Utility of Intravascular Ultrasound Examination during Carotid Stenting
Article Outline
Background
Intravascular ultrasound (IVUS) examination may provide useful information during endovascular procedures. However, its actual clinical utility for carotid stenting remains unclear. We evaluated the usefulness of IVUS as a complementary tool during endovascular procedures in the carotid arteries and its impact on the modification of the therapeutic strategy.
Methods
Between April 2006 and April 2007, 18 symptomatic patients (nine with transient ischemic attack, nine with stroke) underwent angioplasty and stenting of >70% stenosis of the internal carotid artery (ICA). Target lesions were identified with preoperative duplex scanning and further confirmed at angiography. Intraoperative IVUS examination was performed in all patients. Multilevel measurement of the artery as well as virtual histology images, before and after stenting, were obtained.
Results
The technique was 100% successful. There were no complications at the femoral puncture site and no neurological or other events. Compared with angiography, IVUS findings showed an average arterial diameter that was greater than 1.64
±0.22mm. Based on virtual histology information, endovascular treatment was excluded in two patients and carotid endarterectomy was performed. Type or size of the stent was modified after IVUS examination in eight cases.
Conclusion
IVUS examination provides complementary information to that obtained using conventional diagnostic procedures. It may be useful for characterizing the composition and measurement of the target lesion, choosing the type and size of the stent, and evaluating the results after the procedure.
Introduction
Over the last few years, it has been assumed that angioplasty and stenting is a safe and effective alternative to carotid endarterectomy for the treatment of patients with severe carotid stenosis, particularly those with a high surgical risk.1, 2, 3 Target lesions have traditionally been evaluated using Doppler ultrasound and angiography. More recently, intravascular ultrasound (IVUS) examination of the coronary arteries has enabled the morphological characteristics of the lesions to be assessed and, thus, treatment to be optimized.4, 5, 6 An overview of the published literature suggests that preoperative IVUS evaluation of the internal carotid artery (ICA) may provide useful information on the characteristics of the lesions, help in the selection of stent, and make it possible to assess the results after the procedure. On the other hand, manipulation of the carotid bifurcation during endovascular procedures increases the risk for distal embolization, even with the use of low-profile devices. IVUS virtual histology of the ICA may help to identify those lesions at higher risk for distal embolism, further reducing complication rates.7, 8
The objective of this work was to evaluate the utility of intraoperative IVUS examination and to assess its impact on the modification of the therapeutic strategy during endovascular procedures in the ICA.
Patients and Methods
Thirty-nine patients were treated for a symptomatic ICA stenosis (ICAS) >70% between April 2006 and April 2007. Eighteen out of 39 patients were considered to have high surgical risk for carotid endarterectomy and, therefore were elegible for ICA stenting. Intraoperative IVUS examination was performed in all patients.
According to the criteria of the Spanish Society of Angiology, Vascular and Endovascular Surgery, patients considered at high surgical risk are those with unfavorable anatomical characteristics, severe medical comorbidity, or lesions that make it technically difficult to perform an endarterectomy (Table I).9
Table I. High surgical–risk groups: optimal candidates for stenting
| High anatomical risk |
| Ostial or proximal CCA lesions |
| Lesions in distal ICA (>3cm above bifurcation) |
| High carotid bifurcation (C2 or proximal) |
| Short neck of obese patient |
| Contralateral carotid occlusion |
| High medical risk |
| Severe coronary disease |
| Severe pulmonary disorder that contraindicates general anesthesia |
| High technical risk |
| History of radical neck surgery or radiotherapy: hostile neck |
| Previous carotid endarterectomy |
| Paralysis of the contralateral laryngeal nerve |
Diagnosis of ICAS was based on duplex scanning findings and subsequently confirmed with cerebral angiography. Computed tomography (CT) or magnetic resonance imaging (MRI) was obtained before the procedure in all patients. According to our protocol for carotid stenting, cerebral CT scanning or MRI was only repeated after treatment in those patients who developed neurological changes during or after stenting of the ICA.
