Variation in Ultrasound Diagnostic Thresholds for Carotid Stenosis in the United States

Variation in Ultrasound Diagnostic Thresholds for Carotid Stenosis in the United StatesArticle, see p 946 C onsider the case of C.S., a 69-year-old man who has a moderately severe 50% to 69% left internal carotid stenosis, which has been followed for years by his physician with serial duplex scans at accredited Vascular Laboratory A. When that physician retired, C.S. transitioned his care to another physician, who ordered his annual carotid duplex scan to be performed at accredited Vascular Laboratory B. C.S. was alarmed when the report released to his electronic medical record stated that he now had a >70% left internal carotid stenosis.The peak systolic velocity in the left internal carotid artery is 210 cm/s on both examinations.Carotid duplex ultrasound was developed in the 1970s at the University of Washington by a team led by Dr D. Eugene Strandness Jr, 1 and although catheterbased arteriography remains the gold standard imaging modality for carotid artery disease, major societal guidelines now recommend carotid duplex ultrasound as the initial diagnostic imaging modality to evaluate the severity of carotid stenosis.2,3 Furthermore, if carotid duplex ultrasound is unequivocal in the identification of 50% to 99% stenosis in symptomatic patients and 70% to 99% stenosis in asymptomatic patients, carotid duplex findings are sufficient to make decisions regarding further management, including intervention.2 Because carotid duplex ultrasound is widely available and noninvasive, it is the most common imaging examination performed worldwide to diagnose carotid disease.4 Consequently, the criteria used for classifying stenosis severity by carotid duplex ultrasound must be accurate and reproducible.Ultrasound accrediting organizations such as the Intersocietal Accreditation Commission (IAC) and the American College of Radiology attempt to standardize the performance of vascular ultrasound examinations, but they do not require the use of a single set of carotid duplex criteria for the classification of carotid stenosis.Instead, they stipulate that each accredited laboratory have a set of interpretation criteria that are used by all members of the technical and medical staff and are either derived from the literature or developed and validated internally.5,6 Therefore, it is not surprising that among accredited vascular laboratories, there is wide variability in carotid interpretation criteria.7 Even with the publication of proposed standardized velocity criteria for carotid duplex ultrasound by a multispecialty panel in 2003, 4 only 24% of IAC-accredited vascular laboratories were using these standardized criteria in 2011, and there were 17 sets of diagnostic criteria in use among 117 laboratories, with the remaining facilities using locally developed (6 laboratories) or unreferenced or hybrid criteria (29 laboratories).7 Whereas there is clearly wide variability in the diagnostic criteria used in accredited facilities for carotid duplex ultrasound, the clinical implications of this variability are unclear.