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Bifurcation stenting: current strategies and new devices
  1. A Latib1,2,
  2. A Colombo1,3,
  3. G M Sangiorgi1,3
  1. 1
    Interventional Cardiology Unit, San Raffaele Scientific Institute, Milan, Italy
  2. 2
    Division of Cardiology, Department of Medicine, University of Cape Town, Cape Town, South Africa
  3. 3
    Interventional Cardiology Unit, EMO Centro Cuore Columbus, Milan, Italy
  1. Dr G M Sangiorgi, EMO Centro Cuore Columbus, 48 Via M Buonarroti, 20145 Milan, Italy; info{at}emocolumbus.it

Abstract

Based on the results of numerous randomised trials, the provisional approach of implanting one stent on the main branch has become the default approach to most bifurcation lesions. However, bifurcation intervention still remains technically challenging. Dedicated bifurcation stents have been designed to specifically treat coronary bifurcations with the aim of dealing with some of the shortcomings of the conventional percutaneous approach to bifurcation intervention. Most of the devices are aimed at facilitating the provisional approach. They are an exciting and innovative technology that may further simplify the management and current approach to bifurcation treatment. Currently, 11 devices are available that have either completed or are currently undergoing First-In-Man trials. The development of more drug-eluting platforms and larger studies with control groups demonstrating their clinical applicability, efficacy and safety are required before they are widely incorporated into daily practice.

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Coronary bifurcations are frequently encountered and about 15–20% of percutaneous coronary interventions (PCIs) are performed to treat bifurcations.1 PCI for bifurcation disease has been considered technically challenging and historically been associated with lower procedural success rates and worse clinical outcomes than non-bifurcation lesions. In addition, there has also been great uncertainty and debate as to the most appropriate strategy when treating bifurcations. However, in the past few years significant improvements have occurred in our understanding and treatment of bifurcation lesions. First, the introduction of drug-eluting stents (DES), which have significantly reduced restenosis and repeat revascularisation rates demonstrated in both registry studies and a subanalysis of the randomised SCANDSTENT (Stenting Coronary Arteries in Non-Stress/Benestent Disease) trial2 3; second, a more selective use of two stents as intention-to-treat; third, the acceptance of a suboptimal result in the side branch (SB) due to the fact that many residual stenoses at the SB may not be physiologically significant4; fourth, the better performance of two-stent techniques associated with high-pressure postdilatation, kissing inflation and, possibly, intravascular ultrasound and finally, the publication of numerous randomised controlled trials specifically in bifurcations.1 58

As a result of these changes, the outcomes after bifurcation PCI have improved considerably and in some studies approximate those of non-bifurcation PCI.9 There are now five randomised trials1 58 and a large registry9 comparing a provisional strategy of main branch (MB) stenting with a one-DES versus a two-DES strategy of stenting both branches (fig 1). From these data it is apparent that the percutaneous treatment of coronary bifurcations has moved past an important milestone in that the one-stent versus two-stent debate appears to have been resolved. The provisional approach of implanting one stent on the MB is now considered the default approach in most bifurcations lesions. This approach is mainly because routine implantation of two stents does not give better results than selective usage. Despite the simplicity of the provisional approach, this technique frequently leaves the SB with a significant residual stenosis (most trials evaluating the provisional approach quote success as 30% residual on the MB and <50% residual on SB). The results after implantation of two stents are sometimes suboptimal and therefore outcomes at follow-up are not as good as would be expected. Operator experience, willingness to devote sufficient time and effort to optimise the result (especially on the SB) and use of intravascular ultrasound are elements frequently needed when implanting two stents.10 In our experience a stricter adherence to this approach seems to have contributed to the improvement seen over the past few years after implantation of two stents in bifurcation lesions (fig 2). However, the introduction and perfection of dedicated bifurcation stents may simplify this task and change the current proposed approach to bifurcation treatment. Presently, routine stenting of both branches appears to offer no advantage over a provisional approach. Based on these data a practical approach to bifurcation PCI can be summarised as follows:11

