J ENDOVASC THER 2012;19:

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1 303 CLINICAL INVESTIGATION Safety and Feasibility of Intravascular Optical Coherence Tomography Using a Nonocclusive Technique to Evaluate Carotid Plaques Before and After Stent Deployment Carlo Setacci, MD; Gianmarco de Donato, MD; Francesco Setacci, MD; Giuseppe Galzerano, MD; Pasqualino Sirignano, MD; Alessandro Cappelli, MD; and Giancarlo Palasciano, MD Department of Surgery, Vascular and Endovascular Surgery Unit, University of Siena, Italy. Purpose: To evaluate the safety and feasibility of optical coherence tomography (OCT) in patients with carotid stenosis undergoing carotid artery stenting (CAS). Methods: In a prospective study, 25 consecutive patients (15 men; mean age 7464 years) undergoing protected CAS were enrolled and underwent high-definition (homoaxial resolution 10 mm) OCT image acquisition before stent deployment, immediately after stent placement, and following postdilation of the stent (3 scans/patient). Pullbacks were started during a nonocclusive flush, mechanically injecting 24 ml of 50% diluted contrast at 6 ml/s to displace blood from the artery. Two independent physicians judged the quality of images on a predefined 1 10 scale. The proportions of specific agreement and kappa values (k) were calculated. Results: No procedural or in-hospital neurological complications occurred (any stroke/ death 0%). The technical success of OCT pullbacks was 97.3% (73/75). The total amount of contrast was ml/patient. No significant alteration in glomerular filtration rate or any other significant adverse event occurred. The images obtained were of high quality (mean value 8.1 out of 10), with good inter- and intraobserver agreement (k and k50.95, respectively). OCT images revealed innovative features such as rupture of the fibrous cap, plaque prolapse, and stent malapposition in a high percentage of the patients (range 24% 100%). Conclusion: Intravascular OCT during a nonocclusive flush appears to be feasible and safe in carotid arteries. Since some original and unexpected information after CAS has been made available for the first time at such a high definition, future studies with OCT should focus on the interaction between carotid plaque and stent design, which might revolutionize our understanding of the mechanisms of carotid stenting, as well as influence our clinical policies. J Endovasc Ther. Key words: carotid plaque, carotid stenting, intravascular imaging, optical coherence tomography, plaque morphology, plaque prolapse, fibrous cap Optical coherence tomography (OCT) is an optical signal acquisition and processing method that captures micrometer-resolution, 3-dimensional images from within optical scattering media. In the field of interventional cardiology, 1 OCT is a catheter-based invasive intravascular imaging system, which produces high-resolution in vivo images using light rather than ultrasound. It has a homoaxial resolution of 10 mm: 10 times higher than that Presented at ICON 2012; February 12 16, 2012; Scottsdale, Arizona, USA. The authors have no commercial, proprietary, or financial interest in any products or companies described in this article. Corresponding author: Gianmarco de Donato, Policlinico Le Scotte, Viale Bracci 1, Siena, Italy. dedonato@unisi.it ß 2012 by the INTERNATIONAL SOCIETY OF ENDOVASCULAR SPECIALISTS Available at

