First biodegradable metal stent in a child with congenital heart disease: evaluation of macro and histopathology.

New developments in stent technology led to the first biodegradable magnesium stents. To overcome the fundamental restrictions of conventional stent implantation, these new stents may improve interventional therapy, also in small children. What remains after complete degradation of a magnesium stent is of particular interest and concern. At the autopsy, 2 months after the projected complete degradation time of the 3.0 x 10 mm(2) stent, no solid compounds were detected, and the vessel diameter had increased slightly to 3.7 mm. Histological preparation revealed an amorphous to jelly-like substitute of the magnesium struts mainly consisting of calcium phosphate covered by fibrotic tissue. Immunological staining revealed no relevant inflammatory reaction to the stent material. Neointima proliferation was detected around the struts with some cellular infiltration of the calcium-phosphate material. These pathological and histological findings show minimal alteration of the vessel wall and an increase of the arterial diameter after stent degradation. This is an important precondition for further use of biodegradable stents in small infants. Further observations have to prove whether these findings do reproduce in other settings also.     

Coronary stenting with a new, radiopaque, balloon-expandable endoprosthesis in pigs

BACKGROUND. Intracoronary stents may be effective when used as "bail-out" devices for acute complications after percutaneous transluminal coronary angioplasty. Furthermore, preliminary reports have demonstrated some promising results with stents with regard to the reduction of restenosis. Several stent devices are available for preclinical and clinical evaluation. The use of these stainless-steel stents has been limited by poor visibility during fluoroscopy and thrombogenicity during the first days to weeks after implantation. We therefore investigated the immediate and short-term effects on arterial patency of a new, radiopaque, balloon-expandable coil stent in normal coronary arteries of pigs. METHODS AND RESULTS. In 10 animals, a stent was placed in two of the three epicardial coronary arteries. During the implantation procedure, the animals received heparin; after the procedure, no antithrombotic drugs were administered. After 1 week (five animals and 10 stents) or 4 weeks (five animals and 10 stents), repeat angiography was performed, followed by pressure-fixation of the coronary arteries for light and electron microscopic examination. Angiographic analysis revealed that all stented coronary segments were patent and without signs of intraluminal defects. Scanning electron microscopy showed complete endothelial covering of all stents within 7 days. Light microscopy showed a reduced tunica media locally under the stent wires, which resulted from exerted pressure. The neointima on top of the stent wires measured 56 microns (range, 42-88 microns) after 1 week and 139 microns (range, 84-250 microns) after 4 weeks. CONCLUSIONS. Results from this study show that this radiopaque endoprosthesis can be safely placed in normal coronary arteries of pigs. After 4 weeks, all stents were patent and there was no need for additional antithrombotic treatment, whereas neointimal proliferation was limited.     

An internally covered (lined) self-expanding metal esophageal stent: tissue response in a porcine model

BACKGROUND: Self-expandable metal stents (SEMS) palliate malignant dysphagia but may embed in tissue, produce granulation tissue, and prevent removal. OBJECTIVE: Our purpose was to evaluate in a porcine model the tissue response induced by a new esophageal SEMS completely coated internally rather than externally. DESIGN: Eight Yucatan pigs were studied. Each animal underwent placement of 2 stents: 1 study stent and 1 control stent. SEMS were placed proximally or distally by random assignment. Follow-up endoscopy was performed 1, 2, 3, and 4 weeks after implantation. Ease of stent removal was assessed at 2 weeks and 4 weeks after placement. SETTING: Animal laboratory. INTERVENTIONS: Endoscopic placement of study stents (Alveolus ES-STS, Alveolus, Inc, Charlotte, NC; 18 mm diameter, fully covered internally) and control stents (Ultraflex stent, Boston Scientific, Natick, Mass; microvasive, 18 mm midbody, subtotally covered externally). MAIN OUTCOME MEASUREMENTS: Extent of granulation tissue and stent-induced esophageal injury. RESULTS: The tissue hyperplasia response of the study stents was endoscopically graded as mild to moderate. All study stents were endoscopically removed easily and atraumatically. Control stents produced severe granulation tissue formation with complete embedding of the uncovered stent ends; endoscopic removal was possible but resulted in trauma and endoscopically visible bleeding. Histopathologic findings revealed minimal tissue response at the ends of the study stents and severe pseudopolyps in the embedded portion of the control stent. Stent migration occurred in 7 of 8 study stents and 4 of 8 control stents. LIMITATIONS: Animal model lacks stricture. CONCLUSIONS: Fully internally lined SEMS may resist tissue embedding and hyperplasia and may be removable. Human studies are needed to assess applicability to treatment of benign and malignant esophageal disease.     

