Endovascular Treatment of Carotid Stenosis

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THOMAS GERASIMIDIS, DIMITRIOS KARAMANOS, KONSTANTINOS KONSTANTINIDIS, ALEXANDROS MALLIOS

2.6.1 Introduction

Endovascular treatment of carotid stenosis using carotid angioplasty and stenting (CAS) was first implemented experimentally on dogs in 1977 [33]. Since the early 1980s there have been reports of its implementation, mainly on patients suffering from fibromuscular dysplasia [18] and, later on, on patients with atherosclerosis and post-endar-terectomy restenosis [34, 41, 57]. Stenting was performed electively in order to treat possible dissection or residual stenosis after the angioplasty procedure. Later this technique was abandoned to a routine stenting procedure. In 1986 Theron introduced a cerebral protection device using an occlusion balloon in the internal carotid artery (ICA) with simultaneous aspiration of possible microem-boli [54-56].

The aim of the angioplasty and stenting procedure is - as in the case of carotid endarterectomy (CEA) - the prevention of stroke. Although initially it was considered to be an alternative solution only for high-risk patients, it is gradually gaining ground over endarterectomy and the number of patients treated by endovascular procedures is growing rapidly.

Reports from the first trials comparing CAS to CEA came up with equally satisfactory results, raising the question of which of the two methods could be considered as the treatment of choice.

2.6.2 Indications for Surgery

- Indications for Angioplasty

Essential criteria for determining indications for operative treatment of carotid occlusive disease are the grade of stenosis as well as whether the patient is symptomatic. Furthermore, reports indicate that plaque characteristics as given by Duplex ultrasound controls (mainly those re ferring to its composition and eventually to its stability) are to be considered essential for determining the indication for intervention.

Asymptomatic patients are to be presented if they have a stenosis grade >70% with coexistence of contralateral occlusion, with a stenosis grade >80%, or if they are scheduled to undergo another major surgical operation. Clear indication for intervention is for symptomatic patients with a stenosis grade >70%, or a stenosis grade 5070% with the coexistence of contralateral occlusion, or a history of transient ischaemic attacks under antiplatelet treatment.

Stenosis rate should be estimated using digital sub-tractive angiography (DSA) [35]. Two different ways for estimating stenosis grade are reported according to criteria of the NASCET and ECST trials respectively [17, 40]. According to the NASCET trial, the percentage of stenosis was determined by calculating the ratio of the luminal diameter (on two views) at the point of greatest stenosis to that at the normal part of the artery beyond the ste-

Nascet Classification
Fig. 2.6.1 Digital subtraction angiography (DSA) evaluation of stenosis grade based on NASCET and ECST criteria

nosis site. According to ECST, the percentage diameter stenosis is calculated by using as a denominator an estimate of the original width of the artery at the point of the carotid bulb (as if there were no stenosis lesion). This difference in method results in great differences in patient classification, as a calculation of stenosis according to ECST tends to overestimate the percentage diameter stenosis compared to the NASCET method (Fig. 2.6.1). The same results are produced when calculation of stenosis is based on Duplex ultrasound as well as when, instead of an accurate calculation method, stenosis is estimated approximately by comparing DSA images [35].

Plaque characteristics as given by Duplex ultrasound play a vital role in determining indications for intervention treatment of carotid stenosis. Hypoechoic and heterogeneous plaques are very likely to produce microem-boli because of their high lipid content as well as possible intraplaque haemorrhagic lesions (Fig. 2.6.2). Hyperecho-ic and homogeneous plaques, however, are indicative of plaque stability due to their high fibrous element content.

The ICAROS study [8] was planned with the aim of correlating the risk of microemboli migration during carotid stenting to plaque echographic characteristics in order to achieve better patient selection for interventional treatment. Using a computer-programmed Duplex ultrasound device, lesion grey colour imaging was graded according to a grey scale median (GSM). It was proved that hypoechoic lesions with GSM <25 were related to a higher percentage of neurological complications after carotid angioplasty, to such a degree that these lesions are to be

considered contraindicative for interventional treatment. According to the study, stenotic lesions of GSM ranging 25-50 are considered safe to be treated with CAS, however in all these cases the use of a cerebral protection device is mandatory. Finally lesions of GSM >50 are considered so stable and safe that cerebral protection devices are not necessary during the CAS procedure.