2 304 OPTICAL COHERENCE TOMOGRAPHY FOR CAS EVALUATION See commentaries pages 312 and 314 of any other clinically available diagnostic imaging method. Thus, this technology provides in situ images of tissues at nearly histological resolution. OCT is an increasingly popular intravascular modality to study coronary arteries and coronary stent apposition, as it permits accurate measurements of luminal architecture and provides insights into plaque coverage, plaque prolapse, stent apposition, overlap, and neointimal thickening. 2 5 There is great interest in the feasibility of using OCT to study carotid arteries, considering that plaque prolapse through the stent cell has been suggested as one of the major causes of postprocedural complications following carotid artery stenting (CAS). 6 8 Further, available periprocedural imaging systems [angiography, intravascular ultrasound (IVUS), and duplex ultrasound] may not be able to detect micro-prolapse. Moreover, existing intraprocedural imaging systems are not able to clearly define and provide precise details of the conformability of actual carotid stents to lesion contours and vessel tortuosity after deployment (defined as stent apposition/malapposition) or of the ability of the stent to effectively cover the plaque; high-resolution OCT images might provide more satisfactory results. The first-generation OCT systems were suitable for vessels ranging in size from 2.0 to 3.75 mm in diameter. This field of view allowed its clinical application in small arteries such the coronaries, but limited the application of OCT in larger peripheral arteries. The recent availability of a new low-profile imaging catheter allows visualization of arteries up to 10 mm in diameter, extending the application of this imaging technique to the intravascular assessment of carotid arteries and carotid stents. Additionally, a relatively recent technical enhancement of OCT, known as frequencydomain OCT (FD-OCT), has been shown to provide advantages in signal-to-noise ratio, permitting micron-level resolution imaging of the artery, with faster signal acquisition. The latest OCT system has the capability to scan a 55-mm artery segment in about 2 seconds, with obvious advantages concerning its applicability in peripheral arteries. The first application of OCT to the carotid artery was reported in 2010 as a technical case report by Yoshimura et al., 9 and the typical features were detailed in another article from the same group in The aim of this study was to evaluate the safety and feasibility of OCT during nonocclusive flushing in patients with carotid stenosis undergoing CAS. Study Design METHODS This prospective study was performed in a single center between March 2011 and July The local ethics committee approved the study protocol, and written informed consent was obtained from all patients. Patients were recruited if they had.80% asymptomatic internal carotid artery (ICA) stenosis or.70% symptomatic ICA stenosis 11 and had already been considered eligible for endovascular treatment. 12 During the study period, 25 patients (15 men; mean age years) met the study criteria and gave informed consent to participate. At the same time, 7 patients were excluded from the study because of elevated serum creatinine levels (.1.2 mg/dl, n54), a positive history of contrast medium intolerance (n51), and severe tortuosity of the ICA distal to the target lesion (n52) evaluated by the operator as unfit for safe OCT catheter advancement (see OCT Technique section). Echo duplex and independent neurological examinations of all patients were performed before the intervention, at discharge, and 30 days after the procedure. All patients underwent cerebral computed tomography (CT) or magnetic resonance imaging (MRI) scan before treatment, whereas a postprocedure cerebral CT/MRI scan was scheduled only in the case of a documented neurological complication. The operating team prospectively entered demographic and clinical variables and intraoperative and follow-up data into a dedicated database. CAS Technique Carotid artery stenting was performed according to our standard technique using distal

3 OPTICAL COHERENCE TOMOGRAPHY FOR CAS EVALUATION 305 cerebral protection devices [Emboshield Pro (Abbott Vascular, Redwood City, CA, USA; n511), FilterWire EZ (Boston Scientific, Natick, MA, USA; n59), Spider (ev3/covidian, Plymouth, MN, USA; n53), and Angioguard (Cordis, a Johnson & Johnson company, Miami Lakes, FL, USA; n52)]. 13 All patients were pretreated with acetylsalicylic acid (125 mg/d) and clopidogrel (75 mg/d) or ticlopidine (500 mg/d) for at least 4 to 5 days prior to admission. All the procedures were carried out percutaneously via puncture of the right or left femoral artery. Weight-adjusted (70 U/kg) heparin was administered and repeated as necessary to maintain an activated clotting time of 225 to 250 seconds throughout the procedure. The common carotid artery (CCA) was selectively engaged directly using an appropriate 8-F guiding catheter. After visualization of the culprit lesion, a inch guidewire was gently crossed over the lesion, and a cerebral protection device was deployed in a straight segment of the extracranial portion of the ICA. The first OCT scan was then performed during a nonocclusive flush (see OCT Technique section). Carotid stenting was carried out using a variety of self-expanding stents: Carotid Wallstent Rx (Boston Scientific; n512), Precise Pro Rx (Cordis; n58), Adapt (Boston Scientific; n52), Protégé (ev3/covidian; n52), Xact (Abbott Vascular; n51). The stent diameter was selected according to the CCA diameter, while stent length was calculated to cover the entire carotid lesion (at least 0.5 cm below and 0.5 cm above the target lesion). In all cases, postdilation of the stent was performed using short dedicated balloons (maximum size mm) inflated to nominal pressure, considering #20% residual stenosis as acceptable for technical success. In addition to acetylsalicylic acid, clopidogrel (75 mg/d) or ticlopidine (500 mg/d) was continued for at least 30 days after the procedure (hemoglobin and white blood count were checked 7 10 days after intervention). Mono-antiplatelet therapy was continued indefinitely. OCT Technique For the purpose of this study, carotid OCT images were acquired 3 times in each of the 25 patients: before stent deployment, immediately after stent placement, and following postdilation of the stent. For the first 10 patients, a dedicated technician trained to set up and operate the OCT equipment (LightLab Imaging Inc., Westford, MA, USA) was present in the operating theater. During this initial phase of the investigation, one member of our surgical team (G.G.) was trained to configure and use the OCT computer. This team member was exclusively responsible for the OCT system setup and procedures in the remaining 15 patients. The optical fiber of the C7XR FD-OCT system (LightLab Imaging Inc.) is encapsulated within a rotating torque wire (0.014-inch compatible) built in a rapid exchange 2.6-F catheter compatible with a 6-F guiding catheter. It acquires 100 frames per second at pullback speeds up to 25 mm/s. Once the cerebral protection device was deployed in a straight portion of the ICA distal to the culprit lesion, the calibrated OCT catheter was advanced over the inch guidewire of the filter and completely passed over the target lesion. Pullbacks were started during a nonocclusive flush, mechanically injecting 24 ml of 50% saline-diluted contrast medium (Iodinoxanol: Visipaque 320 mg l/ ml; GE Healthcare, Cork, Ireland) at 6 ml/s, 750 psi, using an automatic injection system (Mark V ProVis; Medrad Interventional/Possis, Warrendale, PA, USA) to completely displace blood from the artery. Injections were performed through an 8-F guiding catheter with a minimum internal lumen of 2.3 mm, placed just a few centimeters proximal to the carotid bifurcation. Of note, the pullback was started,1.5 to 2 seconds after the injection of the diluted contrast, when the absence of blood scattering and signal attenuation were noted on the screen of the OCT system (real-time images). After stent deployment, the same OCT maneuvers were repeated; in particular, 2 further scans were performed before and after stent dilation. Images were digitally recorded, automatically stored, and reviewed by 2 independent observers (P.S., F.S.) in a blinded fashion. The quality of the images was judged on a predefined 1 10 scale (Fig. 1) based on the accuracy of vessel wall identification and

