Tissue response to covered Wallstents

Stent Graft versus Balloon Angioplasty for Failing Dialysis Access Grafts: A Long-Awaited Advance in the Treatment of Permanent Hemodialysis Access

Arteriovenous grafts (AVGs) for hemodialysis have a high failure rate, often due to the development of stenosis at the graft-to-vein anastomosis. Angioplasty (PTA) has been used for over two decades to treat AVG stenosis, with good technical success but limited AVG patency. Results of a prospective multi-center randomized trial, comparing stent graft to PTA in AVGs, has demonstrated superior access circuit patency for the stent graft group. Recent publication of this clinical study brings us into an exciting new era of dialysis access management using covered stents to improve durability of catheter-based therapy.

Stent Grafts Provided Superior Primary Patency for Central Venous Stenosis Treatment in Comparison with Angioplasty and Bare Metal Stent: A Retrospective Single Center Study on 70 Hemodialysis Patients

PURPOSE

To compare patency in dialysis patients following different endovascular treatment of symptomatic central venous stenosis.

MATERIALS AND METHODS

A 10-year retrospective evaluation in 70 patients (32 men) dialyzing through vascular access (33, 47%) and tunneled catheters (37, 53%) was made. Three cohorts were compared: angioplasty alone (22), bare metal stent (28), and stent graft (20). Patencies were described with Kaplan-Meier method, and Cox uni- and multivariate models were analyzed to find factors associated.

RESULTS

All patients had a favorable anatomical and clinical outcome. Restenosis occurred in 22 (31%) of 70 patients requiring 41 additional interventions; 34 of 70 patients died (median follow-up 19.4 months). Primary patency at 3, 6, 12, and 24 months was 100%, 100%, 100%, and 84% for stent graft versus 90%, 79%, 58%, and 43% for angioplasty (P = .014) versus 84%, 80%, 75%, and 46% for bare-metal stent (P = .062). The overall comparison was more favorable for stent graft (P = .020) when the sites of lesions were matched. Patencies for angioplasty and bare-metal stents were equivalent (P = .141). A lower risk of restenosis (hazard rate [HR] 0.20, confidence interval [CI] 0.06-0.7) and fewer reinterventions (P < .01) were associated with stent graft, whereas age (HR 1.04, CI 1.001-1.08) and cardiovascular disease (HR 2.26, CI 1.06-4.84) influenced the overall survival. No difference in assisted primary patency was found.

CONCLUSION

Stent graft seems to improve primary patency for central venous stenosis and requires fewer reinterventions in a dialysis population with a high prevalence of long-term catheters.

Tissue responses to endovascular stent grafts for saccular abdominal aortic aneurysms in a canine model

We investigated tissue responses to endoskeleton stent grafts for saccular abdominal aortic aneurysms (AAAs) in canines. Saccular AAAs were made with Dacron patch in 8 dogs, and were excluded by endoskeleton stent grafts composed of nitinol stent and expanded polytetrafluoroethylene graft. Animals were sacrificed at 2 months (Group 1; n = 3) or 6 months (Group 2; n = 5) after the placement, respectively. The aortas embedding stent grafts were excised en bloc for gross inspection and sliced at 5 to 8 mm intervals for histopathologic evaluation. Stent grafts were patent in all except a dog showing a thrombotic occlusion in Group 2. In the 7 dogs with patent lumen, the graft overhanging the saccular aneurysm was covered by thick or thin thrombi with no endothelial layer, and the graft over the aortic wall was completely covered by neointima with an endothelial layer. Transgraft cell migration was less active at an aneurysm than at adjacent normal aorta. In conclusion, endoskeleton stent grafts over saccular aneurysms show no endothelial coverage and poor transgraft cell migration in a canine model.

Preclinical Models of Restenosis and Their Application in the Evaluation of Drug-Eluting Stent Systems

Coronary arterial disease (CAD) is the leading cause of death in the United States, the European Union, and Canada. Percutaneous coronary intervention (PCI) has revolutionized the treatment of CAD, and it is the advent of drug-eluting stent (DES) systems that has effectively allayed much of the challenge of restenosis that has plagued the success of PCI through its 30-year history. However, DES systems have not been a panacea: There yet remain the challenges associated with interventions involving bare metallic stents as well as newly arisen concerns related to the application of DES systems. To effectively address these novel and ongoing issues, animal models are relied on both to project the safety and efficacy of endovascular devices and to provide insight into the pathophysiology underlying the vascular response to injury and mechanisms of restenosis. In this review, preclinical models of restenosis are presented, and their application and limitation in the evaluation of device-based interventional technologies for the treatment of CAD are discussed.

