ABSTRACT: Stroke is the third most common cause of death in the United States. Approximately 30% of all ischemic strokes are secondary to carotid artery disease. Carotid endarterectomy (CEA) is considered the gold standard for the treatment of carotid artery stenosis. Endovascular techniques such as carotid angioplasty and stenting (CAS) have been proposed as possible alternatives for high-risk patients, but not until the advent of embolic protection devices (EPD) were they considered an acceptable alternative to surgery. There are currently two types of cerebral protection strategies employed: distal protection in the form of an occlusion balloon or filter, and proximal protection in the form of flow interruption or reversal devices. Advantages and disadvantages of each type will be reviewed. The selection of an EPD largely depends on anatomy as well as operator preference. Although there is currently a lack of consensus among interventionists performing CAS on the optimal EPD, all have agreed that routine use of an EPD during CAS is beneficial and mandatory.
J INVASIVE CARDIOL 2009;21:413–414
Atherosclerotic occlusive disease of the extracranial internal carotid artery has been cited as a common causative factor for ischemic stroke in approximately 30% of patients. While medical therapy has been shown to be effective in reducing the rate of neurologic complications, published results from several large randomized trials have shown carotid endarterectomy (CEA) to be superior to medical therapy in select groups of symptomatic and asymptomatic patients.1–4 CEA is thus considered the gold standard for the treatment of carotid artery stenosis in this population. The stroke and death rate for both asymptomatic and symptomatic patients appeared to be directly related to the severity of the patient’s underlying risk factors including coronary disease.5
Endovascular techniques such as carotid angioplasty and carotid artery stenting (CAS) have been proposed as an alternative to surgery in high-risk patients. Recently, CAS has gained favorable support due to a decrease in the 30-day morbidity and mortality rates, a reduction in procedural discomfort and faster convalescence when compared to CEA. The risk of neurologic complications from distal embolism remained the major obstacle for this procedure. Embolic protection devices (EPDs) were invented to capture and remove debris generated during the procedure and had been shown to reduce the incidence of neurological complications associated with this procedure.6–11 Recent prospective, multicenter, randomized trials have shown that in high-risk patients, CAS with cerebral protection is at least equivalent to surgery.12,13
Cerebral protection strategies are classified as either distal protection in the form of an occlusive balloon or filter, or proximal protection in the form of a flow interruption or reversal system. All protection devices are not equivalent and no one device can protect against all neurological complications. However, preliminary results suggest that routine use of EPDs, together with specifically designed stents, have combined to reduce the incidence of neurological complications and have made the results noninferior to those achieved in surgical series, especially in high-risk patients.14–19
Distal Protection Strategies
Distal occlusive balloon. A distal protection strategy is based on the principle that neurological complications occur as a result of cerebral embolization of debris generated during angioplasty and stenting of the target vessel lesion. The balloon is placed distal to the target lesion and is inflated to prevent flow to the cerebral circulation. Flow is typically redirected into the external carotid artery or appears as a stagnant column. After the procedure is completed, this stagnant column of blood is aspirated to remove debris loosened during the intervention prior to restoring cerebral blood flow.20
The PercuSurge GuardWire (Medtronic, Inc., Minneapolis, Minnesota) is approved as an EPD for distal protection. Once the balloon is crossed with the GuardWire, it is inflated to completely occlude ipsilateral cerebral blood flow. The balloon can be inflated to variable sizes ranging from 3–6 mm to fit the vessel without causing significant trauma.18 The advantage of the PercuSurge system is its low-profile design and trackability for maneuvering through tortuous anatomy. Unlike filter protection devices, the PercuSurge balloon can also be deployed in a tortuous segment of the artery. The disadvantage of the system is the high incidence of neurological intolerance (5–15%) associated with inflation of the balloon.21 Furthermore, in contrast to proximal protection devices, the balloon must first cross the target lesion without any form of cerebral protection.
