Percutaneous endovascular stents: an experimental evaluation

Insights into the biocompatibility of biodegradable metallic molybdenum for cardiovascular applications-a critical review

Atherosclerotic cardiovascular disease (ACD) is the leading cause of death worldwide. The gold standard of treatment is the implantation of a permanent stent implant that is often associated with complications such as thrombus formation, vascular neointimal response, and stent fracture, which altogether decrease the long-term safety and efficacy of the stent. Biodegradable metallic materials have become an attractive alternative because of the ability to facilitate a more physiological healing response while the metal degrades. Recently, Molybdenum (Mo) has been considered as a potential candidate due to its excellent mechanical and medical imaging properties. Moreover, the biomedical research studies performed to date have shown minimal adverse effects in vitro and in vivo. However, there are still concerns of toxicity at high doses, and the impact of the biochemical mechanisms of Mo on material performance especially in pathophysiological environments are yet to be explored. Mo is an essential co factor for enzymes such as xanthine oxidoreductase (XOR) that plays a critical role in vascular homeostasis and ACD progression. Herein, this review will focus on the biochemistry of Mo, its physiological and pathological effects with an emphasis on cardiovascular disease as well as the recent studies on Mo for cardiovascular applications and its advantages over other biodegradable metals. The limitations of Mo research studies will also be discussed and concluded with an outlook to move this revolutionary metallic biomaterial from the bench to the bedside.

Infrarenal Abdominal Aortic Aneurysm

Abdominal aortic aneurysms are found in up to 6% of men and 1.7% of women over the age of 65 years and are usually asymptomatic. The natural history of aortic aneurysms is continued dilation leading to rupture, which is associated with an overall 80% mortality. Of the patients with ruptured aneurysms that undergo intervention, half will not survive their hospitalization. Reduction in aneurysm mortality is therefore achieved by prophylactic repair during the asymptomatic period. On a population-based level, this is supported by abdominal aortic aneurysm screening programs. Approximately 60% of abdominal aortic aneurysms are confined to the infrarenal portion of the aorta and are amenable to repair with off-the-shelf endovascular devices. Endovascular techniques have now replaced open surgery as the primary modality for aneurysm repair.

Intestinal stents: Structure, functionalization and advanced engineering innovation

Intestinal stents are a palliative treatment option that solves many shortcomings of traditional surgeries for cancer-induced intestinal obstructions. The present review provides an overview of the incidence, clinical manifestations and limitations in the treatment of intestinal cancers. The paper also discusses material property requirements, indications, complications and the future of stent-assisted therapy. The advantages and disadvantages of different materials and processing techniques for intestinal stents are reviewed along with new stent treatment combinations for colorectal cancer. Challenges that require further cooperative studies are also detailed. The future development of intestinal stents will depend on innovation in material designs as well as the utilization of multi-functional strategies and innovative engineering solutions.

Clinical outcomes and overview of dedicated venous stents for management of chronic iliocaval and femoral deep venous disease

OBJECTIVES

Venous stenting of the lower extremities has grown in popularity and is now considered a key component of the primary treatment strategy for the management of pathologically obstructive or stenotic lesions of the deep venous system. This review aims to provide an overview of the role of venous stenting in the management of chronic conditions affecting the deep venous system of the lower limbs.

METHODS

An overview of venous stents design and current role of stenting procedure in individuals presenting with Chronic Venous Insufficiency (CVI) and presenting the current trials of dedicated venous stenting in management of chronic deep venous lesions. This review provides a focused insight on venous stent design, physical properties and the available dedicated venous stents selected studies with their related patency outcome based on selective literature search of the PubMed database and Cochrane library.

CONCLUSIONS

Dedicated venous stent technology is advancing at a rapid pace alongside the increased undertaking of endovascular deep venous stent reconstruction in the management of iliocaval vein pathologies. The ideal design(s) for venous stents remain unknown, although it is hoped that the presence of new dedicated venous stents in clinical practice will allow the generation of experience and data to advance our understanding in this area.

Clinical outcomes and survival following placement of self-expandable metallic stents for central airway stenosis and fistula

Background

Self‐expandable metallic stent (SEMS) placement is an urgent procedure for patients with malignant central airway stenoses (CASs) and central airway fistulas (CAFs). The aim of this study was to determine the outcome and survival after SEMS placement in patients with malignant CASs and CAFs.

Methods

SEMSs were inserted into 20 patients with malignant CASs and four with malignant CAFs. Hospital records, the modified Medical Research Council dyspnea scale (mMRC) grade, performance status (PS), symptoms, procedure‐related complications and survival after placement were retrospectively reviewed.

Results

Spiral Z stents were inserted in nine patients, covered Ultraflex stents in 14, and a bare Ultraflex in one patient. After SEMS placement, 20 patients (83.3%) showed improvement in mMRC grade, 19 (79.2%) showed improvement in PS, and 21 (87.5%) showed improvement in symptoms. There were three patients whose stents migrated out of place, but there were no patients with obstructive granulation, infection, or mucous plugs. Median survival days after stent insertion was 98 days for CAS and 103 days for CAF, and mean survival days was 383 ± 707 days for CAS and 93 ± 33 days for CAF. Two patients with CAS by malignant lymphoma and thymic cancer survived more than six years because they were also treated with efficient therapies. The five‐year survival rate after stent insertion was 7.7%.

Conclusions

SEMS placement for CAS and CAF is associated with improvement in mMRC grade, PS and symptoms in 87.5% of patients. Patients with a malignant CAS are usually terminal, but the possibility of increasing survival rate will become a reality with new efficient therapies.

Key points

Significant findings of the study

Reasonable clinical outcomes and improved survival of patients following SEMS placement for thoracic malignancy with central airway stenosis and fistula.

