Consistency of Doppler parameters in predicting arteriographically confirmed carotid stenosis. Asymptomatic Carotid Atherosclerosis Study Investigators

Carotid Doppler velocity measurements and anatomic stenosis: correlation is futile

BACKGROUND

Duplex ultrasound with Doppler velocimetry is widely used to evaluate the presence and severity of internal carotid artery stenosis; however, a variety of velocity criteria are currently being applied to classify stenosis severity. The purpose of this study is to compare published Doppler velocity measurements to the severity of internal carotid artery stenosis as assessed by x-ray angiography in order to clarify the relationship between these 2 widely used approaches to assess carotid artery disease.

METHODS

Scatter diagrams or "scattergrams" of correlations between Doppler velocity measurements and stenosis severity as assessed by x-ray contrast angiography were obtained from published articles for native and stented internal carotid arteries. The scattergrams were graphically digitized, combined, and segmented into categories bounded by 50% and 70% diameter reduction. These data were combined and divided into 3 sets representing different velocity parameters: (1) peak systolic velocity, (2) end-diastolic velocity, and (3) the internal carotid artery to common carotid artery peak systolic velocity ratio. The horizontal axis of each scattergram was transformed to form a cumulative distribution function, and thresholds were established for the stenosis categories to assess data variability.

RESULTS

Nineteen publications with 22 data sets were identified and included in this analysis. Wide variability was apparent between all 3 velocity parameters and angiographic percent stenosis. The optimal peak systolic velocity thresholds for stenosis in stented carotid arteries were higher than those for native carotid arteries. Within each category of stenosis, the variability of all 3 velocity parameters was significantly lower in stented arteries than in native arteries.

CONCLUSION

Although Doppler velocity criteria have been successfully used to classify the severity of stenosis in both native and stented carotid arteries, the relationship to angiographic stenosis contains significant variability. This analysis of published studies suggests that further refinements in Doppler velocity criteria will not lead to improved correlation with carotid stenosis as demonstrated by angiography.

INFLUENCE OF NORMOVOLEMIC ANEMIA ON DOPPLER-DERIVED BLOOD VELOCITY RATIOS OF ABDOMINAL SPLANCHNIC VESSELS IN CLINICALLY NORMAL DOGS

Doppler spectra of the abdominal aorta (AAo), cranial mesenteric artery (CMA), celiac artery (CA), and left renal artery (LRA) were obtained from 11 fasted, clinically healthy, conscious Beagles before and after inducing severe acute normovolemic anemia (mean +/- standard deviation hematocrit 16.0 +/- 0.77%). Peak systolic, end diastolic, and time-averaged mean velocities were measured. The different vessels were compared with each other. Peak systolic velocity ratio and time-averaged mean velocity ratio of splanchnic vessels to corresponding variables of the AAo were computed and compared between and within vessels during physiologic and anemic states. There was no difference between LRA and AAo, CMA or CA regarding time-averaged mean velocity, time-averaged mean velocity ratio, or end diastolic velocity during the physiological state. During the anemic state, LRA mean time-averaged mean velocity (P < or = 0.008) and mean end diastolic velocity (P < or = 0.041) were significantly lower than those of AAo, CMA, and CA. Mean time-averaged mean velocity ratio of the LRA was also significantly (P < or = 0.004) lower than the CMA and CA ratios, and significantly (P = 0.014) lower during anemic state than physiologic state of the same vessel. End diastolic and time-averaged mean velocities of the AAo, CMA, and CA increased proportionally during anemia, but there was a relatively less increase in the same variables of the LRA, suggesting less increase in blood flow. Doppler-ratios allowed a noninvasive comparison between splanchnic and aortic hemodynamics. Velocity ratios might be useful for clinical detection of relative hemodynamic changes between different vessels.

