difficult stenoses. These two systems consist of a long main sheath with a balloon on its distal end that is inflated in the common carotid artery to occlude forward carotid flow. A second balloon, which is inflated in the external carotid artery, prevents retrograde external flow, thus establishing complete arrest of antegrade flow into the internal carotid artery. The principle of proximal embolic protection systems takes advantage of the cerebral collateral system of the circle of Willis (Fig. 1.1-16). Following balloon occlusion of the external and common carotid artery, collateral flow via the circle of Willis produces what is known as reserve pressure. This prevents antegrade flow into the internal carotid artery. After stent implantation and before deflation of the occlusion balloon, blood in the internal carotid artery, which might contain released particles, is aspirated and removed. One disadvantage of the proximal protection system is that a small percentage of patients are unable to tolerate balloon occlusion due to incomplete intracranial collateralization.
Fig. 1.1–16 The principle used in the proximal protection system (e.g., Gore Neuro Protection System), with reversal of flow in the internal carotid artery and continuous diversion of arterial blood via the protection system (with femoral venous return). This requires an intact anterior circle of Willis or other collateral support.
Stent implantation
Self-expanding stents are usually implanted in carotid stenting. Balloon-expandable stents are recommended in ostial stenoses of the common carotid artery, stenoses located in the distal internal carotid artery, and sometimes in severely calcified stenoses. The disadvantages of balloon-expandable stents are the repeated balloon dilations that are needed to implant the stent adequately, and stent compression that can occur during the long-term follow-up in areas vulnerable to external manipulation.
In vessels with the potential to bend or be manipulated, self-expanding nitinol stents are the best choice. They are designed to adapt to the shape of the vessel and therefore have little tendency to straighten it (Fig. 1.1-17). Stent-induced straightening of the vessel can give rise to a new stenosis distal to the stent due to kinking or folding of the vessel. Stents with a strong radial force are recommended for treatment of severely calcified stenoses. “Closed-cell” carotid stents usually have stronger radial force. Their cell structure may also provide better plaque coverage, which may be theoretically advantageous in stenoses with a high embolic risk. The clinical value of “open-cell” vs. “closed-cell” designs and the importance of the stent cell size is currently still unclear.
Fig. 1.1–17a, b (a) Elongation of the internal carotid artery, with vascular kinking distal to the stenosis before stent implantation. (b) After implantation of a nitinol stent.
The authors recommend a stent diameter 1–2 mm larger than the largest vascular diameter to be stented. Carotid stents with a diameter of 6–8 mm are usually used if the stent is being implanted exclusively in the internal carotid artery, or with a diameter of 8–10 mm if the stent is to cross the bifurcation. Stenting across the external carotid artery is not a problem and priority should be given to the stent covering the entire stenosis, which in most cases will mean crossing the bifurcation to cover the distal common carotid artery plaque. While there are no data suggesting stent length is a determinant of restenosis in the carotid, a stent 20–30 mm longer is usually selected for discrete lesions, while for tandem stenoses, 40-mm stents are recommended.
Postdilation
Postdilation is usually carried out using a balloon with a diameter of ~5 mm, matched but not larger than the diameter of the internal carotid artery, but not referenced to the common carotid artery. A balloon with an unnecessarily large diameter might force particles through the stent cells and cause distal embolization. To prevent dissections, postdilation should be carried out at nominal pressure, and within the stent borders. A residual stenosis ≤ 30% is acceptable, since an adequate blood flow is established and the potentially emboligenic atherosclerotic deposits are compressed sufficiently to induce neointimal formation and eliminate the embolic potential of the lesion. The stent expands further during the following few hours. If contrast-enhancing ulcerations occur outside the stent edge, they do not need to be obliterated and can be left without any untoward effects. Postdilation of the stent segment in the common carotid artery is not necessary. If significant stenosis or occlusion of the external carotid artery develops following postdilation, it does not require treatment.
Following postdilation of the stent, angiography of the carotid arteries and intracranial vessels is carried out. Imaging of the intracerebral vessels should always include the venous phase, to allow objective comparison of conditions before and after stent implantation. For assessment of the intracerebral vessels and in preparation for possible intracranial emergency intervention in case of cerebral embolism, angiography should be carried out with a lateral and anteroposterior 30° cranial (Towne) projection.
Fig. 1.1–18a, b (a) Outlet stenosis of the left vertebral artery before stent implantation. (b) After implantation of an expandable balloon stent.
Technique of vertebral artery stent implantation
The vascular access route for vertebral artery interventions is the same as for carotid artery stent implantation, via the femoral or brachial artery. A contralateral oblique projection is best for demonstrating the ostium of the vertebral artery. The intracranial vertebrobasilar vascular system is best demonstrated in lateral and steep anteroposterior projections. A multipurpose 6F guiding catheter is suitable for the vertebral artery procedure. Balloon-expandable coronary stents should be used for ostial stenoses of the vertebral artery, and self-expanding stents can be used in extracranial vertebral artery stenoses that are located distal to the ostium in the body of the vessel. A 4-mm coronary balloon is usually used for dilation (Fig. 1.1-18). The embolic protection systems currently available cannot usually be recommended for vertebral artery procedures, as they still have relatively large diameters for this application.
Postinterventional follow-up and medication
Following the intervention, blood pressure has to be closely checked for at least 6 h. A neurological evaluation including the National Institutes of Health Stroke Scale (NIHSS) must be carried out before the patient is discharged. Lifelong ASA treatment (100 mg) and clopidogrel during the first month are recommended.
Clinical results
Clinical series/carotid stent implantation registry
A summary of the results in 12,392 carotid stent implantations in a total of 11,243 patients from 53 centers worldwide was published by Wholey et al. in 2003. Complications during the first 30 days included: TIA (3.1%), minor stroke (2.1%), major stroke (1.2%), and death (0.6%) (Wholey et al. 2003). In 2001, Roubin et al. published a series of 528 patients who had undergone carotid stent implantation. The major stroke rate was 1% (n = 6) and the minor stroke rate was 4.8% (n = 29). Overall, the rate of stroke/death after 30 days was 7.4% (Roubin et al. 2001).
In
