Effects of nitinol Strecker stent placement on vascular response in normal and stenotic porcine iliac arteries

PURPOSE: This experimental study was conducted to evaluate neointimal thickness, lumen diameters, and histologic changes in normal and stenotic porcine iliac arteries following placement of self-expanding nitinol Strecker stents. MATERIALS AND METHODS: Neointimal trauma causing slight vascular stenosis was induced unilaterally within external iliac arteries of 12 swines by means of endothelial abrasion and high cholesterol diet. Nitinol Strecker stents were placed within the stenotic and the normal contralateral vascular segments. For histopathologic evaluation, the pigs were killed 12 or 24 weeks after stent placement and luminal diamters were evaluated angiographically. RESULTS: Excluding one occlusion, 15% narrowing of the lumen diameter was induced unilaterally (P = .002). Initial luminal gain after stent placement was greater for stenotic than for normal arteries. The amount of neointima thickness was not different between stenotic and normal vessels (P > .05). Comparing vascular diameters before stent placement and at follow-up, luminal loss due to neointima proliferation was 22% within normal arteries (P = .0002), while a luminal gain by 15% was found within the stenotic arteries (P = .008). Maturation of neointima and endothelial coverage were complete after 24 weeks. CONCLUSIONS: Even though nitinol Strecker stents induce excessive neointimal proliferation, stenotic arteries seem to profit from great early luminal gain resulting in 15% of vascular expansion at follow-up while slight stenosis is induced within normal iliac arteries.     

Self-expanding metallic stents: preliminary evaluation in an atherosclerotic model

The performance of the self-expanding stainless steel (Gianturco) stent in atherosclerotic arteries was examined in a rabbit model. Atherosclerosis was induced by supplementing rabbit chow with 6% peanut oil and 2% cholesterol followed by endothelial disruption of the abdominal aorta with a balloon catheter and continuation on the atherogenic diet for the remainder of the study. Eighteen stents, 1 cm in length and 4 or 5 mm in diameter when fully expanded, were placed in atherosclerotic stenotic lesions in six rabbits. Luminal distention was consistently achieved. At 8 weeks follow-up, no luminal narrowing, stent migration, thrombus formation or branch vessel occlusion had occurred. Atherosclerotic neointimal proliferation occurred around the stent wires following placement, but did not cause significant luminal narrowing.     

Oversizing of self-expanding stents: influence on the development of neointimal hyperplasia of the carotid artery in a canine model

BACKGROUND AND PURPOSE: In carotid artery stent placement, marked oversizing of the stent relative to the internal carotid artery lumen is common. This study was performed to determine the influence of using oversized self-expanding nitinol stents on neointimal hyperplasia. METHODS: In six greyhound dogs, 24 self-expanding nitinol stents (eight SMART stents, eight Easy Wallstents, eight Sinus-Flex stents) were inserted into both common carotid arteries (CCAs). In each CCA, two stents were deployed; a stent of the appropriate diameter was implanted distally and an oversized stent proximally. After 4 months, transverse sections of each stent were examined histologically and at computerized image analysis. Neointimal hyperplasia was determined as the proportion of the residual diameter of the patent vessel lumen compared with the stent lumen. RESULTS: The amount of neointimal hyperplasia did not differ between the normal-sized and oversized stents. The mean preserved luminal diameter (+/-SEM) with normal- and oversized stents, respectively, were as follows: Easy Wallstent, 94% +/- 1.0 and 96% +/- 1.5; SMART stent, 92% +/- 1.6 and 93% +/- 1.8; and Sinus-Flex stent, 93% +/- 2.7 and 93% +/- 2.6. The mean preserved patent lumen with the 12 normal-sized stents (93% +/-1.0) was not significantly different from that of the 12 oversized stents (94% +/- 1.1, P =.502). CONCLUSION: Under experimental conditions, use of self-expanding stents oversized by 30-40% appeared to result in neointimal hyperplasia comparable to that caused by normal-sized stents. All three stent types appeared to have similarly low neointimal responses.     

