Steel Stents Research Articles

The role of self-expanding vascular stent in superior vena cava syndrome for advanced tumours.

Superior vena cava (SVC) syndrome (SVCS) is a life-threatening occurrence that necessitates prompt treatment. At present, endovascular stenting is proposed as a first-line treatment to relieve symptoms. We assessed the effectiveness, safety and outcome of SVC stent positioning in patients affected with advanced cancer. Forty-two patients undergoing stent positioning in the SVC for neoplasms from January 2002 to December 2018 form the basis of this retrospective study. Demographic data, risk factors, associated diseases, symptoms at presentation according to the score proposed by Kishi and the type of SVCS according to Sanford and Doty were collected. Minor and major complications were recorded. Suspected stent occlusion was confirmed by means of recurrence of symptoms followed by a confirmatory computed tomography (CT). Thirty-four (81%) patients had a nonresectable lung tumour invading or compressing the SVC. Five (12%) patients had a non-Hodgkin's lymphoma, and three (7%) had metastatic lymphadenopathies. Nitinol stents (Memotherm®) were employed in 19 (45%) patients, and steel stents (Wallstent™) in the remaining 23 (55%) patients. Thirty-five (85%) patients died during follow up for disease progression and the overall survival rate at 24months was 11% (standard error (SE)=0.058). Thirteen patients (32%) had a recurrence of SVCS because of stent thrombosis in three (23%) and extrinsic compression from uncontrolled cancer progression in ten (77%). The overall symptom-free interval at 24months was 57% (SE=0.095). We recommend the use of the endovascular procedure as a first-line treatment in locally advanced or metastatic tumour in the presence of SVCS.

Continuously Grooved Stent Struts for Enhanced Endothelial Cell Seeding

PurposeImplantation of pre-endothelialized stents could enhance cellular recovery of a damaged vessel wall provided attached cells remain viable, functional and are present in sufficient numbers after deployment. The purpose of this study was to evaluate the feasibility of grooved stainless steel (SS) stents as a primary endothelial cell (EC) carrier with potentially enhanced EC protection upon stent deployment.Materials and MethodsAttachment and behavior of enzymatically harvested human adult venous ECs seeded onto gelatin-coated vascular stents were evaluated in an in vitro setting. Smooth and grooved SS stents and smooth nitinol stents were studied.ResultsAll cells expressed EC markers vWF and CD31. Using rotational seeding for a period of 16–24 h, ECs attached firmly to the stents with sufficient coverage to form a confluent EC monolayer. The grooved SS wire design was found to enable attachment of three times the number of cells compared to smooth wires. This also resulted in an increased number of cells remaining on the stent after deployment and after pulsatile flow of 180 ml/min for 24 h, which did not result in additional EC detachment.ConclusionsThe grooved stent provides a potential percutaneous means to deliver sufficient numbers of viable and functional cells to a vessel segment during vascular intervention. The grooves were found to offer a favorable surface for EC attachment and protection during stent deployment in an in vitro setting.

Layer-by-layer coating of stainless steel plates mediated by surface priming treatment to improve antithrombogenic properties

The stainless steel (SS) stents have been used in clinics since 1994. However, typical drawbacks are restenosis and thrombus formation due to limited endothelialisation and hemocompatibility. Surface modification is a smart strategy to enhance antithrombogenicity by promoting endothelialisation. In this work, the layer-by-layer (LbL) technique was applied for coating SS model substrates, after surface priming by functionalisation with 3-aminopropyl triethoxysilane (APTES). A LbL coating made of 14 layers of poly(styrene sulfonate)/poly(diallyldimethylammonium chloride) and heparin as last layer was deposited. FTIR-ATR analysis and contact angle measurements showed that LbL was an effective method to prepare nanostructured coatings. XPS analysis and colorimetric assay employing 1,9-dimethylmethylene blue dye to detect -COOH groups confirmed the successful polyelectrolyte deposition on the coated samples. Preliminary in vitro cell tests, using whole blood and human platelets, were performed to evaluate how surface modification affects platelet activation. Results showed that SS and SS-APTES surfaces induced platelet activation, as indicated by platelet spreading and filopodia formation. After surface modification by LbL coating, the platelets assumed a round shape and no fibrin nets were detected. Data demonstrated that LbL coating is a promising technique to fabricate antithrombogenic surface.

