A meta-analysis of clinical trials of paclitaxel- and sirolimus-eluting stents in patients with obstructive coronary artery disease

A Study of PLA Thin Film on SS 316L Coronary Stents Using a Dip Coating Technique

The dip coating process is one of the recognized techniques used to generate polymeric coatings on stents in an easy and low-cost way. However, there is a lack of information about the influence of the process parameters of this technique on complex geometries such as stents. This paper studies the dip coating process parameters used to provide a uniform coating of PLA with a 4-10 µm thickness. A stainless-steel tube (AISI 316L) was laser-cut, electropolished, and dip-coated in a polylactic acid (PLA) solution whilst changing the process parameters. The samples were characterized to examine the coating's uniformity, thickness, surface roughness, weight, and chemical composition. FTIR and Raman investigations indicated the presence of PLA on the stent's surface, the chemical stability of PLA during the coating process, and the absence of residual chloroform in the coatings. Additionally, the water contact angle was measured to determine the hydrophilicity of the coating. Our results indicate that, when using entry and withdrawal speeds of 500 mm min-1 and a 15 s immersion time, a uniform coating thickness was achieved throughout the tube and in the stent with an average thickness of 7.8 µm.

Farrerol maintains the contractile phenotype of VSMCs via inactivating the extracellular signal-regulated protein kinase 1/2 and p38 mitogen-activated protein kinase signaling

Farrerol, a dihydroflavone isolated from Rhododendron dauricum L., can inhibit vascular smooth muscle cell (VSMC) proliferation and exert a protective effect on H₂O₂-induced vascular endothelial cells injury. In this study, we investigated the effects of farrerol on VSMC phenotypic modulation and balloon injury-induced vascular neointimal formation and explored the underlying mechanisms. Serum-starved rat thoracic aorta SMCs (RASMCs) were first pretreated with farrerol (3, 10, and 30 μM, respectively), U0126 (a MEK kinase inhibitor), and SB203580 (a p38 kinase inhibitor), and followed by treatment with serum (10% FBS). The expression of several VSMC-specific markers, including α-SMA, SM22α, and OPN, were analyzed by western blot. Phosphorylation of extracellular signal-regulated protein kinase 1/2 (ERK 1/2) and p38 mitogen-activated protein kinase (MAPK) was also investigated. Farrerol inhibited the serum-induced transition of RASMCs from the contractile to the synthetic phenotype, and this was associated with a decrease in α-SMA and SM22α expression, and an increase in OPN expression. Farrerol also inhibited serum-induced phosphorylation of ERK1/2 and p38MAPK in RASMCs. Moreover, U0126 and SB203580 both inhibited the serum-induced phenotypic transition of RASMCs. These findings indicate that farrerol can maintain the contractile phenotype of VSMCs partly via inactivating the ERK1/2 and p38 MAPK signaling pathways. Using a rat model of carotid artery balloon injury, inhibition of VSMC phenotypic transition and suppression of neointimal formation were confirmed in vivo following the perivascular application of farrerol. Our results suggested that farrerol could be a promising lead compound for the treatment of vascular proliferative diseases.

Polymeric coating of surface modified nitinol stent with POSS-nanocomposite polymer

Stent angioplasty is a successful treatment for arterial occlusion, particularly in coronary artery disease. The clinical communities were enthusiastic about the use of drug-eluting stents; however, these stents have a tendency to be a contributory factor towards late stage thrombosis, leading to mortality in a significant number of patients per year. This work presents an innovative approach in self-expanding coronary stents preparation. We developed a new nanocomposite polymer based on polyhedral oligomeric silsesquioxanes (POSS) and poly(carbonate-urea)urethane (PCU), which is an antithrombogenic and a non-biodegradable polymer with in situ endothelialization properties. The aim of this work is to coat a NiTi stent alloy with POSS-PCU. In prolonged applications in the human body, the corrosion of the NiTi alloy can result in the release of deleterious ions which leads to unwanted biological reactions. Coating the nitinol (NiTi) surface with POSS-PCU can enhance surface resistance and improve biocompatibility. Electrohydrodynamic spraying was used as the polymer deposition process and thus a few experiments were carried out to compare this process with casting. Prior to deposition the NiTi has been surface modified. The peel strength of the deposit was studied before and after degradation of the coating. It is shown that the surface modification enhances the peel strength by 300%. It is also indicated how the adhesion strength of the POSS-PCU coating changes post-exposure to physiological solutions comprised of hydrolytic, oxidative, peroxidative and biological media. This part of the study shows that the modified NiTi presents far greater resistance to decay in peel strength compared to the non-modified NiTi.

