Article

Platinum Chromium Stent Series – The TAXUS™ Element™ (ION™), PROMUS Element™ and OMEGA™ Stents

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Abstract

Advances in drug-eluting stent technology have continued to improve clinical outcomes for patients undergoing percutaneous coronary intervention (PCI). The Boston Scientific stent platform has evolved from the 316L stainless steel Express™ stent, to the 316L stainless steel Liberté™ stent, to the cobalt–chromium PROMUS™ stent and, finally, to the platinum–chromium (PtCr) stent series. The PtCr platform, which uses the Element architecture, is designed to have improved deliverability, radiopacity, radial strength and recoil resistance compared with existing stainless steel or cobalt–chromium stents. This review discusses the key points in Boston Scientific’s development programme, which has culminated in the newest generation of coronary stent systems: the PtCr bare-metal OMEGA™ stent, the PtCr paclitaxel-eluting TAXUS Element™ (ION™) stent and the PtCr everolimus-eluting PROMUS Element™ stent systems.

Keywords

Drug-eluting stent, bare metal stent, percutaneous coronary intervention, paclitaxel, everolimus,

Disclosure:All authors are employees and shareholders of Boston Scientific Corporation.

Received:

Accepted:

DOI:https://doi.org/10.15420/icr.2011.6.2.134

Support:The publication of this article was funded by Boston Scientific Corporation.

Acknowledgements:The authors would like to thank Vicki Houle for her editorial assistance in the preparation of this manuscript.

Correspondence Details:Dominic J Allocco, Cardiology, Rhythm, and Vascular Division, One Scimed Place - A285, Maple Grove, MN 55311, US. E: alloccod@bsci.com

Copyright Statement:

The copyright in this work belongs to Radcliffe Medical Media. Only articles clearly marked with the CC BY-NC logo are published with the Creative Commons by Attribution Licence. The CC BY-NC option was not available for Radcliffe journals before 1 January 2019. Articles marked ‘Open Access’ but not marked ‘CC BY-NC’ are made freely accessible at the time of publication but are subject to standard copyright law regarding reproduction and distribution. Permission is required for reuse of this content.

Advances in drug-eluting stent technology have continued to improve clinical outcomes for patients undergoing percutaneous coronary intervention (PCI). The development of the platinum– chromium (PtCr) alloy and Element™ stent architecture (or platform) is the result of more than eight years of research and development by Boston Scientific Corporation (BSC; Natick, MA, US) and builds on a pedigree of innovation, design and processing excellence within the field of intracoronary device manufacturing. Advances in materials science and stent design have allowed the development of the novel thin-strut, low-profile and flexible PtCr platform engineered from a proprietary PtCr alloy. This PtCr platform provides excellent acute deliverability and conformability, increased radiopacity, and improved radial strength and compression resistance. The PtCr stent series consists of the OMEGA™ bare metal, TAXUS™ Element™ (ION™) paclitaxel-eluting and PROMUS Element™ everolimus-eluting coronary stent systems. The TAXUS™ Element stent is marketed as the ION™ stent in the US. In the US, the OMEGA and PROMUS Element stents are investigational devices and not available for sale.

The OMEGA stent (which uses the Element platform) is a bare metal stent that builds on BSC’s experience with the 316L stainless steel (SS) Express and Liberté stent platforms. The TAXUS Element stent is the next-generation paclitaxel-eluting stent from BSC. The TAXUS Element (ION) stent employs an identical polymer, drug, drug formulation and dose density to both the TAXUS Liberté and TAXUS Express stents. The PROMUS Element stent represents the next-generation PROMUS (Xience V™) stent. The PROMUS Element stent employs an identical polymer, drug, drug formulation and dose density to the currently available cobalt–chromium (CoCr) PROMUS (Xience V) stent. The PROMUS Element stent is proprietary to Boston Scientific.

This paper describes the functionality, biocompatibility and vascular compatibility of the PtCr alloy, the unique components of the Element stent architecture and subsequent rigorous testing and investigation of this new product line. Pre-clinical and clinical programmes for the OMEGA, TAXUS Element (ION) and PROMUS Element Stents are also presented.

