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

The Asymptomatic Carotid Atherosclerosis Study established benefit of carotid endarterectomy for 60% to 99% asymptomatic internal carotid artery (ICA) stenosis. Optimal follow-up intervals to detect progression from < 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 velocities (PSVs) of 175 cm/s or more on initial duplex were at high risk for progression. Prospective evaluation of this hypothesis and determination of optimal duplex follow-up intervals for asymptomatic patients with < 60% ICA stenosis form the basis of this report.

All patients who underwent initial carotid duplex examination for any indication since January 1, 1995, with at least one patent, asymptomatic, previously nonoperated ICA with < 60% stenosis; with 6 months' or greater follow-up; and with one or more repeat duplex examinations were entered into the study. On the basis of the initial duplex examination, ICAs were classified into two groups: those with a PSV less than 175 cm/s and those with a PSV of 175 cm/s or more. Follow-up duplex examinations were performed at varying intervals to detect progression from < 60% to 60%-99% ICA stenosis with criteria previously reported (both PSV > or = 260 cm/s and end-diastolic velocity > or = 70 cm/s).

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 occluded 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 progression 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 less 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 than 175 cm/s (P <.0001).

Patients with < 60% ICA stenosis and PSVs of 175 cm/s or more on initial duplex examination are significantly more likely to progress asymptomatically to 60%-99% ICA stenosis, and progression is sufficiently frequent to warrant follow-up duplex studies at 6-month intervals. Patients with < 60% ICA stenosis and initial PSVs less than 175 cm/s may have follow-up duplex examinations safely deferred for 2 years.