Figure 1 Clinical outcomes in trials comparing a one-DES (1S) versus a two-DES (2S) strategy in treating coronary bifurcations (p = not significant for all comparisons between 1S and 2S in all five trials). MACE, major adverse cardiac events; TLR, target lesion revascularisation.
Figure 2 Final kissing inflation, restenosis and target lesion revascularisation (TLR) rates in bifurcations treated with two drug-eluting stents (DES) at our institution over three consecutive periods. The figure demonstrates that as our experience has increased with implanting and performing two-stent techniques with DES in a bifurcation, restenosis and TLR rates have declined.
  1. Two guidewires should be placed in most bifurcations and the SB guidewire should be “jailed” in the majority after deployment of the stent in the MB. This approach is important in protecting the SB from closure due to plaque shift and/or stent struts during MB stenting. The guidewire jailed in the SB by the MB stent facilitates rewiring of the SB12 if SB post-dilatation/stenting or final kissing balloon inflation (FKI) is needed, or if the SB occludes. This jailed guidewire also acts as a marker for the SB ostium by changing the angle of SB take-off. There is usually no need to remove the jailed guidewire during high-pressure stent dilatation in the MB. However, it is preferable to avoid jailing hydrophilic guidewires as there is a risk of removing the polymer coating. Accurate handling of the guiding catheter to prevent migration into the ostium of the coronary vessel is important to allow removal of the jailed guidewire.

  2. SB provisional stenting should be the initial approach in the majority of bifurcations. Depending on the size and importance of the SB, the provisional strategy may be one of just trying to keep the SB open at the end of the procedure in the case of small and/or diffusely diseased SBs. In larger SBs, a strategy of recrossing the MB stent struts to perform SB balloon angioplasty and FKI may be more appropriate. There is no consensus as to whether FKI is mandatory when performing a provisional strategy. However, owing to the risk of dissection with FKI, it would appear prudent that FKI be performed only on SBs that an operator is prepared to stent if dissection occurs.

  3. Treatment of a bifurcation lesion with two stents is performed mainly as a crossover from the provisional approach when a second stent is needed in the SB to treat a flow-limiting dissection or a suboptimal result. Two stents as “intention-to-treat” should be reserved for bifurcations with a SB that has a relatively large diameter and territory of distribution and the following anatomical situations: disease in the SB that extends well beyond the ostium; the SB has an unfavourable angle for recrossing after MB stent implantation; or the SB has a flow-limiting dissection after predilatation. There are no solid data to support the supposition that two stents are more thrombogenic than one—that is, provided correct stent placement has been performed and compliance with antiplatelet therapy is maintained.1 9

RATIONALE AND TYPES OF DEDICATED BIFURCATION STENTING

On the whole, irrespective of whether a one- or two-stent strategy is chosen, the results after bifurcation PCI have improved if one compares the more recently published Nordic Study1 with previous bifurcation studies.5 6 If that is so, one may ask why do we even need dedicated bifurcation stents? The conventional approach to bifurcation PCI still has a number of limitations such as maintaining access to the SB throughout the procedure; MB stent struts jailing the SB ostium, resulting in difficulty in rewiring the SB or passing the balloon/stent into the SB through the stent struts; distortion of the MB stent by SB dilatation; inability to fully cover and scaffold the ostium of the SB; inability of the stent structure to withstand SB balloon dilatation and deformation13 and finally, operator skills and technical experience. Clearly, bifurcation PCI is technically challenging and time consuming, especially in order to achieve an optimal long-term result. As a result, several stents have been specifically designed for bifurcations with the intention of dealing with these shortcomings. However, the first generation of these dedicated bifurcation stents was difficult to deploy as they were stiff, and accurate positioning of the stent at the SB ostium was tricky. Many also had larger crossing profiles and less flexibility than conventional stents, so that they were difficult to deliver in tortuous or calcified arteries. It is hoped that the newer generation of bifurcation stents will overcome these drawbacks.