What this study adds

The possibility of increasing survival rate will become a reality with new efficient therapies.

Effect of the type of electrical stimulation on spinal fusion in a rat posterolateral spinal fusion model

BACKGROUND CONTEXT

Posterolateral fusion (PLF) with autogenous iliac bone graft is one of the most common surgical procedures for lumbar spinal disease. However, its limited success demands new biologically competent graft enhancers or substitutes. Although the use of direct current (DC) electrical stimulation has been shown to increase rate of successful spinal fusions, little is known about the effect of the type of current in DC stimulation.

PURPOSE

To evaluate the effects of various DC stimulators on the strength and success rate of posterolateral fusion facilitated by using a nitinol mesh container, in rats.

STUDY DESIGN

This was an experimental animal study.

METHODS

A conductive, tubular nitinol mesh container was used to carry small pieces of bone grafts. The nitinol mesh container received electrical stimulation via a lead that connected the container to different types of DC stimulators. Sixty male Sprague-Dawley rats were divided into three groups (N=20 in each): a control group that underwent PLF with a nitinol container filled with autograft, a constant DC group that received a nitinol container and constant DC (100 μA), and a pulsed DC group that received a nitinol container and pulsed DC (100 μA, 100 Hz, 200 μs). The rats underwent PLF between L4 and L5, and transverse processes were grafted with bilateral iliac grafts. A stimulator was implanted subcutaneously. The rats were sacrificed 8 weeks postsurgery, and lumbar spines were removed. Spinal fusion was evaluated by microcomputed tomography, manual testing, biomechanical testing, histologic examination, and molecular analysis.

RESULTS

All animals in the DC stimulation groups displayed solid fusion, whereas only 70% of control animals showed solid fusion. Radiographic images, biomechanical testing, histologic examination, and molecular analysis revealed improved fusion in the order control group<constant DC group<pulsed DC group. The volume of new bone mass was significantly higher in the pulsed DC group (p<.05). Fusion was more solid in the pulsed DC group than in control group (p<.05). The pulsed DC group displayed the lowest inflammatory responses.

CONCLUSIONS

Pulsed DC electrical stimulation is efficacious in improving both strength and fusion rate in a rat spinal fusion model. In addition, tubular nitinol mesh, made of conductive suture, appears useful for holding small pieces of bone grafts and maintaining a good environment for bone fusion.

CLINICAL RELEVANCE

Pulsed DC electrical stimulation may be potentially useful to increase the fusion rate after spinal fusion in humans. Future research is required to evaluate the safety and efficacy of tubular nitinol mesh and pulsed DC electrical stimulation in humans.

Reappraisal of Percutaneous Transluminal Laser Angioplasty

Background and aims

We devised a technique to treat peripheral arterial disease (PAD) with laser, i.e. percutaneous transluminal laser angioplasty (PTLA). Considerable good results were obtained with PTLA, but it is apparently considered obsolete as a technique to treat occlusive arterial disease of peripheral arteries, perhaps because of the development and improvement of stents and the ease of their use compared to the somewhat intricate technique required for PTLA. Although the author admits the usefulness of stents, they are foreign to a human body. PTLA does not use a foreign body and contributes to the regeneration of the body's own artery.The aim of this article is to elucidate the beneficial effects of laser procedures in the treatment of PAD and to show the resulting good long-term patency, and to propose PTLA as an option to treat PAD.Some basic experiments and their results useful for PTLA will be introduced.

Materials and Methods

Ninety cases with occlusive peripheral arterial diseases were treated with PTLA during the period of March 1985 to March 1991.Our method of PTLA consists of occlusion of the proximal artery by a dilated balloon of a percutaneously introduced balloon catheter, and flushing with normal saline during irradiation by Nd:YAG laser.We used a ceramic tip attached to a laser catheter most of the time and a bare laser fiber under angioscopy or a bare laser fiber itself to treat smaller arteries in the legs.

Results

The initial success rate was 90%.The patency rates of PAD at 6 years are 91.4% (iliac artery) and 85.8% (femoropopliteal artery), and the patency rate of leg artery lesions is 100% at 5 years.Some clinical cases with long-term patency (6 and 30 years) will be introduced.Some fundamental experiments useful to the application of laser to atheroma or thrombi will be introduced.

Conclusions

PTLA could be a useful option to treat occlusive PAD, because it can produce longterm patency of natural arteries, provided a proper lesion was selected.

Treatment of Tuberculous Bronchial Stenosis with Expandable Metallic Stents

Gianturco expandable metallic stents were placed in 5 patients with dyspnea on exercise due to tuberculous bronchial stenosis. The stents were placed after dilatation with a 10-mm diameter high pressure balloon catheter. In all 5 patients, obstructive changes disappeared following the procedure, and dyspnea on exercise improved markedly. No complications related to the procedure were encountered. At follow-up during a period of up to 38 months, 2 patients showed bronchial restenosis at 11 and 17 months, respectively, after stent placement. Restenosis by granulomatous tissue was successfully treated by laser ablation. One patient showed slight one-day hemoptysis 26 months after stent placement.

PTA Plus Stent Implantation Versus PTA Alone for Central Venous Stenoses

From 1990 through 1992, 17 severely stenosed central venous segments were diagnosed in 13 patients. In 9 patients, 11 stenoses were detected during follow-up after trans- femoral venous thrombectomy. The other 6 stenoses occurred in the venous outflow tract of 4 hemodialysis shunts. Six stenoses were treated by percutaneous transvenous angio plasty (PTA) alone, and 11 stenoses by PTA plus stent implantation (PTA+S). For PTA+S, a flexible, self-expanding stent was used.

