REVIEW ARTICLE

Carotid Artery Stenting: Update

ROBERT S. DIETER & JOHN R. LAIRD

Washington Hospital Center/Georgtown University

Abstract‘‘Extracranial carotid artery stenosis is responsible for approximately 20–30% of ischemic strokes. Traditionally, carotidartery stenosis has been treated with carotid endarterectomy. However, the low periprocedural complication rate and themid term durability of carotid artery stenting has made it a competitive alternative treatment strategy. This update reviewsthe technical aspects of carotid artery stenting, clinical data supporting carotid artery stenting-particularly in high riskpatients, and the complications associated with carotid artery stenting.’’

Key Words: Carotid artery, stent, complication, procedure, trials

Introduction

Strokes represent the third leading cause of death in

the USA and the leading cause of disability in the

elderly. At five years, the mortality rate is roughly

50% with an excess of 50 billion dollars expended

annually on patients who have suffered a stroke (1).

Eighty percent of strokes are ischemic, with the

extracranial carotid artery contributing to twenty

percent of these (1). The risk of sentinel stroke

increases with stenosis severity and plaque morphol-

ogy. Symptomatic patients are at significantly higher

risk of a subsequent event than their asymptomatic

counterparts. Despite medical therapy, the risk of a

recurrent event for symptomatic patients approaches

26% at two years and 11% at five years for asympto-

matic patients (1,3). For the past five decades,

carotid endarterectomy (CEA) has been effectively

employed to reduce the risk of stroke associated with

carotid artery stenosis (4). Despite annual absolute

risk reductions of approximately 1% for asympto-

matic patients and 8% for symptomatic patients,

trials evaluating carotid endarterectomy have sys-

tematically excluded patients considered to be high

risk surgical candidates.

Multiple studies have demonstrated that ‘real-

world’ practice of stroke prevention involves patients

who would have been excluded from the major CEA

trials and are at considerable operative risk. Owing

to the co-morbidities associated with these high-risk

patients, an endovascular approach to the carotid

artery was developed in an attempt to reduce the

morbidity and mortality of the procedure. Based

upon several clinical trials in these high-risk patients,

carotid artery stenting (CAS) for the treatment of

both asymptomatic and symptomatic extracranial

carotid artery stenosis became FDA approved in the

fourth quarter of 2004.

Procedural overview of carotid artery stenting

The carotid artery is generally approached percuta-

neously from the common femoral artery. Initial

anatomic evaluation includes an aortic arch angio-

gram. This aortogram will define the atherosclerotic

burden of the aortic arch as well as the proximal arch

vessels. Furthermore, an assessment of the suitability

for cannulation of the arch vessels can be made as

well as definition of anatomic variants such as the

bovine arch. Selective extracranial carotid angiogra-

phy is performed with an emphasis on the carotid

artery bifurcation. Particular attention is given to the

internal carotid artery with regards to the potential

for positioning an embolic protection device. An

intracranial evaluation of at least the anterior

circulation should be standard both pre-intervention

and post intervention.

Patients undergoing CAS receive systemic anti-

coagulation with a goal ACT of 250 seconds or

greater. All patients should be pre-treated with dual

anti-platelet therapy (aspirin and a thienopyridine

derivative) that is continued for at least two to four

weeks post-procedure and aspirin indefinitely.

Correspondence: Robert S. Dieter, Director of Vascular Medicine, Section of Cardiovascular Medicine, Medical College of Wisconsin, 8701 Watertown Plank

Road, Milwaukee, WI 53226, USA. E-mail: rdieter@mail.mcv.edu

International Journal of Cardiovascular Interventions. 2005; 7: 126–133

ISSN 1462-8848 print/ISSN 1471-1796 online # 2005 Taylor & Francis

DOI: 10.1080/14628840510039559

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Sedation is generally withheld so that accurate

neurological status can be evaluated throughout

the procedure. The use of a ‘squeeze-toy’ in the

contra-lateral hand allows for periodic neurological

assessment.

