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

Color Duplex Ultrasonography for the Evaluation of Innominate, Subclavian, and Common Carotid Artery Stenosis

OBJECTIVE

This study aimed to validate the efficiency of Doppler ultrasonography for predicting the innominate, subclavian, and common carotid artery stenosis.

METHODS

This retrospective multicenter study between 2013 and 2022 enrolled 636 patients who underwent carotid Doppler ultrasonography and subsequent digital subtraction angiography. And 58 innominate artery stenosis, 147 common carotid artery stenosis, and 154 subclavian artery stenosis were included. The peak systolic velocity at innominate, subclavian, and common carotid artery, and velocity ratios of innominate artery to common carotid artery, innominate artery to subclavian artery, and common carotid artery to internal carotid artery were measured or calculated. The threshold values were determined using receiver operating characteristic analysis.

RESULTS

The threshold values of innominate artery stenosis were peak systolic velocity >206 cm/s (sensitivity: 82.8%; specificity: 91.4%) to predict ≥50% stenosis and >285 cm/s (sensitivity: 89.2%; specificity: 94.9%) to predict ≥70% stenosis. The threshold values of common carotid artery stenosis were peak systolic velocity >175 cm/s (sensitivity: 78.2%; specificity: 91.9%) to predict ≥50% stenosis and >255 cm/s (sensitivity: 87.1%; specificity: 87.2%) to predict ≥70% stenosis. The threshold values of subclavian artery stenosis were peak systolic velocity >200 cm/s (sensitivity: 68.2%; specificity: 84.4%) to predict ≥50% stenosis and >305 cm/s (sensitivity: 57.9%; specificity: 91.4%) to predict ≥70% stenosis.

CONCLUSIONS

Symptomatic patients with ultrasonic parameters of velocity at innominate artery ≥206 cm/s, velocity at common carotid artery ≥175 cm/s, or velocity at subclavian artery ≥200 cm/s need to be considered for further verification and whether revascularization is necessary.

Appropriateness of care: Asymptomatic carotid stenosis including transcarotid artery revascularization

Carotid artery stenosis is one of the most common diagnoses treated by vascular specialists in the United States. The optimal management of carotid stenosis remains controversial, however, with notable variation surrounding diagnostic imaging modalities, longitudinal surveillance, medical therapies, and procedural interventions. Data from high-quality randomized controlled trials and observational studies form the foundation for current management paradigms and societal guidelines that inform clinical practice. Presently, a diagnosis of carotid disease is most often established with duplex ultrasound and supplemental cross-sectional imaging using computed tomography or magnetic resonance angiography as needed to provide additional anatomic information. All patients with documented occlusive disease should receive goal-directed medical therapy with antiplatelet agents and a lipid-reduction strategy, most commonly with a statin. Those with severe carotid stenosis and an acceptable life expectancy may be considered for carotid artery revascularization. The proceduralist should optimally consider a shared decision-making approach in which the tradeoffs of revascularization can be carefully considered with the patient to optimize informed therapeutic decision making. In current practice, three distinct procedure options exist to treat carotid artery stenosis, including carotid endarterectomy, transfemoral carotid artery stenting, and transcarotid artery revascularization. It should be noted that each procedure, although often used interchangeably in most clinical settings, carry technical nuances and outcome disparities. In this review, each of these topics are explored and various approaches are outlined surrounding the appropriate use of treatments for patients with asymptomatic carotid artery stenosis.

Progression rate of radiation-induced carotid stenosis in head and neck cancer survivors after statin treatment: a retrospective cohort study

BACKGROUND AND AIMS

Whether statin treatment is effective in retarding the progression of radiation-induced carotid stenosis (RICS) in head and neck cancer (HNC) survivors has not been well studied. The purpose of this study was to assess the association of statin treatment with RICS progression rate in HNC survivors after radiotherapy.

METHODS

We conducted a retrospective cohort study at Sun Yat-sen Memorial Hospital, Sun Yat-sen University in Guangzhou, China. Between January 2010 and December 2021, we screened HNC survivors whose carotid ultrasound scans had shown stenosis of the common and/or internal carotid arteries. The primary outcome was the RICS progression rate. We compared eligible patients treated with statins with those who did not in multivariable Cox regression models.