Newly developed biodegradable stents for benign gastrointestinal tract stenoses: a preliminary clinical trial

We developed an Ultraflex-type stent by knitting polylactic acid monofilaments. The purpose of this study was to evaluate the stent's clinical usefulness for treating benign stenoses in the gastrointestinal tract. The radial force of the biodegradable stent was compared with those of commercially available metallic stents. The measured radial force of the new biodegradable stent was higher than that of commercially available metallic stents. The biodegradable stents were applied in 2 patients with benign gastrointestinal stenoses. The first patient was a 19-year-old female with esophageal stenosis, due to drinking of caustic potash in an attempt to commit suicide. The second patient was a 75-year-old male who had a stenosis at the anastomotic site after esophageal cancer resection. In both cases, the placement of the stent was performed successfully, and the patients' complaints improved immediately after stent placement. There were no complications during stent placement. The stenosis had not recurred at the six-month follow-up examination. In conclusion, the newly developed biodegradable stents were useful in treating benign stenoses of the alimentary tract.     

A novel platinum-iridium, potentially gamma radioactive stent: evaluation in a porcine model.

In-stent restenosis (ISR) is a major problem within stented arteries. Surface treatment of stents with platinum and gold were found to have the maximum charge with least neointima formation (NF). This study was designed to evaluate platinum (maximum electrical charge) as a material to make stents to reduce NF. Iridium was added to make an alloy suitable for stent manufacture, with the potential to make the stent radioactive. We implanted the novel platinum-iridium (PI) stent in 10 porcine coronaries and compared to the Palmaz-Schatz (PS) stent implanted in 8 coronary arteries. Six weeks after implantation, angiography of the stented vessel was performed before sacrifice. The coronaries were perfusion-fixed and stained, and vessel parameters were analyzed by computer-aided histomorphometry. The thrombus formation and the inflammatory response was less in the PI stent (0.04 +/- 0.1 vs. 0.24 +/- 0.2, P = 0.005; and 1.1 +/- 0.5 vs. 2.4 +/- 0.3, P < 0.001). The NF from PI-stented arteries was smaller in size than the PS controls (1.9 +/- 0.6 mm(2) vs. 2.4 +/- 0.4 mm(2), P = 0.06). However, PI stents presented with higher recoil than the PS stent (16% vs. 5%, P < 0.001). Platinum-iridium is a highly biocompatible material with high performance, low inflammatory response with small NF. This stent does not lead to thrombus formation and has the potential (due to the presence of iridium) to be irradiated to form a gamma radioactive stent. Cathet. Cardiovasc. Intervent. 51:364-368, 2000.     

