Reappraisal Of Internal Carotid Artery Stenosis Velocity Thresholds Utilizing High-Resolution B-Mode Ultrasound Validated With CTA: Do Current Practice Thresholds Overestimate Carotid Bifurcation Disease?

Wael E Shaalan, Carl Wahlgren, Tina Desai, Giancarlo Piano, Christopher Skelly, Eileen French-Sherry, Laurie Lozanski, Hisham Bassiouny. 
University of Chicago, Chicago, IL.

OBJECTIVES: Reliability of the most commonly used duplex ultrasound (US) velocity thresholds for internal carotid artery (ICA) stenosis has been questioned since these thresholds were developed using a subjective estimate of the stenosis outer wall diameter on arteriography. In this study maximum % diameter ICA stenosis was objectively measured using high resolution B-mode US validated with CTA and used to determine optimum PSV, EDV, and PSV ICA/CCA ratio thresholds for ≥ 50% and ≥ 80% ICA stenosis.

METHODS: B-mode US and CTA images of 74 ICA stenoses were compared to validate accuracy of the US measurements. In 337 mild, moderate, and severe ICA stenoses, the minimal residual lumen and the corresponding outer ICA or bulb diameter were determined on longitudinal and transverse images. Calcified carotid segments and patients with contralateral occlusion were excluded. In each study, the highest PSV, EDV, and ICA/CCA ratio were recorded. Using ROC analysis, the optimum threshold for each hemodynamic parameter was determined to predict ≥ 50% (n = 281) and ≥ 80% (n = 62) bulb ICA stenosis.

RESULTS: There was excellent agreement between B-mode ultrasound and CTA (r = 0.9, p = 0.002) (graph). The sensitivity, specificity, PPV, and NPV of the different velocity criteria for the diagnosis of ICA stenosis ≥ 50% and ≥ 80% are shown in table below.

When both PSV of ≥155 cms/sec and ICA/CCA ratio of ≥ 2 were combined for the detection of ≥ 50% ICA stenosis, a PPV of 97% and an accuracy of 82% were obtained. For an ≥ 80% ICA stenosis, an EDV of ≥ 140 cms/sec, a PSV of ≥ 370 cms/sec and an ICA/CCA ratio of ≥ 6 had acceptable probability values.

CONCLUSIONS: Compared to established velocity thresholds commonly applied in practice (Strandness criteria), a substantially higher PSV (155 vs. 125 cms/sec) was more accurate for detecting ≥ 50% bulb ICA stenosis. In combination, a PSV of ≥155 cms/sec and an ICA/CCA ratio of 2 have excellent predictive value for this stenosis category. For an ≥ 80% ICA stenosis, an EDV of 140 cms/sec, a PSV of ≥ 370 cms/sec, and an ICA/CCA ratio of ≥ 6 are equally reliable. Current duplex US ≥ 50% ICA stenosis criteria appear to overestimate carotid bifurcation disease and may predispose patient with asymptomatic carotid disease to untoward costly diagnostic imaging and intervention.