RESULTS

A total of 200 patients were included in this study, of whom 108 received statin treatment and 92 did not. Over a mean follow-up time of 1.5 years, 56 (28.0%) patients showed RICS progression, 24 (42.9%) and 32 (57.1%) in the statin and control groups, respectively. The statin group showed less RICS progression than the control group (adjusted-HR 0.49, 95% CI 0.30-0.80, P = 0.005). In the subgroup analysis, there was no significant interaction in the effect of statins on lowering RICS progression rate in the subgroups stratified by baseline low-density lipoprotein cholesterol (LDL-C) levels (P for interaction = 0.53) or baseline degrees of stenosis (P for interaction = 0.50).

CONCLUSIONS

Statin treatment was associated with a lower risk of RICS progression in patients with HNC after radiotherapy, regardless of baseline LDL-C level and baseline stenosis degrees.

Imaging modality-dependent carotid stenosis severity variations against intravascular ultrasound as a reference: Carotid Artery intravasculaR Ultrasound Study (CARUS)

PURPOSE

Different non-invasive and invasive imaging modalities are used to determine carotid artery stenosis severity that remains a principal parameter in clinical decision-making. We compared stenosis degree obtained with different modalities against vascular imaging gold standard, intravascular ultrasound, IVUS.

METHODS

300 consecutive patients (age 47-83 years, 192 men, 64% asymptomatic) with carotid artery stenosis of " ≥ 50%" referred for potential revascularization received as per study protocol (i) duplex ultrasound (DUS), (ii) computed tomography angiography (CTA), (iii) intraarterial quantitative angiography (iQA) and (iv) and (iv) IVUS. Correlation of measurements with IVUS (r), proportion of those concordant (within 10%) and proportion of under/overestimated were calculated along with recipient-operating-characteristics (ROC).

RESULTS

For IVUS area stenosis (AS) and IVUS minimal lumen area (MLA), there was only a moderate correlation with DUS velocities (peak-systolic, PSV; end-diastolic, EDV; r values of 0.42-0.51, p < 0.001 for all). CTA systematically underestimated both reference area and MLA (80.4% and 92.3% cases) but CTA error was lesser for AS (proportion concordant-57.4%; CTA under/overestimation-12.5%/30.1%). iQA diameter stenosis (DS) was found concordant with IVUS in 41.1% measurements (iQA under/overestimation 7.9%/51.0%). By univariate model, PSV (ROC area-under-the-curve, AUC, 0.77, cutoff 2.6 m/s), EDV (AUC 0.72, cutoff 0.71 m/s) and CTA-DS (AUC 0.83, cutoff 59.6%) were predictors of ≥ 50% DS by IVUS (p < 0.001 for all). Best predictor, however, of ≥ 50% DS by IVUS was stenosis severity evaluation by automated contrast column density measurement on iQA (AUC 0.87, cutoff 68%, p < 0.001). Regarding non-invasive techniques, CTA was the only independent diagnostic modality against IVUS on multivariate model (p = 0.008).

CONCLUSION

IVUS validation shows significant imaging modality-dependent variations in carotid stenosis severity determination.

What Is the Role of Transcarotid Artery Revascularization in the Treatment of Carotid Stenosis?

TCAR for the Treatment of Carotid StenosisTwo carotid revascularization strategies, CEA and TF-CAS, have been informed by high-quality randomized trials. In contrast, no randomized trial evidence exists regarding a newer procedural option, TCAR. The authors discuss these procedures and propose a randomized trial to inform the role of TCAR in the treatment of carotid stenosis.

Procedural Safety Comparison Between Transcarotid Artery Revascularization, Carotid Endarterectomy, and Carotid Stenting: Perioperative and 1-Year Rates of Stroke or Death

