Evaluating carotid artery disease. The concordance between pulsed Doppler/spectrum analysis and angiography

Duplex ultrasound for diagnosing symptomatic carotid stenosis in the extracranial segments

BACKGROUND

Carotid artery stenosis is an important cause of stroke and transient ischemic attack. Correctly and rapidly identifying patients with symptomatic carotid artery stenosis is essential for adequate treatment with early cerebral revascularization. Doubts about the diagnostic value regarding the accuracy of duplex ultrasound (DUS) and the possibility of using DUS as the single diagnostic test before carotid revascularization are still debated.

OBJECTIVES

To estimate the accuracy of DUS in individuals with symptomatic carotid stenosis verified by either digital subtraction angiography (DSA), computed tomography angiography (CTA), or magnetic resonance angiography (MRA).

SEARCH METHODS

We searched CRDTAS, CENTRAL, MEDLINE (Ovid), Embase (Ovid), ISI Web of Science, HTA, DARE, and LILACS up to 15 February 2021. We handsearched the reference lists of all included studies and other relevant publications and contacted experts in the field to identify additional studies or unpublished data.

SELECTION CRITERIA

We included studies assessing DUS accuracy against an acceptable reference standard (DSA, MRA, or CTA) in symptomatic patients. We considered the classification of carotid stenosis with DUS defined with validated duplex velocity criteria, and the NASCET criteria for carotid stenosis measures on DSA, MRA, and CTA. We excluded studies that included < 70% of symptomatic patients; the time between the index test and the reference standard was longer than four weeks or not described, or that presented no objective criteria to estimate carotid stenosis.

DATA COLLECTION AND ANALYSIS

The review authors independently screened articles, extracted data, and assessed the risk of bias and applicability concerns using the QUADAS-2 domain list. We extracted data with an effort to complete a 2 × 2 table (true positives, true negatives, false positives, and false negatives) for each of the different categories of carotid stenosis and reference standards. We produced forest plots and summary receiver operating characteristic (ROC) plots to summarize the data. Where meta-analysis was possible, we used a bivariate meta-analysis model.

MAIN RESULTS

We identified 25,087 unique studies, of which 22 were deemed eligible for inclusion (4957 carotid arteries). The risk of bias varied considerably across the studies, and studies were generally of moderate to low quality. We narratively described the results without meta-analysis in seven studies in which the criteria used to determine stenosis were too different from the duplex velocity criteria proposed in our protocol or studies that provided insufficient data to complete a 2 × 2 table for at least in one category of stenosis. Nine studies (2770 carotid arteries) presented DUS versus DSA results for 70% to 99% carotid artery stenosis, and two (685 carotid arteries) presented results from DUS versus CTA in this category. Seven studies presented results for occlusion with DSA as the reference standard and three with CTA as the reference standard. Five studies compared DUS versus DSA for 50% to 99% carotid artery stenosis. Only one study presented results from 50% to 69% carotid artery stenosis. For DUS versus DSA, for < 50% carotid artery stenosis, the summary sensitivity was 0.63 (95% confidence interval [CI] 0.48 to 0.76) and the summary specificity was 0.99 (95% CI 0.96 to 0.99); for the 50% to 69% range, only one study was included and meta-analysis not performed; for the 50% to 99% range, the summary sensitivity was 0.97 (95% CI 0.95 to 0.98) and the summary specificity was 0.70 (95% CI 0.67 to 0.73); for the 70% to 99% range, the summary sensitivity was 0.85 (95% CI 0.77 to 0.91) and the summary specificity was 0.98 (95% CI 0.74 to 0.90); for occlusion, the summary sensitivity was 0.91 (95% CI 0.81 to 0.97) and the summary specificity was 0.95 (95% CI 0.76 to 0.99). For sensitivity analyses, excluding studies in which participants were selected based on the presence of occlusion on DUS had an impact on specificity: 0.98 (95% CI 0.97 to 0.99). For DUS versus CTA, we found two studies in the range of 70% to 99%; the sensitivity varied from 0.57 to 0.94 and the specificity varied from 0.87 to 0.98. For occlusion, the summary sensitivity was 0.95 (95% CI 0.80 to 0.99) and the summary specificity was 0.91 (95% CI 0.09 to 0.99). For DUS versus MRA, there was one study with results for 50% to 99% carotid artery stenosis, with a sensitivity of 0.88 (95% CI 0.70 to 0.98) and specificity of 0.60 (95% CI 0.15 to 0.95); in the 70% to 99% range, two studies were included, with sensitivity that varied from 0.54 to 0.99 and specificity that varied from 0.78 to 0.89. We could perform only a few of the proposed sensitivity analyses because of the small number of studies included.