4 306 OPTICAL COHERENCE TOMOGRAPHY FOR CAS EVALUATION Figure 1 Scoring schemes for assessing the vessel wall, plaque morphology, stent apposition, and complete vessel area with OCT. plaque morphology at 3 different levels (ICA, carotid bulb, CCA; range 0 3 points) and on the visualization of the complete vessel area at the level of the CCA (loss of images defined as out of screen ; range 0 1). The term malapposition was used when the distance measured from the surface of the blooming (the inner and outer contours of each strut reflection) to the lumen contour was greater than the total thickness of the stent strut + one half of the blooming (Fig. 2). Any discontinuity of the inner layer of the plaque profile was considered as a rupture of the fibrous cap (Fig. 3A), while plaque prolapse after stenting was defined as any appreciable tissue prolapse between the stent struts (Fig. 3B). Interand intraobserver variability was determined in 35 randomly selected OCT scans. Endpoints The primary endpoint of the study was the rate of any periprocedural stroke or death after CAS and OCT intravascular imaging with a nonocclusive technique. Secondary endpoints included: technical success of OCT image acquisition, clinical and laboratory signs of contrast-induced nephropathy [based

5 OPTICAL COHERENCE TOMOGRAPHY FOR CAS EVALUATION 307 Figure 2 (A) Correct carotid stent apposition to the arterial wall; (B) carotid stent malapposition. on estimated glomerular filtration rate (egfr) alteration] or contrast-induced encephalopathy, and any in-hospital adverse events. Statistical Analysis The data are expressed as mean 6 standard deviations or as counts and percentages. Comparisons of continuous variables were performed with unpaired Student t tests, considering p,0.05 as indicative of statistically significant differences. Inter- and intraobserver variability were assessed using Cohen s kappa test of concordance.14 A k value of 0.61 to 0.80 indicated good agreement and 0.81 to 1.0 was excellent agreement. All statistical analyses were performed using the SPSS statistical software package (version 13; IBM Corporation, Somers, NY, USA) and MatLab (version 7.0.1; The Math Works Inc., Natick, MA, USA). Figure 3 (A) Rupture of fibrous cap after carotid stent deployment. (B) Plaque prolapse through the stent struts after deployment and dilation. (C) Plaque prolapse and rupture of fibrous cap after carotid stenting.

