(The Lancet) -- Results of an international study in this week's issue of THE LANCET suggest that surgery to widen narrowed carotid arteries could halve the risk of stroke among high-risk patients. However, authors of the study caution that surgery carries its own stroke risks if not done by experts.

There is currently debate as to whether people who have substantial narrowing of the carotid arteries (but who have not had a recent stroke or transient ischaemic attack) should undergo carotid endarterectomy (CEA) -- a complex surgical procedure to widen the carotid arteries which itself carries a risk of stroke.

The UK Medical Research Council (MRC) Asymptomatic Carotid Surgery Trial (ACST) is a ten-year prospective study involving 3120 patients from 126 hospitals in 30 countries. Half the patients were allocated to CEA, the other half to no intervention. Many of the patients were receiving medical therapy (anti-hypertensives, anticoagulants, and cholesterol-lowering drugs). Average follow-up of patients was 3.4 years.

The risk of stroke or death from surgery was 3%. The 5-year risk of stroke among patients younger than 75 years given CEA was around half that of patients given no intervention (6% [including the 3% surgical hazard] compared with 12%). Half this 5-year benefit involved disabling or fatal strokes. However, the investigators caution that 'outside trials, inappropriate selection of patients or poor surgery could obviate such benefits'.

Lead author Alison Halliday from St Georges Hospital, London, UK, comments: "Our trial shows that immediate surgery is the best option for some patients with severe narrowing of the carotid artery. How much this changes practice will depend on how long the benefits last, so we are going to follow up these patients for another 5 years to find this out." (quote by e-mail, does not appear in published study).

In an accompanying Commentary (p 1486), Henry Barnett from the John Roberts Research Institute, Ontario, Canada, concludes: "Problems persist, but the investigators of the ACST are to be congratulated for performing well a monumental task. They are to be commended for their cautionary concluding remarks. Carotid endarterectomy with any less skill than exhibited by ACST and ACAS surgeons quickly casts the procedure into the list of "risk factors for stroke"."