Stroke

Fall 2000
Volume 11, Number 2

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Introduction. During the past 40 years, carotid endarterectomy has become one of the most commonly performed surgical procedures in the United States. Until recently, substantial proof of its efficacy in lowering the rate of stroke has been debated vigorously. Beginning in 1991, with the publication with NASCET (North American Symptomatic Carotid Endarterectomy Trial) study, definitive criteria were established in a large scale multi-center study, which validated the efficacy of surgery for symptomatic patients.5

The results of the NASCET study clearly described a benefit in patients having either hemispheric ischemic symptoms, such as transient ischemic attack (TIA), non disabling stroke, or transient monocular blindness. For patients having such symptoms, who had carotid stenosis >70%, as determined by angiography, the stroke rate over a 2 year period following endarterectomy was lowered from 26% to 9%. In February 1998, the study collaborators group also reported subsequent data for patients with intermediate stenosis. For patients harboring symptomatic carotid stenosis of 50% or greater, a clear benefit for surgery was also substantiated. However, one caveat is that those patients who suffered from more transient monocular blindness sustained a non-significant reduction of the risk of stroke.

In 1995, the Asymptomatic Carotid Artherosclerosis Study (ACAS) released information concerning the benefit of carotid endarterectomy in asymptomatic patients harboring carotid stenosis.3 The results of this study have been debated vigorously and have resulted in the publication of a variety of position statements from a number of organizations concerning the advisability of surgery in these circumstances. The ACAS study demonstrated a reduction of the risk of stroke from approximately 10.8% to 4.8% over a 5 year period of time. This 55% reduction of risk of stroke has been quoted, but must be interpreted with caution as the risk of stroke over this time frame is relatively small even without surgery.

Although the ACAS study demonstrated this benefit for patients with carotid artery stenosis of >60%, The American Heart Association multi-disciplinary consensus group has advised that they consider it acceptable to perform a carotid endarterectomy for patients who are asymptomatic if the stenosis is 75% or greater. This must be weighted in conjunction with the patients life expectancy and their overall surgical risk from a general medical standpoint. Generally, patients over the age of 75 are not considered ideal candidates for this type of prophylactic procedure.4 The American Heart Association Consensus Statement has further classified carotid endarterectomy for asymptomatic stenosis of greater than 75% as an “uncertain indication” if they are at high risk in terms of general medical condition. Surgery should therefore be reserved for patients in whom there is a combined stroke morbidity and mortality of greater than 5% as proven and appropriate.

In light of the comparatively lower incidence of stroke in patients with asymptomatic carotid artery stenosis, it has been suggested, on the basis of the ACAS study, that surgery should only be performed by surgeons who have a combined morbidity and mortality risk in the setting of asymptomatic carotid artery stenosis of 3%. It is especially noteworthy that the ACAS study did not find a statistically significant reduction in the risk of stroke for women, a conclusion whose validity is questionable due to the small number of women in the study.

Given the fact that a carotid endarterectomy is a purely prophylactic procedure, its application should be judiciously applied, using the best available data from the literature.

Recent Trends in Carotid Artery Surgery. Usage of Pre-Operative Ultrasonography vs. Angiography. There has been considerable discussion in the past several years over the value of pre-operative angiography. Some have advocated proceeding to endarterectomy based upon carotid ultrasound, alone or in combination with either spiral CT-angiography or MR-angiography. Arguments in favor of this approach center primarily around the avoidance of morbidity associated with cerebral angiography. It is noteworthy that the NASCET researchers themselves have seriously questioned the reliability and reproducibility of carotid ultrasonography as it would pertain to the assessment of carotid artery stenosis during their study. Carotid ultrasonography is highly operator-dependent and can certainly lead to overestimation of the degree of stenosis. Eliasziw and associates performed an analysis of the prognostic significance of carotid ultrasonography. They concluded that ultrasonography should be used as a screening tool and that conventional angiography should remain an essential investigation prior to determining whether or not a patient should be considered for carotid endarterectomy.2

It is my policy to perform routine, formal 3 vessel cerebral angiography prior to considering any patient for carotid endarterectomy. In addition to satisfying the criteria put forth by the NASCET and ACAS studies, cerebral angiography also provides valuable anatomical information to assist with surgical planning and assessment of the possible need for intraoperative shunting. Further, other pathology can often be detected serendipitously, such as the presence of intracranial aneurysms and siphon stenosis.

