New stent technologies

A biomimetic tri-phasic scaffold with spatiotemporal patterns of gastrodin to regulate hierarchical tissue-based vascular regeneration

Clinical use of small-diameter vascular grafts remains a challenging issue in neovessel regeneration in view of thrombosis and intimal hyperplasia. Developing a vascular graft with structure and function similar to those of the native vessels necessitates a major direction of vascular tissue regeneration. Thus, this study sought to design and fabricate a range of tri-phasic scaffolds (0, 2, and 5 wt% gastrodin-polyurethane (PU)) with spatiotemporally defined structure and gastrodin-release for regulating the highly coordinated processes in growth of the intima and media. While the small pores of inner layer guided infiltration of human umbilical vein endothelial cells (HUVECs), the bigger pores of medial layer could offer smooth muscle cell (SMC)-friendly habitat, and external fibers conferred adequate mechanical properties. Correspondingly, spatial distribution and differential regulation of key proteins in HUVECs and SMCs were mediated by hierarchical release of gastrodin, of which rapid release in inner layer elicited enhanced HUVEC proliferation and migration against those of the SMC via activated endothelial nitric oxide synthase (eNOS) and heat shock protein 70 (HSP70) signal. Of note, superior anti-coagulation was reflected in 2 wt% gastrodin-PU ex vivo extracorporeal blood circulation experiment. After in vivo implantation for 12 weeks, there was no formation of obvious thrombosis and intimal hyperplasia in 2 wt% gastrodin-PU. The scaffold maintained high patency and improved vascular remodeling, including the formation of thin endothelialization in lumen and dense extracellular matrix deposition in medial layer. Taken together, the results demonstrate the positive function of hierarchical releasing system that responded to tri-phasic structure, which not only suppressed intimal thickening but also tightly controlled tissue regeneration.

Drug Delivery Opportunities in Esophageal Cancer: Current Treatments and Future Prospects

With one of the highest mortality rates of all malignancies, the 5-year survival rate for esophageal cancer is under 20%. Depending on the stage and extent of the disease, the current standard of care treatment paradigm includes chemotherapy or chemoradiotherapy followed by surgical esophagogastrectomy, with consideration for adjuvant immunotherapy for residual disease. This regimen has high morbidity, due to anatomic changes inherent in surgery, the acuity of surgical complications, and off-target effects of systemic chemotherapy and immunotherapy. We begin with a review of current treatments, then discuss new and emerging targets for therapies and advanced drug delivery systems. Recent and ongoing preclinical and early clinical studies are evaluating traditional tumor targets (e.g., human epidermal growth factor receptor 2), as well as promising new targets such as Yes-associated protein 1 or mammalian target of rapamycin to develop new treatments for this disease. Due the function and location of the esophagus, opportunities also exist to pair these treatments with a drug delivery strategy to increase tumor targeting, bioavailability, and intratumor concentrations, with the two most common delivery platforms being stents and nanoparticles. Finally, early results with antibody drug conjugates and chimeric antigenic receptor T cells show promise as upcoming therapies. This review discusses these innovations in therapeutics and drug delivery in the context of their successes and failures, with the goal of identifying those solutions that demonstrate the most promise to shift the paradigm in treating this deadly disease.

3D-Printed Shape Memory Poly(alkylene terephthalate) Scaffolds as Cardiovascular Stents Revealing Enhanced Endothelialization

Cardiovascular diseases are the leading cause of death and current treatments such as stents still suffer from disadvantages. Balloon expansion causes damage to the arterial wall and limited and delayed endothelialization gives rise to restenosis and thrombosis. New more performing materials that circumvent these disadvantages are required to improve the success rate of interventions. To this end, the use of a novel polymer, poly(hexamethylene terephthalate), is investigated for this application. The synthesis to obtain polymers with high molar masses up to 126.5 kg mol-1 is optimized and a thorough chemical and thermal analysis is performed. The polymers are 3D-printed into personalized cardiovascular stents using the state-of-the-art solvent-cast direct-writing technique, the potential of these stents to expand using their shape memory behavior is established, and it is shown that the stents are more resistant to compression than the poly(l-lactide) benchmark. Furthermore, the polymer's hydrolytic stability is demonstrated in an accelerated degradation study of 6 months. Finally, the stents are subjected to an in vitro biological evaluation, revealing that the polymer is non-hemolytic and supports significant endothelialization after only 7 days, demonstrating the enormous potential of these polymers to serve cardiovascular applications.

Regulatory perspectives of combination products

Combination products with a wide range of clinical applications represent a unique class of medical products that are composed of more than a singular medical device or drug/biological product. The product research and development, clinical translation as well as regulatory evaluation of combination products are complex and challenging. This review firstly introduced the origin, definition and designation of combination products. Key areas of systematic regulatory review on the safety and efficacy of device-led/supervised combination products were then presented. Preclinical and clinical evaluation of combination products was discussed. Lastly, the research prospect of regulatory science for combination products was described. New tools of computational modeling and simulation, novel technologies such as artificial intelligence, needs of developing new standards, evidence-based research methods, new approaches including the designation of innovative or breakthrough medical products have been developed and could be used to assess the safety, efficacy, quality and performance of combination products. Taken together, the fast development of combination products with great potentials in healthcare provides new opportunities for the advancement of regulatory review as well as regulatory science.