Palliative endoscopic treatment of malignant duodenal stenosis by metal prosthesis

PURPOSE: To evaluate the efficacy of through-the-scope metal stents for palliation of malignant duodenal stenosis. MATERIAL AND METHODS: Fourty two patients with malignant primary or secondary duodenal stenoses who were treated with a through-the-scope metal stent were analysed. When obstructive jaundice occurred either before, during, or after the initial episode of gastrointestinal luminal obstruction, a biliary stent was inserted. RESULTS: Duodenal metal stents were deployed in 40 patients. Endoprosthesis insertion led to restoration of oral intake in 39 patients. The procedure was not associated with morbidity or mortality. During a mean follow-up of 9.7 weeks, adequate oral intake was maintained in 38/39 cases. Tumour in-growth led to stent occlusion in 4 cases and re-cannulation was obtained by placement of another stent within the original stent. Obstructive jaundice occurred during the course of the illness in 32 patients and was successfully treated with a biliary metal stent in all cases. CONCLUSIONS: Endoscopically placed metal stents offer an effective, well-tolerated alternative to surgical palliation in case of incurable malignant obstruction to gastric outflow.     

Stent‐based tempamine delivery on neointimal formation in a porcine coronary model

Background: Tempamine is one of new class of antioxidant agents, the nitroxides, which have shown a wide range of biological effects like suppressing free radical driven reactions to maintain cell functions. The objectives of this study were to evaluate the effect of a biodegradable polymer coated stent loaded with tempamine on in‐stent neointimal formation.

Methods: Stainless steel stents were dip coated in biodegradable elastomeric poly (ester‐amide) (co‐PEA) or in polymer solution mixed with 50%(wt%) and 100%(wt%) tempamine. One group 100% (wt%) tempamine loaded stents were further dip coated in co‐PEA polymer to form a top layer. Stainless steel bare, polymer‐only, and different doses tempanine coated stents were implanted into porcine coronary arteries with a stent to artery ratio 1.2:1. Histomorphometric analysis was performed at 5 days and 6 weeks respectively

Results: Histomorphometric analysis showed that the bare, polymer‐only and tempamine‐coated stents elicited a similar tissue response at 5 days. At 6 weeks, the peri‐strut inflammation and neointimal hyperplasia of polymer‐only stents were comparable to the bare stents. Compared to the bare stents, 50% tempanine coated stents had a trend to decrease the arterial injury (0.62±0.41 versus 0.34±0.18, P = 0.075) and neointimal hyperplasia (1.80±0.77 versus 1.27±0.39 mm², P = 0.085). However, 100% tempanine coated showed significantly increased inflammatory response and neointimal formation

Conclusion: These co‐PEA polymer coatings showed a biocompatible performance. Loaded with 50% tempamine had a trend to decrease neointimal hyperplasia. The 100% tempamine for stent‐based delivery may have potential cytotoxic effects to arterial wall. Using a co‐PEA polymer topcoat could effectively abolish these side effects.     

The Genesis stent: A new low-profile stent for use in infants, children, and adults with congenital heart disease.

Placement of intravascular stents that can reach adult size in infants and smaller children has been limited by the large profile and poor flexibility of currently available stents. In vitro and in vivo testing of the Genesis stent was performed to evaluate crimpability, predeployment flexibility, and radial strength. Comparisons were made to the Palmaz iliac and IntraStent (IS) LD stents. Nine physicians placed 30 Genesis stents in swine pulmonary and systemic arteries to evaluate stent deliverability/crimpability. Two swine were recovered and underwent a second catheterization 8 weeks later, where the stents (n = 8) were reexpanded to maximal size. Angiographic and intravascular ultrasound (IVUS) assessments were performed. In vitro testing revealed the Genesis stent to have superior crimpability, flexibility, and comparable radial strength to the Palmaz iliac stent, and superior crimpability and radial strength and comparable flexibility to the IS LD series. During in vivo testing, the physicians graded the Genesis stent superior to the Palmaz stent regarding crimpability and deliverability, and superior to the IS LD stent in regard to crimpability, and comparable to or superior in deliverability. In the chronic animals, the Genesis stent was expanded up to maximal diameter 8 weeks following implantation. Angiographic and IVUS revealed no fractures no in-stent restenosis. The Genesis stent can be easily delivered through smaller sheaths, which will facilitate their use in infants and smaller children with vascular stenosis.     

First successful implantation of a biodegradable metal stent into the left pulmonary artery of a preterm baby.