The currently available (or under investigation) dedicated bifurcation stents can be broadly divided into:

  1. Stents for provisional SB stenting that facilitate or maintain access to the SB after MB stenting and do not require recrossing of MB stent struts (eg, Petal, former AST stent, (Boston Scientific, Natick, Massachusetts, USA); Invatec Twin-Rail (Invatec S.r.l., Brescia, Italy); Antares (Trireme Medical, California, USA); Y-Med SideKick (Y-Med, San Diego, California, USA); Nile Croco (Minvasys, Genevilliers, France); Multi-link Frontier (Abbott Vascular Devices, Redwood City, California, USA/Guidant Corporation, Santa Clara, California, USA)). These stents allow placement of a second stent on the SB if needed.

  2. Stents that usually require another stent implanted in the bifurcation—for example, Sideguard (Cappella, Massachusetts, USA); Tryton (Tryton Medical, Massachusetts, USA); Axxess Plus (Devax, Irvine, California, USA)). The Tryton and Sideguard are designed to treat the SB first and require recrossing into the SB after MB stenting for FKI. The Axxess Plus is the exception as it is implanted in the proximal MB at the level of the carina and does not require recrossing into the SB but may require the additional implantation of two further stents to completely treat some types of bifurcation lesions.

The stent delivery systems (SDS) of these dedicated bifurcation systems have a number of design features in common which both explain their strengths and weaknesses:

  • Double-balloon SDS have to be tracked over two wires and thus wire wrap (twisting) is a common problem. However, the stent is implanted by simultaneous kissing inflation, possibly resulting in shorter procedure times. In addition, these devices still tend to be bulkier than single-balloon SDS requiring guide catheters larger than the standard 6F and limiting their use in calcified lesions and tortuous vessels.

  • Stents with a preformed SB aperture maintain access to the SB during MB stenting but successful implantation is dependent on accurate positioning with very little tolerance for incorrect placement.

  • An SDS with a side hole needs to have axial and rotational self-positioning properties—that is

    • axial: SDS has a “stopper” to position the side cell at the SB level, closest to the carina;

    • rotational: SDS automatically turns the side hole exactly towards the SB.

  • The Nile, Frontier, Twin-Rail, SideKick and Stentys SDS have struts that only partially cover the ostium and thus leave the potential for a gap and ostial restenosis.

  • Stents that have struts that can be expanded into SB ostium (Petal, Ariste) may be clinically advantageous as they provide complete coverage of the SB orifice and offer the possibility of delivering drug to the SB ostium.

  • SB-specific stents commit the operator to stenting both branches.

  • Unfortunately, most are still bare metal stents (BMS) but with DES currently under development in the majority.

In this review, we describe each of these devices in detail, including their unique design features and implantation technique. Table 1 summarises the main technical characteristics and table 2 gives the available clinical results for their implantation in humans.

Table 1 Summary of the main characteristics of current dedicated bifurcation stents (adapted from Abizaid et al)13
Table 2 Summary of the available data and trials of current dedicated bifurcation stents

Y-MED SIDEKICK

The SideKick (Y-Med, San Diego, California, USA; fig 3) is a low profile 6F guide compatible SDS that integrates a MB fixed-wire platform with a rapid-exchange steerable SB guidewire designed to preserve SB access during bifurcation stenting. There are three models with different exit ports (proximal, mid, distal) that are selected depending on the location of the disease in the bifurcation; for example, proximal exit port for lesion distal to bifurcation or ostial lesion. When the device is close to the carina, a guidewire is passed through the SB exit port and MB stent struts into the SB, thus avoiding recrossing into the SB. Various BMS designs and even a DES platform are currently under investigation. The only clinical data available for the SideKick are unpublished data from a First-In-Man (FIM) study performed in 17 patients with 20 lesions presented at the 2007 Cardiovascular Revascularisation Therapies conference.14 The device success rate was 80% and an additional stent was required in 40% of cases. During the short follow-up period (68±32 days), there was one major adverse cardiac event (MACE) due to a subacute stent thrombosis.

Figure 3 The Y-Med SideKick is a fixed-wire main branch stent delivery system with different exit ports for the side-branch protection wire located either proximally (A), mid (B), or distally.