Endoprótese revestida de jugular preservada de bovino: estudo comparativo da resposta tecidual em aorta torácica descendente e veia cava inferior de suínos

OBJETIVO: Avaliar e comparar a resposta tecidual de uma endoprótese biosintetica implantada na aorta torácica descendente e veia cava inferior de suínos. MÉTODO: Foi implantada uma endoprótese auto-expansível composta de aço inoxidável, revestida por veia jugular de bovino, processada pelo método L-hydro, com auxilio de uma bainha de liberação Taheri-Leonhardt (Flórida, EUA) na aorta torácica descendente, e a veia cava infra-renal de 10 suínos. Sessenta dias após, as endopróteses foram retiradas e analisadas sob o ponto de vista macro e microscópicos. Foram observados: perviedade, grau de incorporação a parede do vaso, tipo de reação inflamatória, e local de maior resposta, tanto em relação a camada do vaso quanto ao local de contato com o anel de aço RESULTADOS: Todas as endopróteses encontravam-se pérvias, e incorporadas à parede. No setor venoso, seis apresentaram traves fibrosas em sua luz, e quatro apresentaram fibrose perivascular. No setor arterial somente uma prótese apresentou discreta estenose, sem fibrose perivascular. A reação inflamatória crônica tipo corpo estranho ocorreu em 100% das peças, a camada média foi a mais acometida no setor venoso, enquanto a íntima foi mais constante na artéria, o grau de incorporação foi mais firme na veia em comparação a artéria. A reação tecidual mostrou maior tendência nas áreas em intimo contato com o anel de aço (intra-anelar), mais intensa na artéria do que na veia. CONCLUSÃO: A prótese apresentou baixa trombogenicidade em ambos os sistemas, houve maior reação tecidual e baixa biocompatibilidade no setor venoso.

Development of in vivo tissue-engineered autologous tissue-covered stents (biocovered stents)

Biocovered stents, which are stents covered with autologous membranous tissues, were developed by applying a novel concept based on in vivo tissue engineering. Balloon-expandable stents crimped on silicone rods as a mold (diameter: 2 mm) were embedded into dorsal subcutaneous pouches in rabbits. After 1 month, the struts of the stents were fully encapsulated with membranous connective tissues formed around the silicone rods. Upon removing the silicone rod, stents covered with tubular connective tissues, in which the struts were completely impregnated, were obtained as biocovered stents. These tissues were composed mainly of collagen and fibroblasts and had a thickness of less than approximately 200 microm with an excellent high burst strength of approximately 1000 mmHg. The luminal surface of the tissues was extremely flat and smooth. The stents could be mounted on balloon catheters with a hand crimping tool and could be expanded by inflation with little damage to the tissues. It is anticipated that these novel stents may greatly enhance early normal vascular reconstruction with high reliability, thereby reducing the rate of in-stent restenosis.

Endovascular Exclusion of an External Carotid Artery Pseudoaneurysm Using a Covered Stent

Aneurysmal lesions of the external carotid artery are extremely rare. A case is presented of a 3.8 cm right external carotid artery pseudoaneurysm treated by transluminal exclusion using an endovascular stent-graft. Following stent-graft placement, complete occlusion of the aneurysmal sac and main vessel lumen patency was successfully demonstrated. This report demonstrates the technical feasibility of utilizing stent-grafts to treat aneurysmal lesions involving the external carotid artery.

Evaluation of Three Polytetrafluoroethylene Stent-Grafts in a Model of Neointimal Hyperplasia

PURPOSE

The authors tested three different porosities of expanded polytetrafluoroethylene (ePTFE)-covered stents and bare stents by using an animal model of restenosis.

MATERIALS AND METHODS

Both iliac arteries in 18 female pigs were injured by overdilating 20-mm-long angioplasty balloons. A 40-mm-long bare stent or one of three 44-mm-long ePTFE-covered stents was deployed at the injury site. To determine restenosis, neointimal area measurements were made with intravascular ultrasonography. Histologic analyses were performed at an independent laboratory to determine neointimal attachment.

RESULTS

Neointimal area was greatest at the middle of the bare stent, where balloon injury was centered. When the middle location of the covered stents was evaluated, the neointimal area of both the medium- and high-porosity covered stents was smaller than that of the matched control stents (P = .0018 and P = .0118, respectively). The neointimal area of the low-porosity covered stents was similar to that of the bare stents. Histologic study showed dehiscence of the neointima of the low-porosity covered stents.

