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66 CAROTID TREATMENT: PRINCIPLES AND TECHNIQUES
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TECHNICAL CONSIDERATIONS DURING THE CAS PROCEDURE
(1) Monitoring
Electrocardiogram and blood pressure monitoring are essential to detect bradycardia and hypotension induced
by carotid sinus reex during carotid dilatation.
Near-infrared spectroscopy (NIRS) is a simple and portable device to effectively detect ischemic intolerance
and hyper-perfusion status (25) during and after CAS. NIRS allows non-invasive and real-time measurement
of cerebral tissue O2 saturation (tissue oxygenation index; TOI). The TOI decreases to 80% of normal levels in
patients with occlusion intolerance during procedure. Likewise, continuous post-procedural NIRS monitoring is
very effective to predict hyperperfusion phenomenon in the bed side. A 3–5% of TOI increase after CAS is considered to suggest hyperperfusion status.
Transcranial Doppler (TCD) is also an excellent predictor of hypoperfusion and microembolism during the
CAS procedure and of hyperperfusion status after CAS (26). Compared with NIRS, TCD is technically not easy
to apply and is not a continuous measurement device, but it allows us to detect not only CBF but embolism into
the intra-cranial arteries during and after CAS. Usually, TCD monitors the blood ow velocity of the ipsilateral
middle cerebral artery (M1 portion). Again, MCA insonation with TCD allows us to detect the microembolism
as microembolic signals (MESs) as well as any low perfusion with proximal balloon occlusion during procedure.
TCD is also an excellent tool to detect hyperperfusion status after CAS. An increase in mean ow velocity of
1.5 times or larger compared to the contralateral artery suggests hyperperfusion status.
(2) Approach Routes
As we have said, preprocedural CTA evaluation provides valuable anatomical information about access routes,
such as iliac artery elongation and stenosis/occlusion, aortic aneurysms, shaggy aorta, types of aortic arch, and
variant images of major aortic arch branches. The transfemoral approach is the standard access route in the
majority of cases. The transbrachial approach is an alternative way to access the common carotid arteries in case
of a difcult or risky transfemoral approach (27). The right common carotid artery is easier as a target vessel in
transbrachial approach than the left in usual cases. A 6-French guiding sheath is available to use in the brachial
artery instead of an 8-French guiding catheter (28). In case of bovine arch, the transbrachial approach is sometimes easier than transfemoral approach to go to the left common carotid artery. The transcervical approach is a
nal alternative approach. Matsuda et al. reported 10 cases treated with this approach (29).
(3) Embolic Protection Methods
Embolic protection methods can be classied into the following three categories (Fig. 2-8)
1. Protection with preservation of ICA blood ow
Several kinds of lter devices (FilterWire EZ® [Stryker], EmboshieldTM [Abbott], RX Accunet® [Abbott],
Spider FXTM [Medtronic], etc.) are available for the distal embolic protection. These kinds of lter devices
preserve ICA blood ow during treatment, decreasing the chance of procedural occlusion intolerance.
The systems are very simple; however the lters could be clogged by large amounts of debris coming
out of a fragile plaque, causing so-called “stop ow” and embolic stroke in the distal intra-cranial vessels.
A balloon guiding catheter will help to decrease the thromboembolic complication resulting from the
lter device. The common carotid artery can be temporarily obliterated by the balloon at the timing of angioplasty, particularly when the angioplasty balloon is deated. The debris coming out of the fragile plaque can
be manually aspirated from the balloon guiding catheter, thus it can prevent from the debris clogging and
leaking from the lter.
2. Protection by arresting the ICA ow
Flow arrest of the ICA by a distal balloon occlusion with Carotid GuardwireTM (Medtronic) is a very simple
protection method. The patients so treated, however, sometimes show occlusion intolerance and hypotension after carotid dilatation which could aggravate the cerebral ischemia. The occlusion time will be around
20 minutes and usually the patient’s ischemic symptoms disappear rapidly after recirculation. Some physicians prefer general anesthesia rather than local anesthesia.
CHAPTER 2: HISTORICAL PERSPECTIVE AND CURRENT PRACTICE OF CAS 67
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FIGURE 2-8
Embolic protection methods.
External and common carotid balloon occlusion is an alternative way to institute ow arrest of the ICA.
Mo.MaTM (Medtronic) with two separate balloons is a standard device for this protection method. Alternately,
Carotid GuardwireTM (Medtronic) for external carotid occlusion and a 9-French balloon guiding catheter can
be used instead of Mo.MaTM. If the superior thyroid artery arises between the two balloons, retrograde collateral blood ow will get into the internal carotid artery in antegrade fashion. In this case, operators should
recognize that some amount of debris may go to the distal intra-cranial arteries. A lter device placed in the
distal ICA could prevent this kind of ischemic complication.
This system seems to be more effective than a simple distal lter but one must aware of the occlusion
intolerance particularly by hypotension induced by carotid dilatation.