Apart from high-risk patients, special indications for CAS exist for patients with a haemorrhagic tendency, postendarterectomy restenosis, occlusion of the contralateral ICA and lesions located high in the neck area where a surgical approach is difficult; and also in hostile neck patients (due to previous neck operations, tracheotomy, local radiation therapy, or cervical vertebrae pathology for example ankylosing spondylitis) [7], or even in nonatherosclerotic lesions such as fibromuscular dyspla-sia or Takayasu's arteritis, which are specific indications for angioplasty [26, 51].

Heteroplaque Images

Fig. 2.6.2 Internal carotid artery (ICA) Duplex image: hetero- Fig. 2.6.3 Atherosclerotic plaque in ICA with ulcer lesion (red geneous plaque possible due to intraplaque haemorrhage (red arrows)

arrow)

2.6.3 Types of Stents

In contrast, unstable plaques with a floating surface clot or aortic arch lesions seem to be related to a high risk of microemboli migration, especially when guide-wire and catheters are advanced through the lesions, and for this reason may be considered contraindications for angioplasty [7]. This is also the case for severely coiled carotid arteries as well as for plaques with intense calcification, which increase the risk of technical failure depending of course on the surgeon's experience. Ulcerative plaques are not considered contraindications for angioplasty (Fig. 2.6.3).

Renal failure is also not considered to be an absolute contraindication for angioplasty, provided that certain precautions and care have been taken to prevent the toxic effects of radiography contrast agents.

Carotid Wallstent

BostonScientific - Carotid Wallstent

Carotid Wallstent

Fig. 2.6.4 Types of stents commercially available

2.6.3 Types of Stents

During the first few years of this method's implementation, the stenting procedure after angioplasty was done electively. Today, stenting is mandatory, as the use of stents produces better results both in preventing micro-emboli migration due to plaque destruction during an-gioplasty and also in avoiding recoiling.

During the early days of stenting, stainless-steel balloon-expandable stents were the most commonly used. Palmaz® stents (Cordis-J&J, Miami Lakes, Fla.) were among the types initially used. Balloon-expandable stents have the advantage of exerting a constant radial force, which prevents stent collapse and allows embedding of

Guidant - Acculink (straight and tapered)

ENDOTEX-NEXSTENT tapered

Fig. 2.6.4 Types of stents commercially available the stent in the vessel wall as well as accurate delivery. They are a reliable choice for lesions located at the origin of the common carotid artery (CCA), or extremely distal stenosis and occasionally in cases of highly calcified recoiling stenosis. However, they are not flexible and there are reports of compression when they are subjected to extreme mechanical force [36]. Also, it is rather difficult to use them in the carotid bifurcation area because of the difficulty of expanding vessels of varying diameter. Consequently, they are considered suitable for short localized lesions.

Self-expandable stents are now considered the best choice for angioplasty and stenting procedures. Wall-stents® (Boston Scientific, Natick, Mass.) were among the first stents of this kind to be used on a large scale. Eventually new types of self-expandable stents employing new materials, such as nitinol, were made. There are certain differences among various kinds of stents, such as in strut design and size. Some types have two different shapes, straight and tapered, with the latter being suitable for cases where stents should be placed partly in the internal and partly in the CCA.

Currently available stents include: Carotid Wallstent® (Boston Scientific, Natick, Mass.), Exponent® (Medtronic, Minneapolis, Mn.), Xact Carotid Stent® (Abbot, South Pasadena, Calif.), RX Acculink® (Guidant, Santa Clara, Calif.), Sinus-Carotid® (OptiMed, Ettlingen), Nexstent® (EndoTex, Cupertino, Calif.), Conformexx® (Bard, Tempe, Ariz.), Precise® (Cordis-J&J, Miami Lakes, Fla.), Zilver Stent® (Cook, Winston-Salem, N.C.) and Protégé GPS® (ev3, Plymouth, Minn.) (Fig. 2.6.4).

Why Mhc Antigens Inherited Haplocyte
Fig. 2.6.5 Schematic image of distal occlusion balloon protection device (PercuSurge GuardWire® )

Filters

Proximal occlusion systems which produce flow reversal, derived from Kachel's technique

2.6.4.1 Distal Occlusion Balloon (Theron's System, PercuSurge GuardWire® Medtronic) (Fig. 2.6.5)

2.6.4 Brain Protection Devices

Neurological events due to micro emboli migration towards the intracranial circulation are the most important among the possible complications of the method. Microemboli can be produced in practically all of the angioplasty phases, including guidewire and catheter manoeuvres inside the aortic arch, the advancement of wires through the lesions into the ICA, balloon advancement and delivery at the lesion area as well as balloon or stent dilatation at the site of stenosis. In order to decrease the risk of embolic events, brain protection devices have been used since the late 1980s, based on different concepts [54-56].