Acute procedure-related complications were not observed. After a median follow-up time of eighteen months (three to thirty-six months), all patients were examined clinically, duplex-sonographically, and angiographically. Following PTA alone (n = 6), there was only 1 excellent result, and 5 patients developed high-grade restenoses. Two of these patients had to be reoperated on, and 1 patient underwent another PTA with stent placement. PTA+S (n = 11) for initial treatment of central venous stenoses gave excellent results in 8 cases, a good result in 1 case, and 2 insufficient results caused by intimal hyperplasia within the stent. These restenoses were successfully treated by another PTA.

Chronic impedance spectroscopy of an endovascular stent-electrode array

OBJECTIVE

Recently, we reported a minimally invasive stent-electrode array capable of recording neural signals from within a blood vessel. We now investigate the use of electrochemical impedance spectroscopy (EIS) measurements to infer changes occurring to the electrode-tissue interface from devices implanted in a cohort of sheep for up to 190 days.

APPROACH

In a cohort of 15 sheep, endovascular stent-electrode arrays were implanted in the superior sagittal sinus overlying the motor cortex for up to 190 days. EIS was performed routinely to quantify viable electrodes for up to 91 days. An equivalent circuit model (ECM) was developed from the in vivo measurements to characterize the electrode-tissue interface changes occurring to the electrodes chronically implanted within a blood vessel. Post-mortem histological assessment of stent and electrode incorporation into the wall of the cortical vessels was compared to the electrical impedance measurements.

MAIN RESULTS

EIS could be used to infer electrode viability and was consistent with x-ray analysis performed in vivo, and post-mortem evaluation. Viable electrodes exhibited consistent 1 kHz impedances across the 91 day measurement period, with the peak resistance frequency for the acquired data also stable over time. There was a significant change in 100 Hz phase angles, increasing from -67.8° ± 8.8° at day 0 to -43.8° ± 0.8° at day 91, which was observed to stabilize after eight days. ECM's modeled to the data suggested this change was due to an increase in the capacitance of the electrode-tissue interface. This was supported by histological assessment with >85% of the implanted stent struts covered with neointima and incorporated into the blood vessel within two weeks.

CONCLUSION

This work demonstrated that EIS could be used to determine the viability of electrode implanted chronically within a blood vessel. Impedance measurements alone were not observed to be a useful predictor of alterations occurring at the electrode tissue interface. However, measurement of 100 Hz phase angles was in good agreement with the capacitive changes predicted by the ECM and consistent with suggestions that this represents protein absorption on the electrode surface. 100 Hz phase angles stabilized after 8 days, consistent with histologically assessed samples.

SIGNIFICANCE

These findings demonstrate the potential application of this technology for use as a chronic neural recording system and indicate the importance of conducting EIS as a measure to identify viable electrodes and changes occurring at the electrode-tissue interface.

Endovascular Stent-Anchored Aortic Grafts: A Comparison between Self-Expanding and Balloon-Expandable Stents in Minipigs

Purpose:

To study endovascular graft attachment with self-expanding Gianturco Z-stents and balloon-expanded Palmaz stents and the effect of these devices on the renal ostia.

Methods:

Ten stent-grafts were constructed, 5 with Gianturco Z-stents and 5 with Palmaz stents. The endografts were implanted under fluoroscopic guidance into the abdominal aorta of 10 pigs so that the uncovered portion of the proximal stent extended over the renal artery orifices. Distal aortic blood pressure and flow were measured before and after graft placement and 1 hour postprocedure. The aorta was then exposed surgically, and the central portion of the stent-graft was inspected through an aortotomy to assess perigraft leakage.

Results:

Stent-graft implantation was accurate and hemostatic in all cases, despite longitudinal folding of the graft due to oversizing. However, transverse folds produced pressure gradients (> 15 mmHg) between the ends of the graft in two cases. In another case, a pressure gradient resulted from partial thrombosis of the graft. In two cases, renal artery occlusion and thrombosis occurred due to coverage by the graft material. In two other animals, one of the renal arteries was entirely uncovered by a stent. The remaining 16 renal arteries were covered by the proximal stent but not the graft, as intended. One (6.25%) of these arteries thrombosed, but the remainder were grossly patent when the animals were sacrificed at 1 hour.

Conclusions:

Both Palmaz and Gianturco Z-stents produced hemostatic endovascular graft attachment, even in the presence of moderate graft oversizing. The risk of acute renal artery occlusion from juxtarenal stenting does not appear to be prohibitive, but longer term observations are needed.

Micro-CT and Histological Evaluation of an Neural Interface Implanted Within a Blood Vessel

OBJECTIVE

Recently, we reported the development of a stent-mounted electrode array (Stentrode) capable of chronically recording neural signals from within a blood vessel with high fidelity. Preliminary data suggested incorporation of the Stentrode into the blood vessel wall was associated with improved recording sensitivity. We now investigate neointimal incorporation of the Stentrode, implanted in a cohort of sheep for up to 190 days.

METHODS

Micro-CT, obtained from the Imaging and Medical Beamline at the Australian Synchrotron, and histomorphometic techniques developed specifically for evaluation of cerebral vasculature implanted with a stent-electrode array were compared as measures to assess device incorporation and vessel patency.

RESULTS

Both micro-CT analysis and histomorphometry, revealed a strong correlation between implant duration and the number of incorporated stent struts. <10% (26/268) of stent struts were covered in neointima in sheep implanted for <2 weeks, increasing to >78% (191/243) between 2 and 4 weeks. Average strut-to-lumen thickness from animals implanted >12 weeks was comparable across both modalities, 339 ±15 μm measured using micro-CT and 331 ±19 μm ( n = 292) measured histologically. There was a strong correlation between lumen areas measured using the two modalities ( ), with no observation of vessel occlusion observed from any of the 12 animals implanted for up to 190 days.

CONCLUSION

Micro-CT and the histomorphometric techniques we developed are comparable and can both be used to identify incorporation of a Stentrode implanted in cerebral vessels.

