Absence of tissue ingrowth through the textile fabric in a series of explanted clinic stent-grafts.

Using the retrieved devices from one autopsy and five reoperations, the biocompatibility of explanted Talent stent-grafts was investigated to highlight the capacity of the fabric to act as an effective scaffold to regenerate a blood conduit. The autopsy device was encapsulated both internally and externally, but the capsules did not penetrate through the fabric structure. The reoperation devices showed discrete patches of compact fibrin and irregularly scattered mural thrombi. Positive staining of α-actin, tissue plasminogen activator (tPA), urokinase (uPA), urokinase receptor (uPAR), and urokinase inhibitors (PAI 1, PAI 2, PAI 3, and protease nexin), and D-dimer was more frequently identified in the autopsy sample than in the reoperation samples. This preliminary assessment shows that the stent-graft retrieved during autopsy was better healed than those explanted at reoperation.

Detailed analysis of a series of explanted Talent AAA stent-grafts: biofunctionality assessment.

Six Talent stent-grafts were harvested at reoperations (N=5) and autopsy (N=1). The explants were observed nondestructively, including gross morphology, X-rays, CT scans and closed pressure system analysis. The Nitinol frames in three devices harvested at reoperations and another harvested at autopsy were intact. One had a stent fracture of the proximal bare stent, and one had a wire fracture of a thin proximal external supporting stent as well as a hole in the fabric just above the bifurcation. For the three devices structurally intact, reoperations were performed for a type 1A endoleak (one patient) and aorto-enteric fistulas (two patients). The healing characteristics were poor or absent. The fabric in the main body of the grafts harvested after aorto-enteric fistula was devoid of biological deposits. Two of the grafts harvested at reoperation demonstrated fabric holes of up to 4 mm 2. The device obtained at autopsy showed an almost continuous internal capsule with variable thickness. The luminal surface was smooth, but the capsule detached easily. The devices explanted at reoperations showed various levels of impaired biofunctionality associated with adverse outcomes. The stent-graft retrieved from autopsy was intact.

Analysis of explanted Latecba modular stent-grafts deployed transrenally to repair AAAs with short necks in 29 dogs.

Twenty-nine modular stent-grafts deployed transrenally to repair AAAs with short necks in dogs were harvested at autopsy of the animals after scheduled durations of implantations of 10 days, one month, three months, and six months. Analyses of the explanted devices included non-destructive techniques such as gross observations, X-rays CT scan, IVUS and angioscopy. Further to appropriate dissection, histological investigations were carried out by means of scanning electron microscopy (SEM) and light microscopy. All the 29 specimens were extensively encapsulated with fibrous tissues but the fibrous capsule was thin in six of them; four capsules were ulcerated. The X-rays confirmed the stability of the devices that were still straight (12), slightly bent (12) or bent (4). The modules were misaligned in only one case. IVUS and angioscopy confirmed the patency of all the stent-grafts with thin internal capsules both proximally and distally with variable capsulation in the mid-section of the grafts. The left renal artery orifices were found to be patent at dissection with no obstruction to flow. The luminal flow surface of the stent-grafts was smooth and glistening proximally and distally containing endothelial like cells and vasa-vasorum. Poor healing was noted in the aneurysm area. Transrenal deployment of this modular stent-graft is feasible and gave excellent results with regard to biofunctionality and biocompatibility. The device proved to be safe and efficient.

Transrenal deployment of a modular stent graft to repair AAAs with short necks: experiments in dogs.

