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Title: Late Stent Expansion and Neointimal Proliferation of Oversized Nitinol Stents in Peripheral Arteries

Abstract

For peripheral endovascular intervention, self-expanding (SE) stents are commonly oversized in relation to target arteries to assure optimal wall apposition and prevent migration. However, the consequences of oversizing have not been well studied. The purpose of this study was to examine the effects of SE stent oversizing (OS) with respect to the kinetics of late stent expansion and the long-term histological effects of OS. Pairs of overlapped 8 x 28-mm Nitinol SE stents were implanted into the iliofemoral arteries of 14 Yucatan swine. Due to variations in target artery size, the stent-to-artery ratio ranged from 1.2:1 to 1.9:1. Lumen and stent diameters were assessed by quantitative angiography at the time of implantation. Following angiographic assessment at 6 months, stented arteries were perfusion-fixed, sectioned, and stained for histological analysis. Immediately following implantation, the stents were found to be expanded to a range of 4.7-7.1 mm, largely conforming to the diameter of the recipient target artery. The stents continued to expand over time, however, and all stents had enlarged to nearly their 8-mm nominal diameter by 6 months. The histological effects of OS were profound, with marked increases in injury and luminal area stenosis, including a statistically significant linear correlation between stent-to-arterymore » ratio and area stenosis. In this experimental model of peripheral endovascular intervention, oversized Nitinol SE stents are constrained by their target artery diameter upon implantation but expand to their nominal diameter within 6 months. Severe OS (stent-to-artery ratio >1.4:1) results in a profound long-term histological response including exuberant neointimal proliferation and luminal stenosis.« less

Authors:
;  [1]; ; ;  [2];  [1]
  1. Abbott Vascular (United States)
  2. CVPath (United States)
Publication Date:
OSTI Identifier:
21428490
Resource Type:
Journal Article
Resource Relation:
Journal Name: Cardiovascular and Interventional Radiology; Journal Volume: 32; Journal Issue: 4; Other Information: DOI: 10.1007/s00270-009-9601-z; Copyright (c) 2009 Springer Science+Business Media, LLC and the Cardiovascular and Interventional Radiological Society of Europe (CIRSE)
Country of Publication:
United States
Language:
English
Subject:
62 RADIOLOGY AND NUCLEAR MEDICINE; ARTERIES; BIOMEDICAL RADIOGRAPHY; EXPANSION; NICKEL ALLOYS; PHENOBARBITAL; PROLIFERATION; SWINE; TITANIUM ALLOYS; TUBES; ALLOYS; ANESTHETICS; ANIMALS; ANTICONVULSANTS; AZINES; BARBITURATES; BLOOD VESSELS; BODY; CARDIOVASCULAR SYSTEM; CENTRAL NERVOUS SYSTEM AGENTS; CENTRAL NERVOUS SYSTEM DEPRESSANTS; DIAGNOSTIC TECHNIQUES; DOMESTIC ANIMALS; DRUGS; HETEROCYCLIC COMPOUNDS; HYPNOTICS AND SEDATIVES; MAMMALS; MEDICINE; NUCLEAR MEDICINE; ORGANIC COMPOUNDS; ORGANIC NITROGEN COMPOUNDS; ORGANIC OXYGEN COMPOUNDS; ORGANS; PYRIMIDINES; RADIOLOGY; TRANSITION ELEMENT ALLOYS; VERTEBRATES

