Determination of sixty percent or greater carotid artery stenosis by duplex Doppler ultrasonography.

PURPOSE

The Asymptomatic Carotid Atherosclerosis Study, demonstrating the benefit of carotid endarterectomy for symptom-free patients with 60% or greater carotid artery stenosis, has given rise to the need for development of screening parameters for detection of these lesions. Traditional duplex categories (50% to 79%, 80% to 99%) are not applicable. We sought to develop duplex criteria for determination of 60% or greater carotid artery stenosis by comparison with arteriography.

METHODS

The duplex scans and arteriograms of 110 patients (210 carotid arteries), obtained within 1 month of each other, were reviewed by blinded readers. Arteriographic stenosis was determined by the method of the Asymptomatic Carotid Atherosclerosis Study. Duplex measurements of peak systolic velocity (PSV) and end-diastolic velocity (EDV) were recorded, and ratios of velocities in the internal and common carotid arteries (ICA, CCA) were calculated. Sensitivity, specificity, positive and negative predictive values (PPV, NPV), and accuracy were determined, and receiver-operator characteristic curves were generated.

RESULTS

Interobserver agreement for measurement of arteriographic stenosis was "almost perfect" (kappa = 0.86). The criteria determined for detection of 60% or greater stenosis were as follows: PSVICA > 170 cm/sec (sensitivity 98%, specificity 87%, PPV 88%, NPV 98%, accuracy 92%), EDVICA > 40 cm/sec (sensitivity 97%, specificity 52%, PPV 86%, NPV 86%, accuracy 86%), PSVICA/PSVCCA > 2.0 (sensitivity 97%, specificity 73%, PPV 78%, NPV 96%, accuracy 76%), EDVICA/EDVCCA > 2.4 (sensitivity 100%, specificity 80%, PPV 88%, NPV 100%, accuracy 88%). If all of the above criteria were met, 100% accuracy was achieved.

CONCLUSION

It is concluded that 60% or greater carotid artery stenosis can be reliably determined by duplex criteria. The use of receiver-operator characteristic curves allows the individualization of duplex criteria appropriate to specific clinical situations of patient screening for lesions (high sensitivity and NPV) or use as a sole preoperative imaging modality (high PPV). Individual vascular laboratories must validate their own results.