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

Review of randomized clinical trials of drug-eluting stents for the prevention of in-stent restenosis

Drug-eluting stents (DESs) have shown significant promise at reducing rates of restenosis and subsequent revascularization compared with bare metal stents (BMSs). The purpose of this report is to provide a systematic review of the randomized clinical trials that have evaluated the efficacy and safety of DESs. A total of 28 randomized clinical trials were identified: 21 comparing a DES (sirolimus, paclitaxel, ABT-578, actinomycin, everolimus, or 7-hexanoyltaxol) with a BMS and 7 comparing a DES with another DES (sirolimus vs paclitaxel). Early sirolimus and polymeric paclitaxel studies in low-risk populations demonstrated marked reductions in restenosis according to angiographic and clinical parameters, compared with BMSs. These promising findings led to the more recent evaluations of DESs in higher risk patients in controlled and head-to-head comparisons. In these subsequent trials, sirolimus and paclitaxel DESs continued to exceed the therapeutic potential of BMSs, with a slight but consistent angiographic advantage being observed with the sirolimus DESs.

The paclitaxel-eluting stent in percutaneous coronary intervention: part I: background and clinical comparison to bare metal stents

The development of coronary artery stents that release (elute) a drug locally into the diseased vasculature has revolutionized the practice of interventional cardiology. These devices were designed to minimize the incidence of in-stent restenosis that may occur with bare metal stents. The paclitaxel-eluting stent is the most recent drug-eluting stent approved for use in the United States and is a bare metal stent coated with paclitaxel that is gradually released from the stent into the vessel wall with undetectable systemic concentrations of the drug. Paclitaxel functions to stabilize the assembly of microtubules, thereby interfering with cell division, motility, and shape, and ultimately inhibiting smooth muscle cell proliferation and migration, key processes in the development of neointimal hyperplasia during in-stent restenosis. Clinical trials have repeatedly demonstrated the superiority of the paclitaxel-eluting stent over the bare metal stent in terms of reducing restenosis rates and percent stenosis diameter as well as other angiographic end points. Although the rates of major adverse cardiac events are reduced with the paclitaxel-eluting stent compared with the bare metal stent, this is primarily the result of a reduction in the need for target vessel revascularization, whereas rates of myocardial infarction and death have not been shown to be significantly affected.

Mechanisms of controlled drug release from drug-eluting stents

The clinical importance of drug-eluting stents (DESs) has been demonstrated by their unparalleled success in preventing restenosis after stenting procedures. The magnitude of success is historic despite their short history. The current DESs deliver a single drug aiming to prevent or minimize proliferation of smooth muscle cells. Since the restenosis process involves several different biological responses, the ability to deliver the right drugs at the right times is critical for further development of the second generation of DESs. As the type of drugs that can be delivered from DESs varies, it is imperative to understand the drug delivery mechanisms and the approaches available for drug coating on the stents. The drug delivery mechanisms of current DESs that have been used clinically and under clinical trials are explained.

Drug-Eluting Stents

Percutaneous coronary intervention has evolved dramatically over the past 25 years as coronary stents replaced stand-alone balloon angioplasty. Improvements in stents were made in the 1990s, but a breakthrough occurred in early 2000 with the development of stents that eluted pharmacology agents directly into the vessel wall by means of a controlled release from a durable polymer coating. Various drug-eluting stents were developed,each varying with its delivery platform, polymer coating (or absence of coating),and drug selected for elution. This article describes the clinically available and late developmental drug-eluting stent programs targeted for treating patients who have coronary artery disease.

Drug-eluting stents studies in mice: Do we need atherosclerosis to study restenosis?

In 2001, the first human study with drug-eluting stents (DES) was published showing a nearly complete abolition of restenosis by using a sirolimus-eluting stent. This success was very encouraging to test new compounds in combination with the DES platform. Nevertheless, several other anti-restenotic compounds have been used in human clinical trials with disappointing outcomes. Little is known concerning potential adverse effects on vessel wall integrity and (re)healing, atherosclerotic lesion formation, progression, and plaque stability of these DES. Although efficacy and safety need to be determined clinically, preclinical testing of candidate drugs in well-defined animal models is extremely helpful to gain insight into the basic biological responses to candidate compounds. Here, we discuss and report an animal model which enables rapid screening of candidate drugs for DES on an atherosclerotic background. The results from drug testing using this novel model could help to quickly and cost-effectively establish the dose range of candidate drugs with reasonable potential for DES.

Coronary artery stenosis

The near exponential rise in percutaneous coronary intervention(PCI) in the treatment of patients with coronary artery disease and the consequent decline in referral of patients for coronary artery bypass grafting (CABG) has lead to a crisis in cardiac surgery. Is CABG, one of the most successful and widely applied surgical procedures, about to follow surgery for peptic ulcer disease into obsolescence? The question has serious implications for service provision and training as well as for informed patient consent. Keith Dawkins puts the case for PCI and gives a very clear and concise account of its inexorable rise to pre-eminence. David Taggart has taken on the Goliath of interventional cardiology and its associated industry by persuasively marshalling the data from the evidence base which strongly favours surgery in triple vessel and left main coronary disease. He points to the lack of long-term results and also to the weaknesses of many of the comparative studies so far published. His arguments have been positively received on both sides of the Atlantic but it is by no means certain that they will bring about the multidisciplinary approach to providing patients with treatment options which he and others advocate. It also remains to be seen whether the evidence base when it is eventually acquired will vindicate the present increasing dominance of PCI over CABG.

Paclitaxel-eluting stents

Percutaneous coronary intervention and stent implantation is rapidly becoming the most commonly used form of revascularization. The long term results of this procedure are limited by restenosis which is a phenomenon predominantly caused by proliferation of smooth muscle cells. Many devices and pharmaceutical agents have been unsuccessful in preventing this problem. Paclitaxel is an antiproliferative drug that has been extensively studied for the prevention of restenosis. This article will review the trial results of the currently available stent platforms and discuss some of the ongoing studies and future directions for the development of new paclitaxel-eluting stents.