Citation Formats

Zhao, Hugh Q., E-mail: hugh.zhao@av.abbott.com, Nikanorov, Alexander, Virmani, Renu, Jones, Russell, Pacheco, Erica, and Schwartz, Lewis B. Late Stent Expansion and Neointimal Proliferation of Oversized Nitinol Stents in Peripheral Arteries. United States: N. p., 2009. Web. doi:10.1007/S00270-009-9601-Z.
Zhao, Hugh Q., E-mail: hugh.zhao@av.abbott.com, Nikanorov, Alexander, Virmani, Renu, Jones, Russell, Pacheco, Erica, & Schwartz, Lewis B. Late Stent Expansion and Neointimal Proliferation of Oversized Nitinol Stents in Peripheral Arteries. United States. doi:10.1007/S00270-009-9601-Z.
Zhao, Hugh Q., E-mail: hugh.zhao@av.abbott.com, Nikanorov, Alexander, Virmani, Renu, Jones, Russell, Pacheco, Erica, and Schwartz, Lewis B. 2009. "Late Stent Expansion and Neointimal Proliferation of Oversized Nitinol Stents in Peripheral Arteries". United States. doi:10.1007/S00270-009-9601-Z.
@article{osti_21428490,
title = {Late Stent Expansion and Neointimal Proliferation of Oversized Nitinol Stents in Peripheral Arteries},
author = {Zhao, Hugh Q., E-mail: hugh.zhao@av.abbott.com and Nikanorov, Alexander and Virmani, Renu and Jones, Russell and Pacheco, Erica and Schwartz, Lewis B.},
abstractNote = {For peripheral endovascular intervention, self-expanding (SE) stents are commonly oversized in relation to target arteries to assure optimal wall apposition and prevent migration. However, the consequences of oversizing have not been well studied. The purpose of this study was to examine the effects of SE stent oversizing (OS) with respect to the kinetics of late stent expansion and the long-term histological effects of OS. Pairs of overlapped 8 x 28-mm Nitinol SE stents were implanted into the iliofemoral arteries of 14 Yucatan swine. Due to variations in target artery size, the stent-to-artery ratio ranged from 1.2:1 to 1.9:1. Lumen and stent diameters were assessed by quantitative angiography at the time of implantation. Following angiographic assessment at 6 months, stented arteries were perfusion-fixed, sectioned, and stained for histological analysis. Immediately following implantation, the stents were found to be expanded to a range of 4.7-7.1 mm, largely conforming to the diameter of the recipient target artery. The stents continued to expand over time, however, and all stents had enlarged to nearly their 8-mm nominal diameter by 6 months. The histological effects of OS were profound, with marked increases in injury and luminal area stenosis, including a statistically significant linear correlation between stent-to-artery ratio and area stenosis. In this experimental model of peripheral endovascular intervention, oversized Nitinol SE stents are constrained by their target artery diameter upon implantation but expand to their nominal diameter within 6 months. Severe OS (stent-to-artery ratio >1.4:1) results in a profound long-term histological response including exuberant neointimal proliferation and luminal stenosis.},
doi = {10.1007/S00270-009-9601-Z},
journal = {Cardiovascular and Interventional Radiology},
number = 4,
volume = 32,
place = {United States},
year = 2009,
month = 7
}
  • Purpose: To test the vascular wall response to an expanded polytetrafluoroethylene-covered stent, compared with conventional stenting, up to 6 months after deployment in the vascular district of a swine model.Methods: Fourteen minipigs underwent implantation of expanded polytetrafluoroethylene-covered stents (CS) and bare stents (BS) in five peripheral arteries. Animals were killed at different time points (from 1 to 180 days). Histopathologic assessment by morphologic and morphometric analysis and by scanning electron microscopy (SEM) were used to assess the incorporation characteristics and re-endothelialization extent of the two types of stents.Results: A total of 70 stents (14 CS and 14 BS in themore » renal arteries; 28 CS in the iliac arteries, and 14 CS in the aorta) were implanted. Microscopic examination confirmed the absence of occlusive thrombi in both the CS and BS groups. Microthrombi were observed in 10 of 13 CS (77% of cases) and in four of four BS (100% of cases, p < 0.05). Inflammation was mild in 69% of segments in which a CS was implanted and in 74% of segments in which a BS was implanted (p= NS), while a severe inflammatory reaction was observed in 6% of CS segments and in 8% of BS segments (p= NS). No differences were detected at the long-term analysis between neointimal thickness in CS compared with BS segments (0.46 {+-} 0.18 mm vs 0.42 {+-} 0.26 mm at 90 days and 0.36 {+-} 0.08 mm vs 0.35 {+-} 0.04 mm at 180 days; pNS, respectively). At SEM analysis, re-endothelization was evident 15 days after the implant in both CS and BS starting from the stent edges.Conclusion: CS implantation did not elicit a more severe thrombotic deposition compared with that of BS. A similar inflammatory reaction of the arterial wall was present in the two stent groups 3 and 6 months following the implant. In addition, CS implantation did not stimulate excessive neointimal formation when compared with BS.« less