Filters. Unlike the PercuSurge balloon, filters are designed to trap larger embolic particles and debris released during the procedure without interruption of cerebral blood flow. Filters are essentially small baskets mounted over a 0.014 inch floppy wire with a steerable tip that allows the system to cross the lesion and maneuver through tortuous anatomy.20 The frame of the basket is typically constructed with self-expanding nitinol material and comes in various predetermined sizes to match the diameter of the vessel to achieve good apposition. The pore sizes can also range between 70–140 microns. Once the procedure is completed, the filters are designed to be retrieveable by collapsing within the recovery sheath to trap the debris for removal from the body. There are currently seven types of filter devices available in the U.S. They include the AccuNet System (Guidant Corp., Indianapolis, Indiana), AngioGuard XP (Cordis Corp., Miami Lakes, Florida), FilterWire EZ (Boston Scientific Corp., Natick, Massachusetts), Emboshield (Abbott Vascular, Abbott Park, Illinois), Spider RX (ev3, Inc., Plymouth, Minnesota), Interceptor Plus (Medtronic), and Rubicon Filter (Rubicon Medical Corp., Salt Lake City, Utah). The main advantage offered by the filter is the continuation of cerebral blood flow during the procedure and a much lower incidence of neurological intolerance compared to distal occlusion balloons. The main disadvantage is the filter’s larger profile and difficulty associated with deployment and retrieval in tortuous anatomy or in severely stenotic lesions. Like the distal occlusion balloon device, the filter must also first cross the lesion without any cerebral protection.
Proximal Protection Strategies
Reversal of flow. The Parodi Anti-Embolization Catheter (PAEC) (Gore and Assoc., Inc., Tempe, Arizona) is a guiding sheath with an occlusion balloon attached distally. The main lumen has an inner diameter of 7.3 Fr, which allows the working passage of balloons and stents. Once the PAEC is positioned in the common carotid artery, the external carotid artery is cannulated for the external balloon inflation to occlude flow to the external carotid artery. The occlusion balloon attached on the outer surface of the device is then connected to a sheath that is inserted percutaneously into the femoral vein to create a temporary arteriovenous shunt. This system in effect creates retrograde flow through the internal carotid artery.20,22,23 During the procedure, debris is then captured externally by a filter placed at the arteriovenous shunt. The main advantage of the system is that the brain is protected, even with the first wire crossing through the lesion. The obvious disadvantage of the system is its large size, increased incidence of neurological intolerance and the need for an additional venous sheath placement.
Interruption of flow. The MOMA device (Invatec, Roncadelle, Italy) achieves cerebral protection by temporarily interrupting cerebral blood flow by occluding both the common carotid artery and external carotid artery. This device has two integrated balloons and a working lumen for delivery of angioplasty balloons and stents.20 Similar to the PAEC, once the flow is interrupted, wire crossing is protected. The debris is essentially trapped in the stagnant column of blood and can be removed by aspiration through the working channel of the device at any time during the procedure.24 As with the PAEC and PercuSurge systems, abrupt interruption of cerebral blood flow is associated with an increased incidence of neurological intolerance. The main benefit of the device is similar to that of the PAEC system, in which complete cerebral protection is achieved prior to the first wire crossing. Similar to the PAEC, both devices require a larger guiding sheath and selecting the common carotid artery with a larger sheath for larger-profile devices also carries the risk of cerebral embolization from debris in the arch or proximal common carotid artery prior to achieving flow interruption or reversal.
Conclusion
While there is no perfect EPD that can prevent all neurological complications, the choice of EPDs should depend on the patient’s anatomy and the operator’s comfort. As demonstrated in this article, each type of EPD has specific advantages and disadvantages. While all EPDs are not equivalent, their use should be mandatory in all CAS procedures. Along with sound technique and appropriate patient and lesion selection, CAS with EPD use can be performed safely with results similar to CEA in high-risk patients.
From the Presbyterian Hospital of Dallas, Heart and Vascular Institute, Dallas, Texas.
The author reports no conflicts of interest regarding the content herein.
Manuscript submitted April 1, 2009 and final version accepted April 15, 2009.
Address for correspondence: Russell C. Lam, MD, Medical Director of Endovascular Surgery, Presbyterian Hospital of Dallas, 8220 Walnut Hill Lane, Prof. Bldg. II, Suite 616, Dallas, TX 75231. E-mail: russell_lam@yahoo.com
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