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Commentary on "the impact of embolic protection device and stent design on the outcome of CAS".

In the current issue, “The Impact of Embolic Protection Device and Stent Design on the Outcome of CAS” is a subject in which Bosiers and his colleagues are eminently qualified. The article describes in detail the choices and the variations that exist in embolic protection devices commercially available. They point out that distal balloon protection, originally designed by Theron, obviously has profile advantages but unfortunately has additional limitations in that cerebral flow is compromised in those patients who have inadequate collateralization via either the anterior or posterior communicating vessels at the circle of Willis. In fact, only 25% of the patient population has a normal complete circle of Willis. A similar limitation also exists for proximal occlusion devices when inadequate collateral circulation is present. Proponents for proximal control maintain that most embolic particles are less than 100 μm in diameter and cannot be captured in conventional distal filters. The problem, however, is that the proximal flow sheaths are 8 F, a profile much larger than desirable, especially for trackability in complex type III aortic arches. They also present a risk factor in passage in the atherosclerotic common carotid artery. Presently, there are 2 randomized trials for proximal control protection that when completed should clarify both time of the procedure and safety and efficacy. For the time being, however, most investigators favor distal filter embolic protection devices. The types of distal filters used in the trials and registries have not shown major differences in outcomes regardless of filter type. This is interesting in that major differences did exist in the bench test analysis. Siewiorek et al attempted to establish goals of bench-top testing by use of computational fluid dynamics modeling to quantify carotid artery flows during cerebral protection. All the distal protection filters have a perforated polyurethane membrane, with the exception of SpiderRX, which represents a nitinol mesh, and Fibernet, which is composed of polyethylene terephthalate. Comparison of Angioguard, Emboshield I, FilterWire EZ, RX Accunet, and SpiderRX were evaluated for capture efficiency, blood flow, vascular resistance, and apposition. Design parameters that most significantly affected device performance were porosity, pore density, permeability, vascular resistance, and the ability to conform to convex configurations in the carotid artery. Porosity and pore density depend on the size of pores, number of pores, and surface area of the filter basket. The smaller the pore size the greater the tendency to “slow flow phenomenon,” with decreased flow volume and increased vascular resistance. There is the suggestion that apposition of the filter basket to conform to the vessel cross section at the site of deployment is a primary design variable responsible for distal embolization. Siewiorek et al have shown that RX Accunet and FilterWire EZ had best overall wall apposition, with no statistically significant differences in capture efficiency. SpiderRX had the most favorable characteristics, with highest flow volume, lowest vascular resistance, and 99% particle capture efficiency. RX Accunet was also efficient, with 95.1% particle capture, and FilterWire EZ had 96.1% particle capture. Angioguard was 64% efficient, and Emboshield I was 72% efficient in terms of particle capture. Vascular resistance was 3.5% for SpiderRX, 12.8% for FilterWire EZ, 24.8% for RX Accunet, 14.7% for Emboshield, and 30.6% for Angioguard. Fibernet has not been subjected to bench-top analysis. The system is delivered on a 0.014-in. wire with the ability to capture 40 μm particles. The issue may be wall apposition, From Interventional Radiology, Pittsburgh Vascular Institute, UPMC Presbyterian Shadyside–Shadyside Campus, Pittsburgh, Pennsylvania.