Background Transcarotid artery revascularization (TCAR) was approved by the Food and Drug Administration in 2015 for patients with carotid artery stenosis. However, no randomized trial to evaluate TCAR has been performed to date, and previous reports have important limitations. Accordingly, we measured stroke or death after TCAR compared with carotid endarterectomy (CEA) and transfemoral carotid artery stenting (TF-CAS). Methods and Results We used the Vascular Quality Initiative registry to study patients who underwent TCAR, CEA, or TF-CAS from September 2016 to June 2021. Our primary outcomes were perioperative and 1-year stroke or death. We used logistic regression for risk adjustment for perioperative outcomes and Cox regression for risk adjustment for 1-year outcomes. We used a 2-stage residual inclusion instrumental variable (IV) method to adjust for selection bias and other unmeasured confounding. Our instrument was a center's preference to perform TCAR versus CEA or TF-CAS. We performed a subgroup analysis stratified by presenting neurologic symptoms. We studied 21 234 patients who underwent TCAR, 82 737 who underwent CEA, and 14 595 who underwent TF-CAS across 662 centers. The perioperative rate of stroke or death was 2.0% for TCAR, 1.7% for CEA, and 3.7% for TF-CAS (P<0.001). Compared with TCAR, the IV-adjusted odds ratio of perioperative stroke or death for CEA was 0.74 (95% CI, 0.55-0.99) and for TF-CAS was 1.66 (95% CI, 0.99-2.79). Results were similar among both symptomatic and asymptomatic patients. The 1-year rate of stroke or death was 6.4% for TCAR, 5.2% for CEA, and 9.7% for TF-CAS (P<0.001). Compared with TCAR, the IV-adjusted hazard ratio of 1 year stroke or death for CEA was 0.97 (95% CI, 0.80-1.17), and for TF-CAS was 1.45 (95% CI, 1.04-2.02). IV analysis further demonstrated that symptomatic patients with carotid stenosis had the lowest 1-year likelihood of stroke or death with TCAR (compared with TCAR, symptomatic IV-adjusted hazard ratio for CEA: 1.30 [95% CI, 1.04-1.64], and TF-CAS: 1.86 [95% CI, 1.27-2.71]). Conclusions Perioperative stroke or death was greater following TCAR when compared with CEA. However, at 1 year there was no statistically significant difference in stroke or death between the 2 procedures. TCAR performed favorably compared with TF-CAS at both time points. Although CEA remains the gold standard procedure for patients with carotid stenosis, TCAR appears to be a safe alternative to CEA and TF-CAS when used selectively and may be useful when treating symptomatic patients.

Extra-Cranial Carotid Artery Stenosis: An Objective Analysis of the Available Evidence

Background and Purpose

Carotid stenosis is arterial disease narrowing of the origin of the internal carotid artery (main brain artery). Knowing how to best manage this is imperative because it is common in older people and an important cause of stroke. Inappropriately high expectations have grown regarding the value of carotid artery procedures, such as surgery (endarterectomy) and stenting, for lowering the stroke risk associated with carotid stenosis. Meanwhile, the improving and predominant value of medical intervention (lifestyle coaching and medication) continues to be underappreciated.

Methods and Results

This article aims to be an objective presentation and discussion of the scientific literature critical for decision making when the primary goal is to optimize patient outcome. This compilation follows from many years of author scrutiny to separate fact from fiction. Common sense conclusions are drawn from factual statements backed by original citations. Detailed research methodology is given in cited papers. This article has been written in plain language given the importance of the general public understanding this topic. Issues covered include key terminology and the economic impact of carotid stenosis. There is a summary of the evidence-base regarding the efficacy and safety of procedural and medical (non-invasive) interventions for both asymptomatic and symptomatic patients. Conclusions are drawn with respect to current best management and research priorities. Several "furphies" (misconceptions) are exposed that are commonly used to make carotid stenting and endarterectomy outcomes appear similar. Ongoing randomized trials are mentioned and why they are unlikely to identify a routine practice indication for carotid artery procedures. There is a discussion of relevant worldwide guidelines regarding carotid artery procedures, including how they should be improved. There is an outline of systematic changes that are resulting in better application of the evidence-base.

Conclusion

The cornerstone of stroke prevention is medical intervention given it is non-invasive and protects against all arterial disease complications in all at risk. The "big" question is, does a carotid artery procedure add patient benefit in the modern era and, if so, for whom?

North American lower-extremity revascularization and amputation during COVID-19: Observations from the Vascular Quality Initiative

INTRODUCTION

The coronavirus disease 2019 (COVID-19) pandemic's impact on vascular procedural volumes and outcomes has not been fully characterized.

METHODS

Volume and outcome data before (1/2019 - 2/2020), during (3/2020 - 4/2020), and following (5/2020 - 6/2020) the initial pandemic surge were obtained from the Vascular Quality Initiative (VQI). Volume changes were determined using interrupted Poisson time series regression. Adjusted mortality was estimated using multivariable logistic regression.