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.

Clinical and angiographic outcomes after multi-link PENTA stent implantation in Japanese patients with coronary artery disease

The flexibility of the Multi-Link (ML) PENTA stent with platform 0.09 to 0.12-mm-thick struts and 12% to 16% metal/artery coverage was improved to facilitate safe delivery in complex coronary lesions. The present study was designed to evaluate the clinical (9-month) and angiographic (6-month) results of the ML PENTA stent in complex coronary lesions (modified American College of Cardiology/American Heart Association lesion type B2 or C) and to determine independent factors correlated with target lesion revascularization. The study population consisted of 86 consecutive patients who had undergone successful coronary ML PENTA stent implantation for coronary artery disease from May 2003 to July 2004 in our hospital. During the follow-up period, cardiac events were documented in 21 (24.4%) of the 86 patients. Target lesion revascularization was required in 16 (18.6%) of the 86 patients. Single logistic regression analysis showed that target lesion revascularization was significantly correlated with lesion length > 2.0 cm, residual percent diameter stenosis after the procedure > 20%, and multiple stents. Multiple logistic regression analysis showed that residual percent diameter stenosis after procedure > 20% (P = 0.0125, odds ratio = 11.585) was the significant explanatory factor of target lesion revascularization. The results of the present study suggest that 9-month clinical and 6-month angiographic outcomes in patients with coronary artery disease treated using the ML PENTA stent were excellent and target lesion revascularization after coronary ML PENTA stent implantation was influenced by residual percent diameter stenosis after the procedure.

Drug-Eluting Coronary Stents

The introduction and widespread use of coronary stents have been the most important advancement in the percutaneous treatment of coronary artery disease since the introduction of balloon angioplasty. Coronary artery stents reduce the rate of angiographic and clinical restenosis compared to balloon angioplasty. This angiographic restenosis was further reduced with the introduction of drug-eluting stents and hence further reduction in the frequency of major adverse cardiac events. Herein we present a comprehensive and up-to-date review about the use of drug-eluting stents in the treatment of coronary artery disease.

Cypher Versus Taxus: Are There Differences?

Today, drug-eluting stents (DES) are the standard stenting procedure in the USA and in Switzerland. The objective of this analysis is to answer the two questions: what clinically relevant data regarding DES have been published, and is there a clinically relevant difference between the Cypher and the Taxus stents? Twenty-two randomized, controlled studies with a total of 11,118 patients were identified: 18 randomized studies compared a DES to a bare metal stent of identical design in 8,301 patients, and 4 randomized studies compared the Cypher and the Taxus stents in 2,817 patients. Three studies regarding Paclitaxel-releasing stents without polymer (1,235 pats) and five studies regarding Paclitaxel released from a polymer (3,513 pats) were analyzed. Sirolimus released from a polymer was investigated in five studies (2,070 pats). Everolimus released from a polymer was investigated in three studies (166 pats), Biolimus A9 released from a polymer in one (120 pats), and Zotarolimus (ABT-578) released from a polymer in also one (1,197 pats) trial. Thirteen studies chose either a surrogate primary endpoint (angiographic or IVUS) or a clinical endpoint insufficient for a power calculation. A primary clinical endpoint with an adequate sample size for a power calculation was chosen in three trials for the Taxus stent (TAXUS-IV, TAXUS-V, TAXUS-VI; 2,916 patients), in one trial for the Cypher stent (SIRIUS; 1,058 patients), and in one trial for the Endeavor stent (ENDEAVOR-II; 1,197 patients). In all these trials, the primary clinical endpoint was reached. Of the four studies comparing Cypher stents to Taxus stents, one did not define the primary endpoint (TAXi), two assumed superiority of the Cypher stent (REALITY with a surrogate endpoint and SIRTAX, a single-center study), and one was designed as a non-inferiority trial (ISAR-Diabetes, single-center study with a surrogate endpoint). Based on the European Society of Cardiology established strict criteria with a clinical primary endpoint as a prerequisite to recommend a DES, only three DES have thus far had proven positive effects on clinical outcome: the Cypher-stents, Taxus-stents, and Endeavor-stents. A trial proving the superiority of one DES over another would require a multicenter study with a clinical primary endpoint at an adequate power. As long as such a trial does not exist, Cypher and Taxus are regarded as being equivalent.

Technology Insight: an overview of research in drug-eluting stents

Drug-eluting stents (DESs) have revolutionized interventional cardiology over the past few years to the extent that balloon angioplasty and bare stents did in the 1980s and 1990s. The first DESs became commercially available in Europe in 2002 and in the US in 2003, and it is estimated that up to 80% of patients who undergo stent implantation in the US now receive a DES. Two devices, Cypher sirolimus-eluting stents (Cordis Corporation, Miami Lakes, FL) and Taxus paclitaxel-eluting stents (Boston Scientific Corporation, Natick, MN), are currently licensed for sale in both regions. Multiple new devices using different drugs, carriers and stents are currently undergoing clinical trials to establish their efficacy and obtain approval for commercialization. While the remarkable reduction of restenosis has accounted for the success of DESs, concerns remain regarding long-term follow-up; published 3-year follow-up results are available for fewer than 200 patients overall. Reports of late stent thrombosis have emerged, particularly in relation to discontinuation of antiplatelet therapy. In patients treated with DESs, long-term administration of at least one antiplatelet agent must be continued following completion of the mandatory dual antiplatelet regimen. In this review, we summarize the findings available for DESs so far, discuss emerging safety and efficacy data, and look at the future directions for these devices.

