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Carotid Endarterectomy - A Surgical Perspective
Roberto C. Heros, M.D.
Symptomatic carotid stenosis
Asymptomatic carotid stenosis
Personal perspective on carotid angioplasty with or without stenting
A. Symptomatic carotid stenosis.
Three major prospective randomized trials reported during this decade have proven conclusively that carotid endarterectomy, as performed in these trials, is an extremely effective operation in the prevention of future stroke and death from stroke in patients who have more than 70% stenosis and who have had recent transient cerebral or retinal ischemic events or a recent stroke with good recovery [6,8,11]. Additionally, we found that, when taking long term costs into account, carotid endarterectomy in symptomatic patients is not only highly effective, but is also extremely cost-efficient when compared to conservative therapy . Some caveats about these results must be acknowledged. The first is that the surgeons participating in these trials were highly experienced with the operation and in fact, were selected for participation because of their experience and good results. Therefore, the relatively low surgical morbidity and mortality encountered in these trials, which ranged from 3 to 5%, may not be representative of the morbidity and mortality encountered by all surgeons currently performing this operation. The second caveat is that the patients selected for randomization were all relatively good surgical risks and did not have major medical co-morbidities known to be associated with a significantly increased surgical risk.
A more recent analysis of the North American Symptomatic Carotid Endarterectomy Trial (NASCET) has indicated that there is also some advantage gained by performing the operation in patients who have 50 to 69% stenosis, but the benefit in this group is only marginal and therefore, individual judgment on a case by case basis must be exercised . There appears to be no significant benefit for patients with less than 50% stenosis.
My own personal bias is to recommend endarterectomy to symptomatic patients with more than 70% stenosis provided that they are in relatively good medical condition and have a reasonable life expectancy. Thus, very elderly or debilitated patients, patients with major medical co-morbidities and patients with severely life-threatening diseases would generally not be considered for endarterectomy. Symptomatic patients with 50 to 70% stenosis are selectively considered for endarterectomy only if they are in excellent medical condition and if they are relatively young. Patients with less than 50% stenosis are not considered for endarterectomy unless they have a plaque with major ulceration and they have been severely symptomatic (multiple TIAs or a recent serious stroke with good recovery).
Before leaving the general heading of symptomatic carotid stenosis, we must emphasize the fact that "symptomatic" refers to definite symptoms of ipsilateral (referable to the cerebral hemisphere supplied by that carotid artery) symptoms that are specific to the vascular territory of the involved carotid artery. This includes cerebral hemispheric symptoms such as numbness and weakness in the contralateral side of the body with can include some degree of dysarthria when the non-dominant cerebral hemisphere is involved and aphasia when the dominant side is involved. The symptoms may be rapidly reversible (transient ischemic attacks) or fixed with variable degrees of recovery when cerebral infarction takes place. When the retina is involved, the symptoms are also unilateral and could be transient (transient monocular blindness) or permanent as it occurs with retinal infarction from emboli from the carotid plaque to the central retinal artery or its branches. Non-specific symptoms such as dizziness, fainting, memory loss, intellectual decline, vertigo, bilateral visual blurring, vague visual disturbances such as due to floaters, etc. are not generally related to carotid artery disease. Likewise, specific vertebrobasilar ischemic symptoms such as diplopia, alternating hemiparesis or hemisensory loss (involving both sides of the body), spells of vertigo associated with other specific symptoms of brainstem dysfunction such as diplopia, dysarthria, dysphagia, etc. are clearly not related to the carotid artery. Vertebrobasilar ischemic symptoms are not an indication for carotid endarterectomy except in the extremely rare circumstance that the involved carotid artery supplies the basilar circulation such as can occur in patients with bilateral vertebral occlusion or where one vertebral artery is occluded and the other ends up as a posterior inferior cerebellar artery without reaching the basilar circulation. Spells of transient global amnesia and falling spells in elderly individuals not associated with any other specific symptoms have even a less certain etiology and clearly should not be related to carotid disease.