Pre-clinical Development of the Platinum–Chromium Stent Series

The Platinum–Chromium Alloy

With newer generations of 316L SS stent platforms, such as the Liberté design, strut thickness was reduced at the expense of radiopacity. The adoption of CoCr alloys improved stent deliverability by enabling a reduction in strut thickness beyond what was possible with 316L SS, while still retaining some degree of radiopacity.1 However, stents produced from CoCr alloys also tend to have higher recoil owing to the elastic properties of the alloy. Although both 316L SS and CoCr were potential alloy choices for BSC’s PtCr stent series, neither could provide a highly deliverable thin-strut stent design with optimal radiopacity while still retaining the low recoil and radial strength characteristic of 316L SS.

PtCr is the first alloy created specifically for coronary stenting. Platinum exhibits biocompatibility, chemical stability and corrosion resistance and was, therefore, a promising candidate for inclusion in a biomedical alloy. Exhaustive characterisation was pursued in an effort to optimise alloy properties, including radiopacity, microstructure/stability and mechanical attributes. The pre-clinical testing surrounding the development of the PtCr alloy has been described in detail previously.2,3 A platinum content of 33 % homogeneously alloyed into the 316L SS base material was chosen as the final alloy composition, with a corresponding reduction in iron and nickel content compared with 316L SS (see review by Menown et al.)2 The higher density of PtCr (9.9g/cm3) compared with 316L SS (8.0g/cm3) or L605 CoCr (9.1g/cm3) results in enhanced radiopacity,4 and thus the thin strut design of the Element platform does not come at the expense of a reduction in stent visibility (see Figure 1A).3 Use of this stronger and more radiopaque PtCr alloy enables the optimisation of other key features of the stent platform, as discussed below. Processing of the PtCr tubes into finished stents required a novel approach in laser cutting, chemical and electrochemical post-processing techniques. The result was a stent with chromium-oxide-rich, smooth, rounded surfaces to help optimise biocompatibility.

The Element Stent Design and Delivery System

The Element stent design incorporates a dimensionally uniform pattern of serpentine segments, each with two offset connectors, that reverse the direction of alternate rows to maintain a balance of forces along the stent (see Figure 1B). This helical design also allows each segment to operate almost independently of the others, improving deliverability and conformability. The peaks are widened at the crown to redirect the strain of expansion to the longitudinal portion, and this, along with the properties of the alloy, minimises the recoil of the expanded stent and helps to maintain radial strength. The offset and nested nature of the peaks minimises potential strut-to-strut contact when delivering and deploying the stent on a bend.

The PtCr stent is mounted on a new, customised stent delivery system that incorporates bi-segment inner lumen technology to maximise pushability, flexibility, trackability, stent securement and stent deployment. The stent architecture incorporates several improved stent performance features with four stent models across the range of diameters. Other stent platforms, such as Express (BSC), Vision™ (Abbott Vascular Corporation, Abbott Park, IL, US), BX Velocity™ (Cordis Corporation, Bridgewater, NJ, US) and Driver™ (Medtronic Corporation, Minneapolis, MN, US) stents, have only two stent models to cover the range of diameters; that is, an identical stent is used for a 2.25 mm up to a 3.0 mm labelled device, but is simply mounted on a different sized stent delivery balloon. For the PtCr stent series, increasing the number of models optimises the surface-to-artery ratio over the range of diameters and provides more uniform drug distribution and scaffolding, which may reduce the risk of plaque prolapse. Most importantly, the PtCr stent series has a specific model for the 2.25 mm diameter that has a lower system profile and shorter (and therefore more) segments per stent than the larger diameter models, thus improving the deliverability and conformability of the stent in more tortuous, challenging and small vessels, as well as providing more uniform drug distribution. This design is the platform for both bare metal and drug-eluting stents.