The procedures were carried out in an angioradiology suite with a fixed C-arm (Philips Integris V5000®; Philips Medical Systems, Best, the Netherlands). All patients were on antiplatelet treatment with acetylsalicylic acid (ASA) 100-300mg/day and clopidogrel 75mg/day for a minimum of 5-6 days before treatment or were given a 300mg loading dose of clopidogrel 6hr before the procedure. In addition, sodium heparin (1mg/kg i.v.) was administered during the operation, maintaining an activated partial thromboplastin time ratio between 1.75 and 2.25. A percutaneous femoral approach was used in all cases. Selective catheterization of the common carotid artery (CCA) was performed, and a 6F×80cm sheath (Cook, Bloomington, IN) was placed in the CCA. Selective angiography was performed, injecting the contrast medium through the sheath; and measurements of the target ICA were obtained. A protection filter (Accunet®; Abbott, Santa Rosa, CA) was positioned in the distal ICA in all cases. After deployment of the protection device, a 2.9F IVUS catheter (Eagle Eye Gold®; Volcano Therapeutics, Rancho Cordova, CA) was advanced over a 0.014-inch wire until it passed over the lesion. Once IVUS imaging of the distal ICA confirmed adequate positioning of the transducer tip, it was gradually withdrawn with a motorized pull-back system at a speed of 0.5mm/sec, or a manual withdrawal was performed. Real-time images were initially obtained in gray-scale format. They were stored in the image generator computer and further analyzed with the color-coding mode, which provides virtual histological mapping of the composition of the carotid plaque. This system allows us to differentiate four components: fibrosis (dark green), lipid area (light green), necrosis (red), and calcification (white). Although there are no defined criteria for plaque instability, this situation was considered under detection of necrosis in more than one-third of the plaque area. Vessel diameters were measured at the distal ICA, area of maximum stenosis, proximal ICA, and CCA. The stent system was then pushed up and deployed to cover the target lesion.
Completion angiography was performed after the procedure. IVUS examination was repeated in those cases in which residual stenosis, incomplete covering of the lesion, or images suggesting dissection were observed. In those patients with residual stenosis >30%, a subsequent dilation was performed after administering atropine (0.01mg/kg i.v.) to overwhelm a possible spasm of the artery.
Results
Patient demographic and clinical data are shown in Table II.
Table II. Demographic and clinical characteristics
| Mean (n) | Range (%) | |
|---|---|---|
| Age (years) | 71 | 61-83 |
| Males | 18 | 100 |
| Smokers | 1 | 5 |
| Arterial hypertension | 13 | 72 |
| Diabetes mellitus | 6 | 33 |
| Dyslipemia | 9 | 50 |
| Coronary disease | 7 | 38 |
| Chronic lung disease | 5 | 27 |
| Lower limb chronic ischemia | 7 | 39 |
Based on European Carotid Surgery Trial measurement criteria, the mean stenosis degree of the ICA was 79±5.4%. Stenting of the ICA without predilation was performed in all cases, achieving a 100% success rate. No neurological events, hematoma at the puncture site, or other complications after the procedure were detected.
After calibrating the measurement software using the diameter of the sheath as a reference, a self-expanding open-cell stent (Acculink, Abbott) was initially chosen for all patients.
IVUS measurements of the ICA showed average diameter values that were 1.64±0.22mm greater than those estimated by angiography. Based on IVUS findings, the stent size was changed from 6-8mm, initially chosen according to the angiographic measurements, to a final one of 8-10mm in five out of the 18 patients. IVUS virtual histological mapping of the target lesion permitted us to differentiate the four components of the plaque in most patients (Fig. 1). Evidence of extreme concentric calcification of the lesion was considered a contraindication for carotid stenting in two patients. A straightforward standard carotid endarterectomy was performed in both of them. On the other hand, detection of extensive areas of plaque necrosis, coded as red in virtual histology mode, was considered to be a sign of eventual plaque instability in three patients. Therefore, a closed-cell stent (Xact, Abbott) was selected for this situation. Postprocedure IVUS examination showed adequate coverage of the target lesion in all cases (Fig. 2). Residual >30% stenosis was detected in five cases. Additional postdilation was performed in these cases, achieving a successful anatomical result. No dissection, thrombosis, or other complications were observed in this series. Clinical and therapeutic indications for carotid stenting as well as plaque characteristics and modification of therapeutic indication after IVUS examination are shown in Table III.
Fig. 1
Virtual histology that shows the morphological characteristics of the carotid plaque.
Fig. 2
Image obtained with IVUS that shows the correct expansion of the stent (arrows).