RESULTS

The final cohort comprised 57,181 patients from 147 US and Canadian sites. Overall procedure volumes fell 35.2% (95% CI 31.9%, 38.4%, p < 0.001) during and 19.8% (95% CI 16.8%, 22.9%, p < 0.001) following the surge, compared with presurge months. Procedure volumes fell 71.1% for claudication (95% CI 55.6%, 86.4%, p < 0.001) and 15.9% for chronic limb-threatening ischemia (CLTI) (95% CI 11.9%, 19.8%, p < 0.001) but remained unchanged for acute limb ischemia (ALI) when comparing surge to presurge months. Adjusted mortality was significantly higher among those with claudication (0.5% vs 0.1%; OR 4.38 [95% CI 1.42, 13.5], p = 0.01) and ALI (6.4% vs 4.4%; OR 2.63 [95% CI 1.39, 4.98], p = 0.003) when comparing postsurge with presurge periods.

CONCLUSION

The first North American COVID-19 pandemic surge was associated with a significant and sustained decline in both elective and nonelective lower-extremity vascular procedural volumes. When compared with presurge patients, in-hospital mortality increased for those with claudication and ALI following the surge.

A Reappraisal of CT Angiography Derived Duplex Ultrasound Velocity Criteria With a Comparison to Digital Subtraction Angiography in Patients With Carotid Artery Stenosis

BACKGROUND

Traditionally, carotid duplex ultrasound (CDUS) velocity criteria have been derived from angiography. Recent studies support a shift toward computed tomography angiography (CTA) derived velocity criteria; however, they lack a comparison to angiography. The purposes of this study are to validate CTA derived measurements with digital subtraction angiography (DSA) and to update our previous CTA-derived velocity criteria for 50% and 80% stenosis.

METHODS

All patients between 2010 and 2019 who underwent CDUS and a neck CTA within 6 months were identified for a retrospective review. Vessel diameter and corresponding CDUS data were recorded. Additional DSA measurements were recorded for a subset of patients. Data from this cohort were added to a previously reported deidentified data set from patients between 2000 and 2009. Receiver operating characteristic (ROC) curves were generated to determine optimal velocity thresholds. Spearman rank correlation was used to correlate measurements obtained by CTA to those obtained by DSA.

RESULTS

A total of 1139 vessels from 636 patients were analyzed. ROC analysis to identify ≥ 50% stenosis resulted in optimized thresholds of 143 cm/sec, 46.2 cm/sec, and 2.15 for peak systolic velocity (PSV), end-diastolic velocity (EDV), and PSV to common carotid artery PSV ratio (PSVR), respectively. ROC analysis to identify ≥ 80% stenosis resulted in optimized thresholds of 319 cm/sec, 87.2 cm/sec, and 3.49 for PSV, EDV, and PSVR, respectively. The degree of carotid artery stenosis for a subset of 124 vessels on CTA correlated well with that of DSA (ρ = 0.89, P< 0.0001).

CONCLUSIONS

These data demonstrate a high correlation between measurements obtained on CTA and DSA while forming reliable CTA-derived CDUS velocity criteria.

Optimization of duplex velocity criteria for diagnosis of internal carotid artery (ICA) stenosis: A report of the Intersocietal Accreditation Commission (IAC) Vascular Testing Division Carotid Diagnostic Criteria Committee