AUTHORS' CONCLUSIONS

This review provides evidence that the diagnostic accuracy of DUS is high, especially at discriminating between the presence or absence of significant carotid artery stenosis (< 50% or 50% to 99%). This evidence, plus its less invasive nature, supports the early use of DUS for the detection of carotid artery stenosis. The accuracy for 70% to 99% carotid artery stenosis and occlusion is high. Clinicians should exercise caution when using DUS as the single preoperative diagnostic method, and the limitations should be considered. There was little evidence of the accuracy of DUS when compared with CTA or MRA. The results of this review should be interpreted with caution because they are based on studies of low methodological quality, mainly due to the patient selection method. Methodological problems in participant inclusion criteria from the studies discussed above apparently influenced an overestimated estimate of prevalence values. Most of the studies included failed to precisely describe inclusion criteria and previous testing. Future diagnostic accuracy studies should include direct comparisons of the various modalities of diagnostic tests (mainly DUS, CTA, and MRA) for carotid artery stenosis since DSA is no longer considered to be the best method for diagnosing carotid stenosis and less invasive tests are now used as reference standards in clinical practice. Also, for future studies, the participant inclusion criteria require careful attention.

Angiographic and Duplex Grading of Internal Carotid Stenosis: Can We Overcome the Confusion?

The stroke risk reduction benefit of surgical intervention in carotid occlusive disease has been validated in multicenter trials for various angiographically defined lesion severity categories. The two divergent angiographic grading methods used for internal carotid artery stenosis in these trials have caused confusion in the clinical application of their recommendations. Moreover, while today's highly accurate carotid duplex scanning can obviate the need for preoperative angiography in many cases, the duplex criteria must be tailored to achieve sufficiently reliable results on which therapeutic decisions can be made. This review offers a clarification of the discrepancies between the angiographic grading techniques and how their measurements of percent stenosis correlate to the duplex criteria needed to support the treatment decision-making process for carotid obliterative disease.

Standardized ultrasound evaluation of carotid stenosis for clinical trials: University of Washington Ultrasound Reading Center

Introduction

Serial monitoring of patients participating in clinical trials of carotid artery therapy requires noninvasive precision methods that are inexpensive, safe and widely available. Noninvasive ultrasonic duplex Doppler velocimetry provides a precision method that can be used for recruitment qualification, pre-treatment classification and post treatment surveillance for remodeling and restenosis. The University of Washington Ultrasound Reading Center (UWURC) provides a uniform examination protocol and interpretation of duplex Doppler velocity measurements.

Methods

Doppler waveforms from 6 locations along the common carotid and internal carotid artery path to the brain plus the external carotid and vertebral arteries on each side using a Doppler examination angle of 60 degrees are evaluated. The UWURC verifies all measurements against the images and waveforms for the database, which includes pre-procedure, post-procedure and annual follow-up examinations. Doppler angle alignment errors greater than 3 degrees and Doppler velocity measurement errors greater than 0.05 m/s are corrected.

Results

Angle adjusted Doppler velocity measurements produce higher values when higher Doppler examination angles are used. The definition of peak systolic velocity varies between examiners when spectral broadening due to turbulence is present. Examples of measurements are shown.

Discussion

Although ultrasonic duplex Doppler methods are widely used in carotid artery diagnosis, there is disagreement about how the examinations should be performed and how the results should be validated. In clinical trails, a centralized reading center can unify the methods. Because the goals of research examinations are different from those of clinical examinations, screening and diagnostic clinical examinations may require fewer velocity measurements.

Imaging in endovascular therapy: our future

The endovascular therapist now has many modern imaging techniques available to plan and execute treatment, whereas in the past vascular surgeons relied mostly on clinical examination and arteriography. Advances in computer technology have enabled fast acquisition and processing of the large amounts of digital data essential to capture the dynamic information from fast-flowing blood at high resolution. Functional imaging has begun to play a role in predicting stability of progressive vascular disease and the need for and risks of intervention. Computing power now affords the interventionist the ability to handle imaging data in powerful 3-dimensional programs and electronically "in-lay" a variety of devices to plan complex endovascular procedures from the familiar platform of a laptop. In four major clinical areas, carotid intervention, peripheral intervention, endoluminal grafting, and cardiac imaging, we review the latest advances and changes with an eye toward how we should best be using imaging in our patients undergoing endovascular treatment...now and into the future.