It is not altogether uncommon to see some arteries which were determined by carotid ultrasonography to be occluded, but in fact have a string sign on angiography, thus making those patients urgent candidates for endarterectomy.

In addition to the only sporadic availability of CT angiography, its reliability is not yet well established. While MR-angiography can be a useful tool in patients with diseases such as hypersensitivity to iodine based dyes, in whom formal angiography would be contra-indicated, it carries a definite tendency toward overestimation of the degree of carotid artery stenosis.

Wong et al, analyzed 291 carotid endarterectomies performed in their region over an 18-month period. They noted that 41% of the patients who underwent surgery were asymptomatic. It was their conclusion that 20% of the patients undergoing carotid endarterectomies did so inappropriately, and the most common reason for this inappropriate application was due to overestimation of the severity of the stenosis. Moreover, they noted an incidence of complications that was higher than that reported the ACAS study in asymptomatic patients. Thus, the judicious employment of the best available data regarding the application of this procedure must be scrupulously utilized by those performing this type of surgery.6

Carotid Angioplasty and Stenting. During the past 3 years, there has been considerable debate in the stroke community regarding the application of carotid angioplasty and stenting for carotid artery stenosis. Discussion concerning this issue has been fairly acrimonious, a sentiment which has been fueled by the fact that this procedure has been applied in a considerable number of patients who were asymptomatic. To date, there have been no controlled trials to determine whether carotid angioplasty and stenting have any effect in terms of reduction of the risk of stroke in patients harboring carotid artery stenosis. Those practitioners of this technique have been fueled by the rather dramatic angiographic appearances that can be obtained and by their anecdotal reports of low incidence of complications. Nevertheless, the short and long term ability of this procedure to reduce incidence of stroke has yet to be established.

Two trials are in the process of being initiated to address this very issue. Until better data is available to determine whether or not this should be applied on a widespread basis, it remains a valuable alternative to have at our disposal in the treatment of complicated patients harboring surgically significant carotid artery stenosis. Stenting is an especially valuable tool in patients with recurrent carotid artery stenosis, in whom surgical risks run as high as 20%. Other situations in which it would be a reasonable alternative would be in the patient with an unstable angina who would be a high risk for a general anesthetic standpoint, and in patients in whom previous carotid endarterectomy has resulted in vocal cord paralysis. For the latter group of patients, the risk of a possible bilateral vocal cord paralysis is too great, as this situation would require tracheostomy and gastrostomy. Thus, until reliable data is available, stenting should be only carefully considered for highly selected patients. Moreover, this technique should be employed only by highly experienced neuroradiologists in conjunction with the involvement of either a neurologist or a neurosurgeon skilled in the management of cerebrovascular ischemic events.1

Combined Carotid and Coronary Artery Surgery. The past several years have also witnessed an increase in the application of simultaneous carotid endarterectomy and coronary artery bypass surgery. The rationale for this procedure is that if a patient harbors a critical stenosis, placing that patient on the extra corporeal pump during cardiac surgery may place that patient at risk for a hemodynamic cerebral ischemic event. The American Heart Association consensus group has classified simultaneous revascularization procedures in patients harboring asymptomatic carotid stenosis as an “uncertain indication.” If the patient is having TIA’s in the presence of carotid artery stenosis greater than 70%, they have classified this indication as acceptable, but not proven. It is my general policy to treat whichever lesion is symptomatic first, as I prefer to not engage in these types of simultaneous procedures due to the lack of definitive data.

Conclusion. The good news is that the guidelines for management of patients with carotid artery stenosis are now becoming increasingly clear. Physicians in primary care practice are key players in the quest for reducing the morbidity and mortality of stroke. Much of the nihilism of the past when caring for patients with stroke is yielding to a newer, more aggressive paradigm for the management of these patients. A strong partnership between the primary care physician, the patient, and the stroke neurologist/neurosurgeon, is critical in our collaborative battle to reduce the burden that stroke has placed upon patients and society.

Address comments and questions to:

Craig Rabb, MD
Rocky Mountain Neurosurgical Alliance, PC
701 E. Hampden Avenue, Suite 510
Englewood, CO 80113 

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