Comparison of the deployment and healing of thin-walled expanded PTFE stented grafts and covered stents

Development and validation of a gel wax phantom to evaluate geometric accuracy and measurement of a hyperechoic target diameter in diagnostic ultrasound imaging

Diagnostic ultrasound (US) scanners are generally evaluated using proprietary quality assurance (QA) phantoms, but their prohibitively high cost may prevent organizations to perform the necessary tests. This study aimed to develop a low-cost gel wax phantom with targets to determine the lateral and axial resolution and diameter of a hyperechoic target in an US scanner. The acoustic property (AP) of gel wax, which includes the speed of sound (cus), acoustic impedance (Z), and attenuation coefficient (µ), were determined for multiple transducers operating at 2.25, 5, 10, 15, and 30 MHz. These results were compared to the AP of soft tissue. Two polytetrafluoroethylene (PTFE) rectangular frames with holes separated by 5, 10, and 20 mm were constructed. Nylon filaments and stainless-steel disc (SS disc) (diameter = 16.8 mm) were threaded through the frames and suitably placed in gel wax to obtain orthogonal targets in the phantom. The target dimensions obtained from computerized tomography (CT) and US images of the phantom were compared for phantom validation. The average cus=1431.4 m/s, mass density ρ = 0.87 g/cm3, Z = 1.24 MRayls, and µ ranged from 0.7 to 0.98 dB/cm/MHz for gel wax at 22 °C. The US image measurement exhibited a maximum error in determining the diameter of the SS disc, resulting in a value of 18 mm instead of its actual value of 16.8 mm. The phantom volume decreased by 1.8% in 62 weeks. The present phantom is affordable, stable, customizable, and can be used to evaluate diagnostic US scanners across multiple centers.

Mid-Term Results of Endovascular Aneurysm Sealing in the Treatment of Abdominal Aortic Aneurysm With Unfavorable Morphology

PURPOSE

To report mid-term results of endovascular aneurysm sealing (EVAS) of abdominal aortic aneurysms (AAA) deemed unsuitable for a standard endovascular aneurysm repair (EVAR).

METHODS

A prospectively maintained database of 42 patients with EVAR-unfavorable anatomy treated by EVAS combined with chimney grafts in case of the proximal AAA neck shorter than 5 mm was analyzed. Early outcomes included final angiographic result, intra- and early post-operative deaths, and complications. Mid-term outcomes included all-cause mortality (ACM), aneurysm-related mortality (ARM), patency of the stents, occurrence of endoleaks, serious complications and graft failures defined as the AAA growth of more than 5 mm, type I endoleak, occlusion of the stent-graft or chimney graft, aorto-duodenal fistula, or aneurysm rupture.

RESULTS

The procedure was completed in all patients. Twenty-eight chimney grafts were implanted in 19 patients. Patients were followed for a median of 24 months (range 12-34 months). There were 2 intraoperative ruptures and 1 patient died in an early postoperative period. The cumulative ACM was 15, 21, and 36% at 12, 24, and 36 months, respectively, and the cumulative ARM was 8, 11, and 27% at 12, 24, and 36 months, respectively. Three out of 5 aneurysm-related deaths were due to a secondary aorto-duodenal fistula. The cumulative incidence of graft failure was 20, 27, and 42% at 12, 24, and 36 months, respectively. The cumulative incidence of an endoleak was 5, 9, and 23% at 12, 24, and 36 months, respectively. The graft failure increased significantly both ACM (p = .012) and ARM (p = .00003). The implantation of chimney grafts at the initial procedure increased ARM significantly (p = .008). The presence of an endoleak did not have any significant influence on ACM and ARM.

CONCLUSION

Patients treated with EVAS for AAAs with EVAR-unfavorable anatomy, especially those with chimney grafts, exhibit a high risk of graft failure and subsequent death.

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.

Prevention of Spinal Cord Ischemia in an Ovine Model of Abdominal Aortic Aneurysm Treated with a Self-Expanding Stent-Graft

Purpose:

To present novel techniques to prevent spinal ischemia during aneurysm creation and chronic bifurcated stent-graft implantation in an ovine model of abdominal aortic aneurysm (AAA).

