Duplex Doppler ultrasonography was accurate in determining 60% or greater carotid artery stenosis
ACP J Club. 1996 May-June;124:75. doi:10.7326/ACPJC-1996-124-3-075
Carpenter JP, Lexa FJ, Davis JT. Determination of sixty percent or greater carotid artery stenosis by duplex Doppler ultrasonography. J Vasc Surg. 1995 Dec;22:697-705. [PubMed ID: 8523604]
To develop duplex Doppler ultrasonography criteria to detect ≥ 60% carotid artery stenosis in symptom-free patients.
Blinded comparison of duplex Doppler ultrasonography with arteriography.
A university hospital in Pennsylvania, USA.
110 patients who were evaluated with both duplex scanning and carotid arteriography for surgical treatment of carotid artery atherosclerosis.
Description of Test and Diagnostic Standard
Duplex Doppler ultrasonography was done using a Hewlett-Packard Sonos 1000 Color Duplex System with a 7.5-MHz linear array transducer with 5.6-MHz Doppler frequency. Velocity waveforms were obtained from the common carotid artery (CCA); the proximal, mid, and distal internal carotid arteries (ICAs); and the external carotid artery. The highest peak systolic velocity (PSV) and end diastolic velocity (EDV) were recorded at each location. The diagnostic standard was percutaneous catheter arteriography.
Main Outcome Measures
Sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), likelihood ratios (LRs), and accuracy were calculated for PSV and EDV in the distal CCA or ICA location (PSVICA, EDVICA), as were their ratios (PSVICA/PSVCCA and EDVICA/EDVCCA).
For detecting ≥ 60% arteriographic stenosis, PSVICA > 170 cm provided high accuracy (92%), EDVICA > 40 cm provided an accuracy of 86%, a ratio of > 2.0 for PSVICA/PSVCCA gave an accuracy of 76%, and a ratio of > 2.4 for EDVICA/EDVCCA gave an accuracy of 88%; test characteristics are displayed in the Table. When all 4 criteria were met, the accuracy, sensitivity, specificity, PPV, and NPV were all 100%. 69% of the carotid arteries with ≥ 60% stenosis met all 4 criteria.
Duplex Doppler ultrasonography was effective in identifying patients with ≥ 60% arteriographic stenosis. Precise cut points could not be made without sacrificing either sensitivity or specificity.
Source of funding: Not stated.
For article reprint: Dr. J.P. Carpenter, Hospital of the University of Pennsylvania, 4 Silverstein/3400 Spruce Street, Philadelphia, PA 19104, USA. FAX 215-662-7476.
*Numbers calculated from data in article.
Table. Diagnostic tests for detecting > 60% carotid artery stenosis using percutaneous catheter arteriography as the diagnostic standard*
|PSVICA > 170 cm/s||98%||87%||7.5||0.02|
|PSVICA > 40 cm/s||97%||52%||2.02||0.06|
|PSVICA/PSVCCA > 2.0||97%||73%||3.6||0.04|
|EDVICA/EDVCCA > 2.4||100%||80%||5.0||0|
*PSV = peak systolic velocity; EDV = end diastolic velocity; ICA = internal carotid artery; CCA = common carotid artery. LRs defined in Glossary and calculated from data in article.
The North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Atherosclerosis Study (ACAS) determined threshold levels of ICA stenosis (70% and 60%, respectively) for carotid endarterectomy. Both studies used the distal cervical ICA as the reference vessel to calculate ICA stenosis by angiography, but duplex ultrasound criteria to determine ICA stenosis have been developed using the ICA bulb as the reference site. The bulb is wider than the distal cervical ICA, and the estimation of stenoses are higher. Several recent studies (1-3), including this one by Carpenter and colleagues, have re-examined duplex criteria for ICA stenosis to try to improve the relevance of duplex scanning with respect to the results from NASCET and ACAS.
Carotid angiography is expensive and accounted for almost 50% of the surgical stroke morbidity in the ACAS. In addition, carotid endarterectomy can be done safely using only duplex scanning to confirm ICA stenosis (4). Unfortunately, the criteria for determining > 60% ICA stenosis presented in this study should not and cannot be generalized to all vascular laboratories. The optimal duplex criteria for threshold levels of ICA stenosis vary with each manufacturer's duplex ultrasound device (1-3, 5). All vascular laboratories should verify criteria for ICA stenosis in their vascular laboratory, a current requirement of the Intersocietal Commission on the Accreditation of Vascular Laboratories.
Based on knowledge of the accuracy of their own vascular laboratories and the level of expertise in doing carotid endarterectomy, individual physicians must decide locally on how to use noninvasive carotid testing. Studies such as this one provide important starting points but do not obviate the need for each vascular laboratory to have ongoing quality control.
Gregory L. Moneta, MD
Oregon Health Sciences UniversityPortland, Oregon, USA
1. Moneta GL, Edwards JM, Chitwood RW, et al. Correlation of North American Symptomatic Carotid Endarterectomy Trial (NASCET) angiographic definition of 70% to 99% internal carotid artery stenosis with duplex scanning. J Vasc Surg. 1993;17:152-9.
2. Faught WE, Mattos MA, van Bemmelen PS, et al. Color-flow duplex scanning of carotid arteries: new velocity criteria based on receiver operator characteristic analysis for threshold stenoses used in the symptomatic and asymptomatic carotid trials. J Vasc Surg. 1994;19:818-28.