentais com endopróteses de maior porosidade e uso de substâncias que permitam maior fibroplasia e aderência da prótese à artéria vêm sendo realizados e parecem ser promissores. Esses aspectos serão discutidos nesta revisão.

Successful endovascular exclusion of a common iliac artery aneurysm: off-label use of a reversed Cook Zenith extension limb stent-graft

Open iliac aneurysm repair has been historically associated with major morbidity and mortality. The introduction of endovascular devices and techniques has expanded the armamentarium available to treat these aneurysms, and several methods have been reported. However, the off-label use of a commercially available, flared extension limb stent-graft to treat a common iliac artery aneurysm (CIA) by preliminary extracorporeal predeployment, endograft reversal, and reinsertion into the delivery sheath to fashion a tapered endograft has not been previously reported. A case report of a CIA aneurysm diagnosed 9 years after transperitoneal tube graft abdominal aortic aneurysm repair treated with ipsilateral hypogastric artery occlusion with an Amplatzer plug and placement of a reversed, tapered extension limb stent-graft is herein presented.

The Endovascular Management of Iliac Artery Aneurysms

BACKGROUND

Isolated aneurysms of the iliac arteries are uncommon. Previously treated by conventional surgery, there is increasing use of endografts to treat these lesions.

PURPOSE

The purpose of this study was to assess the efficacy, safety, and durability of the stent-grafts for treatment of iliac artery aneurysms (IAAs). The results of endografting for isolated IAAs over a 10-year period were analyzed retrospectively. The treatment methods differed depending on the anatomic location of the aneurysms. Twenty-one patients (1 woman, 20 men) underwent endovascular stent-graft repair, with one procedure carried out under emergency conditions after acute rupture. The mean aneurysm diameter was 4.6 cm.

RESULTS

The procedural technical success was 100%. There was zero 30-day mortality. Follow-up was by interval CT scans. At a mean follow-up of 51.2 months, the stent-graft patency rate was 100%. Reintervention was performed in four patients (19%): one patient (4.7%) with a type I endoleak and three patients (14.3%) with type II endoleaks.

CONCLUSION

We conclude that endovascular repair of isolated IAAs is a safe, minimally invasive technique with low morbidity rates. Follow-up results up to 10 years suggest that this approach is durable and should be regarded as a first treatment option for appropriate candidates.

A novel hybrid approach to the treatment of common iliac aneurysms: antegrade endovascular hypogastric stent grafting and femorofemoral bypass grafting

A progressively enlarging left common iliac artery aneurysm developed in a 72-year-old man 7 years after open abdominal aortic aneurysm repair with a bifurcated Dacron graft. Because both the right hypogastric and inferior mesenteric arteries had been ligated at the initial operation, preservation of left hypogastric flow was critical to avoid pelvic or intestinal ischemia. He was a poor open surgical candidate owing to obesity, a hostile abdomen, and multiple medical comorbidities. Therefore, a novel hybrid approach was used consisting of left transbrachial selective left hypogastric artery catheterization, followed by deployment of two, overlapping, antegrade, covered stent grafts extending from the proximal left graft limb into the left hypogastric artery. A right-to-left femorofemoral crossover bypass was added to perfuse the left lower extremity and was performed in end-to-end fashion to the left common femoral artery to exclude and prevent retrograde flow into the iliac aneurysm. Also presented are potential procedural pitfalls and a detailed review of open, endovascular and hybrid options to preserve hypogastric flow when treating iliac aneurysms in complex, high-risk patients.

EndoFit Stent-Graft Repair of Isolated Common Iliac Artery Aneurysms With Short Necks

PURPOSE

To evaluate the feasibility and efficacy of repairing isolated iliac artery aneurysms with short proximal necks (<10 mm) by implanting the EndoFit stent-graft.

METHODS

Seven patients (6 men; median age 73 years, range 70-78) were diagnosed with an isolated common iliac artery (CIA) aneurysm that featured a short proximal landing zone, complicating endovascular treatment. The median aneurysm diameter was 4.4 cm (range 3.5-7.0), and the median proximal neck length was 7 mm (range 5-9).The aneurysms were treated using the EndoFit stent-graft, which can be deployed in a short proximal landing zone. The modified technique involves the deployment of the graft directly above the aneurysm sac without obstructing the contralateral iliac axis, thus affixing the bare proximal stent in the terminal aorta. Follow-up was performed by clinical evaluation and computed tomography at 1, 6, and 12 months postoperatively.

RESULTS

The EndoFit stent-graft was successfully deployed in all cases, with complete aneurysm exclusion. In 1 case, the deployment of a second cuff was necessary to secure complete aneurysm exclusion. The median follow-up was 18 months, during which no deaths occurred, and no endoleak or stent-graft migration was observed. Endograft thrombosis occurred in 1 case due to graft angulation caused by external iliac artery stenosis and kinking. None of the aneurysms has ruptured, and there have been no serious complications.

CONCLUSION

Direct endoluminal repair of isolated CIA aneurysms with short proximal necks is feasible using this technique. Efficacy and long-term results are to be confirmed by larger scale series over a long time period.