Method:

Experimental AAAs were created in 38 sheep. To prevent spinal ischemia, an internal aortic shunt was used during aneurysm creation. In the animals designated to receive bifurcated stent-grafts, a left external iliac-to-internal iliac bypass was performed to revascularize the caudal artery and prevent postdeployment spinal cord ischemia. Specimens were harvested at 1 week, 1, 3, and 6 months, and 1 year.

Results:

Aneurysms were successfully created without paralysis in 35 animals. Two died due to aspiration pneumonia. Of the 33 animals implanted with endografts, 16 (94%) of 17 with straight devices and 15 (94%) of 16 with bifurcated stent-grafts survived with well-functioning, patent stent-grafts. Paralysis developed in 2 animals after endografting due to technical failures.

Conclusions:

The use of an internal shunt during aneurysm creation and internal iliac-to-external iliac transposition prior to bifurcated stent-graft deployment prevented spinal ischemia in an ovine AAA model. Chronically deployed stent-grafts were well tolerated.

Endovascular Treatment of a Posttraumatic Femoral Vein—Profunda Femoris Artery Fistula

Purpose:

To describe successful endovascular management of a posttraumatic arteriovenous fistula (AVF) when a covered stent is unavailable.

Methods and Results:

An AVF developed between the profunda femoris and the femoral vein in a 59-year-old man undergoing a total hip revision procedure. No covered stent being available, a Dacron plug was inserted on top of scaffolding created by a conventional stent and embolization coils. Successful control of hemorrhage and resolution of the AVF was documented. Pulmonary embolization was avoided by using this scaffolding technique.

Conclusions:

Dacron can be used for occlusion of a medium-sized artery in an emergency situation in selected cases.

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.

Torsion and Kinking of Unsupported Aortic Endografts: Treatment by Endovascular Intervention

Purpose:

To describe the management strategies used to deal with twisted aortic endografts.

Methods and Results:

Two patients with successfully excluded aortic aneurysms developed symptoms referable to previously undetected twists in their endografts (one EndoVascular Technologies [EVT] and one customized aortomonoiliac device). The limb graft occlusion in the EVT graft was treated surgically with a femorofemoral bypass, but the aortomonoiliac endograft was salvaged with percutaneous implantation of a Wallstent. During another aortomonoiliac procedure, suboptimal flow through the endograft was traced to contortion of the endograft as it passed over an angulated proximal aneurysm neck. An X-large Palmaz stent was deployed to support the graft at this point.

Conclusions:

Unsupported aortic endografts may develop twists and kinks during deployment that can lead to low outflow and graft occlusion. Endovascular techniques are available to repair these defects postoperatively, although more precise intraoperative assessment tools may identify these problems so that they can be corrected at the initial intervention.

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.

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.

Polymethylmethacrylate (PMMA) as an embedding medium preserving tissues and foreign materials encroaching in endovascular devices

Problems of displacement, poor healing, degradation of the polymers and corrosion of the metallic frame in endovascular devices still require in-depth investigations. As the tissues and the foreign materials are in close contact, it is of paramount importance to efficiently investigate the interfaces between them. Inclusion in polymethymethacrylate (PMMA) permits us to obtain thin slides and preserve the capacity to perform the appropriate stainings. An AneuRx prosthesis was harvested in bloc with the surrounding tissues at the autopsy of a patient 25 months post deployment in a 5.7 cm diameter AAA and sectioned in the direction of the blood flow in two halves. A cross-section of the encapsulated distal segment together with the surrounding aneuryshmal sac was embedded in polymethylmethacrylate (PMMA). Further to complete polymerization, slices of the specimen were cut on a precision banding saw under coolant. They were affixed onto methacrylate slides with a UV cured adhesive. Binding and polishing were done on a numeric grinder and slices 25 to 30 microm in thickness were stained with toluidine blue prior to observation in light microscopy. Additional slices were prepared for scanning electron microscopy and X-ray energy dispersive spectrometry for determination of the elemental composition of the Nitinol stent. The aortic wall did not demonstrate complete integrity along with its circumference. Some areas of rupture were noted. The content of the sac was heavily shrunk and was mostly acellular. The walls of the device were very well encapsulated. The PMMA embedding permitted the polyester wall, the Nitinol wire and the collagen to keep in close contact. Scanning electron microscopy involved backscattered electrons and confirmed the corrosion the Nitinol wire at the boundary with living tissues. Based upon the results obtained, we believe that PMMA embedding is the most appropriate method to process endovascular devices for histological and material investigation. Needless to say, that paraffin embedding would have not been feasible for such a big size specimen involving different materials.