A systematic review and meta-analysis of the risk of death and patency after application of paclitaxel-coated balloons in the hemodialysis access

OBJECTIVE

The comparison between paclitaxel-coated balloon (PCB) angioplasty and plain balloon angioplasty (PBA) for hemodialysis (HD) access stenosis or occlusion has not been well investigated. The objectives of this systematic review and meta-analysis were to compare all-cause mortality, HD access primary patency, and circuit primary patency after endovascular maintenance procedures using PCB angioplasty vs PBA.

METHODS

MEDLINE, Embase, and Cochrane Databases were systematically searched to identify all the relevant studies on paclitaxel-coated devices for stenosis or thrombosis of HD access. A random effects model was applied to pool the effect measures. Dichotomous data were presented using an odds ratio (OR). Effect data were presented using pooled hazard ratio (HR) with 95% confidence interval (CI).

RESULTS

A total of 16 studies were included in this meta-analysis, 12 randomized controlled trials and 4 cohort studies involving 1086 patients who underwent endovascular treatment for HD access stenosis or occlusion. All-cause mortality rates at 6, 12, and 24 months after intervention were similar between the PCB and PBA groups (6 months: OR, 1.06 [95% CI, 0.38-2.96; P = .907; I² = 19.2%]; 12 months: OR, 1.20 [95% CI, 0.66-2.16; P = .554; I² = 0%]; 24 months: OR, 1.43 [95% CI, 0.83-2.45; P = .195; I² = 0%]). There was a significant improvement of primary patency in the PCB group compared with the PBA group (HR, 0.47; 95% CI, 0.33-0.69; P < .001; I² = 67.3%). This benefit was consistent with the analysis of randomized controlled trials, whereas cohort studies were excluded. Further subgroup analysis of target lesions demonstrated that primary patency was significantly higher in the PCB group than in the PBA group, not only for arteriovenous fistula (HR, 0.54; 95% CI, 0.30-0.98; P = .041; I² = 76.8%) but also for central venous stenosis (HR, 0.39; 95% CI, 0.22-0.71; P = .002; I² = 0%). The PCB group was associated with higher 6-month (OR, 0.40; 95% CI, 0.27-0.59; P < .001) and 24-month lesion primary patency (OR, 0.28; 95% CI, 0.11-0.72; P = .009) than PBA and was marginally associated with 12-month lesion primary patency (OR, 0.52; 95% CI, 0.26-1.03; P = .06). Circuit primary patency analysis showed a marginal trend toward better outcome in the PCB group (HR, 0.63; 95% CI, 0.40-1.00) but no statistical significance (P = .052).

CONCLUSIONS

This systematic review and meta-analysis demonstrated that PCB angioplasty is associated with significantly improved primary patency of arteriovenous fistula and central venous stenosis for HD access maintenance, with no evidence of increasing all-cause mortality based on short-term and midterm follow-up. Further large cohort study is needed to investigate long-term mortality.

In vivo canine study of three different coatings applied to p64 flow-diverter stents: initial biocompatibility study

Background

Flow-diverter stents (FDSs) have revolutionised the treatment of intracranial aneurysms. However, associated dual antiplatelet treatment is mandatory. We investigated the biocompatibility of three proprietary antithrombogenic coatings applied to FDSs.

Methods

After Institutional Animal Care and Use Committee approval, four domestic juvenile female dogs (weight 19.9 ± 0.9 kg, mean ± standard deviation) were commenced on three different oral antiplatelet regimes: no medication (n = 1), acetylsalicylic acid (n = 2), and acetylsalicylic acid and clopidogrel (n = 1). Four p64 FDSs were randomly implanted into the subclavian, common carotid, and external carotid arteries of each dog, including both uncoated p64 stents and p64 stents coated with three different antithrombogenic hydrophilic coating (HPC). Angiography and histological examinations were performed. Wilcoxon/Kruskal-Wallis and ANOVA were used with p value < 0.05 considered as significant.

Results

Minimal inflammatory cell infiltration and no device-associated granulomatous cell inflammation were observed. No significant difference in adventitial inflammation (p = 0.522) or neointimal/medial inflammation (p = 0.384) between coated and uncoated stents as well as between the different stent groups regarding endothelial cell loss, surface fibrin/platelet deposition, medial smooth muscle cell loss, or adventitial fibrosis were found. Acute self-limiting thrombus formed on 6/16 implants (37.5%), and all of the thrombi were noted on devices implanted in the common or external carotid artery irrespective of the surface coating. Two of 12 p64 HPC-coated stents (16.7%) and 1/4 uncoated p64 stents (25%) showed severe or complete stenosis at delayed angiography.

Conclusions

In these preliminary in vivo experiments, HPC-coated p64 FDSs appeared to be biocompatible, without acute inflammation.

