Several studies have proven that patients with specific levels of internal carotid artery (ICA) stenosis benefit from endarterectomy, yet a variety of methods of determining the percent of ICA stenosis can result in conflicting data. The authors review duplex ultrasound scanning of the carotid arteries in order to safely, and noninvasively, determine the severity of ICA stenosis.
Drs. Lovelace and Moneta are with the Division of Vascular
Surgery, Oregon Health Sciences University and Portland
Department of Veteran's Affairs Hospital, Portland, OR.
Recent randomized controlled trials comparing combined carotid
endarterectomy (CEA) and medical therapy with medical therapy alone
have determined that patients with specific levels of internal
carotid artery (ICA) stenosis benefit from endarterectomy.
The North American Symptomatic Carotid En-darterectomy Trial
(NASCET) determined that patients presenting with transient
ischemic attacks, nondisabling stroke, or amaurosis fugax and 50%
to 69% or 70% to 99% angiographic internal carotid artery stenosis
achieved significant reduction in stroke rates with ipsilateral CEA
over medical therapy alone.
In patients with high grade stenosis, 70% to 99%, there was an
absolute reduction in stroke risk by 17% at 2 years following
In patients with moderate stenosis, 50% to 69%, benefit of surgery
was less dramatic, with an absolute reduction in stroke risk of
5.5% at 5 years.
The European Carotid Surgery Trial (ECST) also found that
symptomatic patients with internal carotid artery stenosis benefit
from carotid endarterectomy.
In this multi-center, randomized controlled trial of more than 3000
patients, frequency of major stroke or death in the medically
treated group was 26.5% at 3 years, compared with 14.9% for
surgically treated patients. Benefit was confined to patients with
80% to 99% angiographic ICA stenosis.
Asymptomatic patients modestly benefit from CEA.
The Asymptomatic Carotid Artery Surgery (ACAS) trial randomized
1662 patients with angiographic ICA stenosis of 60% to 99% to
receive surgery and medical therapy or medical therapy only.
Aggregate stroke and death rates over a 5-year period were 11% for
the medical group and 5.1% for the surgical group. In addition, the
study documented a 1.2% stroke rate resulting from angiography.
Severity of internal carotid artery stenosis in the NASCET,
ECST, and ACAS studies was determined using angiography.
Angiographic measurement of percent ICA stenosis is usually
calculated by one of three methods.
Each method uses the diameter of the ICA lumen at the point of
maximal narrowing as the numerator, but the reference value used as
the denominator in the equation to calculate percent stenosis
varies. In NASCET and ACAS, the presumably disease-free distal
cervical ICA diameter is used as the reference value, whereas in
ECST the estimated normal diameter of the carotid bulb was chosen.
(Use of the common carotid artery [CCA] diameter has also been
Each method of measurement (NASCET, ECST, and CCA) leads to a
different calculation of percent ICA stenosis. Three different
levels of stenosis will be calculated depending on the value chosen
as the denominator (figure 1). An evaluation of 1001 angiograms
comparing these three methods concluded that calculations using the
distal ICA diameter as the denominator (NASCET method) consistently
result in a lower value of percent angiographic ICA stenosis than
calculations using the estimated normal carotid bulb diameter (ECST
Contrast cerebral angiography is invasive and can be associated
with significant neurologic morbidity that will diminish the
benefit conferred by CEA.
Nearly half of the perioperative morbidity attributed to the
surgical arm of the ACAS trial resulted from cerebral angiography,
not from the actual surgical procedure itself. Conversely, duplex
ultrasound scanning of the carotid arteries is a safe, noninvasive
means of determining severity of ICA stenosis.
Duplex velocity and spectral criteria developed at the
University of Washington (UW) have been the most widely employed
criteria to noninvasively determine levels of "angiographic" ICA
stenosis (Table 1).