Diagnostic criteria to classify severity of internal carotid artery (ICA) stenosis vary across vascular laboratories. Consensus-based criteria, proposed by the Society of Radiologists in Ultrasound in 2003 (SRUCC), have been broadly implemented but have not been adequately validated. We conducted a multicentered, retrospective correlative imaging study of duplex ultrasound versus catheter angiography for evaluation of severity of ICA stenosis. Velocity data were abstracted from bilateral duplex studies performed between 1/1/2009 and 12/31/2015 and studies were interpreted using SRUCC. Percentage ICA stenosis was determined using North American Symptomatic Carotid Endarterectomy Trial (NASCET) methodology. Receiver operating characteristic analysis evaluated the performance of SRUCC parameters compared with angiography. Of 448 ICA sides (from 224 patients), 299 ICA sides (from 167 patients) were included. Agreement between duplex ultrasound and angiography was moderate (κ = 0.42), with overestimation of degree of stenosis for both moderate (50–69%) and severe (⩾ 70%) ICA lesions. The primary SRUCC parameter for ⩾ 50% ICA stenosis of peak-systolic velocity (PSV) of ⩾ 125 cm/sec did not meet prespecified thresholds for adequate sensitivity, specificity, and accuracy (sensitivity 97.8%, specificity 64.2%, accuracy 74.5%). Test performance was improved by raising the PSV threshold to ⩾ 180 cm/sec (sensitivity 93.3%, specificity 81.6%, accuracy 85.2%) or by adding the additional parameter of ICA/common carotid artery (CCA) PSV ratio ⩾ 2.0 (sensitivity 94.3%, specificity 84.3%, accuracy 87.4%). For ⩾ 70% ICA stenosis, analysis was limited by a low number of cases with angiographically severe disease. Interpretation of carotid duplex examinations using SRUCC resulted in significant overestimation of severity of ICA stenosis when compared with angiography; raising the PSV threshold for ⩾ 50% ICA stenosis to ⩾ 180 cm/sec as a single parameter or requiring the ICA/CCA PSV ratio ⩾ 2.0 in addition to PSV of ⩾ 125 cm/sec for laboratories using the SRUCC is recommended to improve the accuracy of carotid duplex examinations.

From Doppler to duplex: A personal early history of the vascular laboratory

In the mid-1970s, a group of clinicians and bioengineers at the University of Washington, under the direction of Dr D Eugene Strandness, Jr, built a prototype duplex scanner that combined B-mode imaging and pulsed Doppler flow detection in a single instrument. At that time, I was a general surgery resident with an interest in vascular disease, and arrangements were made for me to spend a year in the Strandness laboratory. The prototype duplex system was just being completed when I arrived in 1978, and I immediately became involved in a series of validation studies in which patients with carotid disease were scanned and spectral waveform parameters were correlated with independently read contrast arteriograms. This work resulted in the University of Washington duplex criteria for carotid artery disease, which have been widely adopted and modified. Subsequent advances in ultrasound technology expanded the applications of duplex scanning to the peripheral arteries and veins, as well as the abdominal vessels. In 1984, I joined Dr Strandness on the faculty in the Department of Surgery at the University of Washington where I have remained throughout my career. Over the years, I have had the opportunity to participate in many important developments, described in this article, that have helped to make the vascular laboratory the essential clinical resource that it is today.

Association of Adoption of Transcarotid Artery Revascularization With Center-Level Perioperative Outcomes

IMPORTANCE

Transcarotid artery revascularization (TCAR) may serve as a safer alternative to carotid endarterectomy (CEA) for certain patients with carotid artery stenosis.

OBJECTIVE

To determine the center-level association of TCAR adoption with overall perioperative outcomes for TCAR and CEA combined at centers performing both procedures.

DESIGN, SETTING, AND PARTICIPANTS

This comparative-effectiveness research was conducted with a difference-in-difference analysis using retrospective data from 2015 to 2019 from the Vascular Quality Initiative registry, a consortium of more than 400 centers in North America. Included patients underwent TCAR or CEA for carotid artery stenosis. Patients who underwent transfemoral carotid stenting were excluded. Data were analyzed from December 2019 through August 2020.

EXPOSURES

Center-level adoption of TCAR vs not.

MAIN OUTCOMES AND MEASURES

The rate of major adverse cardiovascular events (MACE), a composite of in-hospital stroke, myocardial infarction, or death at 30 days, was measured.

RESULTS

Among 86 027 patients who underwent revascularization for carotid artery stenosis, 7664 patients (8.9%) underwent TCAR (mean [SD] age, 73.1 [9.6] years; 2788 [36.4%] women; 6938 White patients [90.6%]; and 3741 patients with symptoms [48.8%]) and 78 363 patients (91.1%) underwent CEA (mean [SD] age, 70.6 [9.2] years; 30 928 [39.5%] women; 70 663 White patients [90.2%]; and 37 883 patients with symptoms [48.3%]). The number of centers performing both TCAR and CEA increased from 15 centers in 2015 to 247 centers in 2019, a more than 16-fold increase. The proportion of all carotid procedures that were TCARs increased from 90 of 12 276 (0.7%) in 2015 to 2718 of 15 956 (17.0%) in 2019, a 24-fold increase. Overall, the crude rate of MACE was similar for TCAR and CEA (178 patients [2.3%] after TCAR vs 1842 patients [2.4%] after CEA; P = .91). However, the rate of MACE over time decreased for CEA (406 of 16 404 patients [2.5%] in 2015 vs 189 of 10 097 patients [1.9%] in 2019; P for trend < .001). The rate of MACE over time decreased for TCAR as well, but the change was not statistically significant (4 of 128 patients [3.1%] in 2016 vs 59 of 2718 patients [2.2%] in 2019; P for trend = .07). Difference-in-difference analysis demonstrated that centers that adopted TCAR had a 10% decrease in the likelihood of MACE at 12 months after TCAR adoption vs if those centers had continued to perform CEA alone (odds ratio, 0.90; 95% CI, 0.81-0.99; P = .04).