Stent implantation in the youngest patients with a congenital heart disease implicates limitations concerning further vessel growth, the need of staged redilation, and later surgical removal. The search to overcome these restrictions led to open stent designs, with a wide adaptability to the vessel growth and recently to the development of bioabsorbable stent materials. A preterm baby born at 26 weeks of gestation was referred to our clinic following inadvertent ligation of the left pulmonary artery. Despite efficient debanding, the left lung perfusion was absent. Implantation of a biodegradable 3 mm magnesium stent was performed in a hybrid procedure when the baby weighed 1.7 kg. Reperfusion of the left lung was established and persisted throughout the 4-month follow-up period during which the gradual degradation process of the stent completed. Additional interventions, should they become necessary, seem not to be limited. Despite the small size of the baby, the degradation process was clinically well tolerated. The mechanical and degradation characteristics of the magnesium stent proved to be adequate to secure reperfusion of the previously occluded left pulmonary artery. Bioabsorbable stents with different diameters may help develop new strategies in the therapy of vessel stenosis in pediatric patients.     

Evaluation of role of bile flow patterns in process of in vitro stent occlusion

Stent placement above the sphincter of Oddi might have advantages over stent placement across the sphincter of Oddi in prolonging stent patency in the treatment for malignant obstructive jaundice. To evaluate the role of bile flow patterns corresponding to biliary stent positioning in the process of stent occlusion in an in vitro bile perfusion model, one group of polyethylene stents was perfused continuously and another group of stents was perfused with additional flushing three times a day, simulating gallbladder emptying. After 8 weeks, the flow rates through the perfused stents were measured for evaluating the extent of stent occlusion indirectly. The results showed that bile flow rate of stents with additional flushing was significantly higher than the continuously perfused stents (P 0.01). It was demonstrated that after 18 hr of perfusion, additional flushing obviously decreased bacterial adherence to stent when compared to continuously perfused stents. In conclusion, flushing of bile may decrease the build-up of substance in vitro and thus improve stent flow rates, for which decreasing bacterial adherence to stents may be responsible.     

Increased Apoptotic Cell Death in the Neointima after Stent-Based Vascular Irradiation: Role of Radiation-Induced Apoptosis for Restenosis Reduction

Background: Restenosis after stent implantation is a common problem faced today by interventional cardiologists. It is primarily caused by excessive neointimal growth. Early clinical studies showed substantial reductions of neointimal volumes within bodies of³²P radioactive coronary stents. Radiotherapy induces programmed cell death (apoptosis) in tumors but there is still debate whether irradiation causes apoptosis in arteries. Methods: We compared the time course of neointimal apoptosis after implanting 7-mm long ³²P radioactive slotted tubular stents in rabbit iliac arteries. The stents were homogeneously ion-implanted with ³²P at activity levels of 0.5 and 6 μCi. These stents produce continuous beta-particle emission at very low dose rates. Neointima formation was compared with nonradioactive stents by histomorphometry after 1, 4, and 12 weeks. Apoptosis was detected using the terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL) assay method and transmission electron microscopy. Results: At an early follow-up of 1 week after stent implantation, no changes in neointimal apoptosis were found. The ³²P stents at activities of 6 μCi, but not of 0.5 μCi, reduced neointimal crosssectional areas and cell numbers compared with control stents after 4 and 12 weeks. Apoptosis in the neointima increased after 4 weeks and was substantially elevated 12 weeks after implantation of 6 μCi ³²P stents compared with 0.5 μCi and control stents (16% vs 6% and 3%, P < 0.01 for 6 vs 0.5 μCi and control stents, respectively). Conclusions: In this study, a dose dependent decrease in neointimal thickening and cell density within ³²P beta-particle emitting stents was associated with an increased frequency of apoptosis. This increase in apoptosis occurred late in the time course of vascular healing after the implantation of ³²P beta-particle emitting stents. Apoptosis seems to be involved in the mechanisms by which stent-based vascular irradiation reduces neointimal hyperplasia.     