These criteria, however, are not applicable to the threshold levels
of ICA stenosis determined to be of benefit in ACAS and NASCET, in
that there are no cutoffs for >= 60% and
>= 70% ICA stenosis. In addition, the UW criteria were developed
using the estimated normal diameter of the carotid bulb as the
denominator in calculations of percent angiographic ICA
Since the randomized trials were completed, new duplex criteria
for determining angiographic ICA stenosis have been developed to
provide criteria directly relevant to ACAS and NASCET. In our
opinion, these supplemental duplex criteria should not replace
existing UW criteria, which very accurately quantify
atherosclerosis in the carotid bulb. The new criteria are most
useful in properly selecting patients for CEA based on results of
the randomized clinical trials that quantify stenosis using the
distal cervical ICA diameter as the reference value in calculations
of angiographic percent ICA stenosis.
We proposed the first duplex criteria directly applicable to the
initial NASCET report. This study used receiver operator
characteristic (ROC) curves to compare sensitivities and
specificities of different duplex parameters for predicting a 70%
to 99% angiographic ICA stenosis using the distal cervical ICA
diameter as the denominator in calculations of percent stenosis.
Data was obtained from 100 patients with 184 angiographically
patent ICAs. Doppler-derived peak systolic velocity (PSV) and end
diastolic velocity (EDV) in the CCA and ICA, as well as ICA/CCA PSV
ratios were correlated with their ability to predict 70% to 99%
angiographic ICA stenosis. An ICA/CCAPSV ratio of >= 4.0 was the
most accurate overall predictor of 70% to 99% angiographic ICA
stenosis with 91% sensitivity, 87% specificity, and overall
accuracy of 88%.
This data was later confirmed in a prospective study utilizing
duplex scans and angiographic studies from our institution and from
the University of Washington.
A total of 168 angiograms and duplex scans were compared. An
ICA/CCA PSV ratio of >= 4.0 was able to predict 70% to 99%
angiographic ICA stenosis with 90% sensitivity, 90% specificity,
and 90% overall accuracy.
Other investigators have since developed additional duplex
criteria applicable to the initial and final NASCET reports. In a
review of duplex scans and angiograms from 120 patients, Neale et
found that an ICA PSV > 270 cm/s determined 70% to 99%
angiographic ICA stenosis with 96% sensitivity, 86% specificity,
and 88% accuracy. An ICA EDV > 110 cm/s resulted in 91%
sensitivity, 93% specificity, and 93% accuracy. If both PSV >
270 cm/s and EDV >l10 cm/s were present, 96% sensitivity, 91%
specificity, and 93% overall accuracy was achieved.
Faught et al
found a combination of PSV >130 cm/s and EDV >100 cm/s had an
overall accuracy of 95% for detecting 70% to 99% angiographic ICA
stenosis. These variables were subsequently applied in a
prospective study evaluating 457 internal carotid arteries in 248
Overall accuracy of 95% was maintained, with 87% sensitivity and
97% specificity. (The PSV of 130 cm/s is quite low and data from
this institution is likely driven by the requirement for an EDV
>100 cm/s). In another study by Carpenter et al,
PSV >210 cm/s, EDV >70 cm/s, and ICA/CCA PSV ratio >= 3.0
each had an 83% accuracy for detecting 70% to 99% angiographic ICA
stenosis. Finally, Winkelaar et al
studied 188 carotid arteries with both duplex scanning and
angiography to identify duplex criteria for detecting a 50% to 99%
angiographic ICA stenosis by NASCET methods. These investigators
determined that an ICA/CCA PSV ratio >= 2.0 identified a 50% to
99% ICA stenosis with 93% accuracy, 96% sensitivity, and 89%
Additional duplex criteria have also been developed for
asymptomatic patients, incorporating the >= 60% ICA stenosis
threshold defined by ACAS. Assuming a duplex scan suggesting 60% to
99% ICA stenosis in an asymptomatic patient may lead to angiography
or operation, and noting the modest therapuetic benefit of CEA in
asymptomatic patients, we reasoned criteria for asymptomatic
patients should have a high positive predictive value (PPV) for
defining 60% to 99% angiographic ICA stenosis. Cerebral angiograms
and duplex scans of 352 ICAs were compared.