MRI virtual biopsies: analysis of an explanted endovascular device and perspectives for the future

Information that can be obtained by magnetic resonance imaging (MRI) of explanted endovascular devices must be validated as this method is non-destructive. Histology of such a device together with its encroached tissues can be elegantly performed after polymethymethacrylate (PMMA) embedding, but this approach requires destruction of the specimen. The issue is therefore to determine if the MRI is sufficient to fully validate an explanted device based upon the characterization of an explanted specimen. An AneuRx device deployed percutaneously 25 months earlier in a 75-year-old patient was removed en bloc at autopsy together with the surrounding aneurysmal sac and segments of the upstream and downstream arteries. Macroscopic pictures were taken and a slice of the cross-section was processed for histology after polymethylmethacrylate (PMMA) embedding. For the magnetic resonance imaging investigation, the device was inserted in a Biospec 4.7 T MRI system with a 20 mm diameter birdcage resonator used for both emission and reception. A Spin-Echo (SE) was used to acquire both T1 proton density (PD) and T2 weighted images. A gradient-echo (GE) sampling of a free induction decay (GESFID) was used to generate multiple GE images using a single excitation pulse so that four images at different TE were obtained in the same acquisition. The selected explanted device was outstandingly well-healed compared to most devices harvested from humans. No inflammatory process was observed in contact or at distance of the materials. In MRI T1 images display no specific contrast and were homogeneous in the different tissues. The contrast was improved on proton density weighed images. On the T2 weighed images, the different areas were well identified. The diffusion images displayed in the surrounding B region had the greatest diffusion coefficient and the greatest anisotropy. The MRI analysis of the explanted AneuRx device illustrates the possibilities of this technique to characterize the interaction of the endovascular graft with the surrounding tissues. MRI is a breakthrough to investigate explanted medical devices but it also can be advantageously used in vivo to obtain virtual biopsies, because real biopsies to determine the 3 Bs (biocompatibility, biofunctionality and bioresilience) cannot be carried out as they could obviously initiate infection and degradation of the foreign materials.

Short-term results of endovascular AAA repair with the Excluder bifurcated stent-graft

PURPOSE

To evaluate the safety and efficacy of endovascular abdominal aortic aneurysm (AAA) repair with a commercial modular stent-graft.

METHODS

Between February 1998 and May 2000, 66 consecutive patients (56 men; mean age 70 years, range 51-87) were recruited for a single-center study to examine the safety and efficacy of the Excluder stent-graft for endovascular AAA repair. The patients were predominantly asymptomatic (2 symptomatic) and categorized as ASA III or IV (62, 94%), with aneurysms that ranged from 35 to 89 mm in diameter (mean 56). Surveillance included clinical examination and computed tomographic aortography at discharge, 6 weeks, and at 6, 12, and 24 months.

RESULTS

All endoprostheses were implanted as intended, but 1 patient succumbed to an intraprocedural brainstem infarction (1.5% 30-day mortality rate). The major and minor morbidity rates were 21% and 4.5%, respectively. Primary technical success at discharge was 68% (45/66), largely as the result of a 30% (20/66) endoleak rate. The aneurysm exclusion rate at 30 days was 88%. During the mean 5.8-month follow-up, no device migration, limb kinking, aneurysm rupture, or limb thrombosis was observed.

CONCLUSIONS

Endoluminal AAA repair with the bifurcated Excluder stent-graft is safe and efficacious in the short term. Longer surveillance will have to demonstrate if the excellent early results can be maintained over the years.

Endovascular aneurysm repair: Magnetic resonance monitoring of histological organization processes in the excluded aneurysm

BACKGROUND

The purpose of the present study was to systematically analyze the histopathologic organization processes in excluded aneurysms after endovascular stenting and to develop a noninvasive monitoring method for these processes using MRI.