支架携带放射性核素能力的实验研究

目的携带放射性核素32P的支架是实施冠状动脉(冠脉)局部放射治疗以预防再狭窄的重要方法之一。本研究采用一种新的支架包被方法,以评价其携带放射性核素的能力。方法自行研制的四种核素32P支架血浆包被32P支架、明胶包被32P支架、32P直接涂层支架、32P静脉包被支架。每种6支,均含32P胶体10μCi。置于压力为90mm?Hg的流水管中冲洗。冲洗前和冲洗后1、4、14、21d各取1支架测定放射活度。放射性包被支架制作的同时,留置5份5μCi32P胶体液作为自然衰减对照品,于1、4、7、14、21d后各取1份32P胶体液,测定其放射活度。4只犬每只犬冠脉内置入同样方法制成的血浆包被32P支架2个,于术前和术后1d、2周、7周、10周测定放射活度。3只犬冠脉内置入自体静脉包被32P支架1个,于术后1、2、3个月测定放射活度。结果流水冲洗实验示四种支架冲洗前携带32P放射活度分别为4.81、4.32、1.96、4.82μCi,冲洗21天后放射活度分别为0.33、0.12、0.01、1.34μCi,血浆和静脉包被支架时间-放射活度变化曲线接近于自然衰减曲线。冠脉置入支架实验示4条犬每只犬均成功置入血浆包被32P支架1个,术后1天、17天、7周、10周支架残留的放射活度分别为4.98、1.71、0.52、0.09、0.03μCi;3只犬中1只犬成功置入1个静脉包被32P支架,70天处死测定其放射活度为0.3μCi。结论血浆和静脉包被支架均有较好的携带核素能力,抗冲洗能力强。血浆包被支架制备简便,置入冠脉可行,置入机体可达到有效治疗剂量。     

In vivo assessment of stent recoil in normal porcine arteries: evaluation of contemporary stent designs.

Acute stent recoil has been observed following balloon deflation in normal and diseased coronary arteries, and the magnitude varies by stent design. We sought to evaluate acute stent recoil in five new stents. Twenty-five stents (four Crown, five Nir Conformer Royale, five Crossflex, five SupraG, and six GFX) were implanted in six Yorkshire pigs. All stents were expanded using a noncompliant balloon (balloon:artery ratio 1.2:1.0). Continuous ultrasound imaging was performed during stepwise balloon inflation and deflation using a 0.018" imaging core. Maximum cross-section areas (CSA) and minimal luminal diameter (MLD) were measured at 12 atm and immediately following balloon deflation. Maximum stent CSA matched expected balloon CSA. Area and diameter recoil were calculated as 1 - (CSAdeflation/CSAmax) and 1 - (MLDdeflation/MLDmax), respectively. Upon deflation, all stents showed recoil from maximal CSA. Area recoil was significantly lower for slotted-tube stents than modular stents (12.6% +/- 1.6% vs. 23.2 +/- 3.5%; P < 0.05). In compliant, nonatherosclerotic porcine coronary arteries, acute stent recoil for the four slotted-tube designs ranged from 8.4% to 18.0% by area. The modular stent tested was associated with significantly greater acute recoil than the slotted-tube stents.     

Preventive effects of the heparin-coated stent on restenosis in the porcine model.

