The implications of different criteria for grading carotid artery stenosis by duplex ultrasound

Duplex ultrasound is the first-line mode of investigation for carotid stenosis, whose severity could be graded according to NASCET or St. Mary's ratio criteria. The aim of this study was to compare these two methods and review the literature.

All patients who had carotid duplex ultrasound in a 1-month period were included. The reports and images were retrospectively reviewed, and the grade of carotid artery stenosis was then recalculated using the St. Mary's Ratio.

A total of 245 (160 men) patients with a mean age 70.4 years (±11.5) were assessed, and 469 extracranial carotid systems were analyzed. Pearson's Coefficient revealed strong correlation (r = 0.79, p = 0.05) between the two methods. In 114 (24.3%) internal carotid arteries, results were different. Of these, 26 (22.8%) would have gone for surgery had they been assessed using the St. Mary's Ratio and not the NASCET grading criteria. Conversely, two internal carotid arteries (1.75%) went for surgery using the NASCET grading criteria that would not have had to should the St. Mary's Ratio been used.

Although there is a strong level of correlation between the two criteria, choosing one or the other would have a significant impact on the patient' selection for surgery.