Editors: Norris, John W.; Hachinski, Vladimir
Title: Stroke Prevention, 1st Edition
Copyright 2001 Oxford University Press
> Table of Contents > II - Secondary Prevention > 12 - Surgical Measures to Prevent Stroke
Surgical Measures to Prevent Stroke
H. J.M. Barnett
Heather E. Meldrum
Surgical repair of injured arteries on the battlefields World War II set the stage for a surgical attack on arteries to the limbs, the heart, and the brain narrowed by arteriosclerosis. The cervical portion of the internal carotid artery had been shown by Egaz Moniz, the father of angiography, the pathological studies G.T.J. Hultquist, and by the dedicated studies by C. Miller Fisher of the neck arteries at post-mortem to be a commoner site of obstruction than had previously been accepted.1,2,3 The middle cerebral artery, instead of being seen as the primary site of arteriosclerotic mischief, came to be regarded as the artery most commonly causing stroke from lodgment of cardiac and extracranial carotid embolic material. Except in Asian populations, the middle cerebral artery was no longer accepted as the primary site of obstruction due to arteriosclerosis.
As Goethe remarked, What one knows, sees. Quite quickly, an explosion of reports confirmed Moniz's, Hultquist's, and Fisher's observations. As more arterial lesions were identified in the neck, the phenomena of transient and recurrent ischemic events came to light. The stage was set for attempts forestall, by antithrombotics and surgical methods, the strokes threatened these transient events of cerebral and retinal ischemia. This chapter confines itself to the evolution of understanding the appropriate use of surgical measures to prevent stroke.
Development of Carotid Artery Surgery
The credit for the first carotid surgical attempt to prevent ischemic stroke must go to Eastcott, Pickering, and Rob.4 They were the first to publish a report in a peer-reviewed journal, the gold currency of scientific activity. Carotid endarterectomy (CE) quickly replaced localized carotid resection. Many surgeons learned the technique. Neurologists and other practitioners became aware of the significance of focal hemisphere and retinal events. By 1974, 15,000 carotid procedures had been done in the non-veteran hospitals of United States. A small, randomized trial of 316 patients reported results in 1970 that were far from encouraging.5 Too many patients (42%) had vertebral basilar, rather than carotid, symptoms, loss to follow-up was higher than desirable, and the perioperative complication rate was unacceptable (11%).
Despite this negative trial, enthusiasm persisted. It still appeared to be a logical procedure for preventing stroke. Other applications of the were introduced that led to its expanded use. One application arose from the hypothesis that nonspecific symptoms, such as dizziness, vertigo, drop attacks, episodes of loss of consciousness, transitory memory difficulties, and even specific symptoms of vertebral basilar disease, might benefit from a general improvement in blood flowing to the brain by removing the accessible stenoses from diseased carotid arteries. As many as 10% of the increasing number of endarterectomies may have related to this improbable and unproven hypothesis. Another practice that became common was to remove an asymptomatic stenosing plaque as a prelude to major cardiovascular operations, particularly coronary artery bypass grafting. More importantly, the use of the procedure was extended to asymptomatic individuals with carotid artery stenosis. This custom is discussed in detail later in the chapter.
Another innovation was the introduction of ultrasound as an alternative diagnostic tool to be used instead of or with angiography. Safe and noninvasive, it became widely available and very extensively used. More will be said of this but its complete role in patient selection remains uncertain and in some dispute.
In the 11 years between 1974 and 1985, it was estimated that one million individuals worldwide had carotid endarterectomy.6 Figure 12.1 illustrates that enthusiasm increased dramatically in this 11-year period. With doubts expressed about proof of its suitability for its widespread application, the numbers waned for a few years. They doubled again within two or three years of the completion of published trials because of an optimistic interpretation the trial results. By 1999, it was quite certain that two million carotid endarterectomies had been performed worldwide and that a reasonably large number of these (probably at least one-third) were done without firm substantiating evidence, some in situations which the harm may have exceeded benefit.