3. Protection by ow reversal of the ICA (Fig. 2-9)
By connecting an infusion line of the Mo.Ma guiding catheter to the femoral vein, the ICA blood ow will be
reversed from the ICA to the guiding catheter, and nally to the femoral vein, thus ow reversal circuit from
the brain to the peripheral vein will be completed. The debris from the plaque will be captured in the lter
placed between the arterial and venous catheters.
Using this system is a complicated procedure that needs many devices and longer procedural time but
it is very effective to prevent embolic complication. Occlusion intolerance will likely occur because the CBF
goes out of the brain in the retrograde fashion and one should prepare for patient ischemic symptoms during
the treatment. General anesthesia is one of the solutions to this problem.
(4) Stent Selection
Self-expanding stents are used for the treatment of carotid artery. Those stents open by themselves when coming
out of a delivery catheter. Unlike the stents used for coronary artery disease (balloon expandable stents), carotid
self-expanding stents are shaped memory alloys and the shape is restored even when compressed and deformed
by external forces or neck twists. This property is essential for carotid stents because carotid arteries are mobile
and are located in a vulnerable position just beneath the neck skin.
There are several kinds of carotid stents in the market. Those are basically classied into open and closed
cell stents according to the structure. The former are laser-cut stents that look like piled up serrated rings.
68 CAROTID TREATMENT: PRINCIPLES AND TECHNIQUES
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FIGURE 2-9
Staged angioplasty, an example of catheter setting.
Each ring is connected with upper and lower rings with some bridges. Once the most distal ring opens in the
artery, it never comes back into the delivery catheter. On the other hand, the closed cell stent is a braided stent
with metal ber. Unlike the open cell stent, the closed cell stent could be pulled back into the delivery catheter
even when deployed halfway in the artery, i.e., resheathing and repositioning is available if half of the stent
body remains in the delivery catheter. Inherent to the nature of their design, with braided stents the total length
becomes shorter when coming out of the delivery catheter.
Selection choice of the two stent designs should be made according to the vessel anatomy and plaque character. The open cell stents can t well to the vessel wall (better conformity) because every ring of the stents opens
independently, but the coverage rate of the plaque is less than with the closed stents because the open spaces
between the cells are designed to be larger. The closed cell stents tend to stay in the upright or straightened
position in the vessel, therefore when deployed in a tortuous artery, the internal carotid artery often kinks at the
distal end of the stent. Also the closed stents tend to leave some space between the stent and the vessel wall (less
conformity). The coverage rate of the plaque with closed cell stents is higher than the open cell stents. Therefore,
the open cell stents are good for tortuous carotid arteries (better conformity) and the closed cell stents are said to
be good for fragile plaque (better coverage). However, there has been no denite consensus which stent is more
effective for the fragile plaque (30, 31). Closed stents sometimes show delayed shortening after treatment, causing restenosis or ischemic stroke (32, 33). Therefore, the long-term imaging follow-up is always needed.
Recently, dual layer micromesh (braided) stents (Casper RX/Roadsaver® from Terumo, CGuardTM from
InspireMD) have been developed as a new generation device to improve the plaque coverage rate and decrease
thromboembolic complication (34, 35). Meta-analysis of 556 cases treated with the dual layer micromesh stents
demonstrated a 1.44% rate of 30-day stroke and death, which is an excellent initial result. At this writing, effectiveness of these devices and improvement of the clinical results are anticipated, but large clinical studies and
long-term clinical experience will be necessary in the future.
The following products are available in the world market at present (October 2020).
1. Open cell stent: Precise® Pro RX (Cordis), ProtégéTM RX (Medtronic), RX Acculink® (Abbott), RX Xact® (Abbott)
2. Closed cell stents: Carotid WallstentTM (Boston Scientic)
3. Dual layer micromesh stents: Casper RX/Roadsaver® (Terumo), CGuardTM (InspireMD)
Table 2.5 shows the characteristic features of Precise, Protégé, and Carotid Wallstent.
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TABLE 2.5
Specications of Precise, Protégé, and Carotid Wallstent
Precise Protégé Carotid Wallstent
Stent design Open cell Open cell Closed cell
Material Nitinole
(nickel, titanium)
Diameter 6–10 mm 8–10 mm
Size
Length 20, 30, 40 mm 40, 60 mm
2
Free cell area (mm
Radial force
) 5.89 10.71 1.08
++ ++ +
Nitinole
(nickel, titanium)
(tapered: 8–6 mm, 10–7 mm)
(tapered: 30,40 mm)
Elgiloy
(cobalt, chromium, nickel, etc.)
6, 8, 10 mm
21–31 mm
(5) Standard Procedure of CAS (Fig. 2-10)
Summary of Settings and Monitoring
Platelet aggregation function should be monitored, if possible, to maintain the optimal level of platelet aggregation level. The optimal distal protection method for the individual patient should be planned before treatment.
