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PART 2 — CEREBROVASCULAR
trial’s median follow-up of 2.5 years. Also significant was the study’s finding that the outcomes were simi- lar between CAS and CEA in asymptomatic patients.
Participating interventionalists in CREST were well vetted and the devices used for CAS were well con- trolled. In early 2010, an interim report from the In- ternational Carotid Stenting Study (ICSS) group was released at the same time as CREST. The European ICSS trial compared CAS with CEA in symptomatic patients and demonstrated that CAS resulted in a greater statistical risk of stroke, myocardial infarc- tion, or death than CEA (8.5% vs. 5.2%). ICSS in- vestigators recommended CEA as the treatment of choice over CAS.
This result may be interpreted to suggest that, in actual practice, CAS may have a more mixed out- come.9 Major differences between ICSS and CREST were the lesser experience required of ICSS interven- tionalists performing CAS and in the ICSS use of all devices approved. When CREST placed stricter limits on interventionalists and devices, results improved. General CAS use in the United States is not as re- strictive, and the results could be better reflected in the ICSS trial than in CREST and may result in an increased risk of stroke.
Still, the demonstration of equivalence between CEA and CAS in rigorously controlled applications speaks to increased use. Should reimbursement for CAS relax, the vascular laboratory will see greater numbers of patients treated with CAS, and sonog- raphers must be prepared for duplex-related issues associated with CAS.
Pre- and postprocedure ultrasound testing for CAS is performed as it relates to technical issues associ- ated with the CAS procedure and the stent that is im- planted “for life.” There are aspects of the procedure that are important for the sonographer and should be described. These not only relate to the carotid bifurca- tion but also to the path that the catheter follows to- ward the stenosis. The latter is important because the vascular sonographer may be involved in defining the status of that path before or after CAS is performed.
STENTING TECHNIQUES
Catheter manipulations for CAS are typically per- formed after accessing the common femoral artery at the groin. Postprocedural complications are not lim- ited to the carotid bifurcation but may include dis- section, thrombosis, or perforations within the path where devices encounter difficulty.
Once at the carotid bifurcation, the guide wire must be passed across the lesion. The guide wire will usually first be used to position an embolic pro- tection device (EPD), then to position the balloon, and stent catheters that are used subsequently. All
catheters must gain access to the ICA segment that lies distal to the stenosis. After the EPD is placed, a balloon catheter is typically used to predilate the lesion. Following this, a stent catheter is then posi- tioned over the lesion and deployment starts from beyond the distal border of the stenosis. The stent is unsheathed by retracting the stent catheter over the lesion. This deploys a self-expanding stent that should cover the entire lesion from its distal through proximal borders. A second balloon catheter is usu- ally positioned and inflated to ensure full expansion of the stent. For full coverage, a stent length should be selected that will extend 5 mm beyond the lesion proximally and distally once it is deployed. The stent may extend from the CCA into the bulb, and cover- age of the ECA is not considered a contraindication for the procedure.
SONOGRAPHIC EXAMINATION TECHNIQUES
Sonographic evaluation of the post-CAS patient should be approached using the same basic patient positions and techniques as the routine scanning of native carotid arteries. In the normal mid-cervical level bifurcation, the stent should be fully visible by ultrasound. Its proximal and distal borders should be easily identifiable.
There are important additional images required for complete documentation of a stented vessel. B-mode image, color, and spectral Doppler wave- forms should be recorded proximal to the stent, at the proximal attachment site, within the midpor- tion of the stent, at the distal attachment site, and distal to the stent. Because stent border stenosis is most common, documentation of the highest veloci- ties in these locations (Fig. 6-3) can be particularly useful in serial comparisons. Sonographers should evaluate stents by color or power Doppler for nar- rowing (Fig. 6-4). Any evidence of diffuse narrowing within a stent even without velocity changes should be flagged for increased vigilance. Some laboratories choose to use color or power Doppler to aid in the measurement of the minimum stent and flow chan- nel diameters to assist in the categorization of any disease. Any diameter measurement made from the ultrasound image should be used with caution as diagnostic accuracy of these is limited and highly dependent on technique. The B-mode image along the entire stent as well as proximal and distal stent attachment sites must be carefully examined for hy- perplastic growth across the stent itself or for pro- gression of the disease at the attachment sites. In addition, the B-mode image should be examined for any evidence of stent compression, incomplete de- ployment, or other deformation.