Differences in Endothelial Injury After Balloon Angioplasty, Insertion of Balloon-Expanded Stents or Release of Self-Expanding Stents: An Electron Microscopic Experimental Study

Purpose: To evaluate which of six different commonly available stents inserted into an artery without percutaneous transluminal angioplasty (PTA) causes the least endothelial damage. To compare the degree of endothelial injury after insertion of such a stent with injury caused by PTA. Methods: Twelve healthy pigs were used in the experiments. In the first part of the study six different types of stents were inserted into the common iliac arteries. In the second part of the study self-expanding stents with large spaces between the wires were used. PTA was performed in the contralateral iliac artery. The pigs were killed immediately after the procedure and resected specimens examined after fixation, using scanning electron microscopy. Results: All procedures but two were accomplished successfully. More endothelium was preserved after insertion of self-expanding stents with large spaces between the wires, compared with stents with small spaces and balloon-expanded stents. After insertion of self-expanding stents with large spaces, 50.1% ± 16.4% of the endothelium remained intact, compared with only 5.6% ± 7.7% after PTA. The difference was statistically significant (p < 0.001). Conclusion: Self-expanding stents with large spaces between the wires, inserted without PTA, cause less damage to the endothelium than other stents and significantly less damage than PTA.     

Inhibition of neointimal proliferation with 188Re-labeled self-expanding nitinol stent in a sheep model

PURPOSE: To evaluate a self-expanding rhenium 188 (188Re) radiochemically labeled radioactive stent in sheep. MATERIALS AND METHODS: A self-expanding nitinol stent (30 mm in length, 8 mm in diameter) coated with a functionalized polymer layer was radiolabeled with 188Re. Fifty prostheses, 25 of which were radioactive (mean radioactivity, 20 MBq +/- 3.8 [SD]) and 25 of which were nonradioactive, were implanted into the external iliac arteries of 25 sheep. Stent patency was assessed with angiography. Neointimal formation was assessed with intravascular ultrasonography and histologic examination 1 month (in all sheep) and 3 months (in 12 sheep) after implantation. The results were analyzed by using repeated-measures analysis of variance with two repeated factors and paired t tests for comparison at each measuring point. RESULTS: All stents were placed successfully. Data in one animal had to be excluded from the study. After 3 months, a mean neointimal area reduction of 70 mm2 +/- 55 (SD) was observed inside the radioactive stents, and a mean lumen reduction of 126 mm2 +/- 39 was observed inside the nonradioactive control stents (P =.022). An edge effect was observed in the radioactive stents in that they showed an amount of neointimal formation at the edges that was similar to that seen in control stents. This neointimal formation accounted for the maximum lumen loss in the vascular segment with the stent. CONCLUSION: As compared with a nonradioactive stent, a beta particle-emitting stent, through endovascular irradiation, significantly inhibits neointimal formation inside the stent but not at the stent edges.     

Occlusive effect of metallic stents on canine ureters

A three-part study, with successive modifications based on preceding results, was conducted to evaluate ureteral placement of metallic stents. Gianturco self-expanding (10 mm and 4 mm diameter) and balloon-expanded (4 mm diameter) metallic stents were placed in normal and stenotic canine ureters. No migration or ureteral perforation occurred during the follow-up of 10 mm stents. Varying degrees of hydronephrosis and hydroureter were found on all 1-week pyelograms. At 4 weeks, complete occlusion of the stented ureter was noted in all cases because of mucosal hyperplasia around the stent wires. To prevent this reaction, 4 mm self-expanding stents constructed of smaller wire that was uncoated or coated with either Teflon or polyurethane were tested in five dogs. In all cases, results were similar to those obtained with the larger prostheses. Finally, 4 mm balloon-expanded stents were placed in a normal ureter of three dogs. In one dog, the stent migrated out of the ureter. No migration or ureteral perforation occurred in the two remaining dogs. In these animals, mucosal hyperplasia and complete ureteral occlusion occurred 6 and 8 weeks after placement. Therefore, ureteral placement of Gianturco self-expanding as well as balloon-expanded metallic stents leads to occlusion of the ureter instead of maintaining its patency. Stents, therefore, may be useful as ureteral occlusion devices.     