Emerging Implications for Extracellular Matrix-Based Technologies in Vascularized Composite Allotransplantation

Despite recent progress in vascularized composite allotransplantation (VCA), limitations including complex, high dose immunosuppression regimens, lifelong risk of toxicity from immunosuppressants, acute and most critically chronic graft rejection, and suboptimal nerve regeneration remain particularly challenging obstacles restricting clinical progress. When properly configured, customized, and implemented, biomaterials derived from the extracellular matrix (ECM) retain bioactive molecules and immunomodulatory properties that can promote stem cell migration, proliferation and differentiation, and constructive functional tissue remodeling. The present paper reviews the emerging implications of ECM-based technologies in VCA, including local immunomodulation, tissue repair, nerve regeneration, minimally invasive graft targeted drug delivery, stem cell transplantation, and other donor graft manipulation.

Degradable, drug-eluting stents: a new frontier for the treatment of coronary artery disease

This article reviews the clinical use of stents in the treatment of coronary artery disease and the rationale for the use of degradable, drug-eluting polymer stents. The authors note the challenges of using off-the-shelf polymers for the development of degradable stents, as well as the interplay between polymer properties and a functional stent design. Drug-eluting metal stents are the most significant advancement in the treatment of coronary artery disease, and have significantly reduced the occurrence of in-stent restenosis after placement. Some regard drug-eluting metal stents as the final technologic advancement in the treatment of coronary artery disease, others consider the future development of degradable, drug-eluting stents as the next logical step.

Cost effectiveness of drug-eluting stents in acute myocardial infarction patients in Germany: results from administrative data using a propensity score-matching approach

BACKGROUND

The high number of patients with acute myocardial infarction (AMI) has facilitated greater research, resulting in the development of innovative medical devices. So far, results from economic evaluations that compared drug-eluting stents (DES) and bare-metal stents (BMS) have not shown clear evidence that one intervention is more cost effective than the other.

OBJECTIVE

The aim of this study was to measure the cost effectiveness of DES compared with BMS in routine care.

METHODS

We used administrative data from a large German sickness fund to compare the costs and effectiveness of DES and BMS in patients with AMI. Patients with hospital admission after AMI in 2004 and 2005 were followed up for 1 year after hospital discharge. The cost of treatment and survival after 365 days were compared for patients treated with DES and BMS. We adjusted for covariates defined according to the Ontario Acute Myocardial Infarction Mortality Prediction Rules using propensity score matching. After matching, we calculated incremental cost-effectiveness ratios (ICERs) by (i) using sample means based on bootstrapping procedures and (ii) estimating generalized linear mixed models for costs and survival.

RESULTS

After propensity score matching, the sample included 719 patients treated with DES and 719 patients treated with BMS. A comparison of sample means resulted in average costs of € 12 714 and € 11 714 for DES and BMS, respectively, in 2005 German euros. Difference in 365-day survival was not statistically significant (700 patients with DES and 701 with BMS). The ICER of DES versus BMS was -€ 718 709 per life saved. Bootstrapping resulted in DES being dominated by BMS in 54.5% of replications and DES being a dominant strategy in 2.7% of replications. Results from regression models and sensitivity analyses confirm these results.

CONCLUSION

Treatment with DES after admission with AMI is less cost effective than treatment with BMS. Our results are in line with other cost-effectiveness analyses that used administrative data, i.e. under routine care conditions. However, our results do not preclude that DES may be cost effective in specific patient subgroups.

Novel polymeric coatings with the potential to control in-stent restenosis--an in vitro study

Restenosis following percutaneous coronary intervention (PCI) is a considerable problem in long-term performance of cardiovascular stents, with a functional endothelial cell monolayer being important in its prevention. This study evaluates the influence of polymer coatings on human aortic endothelial cells (HAEC) and coronary artery smooth muscle cells (HCASMC) in vitro, in terms of morphology, cell number, and phenotype. It was demonstrated that the polymer coatings can be tailored to enhance adhesion and growth of HAECs whilst suppressing that of HCASMCs. It is concluded that one of the polymer coatings (BTL 01015) shows potential as a stent coating to enhance re-endothelialization.

Approaches for prevention of restenosis

Coronary artery disease is characterized by a narrowing (stenosis) of the arteries that supply blood to the tissue of the heart. Continued restriction of blood flow manifests itself as angina and ultimately myocardial infarction (heart attack) for the patient. Heart bypass was once the only treatment for this condition, but over the years percutaneous coronary intervention (PCI) has become an increasingly attractive alternative to medical therapy and surgical revascularization for the treatment of coronary artery disease. A vascular stent is a medical device designed to serve as a temporary or permanent internal scaffold, to maintain or increase the lumen of a blood vessel. Metallic coronary stents were first introduced to prevent arterial dissections and to eliminate vessel recoil and intimal hyperplasia associated with PCI. Further advancement in the treatment of coronary artery disease is the development of drug-eluting stents that dramatically reduce the incidence of in-stent restenosis to less than 5%. Local drug delivery offers the advantages of allowing a relatively high local concentration of drug at the treatment site while minimizing systemic toxic effect. This review describes approaches for prevention of restenosis. It focuses on drugs for prevention of restenosis, bare metal stents, and drug-eluting stents. It also describes recent advances in bioresorbable stents. One of the chapters is dedicated to our novel composite bioresorbable drug-eluting fibers, designed to be used as basic elements in drug-eluting stents.