Biplane DSA angiography is ideal for CAS; one arm is to see the ICA in a magnied view and the other to see a
wide treatment area. In most cases, CAS can be done using local anesthesia. However, when choosing the ow
reversal method for embolic protection, general anesthesia is a reasonable alternative way to prepare for the
occlusion intolerance. Electrocardiogram and blood pressure monitoring are essential to monitor the bradycardia and hypotension induced by the carotid sinus reex. NIRS will help to monitor the patient’s cerebral ischemia and TCD will allow us to know the MES as well as cerebral ischemia during treatment.
FIGURE 2-10
Standard procedure.
70 CAROTID TREATMENT: PRINCIPLES AND TECHNIQUES
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Procedures
After placement of a guiding catheter in the common carotid artery, embolic protection devices (balloons or a
lter) are set in the target vessels. Pre-dilatation usually with a small balloon (3.0–3.5 mm in diameter) is the rst
procedure to dilate the stenotic part, followed by a stent deployment. Finally, the post-dilatation will be done if
needed. In another way, a large balloon can be selected as pre-dilatation to obtain the optimal diameter before
stent deployment. In this situation, post-dilatation will not be needed. Bradycardia and/or hypotension will
occur at the timing of carotid dilatation. Intravenous injection of atropine and vasoconstrictors like norepinephrine should be kept in use at any time. Drip infusion of dopamine will be effective for prolonged hypotension.
Extracorporeal pacing is an alternative method to address bradycardia.
In cases with distal balloon protection, the blood (and debris) remaining in the occluded ICA should be
aspirated with a coaxial aspiration catheter before recirculation. In cases with ow reversal, the blood (and
debris) in the guiding catheter should be aspirated thoroughly before recirculation.
After these procedures, one should wait for 10–20 minutes to make sure if there is no protrusion of the
plaque or stent thrombosis before nishing the treatment.
Post-Operative Monitoring
Patients’ vital signs, blood pressure, and neurological status should be monitored after treatment. Prolonged
bradycardia or hypotension sometimes occurs even several days after treatment.
Intermittent TCD or continuous NIRS monitoring is effective to detect post-operative abnormal CBF, as
seen in thromboembolic complications and CHS.
Follow-Up of the Patients
Periodic follow-up of CAS patients is important to detect the ischemic complications caused by stent thrombosis
or restenosis. The stent patency can be monitored by ultrasound or CTA (MPR images). MRI is effective to check
for intra-cranial ischemic/hemorrhagic events but importantly it cannot evaluate the stent condition, because of
the metal artifact.
(6) Special Considerations
Two-Staged Angioplasty for Patients with High Risk for Post-Procedural
Hyperperfusion Syndrome (Fig. 2-11)
Retrospective analysis of CAS and CEA evaluating the CHS informs that blood pressure control does not seem
to protect against intra-cranial hemorrhages in CAS, unlike in CEA patients (23). Thus, the idea of staged angioplasty was rst reported by Yoshimura et al in 2009 (36). Patients who are indicated for this staged treatment
have impaired cerebral autoregulation evaluated by
ment. Specically, if the patient has decreased CBF less than 80% of the contralateral hemisphere and poor cerebrovascular reserve less than 10%, staged angioplasty is indicated.
The rst stage is a light angioplasty, usually with a small balloon 2.5 mm in diameter, and the second stage
is a full dilatation by stent deployment. In Yoshimura’s original paper, the time interval between these stages was
1 to 2 months (36), but recently it has been shortened to 2 weeks (37). The optimal time interval between these
two procedures is still not completely dened. A nationwide survey of practitioners in Japan in 2019 suggested
that staged angioplasty was an effective method to prevent hyperperfusion syndrome after CAS in patients with
impaired cerebral autoregulation (38).
123
I-IMP SPECT with acetazolamide challenge before treat-
COMPLICATIONS OF CAS
Complications of CAS can result from each risk factor described earlier.
The basic risk of angiographic procedure is groin hematomas, pseudo-aneurysms, and allergic reaction to
contrast medium including contrast-induced encephalopathy (39).
CHAPTER 2: HISTORICAL PERSPECTIVE AND CURRENT PRACTICE OF CAS 71
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FIGURE 2-11
Staged angioplasty.
Thromboembolic complication is a major concern in the treatment of CAS. The major source of this complication is debris released from a fragile and high volume plaque; other sources include emboli from the aorta
and common carotid artery, and stent thrombosis. Post-procedural ischemic complications ranged from 4.1% (9)
to 7.4% (11) in a recent analysis.
Complications resulting from anatomical risk include rupture of aortic aneurysms, and cholesterol crystal
embolization (renal failure, blue toe syndrome, etc.) in patients with the shaggy aorta. Heart failure and cardiac
arrest are serious complication resulting from hypotension and bradycardia after carotid artery dilatation (cardiac risk). Hyperperfusion syndrome occurs in about 1% of the patients treated with CAS and of these, about half
of the patients with hyperperfusion syndrome presented with intra-cranial hemorrhage (24) (CBF risk). Blood
pressure control may not be effective to prevent intra-cranial hemorrhage but staged angioplasty is a novel suggested preventative solution (36).
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CHAPTER 3
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Radiographic Studies
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