Placement of self-expanding stents with different diameters in the porcine venous system: an experimental study

PURPOSE: To study the vascular histologic response after placement of oversized self-expanding stents in the porcine venous system. MATERIALS AND METHODS: Twenty-four oversized stents (range of oversizing, 119.5%-216.0%) were deployed in jugular and iliac veins of six miniature pigs divided into two groups with follow-up times of 1 and 3 months. Necropsy with histologic evaluation of each stent was performed, and the areas of neointimal proliferation were calculated with slices obtained during follow-up from each stent at 5 mm from the proximal and distal edges and at the midpoint. RESULTS: Neointimal proliferation was observed inside the stent lumen. All segments were patent in both groups. However, one jugular stent in the 1-month group and one jugular stent in the 3-month group had migrated at follow-up and were excluded from analysis. There were no significant differences in neointimal growth between the stent edges (proximal and distal) and middle segments of the stents at follow-up in the 1-month group (P = .970) or in the 3-month group (P = .694). Simple linear regression showed strong positive correlation between stent oversizing and neointimal proliferation in the 1-month model (r = 0.791; P < .001) and the 3-month model (r = 0.718; P < .001). There were no significant differences between 1-month and 3-month groups in the degree of neointimal proliferation (P = .072). Also, branched vessels showed no neointimal proliferation at their intersections with the stent-implanted segments. CONCLUSION: Stent oversizing showed a strong positive correlation with neointimal growth in each follow-up model in this study.     

Carotid Artery Stenting Using a Novel Self-Expanding Braided Nickel–Titanium Stent: Feasibility and Safety Porcine Trial

We studied the deliverability and safety of a braided, self-expanding, closed-cell nickel–titanium (NiTi) stent (E-volution, Jotec GmbH, Hechingen, Germany) especially designed for the endovascular treatment of carotid artery bifurcation stenosis with special regard to in-stent stenosis and thrombosis compared with a laser-cut reference nitinol stent in a porcine model of percutaneous vascular interventions. We aimed to assess histopathologic response in minipig carotid and subclavian arteries. Eight minipigs received a total of 42 stents: 14 reference stents and 28 E-volution stents. Eleven of the E-volution stents were additionally coated with heparin. Control angiography was obtained immediately before and after vascular intervention as well as 4 weeks after the procedure. Primary endpoints were 28 days of angiographic analyses as well as histomorphometric analysis, including injury score, inflammation score, luminal diameter, vessel diameter, maximal neointimal thickness, and area of in-stent stenosis. Secondary end points were procedural success, 28-day mortality, and stent thrombosis. All stents could be delivered successfully without procedural complications, morbidity, or mortality during our observation time. As confirmed by histology, no in-stent thrombosis was observed. Compared with common carotid arteries, subclavian arteries are significantly more vulnerable to developing in-stent stenosis caused by neointima proliferation (p < 0.05). Compared with the use of 1 single stent/artery, serial application of two stents leads to a more excessive but not significantly different neointimal proliferation (p > 0.05). The E-volution stent, especially when heparin coated, is in line with the comparison to the laser-cut reference stent displaying similar results of angiographic, histologic, and histomorphometric analyses (p > 0.05). Compared with the reference laser-cut stent, the self-expanding nitinol stent (E-volution) with its advanced braiding technology is feasible and safe. In our opinion, the high radial resistive force and the advanced braided design with tight stent-strut interstices may be beneficial in terms of plaque stabilization. Further studies are necessary and warranted.     