A 95% PPV for >= 60% ICA stenosis was achieved with a
combination of ICA PSV >290 cm/s and ICA EDV
>80 cm/s. Carpenter et al
also evaluated parameters for defining 60% to 99% angiographic ICA
stenosis. In their study, 210 ICAs were examined with angiography
and duplex scanning. Assuming high PPV remains the discriminating
factor, an EDV
> 60cm/s then provides a PPV of 96%, and a PSV >230 cm/s a
PPV of 94%.
In an additional study comparing magnetic resonance angiography
(MRA) to duplex for determining
>= 60% ICA stenosis, a combination of PSV >245 and EDV >65
cm/s resulted in an 89% PPV.
Each of these studies used different duplex scanners and
determined slightly different criteria for predicting percentage of
ICA stenosis (tables 2 and 3). Differences apparently exist between
duplex equipment, vascular laboratories, and vascular technologists
in measurement of ICA stenosis.
These potential differences were examined by Fillinger et al
in 1996. The study was carried out at two independent centers with
separate duplex scanners and technologists. A total of 360 carotid
bifurcations were examined using Quantum (Siemens Medical Systems,
Inc., Issaquah, WA); Diasonics (Diasonics Ultrasound, Santa Clara,
CA); and ATL (Advanced Technology Laboratories, Bothell, WA) brand
duplex machines. Percent ICA stenosis was measured by angiogram
with the distal ICA diameter as the denominator. Using ROC curves,
PPVs between 90% and 95% were determined while attempting to
maintain >90% accuracy and >80% sensitivity. To meet these
requirements, depending on the scanner empolyed, ICA/CCA PSV ratios
varied from 2.6 to 3.3 and the ICA PSV varied from 190 cm/s to 240
cm/s for prediction of 60% to 99% angiographic ICA stenosis.
Threshold values differed between scanners and appeared to be
machine specific. Investigators determined that relationships
between duplex data and percent angiographic ICA stenosis were
statistically different for one of the machines (ATL). It was
concluded that different duplex-derived criteria determining 60% to
99% angiographic ICA stenosis are not interchangeable from one
machine to another.
In an attempt to standardize supplemental duplex criteria
between different observers and different machines, a recent study
used an entirely different diagnostic variable to determine percent
angiographic ICA stenosis. Ranke et al
used the mean velocity ratio, which is the intrastenotic mean blood
flow velocity divided by the distal ICA mean blood flow velocity,
to evaluate for the presence of a 70% to 99% angiographic ICA
stenosis. In this study, Hewlett-Packard (Andover, MA) and ATL
duplex machines were used. The study was small, with only 44
patients undergoing both duplex scanning and angiography, and 21
patients were examined to compare differences between scanners and
observers. A mean velocity ratio >= 5.0 correlated with a NASCET
70% to 99% angiographic ICA stenosis with a 97% sensitivity and 98%
Direct velocity measurements between the two scanners were
significantly different (P <0.001), but the mean velocity ratios
were not. Due to inherent accuracy problems in calculation of mean
velocities, variability and reproducibility studies will be
required prior to possible acceptance of mean velocities in the
calculation of percent angiographic ICA stenosis. If these findings
are repeated by independent observers in a larger set of patients,
the use of mean velocity ratios may become important in
standardizing duplex determination of ICA stenosis.
Although the University of Washington duplex criteria have had
enormous clinical and research impact, the categories of ICA
stenosis described are only applicable to quantifying stenosis
based on the estimated normal diameter of the carotid bulb in
calculations of percent angiographic stenosis. Clinical trials of
carotid endarterectomy in North America, such as ACAS and NASCET,
have based their results on the distal cervical ICA diameter as the
reference value. Supplemental duplex criteria were developed to
define percent angiographic ICA stenosis using the >= 60% and
>= 70% thresholds determined to be significant in these trials.
