Treatment of experimentally induced atherosclerosis in swine iliac arteries: A comparison of self-expanding and balloon-expanded stents

Atherosclerosis was induced in 20 Hanford miniature swine. Subsequently, one iliac artery lesion in each of 16 pigs was stented with either a self-expanding (8 pigs) or a balloon-expanded (8 pigs) stent. Immediately after stent placement, 4 animals in each group were taken off the atherogenic diet and continued on normal chow for the remainder of the study. Four months after stents were placed, atherosclerosis and the mural changes associated with the stent were more clearly evident in the arteries of the pigs continued on the atherogenic diet. These pigs also exhibited significantly more neointimal proliferation. In addition, the arteries containing the balloon-expanded stents showed more extensive and complex intimal changes when compared with arteries with self-expanding stents. Although both stent designs were equally effective in maintaining vascular patency, the balloon-expanded stent was more traumatic to the vessel wall which resulted in a significantly greater neointimal thickness.     

Self-expanding metallic stents for small vessels: an experimental evaluation

Thirty-three self-expanding metallic stents were placed in 24 arterial segments of the hind legs and nine arteries of the abdominal viscera in seven dogs. Twelve 5-mm stents, eight 4-mm stents, and 13 3-mm stents were inserted. Follow-up ranged from 4 to 30 weeks. All 4-mm and 5-mm stents were patent at follow-up. Seven (54%) of the 3-mm stents remained patent. Stent wires were completely covered by a proliferation of the intima. No stent migration, occlusion of side branches, or vessel wall perforation was observed. A stent/artery ratio (SAR) was computed using stent and recipient vessel diameters. Good vascular patency was observed when the SAR was less than or equal to 1.2. An SAR greater than 1.2 was associated with immediate spasm, immediate or delayed thrombosis, or excessive intimal proliferation. Selection of correct stent size is a major determinant of patency in small arteries.     

Metallic renal artery MR imaging stent: artifact-free lumen visualization with projection and standard renal MR angiography

A cardiac-triggered free-breathing three-dimensional (3D) balanced fast field-echo projection renal magnetic resonance (MR) angiographic sequence was investigated for in-stent lumen visualization of a dedicated metallic renal artery stent. Fourteen prototype stents were deployed in the renal arteries of six pigs (in two pigs, three stents were deployed). Projection renal MR angiography was compared with standard contrast material-enhanced 3D breath-hold MR angiography. Artifact-free in-stent lumen visualization was achieved with both projection MR angiography and contrast-enhanced MR angiography. These promising results warrant further studies for visualization of in-stent restenosis.     

Temporary Strecker Stent for Management of Acute Dissection in Popliteal and Crural Arteries

Stent placement is a widely used bail-out treatment for dissection of peripheral arteries. Below the level of the superficial femoral artery permanent stenting is complicated by a high incidence of subacute thrombosis and restenosis. We present two cases of arterial occlusion due to acute iatrogenic dissection of the popliteal and distal fibular arteries. Successful treatment was achieved with a new bail-out procedure. Strecker stents were implanted to seal off the dissection flap. Stents were retrieved easily after 24 hr using a myocardial biopsy forceps. After stent retrieval the temporarily stented segments were patent and showed a larger lumen compared with segments treated by balloon dilatation alone. Temporary stenting is a simple and safe procedure and offers the advantage of tacking up dissection membranes and preventing recoil. Persistent presence of a metallic implant as a source of continued injury and stimulus for intimal proliferation is avoided.     

Temporary strecker stent for management of acute dissection in popliteal and crural arteries

Stent placement is a widely used bail-out treatment for dissection of peripheral arteries. Below the level of the superficial femoral artery permanent stenting is complicated by a high incidence of subacute thrombosis and restenosis. We present two cases of arterial occlusion due to acute iatrogenic dissection of the popliteal and distal fibular arteries. Successful treatment was achieved with a new bail-out procedure. Strecker stents were implanted to seal off the dissection flap. Stents were retrieved easily after 24 hr using a myocardial biopsy forceps. After stent retrieval the temporarily stented segments were patent and showed a larger lumen compared with segments treated by balloon dilatation alone. Temporary stenting is a simple and safe procedure and offers the advantage of tacking up dissection membranes and preventing recoil. Persistent presence of a metallic implant as a source of continued injury and stimulus for intimal proliferation is avoided.     

Percutaneous production of renal artery lesions. Experiments in the pig

Percutaneous, intraarterial traumatization of both renal arteries in 4 pigs using the stiff end of a guide-wire resulted in intimal lesions in 7 arteries. At repeat angiography healing was demonstrated in 4 of these arteries, suggesting that spontaneous restitution may be more common than usually believed. Balloon catheter dilatation of 2 stenotic segments initially increased the diameter of the stenoses but at repeat angiography both arteries were found to be occluded. Over-distension of the balloon in the renal artery resulted in pseudoaneurysm in one case and rupture in the other.     

Carbon-coated stents implanted in porcine iliac and renal arteries: histologic and histomorphometric study

PURPOSE: 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. MATERIALS AND METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.     

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.     

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.     

