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Cartoid Endarterectomy: An Established Standard for Acute and Chronic Prevention of Stroke

David H. Deaton, MD, FACS
David H. Deaton, MD, FACS
It is important to note that the proof of carotid endarterectomy had little to do with acute results but rather the outcome over a period of years following the procedure.6 While the surgical techniques that are the foundation of carotid endarterectomy have changed little, the patient selection, intraprocedural cerebral monitoring and post-procedural follow-up and care have been greatly refined. While the debate about the rates of acute success with interventional techniques rages on, we should not forget the lessons amply demonstrated throughout the lengthy and rigorous development of carotid endarterectomy: 1) Careful patient evaluation and selection; 2) Specialized clinical and surgical training and practice, and; 3) Careful follow-up and outcomes analysis. The Nature of Prophylactic Therapy for Cerebrovascular Disease Unlike therapy for coronary and most other peripheral vascular occlusive disease, the critical aspect of extracranial cerebrovascular disease is not chronic ischemia and lack of blood flow, for which stents were designed, but rather embolic events. While we continue to use degree of stenosis as a primary objective finding in the evaluation of appropriate candidates for therapy, it is symptoms that are the most predictive finding. We still do not have the ability to determine the nature of plaque stability, nor have we developed an understanding of the critical events that transform a dormant lesion into an active lesion with acute changes and embolic phenomena. The results of therapy directed at removing the plaque (i.e. endarterectomy), rather than trying to stabilize it or cage it with a stent, are independent of our fundamental lack of knowledge about plaque behavior and composition. All therapy for extracranial cerebrovascular disease is prophylactic. Indeed, one must successfully treat over twenty patients with asymptomatic disease to positively affect the outcome of one. Control is the name of the game. Given our inability to determine the fragility and embolic potential of a given plaque, reducing the potential for manipulation of the plaque is a cornerstone of any technique with the potential to achieve very low or below single-digit procedural embolic rates. A single percent increase in stroke or death can negate the efficacy of therapy directed at the carotid bifurcation. It is for that very reason that most centers with high volume have improved their results by avoiding any interventional diagnostic techniques.7-9 The ACAS study demonstrated this best with a stroke rate of 1.2% after diagnostic cerebral angiography.4 Our lack of understanding regarding the characterization and behavior of the plaque itself is fundamental to the principles of not manipulating the plaque in any way until the distal circulatory bed has been protected and in removing the entire plaque. The Physiologic Basis for Carotid Endarterectomy Open surgical exposure of the carotid bifurcation represents a very small physiologic insult to the patient with subcutaneous exposure of the carotid bifurcation that can be done with either local or general anesthesia. Numerous centers use local anesthesia preferentially (i.e. >95% cases). The procedure allows for the maximum amount of control by employing distal control of the internal carotid, reversal of flow in the internal carotid prior to restoring antegrade flow, visual inspection and debridement of the plaque site and control of the proximal and distal endpoints of the endarterectomy. The results of endarterectomy are uniform despite the nature of the lesion (i.e. soft versus calcific), its morphology (i.e. tapering, globular, ulcerated) or the tortuosity of the artery itself. Carotid endarterectomy is based on four fundamental strengths: 1) Control - easily and reliably achieved without additional manipulation 2) Plaque Removal -complete removal of embolic lesion engenders freedom from the poorly understood variables of plaque composition and vagaries of anatomic configuration 3) Lumen Size Enlargement - the endarterectomized vessel is > 100% of native vessel and enhanced further with frequent patch angioplasty, providing redundancy in the prevention of restenosis 4) Minimal Physiologic Insult - focused and predictable location and subcutaneous exposure allow local anesthetics with few cardiac or pulmonary sequelae Current Status of Carotid Endarterectomy Carotid endarterectomy is performed increasingly by surgeons specifically trained and professionally dedicated to peripheral vascular surgery. Most patients in centers with a significant volume of carotid endarterectomy have a completely non-invasive evaluation with duplex ultrasound prior to surgery. The procedure is predicated on initial control of the internal carotid distal to the embolizing lesion, commonly referred to as distal protection in the interventional literature. The offending lesion is entirely removed and the arteriotomy is typically widened by sewing a prosthetic or autogenous patch into the longitudinal defect. This results in a disease-free carotid bifurcation that is typically well over 100% of the lumen of the native carotid bifurcation providing for redundancy in the face of intimal hyperplasia. The typical admission involves arrival at the hospital on the day of surgery, a procedure of one to two hours under local or general anesthetic, a brief stay in the recovery room and a single night in a non-ICU inpatient bed. After discharge, patients can resume all of their normal activities within 1-2 weeks. Fewer than 2% of patients will ever need intervention for the endarterectomized site within their lifetime. The economic impact of this definitive care requires only routine hospitalization and physician care costs (i.e. no expensive medical devices) and has been demonstrated to be cost effective,10 In the rare case that they require an additional procedure, both operative and interventional means are available without significant additional risk.11 The Real World of Carotid Stenting Interventional techniques for carotid therapy continue to develop rapidly. Typically they are compared to the most unfavorable figures available in the medical literature for carotid endarterectomy. There are numerous published series with over 100 consecutive cases of elective carotid endarterectomy or state-wide registries with stroke rates of 3% or less.12-14 There are surgical series with acute stroke rates less than 1% and 5-year follow-up documenting 6 While cranial nerve palsy is a potential complication