Balloon-expandable Stainless Steel Stents Research Articles

STENT-IN-STENT TECHNIQUE FOR MANAGEMENT OF PERIPHERAL MALIGNANT ENDOBRONCHIAL OBSTRUCTION

TOPIC: Procedures TYPE: Medical Student/Resident Case Reports INTRODUCTION: Airway stenting is used to restore patency of airways with malignant obstruction. Stent-in-stent (SIS) technique has been used in central airway obstruction. We describe a case of malignant endobronchial obstruction in the right upper lobe (RUL) managed with SIS technique. CASE PRESENTATION: 56-year-old male with history of Laryngeal Carcinoma managed with surgical resection and chemo-radiation was transferred for management of recurrent hemoptysis and right lung atelectasis. He was tachypneic and hypoxic requiring 2L oxygen. Labs revealed leukocytosis, hemoglobin of 9.6gm/dl and no coagulopathy. CT Chest showed right lung atelectasis due to right mainstem endobronchial mass. Rigid bronchoscopy (RB) demonstrated a friable mass in the right main stem with frank blood in the central airway. Initially Diode laser was employed for removal of the pedunculated tumor originating in the RUL, followed by debulking with RB and cryoprobe from the right main stem and bronchus intermedius (BI). Rigid tamponade and argon plasma coagulation were used for hemostasis. BF-P190 Olympus scope was used to identify the distal airway in the RUL posterior segment and a 7x22 mm iCAST stent was placed for airway patency. Right middle lobe (RML) and lower lobe (RLL) airways were not localized at the time. A staged RB was performed a few days later. BF-P190 Olympus scope was used for inspection which revealed occlusion of distal end of stent with tumor, advancement of scope with mild pressure through the tumor revealed sub segmental airways, under fluoroscopy guidance a second 7x22mm iCAST stent was placed overlapping with the first stent. Additional tumor debulking from the BI revealed RLL segmental branches. Under direct visualization a 10x38 mm iCAST stent was placed to restore airway patency to the RLL. He remained stable off oxygen post procedure, with reinflation of the right lung. He was discharged with bronchodilators and hypertonic saline with significant improvement in his quality of life. DISCUSSION: Rigid bronchoscopy and airway stenting is commonly used for management of complex central airway obstruction. iCAST stent is a balloon expandable stainless steel stent that is fully encapsulated in two layers of polytetrafluoroethylene. The stent deployment is through the scope with the smallest size of 5x16mm and largest 10x38mm. The smaller size stent can be upsized with a larger sized balloon with the stent shortening in length. We present a SIS placement of two 7x22 mm iCAST stents in the airway likely traversing through the right hilar mass to establish airway patency, resulting in complete reexpansion of the lung. CONCLUSIONS: Peripheral airway stenting of occluded airway due to malignancy can result in lung reinflation, resulting in increased pulmonary reserves for patient to tolerate chemotherapy and radiation. We used SIS technique for customization and appropriate stenting of distal airway. REFERENCE #1: Sethi, Sonali, et al. "Clinical Success Stenting Distal Bronchi for 'Lobar Salvage’ in Bronchial Stenosis:” Journal of Bronchology & Interventional Pulmonology, vol. 25, no. 1, 2018, pp. 9–16, doi:10.1097/LBR.0000000000000422. REFERENCE #2: Majid A, Kheir F, Chung J, Alape D, Husta B, Oh S, Folch E.. Covered Balloon-Expanding Stents in Airway Stenosis. J Bronchology Interv Pulmonol. 2017 Apr;24(2):174-177. doi: 10.1097/LBR.0000000000000364.J Bronchology Interv Pulmonol. 2017. PMID: 28323735 DISCLOSURES: No relevant relationships by Muhammad Arif, source=Web Response no disclosure submitted for Ali Saeed; No relevant relationships by Hursh Sarma, source=Web Response No relevant relationships by Andrew Talon, source=Web Response No relevant relationships by Cindrel Tharumia Jagadeesan, source=Web Response

Angiotensin II type 1 receptor blockers suppress neointimal hyperplasia after stent implantation in carotid arteries of hypercholesterolemic rabbits

