Background
Stenting of the carotid artery disease has emerged as a potential alternative to carotid endarterectomy, the current gold standard treatment for carotid artery lesions. The advantages of carotid artery stenting are the less invasiveness and the shorter hospitalisation. The use of balloon angioplasty and stenting in carotid arteries is still limited, due to concern regarding the lack of long term results and neurological complications during CAS. Cerebral embolisation from carotid plaque is indeed the most severe complication of CAS.
Even though it is generally accepted that the composition and the characteristics of the plaque may be influential on the outcome of carotid endarterectomy and carotid stenting, especially in case of CAS where the plaque is not removed but remodelled, indication to either one of the two procedures is mostly based, both in trial and in the clinical practice, on the percentage of stenosis and the presence or absence of pre-procedural neurological symptoms, while the features of the plaque are somehow disregarded if not ignored. The reason for this is related to the fact that the percentage of stenosis, as well as the presence or absence of symptoms, are easy to identify and quantify, whereas the plaque is usually defined as soft, lipidic, fibrolipidic, haemorrhagic, colliquated, ulcerated, pretty homogeneous, etc..., which makes the parameter rather undetermined and unreliable.
However, the advent of high resolution B-mode scanners and the use of a quantitative computer-assisted index of echogenicity, such as Gray Scale Median (GSM), introduced by our team, have greatly improved the correlation between plaque characterisation and clinical features. Only after the introduction of the image normalisation, GSM became an objective index of the echodensity of carotid plaques.
Several studies recently indicated that echogenicity is related to the histological components of carotid plaques and that carotid plaque echolucency (low echogenicity) is associated with the development of neurological events and with an increased number of emboli following CEA and CAS. Based on these assumptions, our group suggested that plaque echogenicity measured by GSM can be a useful indicator of embolic potential in the carotid arteries .
The aim of the ICAROS (Imaging in Carotid Angioplasty and Risk of Stroke) Registry was to determine the preprocedural echographic criteria, which can identify the carotid plaque related to a higher risk of stroke during CAS, so that a better selection of candidates for CAS may be performed.
ICAROS was a registry of carotid angioplasty and stenting procedures, which reported any cerebral event following the procedure and correlated the risk of cerebral embolization with the echographic characteristics of the carotid plaque. The registry was open to all interventionists performing carotid stenting.
Several training courses were organised worldwide for ultrasonographers from the participating centers on how to set up the duplex scanner for the collection of the images. Duplex scanning images were then sent to the Coordinating Centre (Bassini Teaching Hospital) where the image normalization and the calculation of GSM was performed by the same operator (who was blind to clinical data and outcome) by means of Adobe Photoshop‚ 5.0 software.
The ICAROS study collected 418 cases from 11 different centres worldwide. There were 297 male and 121 female patients. In 227 cases the underlying pathology was restenosis (54.3%) and a primary lesion in 191 cases (45.7%). Stent procedures were performed in 415 cases (99.3%). A brain protection device was applied in 219 cases (52.4%).
There were 13 TIAs (3.1%), 9 minor strokes (2.2%), 6 major strokes (1.4%), while no deaths were observed: the 30-day combined death and any stroke rate was 3.6%.
GSM value in complicated patients was significantly lower than in uncomplicated ones (20.80 vs. 35.07, p=0.0036). A receiver operating characteristic (ROC) curve was used to choose the GSM cutoff value with the best sensitivity and specificity: a GSM value of 25 was used as a threshold.
We demonstrated for the first time that echolucent plaques with a GSM value less than 25 have a significantly higher rate of stroke than those with GSM>25 (7.1% vs.1.5%, p=0.005). This finding was also confirmed in a multivariate analysis, revealing that GSM (OR=7.11, p=0.002) and degree of stenosis (OR=5.76, p=0.010) are significant independent predictors of stroke alone, while preprocedural symptomatology (OR=2.92, p=0.061) is borderline significant.
The prevalence of a GSM value less than 25 was 37%, consequently the possibility for an interventionist performing CAS to find this risk factor is high.
There were 5/219 (2.3%) complications in protected and 10/199 (5.0%) in unprotected procedures (p=0.188). However, protection gave different results in the GSM subgroups: in patients with GSM£25 the use of BPD tended to increase the risk of complications (p=0.153), whereas it had a protective value in the GSM>25 subgroup (p=0.010).
The overall complication rate was higher in primitive lesions than that in restenosis (5.2% vs. 2.2%, p=0.117). This difference was observed also in GSM>25 patients (4.0% vs. 0%, p=0.020), but not in GSM<=25 patients (6.6% vs. 7.8%, p=0.762).
The clinical impact of GSM relies on the ability to identify:
1. a wide number of patients (155/418, 37%)
2. at higher risk of stroke during CAS (7.1% vs. 1.5%)
3. and to distinguish subsets of patients with restenosis
4. and with protected procedure in which the rate of complications is different from the overall population
Conclusions
Computer-assisted echogenicity evaluation through GSM is a simple method to identify pre-procedurally high risk carotid plaques, in which endovascular treatment could be burdened with a higher risk. GSM is one of the parameters that should be mandatory for indication to treatment, in order to quantify the individual risk related to the specific procedure. Low GSM value is not an absolute contraindication to CAS, but an index related to a higher risk for the procedure.
Echographic evaluation of carotid plaque through GSM should therefore always be performed before the endovascular treatment of carotid lesions.
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