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October 2010
Sponsored by Boston Scientific Corporation
The Tailored Approach To CAS
By Alberto Cremonesi, MD; Chiara Grattoni, MD; Federico Colombo, MD; Andrea Zuffi, MD; and Fausto Castriota, MD
Case Closed
Closed cell stent technology
for carotid artery disease
Innovations in device technologies have helped to
raise the bar for clinical efficacy in carotid artery
stenting (CAS). One of the primary device considerations
in CAS is stent design, a differentiator of which is
open versus closed cell stent structure. A closed cell
design is intended to provide increased scaffolding for
optimal lesion coverage while also providing a smooth
inner lumen. In the clinical setting, a retrospective
analysis of 30-day outcomes at four sites revealed a statistically
significant difference in all events (death,
stroke, and myocardial infarction) for the symptomatic
population between open cell stent design (27/383;
7.0%) and closed cell stent design (21/934; 2.2%) (P <
0.0001). Also, there was a statistically significant difference
in postprocedural events at 30 days for the symptomatic
population between open cell stent design
(24/383; 6.3%) and closed cell stent design (12/934;
1.3%) (P < 0.0001).1
One of the closed cell carotid solutions available worldwide is the Carotid WALLSTENT® Endoprosthesis (Boston Scientific Corporation, Natick, MA). The Carotid WALLSTENT has been engineered to combine a unique stent design having the smallest free cell area of 1.1 mm2 with a highly flexible, easy-to-use delivery system. The stent is designed to facilitate accurate stent placement, offering high radiopacity and the ability to be reconstrained (Figure 1).
This year, a new closed cell technology, the Adapt™ Carotid Stent System (Boston Scientific Corporation), received CE Mark approval and was launched in respective countries (Figure 2). It incorporates a self-expanding, rolled nitinol sheet with Dynamic Tapering Technology. The ASTI (Adapt Carotid Stent and Monorail Delivery System) clinical postmarket registry is currently enrolling; ASTI is designed to evaluate the Adapt stent in combination with the FilterWire EZ™ Embolic Protection System (Boston Scientific Corporation) for the treatment of carotid artery disease.
The Tailored
Approach to CAS
Comprehensive patient evaluation and case-specific
applications of contemporary technologies.
BY ALBERTO CREMONESI, MD; CHIARA GRATTONI, MD; FEDERICO COLOMBO, MD;
ANDREA ZUFFI, MD; AND FAUSTO CASTRIOTA, MD
GVM Care and Research - Interventional Cardio-Angiology Unit, Maria Cecilia Hospital - Cotignola, Italy
Endovascular carotid interventions have been developed to provide a less invasive and less traumatic revascularization strategy for patients with carotid artery stenosis, especially those who are considered high-risk for open surgery. Over the past 10 years, ongoing advancement in endovascular technologies and techniques has resulted in the evolution of carotid artery stenting (CAS) into a refined procedure with great potential for carotid revascularization.
With the continued development of devices and increase in clinical experience, revascularization outcome targets are rapidly moving, requiring constant re-evaluation of the results. Currently, controversy exists as to whether CAS should be accepted as an alternative therapy to CEA. Unfortunately, randomized controlled trials have not yet provided a clear answer. Nevertheless, it is necessary to recognize that important technical advances have been made in the field, and we must continue to evaluate this progress as a factor in our treatment decisions. The following is a description of our tailored approach to patient selection and the performance of CAS.
THE TAILORED APPROACH TO CAS
To obtain favorable results in CAS, we believe a multifactorial,
patient-specific strategy is required. Our practice
group advocates a tailored approach, where endovascular
technologies and techniques are individually selected for
specific patients based on each device's abilities to address
unique lesions and vascular anatomy characteristics. The
choice of a specific stent, embolic protection device
(EPD), guiding catheter, and sheath is highly dependent
on an in-depth understanding of clinical variables as
demonstrated by neuro assessment, carotid plaque characteristics,
and vascular anatomy. These clinical variables
are evaluated to predict the embolic risk of revascularization
procedures and must be matched to the technical
features corresponding to the array of available endovascular
devices. Having significant experience with a wide
range of devices allows the operator the flexibility to
choose the most appropriate tools and techniques to
optimize CAS in the patient.
Our current approach is primarily based on our experiences in the Cotignola registry.1 This study sought to assess the success, safety, and long-term durability of CAS in stroke prevention for “all comers.” Enrolled patients were managed with mandatory neuroprotection and a tailored approach to interventional device selection. The Cotignola registry is a prospective study analyzing 1,523 tailored CAS procedures in a population with a very high burden of polyvasculopathy. The data collected demonstrate endovascular treatment possibilities with minimal exclusion criteria and a near universal ability to “proceed to endovascular intervention” after conventional diagnostic angiography confirms duplex ultrasound findings; more than 99% of patients who required revascularization proceeded to the endovascular approach. The rate of CAS success in this registry was 99.6%, and the 30-day allstroke/ death rate was 1.5%. These data suggest that very good results can be achieved with the tailored approach to CAS.