Objectives:The purpose of this study was to examine whether oral administration of an angiotensin II type 1 receptor blocker (ARB) inhibited in-stent neointimal hyperplasia in carotid arteries of hypercholesterolemic rabbits.Methods:Eleven male New Zealand white rabbits were subjected to endothelial injuries of the right common carotid arteries using a balloon catheter and then received chow containing 1% cholesterol for 6 weeks. A balloon-expandable stainless steel stent was subsequently inserted at the injured sites of the arteries. After stenting, five rabbits were randomly treated with an oral ARB, candesartan cilexetil (5 mg/kg per day orally), while the remaining six rabbits acted as untreated controls. Four weeks after the implantation, the rabbits were killed, followed by collection of the arteries including the stents. After careful removal of the stents, tissue sections were prepared and analyzed by morphometric and immunohistochemical methods.Results:The mean thickness of the neointima was 53·6±17·0 μm in the ARB-treated group, which was significantly reduced compared to 95·9±16·7 μm in the control group (P = 0·0012). Immunohistochemistry showed a decrease in accumulation of macrophages and tenascin-C expression in the arterial wall in the ARB-treated animals.Discussion:This study suggested that systemic administration of an ARB suppressed neointimal hyperplasia in the carotid artery following stent implantation by the anti-inflammatory effects, although the animal cohort tested was rather small. This finding implies that ARBs may be useful and practical agents for protection against in-stent restenosis in humans, and warrants further basic and clinical studies.

The Odyssey of TAVR from concept to clinical reality.

On 16 April 2002, my colleagues and I performed, in an inoperable and desperately ill man with critical calcific aortic stenosis (AS), the first clinical percutaneous implantation of an aortic valve bioprosthesis. As of 2013, more than 80,000 patients have been treated; and transcatheter aortic valve replacement (TAVR), so strongly criticized by all the experts throughout the early years, continues to grow in parallel with its constant technological improvements. Transcatheter aortic valve replacement can now be recognized as a medical breakthrough. It is a revolutionary technology that meets an unfulfilled clinical need for a common disease, is validated by rigorous evidence-based studies, and is applicable worldwide. We report here the main phases of this 20-year odyssey and briefly consider the prospects of TAVR, which remains in continuous development.

Numerical fatigue life assessment of cardiovascular stents: A two-scale plasticity-damage model

Cardiovascular disease has become a major global health care problem in the last decades. To tackle this problem, the use of cardiovascular stents has been considered a promising and effective approach. Numerical simulations to evaluate the in vivo behavior of stents are becoming more and more important to assess potential failures. As the material failure of a stent device has been often associated with fatigue issues, numerical approaches for fatigue life assessment of stents have gained special interest in the engineering community. Numerical fatigue life predictions can be used to modify the design and prevent failure without making and testing numerous physical devices, thus preventing from undesired fatigue failures. We present a numerical fatigue life model for the analysis of cardiovascular balloon-expandable stainless steel stents that can hopefully provide useful information either to be used for product improvement or for clinicians to make life-saving decisions. This model incorporates a two-scale continuum damage mechanics model and the so-called Soderberg fatigue failure criterion. We provide numerical results for both Palmaz-Schatz and Cypher stent designs and demonstrate that a good agreement is found between the numerical and the available experimental results.

Reocclusion caused by stent fracture implanted in the subclavian artery ostium: a case report

A 47year-old male, a woodcutter by profession, complained of severe pain in the left arm during physical stress. Eighteen months ago, a balloon-expandable stainless steel stent had been implanted in the left subclavian artery ostium. The angiography revealed a stent fracture at the origin of the left subclavian artery, this condition led to a re-obstruction of the stent. After the insertion of a self-expandable Nitinol stent, the side differences of arterial pressure and the symptoms disappeared. This is the first reported case of a stent fracture inserted at the origin of the subclavian artery without severe calcification.

Fatigue life assessment of cardiovascular balloon-expandable stents: A two-scale plasticity–damage model approach

Cardiovascular disease has become a major global health care problem in the present decade. To tackle this problem, the use of cardiovascular stents has been considered a promising and effective approach. Numerical simulations to evaluate the in vivo behavior of stents are becoming more and more important to assess potential failures. As the material failure of a stent device has been often associated with fatigue issues, as a result of the high number of cyclic loads these devices are subjected to in vivo, numerical approaches for fatigue life assessment of stents has gained special interest in the engineering community. Numerical fatigue predictions can be used to modify the design and prevent failure, without making and testing numerous physical devices, thus preventing from undesired fatigue failures. This work presents a fatigue life numerical method for the analysis of cardiovascular balloon-expandable stainless steel stents. The method is based on a two-scale continuum damage mechanics model in which both plasticity and damage mechanisms are assumed to take place at a scale smaller than the scale of the representative volume element. The fatigue failure criterion is based on the Soderberg relation. The method is applied to the fatigue life assessment of both PalmazShatz and Cypher stent designs. Validation of the method is performed through comparison of the obtained numerical results with some experimental results available for the PalmazShatz stent design. The present study gives also possible directions for future research developments in the framework of the numerical fatigue life assessment of real balloon-expandable stents.