Predictive value of asymptomatic cervical bruit for carotid artery disease in coronary artery surgery revisited

OBJECTIVE

To investigate the predictive value of asymptomatic cervical bruit for detecting internal carotid artery disease in consecutive patients undergoing coronary artery bypass grafting (CABG).

DESIGN

A prospective cohort study.

SETTING

Tertiary referral university hospitals.

PATIENTS

153 consecutive patients (mean age 57 years) undergoing CABG, without previous history of cerebrovascular events.

INTERVENTIONS

Patients underwent detailed pre-operative work-up, including coronary angiography and carotid artery duplex scanning. Internal carotid artery diameter stenosis was graded as A: normal; B: < 15%; C: 15%-50%; D: 50-80%; D+: > 80-99% and E=complete occlusion.

RESULTS

72 patients (47.1%) (95% CI: 39%, 55%) had no evidence of internal carotid artery stenosis; 81 (52.9%) (95% CI: 44.9%, 60.9%) had varying grades of disease, unilateral or bilateral. Cervical bruit was detected in 12/153 patients (7.8%) (95% CI: 3.5%, 12.1%) of whom all but one (0.7%) had varying grades of internal carotid artery disease; of these, 4 patients had bilateral cervical bruit (2.6%) (95% CI: 0.06%, 5.2%). The sensitivity, specificity, positive and negative predictive values and overall accuracy of cervical bruit for detection of > or = 50% internal carotid artery stenosis were 23.5%, 95.8%, 25%, 95.5% and 91.8%, respectively. The relative risk of > or = 50% stenosis ipsilateral to cervical bruit in 306 sides was 5.58 (95% CI: 2.0, 15.0) and the odds ratio 7.1 (95% CI: 2.0, 25.0).

CONCLUSIONS

Asymptomatic cervical bruit proved a highly specific clinical sign for detection of internal carotid artery stenosis, whether haemodynamically significant (> or = 50%) or otherwise, in patients undergoing myocardial revascularisation. This was matched by a high negative predictive value and overall accuracy for flow limiting atheroma (> or = 50% stenosis). Yet, steering carotid investigations on the basis of cervical bruit alone would result in > or = 80% internal carotid artery stenosis remaining undetected in 3% of overall patients, in whom cervical bruit is absent.

Region-of-interest-based analysis of clustered BOLD MRI data in experimental arthritis

RATIONALE AND OBJECTIVES

BOLD MRI provides functional information based on minimal changes. Problems inherent in data processing of the very low signal-to-noise-ratio of BOLD experiments have created obstacles for validation of certain techniques using standard strength-field MR scanners. Measures of diagnostic accuracy of clustered data are directly related to the reading parameters used to define regions-of-interest (ROIs). Our primary aim was to determine the combination of ROI-related reading parameters that provides highest accuracy for discrimination of presence or absence of arthritis in acute and subacute stages of the disease using paired comparisons of BOLD MRI data.

MATERIALS AND METHODS

Six male New Zealand white rabbits were injected with albumin into one knee and saline into the contralateral knee, 3 animals had albumin injected into only one of the knees, 2 had saline injected into one of the knees, and 3 animals were not injected. The rabbits' knees underwent BOLD MRI on days 1 and 28 after induction of arthritis, except for the knees of 3 animals (albumin- vs saline-injected knees, n = 2 animals; saline- vs noninjected knees, n = 1 animal) that died before expected and had only the first MRI examination done. Percentage of activated voxels and differences in on-and-off signal intensities were the BOLD MRI methods applied. Data were analyzed using anatomic-driven small ROI, voxel-chaser-driven small ROI and anatomic-driven large ROI techniques.

RESULTS

Diagnostic areas-under-the curve (AUCs) were obtained only for acute arthritis and only when percentage of activated voxels was used. Low threshold, positive voxel activations and small ROIs generated the largest AUCs (AUC +/- SE, .911 +/- .092, P = .014) using either anatomic-driven or voxel-chaser-driven techniques. A sensitivity analysis confirmed the importance of threshold as a parameter for analysis.

CONCLUSION

Low threshold, positive voxel activations and small ROIs constituted the set of reading parameters that provided the most accurate BOLD MRI results.

Reliability of extracranial carotid artery duplex ultrasound scanning: value of vascular laboratory accreditation

OBJECTIVES

The purpose of this study was to evaluate the reliability of carotid duplex ultrasound scanning performed by nonaccredited vascular laboratories and to assess the clinical effect on patient management.