Severely angulated (> 60 degrees ) or short (< 15 mm) proximal necks remain significant anatomical limitations for endovascular stent-graft repairs for abdominal aortic aneurysms. Ensuring proper proximal fixation of the stent-graft to the host artery without the short-or long-term risks of endoleak or migration represents a particular technical challenge for these anatomical circumstances. An innovative balloon expandable stent combined with a weft-knitted prosthesis was specifically designed for these situations by modelling the stent to the neck anatomy without overdistension or potential barotrauma allowing better incorporation of the device. The Latecba stent-graft consists of a 2 parts modular design. The first one, Module A, is deployed at the transrenal level and consists of a Palmaz type stent whose first half is bare and second half is sutured to a crimped weft-knitted polyester graft whose distal end holds a constriction. The second Module B is a non-crimped weft-knitted graft attached to 2 stainless steel stents. The first stent is entirely contained in the proximal textile tube, allowing fixation to module A. The second stent, which is left uncovered over the distal third, ensures proper fixation of the stent-graft distally. Following the creation of a prosthetic aneurysm in the infrarenal aorta in 32 dogs, 29 received the Latecba stent-graft for scheduled durations of 10 days, 1 month, 3 months and 6 months. Proper deployment of the stent-grafts was achieved without difficulty. All 29 animals survived and the devices were all patent at sacrifice. No device defects or migrations were observed and the stent-grafts proved to be efficient in this setting to exclude the aneurysm. Analyses of the explanted devices (gross observations, RX, CT scan, IVUS, angioscopy) confirmed the stability of this modular stent-graft. Further on-going clinical investigations are warranted to validate this concept before this stent-graft becomes commercially available without any restriction.

Specific shortcomings of endograft design.

Further to the rapid enlargement of an aneurysm to 5.6 cm in diameter after 3 years of surveillance, a 79-year-old patient was fitted with a Vanguard modular stent graft and monitored on a regular basis for 6 years. Two years later, the aneurysmal sac ruptured. The patient died 1 month after an open surgery. The device was devoid of any encapsulation and the ipsilateral limb was detached from the body. The Nitinol skeleton was mostly maintained, however, some polypropylene sutures were broken. The resulting motion of the sharp-angled Nitinol wires caused abrasion and resulted in a few localized holes that were sufficient to permit blood to percolate through the textile wall. Some polyester yarns in the warp direction were ruptured. The Nitinol wire used in this device was shown to be corrosion resistant but the selection of the polypropylene suture was inappropriate. Because this technology is maturing rapidly, these weaknesses can be avoided in the future generations of endovascular devices. It is recommended that these Nitinol wires be sutured to the fabric and that polyester yarns stronger than 68 decitex in tubes 8 mm in diameter are selected.

Persistent type II endoleak unrelated to an Anaconda aortic stent graft fulfilling the 3Bs requirements of biofunctionality, biodurability, and biocompatibility.

A patient was fitted with an Anaconda stent graft for which there was a persistent type II endoleak. Two subsequent attempts at embolization were unable to resolve the endoleak. The diameter of the aneurysm varied initially from 5.5 cm in diameter down to 4.8 cm but then later re-dilated to 6.1 cm, with evidence of persistent flow into the aneurysmal sac from the inferior mesenteric artery. Results from serial computed tomography scans demonstrated clear evidence of a type II endoleak that originated from the inferior mesenteric artery with outflow to a distal lumbar artery. The harvested stent graft did not show evidence of a device-related failure. The stent graft and its modular segments were found to have been properly deployed. Only a thin external capsule was evident at explantation. The internal wall of the device showed irregular and thin encapsulation with scattered mural thrombi, which were more prominent at the bifurcation of the main body of the device. Blood deposits and tissue development were sufficient to prevent blood oozing through the wall. The explanted Anaconda stent graft was devoid of any construction flaws or damage (fatigue of the textile or corrosion of the Nitinol wires) after implantation.

Characterization of an endovascular prosthesis using the 3Bs rule (biocompatibility, biofunctionality and biodurability): a recommended protocol to investigate a device harvested at necropsy.