Comparison of Tissue Reaction with Three Different Endografts Used for Exclusion of Carotid Artery Aneurysm in a Dog Model

To assess the efficacy and biocompatibility of balloon-expandable stainless-steel stents covered with various membrane types. Stents covered with biomembrane (ie, piglet greater omentum vein), polyurethane, or expanded polytetrafluoroethylene (ePTFE; n = 12 each) were implanted into the 36 bilateral carotid arteries of 18 dogs to treat 36 surgically created saccular side wall aneurysms. Treated dogs were administered anticoagulation therapy after stent implantation. Angiography was performed immediately after the procedure and at 2, 4, and 12 weeks. Aneurysm isolation, primary parent artery patency, acute thrombosis in the stent, and endoleak were investigated. Two dogs in each group were killed at each follow-up interval, the stent-implanted arteries were removed for light and electron microscopy, and aneurysm thrombosis, stenosis rate, and endothelialization progress were observed. Thirty-six stents were successfully placed and 36 aneurysms completely isolated, with no endoleaks revealed by immediate or follow-up angiography. The primary patency rates of the biomembrane-, polyurethane-, and ePTFE-covered stents were 91.7%, 50%, and 66.7%, respectively. At 12 weeks, a luminal narrowing of 24.27% +/- 6.23% was seen in the biomembrane group, compared with 30.78% +/- 1.41% (P = .025) in the polyurethane group and 20.56% +/- 7.22% (P = .247) in the ePTFE group. All treated aneurysmal pouches had filled with thrombi and stent wires were encased by extended neointima. Endothelialization in the biomembrane group had begun by 2 weeks, which was earlier than in the polyurethane or ePTFE groups. All three stent-grafts successfully excluded carotid aneurysms. Biomembrane-covered stents showed better primary patency and less intimal hyperplasia than polyurethane- or ePTFE-covered stents.

Abstract No. 228: Stent Fractures After Endoluminal Therapy of Ostial Supra-Aortic Trunk Arterial Occlusive Lesions

Abstract No. 228: Stent Fractures After Endoluminal Therapy of Ostial Supra-Aortic Trunk Arterial Occlusive Lesions

Past, Present and Future of Femoropopliteal Stenting

Endovascular stent implantation was introduced to femoropopliteal procedures almost 2 decades ago. Initial results with balloon-expandable stainless steel stents and self-expanding Elgiloy stents, however, were disappointing. In particular, recurrence rates after long-segment femoropopliteal stenting were catastrophically high, in the range of 60% to 80% at 1 year. Also, attempts to resolve the problem of in-stent restenosis (ISR) using first-generation covered stent-grafts led to unsatisfactory results, high procedural complication rates due to large introducers, and a high incidence of graft thrombosis, which did not make these devices convincing alternatives to bare metal stents. After years of stagnation, however, recent developments in femoropopliteal stent technology have been promising. Self-expanding nitinol stents have been evaluated in several prospective studies. Initial problems with stent fractures seem to be resolved using second-generation devices; for the first time, stenting has been shown to be beneficial compared to balloon angioplasty in longer femoropopliteal lesions. Nevertheless, although superior to balloon angioplasty, nitinol stenting is still associated with a considerable restenosis rate, and treatment of ISR remains problematic. Future concepts to further improve long-term patency after femoropopliteal stenting therefore are under investigation, including drug-eluting stents, biodegradable stents, and coated stent-grafts. From a current perspective, femoropopliteal stenting remains the Achilles' heel of the interventionist.

Transcatheter and Transapical Aortic Valve Replacement

Minimally invasive valve replacement is limited to bioprosthetic aortic and pulmonary valves for use in very specific populations of patients. Replacement via trans-catheter and transapical techniques should be used only in patients in whom traditional surgical replacement is deemed an unacceptable risk. Nursing management will focus heavily on care for comorbid conditions because of the high-risk nature of the patients in whom these valves will initially be implanted.