METHODS AND RESULTS

In 36 mongrel dogs, autologous aortic aneurysms were created. Endovascular treatment was performed using covered stents. Follow-up was after 1 week, 6 weeks, and 6 months. MRI was performed with T2-weighted turbo-spin-echo sequences and T1-weighted spin-echo sequences and was repeated after contrast bolus with gadolinium. Histopathologic findings were correlated to signal intensities (SIs) of MRI images. SIs of distinct areas were analyzed and related to the SI of the reference tissue (SI ratio). The histological organization process was gradated in the following 4 classes: class 0, detritus without organization; classes I and II, connective tissue proliferation with increasing fiber synthesis; and class III, dense fibrous connective tissue. The SI ratios of T2-weighted images were significantly reduced from 4.76 in detritus (0) to 1.70 in dense fibrous connective tissue (III) as a function of histopathologic classes. SI ratios of T1-weighted images were reduced from 1.84 (0) to 1.12 (III). Contrast bolus with gadolinium-DTPA showed no change of SI ratio in detritus (0.99) but an increase from 1.12 (I) to 1.70 (III) as organization increased.

CONCLUSIONS

The histological organization of excluded aneurysms can be monitored by MRI. Progressive organization is indicated by decreasing SIs in T2- and an increasing signal increase in T1-weighted images after gadolinium bolus.

Use of a balloon-expandable, radially reinforced ePTFE endograft after remote SFA endarterectomy: a single-center experience

PURPOSE

To report our experience with endovascular femoropopliteal bypass grafting using a distensible, radially reinforced polytetrafluoroethylene endograft combined with remote endarterectomy.

METHODS

Forty-one patients (33 men; mean age 70 years, range 45-79) with symptomatic femoropopliteal occlusive disease underwent remote endarterectomy of the superficial femoral artery (SFA) followed by implantation of a balloon-expandable Enduring endovascular graft. All patients entered an extensive surveillance program, including angiography and duplex scanning at regular intervals.

RESULTS

Endarterectomy and endograft implantation were ultimately successful in all patients; 5 (12%) technical difficulties occurred intraoperatively and were treated with additional endovascular techniques. Control angiography at 1 week postoperatively demonstrated a patent endograft in 39 (95%) patients. Mean ankle-brachial index increased significantly from 0.57 to 0.91 (p < 0.001). Including the 2 early failures, 18 occlusions were documented over a median 15-month follow-up (range 3-24), due mainly to significant stenosis at the proximal and distal anastomoses. In 8 of 10 successfully reopened and revised endografts, reocclusion occurred after a median interval of only 1.8 months. Life-table analysis revealed cumulative primary and secondary patency rates of 42% and 56%, respectively, at 18 months. In the last 12 cases, the proximal end of the graft was sutured end-to-end to the transected SFA, which improved the short-term secondary patency rate to 83%.

CONCLUSIONS

Insertion of the Enduring endovascular graft following remote endarterectomy effectively results in a less invasive treatment for femoropopliteal occlusive disease. Additional technical refinements of the procedure may be required to avoid early procedure- and graft-related failures.

Covered stent implantation by the puncture method for the treatment of a small aneurysm of the common iliac artery

A method to repair endovascular aneurysms with covered stents has recently been developed. In the present paper, the implantation of a covered stent through a 12Fr sheath by the puncture method for the treatment of an isolated aneurysm of the right common iliac artery is reported. The aneurysm was less than 3 cm in diameter, and computed tomography showed no signs of aneurysm rupture, but the patient nonetheless complained of right lower abdominal pain and constipation. It was decided to implant a covered stent in lieu of surgical repair because it was difficult to prove a causal relationship between the aneurysm and the patient's complaints. Fortunately, after implantation, the symptoms were resolved. In conclusion, it is possible to choose this less invasive type of therapy for the treatment of an isolated iliac artery aneurysm if the patient complains only of general malaise and there are no certain signs of an impending rupture, although surgery should be indicated regardless of aneurysm size.

Endovascular femoropopliteal bypass combined with remote endarterectomy in SFA occlusive disease: initial experience

OBJECTIVES

to evaluate the feasibility of endovascular femoropopliteal bypass in combination with remote endarterectomy of the superficial femoral artery (SFA).

DESIGN

prospective, open study.

MATERIALS

thirteen patients with chronic lower-leg ischaemia due to femoropopliteal occlusive disease underwent 14 SFA remote endarterectomy procedures followed by endovascular ePTFE femoropopliteal bypass. Primary endografting was performed in seven cases. The indication for endograft insertion was vessel-wall perforation during endarterectomy in the remaining seven cases.

METHODS

pre- and postoperative clinicl and haemodynamic data were collected and compared. Technical problems and procedure-related complications were noted.