Impact of asymmetric stent expansion on neointimal hyperplasia following sirolimus-eluting stent implantation

To assess whether asymmetric stent expansion affects suppression of neointimal hyperplasia after sirolimus-eluting stent implantation, 64 patients in the SIRolImUS-coated Bx Velocity stent trial who underwent single 18-mm stent implantation and 3-dimensional intravascular ultrasonography at 8-month follow-up were enrolled. To assess the longitudinal stent asymmetric expansion, 2 cross sections with a maximal/minimal stent area were chosen in each patient. To assess for tomographic stent asymmetric expansion, stent eccentricity was determined by dividing the minimum stent diameter by the maximum stent diameter. At the 2 cross sections with a maximal/minimal stent area, a sirolimus-eluting stent reduced neointimal hyperplasia significantly with no interaction between the treatment and stent areas. A sirolimus-eluting stent also significantly reduced neointimal hyperplasia in the concentric and eccentric stent groups.

Robustness of late lumen loss in discriminating drug-eluting stents across variable observational and randomized trials

BACKGROUND

Binary angiographic and clinical restenosis rates can vary widely between clinical studies, even for the same stent, influenced heavily by case-mix covariates that differ among observational and randomized trials intended to assess a given stent system. We hypothesized that mean in-stent late loss might be a more stable estimator of restenosis propensity across such studies.

METHODS AND RESULTS

In 46 trials of drug-eluting and bare-metal stenting, increasing mean late loss was associated with higher target lesion revascularization (TLR) rates (P<0.001). When the class of bare-metal stents was compared with the class of effective drug-eluting stents, late loss was more discriminating than TLR as measured by the high intraclass correlation coefficient (rho) (late loss, rho=0.71 versus TLR, rho=0.22; 95% CI of difference=0.33, 0.65). When the individual drug-eluting stents and bare-metal stents were compared, late loss was a better discriminator than TLR (0.68 versus 0.19; 95% CI of difference=0.24, 0.60). Greater adjustments of study covariates are needed to stabilize assessments of TLR compared with late loss because of greater influence of reference vessel diameter on TLR than on in-stent late loss. Optimization of late loss with the use of a novel method of standardization according to diabetes prevalence and mean lesion length resulted in minor adjustments in late loss (<0.08 mm for 90% of reported trials) and an ordered array of mean late loss values for the stent systems studied.

CONCLUSIONS

Late loss is more reliable than restenosis rates for discriminating restenosis propensity between new drug-eluting stent platforms across studies and might be the optimum end point for evaluating drug-eluting stents in early, nonrandomized studies.

Drug eluting stents: an updated meta-analysis of randomised controlled trials

OBJECTIVE

To confirm the overall benefit of drug eluting stents (DES), to evaluate the effect of different DES, and to assess the global safety of DES compared with bare stents through a meta-analysis of randomised controlled trials.

METHODS

Randomised controlled trials comparing sirolimus and derivates or paclitaxel and derivates eluting stents versus bare stents. Binary restenosis and major adverse cardiac events (MACE) were chosen as primary end points. Death, Q wave myocardial infarction (MI), and stent thrombosis up to 12 months' follow up were also analysed.

RESULTS

MACE overall occurrence was highly reduced with DES from 19.9% to 10.1% (odds ratio (OR) 0.46, 95% confidence interval (CI) 0.41 to 0.52, p < 0.001). A significant heterogeneity (p < 0.001) was found between subgroups according to the drug: MACE OR was 0.28 (95% CI 0.22 to 0.35) in the sirolimus subgroup and 0.62 (95% CI 0.53 to 0.73) in the paclitaxel subgroup. Restenosis was also highly reduced from 31.7% with bare stents to 10.5% with DES (OR 0.25, 95% CI 0.22 to 0.29, p < 0.001) with a similar heterogeneity between subgroups. Mortality, Q wave MI, and stent thrombosis were not significantly different between DES and control group, whereas Q wave MI and stent thrombosis tended to be more frequent with paclitaxel.

CONCLUSION

This meta-analysis confirms the overall benefit of DES on restenosis and MACE with significant heterogeneity between drugs, suggesting higher efficacy of sirolimus eluting stents. Additional data with longer follow up and in high risk populations are needed to clarify issues on stent thrombosis.

Adjusted indirect comparison of intracoronary drug-eluting stents: evidence from a metaanalysis of randomized bare-metal-stent-controlled trials

AIMS

Drug-eluting stents (DES) have been recently investigated, with favorable data for many devices, but comparative data are lacking. We thus performed an adjusted indirect comparison metaanalysis of DES.

METHODS

Randomized trials comparing DES vs. bare-metal stents (BMS) were systematically searched, and random effect odds ratios (OR) were computed for target lesion revascularization (TLR) and binary in-stent restenosis rate (BRR) at 6-12 months. We then generated interaction OR for the comparison of different DES.

RESULTS

We pooled data from 17 studies (allocating 3048 patients to BMS and 3392 to nine different DES). Indirect head-to-head comparison of sirolimus-eluting Cypher (N=1007) vs. polymeric paclitaxel-eluting Taxus (N=959) showed nonsignificant differences in TLR [OR=0.8 (0.5-1.4), p=0.45] but significant reductions in BRR favoring Cypher [OR=0.3 (0.1-0.6), p<0.001]. Everolimus-eluting stents appeared noninferior to Cypher or Taxus (p>0.50 for both TLR and BRR). Actinomycin-, mycophenolate-, and apolymeric paclitaxel-eluting stents (PES) all proved significantly worse than Cypher or Taxus for TLR or BRR.

CONCLUSION

Notwithstanding its inherent limitations, the present metaanalysis confirms the effectiveness of both Cypher and Taxus, supports the promising role of everolimus-eluting stents, and suggests the significant inferiority of most other devices. These post hoc findings, albeit intriguing, await prospective confirmation.

