Coronary artery stenting has evolved substantially since the first use of coronary stenting as an adjunct to balloon angioplasty in the early 1990s. The performance (and particularly the deliverability) of coronary stents has improved such that coronary stenting is now the primary mode of revascularisation for percutaneous coronary interventions in more than 95% of cases.
Although stent delivery systems (SDS) have improved over time, there have been no major innovations in stent delivery since the introduction of monorail delivery systems in the late 1990s. The new Svelte™ stent-on-a-wire (SOAW) delivery system represents one of the first substantive innovations in SDS in more than a decade.
Technical Description of the Svelte Stent-on-a-wire Stent Delivery System
The Svelte Acrobat SOAW is a ‘fixed-wire’ SDS with a balloon-expandable stent and a 0.012-inch (attached) distal guidewire (see Figures 1 and 2). The SOAW delivery catheter has a working length of 145cm. The device includes a proximal stainless steel shaft with two proximal shaft markers (at 90 and 100cm) to indicate the position of the delivery system relative to the distal tip of the guiding catheter. The SOAW has a flexible distal shaft and a high-pressure, relatively non-compliant nylon balloon with proximal and distal radio-opaque markers. There is a spring coil wire tip and proximal and distal balloon control bands (BCBs) at each end of the balloon to protect the leading stent edges from damage during delivery, and to control balloon expansion and re-wrapping of the balloon after balloon deflation. The proximal end of the SOAW has a standard luer fitting to allow attachment to standard balloon-inflation devices. There is an integrated and moveable torque device located on the proximal shaft (see Figure 1).
The SOAW system devices are readily compatible with 5Fr guide catheters. The 0.74mm (0.029-inch)-profile device has excellent torque response, which allows delivery to distal and tortuous anatomy. The stent reaches its nominal diameter at a balloon inflation pressure of 11–12atm, with the balloon having a high-rated burst pressure of 18atm. The SOAW system will be commercially available following its launch with 25 product codes, with diameters of 2.5, 2.75, 3.0, 3.5 and 4.0mm and lengths of 8 13, 18, 23 and 28mm.
The stent itself is a thin-strutted, highly flexible, bare-metal, L605 cobalt–chromium stent. The stent utilises undulating longitudinal connectors to allow excellent stent flexibility in the pre-deployed state and vessel conformability after stent expansion/implantation (see Figures 2B and 2C). The SOAW has a very low crimped stent profile (0.74mm) compared with conventional monorail or over-the-wire SDS. This translates into an SDS cross-sectional profile that is about half the profile of the most commonly used cobalt–chromium stents on the market today (e.g. Abbott Vision or Medtronic Driver stents; see Figure 3). The low profile of the SOAW system should allow downsizing of sheaths and guiding catheters by approximately 1Fr. This should make this system well suited to transradial stenting and bifurcation stenting (e.g. kissing stents) using smaller guiding catheters (e.g. kissing stents in a 6 or 7Fr guiding catheter). The low profile of the SDS may also allow it to more easily pass through the side cells of an implanted main vessel stent in order to stent a side branch in bifurcation cases using a strategy of provisional stenting of the side branch.
The technical specifications are as follows:
- stent material – L605 cobalt–chromium alloy;
- stent length – 8–28mm; • balloon diameters – 2.5–4.0mm;
- guide catheter compatibility – 5Fr (minimum ID 0.056 inches);
- lesion entry profile – 0.30mm (0.012 inches);
- working catheter length – 145cm;
- shaft markers – 90 and 100cm;
- balloon – proximal and distal radio-opaque markers, control bands at each end;
- stent strut thickness – 81μm; and
- length of the wire distal to the stent – 22mm.
Discussion
The original fixed-wire balloon angioplasty systems were developed in the 1980s and were known to be highly deliverable (very low profile), with an ability to cross extremely tight stenoses that could not be crossed with conventional balloon angioplasty catheters.1,2 These devices, such as the Probe (USCI) and the ACE (Boston Scientific), were ultimately relegated to a niche role, particularly after the development of monorail balloon angioplasty catheters and then coronary stents.
The other issue that prevented the widespread adoption of fixed-wire balloon angioplasty was the concern about balloon-angioplasty-induced coronary dissection. Since this is a relatively frequent sequela of balloon angioplasty (without stenting), fixed-wire balloon angioplasty catheters were not felt to be as safe as over-the-wire or monorail balloon catheters. By contrast, a fixed-wire balloon-expandable stent system intended for direct stenting should have an extremely low rate of coronary dissection,3–7 overcoming this limitation of fixed-wire balloon angioplasty catheters. In addition, the majority of the very rare dissections that can be seen with direct stenting (estimated at less than 1–2%) are localised edge dissections rather than severe or flow-limiting dissections, as may be seen after balloon angioplasty. These rare and focal dissections should be readily re-crossable and should not pose significant incremental risk compared with stenting using conventional SDS.
This new SOAW SDS is intended to facilitate direct stenting and has the potential to provide substantial procedural cost savings by eliminating the need for a coronary guidewire and balloon pre- and/or post-dilatation, and by reducing contrast use and the time required to complete the procedure. Operator and patient radiation dosing will also be predictably reduced when directly stenting using an SOAW system. It is estimated that use of a direct stenting approach with the SOAW may save between US$500 and US$800 per case compared with conventional stenting with balloon pre-dilatation. Finally, the low profile and crossability of this SOAW delivery system may make it well suited to stenting via the radial approach.
The first-in-man clinical trial using the Svelte SOAW system has concluded, with encouraging feedback, suggesting that this stent is capable of achieving excellent acute outcomes with direct stenting for many lesion subtypes (see Figure 4), including complex and subtotal lesions. Regulatory approval has been received in the European Union and Brazil for the bare-metal stent version of the Svelte SOAW system. A subsequent release in the US is expected upon receipt of US Food and Drug Administration (FDA) approval.
Conclusions
The Svelte SOAW SDS represents a new, very-low-profile balloon-expandable SDS that should promote direct stenting in percutaneous coronary intervention. The efficiencies and small profile of this SDS may allow procedural cost savings, a reduction in procedure time and radiation exposure for the patient and operator and (potentially) a reduced risk of bleeding complications. These theoretical advantages as well as the safety and efficacy of this device will need to be demonstrated in clinical trials. Ôûá