Benign Tracheal Stenosis Should Never be Stented With Metallic Devices

In this issue of Archivos de Bronconeumologia Serrano et al.1 report the results of an elegant experimental study on the rabbit trachea. The authors hypothesise that drug-eluting stents attenuate granuloma formation leading to inflammatory stenosis, which is a well-known adverse effect of metallic stents on the tracheal epithelium. As commented by the authors in the text, in 2005 the US Food and Drug Administration alerted healthcare professionals “to serious complications associated with the use of metallic tracheal stents in patients with benign airway disorders. . .including all covered and uncovered metallic tracheal stents”.2 In that safety alert for medical products, potential complications were described as “obstructive granulation tissue, stenosis at the ends of the stent, migration of the stent, mucous plugging, infection, and stent fracture”. Moreover, the notification alerted against the use of metallic stents as a bridge for definitive therapies due to the risks associated with removal. FDA recommendations are supported by the authors’ data. In their series, 40% of the cases (14 out of 30 animals) died as a result of the procedure. In the metallic stent series, mortality due to tracheal obstruction occurred in 80% of cases (8/10 rabbits). Therefore, we totally agree with the authors’ main conclusion: steel stents should never be indicated for the treatment of inflammatory tracheal stenosis. The second conclusion of the investigation (nitinol tracheal stents are the least reactive) is arguable, and should be reported in a different manner, since in the authors’ series, 20% of the nitinol stent-treated cases (2 out of 10) died due to airway obstruction. This would be a non-acceptable rate of adverse events in clinical series. Thus, it should be clearly stated that nitinol stents used inside a healthy trachea, in the authors’ experimental setting, were associated with mortality in 20% of cases. The use of drug-eluting stents in the airways has been rarely reported. Chao et al.3 implanted biodegradable cis-platinum

Real world experience with an indigenously manufactured stent Cobal C – A retrospective study

BackgroundSecond generation bare metal stents made of cobalt chromium alloy are superior to first generation stain less steel stents. The thin struts are shown to reduce clinical and angiographic adverse outcomes. ObjectiveTo study the long term clinical and angiographic outcomes in patients who underwent coronary angioplasty with an indigenously made cobalt chromium bare metal stents with thin strut Cobal+C™ (Relisys). MethodsA total of 268 consecutive patients who underwent coronary angioplasty with Cobal+C stents were studied retrospectively. Clinical follow up was done after a minimum period of nine months through telephonic interview and angiographic follow up was done in 80 patients chosen randomly. The end points analyzed included major adverse cardiac events (MACE) at nine months and the rate of binary restenosis at follow up angiogram done between 9 and 15 months post angioplasty. ResultsThirty four percent were diabetic and 33% had acute myocardial infarction. Females constituted 17%. Mean stent diameter was 2.88 ± 0.28 and mean stent length 18.8 ± 4.2. MACE at nine months was 4.5% with TLR 0.3%. The rate of binary restenosis was 21%. Patients with longer stent lengths and non-compliance with medications had significantly higher rates of binary restenosis. ConclusionsThe use of Relisys Cobal+C stents was associated with good long term clinical and angiographic outcomes as evidenced by low incidence of MACE and binary restenosis rates for a bare metal stent.