Comparison of Bare Metal Stent Specifications

The PtCr stents were further evaluated in direct comparison with a number of competitor stents in bench tests. The OMEGA bare metal PtCr stent has demonstrated superior performance to the competitive bare metal stent designs in both conformability and recoil (see Table 1). Recoil is a measure of the ability of a stent to maintain its initial expansion diameter. Low recoil may minimise the risk of malapposition to the vessel wall, and OMEGA has the lowest recoil of all the stents compared. Conformability relates to the ability of a stent to support tortuous vessels without inducing vessel straightening and may be an important predictor of the potential to induce vessel damage, including edge dissection. Increased stent rigidity limits the use of stents in both tortuous anatomy and at bends, which may result in a hinge effect that has been associated with an increase in restenosis.5 The OMEGA stent has the lowest stent rigidity, as measured by conformability, of all the stents compared.

Comparison of Drug-eluting Stent Specifications

The PROMUS Element and TAXUS Element (ION) stents demonstrate comparable or superior performance to the predicate PROMUS (Xience V), TAXUS Express and Liberté stent designs for conformability, compression resistance, recoil and stent-to-artery ratio (see Table 2). By comparison, recoil values are similar to or better than other commercially available stents: PROMUS Element and TAXUS Element (ION) 3.0 %, PROMUS (Xience V) 5.0 %, TAXUS Liberté 3.0 %, Cypher 3.3 % and Endeavor stents 4.9 %.

Compression resistance, a measure of stent scaffolding strength, relates to the ability of a stent to maintain the vessel lumen. The compression resistance, as measured by radial strength, for the PROMUS Element and TAXUS Element (ION) Stent (0.26 N/mm) is similar to that of the TAXUS Liberté (0.24 N/mm). It also compares favourably with PROMUS/Xience V (0.11 N/mm), Cypher (0.17 N/mm) and Endeavor (0.15 N/mm).

The PROMUS and TAXUS Element (ION) stents have improved conformability (0.04 N mm) compared with other platforms (TAXUS Liberte 0.09 N mm, Cypher 1.1 N mm, PROMUS (Xience V) 0.32 N mm and Endeavor 0.06 N mm).

TAXUS Element (ION) Stent Polymer

The coating on the TAXUS Element (ION) stent consists of a polymer, poly (styrene-b-isobutylene-b-styrene), referred to as SIBS (Translute™) and an active pharmaceutical ingredient, paclitaxel. Paclitaxel disrupts many microtubular-dependent cell processes including cell proliferation, cell migration, cellular activation, secretory processes and signal transduction, thereby inhibiting neointimal growth.6,7 In human smooth-muscle cells, low doses (such as those eluted from the TAXUS stent) inhibit cell proliferation via a cytostatic effect.8 Each TAXUS Element (ION) stent is coated with 1.0 μg paclitaxel per mm2 of stent surface area in an 8.8 % formulation (weight per cent paclitaxel in the polymer coating). This is the identical polymer matrix, dose density and formulation used in the TAXUS Express stent and TAXUS Liberte stent, and the average drug release over time is similar across these three stent platforms. The 8.8 % paclitaxel slow-release formulation provides controlled drug delivery to the stented vessel segment. To date, Boston Scientific has successfully transferred this drug/polymer combination across four different platforms: the Nir™ stent, the Express stent, the Liberte stent and now the PtCr stent. Figure 1C demonstrates the strut thickness and polymer loading for the various iterations of BSC’s paclitaxel and PROMUS stents.

PROMUS Element Stent Coating

The coating on the PROMUS Element stent is composed of two layers: a primer layer and an active drug matrix layer blended with the antiproliferative drug everolimus. Everolimus is a novel semi-synthetic macrolide immunosuppressant, obtained through chemical modification of rapamycin.9 On a cellular level, everolimus reversibly inhibits growth-factor-stimulated cell proliferation and subsequently inhibits activation of the regulatory kinase mammalian target of rapamycin (mTOR).10 This inhibition interferes with functions that govern cell metabolism, growth and proliferation by arresting the cell cycle at the late G1 phase.11

