Self-expanding stents are nowadays the only devices that can be deployed within the carotid territory.
In fact balloon-expandable stents are usually avoided because, having the ICA a superficial location, the risk of a stent crush - which may lead to cerebral flow impairment - is too high. Consequently, during a CAS procedure, self-expandable stents working on a 0,014" platform with rapid exchange (monorail) system should be preferred.
The increasing number of stent types today available on the market and the different carotid lesions to be treated make the final choice difficult and worrying.
However, when making a decision, some stent characteristics should be taken into careful consideration.
Foreshortening: is the difference between the lengths of a stent before and after deployment. Generally speaking all nitinol stents present < 10% shortening while the Carotid Wallstent (alloy monofilament wires) can reduce its length more than 20% according to the relationship between the stent and the arterial diameters.
Conformability: ability of the stent to adapt to the vessel tortuosity. This characteristic is more evident using nitinol stents but it is correlated with the structure of the stent itself. Infact stents with low longitudinal connections present a higher flexibility and the morphology of the arteries is maintained.
Flexibility is correlated to stent cell design: open cell stents are more flexible and adapt well to the arterial morphology while close cell design is more rigid.
Adaptability: is the ability of a stent to adjust its diameter to the tapered anatomy of the carotid region. Stents can be available in straight or tapered designs.
Some stents are able to self-taper their design to the anatomical characteristics of the arteries. This is extremely helpful when a big mismatch, in terms of diameter between the ICA and the CCA, is present.
Tapered stents can be distinguished on the basis of their structure: conical when the stent diameter gradually decreases from the proximal to the distal end and shoulder-tapered when a short transition zone in the midsegment of the stent is present.
Free Cell Area: represents the wall coverage, the quantity of stent material covering the arterial wall. High wall coverage may be potential for intimal hyperplasia.
Scaffolding: amount of support given to the vessel wall by the stent. It is higher in those stents with a low free cell area.
Radial strength: represents the stent resistance to the initial elastic recoil and radial crush and indicates the continuous expansive force provided to the arterial wall.
Stent selection must be made in accordance with the anatomical and morphological characteristics of the carotid arteries and with the plaque morphology. Fig.1
The stent diameter must be selected on the basis of the ICA diameter, with a 1-2mm oversize, correlated also with the diameter of the CCA Fig.2
But the selection of a too large stent can result in spasm or dissection of the ICA.
If the distal part of the stent remains floating in the CCA, no stent-misplacement can occur as the stent is well attached to the arterial wall at the level of the ICA and of the bifurcation.
The stent must cover the entire plaque landing in a healthy portion of the artery 0.5 cm above and below the lesion.
As most lesions involve the carotid bifurcation, the distal landing zone should be 1.5-2cm in the CCA to prevent restenosis.
In patients with tortuous anatomy of the ICA, nitinol stents should be preferred because they are softer than stainless steel stents and are able to maintain the arterial curve. A stent with high flexibility (less longitudinal connectors) could as well be chosen.
In case of a mismatch between CCA and ICA -greater than 4mm- a tapered stent or a self-tapered stent could be implanted.
Stents should be selected with an eye to the morphological characteristics of the lesion (soft, calcified, friable) to reduce the risk of distal embolization.
Stents with small meshes (close cell design) are usually preferred in case of unstable or soft plaques to prevent the passage of particles through the meshes.
Open cell design, allowing material to squeeze through the interstices, may put the patient at high risk of embolic stroke in the post-procedural phase.
In case of hard calcified lesions the ideal stent should present a high radial force in order to resist the elastic recoil.

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