FIGURE 12.1. The number of endarterectomies performed annually from 1970 to 1995 indicates a decline after 1985, followed by a doubling after the publication of the first phase of NASCET and ECST the final results of ACAS. Adapted from Pokras R., personal communication with permission.
Later Trials of Carotid Endarterectomy
To fulfill the demands of modern scientific medicine, particularly when the course of a chronic disease is unpredictable and has protean outcomes, therapeutic data must be amassed from randomized trials that are designed, executed, and analyzed to answer the appropriate questions. Three such trials were launched and concluded to evaluate the role of CE in patients with symptomatic disease.7,8,9 Two of these three trials prospectively followed the stroke outcomes relating to the stenosing lesions on the asymptomatic other side. Five were launched for asymptomatic individuals, of which four are concluded and published.10,11,12,13,14 Finally, a study in which symptomatic patients and asymptomatic subjects were randomized to determine the optimum perioperative dose of aspirin allowed some observations to be made about asymptomatic disease.15
In 1981, Warlow and colleagues took up the challenge of appropriateness carotid endarterectomy and from the United Kingdom launched an ambitious trial. The European Carotid Surgery Trial (ECST)7 required that patients have symptoms within 180 days and have angiographic proof of a stenosis caused by arteriosclerosis. Two patients were randomized to receive endarterectomy for
The other large trial, the North American Symptomatic Carotid Endarterectomy Trial (NASCET), 8 randomized 2885 patients between 1987 and 1996. All patients were required to have had recent (120 days for the first 30 months of the trial, 180 days thereafter) focal symptoms appropriate to an angiographically demonstrated stenosing lesion. Surgeons were required to produce evidence of experience and competence in the performance of CE. For each center, randomization
TABLE 12.1. Correlation of NASCET and ECST Measurements of % Stenosis
FIGURE 12.2. NASCET calculated the percentage of stenosis by using narrowest linear diameter in two (or three) planes as the numerator, and the artery well beyond the carotid bulb (circled) and any poststenotic dilatation as the denominator (closed arrow) (1 N/D 100 = % stenosis). Measurement of the artery too close to bulb produced a misleading denominator (asterisk). The European Carotid Surgery Trial (ECST) used the same numerator but took the imagined site of the wall carotid bulb as denominator. Reproduced with permission from
Barnett et al. Current Critical Problems in Vascular Surgery, St. Louis, MO: Quality Medical Publishing, 1994.
Best medical care included therapy to normalize blood pressure, cholesterol, and blood sugar and advice about the avoidance of tobacco. Enteric-coated aspirin was supplied to all NASCET patients at a recommended dosage of 1300 mg daily. Lesser amounts were discretionary, as was the use of other platelet inhibitors. Excluded were patients with symptoms due to nonarteriosclerotic disease of the carotid arteries, previous endarterectomy on symptomatic side, heart disease likely to be associated with early cerebral embolic events, and organ failure or other morbid illnesses likely to cause death within five years. Outcome events in NASCET were adjudicated by independent clinicians blinded to the treatment arm. Data were gathered at entry and at the time of outcome events to assist the NASCET investigators in determining cause, severity, and course of stroke and particularly in identifying the occurrences of hemorrhagic, large artery, lacunar, or cardioembolic stroke.
In neither ECST nor NASCET was ultrasound evaluation alone acceptable for randomization. It was encouraged in the preliminary screening of potential candidates, and in NASCET was performed at the first follow-up after CE and requested annually in all patients.
The third symptomatic trial, confined to 16 Veterans Affairs (VA) Medical Centers in the United States, randomized 189 symptomatic patients with >50% stenosis
The Results of the Trials for Symptomatic Patients
The benefit of CE was similar in the two large trials. Figure 12.3 demonstrates the five-year Kaplan-Meier survival curves from NASCET for any stroke and death and for disabling stroke death in the patients 70% 99% the 50% 69% stenosis range. It is clear that patients with focal symptoms who have severe (70% 99%) stenosis benefit most from the procedure. In the patients with moderate stenosis, the confidence intervals overlap, and the benefit, although present at a p-value of 0.045, is muted.