CONCLUSIONS

The microstructure of the low-porosity covered stents did not provide a suitable surface for neointimal attachment and did not reduce neointimal growth compared to that with the control stents. The microstructure of the medium- and high-porosity covered stents yielded less neointimal growth than both the control stents and the low-porosity covered stents without evidence of neointimal dehiscence. The authors believe that covered stents made with ePTFE with either medium or high porosity could limit restenosis in humans compared to that with bare stents.

Development of self-expandable covered stents

We newly developed self-expandable covered stents by combining two of our original technologies. Of these, the first is the dip-coating covering method that was developed previously for balloon-expandable stents; the other is the newly developed self-expandable Nitinol stents, namely, Sendai stents. The three types of covered stents with the expansion diameter of 4.5, 5.0, or 6.0 mm thus obtained had a laser-processed microporous elastomeric cover film (pore diameter: 100 microm, interpore distance: 250 microm). Although the film was extremely thin (approximately 15 microm), the film could be expanded without causing any damage, the strut was completely embedded within the film, and the luminal surface of the film was smooth and flat. Mechanical properties such as ideal flexibility to follow the shapes of arteries were almost retained even after covering. As appropriate drugs, the blood-contacting inner and tissue-contacting outer surfaces of the film were differentially coated with argatroban for antithrombogenicity or FK506 for anti-inflammation, respectively. The preliminary in vivo study indicated that the covered stents mounted in the delivery catheter were navigated and placed to appropriate position in the arteries, and permissible neointimal thickening after 1-month implantation was observed similarly in noncovered stents.

Utility of Stent-Grafts in Treatment of Porto-Biliary Fistula

A porto-biliary fistula causing hemobilia is a known complication of percutaneous transhepatic biliary drainage (PTBD). We present two patients with hemobilia secondary to porto-biliary fistula, treated successfully by percutaneous placement of stent-grafts. In one case, the stent-graft was placed in the bile duct, and in the other case, it was placed in the intrahepatic portal vein branch. Hemobilia stopped and there were no complications except a small area of hepatic infarction, distal to the stent-graft in the portal vein.

Comparison of the ovine and porcine animal models for biocompatibility testing of vascular prostheses

OBJECTIVE

Evaluation of the pig and sheep models for biocompatibility investigations of vascular prostheses (VP).

DESIGN

Comparative analysis of animal experimental investigations involving two different animal models.

MATERIALS AND METHODS

Commercially available polyester vascular prostheses (PET-VP) were implanted into two different animal models (infrarenal porcine aorta and ovine carotid artery). The costs, surgical handling, patency rate, and healing on the basis of macroscopic, microscopic, and immunohistochemical criteria were analyzed over a period of 3 months.

RESULTS

Handling and operating times (63 +/- 10 versus 76 +/- 16 min; P = 0.125) did not differ significantly. The cost of the two animal models was comparable. Integration of the VP was complete in the sheep model, but varied in the pig model (two complete, four incomplete). Complete endothelialization of all VPs was observed in the pig, which contrasted with the sheep with complete (circular) endothelialization only in the region of the anastomosis. The thickness of neointima in the region of the anastomosis differed insignificantly; immunohistochemically, only periprosthetic Ki67 was significantly reduced (28.7 +/- 9.9 versus 6 +/- 0.9%; P = 0.002) in the sheep.

CONCLUSIONS

In the porcine model, extremely good endothelialization of the VP was observed, with formation of a rapid neointimal hyperplasia. The ovine model was characterized by the fact that postoperative follow-up investigations were easy to perform. Complete endothelialization was not observed.

Bile Resistance of Coated Transjugular Intrahepatic Portosystemic Shunt Stents in a Flow-Model

PURPOSE

We sought to test the bile resistance of transjugular intrahepatic portosystemic shunt (TIPS) stents with 3 different coatings.

MATERIALS AND METHODS

Three stents with different coating materials (monolayer polyethylene terephthalate [PETP], monolayer polytetrafluoroethylene [PTFE], and double layer [PTFE]) were tested in a flow model. After testing the sealing of the system with isotonic saline solution, fresh human bile was circulated. Constant pressure was 50 cm H2O. Bile resistance of the stent membranes was analyzed.

RESULTS

Two of the 3 stents proved completely resistant to water. Only the PETP stent was resistant to bile. The PTFE-coated stents were not bile resistant.

CONCLUSION

The bile resistance of coated TIPS stents and, thus, the dependency of TIPS shunt patency is called into question. The stent with the reported superior patency rates does not show experimental bile resistance.