B. Asymptomatic carotid stenosis.
Although there had been several previous reports suggesting a benefit for carotid endarterectomy on asymptomatic patients, it was not established that carotid endarterectomy was of definite value in asymptomatic patients until the relatively recent report of the large trial supported the National Institute of Neurological Disorders and Stroke was reported . In this study, patients with greater than 60% stenosis, who were relatively good surgical risks, were randomized to either endarterectomy or medical treatment, generally with aspirin. Over a five-year period, the risk of stroke was 4.8% after surgery and 10.6% with medical management. Clearly, the benefit for surgery in this group of patients (asymptomatic from their carotid disease) was only marginal and of a much lesser magnitude than what was found for symptomatic patients who had an average risk of stroke of about 26% over a two year period when managed medically. The same caveats mentioned above for the symptomatic trials apply to the asymptomatic trial, which also selected for randomization only patients who were good surgical risks and where the operations were also performed by highly experienced surgeons who were able to achieve a combined morbidity and mortality rate averaging less than 3%.
My own personal bias is to treat most asymptomatic patients conservatively with periodic non-invasive studies. Endarterectomy is then recommended when there is clear progression of the degree of stenosis in periodic follow-ups by the same reliable non-invasive laboratory and, particularly when the stenosis reaches the 70% mark or, of course, if the patient becomes symptomatic. Endarterectomy at initial presentation (when the stenosis is first detected) is only offered to very healthy patients who are relatively young and who have severe stenosis of generally more than 80%. This reliance on the degree of stenosis is based on the fact that in the trials on symptomatic patients, particularly in the NACSET study, it was clearly shown that the more severe the degree of stenosis, the greater the risk was for patients treated conservatively. Unfortunately, in the asymptomatic trial, this type of subgroup analysis did not yield the same direct relationship between the degree of stenosis and risk for stroke; however the numbers in the subgrouop were relatively small.
C. Other indications.
We occasionally consider carotid endarterectomy for indications that have not been definitely established by properly designed scientific studies. For example, we have performed a number of emergency carotid endarterectomies in patients with acute major stroke [9,14]. When we have compared our results with historical studies of the natural history of the disease, we have concluded that it is likely that the operation may be of benefit under highly selective circumstances which include patients that develop a major deficit while hospitalized or patients that present to the hospital within the first hour or two after their stroke where the endarterectomy can be performed within six hours of the onset of the deficit. Additionally, it is clear that patients who are drowsy or stuporous or who already show an abnormality on the CT scan at the time of presentation do not do well with emergency endarterectomy. Another circumstance under which we have used endarterectomy is in patients with recent complete occlusion of the internal carotid artery who angiographically show good retrograde flow in the proximal intracranial portion of the internal carotid artery via external carotid to ophthalmic collaterals. In the great majority of these patients, the internal carotid artery can be re-opened when the endarterectomy is performed within the first few days after carotid occlusion . We have also infrequently performed external carotid endarterectomies in patients with complete occlusion of the internal carotid artery when there is significant stenosis of an external carotid artery that provides significant collateral intracranial flow . In the past, we performed a few carotid endarterectomies in patients with acute carotid dissection, but the results were not satisfactory and for the last several years, we have chosen to treat these patients conservatively, usually with major anticoagulants for at least three months. Rarely I have preformed a carotid endarterectomy on patients who have significant stenosis of one internal carotid artery with the other internal carotid artery being completely occluded and who are experiencing general intellectual and/or psychosocial decline which could be vaguely ascribed to "cerebral hypoperfusion".
