Non–Polymer-Based Paclitaxel-Coated Coronary Stents for the Treatment of Patients With De Novo Coronary Lesions

Polymer-free stents for percutaneous coronary intervention in diabetic patients: a systematic review and meta-analysis

Aim: To compare the efficacy of polymer-free drug-eluting stents (PF-DES) versus other stents in diabetic patients with coronary artery disease undergoing percutaneous coronary interventions. Materials & methods: A systematic review and meta-analysis were performed to identify pertinent randomized controlled trials. The primary end point was the occurrence of target lesion failure. Results: Eight randomized controlled trials were included for a total of 4854 subjects. The PF-DES group experienced a trend in favor of a lower rate of target lesion failure (Incidence rate ratio = 0.91; p = 0.11) and a significantly lower rate of cardiac mortality, as compared with the control group (Incidence rate ratio = 0.82; p = 0.04). However, statistical significance was lost if bare-metal stent patients were excluded and a trend in favor of the PF-DES strategy was reported only for cardiac mortality. Conclusion: PF-DES could be a valuable strategy in diabetic patients with coronary artery disease undergoing percutaneous coronary interventions.

Study on Mechanical Properties of Nanopores in CoCrFeMnNi High-Entropy Alloy Used as Drug-Eluting Stent

The CoCrFeMnNi high-entropy alloy is commonly used for vascular stents due to its excellent mechanical support and ductility. However, as high-entropy alloy stents can cause inflammation in the blood vessels, leading to their re-narrowing, drug-eluting stents have been developed. These stents have nanopores on their surfaces that can carry drug particles to inhibit inflammation and effectively prevent re-narrowing of the blood vessels. To optimize the mechanical properties and drug-carrying capacity of high-entropy alloy stents, a high-entropy alloy system with different wide and deep square-shaped nanopore distributions is created using molecular dynamics. The mechanical characteristics and dislocation evolution mechanism of different nanopore high-entropy alloy systems under tensile stress were studied. The results showed that the CoCrFeMnNi high-entropy alloy with a rational nanopore distribution can effectively maintain the mechanical support required for a vascular stent. This research provides a new direction for the manufacturing process of nanopores on the surfaces of high-entropy alloy stents.

Early vascular healing after implantation of the polymer-free biolimus-eluting stent or the ultrathin strut biodegradable polymer sirolimus-eluting stent in patients with ST-segment elevation myocardial infarction

OBJECTIVE

To evaluate the difference in early vascular healing between the ultrathin-strut biodegradable-polymer sirolimus-eluting Orsiro stent (O-SES) and the polymer-free biolimus-A9-eluting BioFreedom stent (BF-BES), assessed with optical coherence tomography (OCT) after primary percutaneous coronary intervention (PCI) in patients with ST-segment elevation myocardial infarctions (STEMIs).

METHODS

Eighty patients with STEMI who underwent primary PCI were randomly allocated 1:1 to treatment with BF-BES or O-SES. OCT was acquired after PCI and at 1-month follow-up. The primary endpoint was 1-month OCT-assessed vascular healing index based on the presence of uncovered and malapposed stent struts and intraluminal filling defects where low vascular healing index indicated favorable vascular healing.

RESULTS

At 1-month, the vascular healing index was similar in O-SES 11.5 [interquartile range (IQR) 9.5-17.5], compared to BF-BES 11.5 (IQR 7.1-12.5; P = 0.14). Percentage of uncovered struts [O-SES 31.5% (IQR 20.7-41.9), P = 0.43] vs. BF-BES 27.8% (IQR 19.4-41.9; P = 0.44), and median volume of neointimal hyperplasia [O-SES 4.9 mm3 (IQR 1.4-13.1) vs. BF-BES 7.1 mm3 (IQR 2.8-17.0), P = 0.18] did not differ significantly between the two stent groups. Complete coverage was not observed in any of the stents. The percentages of stents with malapposition did not differ significantly (O-SES 87.1% vs. BF-BES 71.4%, P = 0.14) whereas percentage of malapposed struts [O-SES 3.5% (IQR 0.8-5.5) vs. BF-BES 0.8% (IQR 0.0-1.8), P = 0.003] was lower in the BF-BES group.

CONCLUSION

In patients with STEMI, the drug-coated BF-BES and the thin strut O-SES had similar vascular healing index at 1-month. However, the thin O-SES struts were more often malapposed.

Randomized Comparison of the Polymer-Free Biolimus-Coated BioFreedom Stent With the Ultrathin Strut Biodegradable Polymer Sirolimus-Eluting Orsiro Stent in an All-Comers Population Treated With Percutaneous Coronary Intervention

Background:

In patients with increased bleeding risk, the biolimus A9-coated BioFreedom stent, a stainless steel drug-coated stent free from polymer, has shown superiority compared with a bare-metal stent. The aim of this study was to investigate whether the BioFreedom stent is noninferior to a modern ultrathin strut biodegradable polymer cobalt-chromium sirolimus-eluting Orsiro stent in an all-comers patient population treated with percutaneous coronary intervention.

