Screening for Carotid Artery Stenosis with the Continuous Wave Doppler Listening Examination

Abstract

The Asymptomatic Carotid Atherosclerosis Study (ACAS) demonstrated that carotid endarterectomy was beneficial for selected asymptomatic patients with carotid artery stenoses greater than 60%. However, the optimal technique for identifying these asymp tomatic lesions remains undefined. Carotid duplex is the current standard, but cost limits its use for screening large populations. This study prospectively examines the audible interpretation of the continuous wave (CW) Doppler signal as a screening tool for carotid artery stenoses. Carotid artery listening examinations were performed using CW Doppler immedi ately before standard carotid duplex examinations in 207 patients (414 examinations) by two certified vascular technologists. Stenosis in the extracranial internal carotid artery was classified as <50°/a or ≥50% based on the listening examination alone, and the results were correlated with the duplex findings (duplex ≥50% stenosis—peak systolic frequency [PSF] ≥5 KHz). The results were analyzed in two groups to determine whether accuracy improved with experience (phase I: 107 patients; phase II: 100 patients). The overall sensitivity (95% confidence interval), specificity, positive predictive value, and negative predictive value of the CW Doppler listening examination compared with carotid duplex was 76% (67.4-83.8), 97% (94.4-98.6), 91% (83.0-95.6), and 92% (87.9-94.3), respectively, for the 414 examinations. The sensitivity (phase I: 68% vs phase II: 85%, P<0.05) increased during the second phase of the study although no significant change was noted in the specificity (phase I: 98% vs phase II: 96%, P=0.44), positive predictive value (phase I: 93% vs phase II: 89%, P=0.71), or negative predictive value (phase I: 89% vs phase II: 95%, P=0.11). Twenty-one of the 27 false-negative listening examinations (CW Doppler <50%, duplex ≥50%) occurred in arteries with stenoses between 50% and 69% (PSF 5-<7 KHz) on duplex. There were only six false- negative examinations among 80 lesions ≥70% on duplex (PSF ≥7 KHz). The time (2.1 ±1.0 vs 12.6 ±9.6 min, P<0.05, Student's t test) and cost ($22.95 vs $166.47) of the listening examination were both less than those of duplex. The CW Doppler carotid listening examination is an accurate, cost-effective alterna tive to the carotid duplex examination for screening asymptomatic patients for significant carotid artery stenoses.