Appropriate use of drug-eluting stents: balancing the reduction in restenosis with the concern of late thrombosis

Restenosis is a serious occurrence that can lead not only to recurrent angina and repeat revascularisation but also to acute coronary syndromes. Drug-eluting stents revolutionised interventional cardiology owing to their pronounced ability to reduce restenosis compared with bare-metal stents. Attention has now shifted to safety of these devices because of evidence suggesting an association with late stent thrombosis. Findings of randomised clinical trials have not shown that drug-eluting stents result in excess mortality after 4-5 years of follow-up. Current recommendations are that individuals with a drug-eluting stent should receive at least 12 months of uninterrupted dual antiplatelet treatment; patients must understand the importance of this long-term regimen. Patients' assessment should focus on bleeding abnormalities, pre-existing disorders that need anticoagulation treatment, and possible future surgical procedures, since these factors could all contraindicate use of drug-eluting stents. Many people will do well with a bare-metal stent, whereas for individuals with a high likelihood of restenosis and late thrombosis, medical management or surgical revascularisation might be preferred options.

Are "treatment" bare metal stents superior to "control" bare metal stents? A meta-analytic approach

BACKGROUND

It has been suggested that the benefits of drug-eluting stents compared to bare metal stents (BMS) have been overestimated in part because target lesion/vessel revascularization (TLR/TVR) rates in the BMS control group of these trials were spuriously high.

METHODS

We used meta-analytic techniques to systematically compare clinical event rates among patients treated with BMS in trials where BMS were the experimental (BMS(experimental)) rather than the control (BMS(control)) intervention. MEDLINE searches were performed to identify eligible randomized trials comparing either drug-eluting stents with BMS(control) or BMS(experimental) with balloon angioplasty in patients with nonacute coronary artery disease. Trial characteristics and 6- to 12-month rates for death, myocardial infarction, TLR/TVR, and major adverse cardiac events were extracted and assessed.

RESULTS

Eligible trials yielded 50 BMS cohorts: 19 in the BMS(control) group (4046 patients) and 31 in the BMS(experimental) group (5068 patients). Summary death and infarction rates did not differ between groups. The summary TLR/TVR rates were 16.2% (95% CI 13.5-19.3) versus 13.8% (95% CI 12.0-15.7) in BMS(control) versus BMS(experimental) groups, respectively (P = .15). Among 39 BMS cohorts with < or = 250 patients, TLR/TVR rates were significantly higher in BMS(control) versus BMS(experimental) groups (18.9% [95% CI 16.0-22.2] vs 13.7% [95% CI 11.5-16.3], P = .01). There were no between-group differences among larger BMS cohorts (P = .98).

CONCLUSIONS

Although overall clinical event rates did not differ in the BMS(control) and the BMS(experimental) groups, a higher rate of TVR/TLR was seen in the BMS(control) group among smaller trials.

A meta-analysis of trials comparing Cypher and Taxus stents in patients with obstructive coronary artery disease

AIMS

Drug-eluting stents have been shown to be superior to bare metal stents in reducing restenosis rates. Recently head-to-head trials comparing sirolimus-eluting stents and paclitaxel-eluting stents have been reported. An early combined analysis of these comparative trials is needed. The present meta-analysis was carried out to compare the effects of sirolimus-eluting stents with paclitaxel-eluting stents on the restenosis rate, major adverse cardiac events and late loss of arterial lumen diameter in patients with obstructive coronary artery disease.

METHODS

Electronic (Medline, Cochrane and Embase) and manual search (Index Medicus and cross references of retrieved articles) were carried out for all the relevant articles up till March 2005. Only randomized trials with adequate data for calculation of odds ratio for restenosis rates and major adverse cardiac events using the method of DerSimonian & Laird and standardized mean difference for late loss of arterial lumen diameter were included.

RESULTS

Four studies were found to be eligible for inclusion in the meta-analysis. Restenosis rate and late loss of arterial lumen diameter were significantly reduced by sirolimus-eluting stents as compared with paclitaxel-eluting stents (OR 0.598, 95% CI 0.400, 0.893, pooled mean difference -0.414, 95% CI -0.492, 0.336, respectively). The incidence of major adverse cardiac events was less with sirolimus-eluting stents as compared with paclitaxel-eluting stents (OR 0.727, 95% CI 0.518-1.018) but the results were not statistically significant.

CONCLUSIONS

Sirolimus-eluting stents are superior to paclitaxel-eluting stents in decreasing restenosis rate and late loss of arterial lumen diameter. However, no statistically significant difference in major adverse cardiac events was noted between the two stents.