Self-expanding nitinol stents for treatment of infragenicular arteries following unsuccessful balloon angioplasty

The feasibility of self-expanding nitinol stents for treatment of infragenicular arteries following unsuccessful balloon angioplasty was assessed. Options for lower limb percutaneous revascularization are limited, especially for complex vessel obstruction. Depending on the lesion and the experience of the interventionalist, the failure rate of balloon angioplasty (PTA) ranges between 10 and 40%. Until recently, no self-expanding stent for the use in the infragenicular arteries was available. This is the first report of the results for 18 consecutive patients who received 4F sheath compatible self-expanding nitinol stents following unsuccessful PTA or early restenosis. Twenty-four stents were implanted in 21 lesions for various indications residual stenosis >50% due to heavy calcification, flow-limiting dissection, occluding thrombus resistant to thrombolyis, thrombaspiration, and PTA, and early restenosis after previous PTA. Stent implantation was feasible in all cases. No complications occurred. After the stent implantation, all primarily unsuccessful interventions could be transformed into successful procedures with no residual stenosis >30% in any case. After 6 ± 2 months, two of the 18 patients died, and 14 of the 16 remaining patients improved clinically. At follow-up, the patency could be assessed in 14 stented arteries. Three stents were occluded, one stent showed some neointimal hyperplasia (50–70% restenosis), the remaining ten stents showed no restenosis (0–30%). The use of self-expanding nitinol stents in tibioperoneal and popliteal arteries is a safe and feasible option for the treatment of unsuccessful PTA. The 6-months patency is high.     

Comparison of self-expanding polyethylene terephthalate and metallic stents implanted in porcine iliac arteries

Purpose: Comparison of the biocompatibility of self-expanding polyethylene terephthalate (PET) stents with self-expanding metallic stents (Wallstents). Methods: Diameter- and length-matched PET stents and Wallstents were symmetrically implanted in the paired iliac arteries of 13 crossbred domestic swine. Stent deployment was studied angiographically and with intravascular ultrasound immediately after stent implantation. The angiographic stented lumen diameter was measured using quantitative vessel analysis before, immediately after stenting, and at 6-week follow-up. Cross-section histopathology and area morphometry were performed. Results: Immediately poststenting, intravascular ultrasound revealed proximal dislocation of 5 of the 13 PET stents, whereas all metal stents were firmly embedded at the implantation site. At 6-week follow-up, three of the remaining PET stents were totally or subtotally occluded by organized thrombus, whereas all metal stents were patent. Compared with immediately poststenting, the angiographic lumen diameter within the five remaining PET stents was reduced by 30%, and that of the metallic stents was virtually unaltered (p<0.02). This observation was confirmed by postmortem morphometry, wherein the PET-stented vessel segments a diameter stenosis of 40% was measured vs only 9% in the metallic stents (p<0.0001). Conclusion: PET-stent deployment is difficult to control due to the lack of radiopacity of this stent. PET stents seem to be more thrombogenic and lead to significantly more neointimal proliferation than metallic stents.     

Stent-Based Nitric Oxide Delivery Reducing Neointimal Proliferation in a Porcine Carotid Overstretch Injury Model

BACKGROUND: The effects of nitric acid (NO) on vessel response to injury include the inhibition of platelet adhesion, platelet aggregation, leukocyte adhesion and smooth muscle cell proliferation. Releasing NO from a stent might reduce the clinical problem of restenosis. The present study was designed to examine whether an NO-eluting covered stent can prevent neointimal formation in a porcine carotid overstretch injury model. METHODS: The interior of a self-expanding polytetrafluoroethylene (ePTFE)-covered aSpire stent was coated with silicone, which contained 23.6 microg or 54.5 microg sodium nitroprusside (SNP, NO-releasing compound). The stent was implanted into carotid artery. Six pigs were implanted with stents, one high-dose SNP and one uncoated control, following balloon overstretch injury of the carotid artery with a balloon-to-artery ratio of 1.3:1. RESULTS: No local or systemic toxicity was evidenced in the six pigs after carotid artery implantation with either low- or high-dose stents within a week. At day 28, the mean intimal thickness was 0.12 +/- 0.05 mm for NO-eluting stents and 0.43 +/- 0.09 mm for uncoated stents (p = 0.008). The mean neointimal area was reduced from 2.40 +/- 0.39 mm2 for control stents to 0.49 +/- 0.16 mm2 for NO-eluting stents (p < 0.0001), which resulted in a 24% reduction of angiographic vessel narrowing. CONCLUSIONS: The NO-eluting ePTFE-covered stent is feasible and effectively reduces in-stent neointimal hyperplasia at 28 days in a porcine carotid overstretch model.     