Several conditions were identified in post-hoc observations of perioperative risk from CE that led to a doubling, or near doubling, of the likelihood postoperative outcome complications.16 They included a hemispheric TIA compared with a retinal TIA as the qualifying event, left-sided procedure, the presence of contralateral carotid occlusion, an ipsilateral ischemic lesion on the entry CT scan, and irregular or ulcerated plaque detected by angiography on the side of surgery and a lack of collateral circulation in the hemisphere beyond severe (70% 99%) symptomatic stenosis.17 Despite imposing an increase in risk at the time of the procedure, none these conditions contraindicate CE because, in long-term follow-up of patients with both severe and moderate stenosis, these variables did not eliminate the benefit favoring surgery. The most unexpected of these observations was the increased complication rate for left-sided lesions. The initial impression was that this could be due to a statistical spin of chance. This probably is not the explanation, as it has been encountered in two other series of patients submitted to CE.15,18 In patients who had contralateral occlusion (n = 43), the operative risk was tripled (14%) compared to those patients without contralateral occlusion. Treated medically, patients with this condition have a 69% risk of stroke in two years compared to 29% for patients without contralateral occlusion.19
FIGURE 12.3. (A) Kaplan-Meier curves for event-free survival of medical and surgical patients with severe (70% 99%) stenosis. The results favor endarterectomy for any ipsilateral stroke and disabling ipsilateral (p < 0.001). The 95% confidence intervals are shown for each curve and there is no overlap. The number at risk annually are shown out to 8 years, (b) Kaplan-Meier curves for event-free survival of medical and surgical patients with moderate stenosis (50% 69%). The results favor endarterectomy (p = 0.045), but the confidence intervals overlap throughout, muting importance of the statistical significance. The results for disabling stroke showed no benefit. Reproduced by permission of the New England Journal of Medicine.8
In the severe range (70% 90%), all risk subgroups benefited from procedure. In the moderate range (50% 69%), best results were detected in males, patients with tandem lesions (intracranial disease), in patients with hemisphere rather than retinal symptoms, and in patients presenting with a stroke rather than only transient ischemic attack (TIA). Below 50% stenosis, symptomatic patients received no benefit and were best treated with medical care; the ECST study found that these individuals were significantly worse off with CE than with best medical care.
For patients at ranges of stenosis <60%, 60% 69%, and 70% 99%, outcomes were analyzed as to cause of stroke (large artery, lacunar, or cardioembolic in origin). The breakpoint at 60% was used because this was the minimal degree of stenosis in the Asymptomatic Carotid Atherosclerosis Study (ACAS) trial, and above it a benefit had been claimed for asymptomatic individuals from CE. In Figure 12.4, 83.6% of subsequent strokes were large artery origin when the stenosis was severe (70% 99%). The combination of cardioembolic and lacunar ipsilateral strokes together constituted only 16.4% in patients with this severe degree of stenosis. Strokes non-large artery origin rose to 40% in the patients with moderate stenosis. Lacunar strokes as outcome events were commoner
FIGURE 12.4. Kaplan-Meier proportion (%) of each cause (cardioembolic, lacunar, largeartery) of ipsilateral stroke in the symptomatic arteries and in the asymptomatic other side. The cutpoints at 60% and 70% stenosis correspond to the current American Heart Association guidelines for recommending carotid endarterectomy to asymptomatic and symptomatic patients, respectively.47
The degree of stenosis proved to be the most important risk factor (Figure 12.5). The average annual risk of stroke peaked at 9.4% for those patients with 75% 94% stenosis. In the nearly occluded patients with a collapsing artery (95% 99%), the risk diminished again (6.5%). This decreased risk in the patients with very severe stenosis has been previously reported from NASCET.20
Asymptomatic Carotid Artery Disease
Angiography and noninvasive studies detect atherosclerotic plaque in the extracranial arteries, which increases in amount with the subject's age. From a small number of community surveys, it has been estimated that 2 million people above the age of 50 in the United States have an asymptomatic carotid artery stenosis.21
FIGURE 12.5. The average annual risk of stroke in the involved artery territory over a three-year period is depicted for increasing degrees of stenosis. The rear bars relate to the strokes of the symptomatic artery, the front bars to territory asymptomatic artery on the other side. No symptomatic patient had normal arteries, and the NASCET protocol excluded patients with occlusion of symptomatic arteries. Reproduced by permission of REMEDICA.