MULTI-LINK FRONTIER

The Multi-link Frontier coronary stent system (Abbott Vascular Devices, Redwood City, California, USA/Guidant Corporation, Santa Clara, California, USA; fig 4) is a balloon-expandable 316L stainless steel stent premounted on a dedicated delivery system with two balloons (monorail for MB and over-the-wire inner lumen for SB) and two guidewire lumens. To assist tracking and avoid guidewire crossing, the Multi-link Frontier has an integrated tip design that allows single tip delivery—the MB balloon tip includes a pocket on the distal sleeve for joining the MB and SB balloon tips with a mandrel. The Multi-link Frontier is advanced into the MB over a conventional wire. The joining mandrel is retracted, releasing the over-the-wire SB tip, and a 300 cm wire is inserted into the SB balloon lumen and into the SB. The system is advanced to the carina and simultaneous kissing inflation of the two balloons is performed, using a single indeflator, to expand the stent on the MB and SB. The safety and performance of the Multi-link Frontier stent has been evaluated in a 105 patient multicentre registry.15 Device success was 91% and procedural success 93%. Reasons for failure to deliver the device were vessel calcification in eight cases and wire wrap in one case. Two patients had an in-hospital myocardial infarction secondary to SB occlusion. The late loss for the Multi-link Frontier was 0.84±0.55 mm and the overall bifurcation restenosis rate (44.8%) was high (MB 29.9%, SB 29.1%). At 6-month follow-up, the target lesion revascularisation (TLR) and MACE rates were 13.3% and 17.1%, respectively. No cases of subacute or late stent thrombosis occurred during the follow-up period. The next generation of the Multi-link Frontier, called the Pathfinder, will be a chromium cobalt stent with the Xience V DES platform (ie, everolimus on a non-erodable acrylic and fluoro polymer).

Figure 4 The Multi-link Frontier is a dual lumen, double-balloon stent delivery system with the two balloons joined by a mandrel, thus allowing tracking of the device into the main branch (MB) over a single wire (A); when the device is close to the carina, the joining mandrel is retracted releasing the over-the-wire side branch (SB) balloon, a guidewire is then placed via this balloon into the SB, and the entire system is advanced to the carina (B); the stent is expanded into the MB and SB with simultaneous kissing inflation of the two balloons using a single indeflator (C).

INVATEC TWIN-RAIL

The Invatec Twin-Rail (Invatec S.r.l., Brescia, Italy; fig 5A) is a slotted tube, 316L stainless steel stent premounted on double balloons in its proximal portion, and only on the MB balloon in its distal portion. The stent has a closed-cell type design with variable stent geometry. This 6F-compatible system consists of a single dual lumen catheter splitting into two distal balloons with a central stopper that prevents further advancement of the SDS when the carina is reached. The stent is deployed by simultaneous kissing inflation with a single indeflator. The Twin-Rail is similar to the Multi-link Frontier double-balloon system except that in the latter the SB balloon is a short tapered balloon while in the Twin-Rail there is a full dilatation balloon. The Twin-Rail double-balloon SDS was evaluated in the unpublished DESIRE (DoublE versus SIngle balloon stent deliveRy systEms for bifurcation lesions) trial. This trial presented at the Transcatheter Cardiovascular Therapeutics (TCT) 2005 meeting compared the safety and efficacy of the Twin-Rail double-balloon SDS (15 patients) with a single-balloon SDS (24 patients).16 Although angiographic success was high, device success was only 75% with the Twin-Rail and there was a high rate of guidewire crisscross with both devices. The TLR rate for the Twin-Rail was 14.3% at 7 months. In this small pilot study, there was also a trend for higher device success and better safety profile with the Twin-Rail than with a single-balloon SDS.

Figure 5 The Twin-Rail (A) and Nile Croco (B) are both double-balloon, dual lumen rapid-exchange systems with the main difference being that the Nile Croco (B) has two independent catheters (arrows) that can be manipulated and inflated separately.