United States Feasibility Study of Transcatheter Insertion of a Stented Aortic Valve by the Left Ventricular Apex

Recent US and European registries have indicated 30% to 60% of patients with critical valvular aortic stenosis (AS) are not treated surgically, usually due to advanced age and comorbidities. We report on a Food and Drug Administration approved feasibility study of a less invasive transcatheter approach to potentially treat these high-risk patients. Between December 2006 and February 18, 2008, 40 patients underwent transcatheter insertion of a balloon expandable stainless-steel stent with an internally mounted three-leaflet equine pericardial valve (Edwards Sapien Transcatheter Heart Valve; Edwards Lifesciences, Irvine, CA) into the aortic annulus using a transapical left ventricular insertion (TA-AVI). Patients were inoperable by conventional surgery, or extremely high risk based on Society of Thoracic Surgeons score greater than 15% or other documented risk factors. All 40 valves were successfully delivered and 35 were successfully seated. Two valves embolized and required open aortic valve replacement (AVR), and one case of severe regurgitation later required AVR. In a further two patients placed on cardiopulmonary support, one valve later embolized and one migrated. There were 7 (17.5%) deaths within 30 days, and a further 2 (5%) deaths before discharge at 42 and 72 days. There were no immediate postoperative strokes after successful deployment. Valve area improved from 0.62 cm(2) (SD of 0.13) to 1.61 cm(2) (SD 0.37) at 30 days (p = or<0.0001), with mean perivalvular regurgitation of 1.19 (SD 0.80). Mean follow-up was 143 days (SD 166 days) with 6 further deaths from comorbid disease, none valve or cardiac related. The Kaplan-Meier survival was 81.8% +/- 6.2% at 1 month and 71.7% +/- 7.7% at 3 months. Transapical insertion of a balloon expandable stented valve is feasible but carries considerable risk and will be further evaluated in the PARTNER (Placement of AoRTic traNscathetER valve) randomized trial.

Fenestrated Stent-Graft Repair:Which Stent Should Be Used to Secure Target Vessel Fenestrations?

To investigate in an in vitro model the ability of different covered and uncovered stents to resist displacement/migration of a fenestrated stent-graft. Three different types (2 covered, 1 bare) of commonly used 7-mm balloon-expandable stainless steel stents (Jostent, Advanta V12, and Palmaz Genesis) were investigated in a testing rig consisting of 2 overlapping tubes with 2 sets of 7-mm holes representing bilateral renal artery fenestrations and ostia. The rig was attached to a tensile tester via pneumatic clamps. The stents were deployed without flaring to 7 mm through the overlapping holes. The rig was moved apart at a constant rate of 12 mm/min up to a maximum displacement of 6 mm; force versus displacement values were recorded while stent deformation was observed. Tests were repeated at least 6 times for each stent type at room temperature. The median force required to cause a 25%, 50%, or 75% reduction in cross-sectional area of the bilateral "renal artery" stents was determined. The median force (interquartile range) required to cause a 50% reduction in cross-sectional area of identical bilateral "renal artery" stents securing fenestrations was 25.1 N (8.1) for a covered Jostent, 9.3 N (0.9) for a covered Advanta V12 stent, and 7.5 N (0.7) for a bare Palmaz Genesis stent. The differences were statistically significant (p<0.01) between stents at each of the 3 levels of cross-sectional area reduction. There is a significant difference in the ability of different commercial "non-dedicated" stents to withstand a crushing force when deployed within endograft fenestrations, which has important implications for clinical practice.

Renal artery stent revascularization with embolic protection in patients with ischemic nephropathy