CONCLUSIONS AND RELEVANCE

This comparative-effectiveness study of a cohort of patients who underwent TCAR or CEA found that availability of TCAR at a hospital was associated with a decrease in the likelihood of perioperative MACE after carotid revascularization.

Why are we still debating criteria for carotid artery stenosis?

The risk of new or recurrent stroke is high among patients with extracranial carotid artery stenosis and the benefit of carotid revascularization is associated to the degree of luminal stenosis. Catheter-based digital subtraction angiography (DSA) as the diagnostic gold-standard for carotid stenosis (CS) has been replaced by non-invasive techniques including duplex ultrasound, computed-tomography angiography, and magnetic resonance angiography (MRA). Duplex ultrasound is the primary noninvasive diagnostic tool for detecting, grading and monitoring of carotid artery stenosis due to its low cost, high resolution, and widespread availability. However, as discussed in this review, there is a wide range of practice patterns in use of ultrasound diagnostic criteria for carotid artery stenosis. To date, there is no internationally accepted standard for the gradation of CS. Discrepancies in ultrasound criteria may result in clinically relevant misclassification of disease severity leading to inappropriate referral, or lack of it, to revascularization procedures, and potential for consequential adverse outcome. The Society of Radiologists in Ultrasound (SRU), either as originally outlined or in a modified form, are the most common criteria applied. However, such criteria have received criticism for relying primarily on peak systolic velocities, a parameter that when used in isolation could be misleading. Recent proposals rely on a multiparametric approach in which the hemodynamic consequences of carotid narrowing beyond velocity augmentation are considered for an accurate stenosis classification. Consensus criteria would provide standardized parameters for the diagnosis of CS and considerably improve quality of care. Accrediting bodies around the world have called for consensus on unified criteria for diagnosis of CS. A healthy debate between professionals caring for patients with CS regarding optimal CS criteria still continues.

Carotid duplex criteria: What have we learned in 40 years?

Before the development of the first prototype duplex ultrasound scanner at the University of Washington in the late 1970s, the only noninvasive tests available for extracranial carotid artery disease were indirect methods, such as the periorbital Doppler examination and oculoplethysmography. The duplex scanner combined real-time two-dimensional B-mode imaging and pulsed-Doppler flow detection in a single instrument and provided Doppler spectral waveforms from discrete sites within the vessel lumen. Spectral waveforms allowed characterization of the flow patterns and velocity changes associated with normal and diseased arteries. In a series of validation studies, Dr. D. Eugene Strandness, Jr. and colleagues compared various spectral waveform parameters obtained from internal carotid arteries to independently read carotid arteriograms and established quantitative threshold criteria for classification of carotid artery disease. These criteria were based on peak systolic velocity and end-diastolic velocity, as well as features such as spectral broadening and flow separation. Internal carotid arteries were classified as normal, 1% to 15% diameter reduction, 16% to 49% diameter reduction, 50% to 79% diameter reduction, 80% to 99% diameter reduction, and occluded. Since the 1980s, the University of Washington carotid duplex criteria have been widely used and modified in vascular laboratories throughout the world. Additional clinically relevant criteria have also been developed, such as a threshold for the 70% to 99% North American Symptomatic Carotid Endarterectomy Trial (NASCET) stenosis. Validation of carotid criteria has always depended on comparing spectral waveform parameters to the "gold standard" of contrast arteriography. However, experience has shown that the relationship between velocity and arteriographic stenosis is subject to significant variability. Based on these observations, standardization of carotid duplex criteria should lead to more consistent reporting among vascular laboratories, but it is unlikely to result in improved correlation with arteriography.