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     

Inductively coupled stent antennas in MRI.

The development of intimal hyperplasia following stent deployment can lead to narrowing or even occlusion of the stent lumen. The underlying mechanisms leading to neointimal proliferation within stents remain largely unknown. Long-term evaluation of stent patency requires a noninvasive means for assessing the stent lumen. MR angiography (MRA) has shown potential to provide noninvasive assessment of the vascular system. However, a detailed assessment of the stent lumen with MRI is often hampered by material-dependent susceptibility artifacts, as well as by radiofrequency (RF) eddy currents generated inside the electrically conducting stent mesh. In this study, stent prototypes were designed to act as active resonant structures at the Larmor frequency of the MR system. Employing the principle of inductive coupling, the B(1) fields of the stents were coupled to that of an outside surface coil. The stents thus acted as local RF signal amplifiers. Various stent designs were investigated regarding their coupling to an external coil, signal homogeneity, and suitability for mechanical expansion for implantation purposes. The dependency of flip angle amplification on the quality factor Q of the stents was systematically investigated. Phantom experiments revealed signal amplification in all stent prototypes. Signal enhancement inside and close to the surface of the stents enabled their localization with high contrast in MR images. In vivo imaging experiments in the iliac, renal, and splenic arteries of two pigs confirmed the in vitro findings. Wireless active visualization of stents allows for detailed analysis of the stent lumen with high contrast and spatial resolution. The proposed method could thus provide a powerful diagnostic means for the noninvasive long-term follow-up of stent patency, thereby enhancing our understanding of the mechanisms of restenosis.     

Self-expanding and balloon-expandable stents in the treatment of carotid aneurysms: an experimental study in a canine model.

PURPOSETo assess the efficacy of metal stents for the treatment of different forms and sizes of carotid aneurysms.METHODSA total of 14 experimentally constructed aneurysms in dogs were treated with transfemorally placed balloon-expandable tantalum and self-expanding nitinol stents.RESULTSIn 10 cases, stenting produced either immediate complete occlusion of the aneurysm (n = 7) or complete delayed thrombosis after 7 to 10 days (n = 3). In two cases treated with balloon-expandable tantalum endoprostheses, repeated angiography showed a persistent aneurysmal neck with a diameter of 1 mm. No incompletely occluded aneurysms were visible after implantation of nitinol stents. Nine-month angiographic follow-up revealed maximal stenosis of the stented vessel segment of up to 40% after placement of tantalum endoprostheses. However, no more than 15% stenosis followed the deployment of nitinol stents. Histologic examination confirmed these findings. Significantly greater intimal fibrocellular tissue growth surrounded tantalum filaments than nitinol filaments, which were covered with a smooth, thin neointimal layer. In two carotid arteries a subtotal and total occlusion of the parent vessel occurred after the insertion of a tantalum and nitinol stent, respectively. No recanalization of completely occluded aneurysms or delayed migration of a stent was observed.CONCLUSIONSPorous, tubular self-expanding nitinol stents may become the treatment of choice for broad-based and fusiform aneurysms of the internal carotid artery. However, blood flow dynamics of the aneurysms must be studied carefully in order to select an appropriate mesh size for complete occlusion while preserving the parent vessel. Improvements in the introducing system, stent material, and stent shape are required for simple implantation and reduction of intimal hyperplasia.     

Modified Gianturco arterial stents--preliminary results in iliac arteries of sheep

Modified Gianturco arterial stents were placed in the iliac arteries of 3 non-atherogenic sheep. At three months after placement there was no evidence of migration of the stents or of excessive intimal overgrowth in relation to the stents.     

Thermal balloon angioplasty in a canine model: preliminary results

Preliminary results suggest that thermal balloon angioplasty (BA) may produce plaque welding, decreased elastic recoil, and increased luminal caliber. The authors report results of a simple method of thermal BA in a canine model. Seven mongrel dogs (15-25 kg) underwent conventional BA of each iliac artery with balloons that were 1-2 mm larger than the vessel lumen. The balloons were then perfused with a mixture of saline and contrast material at either 25 degrees C (control) or 100 degrees C for 1 minute. Compared with baseline measurements, thermal BA produced greater lumen enlargement (+16.7%) than control BA (+3.4%) immediately after the procedure (P less than .05). This trend persisted in vessels studied after a delay of 2, 4, or 12 weeks. Histologic sections from specimens studied after a delay demonstrated intimal hyperplasia in both the thermally treated and control arteries. Medial sclerosis was consistently seen in the thermally treated arteries. The authors conclude that thermal BA results in immediate and delayed increases in arterial diameter compared with conventional BA due to decreased elastic recoil and medial sclerosis.     