SIGNIFICANCE

This study demonstrates preliminary safety of a stent-electrode array implanted in cerebral vasculature, which may facilitate technological advances in minimally invasive brain-computer interfaces.

Excellent long-term results with iliac stenting in local anesthesia for post-thrombotic syndrome

Background

Only 20% of iliac veins will recanalize on anticoagulation (AC) treatment alone and may, therefore, develop venous obstruction after iliofemoral deep venous thrombosis (DVT). A considerable number of these patients will suffer from post-thrombotic syndrome (PTS) leading to impaired quality of life in more than 50%. Endovascular treatment for iliac vein obstruction using stents is known to alleviate PTS symptoms in selected patients.

Purpose

To report the Danish long-term results of endovascular treatment with iliac stenting.

Material and Methods

From 2000 to 2013 consecutive patients were evaluated and 19 patients with severe venous claudication were identified and subsequently underwent angioplasty and stenting. AC treatment was prescribed for 6 months, and knee-high class II compression stocking recommended for 1 year. Scheduled follow-up was done in the outpatient clinic at 6 weeks, 3 months, and annually thereafter.

Results

Nineteen patients, all women, all with left-sided iliac vein obstruction, and all with severe PTS symptoms were included. The median follow-up time was 81 months (range, 1–146 months; mean, 69 months). Primary patency rate of the inserted iliac stent was 89% (17/19) and 16 patients (84 %) had almost or total symptom relief at follow-up.

Conclusion

Endovascular stenting of iliac obstruction in local anesthesia is minimally invasive and shows excellent long-term outcomes for patients suffering from PTS.

Slovenian experience from diagnostic angiography to interventional radiology

Background

The purpose of writing this article is to document the important events and people in the first 50 years of diagnostic angiography and interventional radiology in Slovenia. During this period not only did the name of the institutions and departments change, but also its governance.

Conclusions

This depicted the important roles different people played at various times in the cardiovascular divisions inside and outside of the diagnostic and interventional radiology. Historical data show that Slovenian radiology has relatively immediately introduced the new methods of interventional radiology in clinical practice.

Endovascular evaluation and treatment of intrahepatic portosystemic shunts in dogs: 100 cases (2001-2011)

OBJECTIVE

To evaluate short- and long-term outcome following endovascular treatment of intrahepatic portosystemic shunts in dogs.

DESIGN

Retrospective case series.

ANIMALS

100 dogs.

PROCEDURES

All patients had angiographic evaluation with or without endovascular shunt attenuation. The medical records were reviewed for pertinent data, complications, outcome, and survival time.

RESULTS

95 dogs with congenital intrahepatic portosystemic shunts received 111 procedures (83% [79/95] had 1 treatment, and 17% [16/95] had > 1 treatment; 5 dogs had no treatment because of excessive portal venous pressure-central venous pressure gradients). Angiography identified 38 right, 33 left, and 19 central divisional single shunts (n = 90) and 10 complex or multiple shunts. Partial shunt attenuation was performed in 92 dogs by means of caval stent placement and insertion of thrombogenic coils within the shunt, and 3 had complete acute shunt occlusion. Major intraoperative complications (3/111 [3%]) included temporary severe portal hypertension in 2 dogs and gastrointestinal hemorrhage in 1 dog. Major postoperative (< 1 week after surgery) complications (14/111 [13%]) included seizures or hepatoencephalopathy (7/111 [6%]), cardiac arrest (2/111 [2%]), jugular site bleeding (2/111 [2%]), pneumonia (1/111 [1%]), suspected portal hypertension (1/111 [1%]), and acute death (1/111 [1%]). Median follow-up time was 958 days (range, 0 to 3,411 days). Median survival time for treated dogs was 2,204 days (range, 0 to 3,411 days). Outcome was considered excellent (57/86 [66%]) or fair (13/86 [15%]) in 70 of 86 (81%) treated dogs.

CONCLUSIONS AND CLINICAL RELEVANCE

Results suggested that endovascular treatment of intrahepatic shunts in dogs may result in lower morbidity and mortality rates, with similar success rates, compared with previously reported outcomes for open surgical procedures. Gastrointestinal ulceration was a common finding among this population of dogs, and lifelong gastroprotectant medications are now recommended.

CIRSE standards of practice guidelines on iliocaval stenting

Chronic venous insufficiency (CVI) as an advanced stage of chronic venous disease is a common problem that occurs in approximately 1-5 % of the adult population. CVI has either a nonthrombotic (primary) or postthrombotic (secondary) cause involving reflux, obstruction, or a combination of both. The role of venous obstruction is increasingly recognized as a major cause of CVI, with obstructive lesions in the iliocaval segment being markedly more relevant than lesions at the levels of the crural and femoral veins. Approximately 70-80 % of iliac veins develop a variable degree of obstruction following an episode of acute deep venous thrombosis. Nonthrombotic iliac vein obstruction also known as May-Thurner or Cockett's syndrome is the most common cause of nonthrombotic iliac vein occlusion. While compression therapy is the basis of therapy in CVI, in many cases, venous recanalization or correction of obstructive iliac vein lesions may result in resolution of symptoms. This document reviews the current evidence on iliocaval vein recanalization and provides standards of practice for iliocaval stenting in primary and secondary causes of chronic venous disease.