A novel flexible endovascular stent for use in small and tortuous vessels

We assessed in vivo the mode of delivery, short-term patency and cellular response to a prototype endovascular stent. The stent is designed for delivery through a modified microcatheter and is retrievable with detachment from a delivery wire effected by electrolysis. We successfully deployed 12 stents in a range of sizes from 3–4 mm in straight and angled arteries of pigs. At control angiography 3 and 6 weeks later, nine arteries were patent, two occluded and one narrowed; patency was not related to vessel or stent size. The device shows promise as a stent for intracranial arteries since it can be delivered through microcatheters small enough for intracranial navigation and provides the operator with greater control than currently available self- or balloon-expanded stents. Received: 25 March 1998/Accepted: 7 May 1999     

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

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 × 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.     

Self-expanding nitinol stents in canine vertebral arteries: hemodynamics and tissue response.

PURPOSETo evaluate the hemodynamics and tissue response associated with stent placement in low-flow-velocity arteries.METHODSSix self-expanding nitinol stents (5.5 mm caliber) were implanted transfemorally within the proximal segments of vertebral arteries (2.5 mm diameter) in six adult dogs during anticoagulative protection.RESULTSControl angiograms demonstrated patency and 20% dilatation of all stented arteries. One artery was partially thrombosed 1 week later and subsequently showed a 50% stenosis. Throughout the observation period (4 to 9 months after stenting), the other five arteries remained patent without significant narrowing (< or = 15%). Small cervical muscle branches originating from the vertebral arteries within the stented segments remained patent. No major branch occlusions of the vertebrobasilar system were detected. Stent migration or kinking did not occur. MR studies of the brain 4 months after implantation revealed no infarcted areas. These findings were confirmed with brain sections. Stented artery specimens showed delayed stent dilatation. A comparison of the total mean thickness of intima covering the five 30- to 40-mm stents removed at 4, 6, and 9 months showed no significant difference (338, 332, and 389 microns, respectively). Histologic findings verified the macroscopic impression of a thicker intima at the inner curve of the stented artery segments and at the junctions of the stent filaments. The shortest (10 mm) stent had the thinnest neointimal growth (155 microns). Stented vessels showed compression of the media with atrophy, but without necrosis or perforation. Scanning electron photomicrographs revealed intact endothelial cell linings with typical elongated cells.CONCLUSIONSNo significant risk of thromboembolic events exists after implanting these nitinol stents in nonatherosclerotic vertebral arteries in dogs. Thicker neointimal growth after stenting may result from either low wall shear stress with possible flow separation or from changes in the shape and size of the stent, or both.     

Evaluation of three polytetrafluoroethylene stent-grafts in a model of neointimal hyperplasia

PURPOSE: The authors tested three different porosities of expanded polytetrafluoroethylene (ePTFE)-covered stents and bare stents by using an animal model of restenosis. MATERIALS AND METHODS: Both iliac arteries in 18 female pigs were injured by overdilating 20-mm-long angioplasty balloons. A 40-mm-long bare stent or one of three 44-mm-long ePTFE-covered stents was deployed at the injury site. To determine restenosis, neointimal area measurements were made with intravascular ultrasonography. Histologic analyses were performed at an independent laboratory to determine neointimal attachment. RESULTS: Neointimal area was greatest at the middle of the bare stent, where balloon injury was centered. When the middle location of the covered stents was evaluated, the neointimal area of both the medium- and high-porosity covered stents was smaller than that of the matched control stents (P = .0018 and P = .0118, respectively). The neointimal area of the low-porosity covered stents was similar to that of the bare stents. Histologic study showed dehiscence of the neointima of the low-porosity covered stents. CONCLUSIONS: The microstructure of the low-porosity covered stents did not provide a suitable surface for neointimal attachment and did not reduce neointimal growth compared to that with the control stents. The microstructure of the medium- and high-porosity covered stents yielded less neointimal growth than both the control stents and the low-porosity covered stents without evidence of neointimal dehiscence. The authors believe that covered stents made with ePTFE with either medium or high porosity could limit restenosis in humans compared to that with bare stents.     