The primer polymer layer (poly-butyl-methacrylate [PBMA]) functions as an adhesion promoter between the bare metal stent and drug matrix layer. The drug matrix layer is composed of a semi-crystalline random copolymer, poly (vinylidene-fluoride-hexafluoropropylene), or PVDF-HFP, blended with everolimus. The drug-to-polymer formulation ratio is identical to that used on the PROMUS (Xience V) stent. The resulting drug-loading density (total weight of drug per unit of stent surface area) on the coated stent is 10 μg of everolimus/mm2. Pre-clinical testing with the PROMUS Element stent demonstrated comparable drug release profiles, everolimus arterial tissue levels and blood drug levels to the PROMUS (Xience V) stent, with consistent release achieved within the first 24 hours (23–36 %). The majority of the drug was released from the stent by 60 days following implant (75–85 %), with nearly complete (85–90 %) release by 90 days.

Vascular Compatibility of the Platinum–Chromium Alloy

Pre-clinical animal studies have demonstrated equivalent or improved vascular compatibility and early and late healing for PtCr devices compared with CoCr or 316L SS. Using a rabbit iliac model with balloon denudation of the endothelial cell layer,12 at 14 days the luminal surface area is incompletely endothelialised with the 316L SS Express and Liberte stents but nearly complete for the PtCr OMEGA stent. By 21 days, endothelialisation of luminal surface area and stent struts is largely complete for all three stents.13 These studies demonstrated that overall strut coverage, including endothelial cell coverage plus non-endothelial cell coverage (focal platelet and fibrin aggregates inter-mixed with red blood cells and infla mmatory cells), was significantly lower at 14 days with the thicker Express struts (77 %) compared with Liberte (88 %, p=0.05) and OMEGA (95 %, p=0.001).13 Moreover, in a non-injured swine coronary artery model, vessels implanted with bare PtCr alloy stents, bare 316L SS stents and bare L605 CoCr alloy stents were equivalent for all clinical safety parameters, and were histologically indistinguishable at 30, 90 and 180 days.

Additionally, the thinner-strut PtCr stent has been associated with reduced fibrin deposition and more rapid fibrin clearance in porcine coronary arteries compared with the 316 SS TAXUS Express or TAXUS Liberte stents (see Figure 2).4 Specifically, by 180 days, none of the samples with the TAXUS Element (ION) stent had extensive fibrin deposition (evidenced by a fibrin score of 3), whereas five of 14 samples with TAXUS Express and two of 25 samples with TAXUS Liberte had extensive fibrin deposition. These data suggest that the PtCr stent platform may induce less injury compared with previous-generation BSC stents.

Clinical Development of the Platinum–Chromium Stent Series

The OMEGA Clinical Trial

The OMEGA clinical trial is a prospective, multicentre, single-arm investigational device exemption (IDE) trial to evaluate the safety and effectiveness of the OMEGA coronary stent system for the treatment of a single de novo coronary artery lesion of up to 28 mm in length in native coronary arteries of 2.25–4.50 mm in diameter. The OMEGA trial plans to enrol 328 patients at up to 40 investigative sites in the US and Europe to support approval in the US and Japan. The OMEGA stent was CE-marked in February 2011 on the strength of the data supporting the drug-eluting versions of the platform as well as the clinical efficacy of thin-strut bare metal stents.

The primary endpoint of the OMEGA trial is the target lesion failure (TLF) rate at nine months post-index procedure, defined as any ischaemia-driven target lesion revascularisation (TLR), myocardial infarction (MI, Q-wave and non-Q-wave) related to the target vessel or cardiac death. An exact binomial test will be used to assess whether the nine-month TLF rate for OMEGA is less than the pre-specified performance goal, which was calculated based on historical results from existing bare metal stents. Clinical endpoints will be measured in-hospital and at 30 days, nine months and 12 months. Enrolment is anticipated to begin in 2011, with reporting of the primary endpoint in 2013.

The PERSEUS Clinical Programme

The TAXUS clinical programme provides a large body of clinical evidence establishing the safety and efficacy of paclitaxel-eluting stents used in the treatment of coronary artery disease. The predicate TAXUS devices are supported by the TAXUS clinical programmes, which have cumulatively established clinical safety and performance in more than 45,000 patients with greater than 100,000 patient-years of follow-up. Progressively more complex patient populations, lesions and procedures were evaluated by clinical, angiographic and intravenous ultrasound (IVUS) outcomes,14 and these data provide the foundation for the evaluation of the TAXUS Element (ION) stent in the PERSEUS clinical programme.

