:Acta

Acta Neurochir (Wien) (1995) 137:121-127

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N6urochlrurglca 9 Springer-Verlag 1995

Printed in Austria

Carotid Endarterectomy

- W h e n To D o It, H o w To D o It?

H. J. Steiger Neurochirurgische Klinik, Klinikum Grosshadern, Munich, Federal Republic of Germany

Summary With the completion of the major carotid endarterectomy trials the indications for this procedure can be defined. The procedure, if done by experienced teams, has been shown to improve the chance

of stroke free survival in symptomatic and asymptomatic patients with a high-grade stenosis of the internal carotid artery. In asymptomatic patients the risk reduction gained by prophylactic carotid endarterectomy may be small in relation to the risk of coincident factors particularly coronary artery disease. The benefit gained by carotid endarterectomydepends closely on the risk of the procedure itself, and a single little flaw during the management can annulate the benefit of the operation in asymptomaticpatients. There are still considerable controversies with regard to peri-operative management and surgical technique, e.g., the necessity of routine pre-operative arteriography has recently been questioned. Quality control programmes become a requirement with the publication of performance standards for carotid endarterectomy. According to a consensus of the American Heart Association, the surgical morbidity/mortality must be less than 6% for symptomatic carotid lesions and less than 3% for asymptomaticlesions. The present review discusses the steps of the pre-operative work-up, the procedure itself and the post-operativemanagement with the aim to identify accepted safety standards as well as areas of uncertainty.

Keywords: Carotid endarterectomy; cerebrovascular disease; surgical technique; quality control programme.

Introduction The major prospective randomized carotid endarterectomy trials are now completed or nearing completion [1, 4, 8, 14, 29, 36, 37, 43]. More or less conclusive answers with respect to the question of the efficacy of the procedure for symptomatic and asymptomatic lesions are available. The data define which patients can benefit from carotid endarterectomy and give also information with respect to the necessary performance standards required for the procedure to be beneficial. The results of the prospective trials open a number of new issues which call for fur-

ther studies. The purpose of the present review is to extract from the available information practical guidelines with regard to patient selection, optimization of the procedure and quality control.

Which Patients Benefit from Carotid Endarterectomy? For symptomatic lesions proven indications by the N A S C E T (North American Symptomatic Carotid Endarterectomy Trial) and ECST (European Carotid Surgery Trial) data are one or more transient ischaemic attacks (TIA) or mild stroke with a corresponding internal carotid artery stenosis of 70% or more diameter reduction, if the patient is otherwise in good condition and the surgical complication rate of the surgeon is less than 6% [4, 14, 42, 43]. Acceptable according to a recent consensus statement by the American Heart Association but not proven, are symptomatic stenoses of 50-69% with one or more TIAs or mild to moderate stroke within the last 6 months, and acceptable but not proven are TIAs with a stenosis of 70% or more together with required coronary bypass grafting [7, 15, 23, 27, 31, 42, 45, 50]. For asymptomatic carotid stenoses of 60% or more diameter reduction ACAS (Asymptomatic Carotid Atherosclerosis Study) has shown a benefit from surgery in low risk patients/surgeons (< 3% surgical morbidity/mortality) [1, 44]. Since the risk of the disease increases with the degree of stenosis, the benefit from surgery is more relevant in very tight asymptomatic lesions (Fig. 1). Whether a procedure is proven beneficial or not is both a function of the disease/procedure and the study design. The fact that a procedure for a specific disease offers an advantage over the natural history does not

122

H.J. Steiger: Carotid Endarterectomy

13, 18, 26, 30, 46]. In these special circumstances the indications for surgery may be clearer.

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Fig. 1. Distribution of the annual risk of stroke with symptomatic and asymptomatic internal carotid artery stenosis as a function of the degree of diameter reduction. The data are compiled from the major recent carotid endarterectomy trials [4, 6, 14, 29, 36, 37, 42-44]

necessarily imply that the benefit is meaningful for the patient. As a rule for a meaningful benefit, a prophylactic procedure should eliminate the single most important health risk to the patient. For symptomatic high-grade carotid stenosis, endarterectomy clearly achieves this goal, unless the patient is suffering from another life threatening illness. The natural stroke risk of symptomatic high-grade carotid stenosis is 12-13% within the first year after onset of symptoms and 30-35% within 5 years [4, 44]. Patients with very tight stenoses and with frequent TIAs or more severe symptoms such as mild stroke are at an even higher risk [4, 54]. After successful endarterectomy, the risk of suffering a stroke is reduced to 1-3% per year, which is somewhat higher than for other individuals of the same age but not an immediate threat to physical integrity anymore [44]. For asymptomatic carotid stenosis of more than 70% the annual risk of stroke is about 4%, that is about 20% within 5 years [6, 8, 13, 29, 37, 44, 53]. Successful endarterectomy reduces the stroke risk by about 50% [42, 44]. Whether this reduction is meaningful for the patient cannot be answered generally. In the Veterans Affairs Study on carotid endarterectomy in asymptomatic patients, the risk reduction by the operation was negligible compared to the risk of coincident coronary artery disease [29]. Preliminary data indicate that among the group of asymptomatic carotid lesions there may be high-risk subgroups, such as very tight stenoses and ulcerated plaques [4,