  • Purpose: To compare neointima formation following insertion of low-profile Nitinol stents, Palmaz stents, and Wallstents. Methods: Nitinol stents, Palmaz stents, and Wallstents similar in size were transfemorally inserted into the iliac arteries of 12 sheep. Four stents per sheep were deployed; the position of the stents was varied so that each type of stent was placed in each position (right or left, proximal or distal) with equal frequency. Stent patency was followed by angiography. Six sheep were euthanized after 1 month, and the remaining six after 6 months. Iliac arteries were removed en bloc and prepared for histological examination. Neointimalmore » and medial thickness were measured by light microscopy, and measurements were analyzed statistically. Results: Mean neointimal thickness both over (NO) and between (NB) the stent struts was greater in Wallstents (NO = 0.341 mm, NB = 0.368 mm) than in the Nitinol (NO = 0.260 mm, NB = 0.220 mm) and Palmaz stents (NO = 0.199 mm, NB = 0.204 mm), but differences were not significant (p> 0.05). Medial atrophy in the area between the stent struts was greater in Wallstents compared with Nitinol and Palmaz stents (p < 0.007 and p < 0.02, respectively); in the area under the stent struts there was a significant difference only between Palmaz stents and Wallstents (p < 0.02). Conclusion: Under defined experimental conditions, none of the three types of stent appears to be preferable to the others regarding neointima formation in the short- to mid-term follow-up period.« less
  • The purpose of this study was to compare performance of small intestinal submucosa (SIS)-covered endografts (SCEs) to polytetra-fluoroethylene (PTFE)-covered endografts (PCEs) and to bare nitinol stents (BSs) in injured sheep femoral artery (FA). Bare Zilver 6 mm x 40 mm nitinol stents (n = 6), Zilver stents covered with SIS (n = 6), and Palmaz stents 6 mm x 37 mm covered with PTFE (n = 6) were implanted in the balloon-injured FAs of nine female sheep. Follow-up arteriograms were obtained before animal sacrifice at 1, 3 and 6 months, with three animals at each time point. The FAs withmore » the implanted device were explanted for histologic studies and morphologic measurements. Stent implantation was technically successful in all sheep. All BS and SCEs were patent at each time point. Five BSs and five SCEs exhibited formation of progressive eccentric intimal hyperplasia (IH) that was more advanced in SCE at 6 months. Cross-sectional area narrowing averaged 60% for BSs and 67% for SCEs. One BS, one SCE and two patent PCEs exhibited mild-to-moderate formation of concentric IH. Four PCS occluded one at 1 month, two at 3 months and one at 6 months. Performance of the devices placed into sheep FAs depended on their relation to the curving peri-articular portion of the FA during extremity flexion. BSs and SCEs placed in this portion exhibited progressive growth of eccentric IH while PCEs placed in this portion occluded.« less
  • Purpose: To evaluate the necessity of metallic stenting of the sphincter of Oddi in malignant obstructive jaundice when the tumor is more than 2 cm from the papilla of Vater.Methods: Sixty-seven self-expandable biliary stents were used in 60 patients with extrahepatic lesions of the common hepatic or common bile duct and with the distal margin of the tumor located more than 2 cm from the papilla of Vater. Stents were placed above the papilla in 30 cases (group A) and in another 30 with their distal part protruding into the duodenum (group B).Results: The 30-day mortality was 15%, due tomore » the underlying disease. The stent occlusion rate was 17% after a mean period of 4.3 months. No major complications were noted. Average survival was 132 days for group A and 140 days for group B. In group A, 19 patients survived {<=} 90 days and in eight of these, cholangitis occurred at least once. Of 11 patients in group A with survival > 90 days, only two developed cholangitis. In group B, 13 patients who survived {<=} 90 days had no episodes of cholangitis and in 17 with survival > 90 days, cholangitis occurred in three. There is a statistically significant difference (p < 0.05) regarding the incidence of cholangitis in favor of group A.Conclusions: In patients with extrahepatic lesions more than 2 cm from the papilla and with a relative poor prognosis ({<=} 3 months), due to more advanced disease or to a worse general condition, the sphincter of Oddi should also be stented in order to reduce the postprocedural morbidity.« less
  • Purpose: To evaluate the patency and healing characteristics of a woven polyester fabric-covered stent in the canine model.Methods: Twenty-four self-expanding covered stents were placed in the infrarenal aorta and bilateral common iliac arteries of eight dogs and evaluated at 1 (n = 2), 3 (n = 2), and 6 (n = 4) months. Stent assessment was done using angiography prior to euthanasia, and light and scanning electron microscopy.Results: Angiographically, just prior to euthanasia, 8 of 8 aortic and 14 of 16 iliac endovascular covered stents were patent. Histologically, the stented regions showed complete endothelialization 6 months after graft implantation. Amore » neointima had formed inside the stented vessel regions resulting in complete encasement of the fabric-covered stent by 3 months after graft implantation. Medial compression with smooth muscle cell atrophy was present in all stented regions. Explanted stent wires, examined by scanning electron microscopy, showed pitting but no cracks or breakage.Conclusion: The covered stent demonstrated predictable healing and is effective in preventing stenosis in vessels 10.0 mm or greater in diameter but does not completely preclude stenosis in vessels 6.0 mm or less in diameter.« less