These criteria are apparently machine specific. Individual vascular
laboratories must validate their own criteria with internal
quality-control studies. In the future, use of distal ICA mean
velocity ratios, or possibly some other combination of variables,
may help to standardize duplex quantification of ICA stenosis.
1. Executive Committee for ACAS:
Endarterectomy for asymptomatic carotid artery stenosis. JAMA
2. ECST's Collaborative Group:
Randomised trial of endarterectomy for recently symptomatic carotid
stenosis: Final results of the MRC European Carotid Surgery Trial
(ECST). Lancet 351:1379-1387, 1998.
3. Barnett HJ, Taylor DW, Eliasziw M, et al:
Benefit of carotid endarterectomy in patients with symptomatic
moderate or severe stenosis. N Engl J Med 339:1415-1425, 1998.
4. NASCET Collaborators:
Beneficial effect of carotid endarterectomy in symptomatic patients
with high-grade carotid stenosis. N Engl J Med 325:445-453,
5. Rothwell PM, Gibson RJ, Slattery J, Warlow CP:
Prognostic value and reproducibility of measurements of carotid
stenosis. A comparison of three methods on 1001 angiograms. Stroke
6. Rothwell PM, Gibson RJ, Slattery J, et al:
Equivalence of measurements of carotid stenosis. A comparison of
three methods on 1001 angiograms. Stroke 25:2435-2439, 1994.
7. Strandness DE:
Duplex Scanning in Vascular Disorders. New York, Raven Press,
8. 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
17:152-157; discussion 157-159, 1993.
9. Edwards JM, Moneta GL, Papanicolaou G, et al:
Prospective validation of a new duplex ultrasound criteria for
70-99% internal carotid stenosis. JEMU 16:3-7, 1995.
10. Neale ML, Chambers JL, Kelly AT, et al:
Reappraisal of duplex criteria to assess significant carotid
stenosis with special reference to reports from the North American
Symptomatic Carotid Endarterectomy Trial and the European Carotid
Surgery Trial. J Vasc Surg 20:642-649, 1994.
11. 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 asymptornatic
carotid trials. J Vasc Surg 19:818-827; discussion 827-828,
12. Hood DB, Mattos MA, Mansour A, et al:
Prospective evaluation of new duplex criteria to identify 70%
internal carotid artery stenosis. J Vasc Surg 23:254-261;
discussion 261-262, 1996.
13. Carpenter JP, Lexa FJ, Davis JT:
Determination of duplex Doppler ultrasound criteria appropriate to
the North American Symptomatic Carotid Endarterectomy Trial. Stroke
14. Winkelaar GB, Chen JC, Salvian AJ, et al: N
ew duplex ultrasound scan criteria for managing symptomatic 50% or
greater carotid stenosis. J Vasc Surg 29:986-994, 1999.
15. Moneta GL, Edwards JM, Papanicolaou G, et al:
Screening for asymptomatic internal carotid artery stenosis: Duplex
criteria for discriminating 60% to 99% stenosis. J Vasc Surg
16. Carpenter JP, Lexa FJ, Davis JT:
Determination of sixty percent or greater carotid artery stenosis
by duplex Doppler ultrasonography. J Vasc Surg 22:697-703;
discussion 703-705, 1995.
17. Jackson MR, Chang AS, Robles HA, et al:
Determination of 60% or greater carotid stenosis: A prospective
comparison of magnetic resonance angiography and duplex ultrasound
with conventional angiography. Ann Vasc Surg 12:236-243, 1998.
18. Fillinger W, Baker RJ Jr., Zwolak RM, et al:
Carotid duplex criteria for a 60% or greater angiographic stenosis:
Variation according to equipment. J Vasc Surg 24:856-864, 1996.
19. Ranke C, Creutzig A, Becker H, Trappe HJ:
Standardization of carotid ultrasound: A hemodynamic method to
normalize for interindividual and interequipment variability.
Stroke 30:402-406, 1999.