Biocompatibility of Coronary Stents

Cardiovascular disease is the dominant cause of mortality in developed countries, with coronary artery disease (CAD) a predominant contributor. The development of stents to treat CAD was a significant innovation, facilitating effective percutaneous coronary revascularization. Coronary stents have evolved from bare metal compositions, to incorporate advances in pharmacological therapy in what are now known as drug eluting stents (DES). Deployment of a stent overcomes some limitations of balloon angioplasty alone, but provides an acute stimulus for thrombus formation and promotes neointimal hyperplasia. First generation DES effectively reduced in-stent restenosis, but profoundly delay healing and are susceptible to late stent thrombosis, leading to significant clinical complications in the long term. This review characterizes the development of coronary stents, detailing the incremental improvements, which aim to attenuate the major clinical complications of thrombosis and restenosis. Despite these enhancements, coronary stents remain fundamentally incompatible with the vasculature, an issue which has largely gone unaddressed. We highlight the latest modifications and research directions that promise to more holistically design coronary implants that are truly biocompatible.

Managing acute colorectal obstruction by "bridge stenting" to laparoscopic surgery: Our experience

AIM: To verify the clinical results of the endoscopic stenting procedure for colorectal obstructions followed by laparoscopic colorectal resection with “one stage anastomosis”.

METHODS: From March 2003 to March 2009 in our surgical department, 48 patients underwent endoscopic stenting for colorectal occlusive lesion: 30 males (62.5%) and 18 females (37.5%) with an age range from 40 years to 92 years (median age 69.5). All patients enrolled in our study were diagnosed with an intestinal obstruction originating from the colorectal tract without bowel perforation signs. Obstruction was primitive colorectal cancer in 45 cases (93.7%) and benign anastomotic stricture in 3 cases (6.3%).

RESULTS: Surgical resection was totally laparoscopic in 69% of cases (24 patients) while 17% (6 patients) of cases were video-assisted due to the local extension of cancer with infiltrations of surrounding structures (urinary bladder in 2 cases, ileus and iliac vessels in the others). In 14% of cases (5 patients), resection was performed by open surgery due to the high American Society of Anesthesiologists score and the elderly age of patients (median age of 89 years). We performed a terminal stomy in only 7 patients out of 35, 6 colostomies and one ileostomy (in a total colectomy). In the other 28 cases (80%), we performed bowel anastomosis at the same time as resection, employing a temporary ileostomy only in 5 cases.

CONCLUSION: Colorectal stenting transforms an emergency operation in to an elective operation performable in a totally laparoscopic manner, limiting the confection of colostomy with its correlated complications.

Endovascular stent treatment for symptomatic benign iliofemoral venous occlusive disease: long-term results 1987-2009

Venous stenting has been shown to effectively treat iliofemoral venous obstruction with good short- and mid-term results. The aim of this study was to investigate long-term clinical outcome and stent patency. Twenty patients were treated with venous stenting for benign disease at our institution between 1987 and 2005. Fifteen of 20 patients (15 female, mean age at time of stent implantation 38 years [range 18-66]) returned for a clinical visit, a plain X-ray of the stent, and a Duplex ultrasound. Four patients were lost to follow-up, and one patient died 277 months after stent placement although a good clinical result was documented 267 months after stent placement. Mean follow-up after stent placement was 167.8 months (13.9 years) (range 71 (6 years) to 267 months [22 years]). No patient needed an additional venous intervention after stent implantation. No significant difference between the circumference of the thigh on the stented side (mean 55.1 cm [range 47.0-70.0]) compared with the contralateral thigh (mean 54.9 cm [range 47.0-70.0]) (p=0.684) was seen. There was a nonsignificant trend toward higher flow velocities within the stent (mean 30.8 cm/s [range 10.0-48.0]) and the corresponding vein segment on the contralateral side (mean 25.2 cm/s [range 12.0-47.0]) (p=0.065). Stent integrity was confirmed in 14 of 15 cases. Only one stent showed a fracture, as documented on x-ray, without any impairment of flow. Venous stenting using Wallstents showed excellent long-term clinical outcome and primary patency rate.

Mechanical characteristics of composite knitted stents

We used metal wires and fibers to fabricate a composite knitted stent and then compare the mechanical characteristics of this stent with those of a pure metallic stent of the same construction in order to develop a stent that offers a comparable degree of expandability as metallic stents but can be used for highly curved lesions that cannot be treated using metallic stents. We fabricated two types of composite knitted stent (N-Z stents), using nitinol wire with a diameter of 0.12 mm and polypara-phenylene-benzobisoxazole (PBO) multifilament fiber (Zyron AS; Toyobo, Osaka, Japan). Stents were knitted into a cylindrical shape using the same textile pattern as a Strecker stent. Two loop lengths (L) of nitinol wire were used in the N-Z stents: L = 1.84 mm (N-Z stent L = 1.84) and L = 2.08 mm (N-Z stent L = 2.08). For the sake of comparison, we fabricated a metallic stent of nitinol using the same textile pattern (N-N stent L = 1.92). We applied a radial compression force diametrically to each stent and applied a bending force diametrically at the free end of a stent with one end fixed in order to evaluate the relationship between stent elasticity and load values. In addition, we macroscopically evaluated the generation of kinks when the stent was bent 180 degrees . The radial compressive force when the stent diameter was reduced by 53% was 6.44 N in the case of N-Z stent L = 1.84, 6.14 N in the case of N-Z stent L = 2.08, and 4.96 N in the case of N-N stent L = 1.92 mm. The composite stent had a radial compressive force higher than that of a metallic stent. The restoring force to longitudinal direction at a 90 degrees bending angle was 0.005 N for N-Z stent L = 1.84, 0.003 N for N-Z stent L = 2.08, and 0.034 N for N-N stent L = 1.92. The restoring force of the composite stent was significantly lower. Finally, the composite stent generated no definitive kinks at a bending angle of 180 degrees , regardless of loop length. However, the N-N stent clearly produced kinks, causing blockage of the inner cavity. In conclusion, the use of a metal and fiber composite in the construction of a knitted stent ensures an expansion performance comparable to that of metallic stents, while providing better kink resistance.