Methods:

The SORT OUT IX trial (Scandinavian Organization for Randomized Trials With Clinical Outcome IX), was a large-scale, registry-based, randomized, multicenter, single-blind, 2-arm, noninferiority trial. The primary end point, major adverse cardiovascular events, was defined as the composite of cardiac death, myocardial infarction not related to any segment other than the target lesion, or target lesion revascularization within 1 year, analyzed by intention-to-treat. The trial was powered to assess noninferiority for major adverse cardiovascular events of the BioFreedom stent compared with the Orsiro stent with a predetermined noninferiority margin of 0.021.

Results:

Between December 14, 2015 and April 21, 2017, 3151 patients were assigned to treatment with the BioFreedom stent (1572 patients, 1966 lesions) or to the Orsiro stent (1579 patients, 1985 lesions). Five patients were lost to follow-up because of emigration (99.9% follow-up rate). Mean age was 66.3±10.9, diabetes mellitus was seen in 19.3% of patients, and 53% of the patients had acute coronary syndromes. At 1 year, intention-to-treat analysis showed that 79 (5.0%) patients, who were assigned the BioFreedom stent, and 59 (3.7%), who were assigned the Orsiro stent, met the primary end point (absolute risk difference 1.29% [upper limit of one-sided 95% CI 2.50%]; P noni nferiority =0.14). Significantly more patients in the BioFreedom stent group had target lesion revascularization than those in the Orsiro stent group (55 [3.5%] vs 20 [1.3%], rate ratio 2.77 [95% CI, 1.66–4.62]; P <0.0001).

Conclusions:

The biolimus A9-coated BioFreedom polymer-free stent did not meet criteria for noninferiority for major adverse cardiovascular events at 12 months when compared with the ultrathin strut biodegradable polymer sirolimus-eluting Orsiro stent in an all-comers population

Registration:

URL: https://www.clinicaltrials.gov ; Unique identifier: NCT02623140.

Recent Advances in Manufacturing Innovative Stents

Cardiovascular diseases are the most distributed cause of death worldwide. Stenting of arteries as a percutaneous transluminal angioplasty procedure became a promising minimally invasive therapy based on re-opening narrowed arteries by stent insertion. In order to improve and optimize this method, many research groups are focusing on designing new or improving existent stents. Since the beginning of the stent development in 1986, starting with bare-metal stents (BMS), these devices have been continuously enhanced by applying new materials, developing stent coatings based on inorganic and organic compounds including drugs, nanoparticles or biological components such as genes and cells, as well as adapting stent designs with different fabrication technologies. Drug eluting stents (DES) have been developed to overcome the main shortcomings of BMS or coated stents. Coatings are mainly applied to control biocompatibility, degradation rate, protein adsorption, and allow adequate endothelialization in order to ensure better clinical outcome of BMS, reducing restenosis and thrombosis. As coating materials (i) organic polymers: polyurethanes, poly(ε-caprolactone), styrene-b-isobutylene-b-styrene, polyhydroxybutyrates, poly(lactide-co-glycolide), and phosphoryl choline; (ii) biological components: vascular endothelial growth factor (VEGF) and anti-CD34 antibody and (iii) inorganic coatings: noble metals, wide class of oxides, nitrides, silicide and carbide, hydroxyapatite, diamond-like carbon, and others are used. DES were developed to reduce the tissue hyperplasia and in-stent restenosis utilizing antiproliferative substances like paclitaxel, limus (siro-, zotaro-, evero-, bio-, amphi-, tacro-limus), ABT-578, tyrphostin AGL-2043, genes, etc. The innovative solutions aim at overcoming the main limitations of the stent technology, such as in-stent restenosis and stent thrombosis, while maintaining the prime requirements on biocompatibility, biodegradability, and mechanical behavior. This paper provides an overview of the existing stent types, their functionality, materials, and manufacturing conditions demonstrating the still huge potential for the development of promising stent solutions.

Polymer-free drug-eluting stents versus permanent polymer drug-eluting stents: An updated meta-analysis

BACKGROUND

Polymer-free drug-eluting stents (PF-DES) have been demonstrated comparable to permanent polymer drug-eluting stents (PP-DES) during long-term follow-up. As a critical component of drug-eluting stents, antiproliferative drugs may be a confounding factor for the results. Thus, we sought to compare the outcomes of these stents during long-term follow-up, especially in consideration of different stent platforms with the same drugs.

METHODS

A systemic search was performed to identify the related randomized controlled trials comparing PF-DES with PP-DES. Primary outcomes included short (≤1 year) and long-term (>1 year) target lesion revascularization (TLR), short-term in-stent late luminal loss (LLL) and diameter stenosis (DS). Subgroup analyses stratified by the different platforms with the same proliferative drugs were conducted in TLR, LLL, and DS. Standardized mean differences (SMDs) and risk ratios (RRs) were estimated using fixed /random effects models RESULTS:: A total of 6927 patients extracted from 12 RCTs were enrolled in the meta-analysis. No differences were observed in clinical outcomes of short-term and long-term overall mortality, myocardial infarction and stent thrombosis and angiographic outcomes of short-term in-stent LLL and DS between PF-DES and PP-DES for patients with coronary artery lesions. Nevertheless, compared with PP-DES coated with the same proliferative drugs, PF-DES had significantly increased risks of in-stent LLL (SMD, 0.49; 95% confidence interval [CI], 0.25-0.72) and DS (SMD, 0.67; 95% CI, 0.27-1.07), and long-term TLR (RR, 1.64; 95% CI 1.13-2.39). There were no significant differences in other outcomes.