The application of mesh support in periareolar breast surgery: clinical and mammographic evaluation

BACKGROUND

Numerous techniques have been described for the treatment of breast hypertrophy and ptosis. Unfortunately, recurrent ptosis after mammaplasty can occur regardless of the technique used. To avoid this problem, different kinds of supporting devices have been described with variable rates of success. However, the true implications of incorporating prosthetic materials into breast surgery have never been clarified. Therefore, surgeons have traditionally been reluctant to apply any kind of prosthetic material to the breast, fearing inflammation, an unfavorable aesthetic outcome, palpable or visible deformities, and interference with the mammographic evaluation of breast cancer. This study analyzed the aesthetic, clinical, and mammographic implications of using mesh as a supportive device in periareolar breast surgery.

METHODS

For this study, 18 patients (mean age, 42 years) with breast hypertrophy, ptosis, or both were managed with the double-skin periareolar mammaplasty technique, with placement of mixed (60% Polyglactine and 40% polyester) mesh. Clinical assessment was performed by three breast surgeons actively working on cancer surveillance who knew that the patients had experienced mesh application. After a mean follow-up period of 30 months, a standard mammogram was performed for each patient and analyzed by both the surgeons and an expert radiologist. The evaluated factors were hyperemia, calcifications, contour irregularities, capsular contraction, thickening or widening of the scar with extrusion of the mesh, and any palpable or hardened areas.

RESULTS

According to the authors' clinical observations, there were no mesh-related abnormalities in the breast; the mesh was not palpable after the operation; and there was no recurrent ptosis. In terms of mammographic imaging, the mesh was visible as a very fine line in the periphery of the breast's parenchyma (measuring 0.2 mm on the lateral views) in three patients (17%). The mesh did not interfere with the visualization and analysis of the breast's parenchyma. In seven patients (39%), benign localized microcalcifications were detected in the breast and no further investigation was performed. In two patients (11%), grouped calcifications were detected and biopsied, with histopathologic analysis demonstrating epithelial hyperplasia with atypia. In two patients (11%), nodules smaller than 1 cm were detected and biopsied, with histopathologic analysis demonstrating a fibroadenoma in one patient and an invasive ductal carcinoma in the other.

CONCLUSIONS

The use of mesh support in breast surgery can enhance the aesthetic results without inducing visible or palpable deformities or mammographic abnormalities. In terms of surveillance mammograms, the presence of the mesh did not interfere with the diagnosis and treatment of minute lesions such as calcifications and small nodules.

Does large oversizing of self-expandable endoprostheses compensate for aortic growth?

PURPOSE

There is experimental evidence that self-expandable endoprostheses are appropriate for compensation of aortic growth. A potential future application includes their use in the treatment of aortic coarctation. Yet their behavior is poorly investigated. The present study evaluates the performance of largely oversized self-expandable endoprostheses (EPs) in the growing porcine aorta and the biologic response toward them.

METHODS

Twenty oversized EPs (Talent, TalentLoPro, Stenway, and Wallstent; nominal lumen area 314 mm(2) [diameter 20 mm]) were implanted in the descending thoracic aorta of juvenile pigs. Four nonoversized EPs (TalentLoPro; nominal lumen area 154 mm(2) [diameter 14 mm]) served as controls. Cross sections of aorta and EPs were measured by intravascular ultrasound (IVUS) at implantation and 3 months follow-up. The histologic response was assessed by microscopy.

RESULTS

At implantation, the EPs were 99 +/- 41% oversized relative to the aortic area [48 +/- 22% in diameter]. At follow-up, the area of the aortic lumen increased 60 +/- 50%, P <.001 [29 +/- 23% in diameter]. The Stenway EPs demonstrated the largest prosthetic lumen with 80 +/- 10% of their nominal area (P =.001). However, the prosthetic lumen area was reduced by intimal hyperplasia in all devices. The largest perfused lumen was obtained by the TalentLoPro EPs due to their progressive expansion. Nonoversized EPs resulted in a significantly smaller perfused lumen (P =.012). The inflammatory response to polyester was moderate, whereas polyurethane evoked an extensive body-foreign reaction.

CONCLUSION

Large oversizing of self-expandable EPs is essential in order to maintain a large perfused lumen during aortic growth, thereby minimizing the adverse effect of intimal hyperplasia. This was best achieved by the TalentLoPro EPs.