NILE CROCO

The Nile Croco (Minvasys, Genevilliers, France; fig 5B) is a double-balloon SDS similar to the Multi-link Frontier and Twin-Rail but unlike these latter SDSs, which are a single catheter with single inflation port, the Nile Croco has two independent yet joined catheters that require independent manipulation and pressure monitoring. The two parallel rapid-exchange catheters are premounted with a chromium cobalt stent crimped on the MB balloon and the tip of the SB balloon. The MB balloon has three markers with the central marker indicating the position of the SB aperture. After the stent is deployed into the MB, the SB balloon is advanced into the SB and a final kissing inflation is performed. The feasibility, safety and efficacy of bifurcation stenting using the Nile Croco stent is currently being evaluated in the multicentre (10 European centres) Nile Registry.17 Preliminary results of the first 75 patients showed a procedural success rate of 94.7% and a MACE rate of 10.7% in the 45 patients in whom follow-up was available at 7 months.

AST SLK-VIEW

The SLK-View (Advanced Stent Technologies, Pleasanton, California, USA; figs 6A and B) is a 316L stainless steel flexible slotted tube stent with a side aperture located between the proximal and distal section to facilitate access to the SB after deployment of the stent in the MB. The delivery system has a dual over-the-wire design with a proximal dual lumen shaft that separates into two catheters (a balloon and a side sheath) at its distal segment. The stent is premounted in the distal segment of the delivery system with the side sheath running under the proximal segment of the stent and exiting through the side hole. There are a total of three radiopaque markers on the balloon, located at the centre, proximal and distal edges. The SLK-View system is placed over two wires simultaneously and advanced to the bifurcation until the central marker band is aligned to the branch vessel and the side-sheath marker separates from the centre marker. The SLK-View stent is then deployed in the MB leaving the preformed side hole positioned at the ostium. Unlike the Petal or Antares stents, there are no stent struts protruding into and scaffolding the ostium. The SLK-View stent has been assessed in a multicentre non-randomised study of 81 patients with 84 de novo bifurcation lesions.18 The study proved the feasibility of this stent with high procedural success rates (97.6%) while maintaining SB access in all treated lesions. However, the SLK-View BMS was associated with a high restenosis (MB 28.3%, SB 37.7%) and TLR rate (21%) at 6-month follow-up. This stent has been removed from the market and is no longer under investigation since the company has been acquired by Boston Scientific, who have slightly modified the stent creating the Petal stent system.

Figure 6 The SLK-View is a main branch (MB) stent with a preformed aperture (A), without stent struts that scaffold the ostium, which has to be positioned accurately at the ostium; the stent is mounted on a dual over-the-wire stent delivery system that separates into a side sheath and balloon distally; the side sheath runs under the stent and positions the side hole at the ostium (B). The Stentys (C) is placed in the MB across the side branch (SB) ostium like any conventional stent and does not require accurate placement at the ostium; a guidewire and balloon are then passed across the stent struts into the SB; inflation of the balloon disconnects the struts and the self-expanding stent creates an opening and scaffolds the ostium.

STENTYS

The Stentys bifurcated drug-eluting stent19 (Stentys SAS, Clichy, France; fig 6C) is the first of the next-generation bifurcation stents—the Stentys is a self-expanding nitinol stent made of Z-shaped mesh linked by small interconnections. The stent is coated on the abluminal side with paclitaxel on a durable polymer matrix (PESU), a polysulfone, that permits controlled drug elution.19 27 The unique feature of this stent is the ability to disconnect the stent struts with an angioplasty balloon. Thus an opening for the SB can be created anywhere in the stent after it is implanted in the vessel while at the same time the disconnected struts scaffold the SB ostium. Thus in comparison with the implantation of some of the other bifurcation stents such as the Petal and the Antares, the procedural success is not dependent on accurate positioning of the stent and there is significant placement tolerance with the Stentys. However, it would appear from the design that the disconnected struts only partially scaffold the ostium. The implantation procedure is performed in three steps: (a) Stentys is implanted in the MB with an approximate positioning, like a standard stent; (b) the optimal location for the SB opening is chosen by inserting a balloon through the stent mesh; (c) the balloon inflation disconnects the mesh and creates the opening. It is hoped that the self-expanding property of the stent will allow in situ modelling of the stent to fit the patient’s unique arterial anatomy. However, it is not known if the Stentys is more prone to stent fracture owing to its disconnectable strut design. Interim results of the first 13 patients in the FIM study presented at EuroPCR 2008 demonstrated 100% procedural success.20 In eight patients the BMS platform of Stentys was implanted and in the remaining five the DES version was used. Strut disconnection was possible in all stents implanted. At 30 days, there were no adverse events in this small cohort.