6 308 OPTICAL COHERENCE TOMOGRAPHY FOR CAS EVALUATION TABLE 1 Patient Characteristics (n525) Men 15 (60%) Age, y Neurological symptoms 11 (44%) Previous TIA 6 Previous stroke 5 Hypertension 19 (76%) NIDDM 8 (32%) Smoker 12 (48%) CAD 9 (36%) Renal function (egfr, ml/ min/1.73m 2 ) Creatinine, mg/dl Peripheral artery disease 11 (44%) Hypercholesterolemia 15 (60%) Side of carotid lesion (right) 13 (52%) Restenosis after CEA 1 (4%) Carotid plaque composition* Type 1 5 (20%) Type 2 8 (32%) Type 3 8 (32%) Type 4 4 (16%) Carotid plaque ulceration 5 (20%) Continuous data are presented as the means 6 standard deviation; categorical data are given as the counts (percentage). CAD: coronary artery disease, CEA: carotid endarterectomy, egfr: estimated glomerular filtration rate, NIDDM: non-insulin-dependent diabetes mellitus, TIA; transient ischemia attack. * According to the Gray-Weale classification. 11 RESULTS CAS was performed successfully in all 25 patients. Three OCT examinations were performed at 3 different phases of the CAS procedures in each patient for a total of 75 OCT scans. Among these acquisitions, 2 scans were considered inadequate for tissue characterization and any further analysis, limiting the technical success of OCT imaging to 97.3% (73/75). These 2 technical failures were related to premature activation of OCT pullback (,1 second from the injection of diluted contrast medium), resulting in significant scattering of the infrared light due to incomplete blood displacement into the carotid bifurcation. No technical or neurological complications occurred during OCT pullbacks. The mean procedural time was minutes, and the total amount of contrast medium was ml/patient (range ). During the hospitalization period, egfr remained stable in all patients (preoperative vs. postoperative ml/min/ 1.73m 2,p50.3). No procedural or in-hospital complications occurred in the study population (any stroke/death 0% at discharge). The images obtained were judged to be of high quality (mean value out of 10). Interobserver variability was very good for identification of the vessel wall (k50.87), stent apposition (k50.84), plaque prolapse (k50.85), and rupture of the fibrous cap (k50.81). Intraobserver agreement, evaluated by asking each observer to assess the images twice with a 7-day interval, was excellent (k50.95). The OCT images acquired after stent deployment and dilation revealed innovative features (Table 2), such as rupture of the fibrous cap, stent malapposition, and plaque prolapse (Fig. 3C) in a very high percentage of cases. DISCUSSION OCT is becoming a popular intravascular imaging modality for the assessment of TABLE 2 OCT Findings at Different Stages of CAS in 25 Patients OCT Image Acquisition 1 st Scan 2 nd Scan 3 rd Scan Fibrous cap rupture 9 (36%) 15 (60%) 18 (72%) Stent malapposition to ICA NA 25 (100%) 11 (44%) Plaque prolapse NA 6 (24%) 17 (68%) 1 st scan: before stenting, after filter placement; 2 nd scan: immediately after stent deployment; and 3 rd scan: after post-dilation. ICA: internal carotid artery, NA: not applicable.

7 OPTICAL COHERENCE TOMOGRAPHY FOR CAS EVALUATION 309 Figure 4 The C7 Dragonfly OCT catheter. coronary stents, but its use in peripheral arteries is still relatively rare. This study, although it must be considered a preliminary experience, has confirmed that intravascular OCT imaging can also be applied safely in carotid arteries and revealed that good images can be obtained using a nonocclusive technique. From coronary studies 1,4 it is well known that displacement of blood from the artery with saline is essential to obtain satisfactory OCT imaging, as any amount of residual red blood cells causes significant signal attenuation and multiple scattering. The occlusive technique, involving balloon occlusion and saline injection into the coronary artery, is considered the standard technique for OCT image acquisition. Some authors 15,16 have recently proposed a nonocclusive technique, using the continuous injection of contrast medium to replace blood; in combination with the rapid pullback of the new C7 Dragonfly OCT catheter (Fig. 4), they were able to obtain satisfactory coronary OCT images without vessel occlusion. To date, only 2 studies 17,18 have been published on preliminary experiences with OCT imaging to visualize carotid arteries. Both studies propose an occlusive technique, using a proximal cerebral protection device. To our knowledge, no one until now has shown that OCT can also be safely and effectively applied during nonocclusive flushing. Our nonocclusive carotid OCT imaging technique is beneficial because it avoids carotid clamping and offers cerebral protection during the entire procedure. On the contrary, the occlusive carotid OCT imaging technique requires extra carotid clamping time, which can cause cerebral intolerance. 17 Likewise, the occlusive technique includes the injection of a certain amount of saline solution into the ICA when the proximal balloon is inflated, which may be responsible for microdebris moving distally into the cerebral arteries (especially when compensation occurs via the circle of Willis 19 ). Additionally, maneuvers of deflation and reinflation of the proximal protection device may take place between stent deployment and the OCT scans, 18 which may further mobilize debris. On the other hand, OCT with proximal occlusion does not increase the amount of contrast, as the entire volume following imaging can be re-aspirated, making it the method of choice in patients with renal failure. Certain technical aspects need to be considered for satisfactory image acquisition with our nonocclusive technique. The first of these aspects is the distance between the landing zone of the filter and the culprit lesion. In fact, it should be noted that the OCT lens is placed 25 mm distal of the distal tip of the OCT catheter, and it moves from distal to proximal when pullback is activated. This means that a distance of at least 25 mm should be available between the point where the filter is positioned and the distal end of the ICA lesion. In 2 cases in our experience, the severe anatomical tortuosity of the distal carotid artery was judged as a contraindication to filter and OCT catheter advancement. These 2 patients were excluded from the study at the operator s discretion; specific anatomical characteristics limiting nonocclusive carotid OCT application still remain to be identified. A second challenging aspect of our nonocclusive technique is the correct time for pullback, which has to be unequivocally synchronized with blood displacement from the artery to avoid OCT signal attenuation and