Biodegradable nanoparticles for drug and gene delivery to cells and tissue

Biodegradable nanoparticles formulated from poly (D,L-lactide-co-glycolide) (PLGA) have been extensively investigated for sustained and targeted/localized delivery of different agents including plasmid DNA, proteins and peptides and low molecular weight compounds. Research about the mechanism of intracellular uptake of nanoparticles, their trafficking and sorting into different intracellular compartments, and the mechanism of enhanced therapeutic efficacy of nanoparticle-encapsulated agent at cellular level is more recent and is the primary focus of the review. Recent studies in our laboratory demonstrated rapid escape of PLGA nanoparticles from the endo-lysosomal compartment into cytosol following their uptake. Based on the above mechanism, various potential applications of nanoparticles for delivery of therapeutic agents to the cells and tissue are discussed.

Delayed stenosis following placement of a polyethylene terephthalate endograft in the cervical carotid artery. Report of three cases

Three patients with carotid artery (CA) pseudoaneurysms were treated using four polyethylene terephthalate endografts (Wallgraft endoprostheses). Two patients received a single graft and one patient with bilateral pseudoaneurysms received two grafts. Complete occlusion of the pseudoaneurysm with patency of the arterial lumen was achieved following endograft placement in all patients. The clinical follow-up interval ranged from 12 to 18 months and included angiography or ultrasonography studies or both. One patient experienced neurological symptoms, and in-graft stenosis ranging from 50 to 100% occurred in three of the four grafts. Although the Wallgraft endoprosthesis produced good initial results for the treatment of cervical CA pseudoaneurysms, as demonstrated on radiography, it was associated with a high rate of stenosis or occlusion in all three patients.

Perivascular inflammatory reaction to a Hemobahn stent-graft: diagnosis with 3D MR angiography

PURPOSE

To present a rare perivascular inflammatory reaction to a commercially produced polytetrafluoroethylene-covered stent and demonstrate the utility of 3-dimensional (3D) magnetic resonance angiography (MRA) in the diagnosis of this phenomenon.

CASE REPORT

Three weeks after percutaneous deployment of a Hemobahn stent-graft to treat a high-grade stenosis and aneurysm of the proximal left superficial femoral artery (SFA), a 70-year-old diabetic man developed fever, pain, and local swelling of the left thigh. Venous thrombosis was excluded by ultrasound imaging; a normal flow profile was seen in the left common and superficial femoral arteries. Blood analysis found elevated inflammatory markers. MRA revealed extensive soft-tissue edema and perivascular contrast enhancement around the left SFA, but the stent-graft was patent. The clinical symptoms resolved within 7 days after initiation of anti-inflammatory therapy. Follow-up MRA scans demonstrated significantly reduced inflammatory reaction over the next few months.

CONCLUSIONS

Symptomatic perivascular inflammatory soft-tissue response to a stent-graft can be diagnosed with MR imaging studies.

Biocompatibility and performance of the Wallstent and the Wallgraft, Jostent, and Hemobahn stent-grafts in a sheep model

PURPOSE

Three recently developed stent-grafts and the Wallstent were compared directly in an ovine animal model with regard to performance and biocompatibility.

MATERIALS AND METHODS

Three stent-grafts, the Hemobahn (polytetrafluoroethylene [ePTFE]/nitinol), Wallgraft (polyester/Ni-Co-Ti-steel alloy), and Jostent peripheral stent-graft (balloon-expandable ePTFE/stainless steel), and the Wallstent (Ni-Co-Ti-steel alloy), were implanted in sheep iliac arteries (one type of each stent or stent-graft per animal, n = 8). Pre- and postimplantation luminal diameters were measured for each prosthesis and implantation site. Angiography, intravascular ultrasonography (IVUS), and histomorphometric, histologic, and scanning electron microscopic analyses were performed at 3 months.

RESULTS

Early lumen gain, late lumen loss, and patent vessel diameter at angiography were not significantly different. Two stent-grafts had significantly more neointima formation (Hemobahn, 9.88 mm(2) +/- 0.94; Wallgraft, 14.98 mm(2) +/- 0.90) than the other stent-graft (Jostent, 6.52 mm(2) +/- 0.46) and the Wallstent (5.24 mm(2) +/- 0.62; P <.01). Patent lumen area was not significantly different (Hemobahn, 42.57 mm(2) +/- 1.41; Jostent, 39.76 mm(2) +/- 2.04; Wallgraft, 40.22 mm(2) +/- 1.04; Wallstent, 41.64 mm(2) +/- 1.59; P =.57). The Hemobahn had significantly more inflammatory reaction (inflammation score of 0.83 +/- 0.03) than the Jostent (0.58 +/- 0.03), Wallgraft (0.55 +/- 0.04), or Wallstent (0.16 +/- 0.01). Angiography and IVUS demonstrated absence of anastomotic neointima formation. Endothelialization was incomplete and immature for all prostheses.

