The results of a new study, headed by Dr Marc Bosiers, AZ Sint Blasius in Dendermonde, Belgium, have demonstrated that the closed cell design of the carotid artery stents provides superior clinical outcomes compared to open cell stents. The study was presented at the 60th Annual Meeting of the Society for Vascular Surgery in June by Dr Joseph Hart, University of Rochester School of Medicine and Dentistry, Rochester, NY, who helped collect the data during his Marco Polo fellowship in Dendermonde, Belgium.
The investigators wanted to assess how different carotid stents impact patient outcomes, and therefore studied the theoretical difference in closed vs. open-cell stents as well as eccentric vs. concentric embolic protection devices (EPDs). The researchers reviewed an existing single-centre database of 709 carotid artery stenting procedures in an effort to identify factors that negatively impacted patient outcome and compared the clinical results of open versus closed cell carotid stents.
Closed cell stents have overlapping or fully connecting struts and cover five to ten times more of the vascular wall compared to open cell stents that have both connecting and non-connecting struts, thereby potentially reducing the risk of a delayed embolism relative to open cell stents.
Patients undergoing stenting were entered into an investigational database. A subset of patient, lesion or procedure related variables were analysed for association with occurrence of stroke, death or transient ischaemic attack (TIA) within 30 days after stenting. The odds ratio (OR) and 95% confidence interval (CI) and p-value (expressed as OR and 95% CI, p-value) were calculated for each variable to predict adverse outcome. The 30 day stroke, death and TIA rate, expressed as % (±SE), was estimated using Kaplan-Meier methodology.
In the study, the overall combined 30-day rate of stroke, TIA, or death for open and closed cell design stents was 3.7%. The overall rates of stroke or death at 30-days, one year and three years were 1.4%, 6.0% and 15.1%, and restenosis rates were 0.2%, 0.9% and 5.6%, respectively. There was no difference in rates of restenosis between symptomatic and asymptomatic patients. At 30-days post-procedure, symptomatic patients who received the closed cell stent therefore showed a 4.1 times reduction of stroke, TIA or death compared to the open cell stent group. The Carotid Wallstent Monorail (Boston Scientific) represented more than 70% of the closed cell stents used in this study.
The study also reported lower rates of major adverse events within 30 days post-procedure in the patient population treated with eccentric filters (non-central axis design), such as the FilterWire EZ Embolic Protection System (Boston Scientific), compared to the population treated with concentric (centre axis design) embolic protection devices.
The overall rates of stroke or death were 1.4% (±0.5), 6.0% (±1.1), and 15.1% (±2.1) at 30 days, one year and three years respectively. Restenosis rates were 0.2% (±0.2), 0.9% (±0.4), and 5.6% (±2.6) at 30 days, one year and three years respectively. OR for basic risk factors in the total population (age > 70, left sided lesion, symptomatic, nicotine abuse, hypertension, diabetes mellitus, other peripheral vascular disease, hypercholesterolemia, EPD utilisation, predilatation, ulcerated lesion, calcified lesion, restenosic lesion) were analysed and found to not be significant with the exception of hypercholesterolemia, OR=2.7(1.0-7.3, p=0.041).
"There were less adverse events within 30 days with the closed cell stent. The closed cell stent design offers a greater potential to scaffold and support fractured plaque and keep material that could embolise to the brain, from travelling through the vasculature," commented Bosiers. "Closed cell stents cover a greater percentage of the vascular wall in the stented region and have less uncovered cell area. Therefore we would recommend them for symptomatic patients.
"Closed-cell stents and eccentric filter devices were predominately used in this study and performed better in the short term in symptomatic patients or those with echolucent lesions," said Dr Joseph Hart, assistant professor of vascular surgery, University of Rochester School of Medicine and Dentistry in Rochester, NY.
"In a study of 709 patients, 701 were considered a technical success. Also, the paper noted that complex haematologic factors might also contribute to the apparent superiority of closed-cell stents in this series. Some data suggest that eccentric filters are superior to concentric filers for TIA prevention of particle capture. We postulate the better wall apposition in the distal internal carotid artery (ICA) due to axial flexibility may account for this."
He added that concentric filter wires might pull it away from the wall and filter when used in a person whose anatomy has curves. Suboptimal position of the concentric filter within the distal ICA beyond the lesion being treated may lead to incomplete embolic protection. However, floating eccentric filters are potentially more prone to complete wall apposition, thus improved embolic protection.
Hart noted that neurological deficit, even following a period of hypotension with bradycardia, were recorded as a TIA and commented that similar events may be masked under general anaesthesia, particularly if EEG monitoring is not utilised or fails to indicate such activity. "Carotid stenting is here to stay," said Hart. "Although the decision to use it for patients is highly individualised, it is likely that it will be used on even more patients in the future because of the less invasive nature of the procedure."
Due to the limitations of the study alternative explanations for the data does exist, therefore the researchers believe a prospective trial is necessary prior to conclusive resolution that device characteristics under consideration here materially impact patient outcome. As an alternative to prospective trial, it would be possible to consider meta-analysis of the existing trial data to further examine this question without incurring the expense and logistical difficulties of a formal trial.
"These results should give physicians great confidence when treating their patients with the Carotid Wallstent Monorail and FilterWire EZ Embolic Protection System," said Jeff Goodman, president, Boston Scientific International. "The excellent results from this trial build on the existing clinical evidence for using these devices to treat patients with carotid artery disease."
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