CONCLUSIONS

Under the condition of using same antiproliferative drugs (paclitaxel or sirolimus) in different stent systems, PF-DES are associated with the increased risk of restenosis compared to PP-DES.

Polymer-free versus durable polymer drug-eluting stents in patients with coronary artery disease: A meta-analysis

Background

Polymer-free drug-eluting stents (PF-DES) were introduced with the aim of reducing the risk of stent thrombosis associated with durable polymer drug-eluting stents (DP-DES). The comparison of safety and efficacy profiles between these two stent platforms remains unclear.

Materials and methods

We conducted electronic database searches for randomized controlled trials (RCTs) comparing patients treated with either PF-DES or DP-DES. Outcomes included definite or probable stent thrombosis (ST), myocardial infarction (MI), cardiac death, all-cause death, target lesion revascularization (TLR), and target vessel revascularization (TVR). A random-effects model was used to derive risk ratios (RRs) with 95% confidence intervals (CIs). Subgroup analyses based on different variables were also performed. After screening a total of 1026 articles, the present meta-analysis included 13 RCTs comprising 8021 patients.

Results

No significant differences were found for the risks of definite or probable ST (RR, 0.94; 95% CI, 0.62–1.43; P = 0.77), MI (RR, 1.06; 95% CI, 0.85–1.33; P = 0.61), cardiac death (RR, 0.98; 95% CI, 0.80–1.21; P = 0.88), all-cause death (RR, 0.87; 95% CI, 0.76–1.00; P = 0.06), TLR (RR, 1.12; 95% CI, 0.94–1.33; P = 0.22), and TVR (RR, 1.18; 95% CI, 0.87–1.61; P = 0.29). Similarly, no significant differences were found for all outcomes regardless of anti-proliferative drug, except for an increased risk of TLR for polymer-free paclitaxel-eluting stents compared with DP-DES (RR, 2.32, 95% CI, 1.30–4.14; P = 0.005).

Conclusions

Our findings showed that PF-DES and DP-DES confer equivalent safety and efficacy profiles, with similar rates of stent thrombosis.

•

Polymer-free and durable polymer drug-eluting stents confer similar safety and efficacy profiles.

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There were comparable rates of stent thrombosis between the two stent platforms.

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Further trials with greater length of follow-up are warranted to assess long-term safety and efficacy outcomes.

Surface Modification with ECM-Inspired SDF-1α/Laminin-Loaded Nanocoating for Vascular Wound Healing

Surface biomimetic modification with extra-cellular matrix (ECM)-derived biomolecules is an emerging potential method of accelerating the healing of vascular stent lesions. However, insufficient capacity of the constructed biofunctional layer in maintaining its long-term efficiency and preventing thrombus and neointimal hyperplasia continue to be major limitations in clinical application. On the basis of the structure and function of ECM, in this study, we constructed a novel stromal cell-derived factor-1α (SDF-1α)/laminin-loaded nanocoating on the 316L stainless steel (SS) surface to provide improved function in modulation of vascular remodeling. The modified surface was found to control delivery of biomolecules and exhibit promising potential to provide stage-adjusted treatment after injury. An in vitro biocompatibility study suggested that the constructed layer may effectively prevent thrombosis formation by inhibiting platelet adhesion and activation, while accelerating endothelium regeneration by inducing endothelial cell (EC) migration and endothelial progenitor cell (EPC) aggregation. An in vivo animal test further demonstrated that the nanocoating may prevent thrombus and neointimal hyperplasia after implantation for 3 months. Therefore, the ECM-inspired nanocoating described in this study is a promising novel approach for vascular stent surface modification.

Restenosis of the Coronary Arteries: Past, Present, Future Directions

Restenosis is a pathologic response to vascular injury, characterized by neointimal hyperplasia and progressive narrowing of a stented vessel segment. Although advances in stent design have led to a dramatic reduction in the incidence of restenosis, it continues to represent the most common cause of target lesion failure following percutaneous coronary intervention. Efforts to maximize restenosis prevention, through careful consideration of modifiable risk factors and an individualized approach, are critical, as restenosis, once established, can be particularly difficult to treat. Novel approaches are on the horizon that have the potential to alter the natural history of this stubborn disease.

Drug Eluting Stent Technology

The authors discuss the mechanism of action, clinical trial data, and economic impact of both the paclitaxel and sirolimus drug eluting stents (DESs). Both DESs have been approved by the Food and Drug Administration for the treatment of native coronary arteries to prevent in-stent restenosis (ISR), which patients have experienced since the advent of balloon angioplasty and the bare metal stent. In-stent restenosis, which manifests itself as ischemic symptoms in patients, occurs as a result of the healing process after stent implantation. Until now, there has not been an effective method to prevent ISR. The sirolimus and paclitaxel DESs elute agents that act locally by different mechanisms to reduce neointimal hyperplasia, which is primarily responsible for ISR. Both DESs are capable of reducing the rate of ISR. There are certain physical and mechanistic differences between the 2 stents; the stents have not been compared head to head. Currently, they are indicated for uncomplicated native coronary lesions. Further investigation is needed to define their roles in the treatment of more complex lesions.