RESULTS

initial technical success was achieved in all 14 limbs. However, four early reocclusions occurred after 1, 4, 6 and 10 weeks postoperatively. Two late reocclusions were detected after 16 and 22 months without any preceding symptoms or haemodynamic changes. Primary and secondary patency rates were 61% and 70% at two years, probably due to graft-related factors, such as lack of radial force, graft folding or kinking, and possibly altered mechanical or thrombogenetic properties after dilatation of the ePTFE graft.

CONCLUSIONS

endovascular femoropopliteal endo-bypass after SFA remote endarterectomy is a feasible procedure. Further technical improvements are necessary to avoid procedure- and graft-related early failures.

Endovascular treatment of a posttraumatic femoral vein-profunda femoris artery fistula

PURPOSE

To describe successful endovascular management of a posttraumatic arteriovenous fistula (AVF) when a covered stent is unavailable.

METHODS AND RESULTS

An AVF developed between the profunda femoris and the femoral vein in a 59-year-old man undergoing a total hip revision procedure. No covered stent being available, a Dacron plug was inserted on top of scaffolding created by a conventional stent and embolization coils. Successful control of hemorrhage and resolution of the AVF was documented. Pulmonary embolization was avoided by using this scaffolding technique.

CONCLUSIONS

Dacron can be used for occlusion of a medium-sized artery in an emergency situation in selected cases.

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.

Prevention of spinal cord ischemia in an ovine model of abdominal aortic aneurysm treated with a self-expanding stent-graft

PURPOSE

To present novel techniques to prevent spinal ischemia during aneurysm creation and chronic bifurcated stent-graft implantation in an ovine model of abdominal aortic aneurysm (AAA).

METHOD

Experimental AAAs were created in 38 sheep. To prevent spinal ischemia, an internal aortic shunt was used during aneurysm creation. In the animals designated to receive bifurcated stent-grafts, a left external iliac-to-internal iliac bypass was performed to revascularize the caudal artery and prevent postdeployment spinal cord ischemia. Specimens were harvested at 1 week, 1, 3, and 6 months, and 1 year.

RESULTS

Aneurysms were successfully created without paralysis in 35 animals. Two died due to aspiration pneumonia. Of the 33 animals implanted with endografts, 16 (94%) of 17 with straight devices and 15 (94%) of 16 with bifurcated stent-grafts survived with well-functioning, patent stent-grafts. Paralysis developed in 2 animals after endografting due to technical failures.

CONCLUSIONS

The use of an internal shunt during aneurysm creation and internal iliac-to-external iliac transposition prior to bifurcated stent-graft deployment prevented spinal ischemia in an ovine AAA model. Chronically deployed stent-grafts were well tolerated.

Devices for aortic aneurysm repair

Although the technical success and short-term efficacy of endovascular grafts have now been demonstrated, the long-term durability of grafts used in the aorta remains to be proven. No long-term data are yet available regarding device durability or patient outcome beyond the initial few years. Recent evidence shows that the ability of endovascular grafts to cause shrinkage and regression of aortic aneurysms may have a paradoxic effect of distorting the endograft itself, thus causing geometric changes within the supporting metallic framework and, ultimately, device failure (Fig. 9). Thus, the desired positive effect of the device may, ironically, lead to its eventual failure.

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.

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.

Torsion and kinking of unsupported aortic endografts: treatment by endovascular intervention

PURPOSE

To describe the management strategies used to deal with twisted aortic endografts.

METHODS AND RESULTS

Two patients with successfully excluded aortic aneurysms developed symptoms referable to previously undetected twists in their endografts (one EndoVascular Technologies [EVT] and one customized aortomonoiliac device). The limb graft occlusion in the EVT graft was treated surgically with a femorofemoral bypass, but the aortomonoiliac endograft was salvaged with percutaneous implantation of a Wallstent. During another aortomonoiliac procedure, suboptimal flow through the endograft was traced to contortion of the endograft as it passed over an angulated proximal aneurysm neck. An X-large Palmaz stent was deployed to support the graft at this point.

CONCLUSIONS

Unsupported aortic endografts may develop twists and kinks during deployment that can lead to low outflow and graft occlusion. Endovascular techniques are available to repair these defects postoperatively, although more precise intraoperative assessment tools may identify these problems so that they can be corrected at the initial intervention.

Stent versus endovascular graft healing characteristics in the porcine iliac artery

PURPOSE

To evaluate the healing characteristics of stents versus endovascular grafts in the porcine iliac artery.