Ultrasound-guided percutaneous delivery of tissue-engineered endothelial cells to the adventitia of stented arteries controls the response to vascular injury in a porcine model

High restenosis rates are a limitation of peripheral vascular interventions. Previous studies have shown that surgical implantation of a tissue-engineered endothelium onto the adventitia surface of injured vessels regulates vascular repair. In the present study, we developed a particulate formulation of tissue-engineered endothelium and a method to deliver the formulation perivascular to injured blood vessels using a percutaneous, minimally invasive technique. Stainless steel stents were implanted in 18 balloon-injured femoral arteries of nine domestic swine, followed by ultrasound-guided percutaneous perivascular injection of gelatin particles containing cultured allogeneic porcine aortic endothelial cells (PAE). Controls received injections of empty particles (matrix) or no perivascular injection (sham) after stent deployment. Animals were sacrificed after 90 days. Angiographic analysis revealed a significantly greater lumen diameter in the stented segments of arteries treated with PAE/matrix (4.72 ± 0.12 mm) compared with matrix (4.01 ± 0.20 mm) or sham (4.03 ± 0.16 mm) controls (P < .05). Similarly, histologic analysis revealed that PAE/matrix-treated arteries had the greatest lumen area (20.4 ± 0.7 mm(2); P < .05) compared with controls (16.1 ± 0.9 mm(2) and 17.1 ± 1.0 mm(2) for sham and matrix controls, respectively) and the smallest intimal area (3.3 ± 0.4 mm(2); P < .05) compared with controls (6.2 ± 0.5 mm(2) and 4.4 ± 0.5 mm(2) for sham and matrix controls, respectively). Overall, PAE-treated arteries had a 33% to 50% decrease in percent occlusion (P < .05) compared with controls. Histopathological analysis revealed fewer leukocytes present in the intima in the PAE/matrix group compared with control groups, suggesting that the biological effects were in part due to inhibition of the inflammatory phase of the vascular response to injury. Minimally invasive, perivascular delivery of PAE/matrix to stented arteries was performed safely using ultrasound-guided percutaneous injections and significantly decreased stenosis. Application at the time of or subsequent to peripheral interventions may decrease clinical restenosis rates.

SU-E-I-27: Effect of Focal Spot Choice on the System Performance of a High- Resolution Micro-Angiographic Fluoroscope (MAF) Detector.

The generalized metrics of GMTF and GDQE were used to evaluate the effect of focal-spot choice on system performance of the Micro- Angiographic Fluoroscope (MAF) imager with a geometric magnification common for neuro-endovascular interventions. The MAF, a newly developed high-resolution detector with very low instrumentation noise and large variable gain, was used for the study. It has 35-micron pixels and a 500-micron thick CsI HR-type phosphor. The detector MTF was measured using the slanted edge method and the focal spot MTF's were measured using a standard pin-hole assembly. For the comparison analysis, the GMTF and GDQE were determined for three different focal spots (0.3 mm, 0.5 mm and, 0.8 mm) with a magnification factor of 1.25. A stainless- steel stent was also imaged with the same magnification for all three focal spots. The MAF's performance is affected significantly by the choice of focal-spot size because of its very high resolution. The GMTF and GDQE comparison for three focal spots showed significant degradation, increasing from small to large focal spot. The GMTF values were found to be 0.09, 0.05 and 0.01 at 5 cycles/mm for the small, medium and large focal spot, respectively. The corresponding values for GDQE were 0.1, 0.03 and 0.001. These results demonstrating the effect of choice of focal spot on the image quality are supported by line profiles obtained across the stent images. The results of this study demonstrate the significance of focal-spot size on system performance when using a high-resolution detector with a realistic magnification and shows the importance of choosing the minimum focal-spot size. (Support: NIH-Grant R01EB002873) NIH Grants R01-EB008425, R01-EB002873 and an equipment grant from Toshiba Medical Systems Corp.

Transcatheter aortic valve implantation: time to expand?

