Carotid Angioplasty and Stenting (CAS) has evlolved to produce sufficient outcomes to recommend it as an effective intervention for selected patients. Opinions vary and the precise populations that benefit from CAS are continuing to evolve.
Several technologic advances have permitted the incremental improvement in outcomes for CAS. This includes the use of anti embolic devices and stent design. The major goal of CAS is the short and long-term prevention of stroke and associated morbidity. The risk of stoke in CAS increases at the time of access to the target lesion, wire crossing of the lesion and prior to AED deployment. Similarly, the greatest overall risk appears to in the post procedural time period.
Numerous papers have described the contribution of stent cell design to the goal of minimizing embolization. Ill describe some characteristics of carotid stent design today and follow up with a summary table in a future blog.
It is estimated that in 80% of carotid stenosis patients, stent design is a non issue. However, in the remaining group, the presence of unique anatomic factors may present a challenge. These unique factors are primarily arch vessel tortuosity, lesion morphology and target vessel tortuosity. Detailed preprocedural imaging and planning will facilitate making the correct choice. And as always, proceduralist familiarity with the device is also an important consideration. In an anatomical region where the stakes are as high as they are with regards to neurologic injury, detailed knowledge of these advanced design principles should influence patient outcome favorably
When treating a tortuous anatomy, stents with a flexible and comformable open-cell configuration are preferred. In arteries with a significant mismatch between common carotid artery and internal carotid artery diameter, cobalt chromium (Elgiloy) or tapered nitinol stents are selected. Lesions with suspected high emboligenicity are best covered with stents with a closed-cell configuration, whereas highly calcified lesions need treatment with nitinol stents.
Generally, self expanding stents are constructed from a nickel-titanium alloy, nitinol, or a cobalt alloy. The Wallstent is the representative cobalt alloy device.
With regards to tortuous anatomy, the Wallstent appears to be flexible enough to navigate tortuous arch vessels because of its flexibility in the pre deployed state.
For the tortuous target lesion The Precise—an open-cell nitinol stent with a large open-cell area and highly flexible interconnecting bridges—will be selected if preoperative imaging shows a highly tortuous treatment location. With the Wallstent, I have seen kinking at the proximal or distal stent due to the lesion tortuosity interfacing with the rigid Wallstent characteristic
Another factor is the diameter mismatch that is characteristic of the Internal Carotid and Common Carotid artery. The woven mesh structure of the Carotid Wallstent allows the stent to adjust its diameter to the width of the vessel lumen. This ensures optimal vessel wall adaptability, regardless of the selected stent diameter. The stent has to be selected according to the CCA diameter. The downside of this adaptation process is that implanted stent length depends on the diameter of the lumen at the site of deployment, resulting in a variable proximal landing zone.
Therefore, in an attempt to better comply with the carotid anatomy, tapered stents were developed. These are characterized by a smaller stent diameter at the distal end compared with the proximal end, providing a smooth transition between the ICA and the CCA. There are two types of tapered stents: the conical (Acculink, Sinus 5F, X-Act) and the tapered shouldered stents (Protégé) . In the first, there is a gradual decrease in diameter from the proximal to the distal end, whereas in the second, there is a short transition zone in the midsegment of the stent. As in the carotid vasculature, the diameter also changes abruptly at the bifurcation area; the conical tapered stents, if perfectly positioned, best mimic this situation and are theoretically the best option
The tube-form nitinol stents with a small amount of connecting bridges (eg, Precise) are claimed to provide a self-tapering effect because the different rings will interact independently with the vessel wall.
In the few cases in which a significant mismatch between the diameter of the ICA and the CCA is diagnosed, it is recommended to select a tapered shouldered stent (Protégé). If appropriately sized and exactly positioned with its shoulders in the bulb, this stent offers the optimal vessel diameter adaptation.
Ill complete more on this discussion of stent design in an upcoming blog