Impact of platelet glycoprotein IIb/IIIa Inhibition on the paclitaxel-eluting stent in patients with stable or unstable angina pectoris or provocable myocardial ischemia (a TAXUS IV substudy)

Whether the benefits that glycoprotein IIb/IIIa inhibitors confer in patients who undergo bare metal stent implantation extend to drug-eluting stents is unknown. We performed a prespecified subgroup analysis of the TAXUS IV study population to examine the effect of procedural glycoprotein IIb/IIIa inhibition during paclitaxel-eluting stent implantation on periprocedural creatine kinase-MB (CK-MB) levels. Glycoprotein (GP) IIb/IIIa inhibitors were administered to 57.7% of patients who had been randomized to receive the TAXUS stent and to 56.7% of those who had been randomized to receive the control stent. Among patients who received the TAXUS stent, the rate of CK-MB increases of >3 times the normal level was 2.6-fold higher in those who received a GP IIb/IIIa inhibitor than in those who did not (11.4% vs 4.4%, p = 0.0015). Composite rates of major adverse cardiac events and target vessel failure were also higher at 1 month in the GP IIb/IIIa group. By multivariate analysis, use of GP IIb/IIIa inhibitors during stenting with the TAXUS stent was an independent predictor of CK-MB increases >3 times the normal level. Further studies are warranted.

The effect of variable dose and release kinetics on neointimal hyperplasia using a novel paclitaxel-eluting stent platform: the Paclitaxel In-Stent Controlled Elution Study (PISCES)

OBJECTIVES

The aim of this study was to evaluate the effect of variable dose and release kinetics of paclitaxel on neointimal hyperplasia.

BACKGROUND

Conventional paclitaxel-eluting stents use a durable polymer coating as a vehicle for drug delivery. The Conor stent (Conor Medsystems, Menlo Park, California) with intra-strut wells and erodable polymer is specifically designed for drug delivery with programmable pharmacokinetics.

METHODS

Two hundred and forty-four patients with single vessel disease received either a bare metal Conor stent (n = 53) or one of six different release formulations that varied in dose (10 or 30 microg) and elution release kinetics (first order, zero order), direction (abluminal, luminal), and duration (5, 10, and 30 days). End points at six months (bare stent group) and at four months (eluting stent groups) were angiographic late loss and neointimal tissue volume by intravascular ultrasound and the rate of major adverse cardiac events (MACE).

RESULTS

The lowest in-stent late loss (0.38 mm, p <0.01, and 0.30 mm, p <0.01) and volume obstruction (8%, p <0.01, and 5%, p <0.01) were observed with the 10-microg and 30-microg doses in the 30-day release groups respectively, whereas the highest in-stent late loss (0.88 mm), volume obstruction (26%), and restenosis rate (11.6%) were observed in the bare stent group. The overall MACE rate of the eluting stent group was 8.6%: death 0.5%, myocardial infarction 2.7%, and target lesion revascularization (TLR) 5.3%. Sub-acute thrombosis was 0.5%. The TLR rates in the two 30-day release groups were 0% and 3.4%.

CONCLUSIONS

This novel eluting stent platform, using an erodable polymer with complete elution of low doses of paclitaxel, is safe. The inhibition of the in-stent neointimal hyperplasia was best in the long release groups.

Late Loss in Lumen Diameter and Binary Restenosis for Drug-Eluting Stent Comparison

Background— Published rates of coronary restenosis have fallen below 10% in drug-eluting stent trials. Early evaluations of new stents have used continuous end points that are presumed surrogates for restenosis, but the generalizability and power of such end points have not been examined systematically.

Methods and Results— We examined the relationship between incremental changes in observed late loss in lumen diameter and the probability of restenosis using reported late loss from 22 published trials of various types of stents (bare-metal, drug-eluting, and small-vessel stents). Next, the power of late loss differences was compared with that of corresponding binary restenosis rates. The relationship between mean late loss and its SD was linear and did not vary with stent type (drug-eluting or bare-metal) or vessel diameter. At all levels of late loss examined (0 to 1 mm), incremental changes were associated with increasing restenosis risk (with an increasing magnitude of effect at higher levels of late loss). The power to detect a treatment effect was greater for late loss than for binary angiographic restenosis (≥32% relative increase in power, ≥24% absolute increase for late loss between 0.2 and 0.6 mm).

Conclusions— Late loss is monotonically related to restenosis risk in published stent trials. It is a generalizable and powerful angiographic end point in early or small trials of new drug-eluting stents.

Prevention of restenosis by a novel drug-eluting stent system with a dose-adjustable, polymer-free, on-site stent coating

AIMS

Drug-eluting stents (DES) represent a major advance in interventional cardiology. Along with the success shown, current DES also present limitations related to the presence of polymer-coating, fixed drug, and dose used. With the ISAR (Individualized Drug-Eluting Stent System to Abrogate Restenosis) project, a DES system has been developed that permits individualized choice of the drug and dose to use for the given patient. The objective of this prospective dose finding study was to assess the feasibility, safety, and efficacy of a polymer-free on-site stent coating with increasing rapamycin doses.

METHODS AND RESULTS

In this dose finding study, 602 patients were sequentially enrolled in four groups: microporous bare metal stent (BMS), DES stents coated with a 0.5, 1.0, and 2.0% rapamycin solution. The angiographic in-segment restenosis rate at follow-up angiography was the primary study endpoint. In-segment restenosis was significantly reduced from 25.9% with BMS to 18.9, 17.2, and 14.7% with 0.5, 1.0, and 2.0% rapamycin-eluting stents, respectively (P=0.024). Similarly, the need for target lesion revascularization at 1 year follow-up was reduced from 21.5% with BMS to 16.4, 12.6, and 8.8% with 0.5, 1.0, and 2.0% rapamycin-eluting stents, respectively (P=0.006).

CONCLUSION

The placement of polymer-free stents coated on-site with rapamycin is feasible and safe. Furthermore, a dose-dependent efficacy in restenosis prevention is achievable with this new DES concept.

Strut Position, Blood Flow, and Drug Deposition

Background— The intricacies of stent design, local pharmacology, tissue biology, and rheology preclude an intuitive understanding of drug distribution and deposition from drug-eluting stents (DES).