A prospective analysis of renal artery stent revascularization with distal embolic protection in a high-risk patient population with ischemic nephropathy is presented. A total of 63 patients (median age 70.2 years, range 54-86 years) had significant atherosclerotic stenosis of 83 renal arteries documented on pre-procedural imaging. All patients had baseline chronic renal insufficiency with a documented deterioration in renal function in the 6 months before revascularization. The endovascular technique used in all patients involved primary passage of an embolic filter into the distal main renal artery followed by primary stent deployment with a balloon expandable stainless steel stent. The filter baskets were recaptured and contents submitted for pathological analysis. At 6 months post-intervention, 97% of patients demonstrated stabilization or improvement in renal function. Only 3% of patients had an inexorable decline in renal function, unchanged by the intervention. After a mean follow up of 16.0 months (6-27), 94% of patients demonstrated stabilization or improvement in renal function. One patient suffered an acute post-procedural deterioration in renal function. In total, 60% of the filter baskets contained embolic material. This study confirms the technical feasibility of renal artery stent deployment with adjuvant embolic protection. The excellent results for renal preservation at 6 months post-intervention also suggest that a distal embolic protection device may improve the impact of percutaneous renal revascularization on progressive deterioration in renal function. The postulated mechanism is through the prevention of atheromatous embolization and the embolic yield from the distal filters supports this hypothesis. Patients most likely to receive the greatest benefit are those with mild baseline chronic renal insufficiency and a recent decline in renal function.

Feasibility and safety of airway bypass stent placement and influence of topical mitomycin C on stent patency

Airway bypass via transbronchial fenestration has been shown to improve forced expiratory volume and flow in explanted human emphysematous lungs. The aim of this study was to evaluate the feasibility and safety of in vivo airway bypass stent placement by using a canine model and to assess the influence of topical mitomycin C on the prolongation of stent patency. With dogs under general anesthesia, suitable segmental and subsegmental bronchial wall sites were selected by direct visualization with a flexible bronchoscope. Peribronchial blood vessel injury was avoided by using a Doppler probe. Transbronchial fenestration was formed with a 22-gauge transbronchial needle, and the passage was then dilated with a 2.5-mm angioplasty balloon. A balloon expandable stainless-steel stent (3 mm long x 3 mm wide) with a sleeve of silicone rubber covering was placed within the fenestration. Animals were bronchoscoped weekly to assess stent patency. Seventy stents were placed in 12 dogs. Thirty-five served as controls, and the other 35 received transbronchoscopic topical application of mitomycin C once weekly to evaluate the effect on the maintenance of stent patency. Mitomycin C stents were divided into 4 groups according to the number of treatments: group A, 1 treatment only; group B, 4 weeks; group C, 7 weeks; and group D, 9 weeks. Each once-weekly mitomycin C application consisted of 0.2 mL at a concentration of 1 mg/mL, delivered through a small polyethylene catheter. Four instances of minor and brief bleeding occurred during stent placement and resolved without incident. One pneumothorax occurred and was treated by chest tube placement, without any adverse sequelae. There was no mortality associated with stent placement. No delayed hemorrhage or pneumothorax occurred. All control stents were occluded at the 1-week follow-up. The median durations of stent patency for group A (n = 8), group B (n = 9), group C (n = 10), and group D (n = 8) were 3, 8, 13, and greater than 20 weeks, respectively. Airway bypass stent placement can be performed safely. In an animal model, most stents became occluded within 1 week, but topical mitomycin application resulted in significant prolongation of patency.

Early experience with percutaneous transcatheter implantation of heart valve prosthesis for the treatment of end-stage inoperable patients with calcific aortic stenosis

ObjectivesThis study wad done to assess the results of percutaneous heart valve (PHV) implantation in non-surgical patients with end-stage calcific aortic stenosis. BackgroundReplacement of PHV has been shown to be feasible in animals and humans. We developed a PHV composed of three pericardial leaflets inserted within a balloon-expandable stainless steel stent. We report the acute and early follow-up results of the initial six PHV implantations. MethodsAn anterograde approach was used in all cases. The PHV, crimped over a 22-mm diameter balloon, was advanced through a 24-F sheath from the femoral vein to the aortic valve and delivered by balloon inflation. Clinical, hemodynamic, and echocardiographic outcomes were assessed serially. ResultsAll patients were in New York Heart Association functional class IV. The PHV was successfully delivered in five patients. Early migration with subsequent death occurred in one patient who presented with a torn native valve. Acute hemodynamic and angiographic results showed no residual gradient, mild (three patients) or severe (two patients) aortic regurgitation, and patent coronary arteries. On echocardiography, the aortic valve area was increased from 0.5 ± 0.1 cm2to 1.70 ± 0.03 cm2and the aortic regurgitation was paravalvular. Marked and sustained hemodynamic and clinical improvement was observed after successful PHV implants. The first three patients died of a non-cardiac cause at 18, 4, and 2 weeks, respectively, and the other patients are alive at 8 weeks with no signs of heart failure. ConclusionsImplantation of the PHV can be achieved in patients with end-stage calcific aortic stenosis and might become an important therapeutic option for patients not amenable to surgical valve replacement.