MATERIALS AND METHODS

A total of 20 iliac arteries in 10 domestic swine were used to evaluate the healing characteristics of stents versus endovascular grafts. Each animal received one stent and one endovascular graft in opposite iliac arteries. The endovascular grafts were constructed with use of 6 cm of expanded polytetrafluoroethylene (ePTFE) (3 mm inner diameter, 30 microm internodal distance) and Palmaz stents (P204 or P188) secured at each end of the graft. A solitary Palmaz stent (P308 or P294) was used on the opposite side. The devices were explanted at 1, 5, and 12 weeks.

RESULTS

One of three endovascular grafts and two of three stents were patent at 1 week. Two of three endovascular grafts and all three stents were patent at 5 weeks. All three endovascular grafts and stents were patent at 12 weeks. Gross examination, histologic, and scanning electron microscopy demonstrated differences in the healing response of the two devices. A marked abluminal inflammatory response to the graft material was observed. This resulted in neovascularization of the tissue along the abluminal surface of the graft. In addition, marked neointimal thickening at the unsupported section of the endovascular graft resulted in significant luminal narrowing.

CONCLUSION

The porcine model may be used for evaluating the healing characteristics of endovascular grafts. Intravascular placement of ePTFE prosthetic graft material dramatically alters the healing of this type of graft material. The graft material did not prevent the formation of a progressively thickening neointima.

Endoluminal abdominal aortic aneurysm surgery

BACKGROUND

The development of devices designed for the endoluminal repair of abdominal aortic aneurysm has led to the emergence of new endovascular techniques.

METHODS

Articles and case reports obtained from a Medline search of the English language literature from 1989 to 1997 are reviewed. This search was carried out using the MeSH heading 'aortic aneurysm, abdominal' and the keywords 'endovascular' and 'endoluminal'.

RESULTS

Reported mortality and complication rates for endoluminal aneurysm repair are similar to those following conventional repair, with the exception of continued perfusion of the aneurysm sac which remains a major problem following endoluminal repair.

CONCLUSION

Successful endoluminal aneurysm exclusion is associated with reduced aneurysm diameter. However, longer term results of endoluminal repair, in particular of sealed endoleaks, are required before randomized controlled trials of endoluminal versus conventional repair can be undertaken.

Deployment and healing of an ePTFE encapsulated stent endograft in the canine aorta

This study evaluated deployment mechanics and long-term healing of an endoluminally placed stent/graft in normal canine aortas. The endoluminal graft (ELG) consisted of a 8.5 cm segment of expanded polytetrafluoroethylene (ePTFE) graft material (Impra, Inc., Tempe, AZ) encapsulating a series of six Palmaz P-128 stents (Johnson & Johnson Interventional Incorporated, New Brunswick, NJ) along the length of the graft. The prostheses were deployed via the femoral artery using a 14Fr delivery system that contained a balloon catheter to expand the ELG in the infrarenal aorta. Twenty-one prostheses were deployed and evaluated at 1 week (n = 3), 1 month (n = 3), 3 months (n = 3), 6 months (n = 9), and 1 year (n = 3). Dimensions of the infrarenal aorta were determined with intravascular ultrasound (IVUS) and angiography prior to deployment of devices. Real-time fluoroscopy and IVUS were used to monitor device deployment with both imaging modalities repeated following implantation. Gross inspection and microscopic evaluation was performed on the explanted specimens following in vivo evaluation by CT scan, IVUS, and angiography prior to retrieval of the specimens. The prostheses were easily deployed from the femoral access site. Oversizing of the deployment balloon compared to the aortic diameter was necessary to accommodate the 10% device recoil observed following balloon deflation, however, all devices were seated against the aortic wall as evidenced by IVUS. At explant, all devices ware widely patent with limited luminal thrombosis observed in four specimens (19%). Devices were well-incorporated by cellular ingrowth into the ePTFE with the formation of neointima. No device migration or postdeployment recoil was observed. ePTFE graft material between stents protruded slightly into the vessel lumen accounting for a 10% luminal reduction. Fully supported ELG's consisting of balloon expandable stents encapsulated in ePTFE are easily deployed using a low-profile delivery system. Specimens demonstrated uniform long-term patency and healing up to 1 year in a canine aortic model. Those preliminary findings support further study of this fully supported prosthesis in the treatment of arterial disease.

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.