8 310 OPTICAL COHERENCE TOMOGRAPHY FOR CAS EVALUATION artifacts. In our experience, a key move to obtain a blood-free environment was to adopt a high injection flow rate through an 8-F guiding catheter with a large inner lumen (2.3 mm) placed close to the carotid bifurcation. Adhering to these important technical guidelines, in association with prompt pullback starting exactly when OCT real-time images reveal the absence of blood scattering, results in high-quality OCT images. The safety profile of our protocol was confirmed by the good neurological outcome (0% any stroke/death at discharge) and satisfactory tolerance in terms of in-hospital adverse events, including no alterations in renal function. Moreover, the extra dose of contrast agent injected directly into the carotid artery could cause encephalopathy in addition to renal failure. Contrast-induced encephalopathy (CIE) has been described during various endovascular interventions. Although CIE remains a rare and benign complication, a high dose of contrast agent injected directly into the cerebral circulation may cause osmotic disruption of the bloodbrain barrier with a dramatic clinical presentation. Neurological symptoms include visual disturbances, transient cortical blindness, and transient ischemic attacks as consequences of contrast permeation into part of the brain and cortical dysfunction due to increased neuronal excitability. 20 In this study, we endeavored to reducetheamountofcontrastusedduringoct scans by using a 50% saline-diluted isosmolar contrast agent. As a result, the total amount of contrast agent used (mean 86618mL, range ) for the procedure, including OCT scans, was well below the quantities reported in the 3 published cases of CIE after CAS [180 ml of an ionic low osmolar contrast, ml of a nonionic low osmolar agent, 22 and 300 ml of an isosmolar contrast 23 ). Furthermore, no CIE was recorded in our series. Limitations First, the safety and feasibility of this technique was demonstrated in a center dealing with a high volume of CAS cases. Each surgeon in this study had extensive experience of CAS (. 300 cases performed as first operator), being particularly familiar with intraluminal carotid manipulation and extremely prone to limit the use of contrast agent during all the phases of the procedure. It should be noted that the nonocclusive OCT technique proposed here might have a different safety profile and feasibility rate in a center with less experience in carotid stenting. Second, a high level of cooperation between the surgical team and the OCT technician is essential to correctly scan the artery and obtain high quality images. Third, due to the limited number of cases in this series, we were not able to detect any relationship between OCT observations and any clinical or procedural variables. It is our intention to build on our experience with this highresolution intravascular imaging technique and focus future investigations on the interaction between carotid plaque morphology and the design of implanted stents. This will add to the knowledge of some mechanisms of carotid interventions that still appear to be under-investigated. Conclusion The present study confirms that carotid OCT with a nonocclusive technique is safe and effective, allowing the collection before and after CAS of good quality images and informative details that are not available with other existing imaging systems. Due to the cost of the OCT catheter, its use in our center is currently restricted to a research tool in this predefined prospective study; its widespread application in clinical practice is difficult to predict. Nonetheless, in the near future, application of this intravascular imaging system may reveal some innovative details (such as rupture of the fibrous cap, plaque prolapse, and stent malapposition) at such high definition that it might revolutionize our understanding of the mechanisms of carotid stenting and influence our clinical policies. In particular, future studies could investigate the relationship between carotid plaques and carotid stents with regard to stent design and plaque composition. In this context, OCT results could be evaluated on the basis of relevant clinical and procedural variables, offering important new data to help tailor our clinical strategies for carotid artery disease.

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