Carbon-coated Stents Implanted in Porcine Iliac and Renal Arteries: Histologic and Histomorphometric Study

To test in a pig model the biocompatibility and effectiveness of carbon-coated renal and iliac artery stent systems during implantation procedures and at different follow-up periods. Twenty-two miniature pigs received carbon-coated balloon-expandable stainless-steel stents in their renal and iliac arteries. Animals were killed at 7, 30, or 180 days for evaluation of acute, subacute, and chronic biologic response to the implanted devices. Histologic, histomorphometric, and scanning electron microscopy (SEM) analyses were performed to assess inflammatory reaction, endothelialization process, and neointimal growth. Forty-four iliac stents and 42 renal stents were successfully implanted. Mural thrombi were not observed by angiography or histologic examinations. Histologically, no significant inflammatory reaction was detected: the stents appeared covered by a thin monolayer of endothelial cells even at 7-day follow-up. The neointima showed homogeneous growth and moderate thickness at 30-day and 180-day explantations (0.09 mm +/- 0.06 and 0.15 mm +/- 0.13, respectively, for renal arteries; 0.12 mm +/- 0.04 and 0.21 mm +/- 0.12, respectively, for iliac arteries). Internal and external elastic laminae were intact in 82 of 86 cases (95%) of stent-implanted arteries. Histologic validations were obtained with SEM observations for each follow-up group. This study showed good technical results of deployment of carbon-coated renal and iliac stents and very satisfactory biologic behavior in terms of tissue and hematologic compatibility. The devices do not induce thrombus formation.

Initial experience with intratherapeutics Intrastent Doublestrut LD stents in patients with congenital heart defects.

Limitations of the currently available balloon-expandable stainless steel (BE-SS) stents for use in patients with congenital heart defects (CHD) include inflexibility, significant shortening with expansion, sharp ends, and limited sizes. These limitations increase risk and greatly effect success of stent placement in these patients. The recently approved IntraStent DoubleStrut LD (IS-LD) stents are BE-SS stents designed to address such limitations. We report our initial experience with IS-LD stents in patients with CHD. Using standard techniques, 36 stents were implanted in 22 patients whose median age was 11 years (range, 1.4-35 years) and weight was 33 kg (range, 9-96.8 kg). Lesions stented included aortic coarctation (4), branch pulmonary arteries (19), inferior or superior vena cava (11), Mustard baffle (1), and Fontan baffle (1). All attempts at stent placement were successful. Hemodynamic assessment and angiography was performed pre- and poststent placement in all patients. Intravascular ultrasound was performed in four patients. Stenosis diameter increased from 5.7 +/- 0.6 mm (mean +/- SD) to 11.6 +/- 0.5 mm (P < 0.001). Stents did not shorten significantly with dilation (median percent shortening, 3.8%; P > 0.1). Complications included stent recoil (2), stent migration (1), and stent distortion (1). IS-LD stents are a safe and effective treatment for the majority of vascular stenoses in patients with CHD. Stent recoil at large diameters may limit its usefulness in selected lesions. Follow-up studies are required to determine the long-term performance of IS-LD stents.

Effect of endovascular stent strut geometry on vascular injury, myointimal hyperplasia, and restenosis

