ABSTRACT
About 5-10% of the general population aged over 60 years have at least one asymptomatic carotid stenosis (59). However, the natural history of asymptomatic carotid stenosis was only reliably defined in large studies in the 1980s when carotid ultrasound became available. Several large studies showed that the prognosis was much more benign than that of recently symptomatic stenosis, with a risk of ipsilateral ischemic stroke of less than 2% per year in patients with severe asymptomatic stenosis (60,61). Despite inconclusive results from some small early randomized trials of endarterectomy for asymptomatic carotid stenosis vs. medical treatment alone (62-65), the number of operations done for asymptomatic stenosis in North America increased dramatically in the 1980s (35). In 1993, the VA trial demonstrated a significant reduction in the risk of the combined outcome of stroke and TIA in the endarterectomy group, but did not have the power to demonstrate a reduction in the risk of stroke alone (66). In 1995, the Asymptomatic Carotid Artery Study (ACAS) (67) demonstrated a clearly significant reduction in the risk of ipsilateral ischemic stroke in patients with 60-99% asymptomatic stenosis: a reduction in the five-year actuarial risk of ipsilateral ischemic stroke or operative death from 11 to 5.1% (p< 0.001). Unlike the ECST and NASCET trials, the ACAS trial included the risks of stroke and death due to carotid angiography in the overall outcome. However, the operative risk of stroke and death due to endarterectomy was much lower than in the randomized controlled trials of endarterectomy for symptomatic stenosis, an observation that was confirmed by analyses of case series from routine clinical practice (68). More recently, the much larger Asymptomatic Carotid Surgery Trial (ACST) showed a very similar absolute benefit to that in ACAS, despite a higher operative risk (69). Several questions remain, particularly about the benefit of surgery in specific subgroups, the potential for selection of patients on the basis of an increased risk of stroke without surgery, and the long-term benefits of surgery (70), but there is no doubt that endarterectomy for asymptomatic stenosis is of modest overall benefit. Whether it is a cost effective intervention and whether screening will do more good than harm are less certain (71).