Table III. Clinical and therapeutic indications for carotid stenting: plaque characteristics and modification of therapeutic indication after IVUS examination
| Patient ICA stenosis (%) | Clinical indication | Therapeutic indication | Duplex scanning classification | IVUS classification | Modification of strategy after IVUS | |
|---|---|---|---|---|---|---|
| 1 | 73 | TIA | Distal ICA lesion | Homogeneous I–II | Unstable plaque | Change stent design (closed cell) |
| 2 | 72 | TIA | High carotid bifurcation | Homogeneous I | Unstable plaque, residual stenosis | Change stent design (closed cell), PTA poststenting |
| 3 | 76 | TIA | IHD | Heterogeneous III–IV | Different size | Change stent size |
| 4 | 72 | Stroke | Hostile neck | Heterogeneous III-IV | Residual stenosis | PTA poststenting |
| 5 | 84 | Stroke | COPD+IHD | Homogeneous III | Different size | Change stent size |
| 6 | 75 | TIA | IHD | Homogeneous III | Different size | No change |
| 7 | 80 | Stroke | Distal ICA lesion | Homogeneous I | Unstable plaque | Change stent design (closed cell) |
| 8 | 75 | TIA | Restenosis | Heterogeneous III–IV | Different size | No change |
| 9 | 85 | Stroke | Contralateral occlusion | Homogeneous III | Different size, residual stenosis | Different stent size, PTA poststenting |
| 10 | 80 | Stroke | COPD | Heterogeneous III–IV | Different size | Different stent size |
| 11 | 77 | TIA | IHD | Homogeneous III | Different size | No modification |
| 12 | 79 | Stroke | Distal ICA lesion | Homogeneous IV | Severe calcification | Change indication (CEA) |
| 13 | 87 | Stroke | COPD+IHD | Homogeneous I | Unstable plaque | Change stent design (closed cell) |
| 14 | 85 | TIA | Contralateral occlusion | Homogeneous II | Different size | No change |
| 15 | 80 | TIA | Restenosis | Homogeneous III | Different size | No change |
| 16 | 85 | Stroke | COPD | Heterogeneous | Different size, residual stenosis | Different stent size, PTA poststenting |
| 17 | 90 | Stroke | IHD | Homogeneous IV | Severe calcification | Change indication (CEA) |
| 18 | 78 | TIA | Distal ICA lesion | Homogeneous III | Residual stenosis | PTA poststenting |
Discussion
The use of IVUS as a complementary tool in endovascular treatment of ICAS was described by Wilson et al. in 1996.10 Later, experience with IVUS has been reported by other authors, emphasizing its role as a measuring tool for the morphological evaluation of the plaque or to assess the quality of endovascular performance.8, 11, 12
In this series, the utility of IVUS information to modify the therapeutic strategy during angioplasty and stenting of ICAS was analyzed. In order to avoid potential embolization, the protection system was deployed in the distal ICA before advancing the tip of the IVUS catheter through the lesion. No complication was related either to the IVUS catheter or to the rest of the procedure. Real-time imaging of the carotid plaque was initially obtained. Virtual histological mapping provided key information on the situation and extension of calcification, areas of necrosis, and potential instability of the plaque. Axial reconstruction of the images permitted us to measure the lumen and the diameter of the area of maximum stenosis, as well as the CCA and proximal and distal ICA.
In comparison with the findings of Dietrich et al.,7 in this series IVUS measurements showed arterial diameters to be larger than those measured with standard angiography. These discrepancies may be due to a different reference system, based on the known caliber of the introducing sheath in this series. IVUS findings led to a change in the diameter of the stent in five patients, where the use of a smaller-diameter stent could have favored restenosis of the lesion.
Virtual histology of the atherosclerotic lesion provides an accurate color mapping of the characteristics of the plaque. This mode allows isolation and quantification of four relevant histological components of the carotid plaque: fibrosis, necrosis, calcification, and fat. Dietrich et al.7 found a high correlation between IVUS analysis of the carotid plaque and histological examination of specimens obtained after carotid endarterectomy. This finding highlights the potential role of IVUS for the pre- or intraoperative evaluation of the lesion to be treated in order to identify those patients with unstable plaques and, subsequently, at high risk for intraoperative cerebral embolisms.
IVUS findings modified the initially foreseen strategy in 10 patients. The stent size was increased in five, while the presence of heavily concentric calcification precluded endovascular repair in two, shifting the indication toward open endarterectomy.
In addition, suspicion of plaque instability because of core necrosis led the surgeon to use a stent with a closed-cell design instead of a standard one. Overall, this result emphasizes once again the role of intraoperative IVUS for decision making during carotid stenting.
Clark et al.13 used IVUS for completion imaging examination after carotid stenting in order to detect the mechanisms and predictors of restenosis. They concluded that the presence of a stent with suboptimal expansion and a reduced stent area were predictive factors of restenosis. Following the same rationale, we used IVUS evaluation after the procedure to assess the correct positioning and expansion of the stent, presence of residual stenosis, total covering of the lesions, or any other disturbances. However, in order to minimize the risk of repeating the advancement of the tip of the catheter through the stented lesion, examination with IVUS was restricted to those cases in which completion angiography showed doubtful images suggesting one of the above-mentioned complications.
Furthermore, the utility of IVUS to assess the quality of performance during open surgical procedures has been analyzed by Kawamata et al.14 They used IVUS examination during carotid endarterectomy to identify the distal end of the lesion. Other intraoperative applications of IVUS include the evaluation of very proximal lesions or in cases where preoperative angiography does not clearly show the end of the lesion.
In summary, IVUS examination provides relevant information that is complementary to that obtained using conventional diagnostic procedures. It may be useful for characterizing the composition and measurement of the target lesion, choosing the type and size of stent, and evaluating the results after completion of the procedure. Data from this series suggest the utility of IVUS examination for decision making during carotid stenting.
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PII: S0890-5096(09)00100-9
doi:10.1016/j.avsg.2008.09.010
© 2009 Annals of Vascular Surgery Inc. Published by Elsevier Inc All rights reserved.