Purpose: Early restenosis and the development of myointimal hyperplasia in stented blood vessels have been attributed to deep vascular injury with fracture of the internal elastic lamina (IEL). The purpose of this study was the evaluation of the vascular wall response to superficial injury (without IEL rupture) after balloon angioplasty and intravascular stent placement in porcine arteries and the determination of the effect of stent strut geometry on the degree of vessel injury and early restenosis. Methods: Balloon-expandable stainless-steel stents were placed into the iliac arteries of 10 Sinclair miniature swine that had been fed an atherogenic diet. A Palmaz stent, with rectangular struts and smooth corners, was randomly assigned to one iliac artery (group 1), and a novel stent, which was designed and manufactured in the laboratory with thicker struts and sharper corners specifically to induce large wall stress concentrations, was placed in the contralateral iliac artery (group 2). Intravascular ultrasound scan was used in all deployments to ensure accurate balloon sizing and to avoid stent overexpansion and deep vascular injury. At 90 days after implantation, the animals were killed, the stented vessels harvested, and histomorphometric analysis performed. Results: Deployment of novel stents in group 2 resulted in a statistically higher incidence rate of deep vascular injury (fracture of the IEL) compared with group 1, despite identical balloon size used for deployment (with Student t test, P < .05). Vessels with deep injury showed a 10-fold increase in myointimal thickening compared with those vessels in which the IEL remained intact. A statistically higher restenosis rate was observed for group 2 (33.5% ± 19.90%) compared with group 1 (20.39% ± 14.70%). For both stent designs, there was a trend toward lower degrees of restenosis within the mid-portion of the stent. For superficially injured arteries in both groups, no correlation was observed between the amount of vessel wall/medial layer compression and the development of restenosis from myointimal hyperplasia. Conclusion: Maintenance of an intact IEL is an important factor in the prevention of myointimal hyperplasia and restenosis in stented porcine iliac arteries. The alteration of stent strut height and geometry does not significantly affect restenosis and the development of myointimal hyperplasia in vessels with superficial injury. Superficial injury elicits a response that is independent of stent strut geometry and vessel wall compression. Stent strut profile may, however, increase local vessel wall stress concentrations, leading to IEL rupture and an exaggerated response to injury. (J Vasc Surg 2002;36:143-9.)

Stenting of Central Venous Stenoses and Occlusions to Maintain Hemodialysis Vascular Access

The aim of the study was to evaluate the efficacy of stenting for the treatment of central arm vein obstructions in hemodialysis patients in order to maintain hemodialysis from the affected side. Fifteen self-expanding (8) and balloon expandable (7) stainless steel stents were implanted in 10 hemodialysis patients for the treatment of symptomatic central arm vein obstructions. Thirteen lesions were treated: 6 subclavian, 4 innominate and 3 restenoses. Stent deployment was successful in all cases leading to resolution of symptoms by correcting the underlying cause of venous hypertension. Follow-up from 3 months to 4 years revealed four deaths from unrelated causes, three restenoses at 1, 3, 4 months and one occlusion at 6 months respectively for a cumulative primary one-year and two-year patency rate of 70%. Stenting of subclavian and innominate venous stenoses and occlusions effectively corrected the underlying lesions responsible for disturbed hemodynamics and, in most cases, prolonged available hemodialysis access from the affected side.

Dr. Gary J. Becker Young Investigator Award: Comparison of Small-Diameter Type 1 Collagen Stent-Grafts and PTFE Stent-Grafts in a Canine Model—Work in Progress

To report an in-progress experiment in a canine model in which two types of small-diameter stent-grafts-one constructed of polytetrafluoroethylene (PTFE) and the other of a new, type 1 collagen material-were compared regarding vessel patency, intimal hyperplasia formation, and tissue reaction. Six mongrel dogs weighing 30-35 kg were used. Stent-grafts of 4-mm diameter and 20-mm length were constructed with use of balloon-expandable stainless-steel stents wrapped with either PTFE or a new type 1 collagen graft. Stent-grafts were placed in deep femoral arteries bilaterally (PTFE on one side, collagen on the other). Animals were followed for 2 weeks (n = 2), 6 weeks (n = 2), or 12 weeks (n = 2). Percent stenosis based on angiographic findings as well as thickness and area of neointimal hyperplasia were compared at each time point and compared with use of the Student t test. All devices were patent in the immediate postimplantation period. Five of six collagen stent-grafts and five of six PTFE implants were patent at follow-up. In-stent stenosis was undetectable angiographically in all five patent collagen stent-grafts. All five patent PTFE stent-grafts showed demonstrable in-stent stenosis (10%-60%), indicating a trend toward improved patency in collagen stent-grafts versus PTFE stent-grafts (P = .07). Neointimal hyperplasia was absent at 2 weeks in the collagen stent-grafts. Neointimal thickness increased to a maximum of 360 microm at 12 weeks in the collagen stent-grafts. For PTFE stent-grafts, neointimal hyperplasia was present in all samples and reached a maximum of 770 microm at 12 weeks (P = .03). Even in small-diameter vessels, type 1 collagen stent-grafts demonstrate excellent patency rates and favorable histologic findings. The type 1 collagen stent-graft technology merits further developmental efforts in preclinical models.