PETAL

SB occlusion caused by vessel deformation and plaque shift remains a common problem with current approaches to bifurcation PCI. The Petal stent (Boston Scientific, Natick, Massachusetts, USA; figs 7A and B), with a side aperture located mid-stent and deployable struts (a “sleeve”) may be an attractive solution to prevent SB occlusion after MB stenting. A guidewire is placed in the MB and another in the SB. The dual side-exchange (double-balloon) delivery system has a main lumen that guides the catheter to the primary lesion over the MB guidewire. The secondary lumen (side sheath) facilitates proper alignment of the aperture to the SB ostium as it tracks over the SB guidewire. In addition to a conventional cylindrical shaped balloon, there is a secondary elliptical balloon adjacent to the main balloon and connected to the same inflation lumen so that a single inflation device is needed. The Petal stent is crimped over both balloons such that the elliptical balloon is under the side aperture and petal elements. Upon inflation, the main balloon deploys the stent into the MB, while the elliptical balloon deploys the petal elements into the SB ostium The purpose of the “petal” aperture is to retain access to the SB during and after deployment and to scaffold the SB ostium with outwardly deploying strut elements that extend up to 2 mm into the branch during deployment. This unique feature has potential for delivery of antiproliferative drugs to the most common site of bifurcation restenosis.

Figure 7 The Petal (A, B) and Antares (C–E) bifurcation stents both have preformed side apertures with struts that expand into the side branch (SB) to fully cover and scaffold the SB ostium. The Petal is mounted on a dual lumen, double-balloon stent delivery system (A) with an elliptical SB balloon (black arrow) that deploys the SB struts (B; white arrows) when both balloons are inflated by a single indeflator. The Antares stent delivery system consists of a single rapid-exchange balloon catheter (C) with a SB stabilising wire that is advanced into the SB to ensure proper alignment of the side hole (D); inflation of the balloon to deploy the main branch stent results in automatic expansion of the SB elements (E).

The first generation of this stent, called AST Petal, developed by Advanced Stent Technologies was a 316L stainless steel slotted tube design. In a FIM study, the AST Petal was successfully implanted in 12 of 13 patients, with the one failure due to inability to advance the device after vessel dissection from predilatation.21 Of note, in another four patients device delivery was temporarily impeded by wire wrap (three cases) and incomplete device rotation (one case). In nine patients an additional stent was required in the bifurcation and the TLR rate was 15% (2/13) at 6 months. The Petal stent was acquired by Boston Scientific in 2004 and modified into the Taxus Petal stent. This second-generation Petal stent is a platinum chromium alloy stent which is coated with paclitaxel on a Translute polymer (poly(styrene-b-isobutylene-b-styrene)), which is the same polymer currently used by the Taxus stent. The platinum chromium is better than its stainless steel predecessor in that the new alloy allows even thinner stent struts with increased flexibility and radiopacity. The Taxus Petal stent is currently under investigation in a 45-patient FIM trial to assess this device’s acute performance and safety (death, myocardial infarction, target vessel revascularisation) at 30 days and 6 months, as well as continued annual follow-up for 5 years.