Polymer-Free Drug-Eluting Stents: An Overview of Coating Strategies and Comparison with Polymer-Coated Drug-Eluting Stents

Clinical evaluations have proven the efficacy of drug-elution stents (DES) in reduction of in-stent restenosis rates as compared to drug-free bare metal stents (BMS). Typically, DES are metal stents that are covered with a polymer film loaded with anti-inflammatory or antiproliferative drugs that are released in a sustained manner. However, although favorable effects of the released drugs have been observed, the polymer coating as such has been associated with several adverse clinical effects, such as late stent thrombosis. Elimination of the polymeric carrier of DES may therefore potentially lead to safer DES. Several technologies have been developed to design polymer-free DES, such as the use of microporous stents and inorganic coatings that can be drug loaded. Several drugs, including sirolimus, tacrolimus, paclitaxel, and probucol have been used in the design of carrier-free stents. Due to the function of the polymeric coating to control the release kinetics of a drug, polymer-free stents are expected to have a faster drug elution rate, which may affect the therapeutic efficacy. However, several polymer-free stents have shown similar efficacy and safety as the first-generation DES, although the superiority of polymer-free DES has not been established in clinical trials.

Controlled Slow-Release Drug-Eluting Stents for the Prevention of Coronary Restenosis: Recent Progress and Future Prospects

Drug-eluting stents (DES) have become more widely used by cardiologists than bare metal stents (BMS) because of their better ability to control restenosis. However, recognized negative events, particularly including delayed or incomplete endothelialization and late stent thrombosis, have caused concerns over the long-term safety of DES. Although stent-based drug delivery can facilitate a drug's release directly to the restenosis site, a burst of drug release can seriously affect the pharmacological action and is a major factor accounting for adverse effects. Therefore, the drug release rate has become an important criterion in evaluating DES. The factors affecting the drug release rate include the drug carrier, drug, coating methods, drug storage, elution direction, coating thickness, pore size in the coating, release conditions (release medium, pH value, temperature), and hemodynamics after the stent implantation. A better understanding of how these factors influence drug release is particularly important for the reasonable use of efficient control strategies for drug release. This review summarizes the factors influencing the drug release from DES and presents strategies for enhancing the control of the drug's release, including the stent design, the application of absorbable stents, the development of new polymers, and the application of nanocarriers and improvements in the coating technology. Therefore, this paper provides a reference for the preparation of novel controlled slow-release DES.

A new polymer-free drug-eluting stent with nanocarriers eluting sirolimus from stent-plus-balloon compared with bare-metal stent and with biolimus A9 eluting stent in porcine coronary arteries

BACKGROUND

Permanent polymers in first generation drug-eluting stent (DES) have been imputed to be a possible cause of persistent inflammation, remodeling, malapposition and late stent thrombosis. We aim to describe the in vivo experimental result of a new polymer-free DES eluting sirolimus from stent-plus-balloon (Focus np stent, Envision Scientific) compared with a bare-metal stent (BMS) (Amazonia CroCo, Minvasys) and with a biolimus A9 eluting stent (Biomatrix, Biosensors).

METHODS

In 10 juvenile pigs, 23 coronary stents were implanted in the coronary arteries (8 Amazonia CroCo, 8 Focus np, and 7 Biomatrix). At 28-day follow-up, optical coherence tomography (OCT) and histology were used to evaluate neointimal hyperplasia and healing response.

RESULTS

According to OCT analysis, Focus np stents had a greater lumen area and less neointimal hyperplasia response than BMS and Biomatrix had. Histomorphometry results showed less neointimal hyperplasia in Focus np than in BMS. Histology showed a higher fibrin deposition in Biomatrix stent compared to Focus np and BMS.

CONCLUSIONS

The new polymer-free DES with sirolimus eluted from stent-plus-balloon demonstrated safety and reduced neointimal proliferation compared with the BMS and Biomatrix stents at 28-day follow-up in this porcine coronary model. This new polymer-free DES is promising and warrants further clinical studies.

RAPSTROM™ first-in-man study long-term results of a biodegradable polymer sustained-release sirolimus-eluting stent in de novo coronary stenoses

BACKGROUND

Durable polymers used for first-generation drug-eluting stents (DES) potentially contribute to persistent inflammation and late DES thrombosis. We report the first real-life human experience with the rapamycin-eluting biodegradable polymer-coated Rapstrom stent.

METHODS

All consecutive patients with single de novo native coronary stenosis (<30 mm and between 2.5 and 4.0 mm) were enrolled. Major adverse cardiac events (MACE) at 1 year (cardiac death, myocardial infarction [Q and non-Q], or ischemia-driven target lesion revascularization) were the primary end-point.

RESULTS

A total of 123 patients were enrolled. The stent was implanted without complications in all patients, and no MACE were recorded at 30 days. At 12-month follow-up 9 patients (7.3%) experienced a MACE and 4 (3.2%) required a target lesion revascularization, while 1 (1%) stent thrombosis was recorded. A planned angiographic follow-up (FU) was performed in 73 patients (59%) at 9.4 ± 2.6 months following the index procedure. In-stent late loss was 0.16 ± 0.09 mm, and in-segment late loss was 0.18 ± 0.8 mm.