Various strategies have been employed to access

the common carotid artery with either a guiding

sheath or guide catheter. Generally, most involve the

selective wiring of the external carotid artery to

provide support while the catheter is advanced into

the common carotid artery. With stable access to the

common carotid artery, the lesion is crossed with a

distal/embolization protection device. Upon crossing

the lesion, the patient is generally pre-medicated

with atropine to help prevent the carotid baro-

receptor activation during the procedure. Lesions

are typically pre-dilated with a 4mm balloon, stented

with a self-expanding stent, and then gently post-

dilated with a 5 mm balloon. Some degree of residual

stenosis is acceptable after post dilation and overly

aggressive post-dilation is associated with increased

complications. Continuous invasive hemodynamic

monitoring during the procedure is mandatory and

significant alterations should be acutely corrected.

Finally, the embolization protection device is

removed and completion extracranial and intracra-

nial angiograms are performed.

Results from clinical trials

Randomized trials

There are four randomized clinical trials comparing

CEA to CAS. The first trial was published in

1998 and consisted of only seventeen patients.

Symptomatic patients with w70% stenosis were

prospectively enrolled and randomized to either

CEA with patching or to carotid artery stenting.

The expected enrollment was 300, but the study

was terminated early by the data safety and moni-

toring board (5). Primary stenting of the carotid

was attempted with the Wallstent (Schneider,

Minneapolis, MN) and if unsuccessful, the lesion

was pre-dilated. Of the 10 patients who underwent

CEA, none had a periprocedural TIA or CVA or

thirty day disabling CVA whereas, five of the seven

CAS patients had a periprocedural TIA/CVA and

three had a disabling CVA at 30 days. Although the

interventionalist performing the CAS was experi-

enced in the peripheral circulation, only eight prior

CAS had been performed. Furthermore, no distal

protection devices were employed.

The Wallstent trial was a multi-center, equiva-

lency trial of CEA and CAS. Two hundred and nine

symptomatic patients with 60–99% stenosis were

enrolled, 107 to CAS and 112 to CEA. The patients

were treated with the Wallstent, without distal

protection (6). The primary endpoint (ipsilateral

CVA, procedure related death, or vascular death at

one year) was reached by 12.1 and 3.6% of those

randomized to CAS and CEA, respectively

(P50.022). The rate of major CVA was 3.7 and

0.9%, respectively. The 30-day periprocedural com-

plication rate (any stroke or death) occurred in

12.1% of CAS patients and 4.5% of CEA patients

(P50.049). This study was terminated prior to the

planned 700 patient enrollment due to the inferiority

of CAS. The interventionalists in this study were

relatively inexperienced and no distal protection

devices were used.

The Carotid and Vertebral Artery Transluminal

Angioplasty Study (CAVATAS) was published in

2001. This multi-center (Europe, Australia, and

Canada) trial randomized 504 patients (principally

symptomatic) to either CEA (253) or CAS (251)

(7). Lesions had to be amenable to either CEA or

CAS; patients with significant co-morbidities (recent

myocardial infarction, poorly controlled hyper-

tension or diabetes, significant renal or pulmonary

disease) were excluded. Only 26% of patients

received a stent—either the Wallstent, Palmaz stent

(Johnson & Johnson), or the Strecker stent and no

embolic protection devices were used. The results

were essentially equivalent between the CAS and

CEA groups at thirty days (death or any CVA 10%

versus 10%, death 3% versus 2%, disabling CVA 4%

versus 4%, respectively). At one year the restenosis

rate (w70%) was 14% with 4% occlusions in the

CAS group and 4 and 1% in the CEA arm,

respectively. Although equivalency was demon-

strated, this trial is criticized for high event rates

compared to the standard NASCET and ECST

trials; furthermore, this was principally a carotid

artery, angioplasty study—since only 26% received a

stent.

The SAPPHIRE study, published in 2004, was a

randomized, multi-center non-inferiority trial of

high risk patients. Patients with high risk anatomic

or co-morbid conditions, with either symptomaticw

50% or asymptomaticw80% stenosis were rando-

mized to either CAS (n5167) or to CEA (n5167)

(8). The CAS procedure utilized the Smart or

Precise stent (Cordis) and the Angioguard or

Angioguard XP (Cordis) distal protection device.