Detection of coronary artery stenosis after successful percutaneous coronary intervention by dipyridamole stress portable type signal-averaged electrocardiography: a prospective study

In our previous studies, using portable type signalaveraged electrocardiography (portable SAECG) with dipyridamole stress we reported that patients with coronary artery disease were identified at the bedside with high sensitivity and specificity. In this study we prospectively investigated whether coronary artery stenosis after successful percutaneous coronary intervention (PCI) could be detected. Standard 12-lead QRS wave SAECG was performed before and after dipyridamole stress at the bedside in 61 patients 8.0 +/- 9.4 months after successful PCI for myocardial infarction or angina pectoris (46 males and 15 females, mean age 66 +/- 12 years). The filtered QRS duration (fQRSd) before and after dipyridamole stress was determined by the multiphasic oscillation method at each lead of the standard 12 leads, and the maximal value of changes in fQRSd (MAX DeltafQRSd) among the 12 leads was determined. The positive test was defined as MAX DeltafQRSd > or =5 ms, and negative as MAX DeltafQRSd <5 ms based on our previous studies. Then selective coronary arteriography was performed. In the positive group (n = 24), 21 patients had stenosis (> or =50%) of the coronary artery and 3 did not. In the negative group (n = 37), 8 patients had stenosis and 29 did not. The sensitivity, specificity, positive predictive accuracy, and negative predictive accuracy for the detection of coronary artery stenosis by SAECG were 72%, 91%, 88%, and 78%, respectively. Dipyridamole stress portable SAECG is useful to detect patients with coronary artery stenosis after successful PCI.

DRUG-ELUTING BIORESORBABLE STENTS FOR VARIOUS APPLICATIONS

A stent is a medical device designed to serve as a temporary or permanent internal scaffold to maintain or increase the lumen of a body conduit. Metallic coronary stents were first introduced to prevent arterial dissections and to eliminate vessel recoil and intimal hyperplasia associated with percutaneous transluminal coronary angioplasty. The stent application range has expanded as more experience was gained, and encouraging results have been obtained in the treatment of vascular diseases. Stents are currently used for support of additional body conduits, including the urethra, trachea, and esophagus. The rationale for bioresorbable stents is the support of a body conduit only during its healing process. The stent mass and strength decrease with time, and the mechanical load is gradually transferred to the surrounding tissue. Bioresorbable stents also enable longer term delivery of drugs to the conduit wall from an internal reservoir and abolish the need for a second surgery to remove the device. The present review describes recent advances in bioresorbable stents, focusing on drug-eluting bioresorbable stents for various applications. Controlled release of an active agent from a stent can be used to enhance healing of the surrounding tissues, to increase the implant's biocompatibility, as well as to help cure certain diseases. Because a lot of research in this field has been done by us, examples for these functions are described based mainly on developments in our laboratories.

Stenting the undeployed stent

Undeployment of a stent which poses a potential risk for future events may become a serious problem in the catheter laboratory. Herewith, we present a case in which we successfully stented an undeployed stent in the distal right coronary artery.

Bioresorbable polymeric stents: current status and future promise

Metal stents and, more recently, polymer-coated metal stents are used to stabilize dissections, eliminate vessel recoil, and guide remodeling after balloon angioplasty and other treatments for arterial disease. Bioresorbable polymeric stents are being developed to improve the biocompatibility and the drug reservoir capacity of metal stents, and to offer a transient alternative to the permanent metallic stent implant. Following a brief review of metal stent technology, the emerging class of expandable, bioresorbable polymeric stents is described, with emphasis on developments in the authors' laboratory.

Endovascular therapy for stenosis of the petrous or cavernous portion of the internal carotid artery: percutaneous transluminal angioplasty compared with stent placement

OBJECT

The effects of percutaneous transluminal angioplasty (PTA) and stent placement for stenosis of the petrous or cavernous portion of the internal carotid artery (ICA) were compared.

METHODS

Twenty-four patients with symptomatic, greater than 60% stenosis of the petrous or cavernous portion of the ICA were treated using PTA or stent placement; 15 were treated with PTA and nine with stent insertion. Initial and follow-up results (> 3 months posttreatment) were compared in each group. Stenotic portions of the ICA were successfully opened in 13 of 15 patients in the PTA group, and in all nine patients in the stent-treated group. In one case in the PTA group stent delivery was attempted; however, the device could not pass through the vessel's tortuous curve, and PTA alone was performed in this case. Postoperatively, the mean stenotic ratio decreased from 72.1 to 29.6% in the PTA group, and from 75.6 to 2.2% in the stent-treated group. In four patients in the PTA group, stenoses greater than 50% were demonstrated on follow-up angiography performed at 3 to 6 months after PTA. In the stent-treated group, no restenosis was encountered, although in one case acute occlusion of the stent occurred; the device was recanalized with PTA and infusion of tissue plasminogen activator. This case was the only one of the 24 in which any neurological deficits related to the endovascular procedure occurred. Stent placement brought a greater gain in diameter than did PTA at the initial and late follow-up period; this gain was statistically significant.

CONCLUSIONS

Stent placement is more effective than PTA for stenosis of the petrous or cavernous portion of the ICA from the viewpoint of initial and late gain in diameter.