CONCLUSION

The Rapstrom biodegradable polymer rapamycin-eluting stent appeared safe and efficacious in this first real-life human experience, due to a low late lumen loss. Larger randomized studies are required to confirm these preliminary results.

Surface modification with dopamine and heparin/poly-L-lysine nanoparticles provides a favorable release behavior for the healing of vascular stent lesions

Surface biofunctional modification of coronary artery stents to prevent thrombosis and restenosis formation, as well as accelerate endothelialization, has become a new hot spot. However, bioactive coatings on implants are not yet sufficiently developed for long-term activity, as they quickly lose efficiency in vivo and finally fail. On the basis of a novel time-ordered concept of biofunctionality for vascular stents, heparin/poly l-lysine nanoparticle (NP) was developed and immobilized on a polydopamine-coated titanium surface, with the aim of regulating and maintaining the intravascular biological response within the normal range after biomaterial implantation. An in vitro dynamic release model was established to mimic the blood flow condition in vivo with three phases: (1) An early phase (1-7 days) with release of predominantly anticoagulant and anti-inflammatory substances and to a minor degree antiproliferative effects against smooth muscle cells (SMCs); (2) this is followed by a phase (7-14 days) of supported endothelial cell (ECs) proliferation and suppressed SMC proliferation with persisting high antithrombogenicity and anti-inflammatory properties of the surface. (3) Finally, a stable stage (14-28 days) with adequate biomolecules on the surface that maintain hemocompatibility and anti inflammation as well as inhibit SMCs proliferation and promote ECs growth. In vivo animal tests further confirmed that the NP-modified surface provides a favorable release behavior to apply a stage-adjusted remedy. We suggested that these observations provide important guidance and potential means for reasonable and suitable platform construction on a stent surface.

Orbital atherectomy system in treating calcified coronary lesions: 3-Year follow-up in first human use study (ORBIT I trial)

BACKGROUND/PURPOSE

The ORBIT I trial evaluated the safety and performance of an orbital atherectomy system (OAS) in treating de novo calcified coronary lesions. Severely calcified coronary arteries pose ongoing treatment challenges. Stent placement in calcified lesions can result in stent under expansion, malapposition and procedural complications. OAS treatment may be recommended to facilitate coronary stent implantation in these difficult lesions.

MATERIALS/METHODS

Fifty patients with de novo calcified coronary lesions were enrolled in the ORBIT I trial. Patients were treated with the OAS followed by stent placement. Our institution treated 33/50 patients and continued follow-up for 3 years.

RESULTS

Average age was 54.4 years and 90.9% were males. Mean lesion length was 15.9mm. The average number of OAS devices used per patient was 1.3. Procedural success was achieved in 97% of patients. Angiographic complications were observed in five patients (two minor dissections, one major dissection and two perforations). The cumulative major adverse cardiac event (MACE) rate was 6.1% in-hospital, 9.1% at 30 days, 12.1% at 6 months, 15.2% at 2 years, and 18.2% at 3years. The MACE rate included two in-hospital non Q-wave myocardial infarctions (MI), one additional non Q-wave MI at 30 days leading to target lesion revascularization (TLR), and three cardiac deaths.

CONCLUSIONS

The ORBIT I trial suggests that OAS treatment may offer an effective method to modify calcified coronary lesion compliance to facilitate optimal stent placement in these difficult-to-treat patients with acceptable levels of safety up to 3 years post-index procedure.

Drug-eluting stents: from evidence to policy

Drug-eluting stents are a major breakthrough in cardiology, with the Cypher (Cordis Corporation) and Taxus (Boston Scientific) stents preventing 60-70% of repeat coronary revascularizations, compared with bare metal stents. Both evidence- and risk-based application of drug-eluting stents is expected to create relevant financial and equity problems to most public hospitals, as the cost of drug-eluting stents is over 1000 higher than traditional stents. In the perspective of third-party payers, drug-eluting stents are cost-effective revascularization strategies for a large portion of patients actually undergoing stenting. However, adequate guidelines and reimbursement strategies are still awaited in several countries.

Nanoparticle drug- and gene-eluting stents for the prevention and treatment of coronary restenosis

Percutaneous coronary intervention (PCI) has become the most common revascularization procedure for coronary artery disease. The use of stents has reduced the rate of restenosis by preventing elastic recoil and negative remodeling. However, in-stent restenosis remains one of the major drawbacks of this procedure. Drug-eluting stents (DESs) have proven to be effective in reducing the risk of late restenosis, but the use of currently marketed DESs presents safety concerns, including the non-specificity of therapeutics, incomplete endothelialization leading to late thrombosis, the need for long-term anti-platelet agents, and local hypersensitivity to polymer delivery matrices. In addition, the current DESs lack the capacity for adjustment of the drug dose and release kinetics appropriate to the disease status of the treated vessel. The development of efficacious therapeutic strategies to prevent and inhibit restenosis after PCI is critical for the treatment of coronary artery disease. The administration of drugs using biodegradable polymer nanoparticles as carriers has generated immense interest due to their excellent biocompatibility and ability to facilitate prolonged drug release. Despite the potential benefits of nanoparticles as smart drug delivery and diagnostic systems, much research is still required to evaluate potential toxicity issues related to the chemical properties of nanoparticle materials, as well as to their size and shape. This review describes the molecular mechanism of coronary restenosis, the use of DESs, and progress in nanoparticle drug- or gene-eluting stents for the prevention and treatment of coronary restenosis.