CONCLUSIONS

The stent-grafts caused a greater degree of neointima formation and inflammatory vessel wall reaction than the bare stent. However, these changes did not interfere with patent lumen areas and occurred in the absence of excessive anastomotic neointima formation.

Covered stent-graft repair of the brachiocephalic arteries: technical note

OBJECTIVE

The use of a covered stent-graft to repair disruptions of the cervical carotid and vertebral arteries is described. This device maintains vessel patency while effectively excluding pseudoaneurysms, arteriovenous fistulae, and other breaches in the integrity of the arterial wall.

METHODS

Patient 1 bled from a large rent in the proximal common carotid artery as a result of tumor invasion. Patient 2 developed a vertebral arteriovenous fistula after a stab injury to the neck. Patient 3 developed cerebral infarction and an enlarging pseudoaneurysm of the internal carotid artery, also after a stab wound to the neck.

RESULTS

All three patients were treated with the Wallgraft endoprosthesis (Boston Scientific, Watertown, MA). In each case, the vessel wall defect was repaired while antegrade flow through the artery was preserved or restored. No neurological complications occurred as a result of stent-graft deployment.

CONCLUSION

Covered stent-grafts offer an alternative to endovascular occlusion of the parent vessel, thereby expanding the therapeutic options for patients with extracranial cerebrovascular disease. These three cases highlight the usefulness and versatility of these devices for endoluminal reconstruction of the brachiocephalic vasculature.

Histological changes in canine aorta 1 year after stent-graft implantation: implications for the long-term stability of device anchoring zones

PURPOSE

To examine aortic histology 1 year after stent-graft implantation in a canine model as a means of assessing the durability of endograft fixation.

METHODS

Fourteen mongrel dogs each received 1 stent-graft and 1 bare stent placed endoluminally in the abdominal aorta. Eight animals were followed for 1 year, 3 for 4 to 8 weeks, and the remaining 3 for 24 to 48 hours. Aortic specimens were stained with hematoxylin-eosin, elastica-van Gieson, and Masson's trichrome and examined with light and electron microscopy and immunohistochemistry to identify smooth muscle cells (SMC), endothelialization, aortic wall ultrastructure, and changes at the device anchoring sites.

RESULTS

No dilatation or dissection was noted at any of the device anchoring sites. The aortic media at 1 year was remarkably decreased in thickness: 891 +/- 196 microm in the control tissue versus 388 +/- 70 microm for the proximal stent-grafted aorta and 457 +/- 148 microm for the bare-stented aortic segment. Other important histological features were reduced elastic lamellae in the stent-grafted aorta versus control (p<0.0001), increased SMC density in the stent-grafted aortic region (p<0.0001 versus control), and absence of inflammatory infiltrate. Complete neointimal covering and endothelialization of the luminal endograft surface were found. SMCs generally showed no ultrastructural features of necrosis.

CONCLUSIONS

Aortic stent-grafts induce distinctive histological changes in the aortic wall at 1 year, even when implanted in a healthy aorta. Although there is considerable medial elastin loss, an increased medial SMC density, an exuberant neointima, and a general absence of perigraft inflammation suggest an ongoing process of structural restoration at the device anchoring sites.

Three-dimensional contrast-enhanced MR angiography of endovascular covered stents in patients with peripheral arterial occlusive disease

OBJECTIVE

Three-dimensional contrast-enhanced MR angiography was performed to study MR characteristics of Hemobahn devices.

MATERIALS AND METHODS

Changes in endoluminal signal intensities and the precision of the endoluminal diameter measurement were investigated in phantom studies for different concentrations of gadopentetate dimeglumine. Before and after the Hemobahn devices had been implanted, 10 patients with peripheral arterial occlusive disease were examined on MR imaging and three-dimensional contrast-enhanced MR angiography.

RESULTS

Phantom experiments using three-dimensional MR angiography showed stent-related signal void as a dark ring in the axial image orientation, providing a precise delineation of the stent--vessel border (mean endoluminal diameter, 8.2 mm; SD, 0.6 mm). Changes in endoluminal signal intensity were evaluated quantitatively. Stent-related artifacts did not compromise diagnostic imaging quality. All Hemobahn devices were found to be patent without migration of an implanted graft. In one patient, an extensive perigraft reaction (edema and contrast-enhanced perivascular tissue) was postinterventionally detected on MR imaging and corresponded to clinically evident postimplantation symptoms.

CONCLUSION

Three-dimensional contrast-enhanced MR angiography is a suitable tool to follow up the implantation of Hemobahn devices and to detect intra- and extraluminal abnormalities.