It is not appropriate to describe in detail our technique for carotid endarterectomy in this conference. Generally, we use general anesthesia and EEG monitoring. We use a vascular shunt during clamp occlusion when the EEG changes significantly; this occurs in approximately 10 to 20% of all patients, but this percentage goes up to 20 to 30% in patients who have contralateral internal carotid artery occlusion. Other surgeons prefer to use a shunt routinely, which obviates the need for monitoring. Others advocate performing the operation without monitoring and without shunting. The results have not been significantly different in anecdotal reports of these different techniques . It should be stated that carotid endarterectomy is a technically demanding operation that requires exquisite attention to technical detail. Having performed over a thousand carotid endarterectomies, I rarely go through more than a handful of cases without encountering at least one that becomes a very difficult technical challenge. This challenge frequently arises when the plane between the normal wall of the artery and the plaque is not sharply defined, when the bifurcation is very high, particularly if a shunt is needed, when the plaque extends for a long distance along the internal carotid artery, when the distal end of the plaque cannot be removed smoothly or when the anatomy is reversed in such a fashion that the internal carotid artery is medial to the external carotid rather than in the usual more posterolateral location.
We alluded above to the results of endarterectomy in the large randomized trials of symptomatic and asymptomatic carotid stenosis. Our own personal results are similar. In patients with TIAs, we have encountered a combined mortality and permanent neurologic morbidity of approximately 3% (1% mortality, 1% major stroke and 1% minor stroke) [3,12]. There has also been a significant number of other less disabling complications including neck hematomas and mild cranial nerve palsies. Our combined morbidity and mortality rate has been approximately twice as high when operating in patients with recent stroke . Comparable results have been reported from many centers with significant experience with the operation. However, there have been some disturbing reports of morbidity rates in the order of 15 to 18% when all endarterectomies performed in the community are analyzed by independent observers [2,4] .
In addition to death, usually from myocardial infarction or from a major stroke, and significant neurologic morbidity from stroke, there are other complications of carotid endarterectomy. The most serious one is myocardial infarction which occurs with a frequency of approximately 1 to 2% of patients in spite of exclusion of patients with severely symptomatic coronary disease for endarterectomy. Significant neck hematoma, related to the need for anticoagulation during endarterectomy, occurs with some frequency and requires surgical re-exploration in approximately 2 to 4% of the patients. Cranial nerve palsies, particularly of the superior laryngeal and hypoglossal nerves also occur in a small percentage of patients. More rarely, significant dysfunction of the accessory or recurrent laryngeal nerve has been noted. Other less disabling medical complications such as atelectasis, pneumonia and thrombophlebitis occur, as may be expected, in the age group where this operation is generally performed.
Personal perspective on carotid angioplasty with or without stenting
It is my impression that at the present time, the anecdotally reported morbidity and mortality attending carotid angioplasty and stenting is higher than that generally reported by experienced surgeons including those participating in the large, randomized studies . However, it is clear that generally the patients that have been selected for angioplasty with or without stenting have been "high risk" patients that frequently would have been rejected for carotid endarterectomy. It is also clear that the technology is evolving rapidly and that undoubtedly, the results will improve as more experience is achieved. However, as the procedure becomes more generally available and widely practiced, experience will be diluted and, as it is the case with carotid endarterectomy, a higher morbidity and mortality rate will be expected at centers where the procedure is performed only occasionally. We feel that the time is ripe for a carefully designed randomized study comparing carotid endarterectomy with carotid angioplasty, probably with stenting, in a selected group of patients that generally will be considered to be higher than normal risk for endarterectomy. At the present time, it is my opinion that the reported results of angioplasty and stenting are not comparable to those achieved in patients that are generally thought to have low risk for carotid endarterectomy and therefore, it may not be ethically appropriate to randomize this group of patient (no significant medical problems, relatively young age and without significant neurologic or angiographic "risk factors" for endarterectomy recent stroke, contralateral carotid occlusion, very high carotid bifurcation, a plaque extending to the skull base, etc. - ). Pending the results of such randomized trials, we currently consider angioplasty and stenting in patients who present with major medical co-morbidities which would present a significant risk for carotid endarterectomy, in patients who have recurrent carotid stenosis after endarterectomy, in patients who have carotid stenosis in association with previous irradiation of the neck and in patients who have angiographically-detectable risk factors such as an extremely high carotid bifurcation, a plaque that extends to the base of the skull or a plaque that extends into a significant kink in the internal carotid artery.
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