ANTARES SIDE-BRANCH ADAPTIVE STENT (SAS)

The Antares SAS (Trireme Medical, California, USA) with automatic SB support deployment (figs 7 C–E) consists of a single-balloon expandable 316L stainless steel stent. It has a SB support structure in the centre of the stent provided with radiopaque tantalum markers for positioning and orienting at the bifurcation site. The original Antares system had four radiopaque tantalum markers but the current generation system has only two. Stent deployment is achieved using a single rapid-exchange balloon catheter and a SB stabilising wire encased in a peel away lumen to minimise wire crossing. As the stent approaches the targeted bifurcation, the catheter is torqued to align the stent central opening with the SB ostium. The SB wire is advanced into the ostium thus assisting with accurate placement and facilitating access after MB stent deployment. Upon expansion of the main stent body, the ostial crown is automatically deployed with elements protruding approximately 2 mm into the SB to scaffold the ostium. The Antares is similar to the Petal stent but has the advantage of tracking over a single wire and unlike the Petal, which uses a balloon to expand the SB elements, the SB elements expand automatically with this stent. The 30-day results of the FIM study of 11 patients/lesions treated with the Antares stent were presented in 2008 at the SCAI-ACCi2 summit.22 Device success in this small cohort was 100% and there were no adverse events in hospital or at 30 days’ follow-up.

SIDEGUARD

The Sideguard ostium protection device (Cappella, Massachusetts, USA; fig 8A) is a self-expanding trumpet-shaped nitinol stent that is deployed using a special balloon release sheath system. It is currently a BMS but the next generation will be drug eluting with a biodegradable polymer. The Sideguard’s trumpet-shaped design helps the stent conform to the ostium allowing for complete stent-to-wall apposition, optimising scaffolding and drug delivery. Its short length, self-expandable nitinol system, low-profile (less than 3.5 Fr) delivery system allows greater navigability even in very tortuous anatomy. Radiopaque markers located at the distal and proximal ends of the Sideguard delivery system facilitate positioning of the stent at the SB ostium. Sideguard will be indicated for bifurcation angles from 45° to 135° before wiring. The stent is deployed using a nominal pressure balloon, which helps tear a protective sheath that keeps the Sideguard in place until deployment. Once released, the Sideguard self-expands into place. The delivery system and the guidewire are then removed from the SB. A conventional stent is then placed in the MB, the SB is reaccessed with a guidewire and the procedure is completed with a standard FKI. The 6-month results of the first 20 patients enrolled in the Sideguard FIM trial (SG-1) were presented at TCT 2007. Technical success was achieved in 16 (80%) patients. At 6 months, the TLR rate was 12.5% (2/16) and there were no cases of stent thrombosis.23 A second multicentre non-randomised trial has begun enrolment with the next-generation Sideguard device (SG-2). The new device (SG-2) has undergone minor changes to the SDS and a major change to the stent design. The SG-2 stent has a mixed open and closed cell design with a new mid-distal open cell that acts as a built-in anchoring system preventing the Sideguard from migrating after deployment.

Figure 8 The Sideguard (A) and Tryton (B) are both dedicated side-branch (SB) stents. The Sideguard is a self-expanding stent mounted on a low profile balloon delivery system that allows for precise delivery of the SB stent (A). The Tryton SB stent consist of three zones and is positioned with the central transition zone straddling the SB origin (B). After treating the SB with either of these devices a conventional stent can be placed in the MB. The Axxess Plus stent (C) is implanted first at the level of the carina spanning the ostia of both branching vessels, indicated by the presence of one marker in each branch vessel which provides a reference point to guide the placement of distal stents.

