Long-term resistance to fracture and/or corrosion of the nitinol wires of the talent stent-graft: observations from a series of explanted devices.

The biodurability of the Nitinol wires used in stent-grafts retrieved from reoperations and autopsy was analyzed to assess the possible causes of fracture and/or corrosion of the stents. The Nitinol wires of six explanted devices presented a corrosion-free surface after in vivo service. The drawing lines in the control wires were still present, but neither burrs nor flakes were observed. Pits and crevices were rare, but some shallow ones were present. Some abrasions of the surfaces of the Nitinol wires were also observed. The chemical composition of the explanted devices showed the presence of organic contamination that covered the thick layer of titanium oxide before reaching the Nitinol itself. The durability of the Nitinol employed in the manufacture of the Talent stent-grafts was confirmed; the results of this study show the Nitinol to be resistant to corrosion. We have also concluded that the fractures of the Nitinol wires in two devices were unique adverse incidents caused by compression and bending related to the sharp angle of the Nitinol wires.

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.

Fatigue and/or failure phenomena observed in the fabric of stent-grafts explanted after adverse events.

In this study, we aimed to investigate changes to the fabric of Talent stent-grafts following implantation of aortic endografts and to determine the possible causes of fatigue and/or failure of the grafts. Six devices were explanted at reoperation (N=5) and autopsy (N=1). Selected segments were assessed nondestructively by gross observation and destructively by analyzing textile characteristics and chemical properties. All of the devices showed a 4/4 twill woven fabric of monofilament polyester. These devices, explanted at reoperation and autopsy, presented different levels of fatigue and/or failure. Numerous holes were found in the fabric of two devices. The minor damage caused by the passage of the sutures through the weave to fasten the Nitinol wires did not progress significantly over time. The sutures remained relatively intact, except for some distortions. The main failure mode was the abrasion of the yarns at the apices of adjacent Nitinol stents. In two devices, this abrasion resulted in fraying of the yarns and holes in the fabric tubes. This short series of explanted devices provides evidence of damage to polyester fabric used in aortic endografts and raises questions regarding their resistance to abrasion and the risk of endoleak associated with monofilament fabric yarn.

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.

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.

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.

The ROVT Elan Valved Biplex Conduits for the Reconstruction of the Right Ventricular Outflow Tract.

The reconstruction of the right ventricular outflow tract (RVOT) system represents a considerable challenge for both manufacturers and surgeons because the patients requiring this type of devices have a very diverse set of anatomical challenges that can lead to complications and subsequent early device failures. We conducted an indepth investigation of a porcine-valve conduit explanted from a patient following an adverse event. A control device was analyzed as a reference. The rapid aging of the porcine valve in the right side of the heart together with major thrombus formation raises several questions. The difficulties encountered with materials used and also the design features of the conduits are once again highlighted. This group of patients continues to increase in number due to success in the surgical outcomes in early childhood. Therefore, there is a greater demand for an appropriate device. However, much work is still needed to achieve this goal, and the best approach to achieving success remains unanswered.

Improved image contrast with mangafodipir trisodium (MnDPDP) during MR-guided percutaneous cryosurgery of the liver.

The present study was undertaken to measure the gain observed in the liver-to-tumor contrast of perioperative images when using mangafodipir trisodium, a liver-specific contrast agent, during percutaneous cryosurgery of the liver performed under the guidance of magnetic resonance images. Retrospective quantitative analyses of MR images were performed on eleven patients having a total of 30 liver tumors treated by MR-guided percutaneous cryosurgery. An initial group of four patients were treated with no contrast agent, and was compared with a second group of 7 patients who received an intravenous injection of 5 microM/kg of mangafodipir for their cryosurgery. The percutaneous cryosurgery was monitored under the near-real-time-imaging mode of a 0.5T open-configuration MRI system using a T(1)-weighted Gradient-recalled echo pulse sequence. A significant improvement in the liver-to-tumor contrast-to-noise ratio was observed with mangafodipir (p < 0.05, paired t test) in 0.5T preoperative images. Along with the stability of the mangafodipir contrast enhancement during the entire cryosurgical procedure, the resulting gain in contrast allowed for better visualizing the presence of residual untreated tumor margins at the periphery of the cryosurgery iceball directly from perioperative images acquired with patients under narcosis. Consequently, it not only became easier for the interventionalist to determine the need for an additional cryoprobe to increase the size of the iceball during the procedure, but also to decide on the appropriate end point of the cryosurgery.