The prespecified primary endpoint (death, CVA, or

myocardial infarction at 30 days, and death plus

ipsilateral CVA from day 31 to one year) of non-

inferiority of CAS versus CEA was reached in 12.2%

of those assigned to CAS and 20.1% assigned to

CEA, P50.004. The 30-day stroke, myocardial

infarction, or death rate was 4.8% in the CAS arm

and 9.8% in the CEA arm. In symptomatic patients,

the primary outcome was seen in 16.8 and 16.5% of

the CAS and CEA groups, respectively. In asympto-

matic patients, the rates were 9.9 and 21.5%,

respectively. The trial demonstrated both the non-

inferiority of CAS to CEA, but also that this high

risk cohort has significant event rates.

Carotid artery stenting 127

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Randomized trials underway include the National

Institute of Health sponsored Carotid Revas-

cularization Endarterectomy versus Stent Trial

(CREST). This is an on-going prospective, rando-

mized study of conventional risk patients with

symptomaticw50% carotid stenosis. All interven-

tionalists are required to have performed at least 20

procedures with the Acculink and Accunet systems

(Guidant). The Stent Protected Angioplasty versus

Carotid Endarterectomy (SPACE) trial is underway

in Germany and CAVATAS II is underway in

Europe.

Registries

Despite a limited number of prospective, rando-

mized trials there over ten carotid artery stent

registries, primarily in high-risk patients, in various

stages of completion.

There are three Acculink for Revascularization of

Carotids in High Risk Patients (ARCHeR) trials

sponsored by Guidant. ARCHeR 1 and 2 used the

over the wire Acculink and Accunet platforms

(ARCHeR 1 did not use distal protection.

ARCHeR 3 used rapid exchange systems). The

three studies involved patients with high-risk ana-

tomic or co-morbid conditions and symptomatic>

50% stenosis or asymptomatic>80% stenosis.

ARCHeR 1, 2, 3 enrolled 158, 278, and 145 patients

respectively. The 30-day combined endpoint of

death, CVA, or myocardial infarction was reached

in 7.6, 8.6, and 8.3% of patients; death 2.5, 2.2, and

1.4%; CVA 4.4, 5.8, and 6.2% in ARCHeR 1, 2,

and 3 respectively. From day 31 to one year, there

was one major and four minor strokes in ARCHeR 1

and 2. The composite endpoint of death, CVA, and

myocardial infarction within 30 days and ipsilateral

CVA to one year was 8.3% in ARCHeR 1 and 10.2%

in ARCHeR 2. A weighted historical control was

calculated based upon a similar cohort of patients if

they had undergone CEA. Based upon the risk

profile, the weighted historical control event rate if

patients underwent CEA was 14.5% (9). These

findings helped Guidant be the first company to gain

FDA approval for their carotid stent platform.

SECuRITY is a registry Study to Evaluate the

NeuroShield Bare Wire Cerebral Protection System

and Xact Stent in Patients at High Risk for Carotid

EndarTerectomY sponsored by Abbott. Patients in

this registry had symptomatic>50% or asympto-

matic>80% angiographic carotid stenosis and high

risk anatomic or co-morbid conditions. The primary

endpoint was death, all stroke, and myocardial

infarction at 30 days and any ipsilateral stroke to

one year. A total of 305 patients were enrolled after

93 lead-in patients (not included in the final

analysis) and the study was completed in February

2004. The lesion procedural success rate was 96.7%

(stent delivery—94.1% and EmboShield delivery

and retrieval—96.7%). The 30-day major adverse

event rate was 7.5%: myocardial infarction- 0.3%,

minor stroke—4.2%, major stroke 2.0%, and

death—1%. From days 31 to 365, the ipsilateral

stroke rate was 2.0% and the primary endpoint was

seen in 9.5% of the patients. The ultrasound

restenosis rate at one year was 4.1% with a 12-

month target lesion revascularization rate of 0.6%.