Biologic fixation of polyester- versus polyurethane-covered stents in a porcine model

PURPOSE

Migration of endoprostheses remains a concern in endovascular aneurysm treatment. Biologic fixation is supposed to enhance anchorage, but the diseased atherosclerotic aorta in humans has demonstrated a limited capacity to incorporate an endoprosthesis by cellular proliferation. The biologic response of two different types of endoprostheses was evaluated in the porcine aorta.

MATERIALS AND METHODS

Two types of endoprostheses--four polyurethane-covered (PUC) stents with a macroporous polyurethane covering and four polyester-covered (PEC) stents with a woven polyester covering--were implanted in eight infrarenal porcine aortas for 6 weeks. Electron microscopy and qualitative and quantitative microscopy were performed on serial cross sections.

RESULTS

The PUC stents demonstrated an increase in diameter (from 8 mm +/- 1 to 10 mm +/- 1, 12.5%; P = .009), whereas the PEC stents persisted in their original dimensions (8 mm +/- 1, 0%). PUC and PEC stents were covered by continuous thrombus-free neointima (269 microm +/- 51 vs 575 microm +/- 113, respectively; P < .01). The PUC stents demonstrated firm attachment to the aorta as a consequence of a granulation tissue with ingrowth into the pores of the polyurethane covering. The PEC stents remained in loose contact with the aorta in the absence of tissue ingrowth.

CONCLUSIONS

Enhanced biologic fixation was achieved by extensive granulation tissue invading the pores of PUC endoprostheses. This finding can modify the design of future devices.

Histopathologic analysis of endovascular stent grafts from patients with aortic aneurysms: Does healing occur?

BACKGROUND

Research with animal models has demonstrated tissue healing of endovascular grafts in both native arterial segments and in experimentally created arterial aneurysms. Fundamental to the successful clinical use of endovascular grafts for the treatment of aneurysmal disease is the creation of a permanent hemostatic seal between the graft ends and the arterial wall. Characteristics of this healing process in patients with aneurysmal disease have not been fully studied. In this study, we analyzed the macroscopic and histopathologic changes of the arterial wall after endovascular repair of aortic aneurysms.

METHODS

Over a 7-year period, 313 patients were treated with endovascular grafts to exclude arterial aneurysms of the thoracic and abdominal aorta. Of these patients, 11 had their endovascular grafts recovered for analysis. Five graft specimens were recovered during subsequent open aortic surgery. Six grafts were recovered at autopsy after the death of the patient of causes unrelated to the patient's endovascular graft. All specimens were fixed in formalin. Histologic analysis included light microscopy with hematoxylin and eosin and trichrome stains. Well-preserved specimens were selected after light microscopic examination and postfixed in 3% buffered glutaraldehyde for electron microscopy. The aortas from autopsy specimens were removed en bloc and fixed in formalin; representative regions of each graft were sectioned for analysis. Adherence of the graft to the vessel wall was categorized as densely adherent or easily separated after graft explantation. Traction applied to the graft-aortic anastomosis was equal to traction generated by suspending a standardized 2-kg weight. Infrarenal graft specimens were obtained with supraceliac aortic clamping, longitudinal aortotomy, and graft sampling before endograft revision.

RESULTS

In eight patients, endograft fixation was found to be firmly adherent to the arterial wall. A translucent film of fibrinous material was consistently seen across the entire luminal surface of the endograft. Light and electron microscopy failed to demonstrate an endothelial layer or organized pseudointima at the graft-artery interface.

CONCLUSION

Despite suggestive experimental data regarding endograft healing in animals, minimal graft incorporation was apparent in the stent grafts recovered in this study. A greater emphasis on the construction and mechanism of fixation of endograft attachment systems will be important for long-term device function.

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.

Midterm results of endovascular stented grafts for the treatment of isolated iliac artery aneurysms

PURPOSE

Isolated aneurysms of the iliac arteries are uncommon lesions that require surgical repair to prevent rupture.

METHODS

During a 4-year period, we used endovascular stented grafts (EGs) to treat 28 iliac artery aneurysms that were not associated with aortic aneurysms. Twenty-five patients, with a total of 24 common iliac (15 right, nine left) and four internal iliac (two right, two left) artery aneurysms, underwent endovascular grafting. There were 24 men and 1 woman, with a mean age of 74 years (range, 51 to 88 years). Combined common and internal iliac artery aneurysms were present in three patients. Nineteen patients who underwent treatment with EGs were administered epidural anesthesia (22 epidural, two local, one general). Before surgery, one patient had lower extremity embolization and ischemia from the aneurysm, three had abdominal or back pain, and the remaining were asymptomatic. The EGs were constructed of polytetrafluoroethylene grafts and balloon expandable stents.

RESULTS

Four procedure-related complications (12%) occurred (distal extremity embolization, n = 1; wound complications, n = 2; colonic mucosal ischemia, n = 1). Only a minimal reduction in the aneurysmal diameter was seen in 90% of the iliac artery aneurysms treated. The remaining lesions showed no change in size, and no aneurysm had an increase in cross-sectional diameter on computed tomographic images enduring a follow-up period up to 4 years (mean, 24 months). One aneurysm ruptured after successful endovascular exclusion, and the patient underwent treatment with open repair. The 3-year primary patency rate of iliac EGs was 86%.