Noninvasive work-up in patients presenting with TIAs or mild to moderate stroke should be done without delay. There is no reason for a treatment trial with aspirin and delay of diagnosis. Once the diagnosis of carotid stenosis has been made by noninvasive techniques, surgery in patients should be planned as soon as logistically possible if the patient is considered to be an acceptable surgical risk. The available data indicate that the risk of suffering a stroke is highest during the first weeks after a TIA [4, 42]. Timing of carotid surgery in patients with a mild to moderate stroke is much more complicated and few data are available [19, 33, 48, 55, 63]. If surgery is performed within 1-2 weeks after the stroke, the risk of neurological deterioration or even haemorrhage is significant [20, 24, 62]. If surgery is done within this period, the particular vulnerability and the loss of ischaemic tolerance must be taken into account. On the other hand, the natural risk of progression of the neurological deficit or recurrent stroke is highest during the first month and is estimated to be around 10% within this period [54]. Further studies will have to answer the question of the optimal timing of surgery in patients with an established deficit. Unstable patients presenting with crescendo TIAs or progressive stroke are candidates for emergency surgery, since the evolution to a severe established deficit is otherwise programmed. The risk of a surgical complication in unstable patients is higher than with elective endarterectomy [22, 38, 40, 42, 62]. H o w to Do Carotid Endarterectomy? There are several controversies with regard to different methods, beginning with the pre-operative work-up and extending to technical details such as the use of temporary shunts and patch grafts. No single detail in approach has been convincingly shown to be significantly related to the gross complication rate. Most procedural details were evaluated in a series of the order of 100 patients. This number is statistically insufficient to differentiate for example a complication rate of 2% from 6% with 95% confidence. Nonetheless, careful analysis of the available data and corresponding optimization promises to advance the safetay of the procedure (Fig. 2).

123

H. J. Steiger: CarotidEndarterectomy Symptomatic or asymptomatic ICA stenosis > 70% as diagnosed by noninvasive means

Installation of antiplateletmedication Systemic evaluationand confirmationof indicationfor surgery Selective panangiographyor MR angiography,and CT or MRI if neurologicaldeficitspresent Medical control of severe hypertension Carotid endarterectomywith monitoringand electiveuse of a shunt Postoperative ICU surveillanceand control of hypertension.Postoperative assessment of patency and screening for hyperfusion Duplex assessmentof carotid bifurcationprior to dischargeon days 5-7. Counsellingwith regard to risk factors Follow-up with duplex at 2-3 months and then annually Fig. 2. Flow sheet of a proven algorithm for the peri-operative managementof carotid endarterectomy

Pre-operative Work-up Selective arteriography remains the gold standard for pre-operative definition of the surgical pathology and the condition of the other cerebral arteries. This examination is unfortunately still burdened with a complication rate of approximately 1% in this group of patients [4, 12, 44]. This number has to be added to the surgical complication rate. In experienced hands colour coded Duplex sonography is quite reliable for diagnosing a high-grade stenosis [9, 49]. The rate of false positive results is approximately 7% [44]. Duplex sonography has a problem in distinguishing a very tight stenosis from total occlusion, a difference that is crucial for evaluating the surgical indications [4]. In cases where a tight stenosis cannot be excluded by Duplex sonography, arteriography is essential. We refrained from routine arteriography for some years. Although there were few intra-operative surprises and none that resulted in immediate adverse effects for the patient, we finally returned to routine angiography. There was one patient who was readmitted 2 years later with a subarachnoid haemorrhage from an undiagnosed internal carotid artery aneurysm on the side of the endarterectomy (unpublished). The prevalence of incidental aneurysms in carotid endarterectomy patients is estimated as 3% [4]. The second reason why we returned to routine artcriography was that we took a more aggressive attitude toward coincident stenotic lesions of the carotid siphon and the vertebral arteries. Both regions are not