Methods and Results— A coupled computational fluid dynamics and mass transfer model was applied to predict drug deposition for single and overlapping DES. Drug deposition appeared not only beneath regions of arterial contact with the strut but surprisingly also beneath standing drug pools created by strut disruption of flow. These regions correlated with areas of drug-induced fibrin deposition surrounding DES struts in porcine coronary arteries. Fibrin deposition immediately distal to individual isolated drug-eluting struts was twice as great as in the proximal area and for the stent as a whole was greater in distal segments than proximal segments. Adjacent and overlapping stent struts increased computed arterial drug deposition by far less than the sum of their combined drug load. In addition, drug eluted from the abluminal stent strut surface accounted for only 11% of total deposition, whereas, remarkably, drug eluted from the adluminal surface accounted for 43% of total deposition. Thus, local blood flow alterations and location of drug elution on the strut were far more important in determining arterial wall drug deposition and distribution than were drug load or arterial wall contact with coated strut surfaces.

Conclusions— Simulations that coupled strut configurations with flow dynamics correlated with in vivo effects and revealed that drug deposition occurs less via contact between drug coating and the arterial wall than via flow-mediated deposition of blood-solubilized drug.

Stent-based delivery of ABT-578 via a phosphorylcholine surface coating reduces neointimal formation in the porcine coronary model

Stent-based delivery of the antiproliferative and immunosuppressive macrocyclic lactone sirolimus reduces neointimal formation and restenosis by cytostatic inhibition of vascular smooth muscle cell proliferation. The objective of this study was to determine the feasibility and efficacy of stent-based delivery of ABT-578, a structurally unique macrocyclic lactone. Stainless steel balloon-expandable stents were coated with thin layer of phosphorylcholine (PC) or PC with ABT-578 (10 microg/mm). Fifteen juvenile domestic pigs underwent placement of oversized bare metal (n = 15), PC (n = 8), and PC with ABT-578 (n = 9) stents in the coronary arteries. At 28 days, histology demonstrated similar mean injury scores for the control, PC-, and ABT-578-coated stents. The mean neointimal area (mm2) was significantly reduced for ABT-578 (1.70 +/- 0.47) as compared with PC (2.82 +/- 1.24) and control (2.89 +/- 1.91) stents (P < or = 0.05). The 40% reduction in neointimal area resulted in significantly less mean percent diameter stenosis for ABT-578 (19.4% +/- 4.0%) as compared with PC (30.3 +/- 12.1 %) and control (29.4% +/- 15.5%) stents (P < or = 0.03). Twelve of the 45 bare metal stent cross-sections (26.7%) exhibited a giant cell reaction, while none of the sections from the ABT-578-eluting stents had a giant cell reaction (P = 0.004). Stent-based delivery of ABT-578 via a PC surface coating inhibits neointimal formation at 28 days in the porcine coronary model. Further study is necessary to determine the dose-response and long-term effects ABT-578-eluting stents in the porcine coronary model.

Drug-eluting stents versus bare metal stents in percutaneous coronary interventions (a meta-analysis)

This meta-analysis combined the results of randomized clinical trials to compare the efficacy of drug-eluting stents with that of bare metal stents in percutaneous coronary interventions to ascertain which revascularization strategy is most safe and effective. The literature identified 13 published studies, and 8 were included in the main meta-analysis, thus allowing a meta-analysis on 3,860 patients for the effect on all major adverse clinical events (MACEs) combined and for target vessel revascularization. Meta-analyses were performed for combined MACEs, patient MACEs, and thrombosis. Regression meta-analyses were performed to examine the effect of certain variables on the efficacy of drug-eluting stents compared with bare metal stents. Meta-analysis of all trials showed that drug-eluting stents produced significant decreases in the need for percutaneous revascularization (relative risk [RR] 0.30, 95% confidence interval [CI] 0.22 to 0.40) and coronary artery bypass grafting (RR 0.54, 95% CI 0.32 to 0.89). Drug-eluting stents significantly decreased all MACEs combined (RR 0.40, 95% CI 0.33 to 0.49) but were not associated with an increased risk of stent thrombosis or death. These results were confirmed at analysis as stratified by type of eluting stent, because the need for percutaneous revascularization was significantly lower for sirolimus-eluting stents (RR 0.23, 95% CI 0.15 to 0.35) and paclitaxel-eluting stents (RR 0.39, 95% CIl 0.29 to 0.53).

Thrombosis Modulates Arterial Drug Distribution for Drug-Eluting Stents

Background— Drug-eluting stents deliver potent compounds directly to arterial segments but can become clot laden when deployed. The question arises as to whether thrombi affect drug elution and arterial uptake.

Methods and Results— Paclitaxel transport and retention were assessed in clots of different blood components. Diffusivity, affected by clot organization, is fastest in fibrin (≈347 μm 2 /s), slower in fibrin-red blood cell clots (34.98 μm 2 /s), and slowest in whole-blood clots (3.55 μm 2 /s). Blood cells bind and retain paclitaxel such that levels in clot increase linearly with red cell fraction. At physiological hematocrit, clot retains 3 times the amount of paclitaxel in surrounding solutions. Computational models predict that the potential of thrombus to absorb, retain, and release drug or to act as a barrier to drug delivery depends on clot geometry and strut position in clot relative to the vessel wall. Clot between artery and stent can reduce uptake 10-fold, whereas clot overlying the stent can shield drug from washout, increasing uptake. Model assumptions were confirmed and predictions were validated in a novel rat model that introduces thrombosis within stented aortas where nonocclusive thrombus acts as capacitive space for drug and shifts drug levels to decrease tissue uptake 2-fold.

Conclusions— Thrombus apposed on stents creates large variations in drug uptake and can act to either increase or decrease wall deposition according to the clot and stent geometry. Arterial deposition of drug from stents deployed in clots will be highly variable and unpredictable unless the clot can be adequately controlled or removed.

Surgery is the best intervention for severe coronary artery disease

A multidisciplinary approach is essential, but best evidence favours surgery over percutaneous intervention

Outcomes with the polymer-based paclitaxel-eluting TAXUS stent in patients with diabetes mellitus

OBJECTIVES

We sought to determine the safety and efficacy of polymer-regulated site-specific delivery of paclitaxel in patients with diabetes mellitus undergoing stent implantation.

