Optimizing duplex follow-up in patients with an asymptomatic internal carotid artery stenosis of less than 60%

Objectives: The Asymptomatic Carotid Atherosclerosis Study established bene fit of carotid endarterectomy for 60% to 99% asymptomatic internal carotid artery (ICA) stenosis. Optimal follow-up intervals to detect progression fr om < 60% to 60%-99% ICA stenosis are unknown. In a previous study from our laboratory, we found that ICAs with < 60% stenosis and peak systolic veloci ties (PSVs) of 175 cm/s or more on initial duplex were at high risk for pro gression. Prospective evaluation of this hypothesis and determination of op timal duplex follow-up intervals for asymptomatic patients with < 60% ICA s tenosis form the basis of this report. Methods: All patients who underwent initial carotid duplex examination for any indication since January 1, 1995, with at least one patent, asymptomati c, previously nonoperated ICA with < 60% stenosis; with 6 months' or greate r follow-up; and with one or more repeat duplex examinations were entered i nto the study. On the basis of the initial duplex examination, ICAs were cl assified into two groups: those with a PSV less than 175 cm/s and those wit h a PSV of 175 cm/s or more. Follow-up duplex examinations were performed a t varying intervals to detect progression from < 60% to 60%-99% ICA stenosi s with criteria previously reported (both PSV <greater than or equal to> 26 0 cm/s and end-diastolic velocity greater than or equal to 70 cm/s). Results: A total of 407 patients (640 asymptomatic ICAs with < 60% stenosis ) underwent serial duplex scans (mean follow up, 22 months). Three ICAs (0. 5%) became symptomatic and progressed to 60%-99% ICA stenosis at a mean of 21 months (all transient ischemic attacks), whereas four other ICAs occlude d without stroke during follow-up. Progression to 60%-99% stenosis without symptoms was detected in 46 ICAs (7%) (mean, 18 months). Of the 633 patent asymptomatic arteries, 548 ICAs (87%) had initial PSVs less than 175 cm/s, and 85 ICAs (13%) had initial PSVs of 175 cm/s or more. Asymptomatic progre ssion to 60%-99% ICA stenosis occurred in 22 (26%) of 85 ICAs with initial PSVs of 175 cm/s or more, whereas 24 (4%) of 548 ICAs with initial PSVs les s than 175 cm/s progressed (P < .0001). The Kaplan-Meier method was used to determine freedom from progression at 6 months, 12 months, and 24 months, which was 95%, 83%, and 70% for ICAs with initial PSVs of 175 cm/s or more versus 100%, 99%, and 95%, respectively, for ICAs with initial PSVs less th an 175 cm/s (P < .0001). Conclusions: Patients with < 60% ICA stenosis and PSVs of 175 cm/s or more on initial duplex examination are significantly more likely to progress asy mptomatically to 60%-99% ICA stenosis, and progression is sufficiently freq uent to warrant follow-up duplex studies at 6-month intervals. Patients wit h < 60% ICA stenosis and initial PSVs less than 175 cm/s may have follow-up duplex examinations safely deferred for 2 years.