• Distal occlusion balloons, derived from Theron's technique

This technique is based on the temporary occlusion of the ICA, distally to the stenosis area, by inflating a balloon and consequently reversing blood flow towards external carotid artery (ECA) and at the same time aspirating possible microemboli. The most important disadvantage of the method is that it blocks blood circulation. It is now used very rarely.

2.6.4.2 Filters

This technique is based on the advancement and deployment of an umbrella-shaped system inside the ICA and distally to the stenosis area, which blocks possible mi-croemboli. It constitutes of a mesh allowing blood flow through very small pores (100-150 |im), which is essential in cases of poor collateral circulation due to severe

2.6.4 Brain Protection Devices

2.6.4 Brain Protection Devices

Types Vascular Access Surgeries
Fig. 2.6.6 Types of filters commercially available

contralateral ICA lesion or a poor circle of Willis. However, several types of filters have a large cross-sectional profile leading to difficulties in passing tight, tortuous or high-grade stenoses.

Also, filters can cause severe vasospasm or even dissection of the vessel wall and there is the possibility of thrombosis. There are reports of difficulties during closure and retrieval of the filters, sometimes leading to their contents being dislodged. The filter should be of such a size that it matches the lumen diameter in both systole and diastole and also after predilatation or stent deployment, which increase blood flow and lumen diameter.

Like distal occlusion balloons, filters do not offer protection throughout the whole CAS procedure.

A large variety of filters is now commercially available, varying in terms of mesh pore size, delivery systems, ways of embedding in the arterial wall and in other features, details of which are beyond the aims of this chapter. The surgeon's choice is based on personal preference and experience with each device.

Filter protection devices currently available or under evaluation in clinical trials include: AngioGuard XP® (Cordis-J&J, Miami Lakes, Fla.), E.P.I Filter wire® (Boston Scientific, Natick, Mass.), Spider® (ev3, Plymouth, Minn.),

Medical Treatment Boston

Fig. 2.6.7a-c a, b Proximal occlusion system. Parodi Anti-Emboli System®. a, b Extracorporeal flow. c The device inside the carotid artery

Emboshield® (Abbott, South Pasadena, Calif.), Accunet® Kachel's System (Guidant, Santa Clara, Calif.), Interceptor® (Medtronic,

Minneapolis, Minn.) and Rubicon® (Rubicon, Salt Lake The use of this system was first reported in 1996 [28]. It

2.6.4.3 Proximal Occlusion System consists of a double coaxial system with a balloon occluding the upper part of the CCA, producing flow towards the ECA, as well as an angioplasty balloon for the treatment of stenosis.

The concept of this system is to create a reversed flow within the ICA which prevents antegrade blood flow by Parodi Anti-Emboli System® (ArteriA Medical sending the debris to the cerebral circulation. Science, San Francisco) (Fig. 2.6.7a-c)

Parodi created a system that produced flow reversal in the ICA by occluding the CCA and the ECA. The reversed flow is then returned through an arteriovenous shunt with a filter to the femoral vein. It consists of a 10-Fr catheter with an occlusion balloon attached at the distal end. After the guidewire is inserted into the ECA, the catheter is advanced in the ECA and the balloon is inflated in the CCA. A second balloon is then placed in the ECA through the lumen of the catheter and inflated. The proximal end of the catheter is then connected to a femoral vein sheath via a connector with a filter inside to trap the emboli. Due to the difference of pressure, reversed blood flow from the ICA to the femoral vein is then established. The operator is now able to cross the lesion and place the stent under protection. The major advantage of this technique is that the protection starts before crossing the lesion. Disadvantages include the potential danger of spasm or dissection of the CCA or ECA and the intolerance of blood flow occlusion by some patients with reduced collateral supply and large introducer size.

Protection action occurs by interrupting the antegrade flow from the CCA and the retrograde flow from the ECA by inflating two occlusive balloons. Debris is stopped at the bifurcation and, after completion of the angioplasty procedure, removed by syringe aspiration. The balloons are then deflated and blood flow restored. Advantages and disadvantages are the same as in the Parodi Anti-Emboli System®.

Proximal occlusion systems offer protection before crossing the lesion, and in that sense can be considered as safer than other brain protection systems. However, it is understood that they cannot offer protection during guidewire manoeuvres into the aortic arch or during their advance through the carotid arteries.