of carotid endarterectomy, this small group of patients usually experiences only a very mild and transient palsy from operative nerve retraction and protection. There are complications that are unique to a remote approach to the carotid bifurcation. These include femoral access site complications, lower extremity ischemic and embolic events, renal and visceral embolic events, cerebrovascular emboli via the non-operated carotid and vertebral vessels and the arrythmias induced by stenting the baroreceptor at the carotid bifurcation. These complications are rarely reported as they are unique to carotid stenting and are therefore not characterized in the literature of carotid endarterectomy, which is used as the predicate for carotid stenting. Stenting of the baroreceptor at the carotid bifurcation alone results in a significant incidence of bradycardia, requiring i.v. medications and ICU admission. Indeed, in my experience, most series have a higher rate of ICU admission and multi-day admission for stenting than is typical for endarterectomy. The primary method of intervention (i.e. dilatation and plaque disruption) produces the very emboli known to be responsible for cerebral events in patients with carotid bifurcation disease. Studies with transcranial doppler have documented an 8-fold increase in emboli during angioplasty and stenting procedures versus carotid endarterectomy.15 While there is a great deal of work on new protection devices, their efficacy is far from proven. The addition of each new device and technical aspect to a procedure predicated on simplicity and control adds new risks and failure modes, not to mention additional cost. While the arguments for the expectation of a low restenosis rate are good (i.e. high flow, large lumen, short diameter) there are also significant unknowns that may well affect the rate of restenosis in the carotid. These include the interaction of stent design and construction (i.e. rigidity, cell size, metal composition) with an often tortuous vessel in a mobile and compressible location. We also know that stent apposition, a known risk factor for restenosis, is often poor at a bifurcation where there is a sudden and dramatic change in lumen diameter at the transition from the common carotid to the internal carotid. There is a well-documented history of restenosis at the end of stents (i.e. edge effect) that has not been characterized in the carotid application. Given the current application of carotid stenting, this will often occur well distal in the internal carotid near the skull base. When restenosis occurs, the options are significantly impaired versus the options following endarterectomy. Surgical exposure often requires a far more radical and extensive exposure of the carotid vasculature, particularly the more difficult cephalad portion near the skull base.16 Repeat interventional therapy is limited to adding another stent or attempts at redilatation. The Case for a Measured Approach Carotid stenting has achieved more success than most of its proponents and opponents would have imagined ten years ago. Having said that, it is far from mature and its development, refinement and integration into common clinical practice is likely to parallel the timeline of other procedures (i.e. several decades). Carotid endarterectomy is one of the most highly scrutinized, studied and ultimately successful operative procedures available. Given this fact, carotid stenting is most aptly suited to patients with higher risk factors for surgical exposure of the carotid (i.e. prior radiation, prior carotid surgery, adjacent stomas, skull base lesions, etc.). Clinical trials in groups without those risk factors will ultimately determine the role of stenting in those patients. Other distinct patient groups will likely be delineated as reasonable candidates for primary carotid stenting but we’re also likely to find those who are at distinctly higher risk for carotid stenting (i.e. tortuous carotids, bulky irregular lesions, longer lesions, certain calcific lesions). The case for endovascular approaches to coronary occlusive disease or aortic aneurysms is far more compelling on an acute basis, as the open surgical alternative is a much more invasive and morbid option. This is not the case for carotid intervention. In fact, open carotid surgery is less invasive with respect to the diseased vascular tissue manipulated than is the transfemoral approach. Indeed, time to discharge and ICU stay are still less for carotid endarterectomy than for carotid stenting. The cost of carotid endarterectomy is stable and low while carotid stenting expenses continue to grow with the addition of distal protection devices and the advent of drug-coated stent technology. While developments in the technical aspects of carotid stenting are ongoing, equal attention must be focused on the integration of the necessary pre- and postoperative clinical care required to achieve optimal results in cerebrovascular reconstruction. The role of diagnostic procedures prior to the therapeutic procedure cannot be underestimated as to their impact on complications and patient selection. Patients must be adequately educated by clinicians skilled in both endovascular and open vascular reconstruction prior to making a decision about this prophylactic procedure. After the procedure, the patient must be carefully followed by a skilled clinical team with routine ultrasound examinations of the carotid vasculature, and careful history and physical examination to note any changes that might warrant CT or MRI imaging of the brain. Until we understand the magnitude of the new complications engendered by a remote endovascular approach to the carotid bifurcation and the true degree of conventional complications in comparable patient groups over an accepted period of rigorous follow-up, we cannot adopt carotid stenting as a first-line therapy. Carotid stenting will continue to have an excellent environment for development. Vigorous support from medical device manufacturers, patients with anatomic risk factors for open surgical repair (e.g. prior CEA, radiation, stomas, high lesions, etc.), and increased participation in endovascular therapy by clinicians with primary clinical training in the care of patients with cerebrovascular disease will all fuel the appropriate and rational approach to this new method of therapy. Conventional endarterectomy will continue to be regarded as the standard of care by most experienced clinicians and leaves open the possibility for future endovascular therapy for the few patients that experience clinically significant recurrent disease.
References
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