Evaluation of local abciximab delivery from the surface of a polymer-coated covered stent: in vivo canine studies

PURPOSE

To determine the in vitro feasibility of abciximab absorption and elution from a polymer-coated, silicone-covered stent, and to determine the in vivo effect of local delivery of abciximab concerning endothelialization of a polymer-coated, silicone-covered stent in a canine model.

MATERIALS AND METHODS

Six polymer-coated, silicone-lined Wallstents were soaked in 2 mg/mL of concentrated solution of I131-labeled abciximab for a period as long as 48 hours. Quantification of abciximab absorption was determined by photon emission. Six maximally drug-loaded devices were then washed continuously with normal saline with use of a pustule pump apparatus. The quantity of residual abciximab was determined by photon emission for a period as long as 16 days. Eight similar devices (as described previously) were then implanted within the iliac arteries of four adult canines. Devices were identical except that four of eight were maximally loaded with abciximab. For each animal, one control implant was placed in the right iliac artery and one experimental implant (drug loaded) was placed in the left iliac artery, via right carotid cutdown. Animals were allowed to recover and no chronic medications were given. After an interval of 6 weeks, the animals were killed. Implants were isolated and perfused with 10% buffered formalin at a pressure of approximately 100 mm Hg for a period of 1 hour. Each implant was encased in methacrylate, sectioned into six equal segments, ground and polished, and stained with hematoxylin and eosin. Each slide was projected on a screen and the thickness of the neointima quantified. The mean neointima was determined for control and experimental groups, and compared for a potential significant difference with a Student t test.

RESULTS

Mean absorption of abciximab was 21.53 microg +/- 2.99 per device. Devices were fully saturated at 24 hours. Forty percent was absorbed at 1 hour, and 60% and 80% were absorbed at 4 hours and 12 hours, respectively. Regarding elution, 30% of abciximab was washed out after 1 hour. There was a gradual elution of the drug to 16 days, with approximately 40% remaining at the end of the term. Mean neointimal thickness was 995 microm +/- 597 for the experimental group and 1,738 microm +/- 1,042 for the control group. The difference was significant (P <.05).

CONCLUSIONS

Absorption and elution of abciximab from the surface of a covered stent is feasible. Local delivery of abciximab from the surface of this covered stent reduced the thickness of endothelial lining in the canine iliac artery compared to control.

Biocompatibility and performance of the Wallstent and several covered stents in a sheep iliac artery model

PURPOSE

To compare the biocompatibility and performance of various stent-grafts to those of a bare stent in an ovine model with a subchronic (3 months) endpoint.

MATERIALS AND METHODS

Three different types of stent-grafts (ePTFE/nitinol, n = 8; polyester/nitinol, n = 8; and polycarbonate urethane/cobalt-alloy, n = 8) and a bare stent as a control (Ni-Co-Ti-steel-alloy, n = 8) were implanted in the iliac arteries in eight female sheep. One type of each stent-graft was implanted per animal, two implants at each side. The implantation sites for each type varied from animal to animal. Angiographic control and intravascular ultrasound (IVUS) imaging were performed before and after implantation, after 2 months, and before explantation at 3 months and were used to characterize patency and to assess intimal hyperplasia. After 3 months, the implants were retrieved and subjected to histologic evaluation (after methacrylate embedding, cutting, and histologic staining) to characterize the biologic response.

RESULTS

Implantation was technically successful in all procedures. At 2 and 3 months after implantation, all segments in which stents had been implanted were patent. Marked neointima formation was found in the polyester-covered stent-graft that showed significant luminal narrowing of 50%, compared to the ePTFE-covered (24%) and polycarbonate urethane-covered endoprostheses (22%), as well as the bare stent (Wallstent; 9%; P < .001). A minimal inflammatory vessel wall reaction was demonstrated for the polyester-covered and ePTFE-covered endoprostheses; the polycarbonate urethane-covered stent-graft's response was demonstrable but not significantly different from that of the Wallstent. At 3 months, the ePTFE-covered stent-graft showed incomplete (>90%) endothelial coverage; in the other endoprostheses, complete but partially immature endothelialization was found.

CONCLUSION

All stent-grafts induced an inflammatory vessel wall reaction with neointimal hyperplasia. The polyester-covered endoprosthesis caused a marked reaction with 50% luminal stenosis. Endothelialization was retarded with the ePTFE-covered stent-graft. The bare stent performed best in regard to neointimal formation and caused the least inflammatory response.

Transjugular intrahepatic portosystemic shunts formed with polyethylene terephthalate-covered stents: experimental evaluation in pigs

PURPOSE

To evaluate the safety, efficacy, and tissue response associated with Wallstents covered with polyethylene terephthalate (PETP) compared with those associated with uncovered Wallstents for creation of transjugular intrahepatic portosystemic shunts (TIPS) in a porcine model.