BACKGROUND

Percutaneous coronary intervention in patients with diabetes is associated with high rates of restenosis and repeat revascularization due to excessive neointimal proliferation, a process that may be blunted with the site-specific delivery of paclitaxel.

METHODS

In the TAXUS-IV trial, 1,314 patients were prospectively randomized to the slow rate-release polymer-based paclitaxel-eluting TAXUS stent or the bare-metal EXPRESS stent (Boston Scientific Corp., Natick, Massachusetts). Medically treated diabetes was present in 318 patients (24%), 105 of whom required insulin.

RESULTS

Among patients with diabetes, the TAXUS stent, compared to the bare-metal stent, reduced the rate of 9-month binary angiographic restenosis by 81% (6.4% vs. 34.5%, p < 0.0001), and reduced the 12-month rates of target lesion revascularization by 65% (7.4% vs. 20.9%, p = 0.0008), target vessel revascularization by 53% (11.3% vs. 24%, p < 0.004), and composite major adverse cardiac events by 44% (15.6% vs. 27.7%, p = 0.01). The one-year rates of cardiac death (1.9% vs. 2.5%), myocardial infarction (3.2% vs. 6.4%), and subacute thrombosis (0.6% vs. 1.2%) were comparable between the paclitaxel-eluting and control stents, respectively. In the insulin-requiring subgroup, the TAXUS stent reduced angiographic restenosis by 82% (7.7% vs. 42.9%, p = 0.0065), and reduced the one-year rate of target lesion revascularization by 68% (6.2% vs. 19.4%, p = 0.07), a relative reduction similar to patients without diabetes.

CONCLUSIONS

The site-specific delivery of paclitaxel after coronary stent implantation is highly effective in reducing clinical and angiographic restenosis in patients with diabetes mellitus.

Guidelines for percutaneous coronary interventions. The Task Force for Percutaneous Coronary Interventions of the European Society of Cardiology

In patients with stable CAD, PCI can be considered a valuable initial mode of revascularization in all patients with objective large ischaemia in the presence of almost every lesion subset, with only one exception: chronic total occlusions that cannot be crossed. In early studies, there was a small survival advantage with CABG surgery compared with PCI without stenting. The addition of stents and newer adjunctive medications improved the outcome for PCI. The decision to recommend PCI or CABG surgery will be guided by technical improvements in cardiology or surgery, local expertise, and patients' preference. However, until proved otherwise, PCI should be used only with reservation in diabetics with multi-vessel disease and in patients with unprotected left main stenosis. The use of drug-eluting stents might change this situation. Patients presenting with NSTE-ACS (UA or NSTEMI) have to be stratified first for their risk of acute thrombotic complications. A clear benefit from early angiography (<48 h) and, when needed, PCI or CABG surgery has been reported only in the high-risk groups. Deferral of intervention does not improve outcome. Routine stenting is recommended on the basis of the predictability of the result and its immediate safety. In patients with STEMI, primary PCI should be the treatment of choice in patients presenting in a hospital with PCI facility and an experienced team. Patients with contra-indications to thrombolysis should be immediately transferred for primary PCI, because this might be their only chance for quickly opening the coronary artery. In cardiogenic shock, emergency PCI for complete revascularization may be life-saving and should be considered at an early stage. Compared with thrombolysis, randomized trials that transferred the patients for primary PCI to a 'heart attack centre' observed a better clinical outcome, despite transport times leading to a significantly longer delay between randomization and start of the treatment. The superiority of primary PCI over thrombolysis seems to be especially clinically relevant for the time interval between 3 and 12 h after onset of chest pain or other symptoms on the basis of its superior preservation of myocardium. Furthermore, with increasing time to presentation, major-adverse-cardiac-event rates increase after thrombolysis, but appear to remain relatively stable after primary PCI. Within the first 3 h after onset of chest pain or other symptoms, both reperfusion strategies seem equally effective in reducing infarct size and mortality. Therefore, thrombolysis is still a viable alternative to primary PCI, if it can be delivered within 3 h after onset of chest pain or other symptoms. Primary PCI compared with thrombolysis significantly reduced stroke. Overall, we prefer primary PCI over thrombolysis in the first 3 h of chest pain to prevent stroke, and in patients presenting 3-12 h after the onset of chest pain, to salvage myocardium and also to prevent stroke. At the moment, there is no evidence to recommend facilitated PCI. Rescue PCI is recommended, if thrombolysis failed within 45-60 min after starting the administration. After successful thrombolysis, the use of routine coronary angiography within 24 h and PCI, if applicable, is recommended even in asymptomatic patients without demonstrable ischaemia to improve patients' outcome. If a PCI centre is not available within 24 h, patients who have received successful thrombolysis with evidence of spontaneous or inducible ischaemia before discharge should be referred to coronary angiography and revascularized accordingly--independent of 'maximal' medical therapy.

The drug-based pipeline against restenosis

More than 1 million percutaneous coronary interventions (PCIs) are performed yearly worldwide. Restenosis is the recurrent narrowing that can occur within 6 months following an initially successful PCI. Although drug-eluting stents have accomplished remarkable success, restenosis has not been eliminated and optimisation of both the polymers and drugs associated with them is desirable. This article reviews the presently available and potential preventive approaches against restenosis, including the sirolimus and paclitaxel drug-eluting stents.

What is the risk of stent thrombosis associated with the use of paclitaxel-eluting stents for percutaneous coronary intervention?

OBJECTIVES

This study investigated the risk of stent thrombosis associated with the use of paclitaxel-eluting stents (PES) compared to bare-metal stents (BMS).

BACKGROUND

Clinical experience with coronary drug-eluting stents (DES) is relatively limited. There is concern that DES used for percutaneous coronary intervention may result in subsequent thrombosis.

METHODS

We conducted a meta-analysis on eight trials (total of 13 study arms) in 3,817 patients with coronary artery disease who were randomized to either PES or BMS.