Endoluminal insertion of colonic stents

For patients with obstructing colonic tumours endoluminal stents provide an alternative to surgical decompression. Used either as permanent palliation, or as a bridge to surgery, colonic stents have been shown to be effective, safe, and cost effective.

An Experimental Model for the Treatment of Lethal Bleeding Injury to the Juxtahepatic Vena Cava With Stent Graft

BACKGROUND

Juxtahepatic vein injuries present a high mortality rate. Our objectives were to develop an experimental model of endovascular lethal injury of the juxtahepatic inferior vena cava (JHIVC) and to evaluate its hemodynamic alterations; to treat the lesion with volume replacement, and a stent graft (SG); and to follow the animals after treatment.

METHODS

Twenty dogs were anesthetized and monitored [heart rate (HR), mean arterial pressure (MAP), vesical and peritoneal pressures], and submitted to a JHIVC endovascular injury. After volume replacement the dogs were divided into two groups: control (GI) and experimental (GII). GI was observed until death. GII was treated with SG and followed by Doppler ultrasound (DUS) and cavography for 4 (GIIA), and 8 weeks (GIIB), and then sacrificed and IVC and SG were analyzed.

RESULTS

GI presented increased abdominal pressures, arterial hypotension, and death after 80 minutes. GII had a 100% survival rate till sacrifice, without clinical repercussions. At DUS and cavography all SG were patent, with monophasic pulsatile flow. On US, SG diameters after 2, 4, and 8 weeks did not show differences. On cavography IVC diameters presented no difference between groups GIIA and GIIB throughout the experiment. These data analyzed for the GII as a whole, showed statistically significant differences. Average lumen diameter reduction of SG was 27.43+/-20,00%. Pressure values in the IVC cranially, caudally to the SG, and inside the SG, did not show differences. In the IVC with the SG we observed a thicker neointima layer, and the injury in the media layer was covered with fibroconnective tissue.

CONCLUSIONS

We developed an experimental dog model of endovascular lethal injury of the JHIVC with significant increase in abdominal pressures, and a mortality rate of 100%. The treatment of this lesion with SG resulted in a thickened neointima layer, and a 27% reduction in the JHIVC lumen diameter, without clinical repercussion, and with a 100% survival rate.

Physiologic effect of stent therapy for inferior vena cava obstruction due to malignant liver tumor

PURPOSE

To understand systemic the influence of stent therapy for inferior vena cava (IVC) obstruction due to advanced liver tumor.

METHODS

Seven patients with symptomatic IVC obstruction due to advanced primary (n = 4) or secondary (n = 3) liver tumor were subjected to stent therapy. Enrollment criteria included high IVC pressure over 15 mmHg and the presence of edema and ascites. Z-stents were deployed using coaxial sheath technique via femoral venous puncture. Physiologic and hematobiochemical parameters were analyzed.

RESULTS

All procedures were successful, and the stents remained patent until patient death. Promptly after stent placement, the IVC flow recovered, and the venous blood pressure in the IVC below the obstruction level showed a significant decrease from 20.8 +/- 1.2 mmHg (mean +/- SE) to 10.7 +/- 0.7 mmHg (p < 0.01). Transient mild increase of right atrial pressure was observed in 1 patient. During the following week prominent diuresis was observed in all patients. Mean urine output volume in the 3 days before the stent therapy was 0.81 +/- 0.09 l/day compared with 2.1 +/- 0.2 l/day (p < 0.01) in the 3 days after. The edema and ascites decreased in all patients. The caval pressure change correlated well (r > 0.6) with the urine volume increase, and with the decreased volume of edema and ascites. The urine volume increase correlated well with the decrement of edema, but not with that of ascites. Improvements for various durations in the levels of blood urea nitrogen, serum creatinine, lactate dehydrogenase, fibrinogen, and platelet count were found (p < 0.05). These hematobiochemical changes were well correlated with each other and with the decrement of ascites. Two patients showed a low blood sodium level of 128.5 mEq/l after intensive natriuresis, and one of them died on day 21 with hepatic failure, which was interpreted as maladaptation aggravation. The mean survival time was 94.1 +/- 34.1 days (mean +/- SD), ranging from 21 to 140 days after stent treatment.

CONCLUSION

The stent therapy for IVC obstruction due to malignant liver tumors was followed by a series of physiologic and hematobiochemical consequences, most of them favorable but some possibly unfavorable. Rational interpretations and predictions of sequelae based on physiologic science including cardiology, hepatology, and nephrology would facilitate the best management of stent therapy for malignant IVC obstruction.

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.

Tratamento da síndrome da veia cava superior

A veia cava superior é formada pela união das duas veias inominadas, direita e esquerda, e localiza-se no mediastino médio, à direita da artéria aorta e anteriormente à traquéia. A síndrome da veia cava superior representa um conjunto de sinais (dilatação das veias do pescoço, pletora facial, edema de membros superiores, cianose) e sintomas (cefaléia, dispnéia, tosse, edema de membro superior, ortopnéia e disfagia) decorrentes da obstrução do fluxo sanguíneo através da veia cava superior em direção ao átrio direito. A obstrução pode ser causada por compressão extrínseca, invasão tumoral, trombose ou por dificuldade do retorno venoso ao coração secundária a doenças intra-atriais ou intraluminais. Aproximadamente 73% a 97% dos casos de síndrome da veia cava superior ocorrem durante a evolução de processos malignos intratorácicos. A maioria dos pacientes com a síndrome secundária a neoplasias malignas é tratada sem necessidade de cirurgia, através de radioterapia ou quimioterapia, ou através da colocação de stents endoluminais. Quando a síndrome é de etiologia benigna, o tratamento é feito através de medidas clínicas (anticoagulação, elevação da cabeça, etc.) ou, em casos refratários, através de angioplastia, colocação de stents endoluminais e cirurgia.

