Carotid Artery Stenting: Case Selection, Training Requirements and Recommendations for a Successful Procedure

Two carotid artery stent systems consisting of a self-expanding stent and compatible embolic protection filter device have marketing clearance by the United States Food and Drug Administration (FDA). The Guidant Corporation Acculink® Carotid Stent System was granted marketing clearance by FDA on August 30, 2004 and on September 6, 2005 the Abbott Vascular Xact® Carotid Stent System received a market release decision by the FDA. The ev3 Spider Embolic Protection Device was more recently approved for use during CAS with the FDA approved Guidant RX Acculink Carotid Stent. At least five other CAS systems are currently undergoing clinical investigation or are under FDA review toward gaining marketing clearance. CAS is being used with increasing frequency and may eventually be requested over CEA as the patient population becomes more informed through promotional material, as occurred following the introduction of drug-eluting stents. The objective of this clinical update is not to debate whether CAS is better than CEA as a treatment option for symptomatic or asymptomatic patients with internal carotid artery disease but rather to define high surgical risk criteria, identify and illustrate a few patient and lesion characteristics that portend a less-than-ideal CAS outcome (high CAS risk), review current recommendations for training, and finally offer suggestions to improve the overall conduct of a CAS procedure within your catheterization laboratory. Details of the two FDA-approved CAS systems and additional filter protection device are available at the company websites or from a company representative well-prepared to demonstrate component usage and discuss the pivotal clinical trial or registry study results. CAS Patient Selection CAS eligible patients are either symptomatic or asymptomatic. Symptomatic patients typically have a positive history for a transient ischemic attack (TIA), amaurosis fugax or minor/non-disabling stroke in the hemisphere supplied by the target vessel. Common symptoms of a TIA may be any of the following: loss of vision in one or both eyes, slurred speech, weakness or numbness in a limb, facial numbness, or difficulty walking or maintaining balance. In order for these symptomatic patients to be treated under CMS guidelines, a carotid stenosis of at least 70% must be demonstrated by angiography. The treatment requirement for any asymptomatic patient is a carotid stenosis of at least 80% by angiography. These patients are typically referred for evaluation following a Doppler ultrasound (DUS) study, computed tomography angiogram (CTA) or magnetic resonance imaging (MRI). Increased Surgical Risk Patients - Anatomical and Clinical Predictors Table 1 summarizes the CMS and FDA trial guidelines for treating patients with carotid artery disease who are symptomatic or asymptomatic. The FDA-labeled criteria comprise individuals who have consented to participate in a company-sponsored, FDA-regulated clinical trial conducted under a Category B Investigational Device Exemption (IDE). It is important to understand that all CAS-eligible patients must be at increased risk of complications should they undergo a surgical CEA procedure. In order for a CAS patient to be eligible for CMS reimbursement, a statement in the patient’s medical record must clearly define the high surgical risk criteria and symptoms of carotid artery stenosis for that patient. For CAS patients treated under an IDE clinical trial or post market surveillance study, clarification as to why they are being treated should likewise be well defined. The ICD-9-CM procedure codes for carotid artery stenting procedures are a combination of 00.061 for Extracranial PTA and 00.63 for Insertion of Carotid Stent. High surgical risk characteristics are best divided into anatomic and clinical classifications. Many patients requiring treatment of carotid artery disease are elderly, and comorbidities increase the risk of complications from any surgical or endovascular procedure. Table 2 presents established features known to increase the risk of complications following a CEA procedure. Increased CAS Risk Patients- Anatomical and Clinical Predictors The ideal CAS patient is asymptomatic, less than 80 years of age, has well-managed blood pressure, and presents with normal aortic arch and cervicocerebral anatomy, and non-calcified focal stenotic disease within the proximal internal carotid artery. Some patients are not good candidates for CEA or CAS; these are patients that need to be carefully evaluated and probably deferred to best medical therapy only. Increased age frequently presents more complex anatomy with elongation and a more posterior orientation of the arch and great vessels. Calcification within the aortic arch and origin of the left common carotid or brachiocephalic arteries may complicate guide wire or guide catheter placement, sheath advancement, or protection device deployment and subsequent stenting and device retrieval. Vessel tortuosity and the presence of loops or kinks within the internal carotid artery proximal or distal to a