RESULTS

As compared with BMS, PES do not increase the hazard for thrombosis up to 12 months (risk ratio [RR] = 1.06, 95% confidence interval [CI] 0.55 to 2.04, p = 0.86]). There was no evidence of heterogeneity among the studies (chi-square value for Q-statistic = 5.90 [10 degrees of freedom], p = 0.82). Similar results were obtained when the analysis was restricted to trials with a polymeric stent platform (Treatment of de novo coronary disease using a single pAclitaXel elUting Stent [TAXUS]-I, -II, -IV, and -VI) (RR = 1.01, 95% CI 0.40 to 2.53, p = 0.99), trials with longer lesions (TAXUS-IV and -VI) (RR = 0.62, 95% CI 0.2 to 1.91, p = 0.41), and trials that used a higher dose of paclitaxel (ASian Paclitaxel-Eluting Stent Clinical trial [ASPECT], European evaLUaTion of paclitaxel Eluting Stents [ELUTES], and DELIVER-I) (RR = 1.87, 95% CI 0.52 to 6.81, p = 0.34).

CONCLUSIONS

Current evidence suggests that standard dose PES do not increase the hazard of stent thrombosis compared to BMS.

Meta-analysis comparing drug-eluting stents with bare metal stents

We performed a meta-analysis of 10 randomized trials of 5,066 patients with 6 to 12 months of follow-up. The summary risk differences excluded any major differences between the 2 types of stents for death (0.12%, 95% confidence interval [CI] -0.34% to 0.58%, p = 0.60) and overall myocardial infarction (0.04%, 95% CI -0.72% to 0.81%, p = 0.91). There was a modest increase in the risk of Q-wave myocardial infarction with drug-eluting stents (0.36%, 95% CI -0.04% to 0.77%, p = 0.080) but no difference in non-Q-wave myocardial infarction (-0.26%, 95% CI -0.95% to 0.43%, p = 0.47). The trend for increased risk of Q-wave myocardial infarction was seen for paclitaxel and sirolimus stents (risk differences 0.28% and 0.58%, respectively). Drug-eluting stents also had a nonsignificant trend for higher risk of thrombosis (0.29%, 95% CI -0.08% to 0.66%, p = 0.13). We conclude that sirolimus- and paclitaxel-eluting stents are equivalent to bare-metal stents in terms of mortality and overall myocardial infarction risk for the first year of follow-up; the meta-analysis excludes with considerable confidence the presence of large, clinically relevant differences for these outcomes.

Dollars and Stents: The Economics of Drug-Eluting Stents

By averting restenoses, drug-eluting stents (DES) reduce the need for repeat revascularization procedures and improve quality of life. Large, randomized clinical trials including the Sirolimus-Eluting Balloon Expandable Stent in Treatment of Patients With De Novo Native Coronary Artery Lesions (SIRIUS) suggest that DES may be cost-effective to the Medicare system over time. However, the high cost of DES and the loss of revenues from revascularization procedures coupled with inadequate Medicare reimbursement are likely to have adverse effects on hospitals, making it hard to meet their bottom line. Key contributors to this problem include the unequal distribution of Medicare reimbursement based on diagnosis-related groups or diagnosis-related group calculations and the lack of price competition for DES. The economic burden of restenoses, the efficacy of DES in averting restenoses, the cost-effectiveness of DES, and the interaction of Medicare, DES manufacturers, and hospitals are reviewed. Using specific cost-containment strategies, hospitals can better maneuver the financial barriers to optimize DES utilization.

Sirolimus- or paclitaxel-eluting stents to prevent coronary artery restenosis

The restenosis rate is lower with stent implantation than with balloon angioplasty. Nevertheless, even with the use of stenting, restenosis still occurs in approximately one-third of patients with diabetes, small coronary vessels, and long lesions. The two drugs commonly used in eluting stents are sirolimus and paclitaxel. Systemically administered sirolimus decreased vascular proliferation in animal models. After preliminary trials showing benefit with sirolimus-eluting stents in de novo coronary lesions, the large-scale SIRIUS (Sirolomus-coated Bx Velocity balloon-expandable stent in the treatment of patients with de novo coronary artery lesions) trial was undertaken. SIRIUS showed that sirolimus reduced restenosis and target vessel revascularisation, compared to bare stents. These benefits were also apparent in the diabetic, and small- and long vessel subgroups. The RESEARCH (Rapamycin-eluting Stent Evaluated At Rotterdam Cardiology Hospital) registry have established that sirolimus-eluting stents are superior to bare stents in practice. Thus, the benefits of sirolimus-eluting stents over bare stents have been clearly established, and sirolimus can be considered the benchmark eluting agent for the prevention of coronary artery restenosis. Animal studies with paclitaxel-eluting stents, mainly in endothelium denuded normal vessels, have shown that paclitaxel reduces restenosis in the short-term, and that this may be a delay, rather than a prevention of restenosis. In clinical trials, stents eluting the paclitaxel derivative 7-hexanolytaxol, or paclitaxel without a polymer, delay rather than prevent restenosis. Slowing the release of paclitaxel with a polymer base in the TAXUS (Taxol(trade mark) [paclitaxel]-eluting stent) series of clinical trials reduced the revascularisation rate at 12 and 18 months, indicating that polymer-based paclitaxel is effective for longer. The results of the REALITY trial comparing the sirolimus- and paclitaxel-eluting stents in diabetics and other high-risk patients are eagerly awaited.

Comprehensive imaging of coronary artery disease: impact on contemporary treatment approaches

Coronary artery disease remains a major cause of mortality. Together with novel therapeutic and preventive approaches, important advances of coronary imaging are currently emerging. This article describes the status of modern coronary imaging and outlines expected future developments.

Which Parameter Should Be Chosen as Primary Endpoint for Randomized Drug-Eluting Stent Studies?