The coronary stent reduces acute coronary arterial occlusion and late restenosis during and after coronary intervention. However, stent thrombosis and restenosis are still major limitations in the widespread use of the coronary stent. Local drug delivery using the heparin-coated stent may be a new approach, which reduces the incidence of stent thrombosis and restenosis. In order to evaluate the effects of the heparin-coated stent on stent restenosis, heparin-coated stents were compared with control stents in a porcine coronary stent restenosis model. Stent overdilation injury (stent:artery = 1.3:1.0) was performed with bare Wiktor stents (group I, n = 10) and heparin-coated Wiktor stents (group II, n = 20; HEPAMED, Medtronics) in porcine coronary arteries. Follow-up quantitative coronary angiography (QCA) was performed at 4 weeks after stenting, and histo-pathologic assessments of stented porcine coronary arteries were compared in both groups. On QCA, percent diameter stenosis was significantly higher in group I than in group II (16.3% +/- 6.62% vs. 9.6% +/- 5.06%, P < 0.05). The injury score of stented porcine coronary arteries was the same in both groups (1. 26 +/- 0.23 vs. 1.20 +/- 0.22). The area of pathologic stenosis of the stented arteries was higher in group I than in group II (41.6% +/- 12.5% vs. 27.1% +/- 9.9%, P < 0.005). The neointimal area was higher in group I than in group II (4.58 +/- 1.41 mm(2) vs. 2.57 +/- 1.07 mm(2), P < 0.05). By immunohistochemistry, the proliferating cell nuclear antigen (PCNA) index was higher in group I compared with group II (11.2% +/- 6.75% vs. 6.3% +/- 4.14%, P < 0.05). The heparin-coated stent is effective in the prevention of late coronary stent restenosis in a porcine coronary stent restenosis model. This may be related to the inhibition of neointimal cell proliferation.     

Radial force of coronary stents: A comparative analysis

High radial force has become an essential feature of new coronary stents. These stents are expected to exhibit sufficient radial force and minimum radial recoil when deployed in atheromatous lesions of various morphologies. The aim of this study was to compare the radial force of 17 coronary stents in vitro (Anglodynamics, ACS Multilink, AVE Micro II and GFX, Bard XT, Biocompatibles PC, Cook GR II, Cordis Crossflex, Hexacath Freedom, Johnson & Johnson PS 153'PS 154, and Crown, Medtronic Wiktor and BeStent BEL-15, Saint-Côme SC 1616, Scimed Nir 7 and 9). Two in vitro mechanical tests were performed to assess the stent radial force. The first test measured the deformation of coronary stents in a V-stand by using a deformation controlled by a dynamometer based on a longitudinal generatrix. The precision was of 1 micron. This comparative test highlighted the appreciable variation in behavior of the range of tested stents in terms of resistance to local compression. The line graphs obtained show a very small (and in some cases nonexistent) purely elastic behavior area in the stents, with this result reflecting a small (<0.4 Newtons) range of forces applied to all stents. Above this value, the stents did not return to their size before compression and the line graph remains approximately linear for a long period. It was therefore possible to distinguish between two families of stents on the basis of the presence or absence of this elastic area. In the second test, the stent was deployed in a 3.0-mm elastic tube and a pressure gradient created between the interior and exterior of the tube. The precision was of 50 microns. A typical line graph of the pressure-diameter relationship was recognizable for a given stent. No difference in behavior between the different coronary stents was noted up to 0.3 × 10⁵ Pa; subsequently, after 0.3 × 10⁵ Pa, sizable deformation differences were visible between the least resistant stent, the BeStent BEL-15, and the most resistant stent, the Crossflex. Cathet. Cardiovasc. Intervent. 46:380–391, 1999. © 1999 Wiley-Liss, Inc.     

Worse six-month outcome for patients with multiple stents in a single coronary artery

BACKGROUND: Before the "era" of optimal stent deployment, very few data concerning multiple stents in a single coronary artery showed restenosis rates up to 60%. OBJECTIVE: To evaluate the 6-month outcome of patients receiving multiple Palmaz-Schatz stents (> or =2 stents) in a single coronary artery compared to those receiving single stents. METHODS: Three hundred and forty-eight patients having multiple stents were compared to 174 patients receiving single stents during a 6-month follow-up. RESULTS: Repeat target lesion revascularization (RTLR), either repeat PTCA or CABG, was 10.4% in the single-stent group, 22.6% in the two-stent group, and 23.1% in the > or =2 stent group (p = 0.001, single versus 2 or > or =2 stents). There was not a significant difference between single stent and multiple stent groups in myocardial infarction and death during 6-month follow-up. Multivariate analysis showed multiple stents, diabetes mellitus, and type C lesion to be predictors of RTLR. CONCLUSIONS: Placement of two or more stents was associated with a significantly higher RTLR compared with single stent placement. The optimal approach to diffuse coronary artery disease remains to be defined.     