The marvel of percutaneous cardiovascular devices in the elderly.

Thanks to minimally invasive procedures, frail and elderly patients can also benefit from innovative technologies. More than 14 million implanted pacemakers deliver impulses to the heart muscle to regulate the heart rate (treating bradycardias and blocks). The first human implantation of defibrillators was performed in early 2000. The defibrillator detects cardiac arrhythmias and corrects them by delivering electric shocks. The ongoing development of minimally invasive technologies has also broadened the scope of treatment for elderly patients with vascular stenosis and aneurysmal disease as well as other complex vascular pathologies. The nonsurgical cardiac valve replacement represents one of the most recent and exciting developments, demonstrating the feasibility of replacing a heart valve by way of placement through an intra-arterial or trans-ventricular sheath. Percutaneous devices are particularly well suited for the elderly as the surgical risks of minimally invasive surgery are considerably less as compared to open surgery, leading to a shorter hospital stay, a faster recovery, and improved quality of life.

Implant degradation and poor healing after endovascular repair of abdominal aortic aneurysms: an analysis of explanted stent-grafts.

PURPOSE: To study explanted stent-grafts to achieve a better understanding of the mechanisms of failure after endovascular treatment of abdominal aortic aneurysms (AAA). METHODS: Twelve stent-grafts were harvested at autopsy (n=3) or during surgical conversion (n=9). Device alterations were investigated by macroscopic examination, radiography, and surface analysis techniques. Healing around the implants was studied via histology and immunohistochemistry, with particular attention to the stent-graft/tissue interface. RESULTS: Degradation was more important with Vanguard stent-grafts (off the market) than with AneuRx and Talent stent-grafts, but rupture of nitinol wires and poor surface finish in Talent stent-grafts raise concern about their corrosion resistance and long-term stability. Poor healing was observed around stent-grafts even after several years of implantation, with absence of vascular smooth muscle cells, fibroblasts, and collagen formation. In addition to the well-known foreign body reaction around the graft, numerous polymorphonuclear cells characteristic of the first step of healing were present in tissues around stent-grafts retrieved at surgical conversion. Factors explaining the lack of tissue organization around stent-grafts are discussed. CONCLUSION: The long-term stability of implants remains a concern and requires more transparency from manufacturers regarding the surface properties of their devices. Lack of neointima formation impairs biological fixation of the implant to the vessel wall, leading to possible endoleaks and migration. New-generation stent-grafts promoting biological fixation should be developed to improve clinical outcomes of this minimally invasive treatment.

Magnetic resonance-guided percutaneous cryosurgery of breast carcinoma: technique and early clinical results.

PURPOSE: This phase I study was designed to demonstrate the feasibility, safety, efficacy and predictability of percutaneous cryosurgery, guided under magnetic resonance (MR) imaging, in the treatment of invasive breast carcinoma. PATIENTS AND METHODS: Under the guidance of near-real-time T1-weighted FSE images of a 0.5-T open-configuration MR system, percutaneous cryosurgery was performed in 25 patients with operable invasive breast carcinoma, 4 weeks prior to their scheduled mastectomy. Predictive assessments by interventional radiologists using 4 breast-imaging techniques (mammography, sonography, scintigraphy and MR) were correlated with postmastectomy results of histopathology and assessed for predictability. Local and systemic morbidity were also evaluated during the month of follow-up preceding mastectomy. RESULTS: Percutaneous cryosurgery resulted in no serious complications, either local or systemic. All tumoural tissues included in the cryogenic "iceball" were destroyed, with no viable histologic residues. Ablation was total in 13 of the 25 tumours treated. Combining periprocedural MR images with postprocedure scintimammographic findings enabled a 96% rate for predicting the cryosurgical results. CONCLUSIONS: MR-guided cryosurgery of breast carcinoma is feasible, safe and efficient, with predictable results. Major drawbacks are that the cryolesion (a palpable iceball) persists for a month or more after the procedure, undermining the reliability of the physical examination; and that breast imaging (mammography, ultrasound and MR) presents the same difficulty of interpretation as the physical exam even 1 month after the procedure. More studies are required to refine this treatment method.

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.