Vascular responses in normal canine carotid arteries: comparison between various self-expanding stents of the same unconstrained size

RATIONALE AND OBJECTIVES: To compare long-term vascular responses upon the insertion of various self-expandable stents, all the same unconstrained size, in canine carotid artery models. MATERIALS AND METHODS: Twenty-two stents (5 SMARTs, 5 Wallstents, 6 Niti-Ss, 6 Niti-Ds) of the same unconstrained size (6 mm in diameter, 20 mm in length) were endovascularly placed in canine common carotid arteries. The luminal changes were measured on three occasions, on prestenting, immediate poststenting, and angiograms taken before specimens were killed. After en-bloc harvest of the stented carotid arteries at 6 months, the intraluminal surface was evaluated by gross observation and scanning electron microscopy (SEM). Neointimal thickness was measured at several points both over the wire and between the wires. RESULTS: Niti-D was excluded from analysis because of high rate of poststenting occlusion. SMART stent showed the greatest expansibility with average initial luminal gain ( < 0.05) of 21.2% (Niti-S: 16.5%, Wallstent: 12.9%). At 6 months follow-up, the dilated arterial lumen had returned almost to the prestenting caliber without any significant differences among the stent types ( > 0.05). The thickness of neointimal coverage was more prominent with SMART stent (354 microm over the wire and 258 microm between the wires) than Niti-S (228 microm and 83 microm) or Wallstent (187 microm and 78 microm). CONCLUSION: Stent types with its higher initial luminal gain appeared to be associated with thicker neointimal formation at 6 months. The acute expanding force of a self-expanding stent may be the key to the cause of neointimal hyperplasia. Regardless of the inserted stent type, the variations in neointimal response were offset by luminal gains of varying degree, thus preserving the arterial patency almost to the prestenting size.     

Placement of a flexible endovascular stent across the femoral joint: an in vivo study in the swine model.

PURPOSE: To investigate the effects of joint motion on the structural integrity of periarticular stents and on the development of neointimal hyperplasia within these devices. MATERIALS AND METHODS: In four juvenile farm swine, Wall-stents were implanted in the common femoral arteries and contralateral common femoral veins, centered at the point of maximal conformational change during passive hip flexion. Control stents were placed in the aortae and iliac veins. Angiography and transcatheter blood pressure measurements were obtained across each stent, with periarticular stents studied in flexion and extension. Two animals underwent repeated evaluation after 1 month, the others after 3 months. Findings were correlated with gross and histopathologic findings in the harvested stents. RESULTS: No stent fractures occurred. One femoral vein was injured during stent placement and was occluded 1 month later at follow-up. Hemodynamically significant stenoses were identified in one arterial stent and one venous stent at 3 months. The amount of neointimal hyperplasia was greater in periarticular stents than in controls and greater in animals studied at 1 month than in those studied at 3 months. The pattern of neointimal hyperplasia within mobile arteries was circumferentially asymmetric and thicker at the distal ends of the stents. Venous neointimal hyperplasia was thicker and markedly different in character than that seen in arterial stents from the same animals. CONCLUSIONS: Periarticular Wallstents and the underlying vascular anatomy remained structurally intact despite the stresses of repetitive motion during a 3-month period. Stents deployed across joints or in venous locations may be at greater risk for neointimal hyperplasia development and eventual occlusion than those deployed in immobile vessels and arteries. Neointimal hyperplasia may decrease in thickness after an initial period of exuberant development. Additional studies are necessary to determine long-term outcomes.     