METHODS

We retrospectively reviewed concordance of findings of carotid duplex ultrasound scanning between laboratories accredited by the Intersocietal Commission for Accreditation of Vascular Laboratories and nonaccredited laboratories in 174 patients with asymptomatic disease referred to tertiary care community hospitals for surgical evaluation for carotid endarterectomy (CEA) between January 2001 and December 2002, and evaluated changes in clinical management made on the basis of repeat examinations.

RESULTS

Concordant findings were noted in 171 of 348 arteries (49%), predominantly those with minimal or mild disease (114 arteries; 67%). Discordant findings of no clinical significance were found in 54 arteries (16%). Clinically significant discordant findings were noted in 123 arteries (35%) in 107 patients (61%). In 104 arteries (88 patients) stenosis was overestimated by the nonaccredited laboratory secondary to technical error (19 arteries), use of B-mode imaging data alone (36 arteries), and use of inappropriate velocity criteria (49 arteries). None of these patients underwent CEA. Stenosis was significantly underestimated in 19 arteries (19 patients); all of these patients underwent uncomplicated CEA.

CONCLUSIONS

Incorrect physician interpretation of data is the most common cause of error in carotid duplex ultrasound scanning performed in nonaccredited vascular laboratories. Results of carotid duplex ultrasound scanning from nonaccredited laboratories should be considered with extreme caution, and do not appear reliable in planning treatment of obstructive disease.

Computed Tomography Angiography Validates Duplex Sonographic Evaluation of Carotid Artery Stenosis

Controversy regarding the optimal preoperative evaluation for patients with carotid arterial stenosis remains controversial. We hypothesized that carotid artery area reduction measured by computed tomography angiography (CTA) would closely correlate with duplex scanning stenosis. This study was undertaken to evaluate the correlation between duplex, CTA, and conventional arteriography in patients undergoing consideration for carotid endarterectomy. Patients undergoing evaluation for carotid artery stenosis who received at least 2 of the diagnostic tests were included in this study (n = 108); 30 patients underwent all 3 imaging modalities. Linear regression analysis was performed to determine correlation coefficients between the 3 different study modalities. Correlation and P values were as follows: CTA area versus CTA diameter, r = 0.82, P < 0.001; CTA area versus duplex stenosis, r = 0.71, P < 0.001; duplex stenosis versus angio diameter, r = 0.68; P = 0.005; CTA diameter versus angio diameter, r = 0.61, P = 005. CTA was able to identify plaque characteristics more readily than duplex or arteriography. CTA was also able to differentiate critical stenosis from occlusion and to settle discrepancies obtained from duplex scanning. CTA is an acceptable alternative method to validate duplex scanning evaluation of carotid artery stenosis. It can accurately measure lumen stenosis, visualize plaque morphology, and is associated with fewer complications than conventional angiography.

Functional outcome in a contemporary series of major lower extremity amputations

PURPOSE

We undertook this study to document the functional natural history of patients undergoing major amputation in an academic vascular surgery and rehabilitation medicine practice.

METHODS

A retrospective review was conducted of consecutive patients undergoing major lower extremity amputation and rehabilitation in a university and Department of Veterans Affairs hospital. Main outcome variables included operative mortality, follow-up, survival, median time to incision healing, secondary operative procedures for wound management, and conversion from below-knee amputation (BKA) to above-knee amputation (AKA). For surviving patients, quality of life was determined by degree of ambulation, eg, outdoors, indoors only, or no ambulation; use of a prosthesis; and independence, eg, community housing or nursing facility.

RESULTS

From August 1997 through March 2002, 154 patients (130 men; median age, 62 years) underwent 172 major amputations, 78 AKA and 94 BKA, because of either critical limb ischemia (87%) or diabetic neuropathy (13%). Thirty-day operative mortality was 10%. Mean follow-up was 14 months. Healing at 100 and 200 days, as determined with the Kaplan-Meier method, was 55% and 83%, respectively, for BKA, and 76% and 85%, respectively, for AKA. Twenty-three BKA and 16 AKA required additional operative revision, and 18 BKA ultimately were converted to AKA. Survival was 78% at 1 year and 55% at 3 years. Function in surviving patients at 10 and 17 months, respectively, was as follows: 21% and 29% of patients ambulated outdoors, 28% and 25% ambulated indoors only, and 51% and 46% of patients were nonambulatory; 32% and 42% of patients used prosthetic limbs; and 17% and 8% of patients who lived in the community before amputation required care in a nursing facility.

