We agree completely that data from trial subgroups should be interpreted cautiously. Nevertheless, it is disappointing that the survival curves for the secondary analysis of disabling stroke remained superimposed for 4.5 years [1]. The lack of benefit for women could be due to small numbers rather than an absence of benefit. The perioperative complication rate of stroke in women (3.6%) was double that in men (1.7%).

We did not imply that the ACAS was reporting 60% as an area stenosis. Our comment was that "60% is only equivalent to a linear measurement on an arteriogram if the cut-point formula of ACAS is applied" [2]. We stated that "in clinical practice, the description of a 60% stenosis from a Doppler report may be misinterpreted." Practitioners reading a reported "60% stenosis" are less familiar with the nuances of area and linear measurements than are aficionados. We cautioned the readers of the potential of misrepresenting a ultrasound report that indicates stenosis of 60% by presuming that the report is equivalent to arteriography.

Arteriographic linear measurements remain the standard against which endarterectomy has been evaluated in symptomatic patients. Good interobserver and intraobserver agreements indicate that with care and patience, arteriographic measurements are reproducible [3, 4]. The stakes are high, and additional minutes needed for readings are well spent.

The term "inconclusive" denotes that the ACAS results do not translate readily into clinical usefulness. Symptomatic and asymptomatic patients with severe stenosis face major differences in risk. The stroke rate in the medical therapy group of the North American Symptomatic Carotid Endarterectomy Trial (NASCET) was 13.5% per year, in the ACAS, the rate was 2.2%. If the number of patients needed to treat is used as the measure of greatest clinical importance, 67 asymptomatic patients and 6 symptomatic patients require carotid endarterectomy to prevent one stroke in 2 years. Only skilled surgeons can achieve this result. With the morbidity and mortality rate of 4.5% reported in the other randomized trials on asymptomatic patients, the numbers needed to treat to spare stroke at even the highest degrees of stenosis are prohibitive.

It is disappointing that the ACAS could not identify deciles of stenosis that carry the greatest risk. An annual increase in stroke risk as small as 1% would reduce the number needed to treat from 67 to 28 and perhaps tip the scales in favor of surgery. It is a reasonable hypothesis that in asymptomatic patients with the highest risk ( 80% stenosis), favorable benefit will be found. No randomized trial has yet confirmed this hypothesis, but such a finding may emerge from the European Asymptomatic Carotid Surgery Trial [5].