In Europe, 1,108 percutaneous coronary interventions (PCIs) per one Mio inhabitants are currently annually performed, most of them with stent implantation. Drug-eluting stents have been the focus of attention of interventional coronary therapy since the RAVEL study was first presented in September 2001 at the European Society of Cardiology Meeting. Ever since, numerous studies have assessed the effects of various antiproliferative and anti-inflammatory substances and a variety of different stents was used as platform, either covered with polymer carriers of different chemical and physical properties or without a polymer carrier. CE- or FDA-certified drug-eluting stents are increasingly replacing the use of bare metal stents to reduce in-stent restenosis. Today, physicians have a choice of several approved drug-eluting stents and, therefore, need some evidence-based guidance through the "jungle of information" to make the right decisions. Even when focusing on randomized trials, differences between the studies regarding primary endpoints and sample sizes exist, making it difficult to compare the various drug-eluting stent studies. Randomized studies use either nonclinical (i.e., angiographic diameter stenosis, in-stent MLD, or in-stent late lumen loss) or clinical (i.e., TVF, TVR, and MACE) parameters as primary endpoints. Choosing an angiographic parameter as primary endpoint results in two major limitations: first, a significant improvement of an angiographic "surrogate" parameter does not necessarily translate into a better clinical outcome (DELIVER-I); second, conclusions regarding possible improvements of clinical outcome are underpowered, because the sample size calculation is based on the primary endpoint. Usually the number of patients needed is lower for angiographic than for clinical endpoints. Until today, only three trials with a primary clinical endpoint have shown a significantly positive impact on patients' outcome: the SIRIUS trial (Cypher stent) with its reduction of primary endpoint TVF (21.0% vs 8.6%), the TAXUS-IV trial (Taxus stent) with its reduction of primary endpoint TVR (12.0% vs 4.7%) and TAXUS-VI in long lesions with its reduction of primary endpoint TVR (19.4% vs 9.1%). Although the angiographic results of other drug-eluting stents are encouraging, they will have to prove their clinical impact based on adequately powered randomized trials with a primary clinical endpoint at an adequate time interval.

Drug-coated Stents

Since its introduction in 1977, the success of percutaneous interventional cardiology has been limited by the occurrence of restenosis. Drug-eluting stents, particularly sirolimus- and paclitaxel-coated stents, have been shown in randomized controlled trials to dramatically reduce restenosis in single, de novo, native coronary arteries. Over the last 2 years, investigators have reported that these stents can also reduce restenosis in more complex patient situations such as in diabetics, during acute coronary syndromes, in long atherosclerotic lesions and small arteries, and even after in-stent restenosis. These outcomes increase the clinical value of this technology to "real world" practice. This article reviews the current state of our knowledge regarding drug-eluting stents and identifies areas for further research.

Prevention of restenosis after coronary angioplasty

PURPOSE OF REVIEW

Despite numerous advances in coronary interventional techniques, the frequent occurrence of restenosis continues to plague interventional cardiology. With the widespread use of drug-eluting stents, there is a need to reexamine critically the roles of the various interventional techniques currently available.

RECENT FINDINGS

Drug-eluting stents have dramatically reduced the rates of restenosis and target vessel revascularization in a wide spectrum of patients with varying lesion morphologies. However, when restenosis does occur, it still tends to be dependent on the same factors that predict restenosis with bare metal stenting. The routine use of drug-eluting stents entails high initial costs to the health care system. Debulking as a means to improve outcomes after angioplasty has not lived up to expectations. Gene therapy is rapidly evolving into a viable means to reduce neointimal proliferation after angioplasty.

SUMMARY

Careful patient selection and attention to the procedure of stent deployment optimize the results of angioplasty with drug-eluting stents. Because of cost considerations, drug-eluting stents should be used in patients who are expected to have the greatest absolute benefit. In this context, when judiciously used, conventional balloon angioplasty and bare metal stenting still have a definite role in the management of patients with obstructive coronary artery disease.

A hierarchical Bayesian meta-analysis of randomised clinical trials of drug-eluting stents

BACKGROUND

Drug-eluting stents (DES) are associated with lower restenosis rates than bare-metal stents (BMS), but the benefits and safety of the new devices have not been systematically quantified across different trials. We undertook a meta-analysis of randomised trials comparing BMS and stents eluting sirolimus or paclitaxel.

METHODS

A systematic literature search aimed to identify all randomised clinical trials with 6-12 months of clinical follow-up. Results were pooled by a hierarchical Bayesian random-effects model with prespecified stratification for drug and the presence of carrier polymer. The primary outcomes examined were rates of death, myocardial infarction, target-lesion revascularisation, major adverse cardiac events (death, myocardial infarction, and target-vessel revascularisation), and angiographic restenosis.

FINDINGS

We identified 11 eligible trials involving 5103 patients. The pooled mortality rates were low for both DES and BMS with no evidence of any difference between them (odds ratio 1.11 [95% credible interval 0.61-2.06]). Pooled rates of myocardial infarction showed no between-group difference (0.92 [0.65-1.25]). The rate of major adverse cardiac events was 7.8% with DES and 16.4% with BMS (0.42 [0.32-0.53]), and the angiographic restenosis rates were also lower for DES (8.9% vs 29.3%; 0.18 [0.06-0.40]). The pooled rates of major adverse cardiac events for each DES type and the respective BMS were: for sirolimus, 6.8% versus 21.0% (0.28 [0.17-0.41]); for polymer-based paclitaxel 8.7% versus 16.7% (0.47 [0.25-0.71]); and for non-polymer-based paclitaxel 7.7% versus 9.5% (0.64 [0.42-1.00]). We did not observe higher rates of edge restenosis, stent thrombosis, or late incomplete stent apposition with DES, although the credible intervals were wide.

INTERPRETATION

Sirolimus-eluting and polymeric paclitaxel-eluting stents are effective at decreasing rates of angiographic restenosis and major adverse cardiac events compared with BMS. However, there is no evidence that they affect mortality or myocardial-infarction rates. They also appear to be safe in the short to medium term, although definitive conclusions are not possible. Larger studies with longer follow-up are needed to define better the role of these new devices.