An Overview of the ev3 Carotid Innovations
By Mark Vandlik
The past decade has seen significant growth in the interest in and adoption of carotid artery stenting (CAS) as a viable alternative for the treatment of carotid artery disease. An important driver for the growth in CAS procedures has been the accelerated evolution of the technology of stents and embolic protection devices. In this article, we review state-of-the-art requirements for carotid stents and embolic protection devices and present the design features of two of the latest devices for the treatment of carotid artery disease in patients at high risk for endarterectomy–the PROTÉGÉ RX® Carotid Stent System and the SpiderFX™ Embolic Protection Device (ev3 Inc., Plymouth, MN) (Figure 1).
CAROTID STENTING REQUIREMENTS
Carotid artery disease presents the physician with a broad spectrum of anatomical variations that affect the degree of complexity in each case. These variables include a wide range of patient anatomy and vessel tortuosity, plaque morphology, and composition, as well as lesion location and length, among others. As interventionists are acquiring more experience in performing CAS procedures, specific carotid stenting requirements for both stents and embolic protection devices are being formulated.
One of the most important features in a carotid stent is its radial force, as the principal purpose of the device is to open up a stenotic vessel and avoid recoil. Stent designs for the carotid bifurcation need sufficient radial force to open and maintain patency in calcified lesions, which are commonly observed in the carotid arteries. Along with good radial strength, a carotid stent must have good flexibility in order to conform to the natural tortuosity from the common to internal carotid artery. The vessel's natural tendency to "curl" or kink makes the use of more rigid stent designs less desirable because rigid stents will have the tendency to move the kink or curl just distal to the treated area.
Not only must the stent be flexible enough to adapt to the twists and turns of the vessel, it must also conform to the variances in diameter, especially when stenting across the carotid bifurcation. This important feature, commonly referred to as conformability, often makes it desirable to use tapered stents capable of conforming to the vessel diameter transitions while maintaining a balance in the metal-to-artery ratio.
In addition to these important mechanical properties, a carotid stent needs to have sufficient visibility to ensure accurate placement and the ability to visualize the stent after deployment and during postdilatation. Good visibility of the stent will allow the physician to verify vessel wall apposition after deployment and makes it easier to ensure that balloon inflation is performed with the balloon completely inside the stent without any overhang.
Finally, to ensure good results, predictable deployment of the stent is paramount because, in many cases, carotid lesions can be short, focal, and close to the bifurcation, requiring precise placement of the stent.
In the case of embolic protection devices (EPDs), a key requirement is for it to have adequate wall apposition. If an EPD does not appose the vessel wall completely, there is risk of embolic debris passing through gaps between the vessel wall and filter. With good vessel wall apposition, the next key requirement is EPD pore size. There is a balance between having a small enough pore size distribution to capture emboli of clinical consequence and a large enough pore size distribution to maintain filter patency during the procedure. If the ratio of open area to closed area of the filter is too small, there will be a more significant pressure decrease across the filter and a greater chance of a slow-flow/no-flow situation.
In an ideal ancillary device design, the operator should not have to change the way the treatment procedure is performed to accommodate the ancillary device. In the case of an EPD design, it should still allow physicians to use their guidewire of choice for the initial lesion crossing, just like in any other peripheral endovascular intervention. Also, EPDs should provide visual feedback to the operator to confirm vessel wall apposition and to allow fast and precise filter positioning.
Finally, EPDs should remain stable as they are functioning as guidewires and devices track over them. Inadvertent filter migration during the intervention represents a high risk for procedure complications that can be avoided with well-designed EPDs.
THE PROTÉGÉ RX CAROTID STENT SYSTEM
Predictable Deployment, Visible Results
Approved by the FDA in early 2007, the PROTÉGÉ RX Carotid Stent System is the latest entry into the carotid stenting market. The many design features of the PROTÉGÉ RX Carotid Stent System set it apart from other available carotid stent systems and make it an ideal choice for CAS.
The right balance. The PROTÉGÉ RX Carotid Stent System is designed to provide an optimal balance between radial strength and flexibility. The open-cell design provides expansion forces that resist compression while providing excellent wall apposition and, at the same time, provides the stent with the flexibility necessary for the carotid anatomy.
Anatomically tapered to fit like a glove. The PROTÉGÉ RX Tapered Stent is designed to match the anatomy of the carotid bifurcations, giving it outstanding conformability to the ICA/CCA transition. Unlike tapered stents with conical designs, the PROTÉGÉ RX Stent is anatomically tapered, more closely reflecting the alternating "straight-tapered-straight" anatomy of carotid bifurcations (Figure 2).
Solving the predictable deployment challenge. The proprietary EX.P.R.T Release Technology essentially eliminates jumping or premature stent deployment, very relevant to CAS because this is observed more frequently in short (20 mm and 30 mm) and large-diameter (>8 mm) stents, which are commonly used in CAS (Figure 3). Also, the PROTÉGÉ RX Stent has minimal stent shortening, providing physicians with accurate stent deployment.
Seeing is believing. The PROTÉGÉ RX Stent is the only approved carotid stent with GPS™ Tantalum radiopaque markers at the distal and proximal ends of both straight and tapered configurations, providing excellent visibility for accurate placement.
THE SPIDERFX EMBOLIC PROTECTION DEVICE
Cross With Confidence–It's Your Choice
A new version of ev3's original SpideRX Embolic Protection Device, the second-generation SpiderFX Embolic Protection Device, received FDA 510(k) clearance just 10 months after the first generation was approved. The design features of the new-generation SpiderFX Embolic Protection Device not only meet the state-of-the-art requirements outlined previously, they also offer a number of unique advantages.
Which guidewire? It's your choice. The SpiderFX device is the only distal filter embolic protection device currently available that allows using the physician's guidewire of choice. The operator can cross even the most challenging lesions with confidence, using any preferred .014-inch or .018-inch guidewire.
The right fit. The SpiderFX filter is available in a broad selection of sizes to treat carotid arteries from 3 mm to 7 mm with the appropriate filter size.
Get the whole picture. Clearly visible radiopaque markers enable fast positioning and visualization of the filter during the entire intervention. The SpiderFX filter's new mouth indicator ensures accurate visualization of the filter mouth opening (Figure 4).
The wire moves; the filter stays. A key characteristic of the SpiderFX Filter is its stability, provided by the braided nitinol design that gives it full wall apposition and the ability of the capture wire to rotate and move longitudinally, independent of the filter (Figure 5).
The innovative design features of the ev3 PROTÉGÉ RX Carotid Stent System and the ev3 SpiderFX Embolic Protection Device have contributed to the rapid acceptance of the devices. The case study in the following article illustrates how these features may translate into clear advantages for the endovascular specialist during carotid artery interventions.
Complete indications, contraindications, warnings, precautions, and device instructions for the PROTÉGÉ RX Carotid Stent System and the SpiderFX Embolic Protection Device are provided in the Instructions For Use supplied with each device.
Mark Vandlik is Director of Research and Development at ev3 Inc. and is responsible for carotid stent and embolic protection technology development. Mr. Vandlik may be reached at email@example.com.