Is coronary stent deployment and remodeling affected by predilatation? An intravascular ultrasound randomized study Stenting with or without predilation: an IVUS study

In this intravascular ultrasound (IVUS) randomized trial we compared a strategy of direct stenting (DS) without predilation (n = 30) vs. conventional stenting with predilation (SWP) (n = 30) in patients with suitable type A or B non-calcified lesions in native vessels > or = 3 mm. Optimal deployment was achieved using angiographic criteria without interactive IVUS. The goal of our study was to determine whether stent expansion and coronary remodeling were similar. Maximal pressure inflation was comparable in the two groups (11.4 +/- 2.2 vs. 11.8 +/- 1.9 atm; NS). Stent deployment was obtained in all patients with complete apposition to the vessel wall. DS and SWP resulted in comparable lumen enlargement (5.4 +/- 2.5 vs. 5.5 +/- 2.1 mm2) with an identical mechanism: 66% of lumen enlargement was due to increased enlarged elastic membrane (EEM)-cross sectional area (CSA) (delta = 3.7 +/- 2.1 mm2 and delta = 2.4 +/- 6.8 mm2, respectively, p < 0.49) and 34% was due to a reduced P + M-CSA (delta = 0.02 +/- 6.9 mm2 and delta = 1.2 +/- 6.3 mm2, respectively, p < 0.50). We conclude that at the same maximal pressure inflation the mechanisms of stent expansion are similar in both DS and SWP groups. In this observational study, the IVUS data showed clearly under-expansion of stents in both groups in comparison with previously published CSA values (minimum stent CSA of 7.5 mm2).

Various reasons for repeat dilatation of stented pulmonary arteries in paediatric patients

OBJECTIVE

To evaluate the reasons for repeat intervention in patients treated with balloon expandable stents for pulmonary artery stenoses, with particular analysis of the time intervals between interventions.

DESIGN

A retrospective observational study.

SETTING

A single paediatric cardiology centre.

PATIENTS

38 patients, mean age 6.9 years, range 6 days to 34 years (one adult patient); mean weight 19.7 kg, range 2.5-75 kg.

INTERVENTION

Implantation of balloon expandable stents in 46 cases of main pulmonary artery stenosis, right pulmonary artery stenosis, left pulmonary artery stenosis, or right ventricle to pulmonary artery conduits.

MAIN OUTCOME MEASURES

Adaptation of stent diameter to patient growth; development of pulmonary arteries; pressure gradient in the right ventricle.

RESULTS

56 stents were implanted in 46 lesions. During a mean follow up time of 2.2 years, 40 repeat dilatations were performed on 28 of 42 reinvestigated stents. A second repeat dilatation was performed on eight stents, and a third on four stents. The mean time period between implantation and repeat dilatations was 15.5 months.

CONCLUSIONS

Repeat dilatation of stented pulmonary arteries was done mainly to adapt the stent diameter to the patient's growth. However, repeat dilatations were also performed to relieve stent obstruction caused by intimal proliferation (17.5%), or to overcome progressive external compression (25%). While most repeat interventions in adult patients are for intimal hyperplasia, in paediatric patients they are needed for a variety of reasons.

Thrombogenicity of various endovascular stent types: an in vitro evaluation

PURPOSE

The aim of this study was to evaluate the thrombogenicity of different peripheral stent types in a standardized in vitro model with fresh human whole blood.

MATERIALS AND METHODS

Different stents (N = 77; n = 7 of each of 11 types) were implanted in polyvinyl chloride tubing loops and filled with donor blood samples. After 120 minutes of blood circulation, the thrombin-antithrombin III complex (TAT) levels, beta-thromboglobulin (beta-TG) levels, and platelet counts were assessed.

RESULTS

After 2 hours, significant differences were seen. TAT values (+/- SD) with the investigated stents were 31 micro g/mL +/- 20 (control, no stent), 328 micro g/mL +/- 206 (Saxx stent, peripheral medium CrNi31 L), 651 micro g/mL +/- 760 (Palmaz Corinthian Stent, 316 L stainless steel, electropolished), 1,609 micro g/mL +/- 1,264 (Palmaz Corinthian Stent, 316 L stainless steel, not electropolished), 810 micro g/mL +/- 578 (Palmaz Schatz long medium stent), 569 micro g/mL +/- 347 (Smart Nitinol stent), 1,037 micro g/mL +/- 577 (Megalink peripheral stent), 543 micro g/mL +/- 487 (peripheral stent, electropolished), 1,674 micro g/mL +/- 2,057 (peripheral stent, not electropolished), 3,128 micro g/mL +/- 1,812 (SelfX Nitinol stent, polished), 5,897 micro g/mL +/- 2,380 (SelfX Nitinol stent, unpolished), and 1,458 micro g/mL +/- 887 (bridge stent). The platelet count (x1,000/ micro L +/- SD) was 218 +/- 35 (control, no stent), 188 +/- 22 (Saxx stent), 187 +/- 20 (Palmaz Corinthian stent, electropolished), 135 +/- 37 (Palmaz Corinthian stent, not electropolished), 170 +/- 24 (Palmaz Schatz stent), 180 +/- 36 (Smart Nitinol stent), 159 +/- 26 (Megalink peripheral stent), 173 +/- 17 (peripheral stent, electropolished), 133 +/- 51 (peripheral stent, not electropolished), 123 +/- 37 (SelfX Nitinol stent, polished), 52 +/- 27 (SelfX Nitinol stent, unpolished), and 130 +/- 31 (bridge stent).