Although not sponsored by a device manufacturer,

nor under the same rigorous criteria and follow-up

as other registries, The Global Carotid Artery Stent

Registry provides insight into the ‘real-world’ prac-

tice of carotid artery stenting around the world. First

initiated in 1997 with 24 surveys in Europe, South

America, North America, and Asia, the Global

Carotid Artery Stent Registry, now has 53 centers

and was required in September 2002.(10) A total of

11 243 patients and 12 392 lesions are included in

the registry. The technical success was very high at

98.9%. Aproximately half of the patients were

symptomatic (53.2%). As the learning curve of

stenting progressed, there was a shift away from

balloon expandable stents to the use of self-

expanding stents with the Wallstent (Boston

Scientific, Natick, MA) and the Cordis Smart and

Precise stents (Cordis, Johnson & Johnson, Warren,

NJ) being the most commonly deployed. The 30-day

complication rates were 3.07% TIAs, 2.14% minor

strokes, 1.20% major strokes, and 0.64% deaths (per

lesion analysis) with a combined stroke and death

rate of 4.75% (of which 0.77% were not procedure

related deaths). The 30-day rate in asymptomatic

patients was 2.95% and 4.94% in symptomatic

patients.

The preliminary results from a number of other

carotid artery stenting registries have been reported

with 30-day major adverse event rates usually

between 5 and 8%. (See Table 1.)

Embolic protection devices

There will likely never be a prospective, randomized

trial comparing carotid artery stenting with and

without distal embolization protection devices

(EPDs). Studies have demonstrated that cerebral

embolization occurs during all stages of carotid

artery stenting. Analysis of the Global Carotid Artery

Stent Registry suggests that EPDs reduce the stroke

risk involved with CAS. Among the 6753 lesions that

underwent treatment without EPD, the stroke and

death rate was 6.15% whereas among the 4221

patients in which an EPD was used, the stroke and

death rate was 2.85%. This protection is seen in

the asymptomatic patients (without—4.78% death/

stroke rate, with—2.51%) and the symptomatic

patient subgroups (without—6.93% death/stroke

rate, with—3.22%). The most commonly used

EPDs in the Global Carotid Artery Stent Registry

were the PercuSurge (Medtronic, Sunnyvale, CA),

128 R. S. Dieter & J. R. Laird

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Table 1. Summary of carotid artery stenting trials and registries (courtesy of Endovascular Today).C

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the Angioguard (Cordis) and the EPI Filterwire

(Boston Scientific).

There are essentially three types of EPDs—those

that arrest antegrade ICA flow, those that reverse

ICA flow, and the filters. (See Table 2.) The

PercuSurge GuardWire is representative of the

EPD which arrests antegrade flow. The GuardWire

has an inflatable balloon approximately 3.5 cm

proximal to the guide-wire tip that can be inflated

to 6 mm to arrest antegrade flow. The column of

blood and any debris that is dislodged during the

procedure is then aspirated and the balloon is then

deflated. With the PercuSurge inflated and the

cessation of antegrade flow, contrast injections

cannot be performed for vessel visualization. The

second class of EPD involves reversing the flow in

the ICA. Occlusive balloons are placed in the

proximal ICA as well as the ECA, blood flow is

then reversed and auto-transfused after being passed

through a filter. This is the only type of EPD that

allows crossing of the stenosis under protection. The

final category of EPDs is filters. A variety of filters

have been developed (e.g. Accunet, EmboShield, EZ

Filter, AngioGuard, Spider). There have been

several iterations of the filters to allow for easier

delivery and recovery with varying porosity of the

filter. The filters are perhaps the easiest to use and

allow for contrast injections for lesion and arterial

visualization during the procedure.

There have been no trials directly comparing the

various EPD, although there have been retrospective

studies evaluating the clinical efficacy of different

EPDs. In ex-vivo models of carotid tortuosity, the

Angioguard protection system performed the worst

while the FilterWire EX demonstrated no reduction

in efficacy in tortuous arteries (11). Clinically,

however, there has been no difference in the

outcomes when comparing various filters and

balloon occlusion devices (12). We compared the

clinical outcomes in 151 patients undergoing carotid

artery stenting at our institution—77 utilizing the

FilterWire and 74 with the PercuSurge GuardWire.

We found no difference in the periprocedural stroke

rate, in-hospital, 30-day, or six-month mortality

rate.