Neointima formation following arterial placement of self-expanding stents of different radial force: Experimental results

Purpose: Radial force delivered by self-expanding stents has been discussed as a factor affecting thickness of neointima formation. Methods: Two types of Wallstents were studied experimentally in vitro and in vivo. Due to an altered braiding angle of the stent filaments, one stent type (LS type) delivers half the radial force to the vascular wall than the conventional type. The radial force was evaluated in a compression-expansion test which related changes in stent length to the compressing force. Fourteen LS and 16 conventional stents were implanted into 15 femoropopliteal arteries of 10 dogs. Autopsy was performed after 4 weeks (14 stents) or 6 months (16 stents). Results: All stents remained patent over the follow-up period with no evidence of stenosis. Neointimal overgrowth was complete and smooth in all. Medial atrophy was a constant finding after placement of both types. Neointimal thickness did not exceed 100 m after 4 weeks and 6 months and did not significantly differ between LS stents and conventional stents. Conclusion: It is concluded that in normal dogs self-expanding stents of the Wallstent type do not induce neointimal buildup that exceeds 100 m in the femoropopliteal artery. A reduced radial force was not found to result in reduced neointima formation.     

Comparison of diamond-like carbon-coated nitinol stents with or without polyethylene glycol grafting and uncoated nitinol stents in a canine iliac artery model

Objective

Neointimal hyperplasia is a major complication of endovascular stent placement with consequent in-stent restenosis or occlusion. Improvements in the biocompatibility of stent designs could reduce stent-associated thrombosis and in-stent restenosis. We hypothesised that the use of a diamond-like carbon (DLC)-coated nitinol stent or a polyethylene glycol (PEG)-DLC-coated nitinol stent could reduce the formation of neointimal hyperplasia, thereby improving stent patency with improved biocompatibility.

Methods

A total of 24 stents were implanted, under general anaesthesia, into the iliac arteries of six dogs (four stents in each dog) using the carotid artery approach. The experimental study dogs were divided into three groups: the uncoated nitinol stent group (n = 8), the DLC-nitinol stent group (n = 8) and the PEG-DLC-nitinol stent group (n = 8).

Results

The mean percentage of neointimal hyperplasia was significantly less in the DLC-nitinol stent group (26.7±7.6%) than in the nitinol stent group (40.0±20.3%) (p = 0.021). However, the mean percentage of neointimal hyperplasia was significantly greater in the PEG-DLC-nitinol stent group (58.7±24.7%) than in the nitinol stent group (40.0±20.3%) (p = 0.01).

Conclusion

Our findings indicate that DLC-coated nitinol stents might induce less neointimal hyperplasia than conventional nitinol stents following implantation in a canine iliac artery model; however, the DLC-coated nitinol stent surface when reformed with PEG induces more neointimal hyperplasia than either a conventional or DLC-coated nitinol stent.     

Insertion of Self-Expandable Nitinol Stents Without Previous Balloon Angioplasty Reduces Restenosis Compared with PTA Prior to Stenting

PURPOSE: To compare the development of intimal hyperplasia after deployment of a self-expanding nitinol stent with and without previous percutaneous transluminal balloon angioplasty (PTA), with the results after PTA alone. METHODS: In nine healthy pigs, the iliac arteries were divided into three groups: group 1 (n = 6 arteries) was treated with PTA; group 2 n = 6) with insertion of self-expanding stents after PTA; and group 3 (n = 6) with stent insertion without previous PTA. After 8 weeks the vessels were examined with intravascular ultrasonography, histologic examination and morphometric analysis. RESULTS: Although the injury index in group 1 (0.17 +/- 0.57) was lower (p <0.05) than in group 2 (0.26 +/- 0.06) and group 3 (0.26 +/- 0.08), PTA-treated arteries showed significantly (p <0.05) reduced mean luminal gain (0.53 +/- 2.84) compared with arteries treated with PTA prior to stenting (2.58 +/- 1.38) and compared with stenting alone (4.65 +/- 5.34). Stenting after PTA resulted in a higher (p <0.05) restenosis index (2.63 +/- 1.06) compared with stenting without PTA (1.35 +/- 0.59). Group 2 also had a significantly thicker intima p <0.05) and 83% and 74% higher intima/media ratio (p <0.05) compared with groups 1 and 3, respectively. CONCLUSION: Insertion of a self-expandable nitinol stent without previous PTA results in less intimal hyperplasia than if PTA is performed prior to stenting, suggesting that direct stenting can be used in angioplasty sessions with a favorable outcome.