TRYTON

The Tryton SB stent (Tryton Medical, Massachusetts, USA; fig 8B) is a slotted tube, cobalt chromium balloon expandable stent designed to be implanted in the SB of a bifurcation. The stent consists of three zones: a distal SB zone (that treats the disease in the SB); a transition zone (positioned at the SB ostium) and a MB zone. The central transition zone has a specific geometry, which contains three panels, each of which can be deformed in an independent fashion. The proximal MB zone is composed of three fronds that are connected proximally to the transitional panel and terminate in a circumferential band, and the distal zone has the design characteristics of a standard slotted tube workhorse stent. Treatment of a bifurcation with the Tryton stent generally commits the operator to implanting two stents in the bifurcation and the technique is identical in approach to that used when performing the Culotte technique. The Tryton stent is deployed across the SB ostium first. The initial FIM experience has shown that predilatation of the Tryton is essential to allow a MB stent to be advanced though the Tryton struts.24 25 A standard MB stent is then tracked through the proximal MB zone of the Tryton into the distal MB and deployed. The MB stent struts then have to be recrossed in order to perform a FKI. The Tryton I FIM trial assessed the safety and performance of the Tryton SB stent in conjunction with a standard DES in 30 patients.24 25 The Tryton was successfully implanted in all but one patient (96.7% angiographic success) and at 6-months’ follow-up three (9.9%) patients had experienced a MACE. Angiographic follow-up was performed in 78% of patients and demonstrated a late loss of 0.17±0.35 mm and in-segment restenosis in one patient (4.3%) in the MB proximal to the stent.

AXXESS PLUS

The Axxess Plus stent (Devax, Irvine, California, USA; fig 8C) was the first of these dedicated bifurcation stents designed to elute an anti-restenotic drug. It delivers Biolimus-A9, a sirolimus derivative, via a bio-erodable polylactic acid polymer carrier. The Axxess Plus is a self-expanding, nickel–titanium, conically shaped stent that is placed at the level of the carina. It has a rapid-exchange delivery system with hydrophilic coating with controlled deployment upon withdrawal of a cover sheath using the actuator. However, the Axxess stent may be limited by the fact that it needs to be precisely nested at the carina to be effective and in most cases will need another stent to treat the bifurcation fully. Grube et al have published the results of the prospective multicentre single-arm Axxess Plus trial that enrolled 139 patients.26 The Axxess stent was successfully implanted in the MB in 93.5% of cases with 80% of the patients receiving an additional stent to the MB or SB and 42% of patients requiring three stents to treat the bifurcation completely. Six of the nine device failures were due to improper alignment when the stent was placed distal or proximal to the intended location. At 6 months’ follow-up, the in-stent late loss was 0.09±0.56 mm, in-stent restenosis within the Axxess stent was 4.8% and the overall TLR rate was 7.5%.

PRELIMINARY CLINICAL RESULTS WITH DEDICATED BIFURCATION STENTS

The first-generation bifurcation stents have been tested in FIM studies and multicentre registries only (table 2). Although the device success was excellent with most of the devices tested, they have technical problems that may hamper acute clinical results. Restenosis rates with the first-generation devices are similar to that reported for BMS in bifurcations,28 with a range varying from 28% to 54%, which is in turn coupled with high rates of repeat revascularisation and MACE. Second-generation drug-eluting devices have only been very recently introduced and only one study has been published. Such experience pertains to the Axxess Plus biolimus-eluting stent, which demonstrated a favourable rate of restenosis for the MB and SB, although most patients required at least one other stent implanted in the bifurcation.26 A number of FIM studies and multicentre registries are continuing and the results are eagerly awaited to establish if these new devices will become a good alternative to current bifurcation strategies in different bifurcation scenarios. However, as has been seen with the use of two-stent techniques in bifurcation PCI (fig 2), there will be a learning curve in the optimal deployment and use of these new devices.

CONCLUSION

In conclusion, the provisional approach of implanting one stent on the MB has become the default approach to most bifurcation lesions. However, bifurcation PCI still remains technically challenging, especially when two-stent strategies are required. Dedicated bifurcation stents are an exciting technology as they are an attempt to find specific technological solutions to a specific subset of coronary lesions. These devices will hopefully not only improve outcomes but also simplify the management of this complex lesion subset. Albeit that the preliminary results with the first-generation devices have been hampered by a high rate of restenosis, the development of more drug-eluting platforms and larger studies with control groups, in the near future, will demonstrate their true clinical applicability, efficacy and safety before they are widely incorporated into daily practice.

REFERENCES

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Footnotes

  • Competing interests: Declared. AL has none. AC was a co-founder of Capella Inc and is a minor shareholder. GMS is a consultant for Boston Scientific.

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