The question of appropriate treatment in the presence asymptomatic lesions has been the subject of considerable enquiry. Uncertainty continues to surround the application of CE for these subjects, who in this discussion will not be described as patients : they carry on normal lives with freedom from symptoms, and the likelihood is that a majority will never require aggressive therapy. The assumption that they are all patients requiring CE would increase by 10-fold the number currently being performed.
The risk of stroke facing these individuals was subjected to enquiry in large observational case-series. The best data came from approximately 1000 subjects in two studies who came under observation in two vascular ultrasound imaging laboratories and were examined at intervals over a five-year period.22,23 These two studies concluded that the annual risk of stroke with lesions producing stenosis below 75% and 80%, respectively was less than 2% per year and rose to 5% only when the stenosis was above 80%. This risk for stroke decreased to 3% when only events ipsilateral to the lesion were included. Men were at higher risk than women. Some other observations about the risk came to light from Toronto asymptomatic series. In a mean follow-up of 52 months involving 500 persons, Norris and Zhu detected a bi-modal distribution of ischemic events, observing a peak risk in the 75% 90% range of stenosis, and then reduced in subjects with 91% 99% stenosis.24 Fifty-one cerebral ischemic events were reported, most in the 75% 90% range. TIA, a harbinger of potential stroke, was four times as likely to occur (n = 40) as was ischemic stroke 11). From this study and from other reports, evidence indicates that there is an increased likelihood of the development symptoms when the lesion under observation increases rapidly in size. The postulate is that the increase size due either to rapid increase in atheromatous deposit or to intraplaque hemorrhage. More data are needed in this regard. It would appear to be an uncommon occurrence. NASCET has data indicating that the average rate of increase in stenosis is only 4% per year in long-term annual ultrasound observations.25 The question remains unsettled about how often individuals with known stenosis should be reexamined for evidence of rapid increase while still asymptomatic. Studies at less than annual intervals appear to be excessive.
The gold standard of the randomized clinical trial has been applied in evaluating both medical and surgical therapy for asymptomatic subjects. The number of subjects has been smaller than ideal. The one medical trial, involving 372 subjects, was of meticulous design but was unable to determine any benefit from prophylactic aspirin therapy (325 mg daily) compared to placebo.26 Larger studies are required to confirm or deny these observations, possibly using different dosages of aspirin.
Five randomized trials evaluating surgical treatment have been started, and four of these have been completed and published. Table 12.2 sets out the numbers admitted to the relevant trials and contrasts those with symptomatic disease those with no symptoms. It identifies the outcome events of any stroke, vascular death, and other death extracted from the trials in which the information was available. Clearly, the symptomatic patients face an increasing annual risk of stroke and vascular death with the increasing degree of stenosis. The annual stroke risk in NASCET's medically treated symptomatic patients was 9.6% in those with severe disease and 4.7% in those with moderate disease. In ECST, the figures were 6.2% and 2.6% respectively. In asymptomatic subjects the annual risk varied between 2.6% and 2.9%. To improve on these medical risk figures with CE is realistic for the severe patients, as shown in ECST and NASCET, for some moderate patients, as shown in NASCET. The challenge appears to be more daunting and may be impossible when the medical risk figures are below 3%, as they were in the asymptomatic trials and in the moderate patients ECST. The trials involving asymptomatic subjects numbering in aggregate 2584 involved less than half the numbers in the trials of symptomatic patients (n = 6092). The lesser risk of stroke experienced in the asymptomatic artery suggests that larger trials would have been desirable. Perhaps as many 10,000 subjects may be needed to establish efficacy with certainty. Whether seeking benefit by using such large numbers of subjects with such low risk of stroke is worthwhile remains in doubt.27
Two of the asymptomatic trials had sufficient design problems that they will not be further considered.10,11 The Veterans Administration Cooperative Study trial randomized 444 men, and had it not been accompanied by a high perioperative risk, modest benefit in stroke reduction might have been shown. With a 4.4% complication rate, neither immediate nor long-term stroke-free survival resulted.