Cypher versus Taxus: the stent war

Cypher (sirolimus-eluting stent) and Taxus (paclitaxel-eluting stent) have been approved for use in percutaneous coronary intervention. Both of the stents have shown superiority over bare metal stents in reducing major adverse cardiac events, restenosis rates and target vessel revascularisation. Results of clinical trials with head-to-head comparison of Taxus and Cypher stents in patients with obstructive coronary artery diseases have recently been reported. This review compares the performance of Cypher and Taxus stents as noted in observational studies and clinical trials in various types of coronary artery lesions.

Efficacy and Safety of Drug-Eluting Stents: Current Best Available Evidence

The development of drug-eluting coronary stents has proved to be a quantum advance in interventional cardiology, rivaling the impact of stenting itself. Drug-eluting coronary stents deliver effective local concentrations of antiproliferative drugs (thus avoiding systemic toxicities), without substantially modifying the technique of percutaneous coronary intervention. Studies involving several different stent platforms and antiproliferative drug coatings have recently demonstrated dramatic reductions in restenosis rates, compared to conventional bare metal stents. Although the clinical benefits of drug-eluting stents are increasingly evident, important concerns about their long-term safety and costs have been raised. Furthermore, drug-eluting stents are being claimed to replace coronary artery bypass surgery in the near future. This review article evaluates the current best available evidence on the efficacy and safety of drug-eluting stents with a focus on the impact of this "revolutionary" new technology on the practice of coronary artery bypass surgery.

Neointima Inhibition: Comparison of Effectiveness of Non–Stent-based Local Drug Delivery and a Drug-eluting Stent in Porcine Coronary Arteries

PURPOSE

To compare the inhibition of neointimal proliferation by using non-stent-based local drug delivery and a drug-eluting stent in porcine coronary arteries.

MATERIALS AND METHODS

Experiments were conducted with permission of the animal protection committee of the local government. Paclitaxel was either dissolved in a nonionic contrast medium or coated on balloons. Stents were crimped on the coated balloons. Effectiveness was tested in 22 pigs. Two coronary stents were placed in each pig, and slight overstretch was applied. The animals were treated as follows: group A (control group), uncoated balloons, bare stents, and "plain" contrast medium; group B, same treatment as group A, but with paclitaxel in the contrast medium; group C, paclitaxel-coated balloons, with premounted bare stents and plain contrast medium; and group D, sirolimus-eluting stents, noncoated balloons, and plain contrast medium. Stenosis was assessed 4 weeks later at angiography and histomorphometry. For exploratory purposes, continuous variables of quantitative coronary angiography and histomorphometry were compared by using analysis of variance.

RESULTS

Results at follow-up angiography indicated a mean of 1.00 mm +/- 0.18 (standard deviation) lumen diameter loss in the control group and 0.14 mm +/- 0.18 loss in the group treated with the paclitaxel-coated balloon (group C; P < .001). Findings at histomorphometry confirmed the effectiveness of drug delivery, with the most impressive inhibition of neointimal proliferation from coated balloons-the neointimal area was 2.4 mm2 +/- 0.3 (P < .01 vs all other groups), compared with 5.2 mm2 +/- 0.3 in group A (control group), 4.3 mm2 +/- 0.3 in group B, and 3.8 mm2 +/- 0.3 in group D.

CONCLUSION

In spite of the short intima contact time, paclitaxel coated on the balloon inhibits neointimal formation in the porcine model of coronary stent placement.

Drug-Eluting Stents and the Future of Coronary Artery Bypass Surgery: Facts and Fiction

The treatment of patients with coronary artery disease continues to evolve. Recent, exciting data on the use of drug-eluting stents in diseased coronary vessels has generated immense enthusiasm within the interventional community leading to claims that "drug-eluting stents will put bypass surgeons out of business." However, despite promising short-term and midterm outcomes of this revolutionary new technology, valid concerns regarding long-term safety and efficacy of drug-eluting stents persist. This review article evaluates current status of drug-eluting stents with special emphasis on real and potential drawbacks of this emerging percutaneous coronary interventional modality and its impact on the practice of coronary artery bypass surgery.

Paclitaxel-eluting stents in coronary artery disease

PURPOSE

Clinical information regarding paclitaxel-eluting coronary artery stents is reviewed.