Transcatheter aortic valve implantation is a new, emerging technique that has been performed in elderly and higher-risk patients suffering severe, symptomatic aortic stenosis. Initial clinical results are promising. Important technological progress, i.e. the development of two stent-based aortic valve xenografts (the CoreValve prosthesis with a nitinol frame and the Edwards Sapien prosthesis with a steel stent), has allowed these achievements. Both prostheses can be crimped to small diameters, allowing for implantation by either a transfemoral or a transapical approach. Recently, CE mark approval has been obtained for both prostheses for transfemoral implantation. This will likely lead to an increased number of implantations. Current clinical studies are of prospective design with observational character. No prospectively randomized clinical trials have been reported so far; however, one randomized trial is under way. Transcatheter aortic valve implantation has become a clinical reality and will be performed more frequently in the future. Patient selection is critical and current indications include only higher-risk patients suffering severe aortic stenosis. When selecting the optimal therapy for individual patients, the advantages and disadvantages of this novel approach must be carefully weighed against the excellent results achieved with conventional surgery.

In vitro evaluation of intravascular stent artifacts in three-dimensional MR angiography.

To evaluate the intraluminal signal characteristics of various stents and stent-grafts in contrast-enhanced three-dimensional MR angiography (3D MRA) in vitro. Fourteen stents made of different materials (steel, nitinol, tantalum, cobalt-based alloy, polyethylene) and six stent-grafts were implanted in plastic tubes simulating the common iliac artery. The tubes were filled with gadopentetate dimeglumine in water at a concentration of 25 mmol/L and positioned in a plastic container filled with water. For imaging, the container was placed in the center of the magnet, parallel, orthogonal, and diagonal to the z axis. A 3D gradient-echo sequence (T1-FFE) was acquired with the following parameters: repetition time 5.3 ms, echo time 1.6 ms, flip angle 50 degrees, slice thickness 1.5 mm, and acquisition matrix 256 with zero filling to 512. To evaluate the influence of the frequency-encoding gradient on the appearance of the artifacts, stents were examined with their axes oriented in all three directions both with the frequency-encoding gradient in the feet-head and right-left directions. The size and pattern of stent-related artifacts were evaluated semiquantitatively for each measurement. Five different components of artifacts could be distinguished: homogeneous signal reduction inside the stent, narrowing of the stent lumen, structures of various shapes inside the stents, signal reduction or signal increase at the ends of the stents, and shift of the intraluminal signal orthogonal to the longitudinal axis of the vessel. The size of the artifacts depended heavily on the material of the stent. The polyethylene stent showed no artifacts, the tantalum stent only minor artifacts. Nitinol stents were characterized by artifacts at both ends and signal reduction intraluminally. Stents made of steel demonstrated the strongest artifacts, characterized by almost complete signal loss intraluminally. The characteristics of the artifacts of all stents depended on the direction of the stent relative to the frequency-encoding gradient. Three-dimensional MRA follow-up after stent placement may be applicable for stent patency evaluation in all instances. However, grading of stenoses seems to be unrealistic in steel stents and in most nitinol stents.

MR Imaging of Vascular Stents: Effects of Susceptibility, Flow, and Radiofrequency Eddy Currents

The purpose of this in vitro study was to examine the various sources of artifacts in magnetic resonance (MR) imaging and angiography of vascular stents. Five low-artifact stents-Wallstent (cobalt alloy), Memotherm (nitinol), Perflex (stainless steel), Passager (tantalum), and Smart (nitinol)-were imaged in a vascular flow phantom, consisting of a thin-walled cellulose vessel model connected to a pump system. The echo time and the angulation of the stents with respect to the direction of the main magnetic field were varied. Spin echo and gradient echo images as well as three-dimensional MR angiograms were obtained to study the effects of flow, magnetic susceptibility, and radiofrequency-induced eddy currents. Susceptibility artifacts were restricted to the stents' direct environment and were mildest at short echo times and with the stents aligned with the main magnetic field. Nitinol stents showed less artifacts than steel stents did. Radiofrequency artifacts obscuring the stent lumen and flow-related lumen displacement were seen in all stents. The extent to which these occurred depended on strut geometry and orientation. For low-artifact stents, the material the stent is made of is not the only important factor in the process of artifact formation. Susceptibility artifacts, radiofrequency eddy currents and flow-related artifacts all contribute to the image distortion, and are dependent on the geometry and orientation of the struts and on the orientation of the stent in the main magnetic field.