Elutax paclitaxel-eluting balloon followed by bare-metal stent compared with Xience V drug-eluting stent in the treatment of de novo coronary stenosis: a randomized trial

BACKGROUND

Paclitaxel-eluting balloons (PEBs) are a promising alternative to drug-eluting stent (DES) in the treatment of coronary stenoses. The aim of our study was to compare the 9-month restenosis rates of a strategy of predilatation with PEB followed by bare-metal CoCr stent (PEB + BMS group) versus implantation of everolimus DES (DES group).

METHODS

This randomized, single-center study planned to enroll 366 patients with stable angina (183 patients per arm) undergoing percutaneous coronary intervention of a de novo, native coronary artery stenosis ≤ 15 mm in length. Primary end point, in a noninferiority study design, was 9-month binary angiographic restenosis. A frequency-domain optical coherence tomography substudy investigated the percentage of uncovered stent struts per lesion, the percentage of malapposed/uncovered struts per lesion, and the percentage of net volume obstruction at 9-month follow-up among the first consecutive 30 patients enrolled in the PEB + BMS group.

RESULTS

The study was prematurely halted after enrollment of 125 patients, 59 in the PEB + BMS group and 66 in the DES group, because of excess of ischemia-driven target lesion revascularization in the PEB + BMS group. When all the enrolled patients completed their follow-up, IDLTR rates were 14% in the PEB + BMS versus 2% in DES group (P = .001). Binary restenosis, either in-stent or in-segment, was significantly higher in the PEB + BMS compared with DES group (17% vs 3% [P = .01] and 25% vs 4% [P = .009] respectively). Frequency-domain optical coherence tomography demonstrated important neointimal regrowth in the PEB + BMS group, similar to historical BMS data.

CONCLUSION

In the treatment of de novo coronary stenosis, a strategy of predilatation with PEB before BMS implantation was significantly inferior to implantation of an everolimus DES stent in terms of 9-month target lesion revascularization. Frequency-domain optical coherence tomography data confirm the lack of efficacy of this strategy.

Second generation drug-eluting stents: a review of the everolimus-eluting platform

Everolimus-eluting stents (EES) represent the next generation of drug-eluting stents (DES). Important design modifications include thin strut stent backbones, less inflammatory and more biocompatible polymers, and lower drug dosing. The cobalt chromium EES fluoropolymer XIENCE V stent has been the most extensively studied of such stents. In animal models, this stent demonstrated minimal vessel inflammation, a biologically active endothelium with strut coverage similar to a bare metal stent, and inhibition of intimal hyperplasia comparable to that seen with sirolimus-eluting stents. The SPIRIT family of clinical trials demonstrated low rates of late loss, and clinical restenosis, as well as low rates of very late stent thrombosis. These excellent clinical outcomes addressed limitations of the 1st generation DES, and substantiated widespread clinical use of the EES platform.

Comparison of the safety between first- and second-generation drug eluting stents: meta-analysis from 19 randomized trials and 16,924 patients

BACKGROUND/OBJECTIVE

Despite the effectiveness of first generation drug eluting stent, DES-1 (Taxus and Cypher) in avoiding restenosis and the need for new revascularizations, a slightly increase in stent thrombosis, ST have been published. Second generation drug eluting stent, DES-2 has been developed to optimize the results of percutaneous coronary intervention in terms of efficacy and safety, for avoiding early and late ST. Our objective was to compare the risk of ST between DES-1 and DES-2.

METHODS

We performed a meta-analysis of 19 randomized trials. Overall 16,924 patients; 7294 were allocated to DES-1 and 9630 were allocated to DES-2. The primary endpoint was to compare the risk of overall ST during the first year. Other clinical outcomes of interest were to compare the incidence of early (<1 month) and late ST (>1 month-<1 year).

RESULTS

The incidence of overall ST was not increased in patients receiving DES-1 (1.13% DES-1 vs 0.75% DES-2, OR 0.79, 95% CI:0.45-1.40, p 0.43). There were no significant differences in the incidence of; early ST (0.85% DES-1 vs 0.53% DES-2, OR 0.68, 95% CI:0.31-1.51, p 0.35) and late ST (0.40% DES-1 vs 0.25% DES-2, OR 0.69, 95% CI:0.39-1.24, p 0.22).

CONCLUSIONS

During the first year after stent implantation, we didn't found differences in ST between DES-1 and DES-2. Most of ST was produced under appropriate anti-platelet therapy so it is possible that many other factors such as; clopidogrel resistance, procedural complications or stent malapposition were implicated. Safety after longer follow-up (>1 year) remains unclear.