Also as with distal occlusion balloons, some patients cannot tolerate blood flow occlusion of the ICA. In order to deal with this problem, Parodi implemented a combination of two techniques calling it the "seatbelt and airbag technique". According to this technique the Parodi Anti-Emboli System® is initially used, creating reversed blood flow into the ICA, and then a second type of protection device using a filter is advanced distally into ICA. After filter deployment blood flow reversal is stopped and the procedure is continued under filter protection.

2.6.5 Preoperative Evaluation

Patient history is vital in choosing and posing indication for treatment. Patients also undergo routine preoperative control, including physical examination, chest X-ray, electrocardiography (ECG), blood tests (haematological and biochemical profile as well as screening tests of the coagulation system). Special attention is given to renal function as any disorder may negatively affect the patient's postoperative recovery.

Fig. 2.6.8 Proximal occlusion system. MO.MA*

2.6.5.1 Neurological Examination

Clinical evaluation by an independent neurologist is necessary both to determine indications for intervention and to estimate accurately the patient's preoperative condition and possible residual neurological signs due to previous brain ischaemic attacks. It is also necessary to have a postoperative clinical evaluation by the same neurologist in order to make sure there are no neurological complications due to the angioplasty procedure.

2.6.5.2 Special Imaging Examination

Patients undergo a thorough imaging control, consisting of Duplex ultrasound, digital subtraction angiography (DSA) of the aortic arch and its branches [or magnetic resonance angiography (MRA) if necessary] and brain computed tomography (CT) scan.

2.6.5.3 Duplex Ultrasound

Duplex ultrasound usually acts as the screening test for diagnosis of carotid occlusive disease. In most cases it is part of a diagnostic procedure following a brain isch-aemic incident, the onset of neurological signs or just the detection of a bruit in neck vessels during clinical examination. Duplex ultrasound provides information regarding carotid artery morphology, detection of stenosis site, as well as a rough estimation of the grade of stenosis and special plaque features regarding its stability and composition [6]. Using computerized programs for analysing grey scale images, Duplex enables the discrimination between homogeneous and heterogeneous plaques, with hyperechoic sites representing fibrous elements and hy-poechoic sites representing lipids or places of intraplaque haemorrhage. It has been proved that heterogeneous and hypoechoic plaques, especially on the surface, are prone to be unstable and have a poor prognosis [38]. Using Doppler and coloured Duplex ultrasound an indirect functional evaluation of stenosis grade can be done by calculating maximum blood flow velocity. When values are >120 cm/s stenosis grade is estimated to be over 50%, thus being of clinical relevance and in need of thorough evaluation and treatment. Duplex ultrasound has the advantage of being atraumatic, repeatable (both for preop-erative control and also for follow-up), reliable and cost-effective. It has, however, some significant disadvantages:

it is very dependent on the examiner, it is subject to over-estimation, and it cannot provide information regarding the aortic arch and most of the proximal part of the carotid arteries where the cause of the patient's symptoms may lie.

2.6.5.4 Digital Subtraction Angiography (DSA)

While the decision for endarterectomy can be based only on results of Duplex ultrasound, this cannot be the case for angioplasty. Preoperatively, precise evaluation of the grade of stenosis and of the anatomical features of the aortic arch and its branches are necessary. There are cases where excessive coiling, extreme angulations or other anatomical variations (for example, bovine arch) (Fig. 2.6.9) may be considered as either contraindicative for the an-

Fig. 2.6.9 Abnormal origin of the left common carotid artery from the innominate artery (bovine arch) (red arrow). Significance of sufficient preoperative mapping of the aortic arch

gioplasty procedure, or requiring a different approach (brachial access or direct catheterization of the CCA). DSA may also detect proximal lesions of the aortic arch, which may be thought responsible for the patient's symptoms and must be treated at the same time as the carotid stenosis, as they have a high risk of causing perioperative embolic events.

2.6.5.5 Magnetic Resonance Angiography (MRA) (Fig. 2.6.10)

MRA is based on different features of moving blood protons when detected under a strong magnetic field. MRA actually produces images of blood flow inside the lumen and not the exact anatomical morphology of the lumen. It is safer than DSA and has a high sensitivity but low specificity. A normal MRA is quite preclusive of possible significant stenosis, while pathological results cannot give the stenosis grade with high accuracy thus it is not absolutely positive for angioplasty indication [32]. In patients with impaired renal function the combination of Duplex ultrasound and MRA can provide a reliable preoperative evaluation while MRA has the advantage of providing brain scan images during the same examination. MRA is an evolving method whose results are improving.