The AC AS study randomized 1662 individuals, 3 of whom in the surgical arm were not followed. Approximately 45% had previous symptoms or surgical procedures. The final publication reported a relative risk reduction of 53% favoring stroke-free survival for the subjects in the surgical arm compared to those medical arm. Unhappily, the absolute risk reduction was only 5.9% at five years, yielding little more than an annual risk reduction of 1%. The difference in the impact of relative and absolute risk reductions are seldom better demonstrated than in this differential of 53% and 1%. The relative risk reduction may be unduly optimistic. A statistically significant difference may not amount to an important clinical difference. For example, a relative risk reduction of 50% is obtained when the absolute risk is reduced from 50% to 25%. A 50% relative reduction also ensues when the absolute risk is reduced from 2% to 1%. In such low-risk situations, as in subjects who have asymptomatic carotid stenosis, attention should concentrate on the absolute reduction of risk.
The benefit claimed for CE based on the ACAS reports has not received universal acceptance.6,28,29,30,31,32,33 The controversies of interpretation arise from a combination
TABLE 12.2. Number of Patients and Outcomes in the Symptomatic and Asymptomatic Randomized Trials
A major problem with ACAS was that too few patients were entered into the study to produce enough outcome events answer pertinent questions. Neither the numbers entered nor the reliance on Doppler examinations alone for the analyses allowed a distinction in benefit among any deciles of stenosis. It is counterintuitive to believe that a person without symptoms, shown have 60% narrowing by ultrasound alone, can be given a green light to have CE, while symptomatic patient with a 60% angiographic lesion is only to be considered for CE under certain circumstances.
Subgroup analyses were unable to declare benefit or lack of for disabling stroke. This could be misleading again because of the small numbers. Women were not shown to benefit. This may be due to the better prognosis for recurrent ischemic events in women compared to men, or solely due to the higher perioperative complication rate in ACAS for women (3.3% compared to 1.7% for men). The reported combined perioperative complication rate of 2.3% for men and women would be a challenge to most institutions surgical departments. The surgical complication rate is reduced to a daunting 1.1% when the inclusion of an unexpectedly high complication rate 1.2% from angiography is subtracted from the 2.3%.
Large Medicare surveys report hospital mortality alone. They do not provide data about stroke morbidity nor distinguish between CEs performed for symptomatic patients or asymptomatic individuals. The latest mortality figures from the Medicare source indicate that 1.8% of patients submitted to CE under Medicare leave the hospital dead (Robert Pokras, personal communication, 1998). Because morbidity is 3 to 4 times this figure, no comfort can be taken from the possibility of a complication rate stroke and death approaching 8%.
The databases of NASCET and ECST have been able to provide some useful information about asymptomatic arteries. Of 2377 NASCET patients from whom bilateral angiograms were available and who had never had symptoms on the other (asymptomatic) side, 509 had a stenosis of 50%, and 1330 had <50%, but a detectable amount of stenosis. The average annual risk of stroke over three-year period from these asymptomatic arteries was calculated, and a comparison by different degrees of stenosis is depicted in Figure 12.5. At all of stenosis, the annual risk is one-third, or at most one-half, that in the territory of the symptomatic artery. Only at the stenotic range of 75% 94% does risk exceed what could be improved upon by good surgeons. The risk for subjects with nearly occluded arteries was less than for the two deciles below this. This seeming paradox was observed by Norris and Zhu in their case-series of asymptomatic subjects.24 It appears that the flow beyond stenosis in the severely narrowed artery is diminished to the point where the hemisphere no longer dependent on it and emboli travel less frequently through the severely narrowed
NASCET prospectively recorded all strokes in the asymptomatic arteries. The causes of strokes were identified as related either to the large artery lesion or to be of cardioembolic or lacunar origin. Either cardioembolic or cause was ascribed to more than 40% of these strokes, and the high percentage of strokes not of large artery origin was observed at all degrees of stenosis (Figure 12.4). A figure of 50% is probably the accurate number in the series endarterectomies not restricted by protocol to exclude threatening cardiac lesions. In any population of asymptomatic individuals, a recalculation the annual risk of stroke must be made, accounting for the fact that approximately 50% of the risk is not subject to reduction by a carotid CE. For example in the 75% 94% stenosis category, the highest risk group, only a 1.9% annual large-artery stroke would be predicted. This is not a risk that would improved upon by CE.