CONCLUSIONS

We were surprised to find that vascular patients in a contemporary setting who require major lower extremity amputation and rehabilitation often remain independent despite infrequent prosthesis use and outdoor ambulation. Although any hope for postoperative ambulation in this population requires salvaging the knee joint, because of the morbidity incurred in both wound healing and rehabilitation efforts, aggressive effort should be reserved for selected patients at good risk. Ability to predict ambulation after BKA in the vascular population is poor.

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.

Colour flow Doppler ultrasound of the carotid bifurcation: can it replace routine angiography before carotid endarterectomy?

The objective of this study was to assess the diagnostic accuracy of colour flow Doppler ultrasound (CFD) and its potential to replace digital subtraction angiography (DSA) before carotid endarterectomy (CEA). All patients undergoing CFD of the carotid bifurcation in our department over a period of 1-1/2 years for whom both CFD and DSA results were available were included in the study. We evaluated the feasibility of CFD, its diagnostic accuracy and its potential to diagnose clinically significant stenosis (50%, 70% and 90% NASCET type diameter stenosis) compared with DSA. 225 carotid bifurcations in 116 patients met the criteria for evaluation (biplane arterial DSA without superimposition). Data analysis yielded the following diagnostic performance of CFD: sensitivity for a 50% stenosis 91.4% (95% confidence interval (CI) 83.3--96.2%), specificity 93.2% (95% CI 87.1--96.8%) and accuracy 92.4% (95% CI 88.4--95.4%); sensitivity for a 70% stenosis 89.2% (95% CI 81.9--94.1%), specificity 96.2% (95% CI 90.5--98.6%) and accuracy 92.4% (95% CI 88.4--95.4%). In 9 of 116 cases, carotid angiography was used to evaluate inconclusive CFD results. DSA disclosed relevant information not suspected by CFD in only 1 of the 116 cases. Thus, 91% (106/116) of the angiographies could have been dispensed with without loss of information. One major stroke occurred during diagnostic DSA. We conclude that DSA of the carotid arteries is unnecessary when CFD is unequivocal. The diagnostic gain of DSA must be counterweighted against its potential risks.

Carotid endarterectomy without angiography: can clinical evaluation and duplex ultrasonographic scanning alone replace traditional arteriography for carotid surgery workup? A prospective study

BACKGROUND

The aim of this study was to determine whether clinical evaluation and duplex ultrasonography (DUS) alone can replace contrast cerebral arteriography (CA) for the detection of patients suitable for surgery at our institution.

METHODS

During an 18-month period, 100 patients underwent DUS and CA during evaluation for carotid endarterectomy (CEA). All patients were studied prospectively; in each case an initial decision for or against CEA on the basis of DUS evaluation of the internal carotid arteries (ICAs) was subsequently compared with the surgeon's final management plan after CA. Of the 200 ICAs evaluated, 113 were considered for CEA but 14 were excluded from the study because the patient could not be evaluated before and after CA. This left 99 ICAs (86 patients) available for comparative analysis.

RESULTS

The outcome of the 2 diagnostic modalities was perfectly consistent in 95.3% of the ICAs (kappa = 0.969). The clinical management decision was altered by the CA findings in only 2 cases (2%). Of the 99 ICAs considered suitable, 97 underwent CEA. No arteriographic complications occurred among the 100 patients undergoing CA. The perioperative stroke risk and mortality rates were 0%.

CONCLUSIONS

Ninety-eight percent of the ICAs considered for surgery would have received appropriate clinical treatment on the strength of the patients' neurologic history and the outcome of DUS alone. Our results indicate that DUS is sufficient to establish the need for surgery in symptomatic and asymptomatic patients being considered for CEA and can replace CA in most clinical circumstances.

Analysis of clustered data in receiver operating characteristic studies

Clustered data is not simply correlated data, but has its own unique aspects. In this paper, various methods for correlated receiver operating characteristic (ROC) curve data that have been extended specifically to clustered data are reviewed. For those methods that have not yet been extended, suggestions for their application to clustered ROC studies are provided. Various methods with respect to their ability to meet either of two objectives of the analysis of clustered ROC data are compared to consider a variety of ROC indices and their accessibility to researchers. The available statistical methods for clustered data vary in the range of indices that can be considered and in their accessibility to researchers. Parametric models permit all indices to be considered but, owing to computational complexity, are the least accessible of available methods. Nonparametric methods are much more accessible, but only permit estimation and inference about ROC curve area. The jackknife method is the most accessible and permits any index to be considered. Future development of methods for clustered ROC studies should consider the continuation ratio model, which will permit the application of widely available software for the analysis of mixed generalized linear models. Another area of development should be in the adoption of bootstrapping methods to clustered ROC data.