PERSEUS Clinical Programme

The data from the PERSEUS clinical programme directly support the safety and efficacy of the TAXUS Element (ION) stent.4 In the US, the PERSEUS clinical trials were the basis for US Food and Drug Administration (FDA) approval for the ION paclitaxel-eluting PtCr coronary stent system in April 2011. The PERSEUS Workhorse study was a randomised non-inferiority clinical trial comparing the TAXUS Element (ION) stent with the TAXUS Express Stent. The PERSEUS Small Vessel study was a single-arm superiority study evaluating use of the TAXUS Element (ION) stent for the treatment of lesions in vessels with a reference vessel diameter between ≥2.25 and <2.75 mm. The data from the PERSEUS clinical programme will also support Japanese regulatory approval for this product.

The PERSEUS Workhorse trial met both its primary and secondary endpoints (see Table 3), demonstrating non-inferiority in the safety and efficacy profile of the TAXUS Element (ION) stent compared with the TAXUS Express stent.15 The TAXUS Element (ION) stent was non-inferior to the TAXUS Express stent with respect to both the incidence of TLF (5.57 % versus 6.14 %; p=0.9996) and per cent diameter stenosis (ln [%DS] 3.09 versus 3.12; p=0.9970). No differences in clinical outcomes to 12 months were observed between stent treatments, and stent thrombosis (ST) was infrequent with either stent (0.3 % TAXUS Express stent, 0.4 % TAXUS Element (ION) stent).15

The PERSEUS Small Vessel study met its primary and secondary endpoints (Table 3), demonstrating the safety and effectiveness of the TAXUS Element (ION) stent in small vessels.16 In comparison with the historical control of the bare metal Express stent, the TAXUS Element (ION) stent was superior for late loss (0.38±0.51 mm versus 0.80±0.53 mm; p<0.001), and the TLF rate of 7.3 % was significantly less than the 19.5 % performance goal (p<0.001). No differences in mortality, myocardial infarction or ST were observed up to 12 months.16 A post hoc patient-level pooled analysis involving 2,298 subjects enrolled into the TAXUS ATLAS trials (which evaluated the TAXUS Liberte stent) and PERSEUS trials was performed. Propensity score matching was used to adjust for covariate imbalance between groups. In this analysis, the TAXUS Element (ION) stent was associated with fewer adverse clinical events at 12 months, including significantly lower MI, TLF and major adverse coronary events, compared with the TAXUS Liberte stent. The TAXUS Element (ION) stent was also associated with significantly lower in-stent late lumen loss compared with the TAXUS Liberte stent at nine months.

The SPIRIT Clinical Programme

The PROMUS (Xience V) stent has been studied in patients with symptomatic ischaemic heart disease owing to de novo lesions in native coronary arteries in the SPIRIT First, SPIRIT II and SPIRIT III clinical trials, all of which have achieved their primary endpoint. Long-term outcome studies of PROMUS (Xience V) continue to support safety and performance in the treatment of de novo lesions.17,18 The SPIRIT trials demonstrate the safety and efficacy of the everolimus drug and polymer combination in the treatment of coronary artery disease when delivered on a coronary stent platform.

The safety and performance of the PROMUS (Xience V) stent in patients with de novo native coronary artery lesions were first demonstrated in the SPIRIT First clinical trial.19,20 SPIRIT II was a further assessment of the safety and performance of the PROMUS (Xience V) stent in more complex anatomy, including patients with a maximum of two de novo native coronary artery lesions located in two different epicardial vessels.21,22 SPIRIT III was the pivotal clinical trial designed to demonstrate the non-inferiority of the PROMUS (Xience V) stent to the TAXUS Express stent.17,23 Finally, the SPIRIT IV study was a prospective randomised clinical trial evaluating TLF and ischaemia-driven TLR in patients receiving the PROMUS (Xience V) stent compared with the TAXUS Express stent in up to three de novo native coronary artery lesions, with a maximum of two lesions per epicardial vessel.24,25 Taken together, the SPIRIT clinical trials demonstrate the excellent safety and efficacy profile of everolimus and the polymer delivery system in the treatment of coronary artery disease.