Effect of Stent Oversizing on In-Stent Stenosis and Lumen Size in Normal Porcine Veins

PURPOSE

To present an in vivo evaluation of the effects of stent oversizing on in-stent stenosis and on actual lumen size in normal veins.

METHODS

Twelve self-expanding stents were implanted in the common iliac veins of 6 minipigs, which were divided in 2 groups for follow-up at 1 and 3 months, respectively. Oversizing ranged from 119.5% to 216% of the original vessel diameter. Intravascular ultrasound (IVUS) was used to measure vessel areas at the stent edges and midpoint. In-stent stenosis and decrease in actual lumen size were evaluated with IVUS immediately after implantation and during follow-up.

RESULTS

There was a very strong positive linear regression between stent oversizing and in-stent stenosis in the 1-month model (r=0.947, p=0.004), in the 3-month model (r=0.931, p=0.007), and in the sum of these 2 groups (r=0.83, p<0.001). Regarding the change in actual lumen size, we found a strong negative linear regression with stent oversizing in the 1-month (r=-0.754, p=0.083) and the 3-month (r=-0.562, p=0.246) groups, but these did not attain statistical significance. However, a strong correlation between stent oversizing and a decrease in lumen size in all samples proved to be statistically significant (r=0.619, p=0.032).

CONCLUSIONS

Stent oversizing was strongly correlated with increased in-stent stenosis and decreased actual lumen size at follow-up in normal non-stenotic porcine veins.

Nonmalignant superior vena cava syndrome: Pathophysiology and management

Superior vena cava (SVC) syndrome occurs following obstruction either from external compression or internal thrombosis or scarring. In the past, treatment was limited to medical therapy or surgical bypass but now percutaneous revascularization presents a viable therapeutic option. We present our experience in the percutaneous therapy of patients with nonmalignant SVC syndrome and review the condition with regard to its pathophysiology and management.

Mechanical properties of various z-stent designs: an endovascular stent-grafting perspective

PURPOSE

To comparatively assess the mechani-cal behavior of various clinically relevant Z-stent designs.

METHODS

A total of 16 Z-stents of original, biliary, spiral, and double-skirted designs (n=4 for each) were constructed using similar specifications for all. Stents were then evaluated for stiffness, snap opening force (SOF), flexibility, and displacement force using a novel tensiometer. Differences among the stents were determined using statistical methods. Stents explanted from dog aorta after a mean follow-up of 13 months were examined under a scanning electron microscope for surface defects.

RESULTS

Forces required for about 50% reduction in diameter were 1.88 +/- 0.16 N, 3.81 +/- 0.21 N, 2.76 +/- 0.22 N, and 3.35 +/- 0.19 N for original, biliary, spiral, and skirted designs, respectively. Differences among the four designs were statistically significant at almost all points of measurement (P < 0.0001). Biliary and skirted designs showed higher SOF values in the early measurements. Stents explanted from dog aorta after a mean duration of 13 months showed no obvious corrosion or breakage in the wire struts.

CONCLUSIONS

Significant differences exist among the various Z-stent designs in terms of their mechanical properties. Understanding them should help to select the appropriate stent for a given lesion. 316L stainless steel shows a favorable long-term tissue interaction.

Placement of self-expanding metal stents for acute malignant large-bowel obstruction: a collective review

BACKGROUND

The purpose of this study was to review our experience with self-expanding metal stents as the initial interventional approach in the management of acute malignant large-bowel obstruction.

METHODS

Twenty-six patients who underwent placement of colonic stents at our institution between June 1994 and June 2000 were identified and reviewed.

RESULTS

In 14 patients, the stents were placed for palliation, whereas in 12, they were placed as a bridge to surgery. In 22 patients (85%), stent placement was successful on the first occasion. In the remaining four individuals, one was successfully stented at the second occasion, and three required emergency surgery. Nine of the 12 patients (75%) in the bridge-to-surgery group underwent elective colon resection. In the palliative group, four patients (29%) had reobstruction of the stents, and in one (9%), the stent migrated. In the remaining nine patients (64%), the stent was patent until the patient died or until the time of last follow-up (median, 156 days).

CONCLUSIONS

In our experience with 26 patients who developed a complete bowel obstruction as a consequence of a malignant tumor, placement of colonic stents to achieve immediate nonoperative decompression proved to be both safe and effective. Subsequent elective resection was accomplished in the majority of resectable cases.

Characterization of radial forces in Z stents

RATIONAL AND OBJECTIVES

The purpose of this study was to evaluate the effects of variation in design parameters on the resultant radial force. We evaluated the influence of wire gauge, leg length, and number of bends on the radial force produced by z stents and compared these with radial forces produced by commercial stents. A second goal was to develop an engineering model for predicting radial forces generated by z stents.

METHODS

Z stents were fashioned by hand using stainless steel wire and solder that connected the ends. The radial force was measured as a function of wire gauge, vessel diameter, leg length, and number of bends and compared with the theoretical values of radial force calculated by combining Castigliano's theorem and the law of Laplace.

RESULTS

Theoretically predicted radial forces were within 8% of each observed value of radial force up to 70% spring compression.

CONCLUSIONS

These results suggest that the z-stent model can be used to build custom stents with preselected values of radial force for clinical use. In addition, they can be used to design model investigational stents made of similar materials and surface areas to test the effects of radial force on biological response.