2.6.5.6 Brain Computed Tomography (CT)

Computed tomography (CT) of the brain is considered necessary for preoperative evaluation according to many reports [32]. Old or recent brain ischaemic incidents, history of neurosurgical operations or of accidents involving brain damage are absolute indications for preopera-tive brain imaging. This author's view is that recent brain imaging, whether it involves CT or MRI, is easy, quick, inexpensive, safe and is necessary for all patients as a basic preoperative procedure in case of postoperative neurological complications.

Fig. 2.6.10 Magnetic resonance angiography (MRA): image of bilateral lesions (red arrow)

2.6.6 Technique

2.6.6.1 Step 1: Approach to the Common Carotid Artery Access Site carotid artery, which was used previously, has now been abandoned because of serious disadvantages (difficulties with haemostasis, collapsed stents during manual compression for haemostasis or even puncture at the site of the plaque).

The most common and widely used access site is via percutaneous catheterization of the femoral artery. Brachial or radial access or direct catheterization of the CCA following neck incision can be chosen in cases of severe aorta-iliac stenosis or occlusion, or in cases of a difficult approach to the aortic arch with an angulated carotid artery origin. Direct percutaneous catheterization of the

Femoral Access

• Local anaesthesia of the inguinal area.

• Percutaneous transfemoral catheterization followed by advancement of a stiff hydrophilic guidewire (0.035 inch, 0.1 cm) and then a sheath over the wire.

Direct Neck Incision
Fig. 2.6.11 Common carotid artery's puncture after neck incision and preparation

2.6.6 Technique

2.6.6 Technique

Aortic Arch Types
Fig. 2.6.12 Various types of catheters and catheterization techniques regarding aortic arch anatomy

• Over the wire and through the sheath - a guide catheter is advanced along with the wire into the aortic arch.

Brachial Access

This technique is used in cases of severe aorta-iliac stenosis or occlusions. Technical aspects are the same. For catheterization of the left ICA, right brachial or radial artery access is preferred; for the right ICA, the left brachial or radial arteries.

Cervical Access Via Preparation (Fig. 2.6.11)

• Local neck anaesthesia

• Preparation of the CCA following small incision

• CCA puncture (antegrade or retrograde depending on the stenosis site)

• Advancement of guidewire and sheath

• Pre-interventional angiography to determine ICA's morphology and stenosis site.

2.6.6.2 Step 2: Cannulation of the Common Carotid Artery (Fig. 2.6.12)

Cannulation of the left or the right CCA is achieved using the proper guide catheter, by first advancing the guide-wire just proximally to the bifurcation site and then proceeding with guide catheter advancement.

Alternatively, CCA cannulation can be achieved by placing a soft guidewire and diagnostic catheter in the external carotid, exchanging that with a stiff wire and then withdrawing the catheter and inserting a guide catheter into the CCA.

Finally, an alternative option is to use a long guide sheath instead of a guide catheter.

When cannulation of the CCA and angiographic control are completed, the decision can be made as to whether a cerebral protection device can be used.

Fig. 2.6.13a,b Left ICA angioplasty: perioperative DSA before the use of a brain protection system (red arrow)

2.6.6.3 Step 3: Angioplasty and Stenting

Without Cerebral Protection (Fig. 2.6.13a,b)

A 0.035-cm (0.014-in) or 0.046-cm (0.018-in) guidewire is advanced distally to the stenosis site in the ICA. Then, after verifying the proper position of the guidewire, the stent is inserted at the site of stenosis. The stent can be inserted using either the over-the-wire-technique or the rapid exchange monorail technique (Fig. 2.6.14). The second technique is easier and quicker, and therefore more popular. The stent can be self-expandable or balloon-expandable. In cases of high-grade stenosis insertion of the stent can prove impossible, and there is also the danger of the premounted stent of the balloon slipping. In these cases, predilatation of the stenosis using a coronary balloon of 2-4 mm diameter and 20-40 mm length can help when inserting the stent at the stenosis site.

With Cerebral Protection (Fig. 2.6.15a,b)

The stenting technique, in which a distal occlusion balloon or filter is used for cerebral protection, is quite similar. Crossing of the lesion with the protection device and inflation of the protection balloon or filter deployment angioplasty (a) and after balloon-expandable stenting (b) without angioplasty (a) and after balloon-expandable stenting (b) without

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