Examination of drug release and distribution from drug-eluting stents with a vessel-simulating flow-through cell

The recently introduced vessel-simulating flow-through cell offers new possibilities to examine the release from drug-eluting stents in vitro. In comparison with standard dissolution methods, the additional compartment allows for the examination of distribution processes and creates dissolution conditions which simulate the physiological situation at the site of implantation. It was shown previously that these conditions have a distinct influence on the release rate from the stent coating. In this work, different preparation techniques were developed to examine the spatial distribution within the compartment simulating the vessel wall. These methods allowed for the examination of diffusion depth and the distribution resulting in the innermost layer of the compartment simulating the vessel wall. Furthermore, the in vitro release and distribution examined experimentally were modelled mathematically using finite element (FE) methods to gain further insight into the release and distribution behaviour. The FE modelling employing the experimentally determined diffusion coefficients yielded a good general description of the experimental data. The results of the modelling also provided important indications that inhomogeneous coating layer thicknesses around the strut may result from the coating process which influence release and distribution behaviour. Taken together, the vessel-simulating flow-through cell in combination with FE modelling represents a unique method to analyse drug release and distribution from drug-eluting stents in vitro with particular opportunities regarding the examination of spatial distributions within the vessel-simulating compartment.

Comparisons of the effects of stent eccentricity on the neointimal hyperplasia between sirolimus-eluting stent versus paclitaxel-eluting stent

PURPOSE

Previous studies suggested that asymmetric stent expansion did not affect suppression of neointimal hyperplasia (NIH) after sirolimus-eluting stents (SES) implantation. The aim of this study was to evaluate the effects of stent eccentricity (SE) on NIH between SES versus paclitaxel-eluting stents (PES) using an intravascular ultrasound (IVUS) analysis from the randomized trial.

MATERIALS AND METHODS

Serial IVUS data were obtained from Post-stent Optimal Expansion (POET) trial, allocated randomly to SES or PES. Three different SE (minimum stent diameter divided by maximum stent diameter) were evaluated; SE at the lesion site with maximal %NIH area (SE-NIH), SE at the minimal stent CSA [SE-minimal stent area (SE-MSA)], and averaged SE through the entire stent (SE-mean). We classified each drug-eluting stents (DES) into the concentric (≥ mean SE) and eccentric groups (< mean SE) based on the mean value of SE.

RESULTS

Among 301 enrolled patients, 233 patients [SES (n = 108), PES (n = 125)] underwent a follow-up IVUS. There was no significant correlation between %NIH area and SE-NIH (r = - 0.083, p = 0.391) or SE-MSA (r = - 0.109, p = 0.259) of SES. However, SE-NIH of PES showed a weak but significant correlation with %NIH area (r = 0.269, p < 0.01). As to the associations between SEmean and NIH volume index, SES revealed no significant correlation (r = - 0.001, p = 0.990), but PES showed a weak but significant correlation (r = 0.320, p < 0.01). However, there was no difference in the restenosis rate between the eccentric versus concentric groups of both DES.

CONCLUSION

This study suggests that lower SE of both SES and PES, which means asymmetric stent expansion, may not be associated with increased NIH.

In vivo and in vitro characterization of poly(styrene-b-isobutylene-b-styrene) copolymer stent coatings for biostability, vascular compatibility and mechanical integrity

The TAXUS Express 2 Paclitaxel Eluting Coronary Stent System employs a coating consisting of the thermoplastic elastomer, poly(styrene-b-isobutylene-b-styrene; SIBS), selected for its drug-eluting characteristics, vascular compatibility, mechanical properties, and biostability. This study was conducted to evaluate the impact of different SIBS (17-51 mole % styrene) compositions on mechanical properties, chemical stability, and vascular compatibility. Mechanical property (stress-strain measurements) and stability studies were conducted on polymer films with five different styrene contents (17, 24, 32, 39, and 51 mole %). The ultimate tensile strength did not change significantly with composition, but the elongation at break decreased with increased styrene content. A pulsatile fatigue test further confirmed the mechanical stability of SIBS up to 39 mole % styrene. The vascular compatibility of five different SIBS compositions was assessed using SIBS-only coated stents, in the coronary and carotid arteries in a porcine model study. The stability of the vessel wall, rate/degree of endothelialization, inflammation, and thrombus at timepoints from 30 to 180 days were evaluated. The results confirm vascular compatibility over the range of 17-51 mole % styrene.

Stent gap by 64-detector computed tomographic angiography relationship to in-stent restenosis, fracture, and overlap failure

OBJECTIVES

The goal of this study was to define the frequency of stent gaps by 64-detector computed tomographic angiography (CTA) and their relation to in-stent restenosis (ISR), stent fracture (SF), and overlap failure (OF).

BACKGROUND

SF defined by catheter angiography or intravascular ultrasound has been implicated in ISR.

METHODS

A total of 292 consecutive patients, with 613 stents, who underwent CTA were evaluated for stent gaps associated with decreased Hounsfield units. Correlations with catheter coronary angiography (CCA) were available in 143 patients with 384 stents.

RESULTS

Stent gaps were noted in 16.9% by CTA and 1.0% by CCA. ISR by CCA was noted in 46.1% of the stent gaps (p < 0.001) as determined by CCA, and stent gaps by CTA accounted for 27.8% of the total ISR (p < 0.001). In univariate analysis, stent diameter > or =3 mm was the only CCA characteristic significantly associated with stent gaps (p = 0.002), but was not a significant predictor by multivariate analysis. Bifurcation stents, underlying calcification, stent type, location, post-dilation, and overlapping stents were not observed to be predisposing factors. Excessive tortuosity and lack of conformability were not associated with stent gaps; however, their frequency was insufficient to permit meaningful analysis.