A new biodegradable stent for the pancreaticojejunal anastomosis after pancreaticoduodenal resection: in vitro examination and pilot experiences in humans

We sought to develop a biodegradable pancreatic stent that could be easily placed at operation into the human pancreatic duct and the degradation of which could be easily followed up. Spiral-shaped, gamma-sterilized stents were manufactured of 0.4-mm polylactide wire in which there was added 23 weight-% barium sulfate. The biodegradability of the stents was studied in vitro at two different pH values, the first resembling that of pancreatic juice and the other that of bile. The effects of enzymoactivity in the test solution and the composition of the stents (with or without barium addition) also were tested. These kinds of stents have been experimented with in two pilot patients. Degradation of the stents occurred from 24 to 52 weeks of incubation. Alkaline milieu together with the presence of pancreatic enzyme made the stents degrade twice as fast as when either alkaline milieu or enzyme was present. In the milieu resembling pancreatic juice, barium sulfate had no effect on the degradation time. Neither of the pilot patients had any postoperative complications. Biodegradable, x-ray-positive stents degrade faster in pancreatic than in biliary milieu. Their safety and efficacy in human pancreaticojejunal anastomoses need further study.     

Angiographic and Histologic Course after Implantation of Balloon Expandable Intravascular Stents in Miniswine Coronary Arteries: Short- and Mid-Term Observations

Sixteen balloon expandable Medtronic Wiktor tantalum stents were implanted in the major coronary arteries of six minipigs, which were maintained on a normal diet and given 500 mg aspirin per day. Angiographic and histologic examinations were performed 6 and 26 weeks after implantation. Angiographically reviewed, stenting increased the inner diameter of the coronary arteries from 2.61 ± 0.44 to 3.02 ± 0.34 mm (n = 16, P ≤ 0.001). Six weeks later, this value was reduced from 2.98 ± 0.35 to 2.33 ± 0.46 mm (n = 9, P ≤ 0.05), and between 6 and 26 weeks, an increase from 2.17 ± 0.44 to 2.93 ± 0.40 mm occurred (n = 6, P ≤ 0.05). Histologic evaluation at 26 weeks after stent implantation revealed an increase of the cross-sectional area of the total vessel from 4.30 ± 1.09 to 5.50 ± 1.67 mm² (n = 9; P ≤ 0.01). This was due to widening of the total vessel and intimal proliferation, which amounted to 1.19 ± 0.46 mm² within the stented segment, as compared to 0.03 ± 0.03 mm² in control sections (P ≤ 0.01). The areas of free vessel lumen, media muscularis, and adventitia remained unchanged. In 15 of the 16 hislologically examined coronary arteries, the internal elastica was fractured at the site of stent implantation. Twelve stents had also penetrated through the external elastica without evidence of wall hemorrhage. Thirteen out of 16 stents were angiographically followed, of which 12 were patent at the final reangiography. In one animal, acute thrombosis of the stented vessel after guidewire induced coronary artery spasm caused chronic right heart failure due to right ventricular myocardial infarction. Sudden death occurred in another pig 2 hours after successful implantation of three grossly oversized stents (inner vessel diameter: 2.4 ± 0.2 mm, stent diameter 3.2 ± 0.5 mm). Autopsy revealed extensive dissections of the media with subsequent vessel occlusion. It is concluded that Medtronic Wiktor stents can be placed easily, even in more distal or curved coronary arteries. Despite antiaggregational medication, intimal proliferation is observed early after implantation, reaches a maximum at about 6 weeks, and is followed by a regression 26 weeks poststenting. At 26 weeks follow-up, the free vessel lumen at the stent site was not significantly reduced as compared to control segments. Proper adjustment of internal vessel diameter and stent diameter is necessary to prevent major dissections and thrombotic occlusions.     