Although designed to minimize complications

during CAS, all EPDs have the potential for com-

plications. The PercuSurge system of arresting

antegrade flow is generally well tolerated, however,

intolerance to balloon occlusion occurs in 5–15% of

patients (13,14). Intolerance to cessation of ante-

grade flow with the balloon occlusion EPDs has a

bimodal presentation. An immediate intolerance is

usually manifested by the loss of consciousness or

seizure activity. Patients with severe contralateral

carotid, concomitant vertebral artery, or intracranial

disease may be at higher risk of this complication.

A later intolerance develops in some within a few

minutes of the procedure. This intolerance is usually

manifested by more localized neurological signs-

such as a transient neurological deficit, temporary

loss of consciousness, or agitation (13,14). Other

major complications of EPDs include arterial dis-

section and filter entrapment (14). Not uncom-

monly, EPDs result in arterial spasm. Finally, it is

important to recognize that all EPDs have the

potential of causing embolization- either while

crossing the lesion or during device deployment in

the more proximal vessel.

Complications of carotid artery stenting

Stimulation of the carotid sinus, which is located at

the carotid bifurcation, can lead to an increased vagal

tone and reduction in sympathetic tone. Clinically,

this results in bradycardia and hypotension. Variably,

between 13 and 38% of patients develop bradycardia

and 5–26% will develop hypotension (15). Sustained

hypotension and bradycardia can be seen in up to a

third of patients undergoing CAS. Hypertension in

the periprocedural period is seen in up to 40% of

patients. Patients at particular risk of complications

from the hemodynamic alterations include those with

a cardiomyopathy, severe coronary artery disease,

valvular heart disease, preload dependent states,

and those with critical contralateral or intracranial

stenosis.

Cerebral reperfusion hemorrhage can be a devas-

tating consequence to the loss of intracerebral

autoregulation and blood flow being directly propor-

tionate to mean arterial pressure. Patients thought to

be at increased risk include those with significant

contralateral carotid stenosis, history of contralateral

endarterectomy, those with significant asymmetry in

hemispheric cerebral blood flow, and those with

periprocedural hypertension (16,17). Patients may

present with a headache with or without neurological

alterations such as seizures, focal symptoms, or a

depressed level of consciousness. Rarely, contrast

encephalopathy can mimic diffuse intraparenchymal

hemorrhage.

As already discussed, although CAS is directed at

the reduction of future strokes, the procedure itself

can lead to both intracranial embolization and

hemorrhage. Intracranial hemorrhage, particularly

in the aged population that undergoes CAS, is not

only more common with the systemic anticoagula-

tion that is necessary for the procedure, but also

frequently fatal. In part because of the potential of

increased hemorrhagic complications and the lack of

proven efficacy in CAS, intravenous glycoprotein

IIb/IIIa antagonists are not routinely advised for

CAS (18). Embolization can occur during nearly any

stage of the carotid artery stenting procedure—even

diagnostic angiography carries approximately a 1%

risk of stroke. Meticulous technique is mandatory

throughout the CAS procedure and the use of distal

embolization devices should be standard.

130 R. S. Dieter & J. R. Laird

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Table 2. Carotid artery stent device overview (courtesy of Endovascular Today).C

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The aging process can elongate the aortic arch

resulting in the great vessels originating from the

ascending aorta. Such arch types are more difficult

to engage and to perform the CAS procedure.

Proximal arch vessel disease can increase the risk

of embolization as well as vessel injury and dissec-

tion. Not uncommonly, the ICA is tortuous or has

distinct kinks or coils. Such anatomic variations or

changes with aging can make the safe landing of an

EPD difficult and the distal landing zone of the stent

can lead to distortion and translation of the kinks

cephalad with the creation of pseudolesions.

Ulcerated lesions or those filled with thrombus are

at particular risk for embolization and the approach

to these must be done with great care. Accordingly,

echolucent plaques and by inference less stable

plaques, have increased neurological complications

following CAS (19). Significant lesion calcification,

increases the risk for periprocedural complications,

(especially in the patient with renal insufficiency

who is independently at increased risk of contrast

induced nephropathy), particularly if there is a

concentric arc of calcium.