The PLATINUM Clinical Programme

The PLATINUM clinical trial programme directly supports the use of the PROMUS Element stent in PCI patients. The data from this programme will support the regulatory submissions for the US and Japan. The PLATINUM clinical trial programme is summarised in Table 4.

PLATINUM QCA Trial

The PLATINUM QCA trial is a prospective, single-arm, multicentre, observational study of the next-generation PROMUS Element stent. The objective was to compile acute (30-day) clinical outcome data and nine-month angiographic and IVUS data. The primary clinical end-point was the 30-day composite rate of cardiac death, MI, TLR and definite/probable ST.

The pre-specified efficacy end-points were in-stent late loss by quantitative coronary angiography (QCA) at nine months in workhorse lesions – defined as visual reference vessel diameter (RVD) ≥2.50 mm and ≤4.25 mm and visual lesion length ≤24 mm – and incomplete stent apposition (ISA) by post-procedure IVUS. Enrolment in the PLATINUM QCA study was completed in July 2009 with 100 patients, including 85 workhorse, three small vessel (RVD ≥2.25 mm and <2.5 mm) and 12 long lesion (lesion length >24 mm to ≤34 mm) patients. Technical success (defined as successful delivery and deployment of the study stent to the target lesion without balloon rupture or embolisation) was 100 % and procedural success (defined as mean lesion diameter stenosis <30 % with TIMI-3 flow and no in-hospital MI, TVR or cardiac death) was 99 %. The 30-day composite rate of cardiac death, MI, TLR and ST was 1.0 %, with one subject suffering a peri-procedural ST, TLR and non-target-lesion TVR. There were no additional major cardiac events or deaths up to 12 months (see Table 5).26

In-stent late loss in workhorse lesions using the PROMUS Element stent was significantly less than the performance goal based on historical results with TAXUS Express (0.17±0.25 mm versus 0.44 mm; p<0.001; see Figure 3). This late loss is similar to the eight-month in-stent late loss of 0.16±0.41 mm observed with the PROMUS (Xience V) stent in the SPIRIT III trial. Post-procedure incomplete stent apposition with the PROMUS Element was also significantly less than the performance goal based on outcomes with PROMUS (Xience V) in the SPIRIT III trial (5.7 % versus 34.4 %; p<0.001; see Figure 3).26 Of those patients with post-procedure ISA by IVUS, all had resolved by the nine-month IVUS, and there were no instances of persistent or late acquired incomplete apposition in the PROMUS Element cohort. Multiple factors, including stent design and a high rate of post-dilatation, potentially explain the low rate of ISA seen with the PROMUS Element stent in PLATINUM QCA. The mechanical properties of the stent (particularly its low recoil and high conformability) could result in a lower risk of ISA. This could also be related to other factors, including the extensive use (91.0 %) of post-dilatation and/or the maximum post-dilatation balloon pressure (18.0±3.6 atm) in the PLATINUM QCA study. By comparison, among SPIRIT III patients with both post-procedure and eight-month IVUS follow-up (110 patients, 117 lesions), the post-dilatation rate was 48.7 % with 15.7±3.3 atm maximum post-dilatation balloon pressure.26

Vessel and lumen volumes were similar at nine months compared to post-procedure, with low neointimal volume and net volume obstruction observed at nine months.26