CONCLUSION

EGs appear to show satisfactory safety and efficacy for the repair of isolated aneurysms of the iliac arteries.

Histology and electron microscopy of explanted bifurcated endovascular aortic grafts: evidence of early incorporation and healing

PURPOSE

To report an examination of explanted bifurcated endovascular aortic grafts for histologic evidence of early healing and incorporation.

METHOD

Two bifurcated endovascular aortic grafts composed of polycarbonate urethane and Elgiloy wire were explanted 42 and 21 days after successful endovascular exclusion of abdominal aortic aneurysms. Both patients expired from causes unrelated to endograft deployment. The explanted devices were examined using immunohistochemical analysis and electron microscopy.

RESULTS

On explantation, both grafts appeared to have excluded the aneurysm with no evidence of endoleak, graft migration, or thrombosis. Histological examination showed numerous inflammatory cells and good ingrowth of tissue into the proximal 2 cm of the graft. Collagen and smooth muscle cells were evident in the proximal portion of the graft with only collagen in the distal segments. Neointimal formation was seen within the proximal 2 cm also, but not at the distal segments. Macrophages were present in the graft. Scanning electron microscopy showed an extensive matrix of fibers that most likely represented collagen.

CONCLUSIONS

Bifurcated endovascular aortic grafts show inflammatory and mild foreign body reactions, collagen formation, and intimal ingrowth during healing. These findings are similar to some of the healing properties reported for sutured grafts, as well as other endovascular grafts.

Placement of a PTFE-covered Wallstent through a 12 Fr sheath for the exclusion of a common iliac artery aneurysm

We describe a technique for transfemoral endovascular exclusion of an iliac artery aneurysm with a reconstrained polytetrafluoroethylene (PTFE)-covered Wallstent inserted through a 12 Fr sheath after right femoral artery cutdown. The procedure was successfully performed, with evidence of complete aneurysm exclusion at 4-month follow-up. This technique reduces the caliber of the introducer needed to deploy the covered Wallstent. It should be noted that because of a leak, an additional covered Palmaz stent was also deployed.

Intravascular ultrasound in endovascular stent-grafts for peripheral aneurysm: a clinical study

PURPOSE

To evaluate the potential diagnostic information of intraprocedural intravascular ultrasound (IVUS) in patients undergoing endovascular stent-grafting for peripheral aneurysm.

METHODS

IVUS was used in 17 patients preprocedurally to measure the diameter of the proximal and distal neck and the length of the aneurysm. Balloon and stent-graft sizes were selected based on these measurements. Following stent-graft deployment, angiography and IVUS were used to document stent apposition and the configuration and diameter of the stent-graft.

RESULTS

Stent-graft insertion was considered successful in 8 patients based on angiography and IVUS images. In 9 others, both imaging modalities showed inadequate results, necessitating 12 additional procedures: balloon angioplasty for stent-graft stenosis (2) and inadequate stent-graft apposition (1); an additional stent-graft (4); an extra stent (1); thrombectomy (2); and conversion (2) for inadequate stent-graft position and a graft rupture. In these patients, intraprocedural IVUS was superiorto angiography in contributing vital information to aid in the selection of the additional interventions.

CONCLUSIONS

During management of peripheral aneurysms with endovascular stent-grafts, IVUS monitoring was a useful adjunct when the initial procedure was unsatisfactory and/ or when intraprocedural angiographic studies were inconclusive.

Regression of an abdominal aortic aneurysm after endograft exclusion

We describe the regression of a 6.5 cm diameter abdominal aortic aneurysm in a 71-year-old patient within 1 year of aortic endograft placement. The aneurysm decreased in size to 4 cm at 3 months and was 3.3 cm at 8 months on duplex examination. By 1 year a spiral computed tomographic study confirmed complete regression of the aneurysm, with mild shortening and angulation of the unsupported body of the aortoiliac endoluminal prosthesis. The case demonstrates a potential of endograft treatment of aortic aneurysms and decribes the changes in prosthesis configuration and position that occurred after implantation.

Intravascular ultrasound: the ultimate tool for abdominal aortic aneurysm assessment and endovascular graft delivery

Intravascular ultrasound (IVUS) imaging is a relatively new, rapidly evolving technology that enables precise catheter-based assessment of the dimensions and morphology of vascular structures and lesions. In extensive preclinical laboratory developmental studies and in clinical cases of endograft deployment for treatment of abdominal aortic aneurysms, we have found IVUS invaluable for determining key parameters of aortic morphology before and during interventions and for assessing the accuracy of deployment after device placement. By combining the IVUS data with information obtained from angiography, magnetic resonance imaging, and computed tomography (axial and three-dimensional reconstructions), we have been able to size devices and choose optimal fixation sites to prevent endoleaks and maintain luminal patency acutely and in the long term.