Use of prostatic stents for the treatment of benign prostatic hyperplasia in high-risk patients

Benign prostatic hyperplasia (BPH) is a frequent disease in men and a major cause of lower urinary tract symptoms (LUTS). Transurethral resection of the prostate (TURP) or open surgery remains the gold standard of treatment for symptomatic BPH. However, 10% to 15% of patients with BPH cannot undergo surgery due to grave concomitant diseases. For patients presenting with contraindications to surgery or anesthesia, several minimally invasive alternative treatment modalities are available. One such therapeutic alternative is prostatic stenting, which can serve as a temporary or permanent solution for bladder outlet obstruction caused by BPH. Although not a new concept, this is a relatively new treatment modality in the United States, primarily because of the strict regulatory forces governing the use of these devices. Prostatic urethral stents have been widely demonstrated to be safe and effective for the treatment of symptomatic BPH. In addition to being minimally invasive, prostatic stenting is generally rapid, easy to perform, immediately effective, and has a low cost compared with conventional surgical treatment. Prostatic stents are therefore well suited to treat the frail elderly patient who would not be able to withstand the stress of undergoing surgery. This report reviews the current use of prostatic urethral stents in the treatment of high-risk surgical patients with BPH.

The management of neoplastic colorectal obstruction with colonic endolumenal stenting devices

BACKGROUND

Colonic endolumenal stenting (CELS) to treat obstructing colorectal neoplasms was first described in 1991. The aim of this study was to review the published world literature and make recommendations for its use in current clinical practice.

METHODS

Suitable English language reports were identified using a Medline search.

RESULTS

CELS can been successfully accomplished in 64% to 100% of obstructing malignant colonic lesions. Distal lesions are more common and theoretically more easy to stent although lesions within the ascending colon have been successfully managed. Minor complications include transient anorectal pain and rectal bleeding, however, significant complications of stent dislocation and colonic perforation are also well recognized.

CONCLUSION

CELS can aid the palliative management of malignant colorectal obstruction. Its role in relieving obstruction prior to resection remains to be defined. Increasing experience has allowed the safe placement of stents and relief of obstruction of virtually any lesion throughout the large bowel.

Superior vena cava syndrome

Lung cancer is the most common cause of superior vena cava syndrome (SVCS) and requires timely recognition and management. The syndrome is rarely an oncologic emergency in the absence of tracheal compression and airway compromise. Treatment depends on the etiology of the obstructive process. Treatment should also be individualized and should not be undertaken until a diagnosis is obtained. Most patients with SVCS secondary to lung cancer can be treated with appropriately directed chemotherapy or radiotherapy. With the refinement of endovascular stents, percutaneous stenting of the SVC is being increasingly used as primary treatment modality. Thrombotic occlusion can be treated with appropriate lytic agents. In rare circumstances, surgical decompression can be performed; bypass or replacement of the SVC results in immediate improvement in the majority of cases and can be accomplished with low morbidity.

Focal elastic obstruction of the inferior vena cava

Obstruction of the supra-hepatic inferior vena cava (IVC) is a common cause of hepatic venous hypertension and the most common cause of Budd-Chiari Syndrome. Because most cases of IVC obstruction go undiagnosed until Budd-Chiari Syndrome develops, the natural history of IVC obstruction is not well defined. We report a case of a focal, elastic, non-membranous obstruction of the IVC causing hepatic venous hypertension and elevated serum transaminases in a 36-year-old man. The obstruction was successfully treated with placement of a self-expanding metallic stent with normalization of hepatic transaminases.

Clinical efficacy of the polyurethane stent without fluoroscopic guidance in the treatment of nasolacrimal duct obstruction

PURPOSE

To evaluate the clinical efficacy of the polyurethane (Song) stent in the treatment of nasolacrimal duct obstruction without fluoroscopic guidance, especially at the junction between the lacrimal sac and nasolacrimal duct or at the nasolacrimal duct.

DESIGN

Retrospective noncomparative case series.

PARTICIPANTS

This study evaluated 59 cases of nasolacrimal duct obstruction in 53 patients, with mean epiphora of 36 months (range, 2 months-17 years).

METHODS

Without the assistance of a radiologist, a polyurethane nasolacrimal stent was placed by introducing a guidewire through the superior or inferior punctum into the canaliculus and advancing it across the obstruction into the opening of the inferior meatus of the nasal cavity. The mean follow-up period was 22 months (range, 12 months-48 months).

MAIN OUTCOME MEASURES

Patency of the lacrimal passage to irrigation and the duration of this procedure.

RESULTS

Complete resolution of epiphora was accomplished in 55 (93.2%) of the 59 eyes. There was recurrence of epiphora in four cases because of obstruction of the stent in three cases and obstruction of the common canaliculus by recurrent dacryocystitis in one case.

CONCLUSIONS

Polyurethane stenting without fluoroscopic guidance seems to be a valuable technique for primary management of nasolacrimal duct obstruction before dacryocystorhinostomy.

Use of a self-expanding stent in the palliation of rectal cancer recurrences. A report of three cases

BACKGROUND

Patients with nonresectable rectal cancer recurrences and elderly high risk patients are currently given a colostomy as a palliative therapy. To improve the quality of life in these patients, we inserted a self-expanding metal stent to relieve the symptoms of obstruction caused by a rectal cancer recurrence.

METHODS

Three patients (two male, one female; ages 61, 69, and 59), all suffering from a rectal cancer pelvic recurrence and diffuse metastases, had a stent inserted. Using fluoroscopic and endoscopic control, a metal guidewire was passed through the obstruction. A mild dilatation of the stenosis was carried out before positioning of the expandable metal stent.

RESULTS

The procedure was successful at the first attempt in all the patients, and stool evacuation was immediate. Patients complained of rectal tenesmus during the first 48 h, which was treated with nonsteroid anti-inflammatory drugs. However, there were no serious complications related to the procedure. Regular endoscopic and clinical follow-up were carried out. No patient had any evidence of recurrent obstruction.

CONCLUSION

In cases of inoperable rectal cancer recurrence, the placement of self-expanding metal stents is technically feasible and safe, and it avoids a permanent colostomy.