CONCLUSION

This standardized study showed a wide range of platelet activation after stent implantation. Electropolishing clearly reduced the thrombogenicity of the stents.

Influence of blood-pool contrast media on MR imaging and flow measurements in the presence of pulmonary arterial stents in swine

PURPOSE

To compare the effects of various stents on magnetic resonance (MR) imaging flow volume measurements and to determine the value of a blood-pool MR imaging contrast medium in assessment of vascular stents.

MATERIALS AND METHODS

In 11 pigs, six nitinol stents (Memotherm), four platinum stents (NuMed), and one elgiloy stent (Wallstent) were placed in the main pulmonary artery under x-ray fluoroscopic guidance. MR imaging was performed 3 months after stent placement before and after injection of NC100150 contrast medium. Blood flow volumes were assessed with velocity-encoded cine MR imaging through and next to the stent. The signal-to-noise ratio and width of susceptibility artifacts of the stents also were determined. Measurements were analyzed with the paired Student t test and Bland-Altman test, where appropriate.

RESULTS

Blood flow volumes measured through the nitinol and platinum stents disclosed no significant difference between velocity-encoded cine MR imaging measurements through and next to the stent. On cine MR images, small susceptibility artifacts were observed around the nitinol and platinum stents. Signal-to-noise ratio in the stent lumen was reduced in nitinol and platinum stents when compared with that next to the stent. The elgiloy stent produced severe susceptibility artifacts, making measurement of flow volumes impossible. NC100150 injection caused no significant effect on flow volume measurements. It improved the signal-to-noise ratio of the pulmonary arterial lumen outside and, to a lesser extent, inside the stent.

CONCLUSION

Assessment of morphology and flow volumes through nitinol and platinum stents is feasible with MR imaging. Blood-pool contrast media provide persistent signal enhancement in the pulmonary artery and, to a lesser extent, in the lumina of nitinol and platinum stents.

Development of high-performance stent: gelatinous photogel-coated stent that permits drug delivery and gene transfer

Hydrogel-coated metallic stents may provide supplementary functions such as local drug delivery and gene transfer in addition to mechanical dilation function. To this end, we used a photoreactive material consisting of gelatin macromer (multiple styrene-derivatized gelatin) and carboxylated camphorquinone (photo-initiator). A few minutes of visible light irradiation of a stent after dip-coating of an aqueous solution of the photoreactive material resulted in the formation of a homogeneously crosslinked gelatinous layer on the entire exterior surface of the stent. As the metal stent, gold stents under development were used. Rhodamine-conjugated albumin as a model drug or adenoviral vector expressing bacterial beta-galactosidase (AdLacZ) as a model gene were photo-immobilized in the gelatinous gel layer. In vitro experiments using hybrid tubular tissue, which is a self-shrinkaged, vascular smooth muscle cell-incorporated type-I collagen gel, as a vascular model, showed that the immobilized dye-derivatized albumin was released on and permeated into tissues, as observed by confocal laser microscopy, and that the cells transfected with immobilized AdLacZ produced beta-galactosidase up to almost 3 weeks, as observed by x-gal staining. In preliminary in vivo experiments these drug- or adenovirus-immobilized stents were implanted in rabbit common carotid arteries. Within 3 weeks of implantation, drug permeation and gene expression in the vascular tissues were observed, indicating that the gelatinous photogel effectively serves as a matrix or coating for a bioactive stent,which permits drug release as well as gene transfer. This intraluminal approach has the potential to realize drug and gene therapy in atherosclerotic plaque.

Comparison of direct coronary stenting with and without balloon predilatation in patients with stable angina pectoris. BET (Benefit Evaluation of Direct Coronary Stenting) Study Group

The purpose of this study was to compare the effects of stent placement with and without balloon predilatation on duration of the procedure, reduction of procedure-related costs, and clinical outcomes. Although preliminary trials of direct coronary stenting have demonstrated promising results, the lack of randomized studies with long-term follow-up has limited the critical evaluation of the role of direct stenting in the treatment of obstructive coronary artery disease. Between January and September 1999, 338 patients were randomly assigned to either direct stent implantation (DS+; 173 patients) or standard stent implantation with balloon predilatation (DS-; 165 patients). Baseline clinical and angiographic characteristics were similar in the 2 groups. Procedural success was achieved in 98.3% of patients assigned to DS+ and 97.5% of patients assigned to DS- (p = NS), with a crossover rate of 13.9%. Compared with DS-, DS+ conferred a dramatic reduction in procedure-related cost ($956.4 +/- $352.2 vs $1,164.6 +/- $383.9, p <0.0001) and duration of the procedure (424.2 +/- 412.1 vs 634.5 +/- 390.1 seconds, p < 0.0001). At 6-month follow-up, the incidence of major adverse cardiac events including death, angina pectoris, myocardial infarction, congestive heart failure, repeat angioplasty, or coronary artery bypass graft surgery was 5.3% in DS+ and 11.4% in DS- (p = NS). Multivariate analysis demonstrated that major adverse cardiac events rates were related to stent length of 10 mm (relative risk [RR] 3.25, 95% confidence intervals [CI] 1.36 to 7.78; p = 0.008), stent diameter of 3 mm (RR 2.69, 95% CI 1.03 to 7.06; p = 0.043), and complex lesion type C (RR 2.83, 95% CI 1.02 to 7.85; p = 0.045). Thus, in selected patients, this prospective randomized study shows the feasibility of DS+ with reduction in procedural cost and length, and without an increase in in-hospital clinical events and major adverse cardiac events at 6-month follow-up.