reliably assessable by any noninvasive method at the present time. High-grade carotid siphon stenoses have been shown to be a negative predictor for the outcome of carotid endarterectomy and these lesions can be dilated by intra-operative balloon angioplasty during endarterectomy [21]. Patients who have neurological deficits should have a cranial CT or MRI in order to document areas of infarction and other possible lesions such as tumours and haematomas [42]. Appreciation of the surgical risk is the second point of discussion within the pre-operative work-up. Particularly the cardiac condition is crucial since roughly half of the complications of carotid endarterectomy are of cardiac origin [21, 62]. About 70% of all candidates for carotid endarterectomy have symptoms or electrocardiographic signs of coronary artery disease [64]. Routine extensive cardiological testing prior to carotid endarterectomy has not proved to be of any value with regard to postendarterectomy cardiac complications. It is recommended to reserve extensive cardiological work-up for those patients with significant symptoms of coronary artery disease which would justify surgical intervention [42]. For the remainder of the patients precautions should be taken during the anaesthetic and postoperative management as if the patient had coronary artery disease. On the other hand, if the carotid bifurcation stenosis is less than high-grade or if there are transient symptoms not clearly attributable to the carotid lesion, transoesophageal echocardiography is indicated to define other possible embolic loci in the heart or the aortic arch. Since carotid atherosclerosis is part of a systemic disease, pre-operative evaluation should include a thorough history and physical examination in order to identify coincident coronary and peripheral vascular disease, pulmonary disease and vascular risk factors such as hypertension, tobacco abuse, hyperlipidaemia, and diabetes mellitus. In addition to the routine preoperative laboratory testing, a lipid profile should be added. Extensive screening for exotic laboratory parameters occasionally associated with vascular disease has proved to be of little value [4, 42, 64]. Local or General Anaesthesia? Current practice ranges from local anaesthesia to deep barbiturate anaesthesia for cerebral protection [39, 56, 58, 59]. Prior to routine intra-operative monitoring, neurological complications appeared to be

124 fewer with local anaesthesia [2, 34, 57, 65]. However, with the advent of intra-operative monitoring the majority of surgeons changed to general anaesthesia mainly because of the comfort for the patient and the surgeon.

What Kind of Monitoring? Monitoring cerebral perfusion is part of the surgical state of the art if the procedure is done under general anaesthesia. Transcranial Doppler gives constant real-time information but has the drawback that no cranial window is available in 10-20% of the patients [25, 59]. Xenon cerebral blood flow measurement gives no real-time information [ 16, 62]. EEG is useful only if no barbiturate suppression is used [ 10, 11, 16]. Transcranial oxymetry has not been sufficiently validated [34]. Measurement of the internal carotid artery stump pressure is a very simple method, which is probably good enough to identify those patients with a critically low flow after crossclamping [3].

Temporary Shunts -Always, Sometimes or Never? The use of shunts was an issue of discussion for many years [16, 62]. With regard to this question the answer appears to be settled - sometimes. In a cooperative study, Halsey demonstrated that both absolute attitudes resulted in more complications than a selective approach [25]. There is a proportion of around 10-20% of the patients with insufficient collateral circulation who are at a high risk to suffer an intra-operative stroke if operated on without a shunt. However, intraluminary shunts have a risk of producing emboli. Therefore, no shunt should be used in the 80% of patients who do not need it.

Patch or No Patch? Some groups advocate the routine use of a vein or fabric patch for arteriotomy closure in order to prevent restenosis [28]. Vein patches have a small risk of rupture [47, 5 t]. We and others prefer direct suture with the use of the surgical microscope whenever there is no external constriction of the arterial wall [56, 58]. In a series of 150 consecutive cases that were followed by means of Duplex sonography there were two instances of late symptomatic high-grade restenosis. One was re-operated upon and the other was treated by transfemoral balloon dilatation [58, 59].

H.J. Steiger: Carotid Endarterectomy Postoperative Management The most serious postoperative complication is intracerebral haemorrhage [24, 52, 62]. This complication is the result of hypertensive episodes in conjunction with disturbed autoregulation. This complication is mainly seen in patients with very tight stenoses and pre-operative hemispheric "misery" perfusion. Postoperative headache is a warning sign of hyperperfusion. Strict control of postoperative hypertension is the key to prevention of intracerebral haemorrhage. Patients should therefore be kept on the intensive care unit overnight. We perform routine cervical and transcranial Doppler examinations on the evening of surgery in order to identify hyperperfusion and also to assess carotid patency [59]. Carotid thrombosis is the second potential postoperative problem. Thrombosis is a consequence of intimal dissection, stenotic arterial closure, kinking, or haemorrhage into the common carotid wall. Carotid occlusion may initially remain silent, provided that the collateral circulation is sufficient. Identification of carotid thrombosis on the evening of surgery may provide the opportunity for correcting the problem prior to the occurrence of distal embolization. An alternative approach to assess carotid patency is intra-operative Duplex sonography [17]. Myocardial infarction accounts for about half of the complications of carotid endarterectomy [62, 64]. Postoperative ECG monitoring overnight should therefore be done routinely and analysis of cardiac symptioms and signs should be done promptly. Anticoagulants are not necessary postoperatively with the exception of antiplatelet agents, which should be taken pre- and postoperatively without interruption [41]. The Mayo Asymptomatic Carotid Endarterectomy Study had to be terminated prematurely, because in this study aspirin was stopped in the surgical group, which resulted in a higher incidence of myocardial infarctions [37].