target lesion are more prevalent in the elderly patient. Acute bends not only make access difficult but also, more importantly, preclude placement of a filter device requiring a relatively straight access and 3 cm or more of straight artery for deployment. Having deployed a filter device distal to tortuous anatomy, the later advancement of a retrieval catheter may become problematic. Table 3 completes the list of anatomic and physiologic features that should dissuade continuation of a CAS procedure and encourage optimal medical management without further intervention. Physician Training for CAS The CMS decision memorandum requires each institution intending to perform CAS to establish written standards to determine competency of each physician performing the CAS procedure, required facility angiographic equipment, post procedure patient care requirements and data collection with biannual reporting to CMS to evaluate outcomes overtime. A minimum standards model is defined based on professional society statements on competency. Each facility is required to meet CMS standards in order to receive coverage for carotid artery stenting for high risk surgical patients. Hospitals that have demonstrated an acceptable competency and met the CMS’s minimum facility standards for performing carotid artery stenting for high risk patients are listed at the CMS website. A clinical competence statement by the Society of Cerebral Angiography and Interventions, the Society of Vascular Medicine and Biology, and the Society for Vascular Surgery is one of two position papers on clinical competence requirements for CAS. There is discordance between the two position papers as to the number (30 - 200) of diagnostic cerebrovascular angiograms a physician should successfully perform and number (25 -10) of supervised CAS procedures required to demonstrate competence with the CAS procedure. The actual number of supervised procedures required for CAS credentialing will ultimately be determined by the hospital IRB/ethics committee and department chairman. Simulator-based training has also become an important component of physician training for CAS, with companies offering and in some cases requiring completion of simulated CAS procedures. Steps Toward a Successful CAS Procedure Each CAS procedure should be performed with alacrity and Alan in order for these elements to be present, everyone must work as a team to ensure efficient use of time, quick access to the required guidewires, guide catheters, balloon catheters, stents, and proper use of the embolic protection system components. There is no alternative to appropriate training followed by careful selection of patients for this procedure. Currently, excellent training programs are provided by industry to facilitate the best possible support for their devices in use of CAS, e.g., Abbott Vascular Regional Center of Excellence and online training. Similar programs are planned by other vendors for their device training, pending approval of their device by FDA. Suggestions toward a successful procedure include: 1. Be familiar with the embolic protection and stent delivery systems, specifically preparation, deployment, and retrieval. 2. Plan ahead. Ensure pre/post dilation balloons are readily available along with requisite guide wires and guide catheters or sheaths. Know the size requirements of the various systems. 3. Be familiar with the pharmacologic requirements of a CAS procedure and have medications prepared according to cath lab protocols before the case starts. 4. Dedicate a nurse to patient care and monitoring. Talk to the patient before any sedation to appreciate their ability to talk, hear, see, etc. Does the patient wear a hearing aid? Perhaps the patient should leave it in during procedure to allow for conversation and awareness of commands. 5. Anticoagulation and antiplatelet therapy. Ensure patient has taken aspirin and Plavix at least 4 hours before the start of the procedure. Know what anticoagulation the physician will be using and be familiar with dosing requirements. 6. Elapsed time is important during a CAS procedure. Shorter embolic protection device deployment times appear to be helpful in reducing the incidence of peri procedural adverse MACCE. 7. Don’t stent pseudospasm. Pull back the guide or sheath to relieve axial stress on artery. Conclusion When performed using meticulous technique in the right patient to treat the appropriate lesion, CAS is an excellent alternative to CEA for the treatment of atherosclerotic carotid artery disease. The long and longer term durability of this endovascular procedure relative to that achieved for CEA will be determined over the next few years as many high and low surgical risk registries and randomized trials conclude enrollment and enter into requisite 3- to 5-year follow-up and reporting. We look forward to learning these results and hopefully a broader acceptance of CAS as a reasonable and necessary, and safe and effective stroke preventative treatment for symptomatic and asymptomatic patients with carotid artery disease. Dr. Dave can be contacted at rdintervention @ yahoo. com

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