Biocompatibility Comparison of Stainless Steel, Gold-Coated, and Heat-Treated Gold-Coated Endovascular Stents

ABSTRACTEndovascular stents can be altered to improve radioopacity by applying a gold coating. We examined the vascular response in porcine coronary arteries to implantation of 9 mm NIR® stents that were either left intact, gold-coated, or heat-treated following gold coating. Our results show that while gold coating exacerbates neointimal hyperplasia and the inflammatory response, heat treatment removes this negative effect. Heat treatment was shown to increase the diffusion at the gold-steel interface and reduce the surface roughness.

Neointimal thickening after stent delivery of paclitaxel: change in composition and arrest of growth over six months

OBJECTIVESThe purpose of this study was to determine long-term effects of stent-based paclitaxel delivery on amount, rate and composition of neointimal thickening after stent implantation.BACKGROUNDPaclitaxel prevents vascular smooth muscle cell proliferation and migration in vitro and in vivo. These actions, coupled with low solubility, make it a viable candidate for modulating vascular responses to injury and prolonged effects after local delivery. We asked whether local delivery of paclitaxel for a period of weeks from a stent coated with a bioerodible polymer could produce a sustained reduction in neointimal hyperplasia for up to six months after stenting.METHODSStainless steel stents were implanted in the iliac arteries of rabbits after endothelial denudation. Stents were uncoated or coated with a thin layer of poly(lactide-co-Σ-caprolactone) copolymer alone or containing paclitaxel, 200 μg.RESULTSPaclitaxel release in vitro followed first-order kinetics for two months. Tissue responses were examined 7, 28, 56 or 180 days after implantation. Paclitaxel reduced intimal and medial cell proliferation three-fold seven days after stenting and virtually eliminated later intimal thickening. Six months after stenting, long after drug release and polymer degradation were likely complete, neointimal area was two-fold lower in paclitaxel-releasing stents. Tissue responses in paclitaxel-treated vessels included incomplete healing, few smooth muscle cells, late persistence of macrophages and dense fibrin with little collagen.CONCLUSIONSPoly(lactide-co-Σ-caprolactone) copolymer-coated stents permit sustained paclitaxel delivery in a manner that virtually abolishes neointimal hyperplasia for months after stent implantation, long after likely completion of drug delivery and polymer degradation.

Antithrombogenic Coating of Stents Using a Biodegradable Drug Delivery Technology

To reduce the thrombogenic properties of coronary artery stents, a biodegradable polylactic acid (PLA) stent coating with an incorporated thrombin inhibitor and a platelet aggregation inhibitor has been developed. In an ex vivo human stasis model, its effect on platelets, plasmatic coagulation and its release characteristics were studied using whole blood. Bare steel and bare gold-surface stents were compared to steel and gold-surface stents coated with PLA (30 kDa) containing 5% polyethyleneglycol (PEG)-hirudin and 1% iloprost, with an empty tube as control. Markers of activated coagulation (prothrombin fragment F1-2 and thrombin-antithrombin III complex, TAT), were assayed and the release of drugs from the coating was assessed by aPTT and collagen-induced platelet aggregation. Bare steel and gold stents were completely covered by a blood clot, and high levels of coagulation markers (F1-2 fragment and TAT) were detected. No differences in the thrombogenic properties were found between bare gold or steel stents. Coated stents were free of blood clots and only minor elevations of markers were detected. Release data from in-vitro studies over 90 days showed a gradual release of the drugs with an initial exponential release characteristic for PEG-hirudin, slow release of iloprost and a 10% degradation of the PLA carrier. This drug releasing biodegradable coating effectively reduced thrombus formation independent of the metallic surface.