Intravascular and intracardiac stents used in congenital heart disease

Intravascular or intracardiac stenoses occur in many forms of congenital heart disease or after attempted surgical repair. Although balloon dilation is one option for management, restenosis can occur due to elastic recoil immediately after the procedure. To address to such stenotic lesions, many reports support implanting endovascular stents to provide a framework for vessel expansion. Both balloon-expandable fixed tubular mesh stainless steel devices, and self-expandable stents have had an extensive clinical application. In pediatric patients, stents are used for a variety of stenoses, such as systemic venous obstruction pathways (eg, Mustard, Fontan baffle, or bidirectional cavopulmonary connections), pulmonary artery, right ventricular to pulmonary conduits, aortic coarctation, the arterial duct, aorticopulmonary collaterals, or postoperative systemic to pulmonary shunts. Because of improvements in device profile, implantation rates have increased. Complications such as stent fracture, migration, aneurysm formation, and in-stent restenosis occur but only rarely. This latter event may be because of intimal hyperplasia and/or continued vessel (and patient) growth related to the stent diameter. As such, some instances require redilation to manage the acquired lesion. Stent application has importantly altered management algorithms in congenital heart disease.

MR imaging in the presence of vascular stents: A systematic assessment of artifacts for various stent orientations, sequence types, and field strengths

A systematic evaluation of the potential quality of magnetic resonance images recorded in the presence of metallic stents was performed on a low-field open imager operating at 0.2 T and on a high-field closed unit operating at 1.0 T. Eight different stent types were examined by two-dimensional gradient-echo sequences with echo times of 4 and 10 msec and by a fast spin-echo technique. In addition, a three-dimensional gradient-echo sequence was applied with an echo time of 2.4 msec. A set of sequence and slice parameters was used on both scanners. Thus, artifacts due to susceptibility effects depending on the magnetic field strength could be distinguished from radiofrequency shielding effects in the lumen of the stents (independent of the field strength). Nine different orthogonal orientations of the stent axis and the image (in terms of slice, read, and phase-encoding direction) were tested, and the artifacts (extension of signal void and visibility of the lumen) were compared. The optimal strategy for visualization of vascular and perivascular regions outside the stents was fast spin-echo imaging with the stent axis and read direction parallel to the static field. Susceptibility-induced signal void in gradient-echo images was minimal using the three-dimensional approach. Increased transmitter amplitudes above usual values provided clearly improved insight in the lumen using gradient-echo sequences.

Physical properties of endovascular stents: an experimental comparison

PURPOSE

Different endovascular stent types (AVE Bridge, AVE Bridge X, Memotherm, Palmaz Large, Palmaz Medium, Palmaz-Schatz Long-Medium, Perflex, S.MA.R.T., Symphony, and Wall-stent) of 4 cm length and 8 mm diameter were subjected to standardized physical tests.

MATERIALS AND METHODS

The metal mass of each stent was assessed by weighing. The balloon-expandable stents were pneumatically tested for hoop strength. In self-expanding stents, radial resistive force and chronic outward force were determined with use of a loop test. Stent delivery system pushability was assessed in a crossover model. Stent radiopacity was analyzed quantitatively.

RESULTS

The hoop strength of the balloon-expandable stents ranged from 15.8 N/cm (Perflex) to 28.9 N/cm (AVE Bridge X). The stent weight increased with greater hoop strength (Perflex, 0.046 g/cm vs. AVE Bridge X, 0.061 g(cm). The self-expanding stents had a radial resistive force between 0.39 N/cm (Wallstent) and 1.7 N/cm (Smart). The flexible balloon-expandable stents showed pushability values between 0.13/N (AVE Bridge) and 0.20/N (Perflex). The self-expanding stents had flexibilities between 0.13/N (Memotherm) and 0.24/N (Symphony). Radiopacity assessed with use of a phantom simulating the iliac region ranged from 92 (Palmaz Large) to 115 (AVE Bridge) on a 256-point gray scale (0 = black, 256 = white).

CONCLUSIONS

There is no stent with ideal physical properties. However, depending on the characteristics of the arterial lesion to be treated, the most appropriate stent can be chosen.

Coronary stenting without predilatation (SWOP): applicable technique in everyday practice

To evaluate the feasibility of stenting without predilatation, we registered all interventional procedures over a 6-month period. Six hundred patients were registered, and 684 lesions were treated. Interventions were divided into four groups: stenting without predilatation (SWOP), 221 lesions (32.4%); primary stenting with predilatation (PDS), 161 lesions (23.5%); provisional stenting (PRS), 131 lesions (19.2%); and plain-old balloon angioplasty (POBA), 171 lesions (25%). Interventional strategy was at the discretion of the operator based on few simple angiographic criteria and his clinical judgment. Procedural success was similar in all stent groups. We conclude that when primary stenting is planned, about 60% of lesions can be treated by SWOP effectively with excellent procedural results and considerable cost saving.

