Improving selection of patients with less than 60% asymptomatic internal carotid artery stenosis for follow-up carotid artery duplex scanning

Purpose: The Asymptomatic Carotid Atherosclerosis Study (ACAS) indicated significant benefit fi om endarterectomy compared with medical therapy for patients with 60% to 99% asymptomatic internal carotid artery (ICA) stenoses. To date, optimal selection of patients for vascular laboratory follow-up to determine progression from <60% to greater than or equal to 60% asymptomatic ICA stenosis is unknown. To determine which patients with <60% asymptomatic ICA stenoses are at greatest risk for short-term progression to greater than or equal to 60% without symptoms, we reviewed vascular laboratory results and clinical risk factors of consecutive patients who were prospectively observed in a study of atherosclerosis progression. Methods: Carotid duplex studies were obtained every 6 months and were reviewed for progression from <60% to greater than or equal to 60% asymptomatic ICA stenosis by using criteria that were developed and reported by our laboratory. Clinical risk factors and velocities from initial duplex scans were analyzed for association with progression from <60% to greater than or equal to 60% ICA stenoses without symptoms. Results: Two hundred sixty-three patients (mean age, 66 years) with 434 asymptomatic <60% ICA stenoses were prospectively observed for a mean of 20 months, with a mean of four examinations per patient. Seventeen patients (6.5%) and 18 ICAs (4%) progressed without symptoms to greater than or equal to 60% ICA stenoses at a mean of 18 months, Clinical risk factors associated with progression to greater than or equal to 60% asymptomatic ICA stenosis included elevated systolic blood pressure and decreased ankle-brachial index (p = 0.05). The mean initial ICA peak systolic velocity (PSV) in ICAs that progressed to greater than or equal to 60% asymptomatic stenoses was 180 cm/sec, compared with 104 cm/sec in asymptomatic ICAs that did not progress to greater than or equal to 60% (p = 0.0003). Thirty-one percent of asymptomatic ICAs that had initial PSVs of 175 cm/sec or greater progressed to greater than or equal to 60% stenosis, whereas only 1.8% that had initial PSVs less than 175 cm/sec progressed to greater than or equal to 60% asymptomatic stenoses (p < 0.001). The life-table-determined rate of freedom from progression to greater than or equal to 60% stenosis was 94% at 4 years for asymptomatic ICA lesions that had initial PSVs less than 175 cm/sec, compared with 14% at 3 years for lesions that had initial PSVs greater than or equal to 175 cm/sec. Conclusions: Early progression from <60% asymptomatic ICA stenoses to greater than or equal to 60% asymptomatic ICA stenoses occurs infrequently. Patients who are at the greatest risk of early progression without symptoms to an ACAS-positive lesion can be identified from the ICA PSV at their initial duplex examination. Early vascular laboratory follow-up of asymptomatic ICA stenoses may be limited to a relatively small group.