CONCLUSIONS

Stent gap by CTA: 1) is associated with 28% of ISR, and ISR is found in 46% of stent gaps; 2) is associated with > or =3-mm stents by univariate (p = 0.002) but not by multivariate analysis; 3) is infrequently noted on catheter angiography; and 4) most likely represents SF in the setting of a single stent, and may represent SF or OF in overlapping stents.

Impact of polymer hydrophilicity on biocompatibility: implication for DES polymer design

Polymer coatings are essential for local delivery of drug from the stent platform. In designing a DES, it is critical to balance the hydrophilic and hydrophobic components of the polymer system to obtain optimal biocompatibility, while maintaining controlled drug elution. This study investigates the impact of polymer composition of the BioLinx polymer blend on in vitro biocompatibility, as measured by monocytic adhesion. Comparable evaluation was performed with polymers similar to those utilized in various DES that are currently being marketed. Relative hydrophilicities of polymer surfaces were determined through contact angle measurements and surface analyses. Polymer biocompatibility was evaluated in a novel in vitro assay system in which activated monocyte cells were exposed to polymer coated on 96-well plates. Enhanced monocyte adhesion was observed with polymers of a more hydrophobic nature, whereas those which were more hydrophilic did not induce activated monocyte adhesion. Our data supports the hypothesis that polymer composition is a feature that dictates in vitro biocompatibility as measured by monocyte driven inflammation. Monocyte adhesion has been shown to induce local inflammation as well as promote vascular cell proliferation factors contributing to in stent restenosis (Rogers et al., Arterioscler Thromb Vasc Biol 1996;16:1312-1318). Observed results suggest hydrophobic but not hydrophilic polymer surfaces support adhesion of activated monocytes to the polymer scaffold. The proprietary DES polymer blend BioLinx has a hydrophilic surface architecture and does not induce an inflammatory response as measured by these in vitro assays.

Atherosclerotic and thrombogenic neointima formed over sirolimus drug-eluting stent: an angioscopic study

OBJECTIVES

We sought to examine by angioscopy the neointima formation and thrombogenic potential of the neointima after deployment of a drug-eluting stent (DES).

BACKGROUND

Late stent thrombosis after DES implantation, a major safety concern, has been associated with poor strut coverage by neointima. Intracoronary angioscopy provides a method for visual evaluation of stent coverage by neointima and detection of thrombus in the stented coronary segment.

METHODS

Patients undergoing implantation of a sirolimus DES (n = 57) were serially examined by angioscopy immediately after (baseline) and again at 10 months (follow-up) after implantation. The angioscopic color grade of the neointima from white to yellow was assessed in a semiquantitative manner. Stent coverage was classified into not covered (Grade 0), covered by a thin layer (Grade 1), or buried under neointima (Grade 2). The thrombogenic potential of the neointima was evaluated by the prevalence of thrombus on the neointima.

RESULTS

The maximum yellow color grade of the neointima within DES-implanted lesions increased significantly from baseline to follow-up (1.4 +/- 1.1 vs. 1.9 +/- 0.6, p = 0.0008). Even among lesions without yellow color at baseline, yellow color was detected in 94% (17 of 18) of lesions at follow-up. The prevalence of thrombus was significantly higher on the yellow than on the white neointimal areas. Thrombus was detected on yellow and/or Grade-0/1 neointima, but never on the white Grade-2 neointima.

CONCLUSIONS

Sirolimus DES promoted formation of atherosclerotic yellow neointima in the stent-implanted lesion at 10-month follow-up. Thrombus was detected more often on the yellow area than on the white area and was never detected where a stent was buried under white neointima. These data suggest that the increased potential risk of late stent thrombosis in DES lesions may be due to the newly formed yellow neotima and cholesterol-laden plaque.

Stent‐based percutaneous coronary interventions in small coronary arteries

A third to half of all percutaneous coronary interventions involve small diameter vessels of less than 3 mm. Small vessel size is a predictor of restenosis after balloon angioplasty, as well as after stent placement. Stents deployed in small arteries, have a higher metal-to-artery ratio; this may increase the risk of sub-acute thrombosis or restenosis. Various studies have shown that stent design, stent coating, and stent strut thickness may determine event-free survival. Dedicated stents for small vessels with less amount of metal, appropriate expansion to the vessel size with correct radial force and cells morphology, and less prothrombotic properties, may further improve the results of stenting in this setting (thinner struts, fewer cells, or loops per circumference). This review provides an update on the current status, review the major trials and define the clinical utility of small vessel stenting, particularly in the era of drug-eluting stents.

Advances in stent drug delivery: the future is in bioabsorbable stents

This expert opinion review offers a perspective on the future developments in drug-eluting stent design. Initial efforts were focused on reduction of in-stent restenosis, which the drug-eluting stents addressed effectively. Current concerns are predominantly with regard to risk of stent thrombosis and delayed endothelialization. All three components of the stent have been modified to achieve the goal of endothelialization and vessel healing: drug, polymer and the platform. We review different approaches to reduce this risk from design of different drug combinations, through less traumatic metallic stent platforms, via biodegradable polymers and, finally, fully biodegradable stents. It seems at this time that fully biodegradable solutions to stenting hold the greatest promise, but larger long-term studies are needed to evaluate fully their safety and efficacy in 'all-comer' patient populations. At the time of this review, design of a safe drug-eluting stent still remains a challenge.