Spectral waveform analysis of major arteries in conscious dogs by Doppler ultrasonography

Normal values of arterial blood flow velocity and waveforms in major arteries of 10 healthy conscious Beagle dogs were determined using Doppler ultrasonography. Peak systolic, early diastolic, and end-diastolic velocities of the basilar artery, common carotid artery, abdominal aorta, external iliac artery, femoral artery, and peak ejection velocity of the valvular aorta were evaluated. Pulsatility index (PI) of the basilar artery and blood pressure were recorded. All arteries had a high-resistance flow pattern with triphasic flow velocity except the basilar artery, which had a low-resistance pattern. Mean peak systolic velocities of the basilar artery, common carotid artery, abdominal aorta, external iliac artery, and femoral artery were 72 +/- 19, 115 +/- 17, 121 +/- 24, 105 +/- 25, and 110 +/- 17 cm/s, respectively. The PI of the basilar artery and peak ejection velocity of the valvular aorta were 1.37 +/- 0.13 and 96 +/- 16 cm/s, respectively. Mean systolic and diastolic blood pressures were 137 +/- 13 and 78 +/- 15 mmHg, respectively. Present findings may be used as references in future studies on vascular diseases and hemodynamics in dogs.

Critical review of non- or minimally invasive methods (duplex ultrasonography, MR- and CT-angiography) for evaluating stenosis of the proximal internal carotid artery

OBJECTIVE

to assess the performance of non- or minimally invasive methods (duplex ultrasonography, MR- and CT-angiography) in measuring stenosis of the proximal internal carotid prior to endarterectomy without preoperative intra-arterial digital subtraction angiography (DSA).

METHODS

systematic review of the literature (five databases, 1990 to February 2001). The value of each imaging technique was studied through its reproducibility and its sensitivity/specificity compared to DSA.

RESULTS

sensitivity exceeded 80% and specificity 90% in over two-thirds of the methodologically sound studies, regardless of technique, although direct comparisons between results had to be avoided since the findings originated from different populations. The main drawback of duplex ultrasonography is its levels of reproducibility. In contrast, only a few studies have addressed the reproducibility of MR- and CT-angiography. When the results of duplex and MR-angiography agree, the combination use of these two techniques provides a better diagnosis than either technique taken alone.

CONCLUSIONS

all three techniques appear suitable for measuring stenosis of the proximal internal carotid when compared to DSA.

Which Doppler velocity is best for assessing suitability for carotid endarterectomy?

OBJECTIVE

To evaluate which velocity, or combination of velocities, from carotid Doppler ultrasonography (DU), achieved the closest agreement with an assessment of suitability for carotid endarterectomy from intra-arterial angiograms (IAA).

METHODS

We prospectively collected data from 148 consecutive patients (288 carotids), who had DU and IAA (blinded assessment) before possible carotid endarterectomy. We halved our data by randomly selecting the left or right carotid artery for each patient. We used one half to calibrate our DU results to IAA (to decide which velocity corresponded with what degree of angiographic stenosis). Using this analysis, each artery in the other half of the data was defined as suitable (80-99% stenosed) or unsuitable for carotid endarterectomy. We evaluated every individual, and combination of, velocities (strategies) to see which gave the closest agreement with IAA.

RESULTS

Of all 80 strategies, six resulted in better agreement than others of the same or lower complexity. Five of these strategies gave better agreement than the internal carotid artery peak systolic velocity (ICA PSV) (kappa 0.78), but the improvement was small.

CONCLUSION

Using the ICA PSV alone is adequate for assessing carotid stenosis before endarterectomy using DU, as long as the machine is calibrated to IAA. However, the addition of the ratio of the ICA PSV to the common carotid artery PSV adds only one further measurement, slightly increases the agreement with IAA, and would be reasonable to use on a daily basis.

Doppler velocity criteria based on receiver operating characteristic analysis for the detection of threshold carotid stenoses

BACKGROUND AND PURPOSE

Duplex scanning is an accepted method for noninvasive evaluation of carotid stenosis. However, the ultrasound criteria used for the detection of threshold stenoses vary widely between laboratories, and quality assurance measures to allow adjustment of criteria are often lacking. This study was completed using receiver operating characteristic (ROC) analysis to determine Doppler velocity criteria for threshold carotid stenoses, compared to an accepted standard, and to demonstrate methods to allow adjustment of criteria.

METHODS

The study cohort included 134 patients who had carotid endarterectomy. Ultrasound and arteriographic data were collected for both the operated and nonoperated sides. Each carotid artery was treated as an independent case in the final analysis. Angiograms were used as the gold standard in ROC analysis to determine the Doppler velocity criteria for the detection of different threshold stenoses.