Numerous endovascular stent grafts to treat intrarenal aortic aneurysms are now commercially available, and many new concepts are currently in development worldwide. In order to objectively quantify their outcomes, we propose a detailed protocol to examine a reference device that was harvested from a patient who died a few hours after endovascular stent-graft deployment for an abdominal aortic aneurysm according to the 3Bs rule (biocompatibility, biofunctionality, and biodurability). Relevant patient history of this 63-year-old man included radiotherapy treatment for lung cancer. Following the patient's death, the device was harvested en bloc together with the aneurysmal sac. The analysis of the device was conducted using nondestructive testing (X-rays, CT scan, magnetic resonance imaging [MRI], and endoscopy) and destructive testing (dissection, histology, and fabric and wire component analyses). Results from the gross examination demonstrated that the outer layer of the aneurysm sac was white, stiff, and continuous without any disruption. The Xray analysis, CT scan, and MRI confirmed that the device together with its modular segments was properly deployed at implantation. Endoscopy showed that the device was deployed securely immediately distal to the renal arteries. As anticipated, thin scattered mural thrombi at the blood/foreign material interface were observed on the blood tight flow surface. There were no tears in the fabric, and the dimensions and textile structure were well preserved. The metallic wires were intact. This fatality had no association with the stent graft as the patient's death was caused by the rupture of the pulmonary artery following intensive radiotherapy. In conclusion, autopsy, nondestructive testing, and destructive testing are therefore the necessary steps to validate any explanted endovascular stent graft in terms of biocompatibility, biofunctionality, and biodurability. In this specific case, the endovascular device fulfills the 3Bs rule. The authors recommend this protocol to investigate explanted endovascular devices.

Viscoelastic characteristics of in vitro vital and devitalized rat aorta and human arterial prostheses.

The arterial wall viscoelasticity plays an essential role in the vascular responsiveness to vasoactive drugs or pathologies. The aim of this investigation was to derive and compare resonance curve (RC), natural frequency (f(0)), dynamic modulus of elasticity (E'), and coefficient of viscosity (beta) of (i) vital and devitalized preparations of rat thoracic and abdominal aorta, (ii) human arterial prostheses, and to study the histomorphology of vital and devitalized rat aorta. The method of low frequency forced oscillations was employed. RC of vital preparations showed a hardening type of elasticity whereas in devitalized preparations it was of softening type. E' increased nonlinearly, f(0) decreased and beta increased linearly with equivalent intraluminal pressure (p(eqi)). Distensibility of abdominal aorta was lower than thoracic aorta. Distensibility decreased with increasing p(eqi). E', f(0), and beta increased significantly after devitalization. It was suggested that postmortem viscoelastic characteristics should not be used directly to specify the vital arteries viscoelasticity. RC of human prostheses showed a softening type of elasticity. Arterial prostheses have low circumferential distensibility with E'-values higher than reported in the literature for human arteries. The method of forced oscillations could be employed for studying the arterial wall biomechanics and viscoelasticity of arterial prostheses.

Biocompatibility studies of the Anaconda stent-graft and observations of nitinol corrosion resistance.

PURPOSE: To validate the deployment, in vivo performance, biostability, and healing capacity of the Anaconda self-expanding endoprosthesis in a canine aortic aneurysm model. METHODS: Aneurysms were surgically created in 12 dogs by sewing a woven polyester patch onto the anterior side of the thoracic or abdominal aorta. Anaconda prostheses were implanted transfemorally for prescheduled periods (1 or 3 months). Aneurysm exclusion and stent-graft patency were monitored angiographically. Healing was assessed with histological analysis and scanning electron microscopy (SEM). Textile analysis determined the physical and chemical stability of the woven polyester material, while the biostability of the nitinol wires was evaluated with SEM and spectroscopy. RESULTS: All prostheses were intact at explantation. After 1 month, endothelial-like cells were migrating in a discontinuous manner both proximally and distally over the internal collagenous pannus at the device-host boundary. After 3 months, endothelialization had reached the midsections of the devices, with a thicker collagenous internal capsule. Patches of endothelial-like cells were sharing the luminal surface with thrombotic deposits. However, the wall of the device at the level of the aneurysm was generally poorly healed, with multiple thrombi scattered irregularly over the luminal surface. The polyester fabric was intact except for some filaments that were ruptured adjacent to the sutures and some abrasion caused by the nitinol wires. No evidence of corrosion was found on the nitinol stents. CONCLUSIONS: This Anaconda stent-graft has demonstrated its ability to exclude arterial aneurysms. The device used in this study was an experimental prototype, and the manufacturer has incorporated new immobilization features into the model for clinical use. The constituent materials appear to be suitable in terms of biocompatibility, biofunctionality, and short-term durability.