MATERIALS AND METHODS

Thirteen TIPS were created in 13 minipigs: eight with PETP-covered Wallstents, five with standard Wallstents. Shunt venography was performed at 5-8 weeks, and necropsy was performed at 7-8 weeks. Histopathologic, immunohistochemical, and scanning electron microscopic examinations were performed.

RESULTS

Mean shunt stenoses of the control and graft groups were 45% and 53%, respectively. Graft stenoses involved the entire graft-bearing segment, whereas bare stent stenoses were localized within the liver tract. Myofibroblast and extracellular collagen matrix proliferation encompassed both control and graft-covered stents. There was one graft TIPS occlusion. One control TIPS stenosis was due to transstent proliferation of normal porcine hepatic tissue. A small focus of bile staining was seen on the abluminal surface of one TIPS, which was a patent PETP-lined shunt.

CONCLUSION

PETP graft TIPS provided equal, but not superior, patency to that of bare stent TIPS. The pattern of PETP TIPS graft healing differed from that of bare stents but was similar to that reported with other polyester graft vascular implants and consisted of diffuse transmural penetration and paving of the graft surface by extracellular collagen matrix and myofibroblasts.

Porous and nonporous polycarbonate urethane stent-grafts for TIPS formation: biologic responses

PURPOSE

To evaluate the biologic response to transjugular intrahepatic portosystemic shunts (TIPS) lined with polycarbonate urethane endografts and the effects of different porosity formulations.

MATERIALS AND METHODS

Seventeen TIPS were created in non-modified portal hypertensive miniswine with use of porous (n = 6), nonporous (n = 7) polycarbonate urethane stent-grafts, and control Wallstents TIPS (n = 4). Eight-week venography, histology, scanning electron microscopy, and immunohistochemical analyses were performed.

RESULTS

The mean 8-week percent parenchymal tract shunt stenosis was 75%, 46%, and 26% in the control, porous, and nonporous groups, respectively. Occlusions developed in one control, one porous, and two nonporous shunts. The biologic response to porous grafts included marked inflammation and encapsulation and permeation of the grafts by a thick fibrous pseudointima. Nonporous grafts evoked little inflammation or pseudointima. Mature thrombus lined the occluded shunts (under which little luminal pseudointima or endothelium was present). The control group showed typical pseudointimal hyperplasia enveloping the intraparenchymal portions of the stents.

CONCLUSIONS

The healing response of the porous and nonporous grafts markedly differed. Unlike the porous grafts and control stents, the nonporous endografts elicited little inflammation or luminal pseudointimal hyperplasia, although sporadic thrombosis was problematic in this normotensive model. Graft use in high-flow situations (ie, human TIPS, possibly in concert with antiplatelet agents) may allow desired shunt patency prolongation.

Histopathologic evaluation of an expanded polytetrafluoroethylene-nitinol stent endoprosthesis in canine iliofemoral arteries

PURPOSE

The authors assess a new ePTFE-nitinol stent for its long-term patency, healing, and properties of endothelialization.

MATERIALS AND METHODS

Adult greyhounds (n = 18) underwent bilateral iliofemoral placement of an endoprosthesis (Hemobahn) consisting of a nitinol stent lined with an ultrathin expanded polytetrafluoroethylene (ePTFE) material. Histologic and quantitative morphometric analyses were performed on devices explanted at 2 weeks and 1, 3, 6, and 12 months. The source of endothelialization was examined in four additional devices modified by sealing either the proximal and distal ends or the entire graft with poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP), a nonporous laminate to prevent potential transgraft endothelial cell migration.

RESULTS

Device patency assessed with both intravascular ultrasound and histologic study showed minimal arterial stenosis, irrespective of implant duration. The neointima at less than 3 months consisted of fibrin and inflammatory infiltrate; at later time points, it was composed of mostly smooth muscle cells. Flow surfaces were more than 75% endothelialized by 3 months, which was nearly complete by 6 months. Modified endoprostheses entirely enveloped with FEP resulted in endothelialization of only the proximal and distal ends; the middle regions showed nonocclusive thrombi. Conversely, devices wrapped proximally and distally showed nearly complete endothelialization.

CONCLUSIONS

This ePTFE-nitinol endoprosthesis demonstrated long-term patency at up to 1 year after implantation and showed early and nearly complete endothelialization by 6 months. The design promoted rapid endothelialization of flow surfaces, particularly in the midregion of the device possibly by transgraft migration.