Development of gold stents for the treatment of intracranial aneurysms: an experimental study in a canine model

BACKGROUND AND PURPOSE: Gold has often been used in medicine because of its radiopacity and flexibility. To perform stent-supported coil embolization of intracranial aneurysms, we prepared a gold stent and examined its flexibility, radiopacity, and thrombogenic properties in comparison with a stainless steel device implanted in vitro and in vivo. METHODS: Gold stents were prepared by plating gold on stainless steel stents as a template. Their mechanical properties and trackability in vitro were determined and compared with those of stainless steel stents of the same design. Twenty gold stents and two stainless steel stents were implanted in canine external carotid, vertebral, and renal arteries, as a muscle branch of the maxillary arteries, to examine their performance in vivo. RESULTS: The gold stent exhibited much less radial force and greater flexibility than the stainless steel stent. It also demonstrated superior trackability and radiopacity in the experimental endovascular procedures in canines. Histologic examination showed good patency of the stented artery with slight endothelial hypertrophy. CONCLUSION: Although there is still room for more radial strength, less influence on intimal hypertrophy, a more suitable flexibility, and a smoother surface, the superior trackability and radiopacity of gold stents seem to support use of this device for the endovascular treatment of intracranial aneurysms.     

自制Palmaz支架的动物实验研究

目的 观察自制Ｐａｌｍａｚ支架植入动脉后的通畅率、病理学改变、理化稳定性及支架的释放系统等。方法 自制的Ｐａｌｍａｚ支架由国产３１６Ｌ医用不锈钢超薄钢管制成。实验动物为正常家猪６头,植入支架共９个,部位包括：颈动脉、肾动脉、髂动脉。置入后分别于２周、１个月、３个月造影复查,并处死取出支架段血管行光镜及扫描电镜检查。结果 ９个支架成功植入靶血管,所有支架即时复查均通畅。外死前复查８个架仍通畅。光镜及     

Palmaz stent in atherosclerotic stenoses involving the ostia of the renal arteries: preliminary report of a multicenter study

Palmaz balloon-expandable stents were placed in 28 hypertensive patients with atherosclerosis involving the ostia of the renal arteries. Stents were placed to treat elastic recoil immediately after conventional angioplasty in 20 patients and restenosis after percutaneous transluminal angioplasty in eight patients. Technical success (greater than 30% residual stenosis) was achieved in 27 patients. Complications occurred in five patients. At follow-up (1-25 months), hypertension was cured in three patients and improved in 15 patients, with a cumulative cure or improvement of 64% at 6 months. Of 14 patients with a serum creatinine level of 1.5 mg/dL (132.6 mumol/L) or greater before the placement of stents, five demonstrated improved renal function, five showed stabilization of their condition, and four demonstrated deterioration. Follow-up angiography (2-18 months) was performed in 18 patients. Restenosis was present in seven patients and was accompanied by a relapse of hypertension in only three patients. Of the other four patients with restenosis, two had no initial improvement and two had an initial response without a relapse of hypertension. In this preliminary study, renal stents were beneficial in many patients with poor results from conventional angioplasty for ostial atheroma.     

Iliac and femoropopliteal vascular occlusive disease treated with flexible tantalum stents

Two hundred patients were treated with tantalum stents, 2 in the aortoiliac bifurcation, 114 in the iliac, and 84 in the femoropopliteal arteries. The indications for stenting were technically unsuccessful percutaneous transluminal angioplasty (PTA) due to arterial recoil, dissection (156 patients), or acute occlusions (15 patients). Long iliac artery occlusions (29 patients) were indications for primary stenting. Life-table analysis revealed a 3-year patency rate of 95% for stented iliac arteries, and a 1-year patency rate of 80% for stented femoropopliteal arteries. Restenosis of the stented femoropopliteal lumen was particularly frequent in stents placed for restenosis following prior PTA (7 of 12 patients), in stents placed into the distal superficial femoral and popliteal arteries (14 of 24 patients), and in stents positioned over a longer than 4-cm artery segment (9 of 16 patients). For the aortic bifurcation and iliac arteries, arterial stenting has proved to be a valuable adjunct to PTA; for femoropopliteal arteries, stenting should be restricted to acute arterial occlusions or severe residual stenosis following PTA.     

Balloon catheter dilatation of stenotic renal artery anastomoses. Experiments in the pig

Stenotic renal artery anastomoses were produced in pigs in order to investigate the effects of transluminal angioplasty. Six weeks after surgery unilateral dilatation with a modern balloon catheter was performed in 8 pigs. These animals were reexamined with angiography and pressure gradient recording 8 to 10 weeks after dilatation and with post-mortem angiography 8 to 10 weeks later. Only 2 arteries had minimal residual stenoses, while in 6 arteries the stenoses were completely eliminated. Microscopic examination showed thinning of the fibrotic vessel wall, with defects in the internal elastic lamina.     

多支架治疗颅内外动脉狭窄

目的 探讨多支架治疗颅内外动脉狭窄的临床体会。方法 采用2枚或2枚以上支架对8例颅内外动脉狭窄的患者12支狭窄血管行血管成形术，共植入17枚支架，其中颈动脉颅外段狭窄使用自膨胀支架，颅内段和椎动脉使用球囊膨胀型支架。结果 所有患者的手术均成功，术后狭窄均明显改善，随访6～12个月，所有患者均无脑缺血发作，除1例动脉闭塞外，其余无再狭窄发生。结论 多个支架治疗颅内外动脉狭窄安全有效，但仍需长期随访。