Coronary stent deployment without predilation in acute myocardial infarction: a feasible, safe, and effective technique

Direct percutaneous transcatheter revascularization (PTCR) is becoming an acceptable therapy for acute myocardial infarction (AMI). Stenting in the setting of AMI, once considered contraindicated, is emerging as a suitable option in this situation. Coronary stenting without predilation (SWOP) may potentially shorten the procedure and radiation time, reduce costs, and decrease procedural complications such as coronary dissection and distal embolization. It is expected to cause less vascular injury, with a reduction in the rate of in-stent restenosis. In this preliminary study the authors evaluated the feasibility of the SWOP procedure in 22 selected patients with AMI. Indications for catheter-based myocardial reperfusion were the following: extensive anterior wall MI (68%), inferior wall and right ventricular MI (23%), and inferior wall MI with contraindication for thrombolytic therapy (9%). Patients with cardiogenic shock or with contraindications for aspirin or ticlopidine were excluded. SWOP was successful in 21 attempts (95%), and final procedural success was achieved in all. Proximal or distal dissections were seen in three cases and were treated by additional three stents. Thrombolysis in myocardial infarction (TIMI) flow 3 was restored in all patients. There were no distal embolizations, side branch occlusions, coronary perforations, procedure-related emergency bypass operations, or deaths. It is concluded that in selected patients with AMI, coronary artery stenting without predilation is feasible and safe and does not introduce additional risk to the patients.

Effectiveness of coronary stent deployment without predilation

The feasibility of coronary stenting without predilation is demonstrated in 240 patients. In all, 249 stents were placed. Primary implantation was successful in 93% of cases. In 17 lesions the stents could not be advanced through the stenotic lesion. The unexpanded stents were removed through the guiding catheter, and stenting was performed after prediction. Minor complications (side branch compromise and intimal dissection), which were successfully treated, occurred in 26 patients (10.6%).

Polypyrrole-heparin composites as stimulus-responsive substrates for endothelial cell growth

Heparin is a potent anticoagulant which can be immobilized on biomaterial surfaces to increase their hemocompatability. In the present work, we have electrochemically synthesized composites comprising heparin and the electrically conducting polymer polypyrrole. The incorporation and exposure of heparin were controlled by varying key conditions of polymer synthesis (i.e., applied current and synthesis time). The resulting composite polymers were electroactive after synthesis and the amount of heparin exposed in the polymer could be increased (up to threefold) by switching the polymers from their oxidized to reduced states. Polymer reduction was achieved by either application of negative potentials (-0.4 to -0.7 V for 90 s) or exposure to aqueous reductant (0.1M sodium dithionite for 30 min). Heparin-polypyrrole composites remained stable after autoclaving, displaying no significant loss of electroactivity, and had a shelf life of at least 2 years postautoclaving. Finally, the composites were found to be excellent substrates for the growth of human endothelial cells.

Coronary stent deployment without predilation: prevention of complications of venous graft angioplasty

Saphenous vein graft stenting without predilation may potentially decrease procedural complications such as distal embolization and no-reflow phenomenon. In this report the authors describe the deployment of stents (three Wallstents, one Palmaz-Schatz, one Multilink, and one NIR) without predilation in five patients with unstable angina pectoris due to high-grade stenosis in old saphenous vein grafts. Stent deployment was successful in all patients without procedure-related complications. Stenting without predilation appears to be feasible in old bypass grafts with significant stenosis. The potential of this new stenting technique to reduce the risk of stenting complications should be tested by a randomized trial.

Recent progress in coronary interventions--assessment by quantitative coronary angiography

Coronary balloon angioplasty is now well accepted as an effective therapy for patients with significant coronary artery stenosis. However, a number of deficiencies, including short-term complications, long-term restenosis, and limited application to complex morphologic lesions, restrict the widespread use of this technique. The precise lesion measurement provided by quantitative coronary angiography and intracoronary ultrasonography is a prerequisite for the optimization of balloon dilation or stent implantation. The short-term outcome may be improved by stent implantation, as this can prevent acute closure by acting as a scaffold for the disrupted vessel wall. The indications for percutaneous revascularization have been extended to chronic total occlusion by using a special guidewire, a laser wire and a coronary stent. Local drug delivery techniques to distribute agents to target revascularization sites may play a role in reducing the restenosis rate. Although the limitations of balloon angioplasty have led to the introduction of new devices, it remains to be seen whether these new devices can demonstrate, in a scientific manner, their safety, feasibility and superiority over conventional balloon angioplasty. Percutaneous coronary revascularization therapy may be an acceptable alternative to coronary bypass surgery in the future. However, to confirm this, a large multicenter randomized study is necessary to compare new percutaneous coronary interventional devices with bypass surgery. Additionally, further studies are required to demonstrate the most effective device for treating specific lesions in each individual patient.