The comparable ECST database contained 843 randomized patients with an asymptomatic (other side) artery with 30% 69% stenosis by ECST measurement, and 127 with 70% 99% stenosis.34 During follow-up, 69 patients had a first stroke on the previously asymptomatic side lasting longer than 7 days, giving an estimated Kaplan-Meier stroke risk at three years of 2.1%. The risk for patients with 70% 99% stenosis was 5.7%. By degrees of there a sharp gradient of risk when the stenosis reached 80%. The three-year risk was 9.8% for patients with 80% 89% stenosis and 14.4% with 90% 99% stenosis. Data were not available identifying stroke by cause. There is no reason to believe that the distribution of large artery, cardioembolic, and lacunar strokes differed from the percentages found in NASCET.
Additional data have become available from the Aspirin and Carotid Endarterectomy trial (ACE), which ran parallel to NASCET in the centers. Altogether, 2804 CEs were performed, 1521 for asymptomatic subjects, and 1283 for symptomatic patients. The complication rate at 30 days was 6.4% for the symptomatic patients and 4.6% for the subjects without symptoms. Superimposing the 4.6% obtained from ACE upon Kaplan-Meier medical-surgical curves from ACAS, as Figure 12.6 demonstrates, no benefit was achieved CE out to six years. This is of particular concern because the ACE trial submitted twice as many asymptomatic subjects to CE as did the ACAS trial. Harm was done, and medical therapy should become the preferred treatment.
A fifth asymptomatic trial is ongoing with a goal of 3200 individuals to be submitted to best medical therapy or to CE.14 The larger numbers may confirm or deny the ACAS observations. This study may find a subgroup with convincing evidence of benefit. A large, long-term observational study risk factors is also being carried out that may identify the risk profile of asymptomatic individuals more likely to benefit from CE than the best contemporary medical care.35
FIGURE 12.6. The medical and surgical five-year Kaplan-Meier freedom from ipsilateral stroke and perioperative stroke and death curves indicate a 5.9% difference (11.0% minus 5.1%) favoring endarterectomy at five years in the AC AS study. A marginal but definite statistical significance by Greenwood's formula (p < 0.05) can be claimed for this difference at five years, which time only 149 patients were available for analysis. Superimposed on the curves is the outcome projected to five years for 1521 individuals receiving carotid endarterectomy for asymptomatic lesions in the ACE trial, based upon an actual 4.6% stroke and death rate at 30 days. The outcomes were then extrapolated beyond 30 days from the ACAS data. Using projected 7.4% rate of outcomes at five years, the difference between surgical and the medical group is 3.6% (11.0% minus 7.4%), only a 0.7% risk reduction per year (p [approximate, equals] 0.10). Adapted from ACAS.13 Reproduced by permission of
Barnett HIM, Meldrum HE. Carotid Endarterectomy: A Neurotherapeutic Advance. Arch Neurol 2000;57:40 45.