PLATINUM Workhorse (WH) Trial

The PLATINUM WH trial is a randomised, controlled trial, initiated in January 2009, comparing the PROMUS Element stent with the PROMUS (Xience V) stent in a 1:1 fashion in a total of 1,530 patients. The primary end-point of PLATINUM WH was the 12-month TLF rate, defined as any ischaemia-driven TLR, MI (Q-wave and non–Q-wave) related to the target vessel, or cardiac death related to the target vessel. The analysis set for the primary end-point was the per protocol population (defined as patients who received the assigned study stent). This study met its primary end-point (see Figure 4), demonstrating that the PROMUS Element stent is non-inferior to the predicate PROMUS (Xience V) stent in patients undergoing PCI of de novo coronary artery lesions.27 The 12-month rate of TLF was 2.9 % in the PROMUS (Xience V) group and 3.4 % in the PROMUS Element group (Pnoninfereiority = 0.001). The 12-month rate of TLF was not significantly different between the two stent groups regardless of whether the per protocol population (primary endpoint definition) or the intention-to-treat population was examined.27

Technical success was achieved in 99.4 % and 98.8 % of patients receiving the PROMUS Element stent and the PROMUS (Xience V) stent, respectively (p=0.14), and clinical procedural success was achieved in 98.3 % and 98.2 % (p=0.83). However, a higher rate of unplanned (bail-out) stenting was required in patients receiving the PROMUS (Xience V) stent compared with those receiving the PROMUS Element stent (9.8 % versus 5.9 %; p=0.004). This was due in part to a higher rate of inadequate lesion coverage in the PROMUS (Xience V) group versus the PROMUS Element group (3.4 % versus 1.4 %; p=0.01).27 The increased radiopacity and deliverability with the PROMUS Element stent is likely to be a significant factor in the lower rate of geographic miss compared with the PROMUS (Xience V) stent.

There were no significant differences in any safety or efficacy measure between the stent types. The one-year rate of TLR was 1.9 % for both groups, and ARC definite or probable ST occurred in three patients (0.4 %) in each group (see Table 6).27

PLATINUM Small Vessel (SV) Trial

The PLATINUM SV trial is a multicentre, prospective single-arm study, initiated in January 2009, evaluating the PROMUS Element stent in 94 patients for treatment of de novo lesions ≤28 mm long in a native coronary artery ≥2.25 mm to <2.50 mm in diameter (visual estimate). The primary end-point of PLATINUM SV is the 12-month TLF rate, defined as any ischaemia-driven TLR, MI (Q-wave and non–Q-wave) related to the target vessel or cardiac death related to the target vessel. The comparator is a pre-defined performance goal based on historical TAXUS Express results in small vessels.

The primary endpoint was met with a 12-month TLF rate of 2.4 % in the per-protocol group (89 patients receiving the PROMUS Element stent), which was significantly below the performance goal of 21.1 % (p<0.001).28 Technical and procedural success was 96.8 %. In the intent-to-treat group, there were three cardiac deaths, no MIs and no STs. These results support both the safety and efficacy of the PROMUS Element 2.25 mm stent.

In total, the outcomes of the PLATINUM clinical trial programme suggest that the safety and efficacy observed with the everolimus and polymer combination in the PROMUS (Xience V) stent can be successfully transferred to the PtCr stent platform.

Summary

The thin-strut PtCr stent series has fulfilled the design goals of improved acute performance while maintaining excellent safety and efficacy in patients undergoing PCI. The PtCr stent is a highly deliverable, flexible and conformable thin-strut stent with excellent radiopacity, recoil and radial strength. Pre-clinical data with the PtCr stent demonstrated safety and vascular compatibility equivalent to the predicate devices. Clinical outcomes directly support the safety and efficacy of the PtCr stents in patients undergoing PCI. The OMEGA bare metal PtCr stent received CE Mark approval in March 2011. The drug-eluting stents which use the same PtCr alloy and stent platform, the everolimus-eluting PROMUS Element and the paclitaxel-eluting TAXUS Element (ION) stents, received Conformite Europeene Mark approval in October 2009 and May 2010, respectively, while the TAXUS Element stent received FDA approval in April 2011 and is marketed in the US as the ION stent. The PROMUS Element stent is currently under review by the FDA.

Extensive investigation and analysis of the OMEGA, TAXUS Element (ION) and PROMUS Element stents has been undertaken, and additional corroborating data from ongoing clinical studies using all three PtCr stents will further define the potential of these new stent systems.

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