RESULTS

The ROC analysis results showed that for the detection of 70% stenosis, the best Doppler systolic criterion was 200 cm/s (sensitivity 93.6%, specificity 71.7%, area under the curve [AUC] 87.6%), the best diastolic criterion was 65 cm/s (sensitivity 85.1%, specificity 74.6%, AUC 84.3%), and the best criterion of carotid ratio (CR) (internal carotid artery systolic velocity/common carotid artery systolic velocity) was 3.0 (sensitivity 78.7%, specificity 75.4%, AUC 81.3%). For 50% stenosis, the best systolic criterion was 140 cm/s (sensitivity 90.3%, specificity 95.2%, AUC 97.0%), the best diastolic criterion was 60 cm/s (sensitivity 98.6%, specificity 77.8%, AUC 92.1%), and the best criterion of CR was 2.5 (sensitivity 93.1%, specificity 72.0%, AUC 89.0%).

CONCLUSIONS

This study showed that duplex scanning is able to detect threshold carotid stenoses. For the best performance, each laboratory should have its own criteria; however, the criteria provided here could be a helpful reference to those laboratories that have not yet established their own criteria. Most important, this study provides an example of how to evaluate the performance criteria, how to modify them, how such changes can affect performance, and how performance can be modified depending on the goals of the laboratory.

The impact of theoretical errors on velocity estimation and accuracy of duplex grading of carotid stenosis

Two potential errors in velocity estimation, Doppler angle misalignment and intrinsic spectral broadening (ISB), were determined and used to correct recorded blood velocities obtained from 20 patients (38 bifurcations). The recorded and corrected velocities were used to grade stenoses of greater than 70% using two duplex classification schemes. The first scheme used a peak systolic velocity (PSV) of > 250 cm/s in the internal carotid artery (ICA), and the second a PSV ratio of > 3.4 (ICA PSV/common carotid artery PSV). The "gold standard" was digital subtraction angiography (DSA). The maximum error in velocity estimation due to Doppler angle misalignment was 33 cm/s, but this did not alter sensitivity of stenosis detection. ISB correction caused a reduction in PSV that decreased the sensitivity of the PSV scheme from 65% to 45%. The PSV ratio classification was not affected by ISB errors. Centres using a PSV criterion for grading stenosis should use a fixed Doppler angle and should establish velocity thresholds in-house.

Influence of poststenotic collateral pressure on blood flow velocities within high-grade carotid artery stenosis: differences between morphologic and functional measurements

PURPOSE

The driving force for blood flow through a high-grade stenosis in the internal carotid artery can be expressed as the pressure gradient over the stenosis itself, which, however, might be reduced by the back pressure exerted by distal collateral vessels. Theoretically the maximum blood flow velocity as a measure of the functional grade of obstruction may therefore be lower than what is expected from morphologic gradations of the stenosis. This study was designed to test prospectively the influence of intracranial collateral vessels on blood flow velocities within high-grade internal carotid artery stenoses.

PATIENTS AND METHODS

Forty-five consecutive patients (age 66 +/- 11) with high-grade internal carotid artery stenoses were investigated before and during carotid endarterectomy. The preoperative investigations included duplex ultrasound scanning of the neck vessels, transcranial Doppler scanning for assessment of collateral flow to the middle cerebral artery and angiography. Carotid endarterectomy was performed with patients under deep general anesthesia without a shunt. Systolic and diastolic internal carotid artery blood pressures were measured before and during intraoperative cross-clamping (ie, stump pressure) of the carotid arteries.

RESULTS

Within high-grade internal carotid artery stenoses, maximum systolic and end-diastolic blood flow velocities showed a significant inverse correlation to the corresponding systolic and diastolic stump blood internal carotid artery blood pressures. All patients with spontaneous collateral flow to the ipsilateral anterior part of the circle of Willis were divided into a group with relatively high and another one with low end-diastolic blood flow velocities. The stump pressure was significantly lower in patients with high end-diastolic blood flow velocities in spite of the fact that the mean angiographic grade of stenosis did not differ significantly between the groups.

CONCLUSIONS

Flow velocities within a high-grade internal carotid artery stenosis are inversely dependent on the stump pressure, that is the poststenotic collateral perfusion pressure. This should be taken into consideration in case of discrepancies between angiography and ultrasound outcome.

Carotid ultrasound

This article provides an overview of basic diagnostic carotid ultrasound applications, and emphasizes practical aspects of this examination. Areas currently being investigated include carotid plaque characterization and applications relative to IMT measurements. Contrast-enhanced ultrasound imaging also offers promise to improve plaque characterization, which in turn may link these evaluations to outcome studies.