In two other circumstances, a practice has developed to perform CE in subjects without carotid symptoms. The first has been based on the unsubstantiated hypothesis that nonhemisphere symptoms, including symptoms clearly of vertebral basilar origin, will benefit from CE. This has never been convincingly established. The second hypothesis was that the risk of stroke in the performance of major cardiovascular and aortic surgery would be reduced by performing CE on stenosing lesions incidentally found in the carotid arteries of these patients. Later studies have indicated, first that the strokes complicating procedure occur as often in the territory of nonstenotic artery or in the posterior circulation as in the territory of the stenosed artery. Second, the cause strokes complicating coronary artery bypass grafting (CABG) is most commonly related
Causes of Stroke in the Presence Carotid Stenosis
Therapeutic trials in stroke prevention have been justifiably criticized for regarding stroke as a generic phenomenon and not attempting to distinguish among stroke outcome events by cause.37,38 A striking example was the huge (19,000- patients) International Stroke Trial (1ST), which evaluated anticoagulants compared with platelet-inhibiting therapy.39 Concern was expressed that a different type of protocol, designed to distinguish among outcomes stroke by cause, may have found different results in the treatment for strokes of cardioembolic origin, lacunes, or those of large artery origin.40 It requires a leap faith to accept the contention that all of these causes of stroke will have comparable responses to identical medical therapy. To identify the cause of stroke outcomes is equally important in evaluating the benefit of CE. NASCET identified stroke events by cause. In patients with moderate disease and in strokes that occurred in the territory of the arteries asymptomatic other side, combination of lacunar and cardioembolic strokes was approximately 40% and occurred regardless of the degree stenosis (Figure 12.4).41
Lacunar strokes were not excluded as entry phenomena into NASCET. The contention was that data did not exist at the time of writing the protocol for this trial to state with assurance that patients with lacunar stroke would or would not benefit from CE. At the conclusion of the trial, the nonlacunar patients were compared with the patients who entered with lacunar syndromes. Clear benefit was seen from CE for the nonlacunar patients, but less benefit was seen in the patients who entered the trial after a lacunar stroke.42 Because number of patients who came into NASCET with probable lacunar syndromes was small, further evaluation in other trials is desirable.
Decisions About Ce Based on the Number-Needed-to-Treat Calculations
For symptomatic patients and asymptomatic subjects, it is possible from published randomized trials and from the observations made in the ACE trial to calculate the number needed to treat (NNT) by CE to prevent one additional stroke (in the case of symptomatic patients) or a first stroke (in asymptomatic subjects). These calculations, set out in Tables 12.3 and 12.4, are dependent particularly on
TABLE 12.3. Number Needed to Treat (NNT) by Endarterectomy: Symptomatic Patients
TABLE 12.4. Number Needed to Treat (NNT)by Endarterectomy Asymptomatic Individuals
Requirements for an Institution Performing Ce
The appropriateness of CE in certain circumstances has been established. Expert surgeons, trained and capable of performing CE, and knowledgeable about how to deal with brain ischemia, working with a team of experts in intensive care, and whose anesthetists are familiar with the best neuroanesthetic methods for a brain with compromised circulation, must function as a cohesive team. This cooperation is required to keep the 30-day perioperative morbidity and mortality at a maximum of 7% for death and any stroke (regardless site severity). When the degree of disability is evaluated at 90 days, a death and disabling stroke rate of no more than 2% must be achieved. The team must aware that the first 48 hours are more critical than all the rest of days making up 30-day postoperative period combined (Figure 12.7). The surgeons and intensive care staff must be prepared to cope with wound hematoma, wound infections, and the rare life-threatening injury to the vagus nerve that may cause acute dysphagia and aspiration.
Ideally, the team will include a stroke neurologist involved from early selection of appropriate patients to the conclusion long-term follow-up. In evaluation of stroke occurrence and in the assessment its severity, neurologists provide the most reliable data.43 Such data are necessary to obtain an accurate complication rate for the institution.