Post-intervention follow-up

Prior to initiating the CAS procedure, all patients

should be on dual antiplatelet therapy consisting of

aspirin and a thienopyridine derivative, preferably

clopidogrel due to fewer side effects compared to

ticlopidine. Although there have been no rando-

mized, placebo controlled trials of clopidogrel after

carotid artery stenting, most trials have prescribed

clopidogrel for two to four weeks after the procedure

(8). Arguably, however and neither based upon firm

clinical data nor FDA approval, dual antiplatelet

therapy should be continued indefinitely in this

high-risk cohort. Every patient requires aggressive

attention to his or her cardiovascular risk factors

(20).

As with patients who have undergone CEA, CAS

require surveillance imaging to evaluate patency and

possibly to follow a contralateral carotid artery

stenosis. A duplex evaluation should be done prior

to the patient being discharged, at six months, one

year, and then yearly thereafter. If any duplex

demonstrates lesion progression or clinical symp-

toms dictate, then more frequent carotid duplex

evaluations are recommended. There is a consider-

able amount of interest in how CAS affects the

biomechanical properties of the carotid artery.

Stenting likely changes the compliance of the carotid

artery thereby affecting the detected velocities by

ultrasound duplex examination (21). Studies corre-

lating the velocities in the carotid artery immediately

after stenting to the final angiogram and existing

duplex criteria have found that existing criteria

overestimate the stenosis severity (21). Our practice

is to downgrade the stenosis severity, based upon

duplex findings, one-grade on the side that has

undergone CAS as well as integrate the velocity

criteria with the B-mode imaging. Post CAS

intracranial evaluation with MRI or CT may be

necessary if the neurological status of the patient

changes, but otherwise routine post CAS intracra-

nial imaging is not required.

The carotid arteries are elastic (conductance)

arteries, and therefore the in-stent restenosis rate

should be low. Systematic review of 34 studies

involving 4185 patients found that the restenosis

rates (>50–70%) at one and two years were

approximately 6 and 7.5%, respectively (22).

Criteria for restenosis were heterogeneous, but these

rates are consistent with the individual CAS studies.

In the SECuRITY trial, the one year ultrasound

restenosis rate was 4.15% with a target vessel

revascularization rate of 0.6%. In the SAPPHIRE

trial, the target vessel revascularization rate was

0.7% after CAS and 4.6% after CEA. The ARCHeR

1 and 2 trials had target lesion revascularization rates

of 2.2 and 2.8%, respectively; the weighted historical

control rate was 4–7%. Risk factors for in-stent

restenosis include female gender, advanced age

(unlike after CEA), treatment for CEA restenosis

or after radiation therapy, and possibly the number

of stents implanted (23).

Training and credentialing

Most new procedures do not generate such enthu-

siastic forums regarding training and credentialing,

as has CAS. The discussion of training and

credentialing for CAS is particularly involved

because complications in the territory at risk can

be devastating. Furthermore, several disciplines with

catheter-based skills would like to perform CAS. In

an effort to form a consensus regarding training,

the Society for Vascular Medicine and Biology,

the Society for Cardiovascular Angiography and

Intervention, the Society for Vascular Surgery, the

Society for Clinical Vascular Surgery, and the

American College of Cardiology Foundation either

approved or endorsed a document outlining creden-

tialing and training processes for CAS in 2004 (24).

Since neither neuroradiology nor radiology societies

endorsed this statement, the American Heart

Association because of its policy on unanimity was

unable to as well. A complete discussion of

credentialing and reimbursement is well beyond

the scope of this review.

Conclusions

The development of CAS is a significant advance-

ment in the treatment of carotid artery stenosis.

Patients who otherwise underwent CEA with a high

surgical morbidity rate can now have the option of a

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potentially safer treatment modality for stroke

prevention. Although technically, the procedure

may be similar to others that are performed by

interventional cardiologists, the carotid artery dis-

ease and the complications of treatment are likely

somewhat unfamiliar. It is crucial that for this

procedure to move forward with continued success,

interventionalists undergo proper education into the

pathophysiology and treatment of carotid artery

disease and stroke. CAS also is an opportunity for

the development of a collaborative and multi-

disciplinary approach to patient care.

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