POINT/COUNTERPOINT: Asymptomatic carotid stenosis: medical treatment, CEA, or CAS?

POINT: Medical treatment ends need for CEA or CAS.

By Anne L. Abbott, M.D.

The medical profession and the wider community must be congratulated upon their sustained efforts over recent decades that have seen an 80% fall in the average annual risk of stroke associated with moderate and severe (50%-99%) asymptomatic carotid stenosis (ACS).^1-6 This has been achieved by better medical treatment which consists of encouraging healthy lifestyle habits and appropriate use of medication. This major impact results from the combined effect of addressing all vascular risk factors in individual patients and efforts to use the best medical treatment available at the time. Rates are now so low (around 0.5% per year for ipsilateral stroke) that procedures, such as carotid endarterectomy (CEA), are now more likely to harm than help patients.⁷

Even if procedures were always completely risk-free, improved medical treatment may mean we have now reached the point where carotid procedures for ACS are safe but essentially ineffective for reducing stroke risk. The latest measurements of stroke risk using medical treatment alone indicate that only about 2.5% of patients with 50%-99% ACS will have a an ipsilateral stroke due to the carotid lesion during their remaining lifetime if they are receiving pretty good quality, current medical treatment alone. This is because the average age of identifying patients with ACS in past studies was about 70 years and the average survival following diagnosis was 10 years.¹ Further, only about half the strokes occurring in the distribution of an internal carotid artery with >60% proximal stenosis are due to the carotid lesion.⁸

Guidelines recommendations for CEA for 50%-99% or 60%-99% ACS rely on marginal, 20- to 30-year-old differences in stroke rates between patients given medical treatment alone versus those given additional CEA in best practice settings.^9-11  Such recommendations are not relevant to current clinical practice largely because the medical treatment used in these studies is obsolete. Multiple independent observations regarding the improved stroke prevention efficacy of medical treatment,^1-6,12 and the additional observations below, provide ample evidence that current medical treatment alone is the only routine-practice (nontrial) approach we should use for  patients with 50%-99% ACS and any future role of carotid procedures in these patients could only apply to very small minority subgroups:

i. Current optimal medical treatment for patients with ACS has not been defined nor its impact measured. This means that it is likely we can lower the risk of stroke and other vascular complications in patients with ACS stenosis even further than has been achieved in the most recent studies. The definition of current optimal medical treatment will vary from patient to patient depending on which vascular risk factors they have and what has been shown effective in modifying these to reduce the risk of any complications of vascular disease.

ii. The 30-day peri-operative risk of stroke or death (and other significant complications) remains above 0% in the most recent results of trials and registries^13-15 and is usually not measured in routine practice. Latest measurements of average annual ipsilateral stroke risk with medical treatment alone are about 2-3 times lower than for patients who had CEA or CAS in the Asymp tomatic Carotid Atherosclerosis Study (ACAS)10 or the Carotid Revascularization Endarterectomy versus Stenting Trial (CREST).^{7, 13}

iii. Patients with 50%-99% ACS receiving current optimal medical treatment and with a sufficiently high average annual risk of ipsilateral stroke, indicating they may benefit from CEA, have not been identified. This rate would need to be in excess of at least 2.5%-3.0%, using results from ACAS,¹⁰ to expect any surgical benefit in routine practice. Studies of baseline degree of  ACS within the 50%-99% range,^10,11,16 plaque echolucency¹⁷ and most studies of detecting asymptomatic stenosis progression18-21 show that these parameters (used separately) confer a relative risk of stroke of only about 2.0-2.5. Therefore, a higher degree of baseline stenosis within the 50%-99% range, the detection of predominantly echolucent carotid plaques  or asymptomatic progression are too weak on their own to identity patients likely to benefit from an additional carotid procedure. Combinations of risk markers are required for sufficient risk discrimination. For instance, results from the Asymptomatic Carotid Stenosis and Risk of Stroke Study (largest study so far of medically managed patients with moderate or severe ACS) showed that a combination of clinical features, baseline degree of stenosis and standardized ultrasonic plaque characteristics can achieve average annual ipsilateral stroke risk stratification ranging  from <1.0% to 10%.¹⁶ However, like all stroke risk stratification studies performed so far, this study was performed before the era of current medical treatment and the results have not been independently tested.

iv. Even if patients with sufficiently higher than average annual risk of ipsilateral stroke are one day reliably identified, randomized trials of an additional carotid procedure will be required to determine if, and to what extent, that procedure is likely to reduce ipsilateral stroke risk in routine practice.

v. The available evidence from randomized trials and registries indicates that CAS causes about twice as many strokes or deaths as surgery (just like it does for symptomatic carotid stenosis). Therefore, currently CAS cannot be recommended.⁷  In conclusion, the available evidence clearly indicates that current medical treatment alone now offers the best chance of reducing the risk of ipsilateral stroke in patients with 50%-99% ACS. There is no current evidence of benefit from CEA or CAS in these patients overall, or in any particular subgroups. However, there is much evidence regarding procedural risk and unaffordable cost.  Risk of ipsilateral stroke is now so low without carotid procedures it is time to shift from the historic approach of identifying ACS primarily to administer CEA. Rather, it is time to properly recognize that carotid stenosis is a risk factor of all complications of vascular disease, more than it is for ipsilateral stroke.²²

The priority is to define current optimal medical treatment as best we can, recognising that patients with ACS are a risk-heterogenous population. Then we need quality independent measurements of its impact on risk of all vascular disease complications using quality prospective cohort studies. Risk stratification models should be used to identify those who may benefit from trials of more intensive medical treatment, motivational strategies, plus/minus the safest carotid procedures. If identifying patients with ACS for CEA in routine practice is to be feasible, this needs to be done within well organized environments that support patients with a wide range of stenosis severity with the primary aim of implementing current optimal medical treatment to prevent all vascular complications. Finally, it must be accepted that as medical treatment and its implementation continue to improve, the added value of carotid procedures, including for symptomatic carotid stenosis, will continue to recede until we can say, ‘good job - it is finally fixed and it is time to move on to other major health issues.’

Dr. Abbott is a neurologist and an associate professor at Monash University, Melbourne, Australia.