Development of a polymer endovascular prosthesis and its implantation in porcine arteries

A polyethylene-terephthalate braided mesh stent has been developed for application in the (coronary) arterial tree. In vitro measurements showed that the radial pressure delivered by this device was in the same range as that of a stainless steel stent. Hysteresis-like behavior, however, occurred after constraining the polyester stent for a period of only 15 minutes on a delivery system for percutaneous implantation. This implies that the polymer stent must be mounted on this delivery system immediately before the placement procedure, and that either a diameter in the unconstrained condition must be selected, which is considerably larger than the diameter of the target vessel, or stent expansion has to be enhanced by balloon expansion. Taking into account the results obtained during the in vitro studies, we investigated the angiographic patency and histologic features after implantation of this polyester stent in peripheral arteries of pigs. In four animals eight stents were placed. Except for heparin during the implantation procedure only, antithrombotic or antiplatelet drugs were not administered. After 4 weeks repeat angiography was performed. Angiography revealed that five of the six correctly placed stents were patent. At autopsy, two additional patent stents proved to be located in the aortic bifurcation, probably due to failure of the delivery system. Quantitative assessment showed that the mean luminal diameters of the site of stent placement were 3.3 +/- 0.2 mm before, 3.2 +/- 0.2 mm immediately after, and 3.1 +/- 0.3 mm at 4 weeks after implantation. Histology demonstrated an inflammatory reaction of variable severity around the stent fibers. Quantitative histologic measurements showed that the thickness of the neointima was 114 +/- 38 mum after 4 weeks. In conclusion, polyester stents can be constructed with mechanical properties similar to stainless steel stents. Hysteresis-like behavior of polyester stents, however, influences the selection of the nominal stent diameter as well as the forces exerted to the vessel wall. After implantation in porcine peripheral arteries, five of six correctly placed stents were patent at 4 weeks. The extent of neointimal proliferation was similar to that observed after placement of metal stents in swine, despite the presence of a more pronounced inflammatory reaction.     

Optical diagnosis of gastric cancer using near-infrared multichannel Raman spectroscopy with a 1064-nm excitation wavelength

Background Gastric cancer is one of the most common cancers in Japan. The use of endoscopy is increasing, along with the number of histological examinations of specimens obtained by endoscopy. However, it takes several days to reach a diagnosis, which increases the medical expense. Raman spectroscopy is one of the available optical techniques, and the Raman spectrum for each molecule and tissue is characteristic and specific. The present study investigated whether Raman spectroscopy can be used to diagnose gastric cancer. Methods A total of 251 fresh biopsy specimens of gastric carcinoma and non-neoplastic mucosa were obtained from 49 gastric cancer patients at endoscopy. Without any pretreatment, the fresh specimens were measured with a near-infrared multichannel Raman spectroscopic system with an excitation wavelength of 1064 nm, and Raman spectra specific for the specimens were obtained. A principal component analysis (PCA) was performed to distinguish gastric cancer and non-neoplastic tissue, and a discriminant analysis was used to evaluate the accuracy of the gastric cancer diagnosis. Results The Raman spectra for cancer specimens differed from those for non-neoplastic specimens, especially at around 1644 cm⁻¹. Sensitivity was 66%, specificity was 73%, and accuracy was 70%. The accuracy of diagnosis using the single Raman scattering intensity at 1644 cm⁻¹ was 70%, consistent with the PCA result. Conclusions The present results indicate that near-infrared multichannel Raman spectroscopy with a 1064-nm excitation wavelength is useful for gastric cancer diagnosis. Establishment of a Raman diagnostic system for gastric cancer may improve the clinical diagnosis of gastric cancer and be beneficial for patients.