The team must be alert to the fact that the common nonstroke medical problems that arise in the postoperative period are of cardiac and respiratory origin.44 Of 1415 patients treated with CE in NASCET, postoperative fatal and nonfatal myocardial infarction combined with sudden death occurred in only 1.1%. The figure will be higher in the routine practice of CE, where cardiac conditions threatening emboli are not necessarily excluded, as they were in NASCET. Rhythm disorders in this population occurred 22 patients, of which 11 were nonvalvular atrial fibrillation. New or recurrent angina pectoris occurred in 19 patients. Respiratory complications were the next most common cause of medical
FIGURE 12.7. The time of onset 92 perioperative outcome events in NASCET. Most strokes occurred during the endarterectomy and within succeeding 24 hours. Reproduced by permission of Stroke.16
Carotid Artery Imaging Methods
The symptomatic patients who entered into the randomized trials were studied by conventional angiography, and diameter stenoses were assigned. It is against these well-defined levels of stenosis that decisions must be made about the potential benefit or lack of from CE. Because no more powerful predictor of prognosis has been identified, and because the differences in are so striking for different degrees of stenosis, its accurate evaluation is of paramount importance.
Some progress has been made in efforts to determine which of the parameters of ultrasound measurements correspond to the levels of stenosis known from angiography to be within the range of benefit from CE. The correlations will never be exact, because angiography is a measurement to map the lumen, any intrusion into it, or any ulceration within the plaque, while ultrasound is a measurement of the velocity and volume blood flowing through the artery. Approximations are achievable, but at two important levels of angiographicallymeasured stenosis, difficulties in correlation between ultrasound and angiography
Several reasons are advanced by some practitioners to persuade themselves and their colleagues that angiography can now be replaced by noninvasive studies. Poor angiograms are displayed that have failed to detect a severe stenosis because of failure to take oblique views the site lesion. Such poor imaging is inexcusable, and expert neuroradiologists will not tolerate it. High risk of stroke from angiography is reported.45 This too is unacceptable and denotes the need for proper training. The reports disclaiming the need for angiography make much of the complications from procedure. They fail to report fact that majority (about 80%) of patients who suffer this complicating stroke make good to excellent recovery, and only one in five patients is left with a disabling stroke.46 NASCET recorded nondisabling strokes throughout the trial from 2885 angiograms. The nondisabling stroke rate was 0.6%, from which may be extrapolated a risk of disabling stroke of 0.1%. This low risk is a small price to ask patients to pay so that none without an appropriate lesion be submitted to the 20-fold increase of risk from disabling stroke (2%) that confronts patients who undergo CE, even in the best centers.
Cost has been an argument supporting ultrasound as a replacement for conventional angiography. In some centers the cost attached to the performance of angiography and film interpretation is as much as the cost of CE. Moderate savings are not a reason to settle for the second-best in imaging methods. The economic cost of permanent disability resulting from stroke after CE exceed the savings by a wide margin.
Other methods may make conventional angiography obsolete in the future. Furthur improvements may occur in ultrasonography, so that the over-reading in the mid-ranges of stenosis is eliminated and the under-reading in the highest range is overcome. Angiography can then be replaced. To date, this remains a hope. Magnetic resonance imaging over-reads stenosis. When and if the problem of signal void is overcome, another possible replacement for angiography
CE prevents stroke in the territory of arteries with symptoms related to stenoses of 70% 99%, validated angiographically by the NASCET method of measurement.
Surgeons who perform the procedure with 7% perioperative complication of stroke and death will achieve benefit in the presence of severely stenosed symptomatic lesions.
Patients with <70% stenosis and appropriate symptoms cannot be assigned automatically to surgical therapy. Careful consideration must be given all risk factors, as well to the patients identified likely to benefit the most.
Conventional angiography must be seriously considered as a prelude to CE for most patients.
Individuals with asymptomatic stenosis have not been shown convincingly to benefit from CE.
The risk with medical therapy in asymptomatic individuals is less than onethird that for symptomatic patients with severe stenosis and one-half that symptomatic patients with moderate stenosis.
Approximately half the stroke risk facing asymptomatic individual is for lacunar or cardioembolic stroke, neither of which are responsive to CE.
The consensus statement provided by the American Heart Association interprets the data supporting CE for asymptomatic subjects in an optimistic fashion. This statement recommends that all patients with >60% asymptomatic stenosis be considered for CE, provided the surgical risk is <3%.47
The authors regard CE for asymptomatic lesions as an overutilized therapeutic strategy. Future investigations of the highest risk subgroups may identify some patients who will benefit convincingly from CE.
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