SUMMARY

Restenosis is a significant complication of percutaneous coronary intervention. Coronary artery stenting has reduced restenosis compared with traditional balloon angioplasty, although restenosis still occurs with bare-metal coronary artery stents. The pathogenesis of in-stent restenosis is believed to involve smooth-muscle-cell proliferation and migration in response to vessel injury. A neointimal layer of extracellular matrix and collagen forms, which may impinge on the vessel lumen. Paclitaxel inhibits vascular smooth-muscle-cell proliferation and reduces neointimal mass. Local delivery of paclitaxel through a coronary stent has been shown to reduce restenosis rates and percent diameter stenosis and to produce other angiographic benefits compared with bare-metal stents. Fewer major adverse coronary events are seen with paclitaxel-eluting stents, predominantly because of a reduction in the need for target-vessel revascularization with minimal impact on rates of mortality and myocardial infarction (MI). The Taxus Express(2) stent, the only approved paclitaxel-eluting stent in the United States, costs about three times as much as a bare-metal stent. Cost-effectiveness analyses are needed to determine if the Taxus stent is cost-effective in clinical practice.

CONCLUSION

Paclitaxel-eluting stents reduce the rates of restenosis and target-vessel revascularization compared with bare-metal stents and have comparable effects on mortality and MI rates.

Rapamycin-coated expanded polytetrafluoroethylene bypass grafts exhibit decreased anastomotic neointimal hyperplasia in a porcine model

OBJECTIVE

We tested the hypothesis that rapamycin coated onto, and eluted from, expanded polytetrafluoroethylene (ePTFE) grafts would diminish neointimal hyperplasia in a porcine model.

METHODS

Rapamycin (also called sirolimus) was coated onto the luminal surface of 6-mm-internal-diameter thin-walled ePTFE grafts by using an adhesive polymer that allows timed release of the drug. An adhesive polymer that allows timed release of rapamycin from ePTFE was developed with commercially available chemicals and applied on 6-mm ePTFE grafts. Graft integrity was characterized by scanning electron microscopy, and rapamycin levels were quantified by using high-performance liquid chromatography. Twenty-two mongrel pigs were randomized into three groups: untreated ePTFE (n = 6), adhesive-only coated ePTFE (n = 6), or adhesive- and rapamycin-coated ePTFE (n = 10). End-to-side unilateral aortoiliac bypasses were performed by using 6-mm-internal-diameter ePTFE grafts and standardized anastomotic lengths. Unilateral end-to-side aortoiliac ePTFE grafts (6-mm internal diameter) were inserted by using polypropylene sutures, 6-0 proximally and 7-0 distally; all anastomoses were 12 mm long. All animals received aspirin (325 mg orally) daily. All animals were given oral aspirin (325 mg) daily beginning on the day before surgery. At 28 days, the animals were killed, and the grafts were explanted in continuity with the adjacent aortic cuff and the outflow iliac artery. Variables compared between groups included graft patency, distal anastomotic length and cross-sectional narrowing, and intimal thickness at the arterial-graft junction indexed to the adjacent graft thickness. Microscopic analysis was performed with hematoxylin and eosin and Masson trichrome stains on paraffin sections. A pathologist blinded to experimental groups graded sections for collagen deposition, neointima formation, inflammatory cellular infiltrates, medial necrosis, and aneurysmal degeneration.

RESULTS

All animals survived until they were killed without clinical evidence of limb ischemia or graft infection. Preplanned t tests in the context of one-way analysis of variance showed no difference in outcome measures between the untreated ePTFE and adhesive-only coated ePTFE groups; therefore, they were combined in further comparisons with the adhesive- and rapamycin-coated ePTFE group. The Rapamycine eluting expanded polytetrafluoroethylene group had longer anastomoses (85.6% vs 60.6% of the initial anastomotic length maintained; P < .0001) and less cross-sectional narrowing in the outflow graft (16.2% vs 28.5%; P = .0007) when compared with the other two groups by using two-tailed Student t tests. There was no evidence of medial necrosis or aneurysmal degeneration. All patent grafts had complete endothelialization on hematoxylin and eosin sections. Rapamycin was detectable and quantifiable in the arterial wall at 28 days after implantation.

CONCLUSIONS

Rapamycin can be coated onto and eluted from ePTFE by using a nonionic polymer and a simple coating technique. At 4 weeks after implantation, the rapamycin-eluting ePTFE grafts demonstrate gross, pathologic, and morphometric features of diminished neointimal hyperplasia when compared with non-drug-eluting ePTFE. Four weeks after implantation in a porcine model, rapamycin-eluting ePTFE grafts demonstrated gross, pathologic, and morphometric features of diminished neointimal hyperplasia when compared with untreated and adhesive-only coated ePTFE grafts.

CLINICAL RELEVANCE

Rapamycin-eluting ePTFE grafts decrease neointimal hyperplasia in a porcine model. Further studies are needed to evaluate whether patency will be improved. Rapamycin-eluting ePTFE grafts may allow the use of prosthetic grafts in situations in which autologous vein is unavailable and in which neointimal hyperplasia is pronounced, such as in small-diameter (<6-mm) vessels typical of infrapopliteal interventions.