Self-Expanding Stents for Carotid Interventions: Comparison of Nitinol Versus Stainless-Steel Stents

Angioplasty and stenting are becoming increasingly accepted techniques for the treatment of carotid stenosis. Compared to endarterectomy, carotid stenting is a less invasive procedure that provides an attractive treatment alternative for some patients, particularly those with severe cardiac co-morbidities. The feasibility and safety of the carotid stenting procedure as a treatment for severe carotid stenosis has improved with recent technological advances. However, the optimal stent for carotid revascularization is unknown. The objective of this study was to assess immediate angiographic results and intermediate-term outcomes (i.e., death, myocardial infarction, and stroke) following carotid stenting with stainless-steel and nitinol self-expanding stents. METHODS From a comprehensive database of all interventional cerebrovascular procedures maintained at our institution (the Cleveland Clinic Foundation, Cleveland, Ohio), patients treated for carotid artery stenosis between February 1998 and January 2000 were identified. One hundred and seventy-eight patients with carotid artery stenosis underwent stenting during this time. Of these, eighty-nine patients received stainless-steel and the other 89 patients received nitinol stents. Clinical follow-up was systematically obtained by chart review for outpatient visit evaluation and telephone interview by physicians. All patients had a follow-up of >= 6 months. Measurements of reference vessel size and stenotic segments were made using hand-held electronic calipers in a standardized fashion. Lesion length was measured shoulder to shoulder, and vessel diameters were determined relative to the guiding catheter. Procedural success was defined as a final stenosis of 20%, Thrombolysis in Myocardial Infarction (TIMI) grade 3 flow, with no in-hospital major complications [death, Q-wave myocardial infarction (MI), or stroke]. Clinical endpoints on follow-up evaluation were 1) death; 2) MI; and 3) stroke. All patients had independent neurological assessment pre- and post-procedure. Data are presented as means ± standard deviation unless stated otherwise. Categorical variables are expressed as percentages. Statistical analysis was done using Statistica for Windows 4.0, Statsoft Inc. (Tulsa, Oklahoma). Carotid artery stenting technique. The patients were sedated with short-acting intravenous sedation, and an arterial sheath was inserted into the femoral artery. An aortic arch angiographic study (left anterior oblique 30° projection) was initially performed to determine the origin of the great vessels to choose an appropriate catheter for selective angiography. A baseline angiographic study was then performed of the bilateral subclavian, vertebral, and carotid arteries to determine the extent of vascular disease and presence of collateral circulation. An activated clotting time (ACT) was obtained before onset of the angiographic procedure. The patients then received a weight-adjusted bolus of 50 U/kg body weight unfractionated heparin. The ACT was obtained after initial heparin bolus to ensure a value greater than twice baseline ACT, or > 250 seconds. A 125 cm, 5 French (Fr), JR4 diagnostic catheter (Cordis Corporation, Miami Lakes, Florida) was placed inside a 90 cm, 7 Fr Cook Shuttle Sheath (Cook Incorporated, Bloomington, Indiana). The origin of the common carotid artery was carefully intubated with the JR4 catheter and a 0.035´´ Storq guidewire (Cordis Incorporated) was advanced into the external carotid artery. The 7 Fr Cook Shuttle Sheath was advanced into the common carotid artery over the JR4 catheter. The JR4 catheter was withdrawn at this time and diagnostic angiograms were performed in the ipsilateral 30° oblique and left lateral projections for vessel sizing. The lesion in the carotid artery was traversed with a 0.014´´ exchange-length BMW wire (Guidant Corporation, Temecula, California). A 4.0 x 20 mm Ranger™ angioplasty balloon catheter (Boston Scientific/Scimed, Inc., Maple Grove, Minnesota) was used to predilate the lesion to allow subsequent passage of a self-expanding stent. Stenting was performed either with a stainless-steel Wallstent (Boston Scientific/Scimed, Inc.) or a nitinol stent (SMART stent, Cordis Corporation). The Wallstent is constructed from a woven stainless-steel super alloy and is composed of filaments of a cobalt-based alloy braided in the form of a tubular mesh. Before deployment, angiograms were performed in orthogonal projections to determine appropriate placement of the stent. The stent was post-dilated with a 5.5 x 20 mm Speedy Bypass balloon catheter (Boston Scientific/Scimed, Inc.). All patients received 325 milligrams of aspirin and 300 milligrams of clopidogrel prior to the procedure and were discharged home the following day on clopidogrel 75 mg orally four times daily for 4 weeks and on aspirin 325 mg orally four times daily. RESULTS Baseline characteristics of the patient population undergoing carotid artery stenting are shown in Table 1. The groups were similar with respect to age, gender, diabetes, hypertension, left ventricular function and symptom status. There were more patients with contralateral carotid occlusion in the nitinol stent group. The angiographic characteristics are listed in Table 2. There were no significant differences in reference diameter or pre-procedure stenosis. Patients in the nitinol arm had slightly higher residual post-procedure stenosis (Study limitations. Our study has several limitations. This is a retrospective analysis, and since patients were not randomized there were some baseline differences among the groups (although not statistically significant). Another limitation is the modest sample size. The patients in the nitinol group were treated more often with glycoprotein IIb/IIIa inhibitors, which might have some salutary effect on cardiovascular mortality. CONCLUSION In summary, in a single-center patient cohort with similar baseline characteristics, patients receiving nitinol stents and stainless-steel stents had similar neurological outcomes. Thus, either stainless-steel or nitinol self-expanding stents may be acceptable for carotid stenting. Acknowledgment. We would like to thank Cindie Davidson for her expert editorial assistance.

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