Variability of Doppler US measurements along the common carotid artery: effects on estimates of internal carotid arterial stenosis in patients with angiographically proved disease

PURPOSE

To determine the effect of variability of common carotid arterial (CCA) velocities on velocity ratios used to assess internal carotid arterial (ICA) stenosis.

MATERIALS AND METHODS

Doppler ultrasonographic (US) velocity measurements were obtained at three levels in the CCA and in the carotid bulb and ICA in all patients referred for carotid US between September 1996 and October 1997. Only ICAs (n = 98, in 57 patients) without ipsilateral CCA disease at angiography were analyzed. The range of CCA peak systolic velocities (PSVs) and end diastolic velocities (EDVs) and velocity ratios were calculated for each CCA measurement. For each ICA/CCA velocity ratio, receiver operating characteristic analysis was performed.

RESULTS

CCA PSV and EDV ranges averaged 23.1 cm/sec +/- 15.7 (SD) and 5.1 cm/sec +/- 3.6, respectively. For a given side, the difference averaged 1.0 +/- 1.3 for PSV ratios and 2.7 +/- 6.9 for EDV ratios, depending on where CCA measurements were taken. By using a threshold of 60% stenosis as indication for endarterectomy, variability in CCA velocities could have altered recommendations in 16 (28%) of 57 patients. Receiver operating characteristic analysis showed that ratios made by using the three CCA velocities or their mean were not significantly different.

CONCLUSION

Variability in velocity measurements along the course of the CCA in patients with ICA disease can be substantial and can result in inaccuracies in assessment of carotid stenosis.

Assessment of stenosis: implications of variability of Doppler measurements in normal-appearing carotid arteries

PURPOSE

To examine the variability of Doppler measurements along the extra-cranial courses of the nondiseased common carotid artery (CCA) and internal carotid artery (ICA) and determine the effect of this variability on assessment of carotid arterial stenosis.

MATERIALS AND METHODS

During the study period, 580 patients were referred for carotid arterial ultrasonography (US), including Doppler measurements of flow velocities in the proximal, middle, and distal portions of the CCA, in the bulb, and in the proximal and distal portions of the ICA. Eighty-five patients (average age, 59 years) with normal ICAs and CCAs formed the cohort for this study.

RESULTS

The range of peak systolic velocity (PSV) measurement (maximum minus minimum) averaged 20 cm/sec +/- 13 in the CCA and 15 cm/sec +/- 13 in the ICA. ICA/CCA velocity ratios varied, depending on the CCA measurement location. In five arteries, PSV ratios exceeded a threshold of 1.8 (suggesting > or = 60% stenosis); in 23 arteries, end diastolic velocity ratios exceeded a threshold of 2.4 (also suggesting > or = 60% stenosis). Right-to-left CCA PSV ratios were abnormal in up to 26 patients (suggesting > 50% ICA stenosis), depending on where CCA measurements were obtained. When the CCA ratios were obtained at the same level, 16 were in the abnormal range.

CONCLUSION

Variability of Doppler measurements in the CCA and ICA in patients without visible disease is substantial and could lead to inaccuracies in carotid arterial stenosis assessment.

Evaluating institutional variability of duplex scanning in the detection of carotid artery stenosis

PURPOSE

Duplex scanning is widely used to measure carotid artery stenosis, but the issue of variability between institutions must be raised. To examine for this potential variability, we evaluated two ATL Ultramark 9 duplex machines at two hospitals within our institution.

METHODS

Stenosis was calculated angiographically as in the North American Symptomatic Carotid Endarterectomy Trial (NASCET). Internal carotid artery (ICA) to common carotid artery (CCA) peak systolic velocity (PSV) ratios were determined using the two ATL machines. Receiver operating characteristic (ROC) curves were generated for each hospital.

RESULTS

ROC curves varied significantly. The area under the curve from hospital 1 was 0.95 (SE = 0.021); the area under the curve from hospital 2 was 0.87 (SE = 0.034). The curves were essentially statistically different (P = 0.0516).

COMMENTS

We showed a difference in predicting diameter stenosis utilizing ICA PSV/CCA PSV ratios at two hospitals within our institution. Variability is likely due to technologists, since equipment and physician interpreters were the same. Criteria must be developed for each different machine in each laboratory. Quality assurance is critical to minimize variability.