The Necessity for Quality Control The fact that the benefit of carotid endarterectomy is a direct function of the surgical complication rate makes quality control programmes inevitable [5, 32, 42, 60]. Review of the literature provides data that endarterectomy in asymptomatic patients has a lower complication rate than surgery in symptomatic patients [42]. Patients with an established stroke have an even higher risk and the highest complication rate is encountered in emergency procedures done for pro-

H. J. Steiger: Carotid Endarterectomy g r e s s i v e stroke. A n ad h o c c o m m i t t e e o f the A m e r i can H e a r t A s s o c i a t i o n d e f i n e d the m a x i m u m surg e o n / c e n t r e c o m p l i c a t i o n rates as 3% for a s y m p t o m a t i c and as 6% for s y m p t o m a t i c p a t i e n t s [42]. R e c o m m e n d a t i o n s are m a d e for i n s t i t u t i o n a l l y b a s e d q u a l i t y c o n t r o l p r o g r a m m e s i n c l u d i n g the f o l l o w i n g safeguards: 1) A c o m p u t e r i z e d r e g i s t r y o f the results o f all c a r o t i d e n d a r t e r e c t o m i e s s h o u l d be m a i n t a i n e d on an o n g o i n g basis. 2) A n e x t e r n a l r e v i e w s h o u l d be c o n d u c t e d b y an i n d e p e n d e n t o b s e r v e r o f s e l e c t e d r e c o r d s o f patients to e n s u r e that all m a j o r c o m p l i c a t i o n s are a c c u r a t e l y r e p o r t e d to the registry. 3) P e r f o r m a n c e s t a n d a r d s s h o u l d be e s t a b l i s h e d to d e f i n e a c c e p t a b l e s u r g i c a l v o l u m e as w e l l as u p p e r a c c e p t a b l e l i m i t s o f surgical m o r b i d i t y / m o r t a l i t y b e f o r e a c h a r t r e v i e w is begun. L a r g e r e t r o s p e c t i v e m u l t i - i n s t i t u t i o n a l d a t a as w e l l as r e c o m m e n d a t i o n s b y the A m e r i c a n H e a r t A s s o c i a t i o n can be u s e d to h e l p to d e f i n e the a c c e p t a b l e n o r m s for e a c h i n d i c a tion for c a r o t i d e n d a r t e r e c t o m y . 4) T h e r e g i s t r y s h o u l d be r e g u l a r l y audited, and the results s h o u l d be m a d e a v a i l a b l e to e a c h s u r g e o n p r o m p t l y . S a f e g u a r d s s h o u l d b e i n s t i t u t e d to p r o v i d e rigorous confidentiality. 5) W h e n c o m p l i c a t i o n s s i g n i f i c a n t l y e x c e e d the a c c e p t a b l e limits, an institutional p e e r r e v i e w c o m mittee should investigate. If extenuating circumstances c a n n o t be i d e n t i f i e d , a p p r o p r i a t e c o r r e c t i v e a c t i o n should be implemented. T h e s e r e c o m m e n d a t i o n s c o u l d be a d o p t e d in the E u r o p e a n e n v i r o n m e n t with s o m e m o d i f i c a t i o n s . T h e n e c e s s i t y for q u a l i t y c o n t r o l p r o g r a m m e s is not s p e cific to c a r o t i d e n d a r t e r e c t o m y . It a p p e a r s i n e v i t a b l e that p e r f o r m a n c e d a t a with r e g a r d to any p r o c e d u r e w i l l h a v e to b e p r o v i d e d at r e g u l a r intervals b y all institutions w i t h i n the n e a r future. T h e tools for n e u r o s u r g i c a l e l e c t r o n i c r e g i s t r i e s are b e i n g d e v e l o p e d now.

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65. Zuccarello M, Yeh H, Tew JM (1988) Morbidity and mortality of carotid endarterectomy under local anesthesia: a retrospective study. Neurosurgery 23:445-450 Correspondence: Dr. H. J. Steiger, Neurochirurgische Klinik, Klinikum Grosshadern, D-81377 Munich, Federal Republic of Germany.