Surgery for carotid artery stenosis

The US Veterans' Administration study followed by the asymptomatic carotid artery stenosis study (ACAS) and now the asymptomatic carotid stenosis trial (ACST) have all affirmed that elective endarterectomy for patients carefully selected by neurologists and operated on by skilled surgeons can prevent stroke.^{1-2 w1} The results of ACST and ACAS are almost identical, with 5.4% absolute risk reduction for stroke in ACST compared with 5.9% for ACAS. The surgical advantage persists despite multimodal medical management with statins, platelet antiaggregants, and stringent control of risk factors. Moreover, nearly 20% of asymptomatic patients randomised to the medical management arm of ACST developed symtoms during the trial, often necessitating urgent surgery. These three randomised trials all show that if medical management has failed elective endarterectomy performed by skilled surgeons is a worthwhile additional option for management of presymptomatic carotid stenosis that exceeds 60%, for otherwise healthy men and women regardless of their age, if medical management has failed.

On the other hand, using transient ischaemic attack or minor stroke as the marker for surgery entails a complication rate of about 6%. To be added to this figure is the additional hazard of contrast arteriography (about 1%). Advising patients with carotid stenosis to await a transient ischaemic attack^w2 or, even worse, an acute infarction for which an urgent endarterectomy is required^w3 is therefore not good advice. However, others take a contrary view, perhaps because of a lack of facilities, excessive competition rates owing to poor selection of candidates, or inept surgery. Moreover, an attitudinal bias may also exist regarding prevention among doctors who have been trained to intervene only if malfunction of an organ becomes symptomatic.

The degree of stenosis is measured by different methods, and for most specialists 60% stenosis is the cut-off point for selecting patients for endarterectomy. This has led to an erroneous concept that a minimum of 60% stenosis of the internal carotid lumen is the essential criterion.³ However, other key indicators are turbulent flow caused by stenosis, sludge due to eddy currents, particulate microemboli, and wall abnormalities that are resistant to medical management.⁴

Screening for asymptomatic carotid atherosclerosis by using auscultation for bruits and duplex ultrasonography is feasible and is currently the best way of identifying preclinical atherosclerosis.⁵ Patients identified by preliminary screening to determine flow dynamics, arterial wall characteristics including stenosis and ulceration, and microemboli, to identify those for whom medical management is needed and to assess the effect of medical remediation.^{6 w4} If medical intervention fails, ACST has proved once and for all that carotid endarterectomy can be worth the risk if surgical and anaesthetic skills are such that operative complications are rare.⁷

International collaborative studies such as these require a huge investment of time, skill, and money and are an endorsement of evidence based medicine first promulgated by Austin Bradford Hill and Sir Richard Doll.^{8 w5} For the field of stroke, the baseline from which they evolved were the autopsy findings of Miller Fisher,^w6 followed by the landmark report by Eastcott, Pickering, and Robb at St Mary's Hospital in London.⁹ Carotid endarterectomy has now come full circle, having been validated by Halliday, Thomas, and colleagues of the same institution.² Their multinational effort continues the search for better methods by which to identify people with atherosclerosis who should be considered for medical and surgical intervention.

So far, differentiating symptomatic from asymptomatic stenosis of the carotid artery has traditionally been the way to decide on treatment. But this requires a doctor skilled in neurology to make the judgment. Moreover, the occurrence of transient ischaemic attacks is not a satisfactory means of categorisation because they are very seldom witnessed, cannot be assessed objectively, are confounded by many other transitory phenomena, and may occur during sleep when they cause no recognisable phenomena or in parts of the brain that do not produce symptoms or signs.¹⁰,¹¹ Moreover, 3-10% of people older than 65 have asymptomatic infarcts visible on brain imaging.¹²

Depending on transient ischaemic attacks for categorising patients is therefore unacceptable as the sole criterion for choosing treatment, and preclinical stenosis and unrecognised transient ischaemic attacks need to be identified by screening.