CAROTID PLAQUE AND VASCULAR
ANATOMY EVALUATION
Precise evaluation of the patient's carotid plaque profile
is the essential first step in the tailored approach. The evaluation
should describe (1) the degree of stenosis and the
precise vessel dimensions, and (2) the length and bulk of
disease present, as well as the morphologic features of the
lesion. These factors predict potential procedural complexities
such as the degree of calcification and the possibility
of embolization (ie, vulnerable plaque). Long, irregular, or ulcerated lesions and clinically unstable plaques
define a high-risk disease subset. Plaques characterized by
a large lipid pool covered by a thin fibrous cap are more
prone to perioperative embolization as compared to
fibrous plaques.2 These vulnerable plaques, sometimes
called soft lesions, are less echogenic on B-mode ultrasound
and can be quantified by the Gray-Scale Median
method (see Vascular Profile Assessment sidebar). In the
ICAROS study,3 the risk of CAS-related stroke was significantly
higher in lesions with Gray-Scale Median < 25.
PUTTING THE TAILORED CAS APPROACH
INTO PRACTICE
Embolic Protection
Although there are no large, randomized, controlled trials
assessing the efficacy of neuroprotection, some retrospective
studies have suggested that the routine use of
EPDs results in favorable outcomes.4-8 The results from our
study firmly add to the evidence that neuroprotection
should be the standard of care.1 In the Cotignola practice,
neuroprotection is mandatory, and the inability to place a
suitable EPD in a patient is considered a contraindication
to CAS. We believe the advantage of such a strict protocol
for procedural embolic containment is that it standardizes
the procedure, which contributes to its effectiveness and
predictability. Experience is maintained at a high level, an
essential element in the safe application of these devices
and techniques.
The choice between placing a distal filter or employing a proximal occlusion system is highly dependent on the patient's symptomatic status, vascular anatomy, and plaque characteristics. Large studies comparing proximal and distal protection are lacking, so device selection should be based on the tailored approach as well as the operator's experience. In challenging anatomies, with angulated internal carotid–common carotid artery takeoff and/or lack of a suitable internal carotid landing-zone, proximal protection should be strongly considered.
This practice requires that experience be gained in the use of multiple tools that should be readily available on the shelf, to optimize the individualized treatment strategy. Distal filters, allowing antegrade blood flow during procedure, are mostly indicated in the presence of contralateral carotid occlusion or isolated hemisphere. With respect to neurological symptoms, we primarily use proximal protection in symptomatic patients.
Stent Choice
The structural and functional characteristics of the various
self-expanding carotid stents are highly dependent on
the specific elements of their designs. The type of stent
implanted may play a vital part in preventing neurological
events due to plaque prolapse. Whereas in open surgical
techniques the atheroma and thrombus burden are
excised, the CAS procedure compacts this material to the
artery wall, retaining it with the stent's scaffolding and wallcoverage
properties. The stent's cell geometry may exert an
intrinsic antiembolic property, influencing the risk of
plaque prolapse and distal embolization during the postprocedural
and recuperative periods, until re-endothelialization
is complete.
Recognizing the individual technical characteristics of various carotid stents, it is clear that the interaction between a particular stent and the diseased vessel is unique, and no single stent is applicable for all situations. Different stent designs demonstrate functional equivalence when used in uncomplicated scenarios, such as simple supra-aortic anatomies, straight carotid bifurcations, and stable fibrous plaques.
However, when faced with more challenging situations, braided-mesh frames, nitinol closed cell design, and hybrid stents are our first choice when the greatest need is to achieve reliable plaque coverage and long-acting plaque prolapse prevention due to their constant radial force properties (eg, soft and long dishomogeneous lesions prone to distal embolization). This condition is encountered primarily in symptomatic patients in whom unstable risky plaques are the standard pathologic substrate.
When the primary technical challenge of a particular case is represented by the carotid bifurcation and plaque complexity (eg, severely angled lesions, plaque ulceration), or the main goal is to maintain the original anatomy/course of a very tortuous vessel, the invessel flexibility and the wall/plaque conformability of nitinol open cell stents as well as hybrid stents are unmatched. Nitinol closed cell and hybrid stents represent a strong technical solution for focal, concentric lesions, especially if they are resistant or calcified; in this clinical subset, the functional key point is the outward radial force exerted by the stent over time.
FURTHER CONSIDERATIONS
After many years spent in stroke prevention, we strongly
believe that endovascular carotid intervention can be considered
to be a safe and durable therapy. Data from high
volume centers demonstrate that CAS is highly feasible,
with clinical outcomes comparable with those from surgical
series. The future role of CAS will be defined by strategies
aimed at reducing complications. Does it appear feasible
that we can reduce major complication rates to a new
threshold of less than 1% at 30-day follow-up?
We believe that we can successfully address this challenge only if we extensively apply the individual, “tailored approach” treatment strategy. Stent scaffolding properties may play a critical role in reducing postprocedural embolic events; the design and geometry of the stent frame may contribute in plaque prolapse containment and wall coverage improvement. From this point of view, regular interaction between endovascular experts and the companies involved in carotid device development is essential in ensuring future technical evolutions and material improvements.
Finally, the identification of patients who are likely to be high-risk carotid stenting cases requires a skilled interventional vascular specialist. Although this is the case in all areas of percutaneous intervention, the importance of proper physician training and patient screening in CAS procedures cannot be understated. It is imperative for CAS specialists to be actively involved in continuous learning programs.
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