Complete MR angiography and Doppler ultrasound as the sole imaging modalities prior to carotid endarterectomy

OBJECTIVE

To assess the combination of duplex Doppler ultrasound (DUS) and complete carotid magnetic resonance angiography (MRA) for the non-invasive imaging of carotid disease and their effect on outcomes. Determine inter-reader agreement of carotid MRA.

MATERIALS AND METHODS

One-hundred and ten carotid bifurcations were evaluated using DUS, 2D and 3D time-of-flight MRA from the aortic arch to the Circle of Willis in 55 patients. Percentage stenoses were determined by two blinded readers using standardized criteria. Clinical follow-up was by chart review.

RESULTS

Correlation of Doppler and MRA was excellent (r=0.903, P<0.001). Inter-reader agreement (K) for MRA was good: internal carotid artery (ICA) (0.750), external carotid artery (ECA) (0.674) and common carotid artery (CCA) (0.410). Differences in CCA readings were due to minor differences in categorizing lesions as CCA versus ICA or ECA. MRA and Doppler detected nine occluded ICAs. Two DUS occlusions had ICA flow by MRA; one due to a reconstituted precavernous ICA, one a near occluded vessel. Five patients (9%) had surgical management modified by MRA with four not having surgery: three distal ICA/Siphon occlusions and one less severe stenosis by MRA. One tandem lesion not visualized by DUS was surgically significant. Nine aortic arch abnormalities had no surgical impact, possibly due to small sample size. Of 41 endarterectomies, there were no complications from errors of diagnosis.

CONCLUSION

Carotid MRA correlates well with DUS with good inter-reader agreement. MRA confirms Doppler findings, expands anatomical information and identifies tandem lesions from the aortic arch to the Circle of Willis which can affect surgical management. This approach to carotid artery imaging appears to have no negative effect on surgical outcome.

Are we detecting and operating on high risk patients in the asymptomatic carotid surgery trial? The Asymptomatic Carotid Surgery Trial Collaborators

OBJECTIVE

This study aims to determine whether asymptomatic carotid surgery trial (ACST) centres have entered and can identify high risk patients using duplex.

DESIGN

Retrospective study.

MATERIALS AND METHODS

Eighty-six vascular laboratories collaborating in ACST were studied, Equipment, operator experience, methodology and interpretation criteria were assessed. The ACST randomisation data were examined to determine whether patients believed to be at higher risk of stroke because of tight stenosis, contralateral occlusion or echolucent plaque were randomised.

RESULTS

Laboratories (92%) had colour duplex and 62% of all operators had > 3 years experience in carotid evaluation. The Doppler angle used to obtain peak velocity was 30-60 degrees in 65%, 60 degrees in 28% and 60-80 degrees in 6% of laboratories. Sixty-two per cent reported diameter reduction, 27% area reduction, and 11% used both methods. One-third of 1657 randomised patients were reported to have ipsilateral echolucent plaque. Median ipsilateral stenosis was 80%, 8% had contralateral occlusion and 8.5% had bilateral > 80% stenosis.

CONCLUSIONS

Centres in ACST use experienced operators, high quality equipment and conscientious data recording. Variations in methods of determining carotid stenosis exist, but can be smoothed by simple data collection. Patients at higher perceived risk of stroke are being entered and with continued recruitment it should be possible to determine whether surgery improves disabling stroke-free survival.

Retrograde balloon angioplasty of brachiocephalic or common carotid artery stenoses at the time of carotid endarterectomy

OBJECTIVES

This study was performed to demonstrate the value and durability of intraoperative retrograde angioplasty for stenotic lesions of the aortic arch branches at the time of carotid endarterectomy for the treatment of tandem proximal and bifurcation carotid lesions.

DESIGN

Retrospective analysis of the clinical data.

METHODS

Forty-four patients were included in this study when they presented with symptomatic extracranial vascular disease due to stenosis of both a proximal aortic arch branch and carotid bifurcation disease. Tandem disease was detected in the vascular laboratory and confirmed by angiography. Each patient was subjected to conventional carotid endarterectomy, and at the time of operation, the proximal lesion was subjected to transluminal angioplasty through the endarterectomy arteriotomy (brachiocephalic 24; left common carotid 15; right common carotid artery five). Patients were then followed up clinically and by non-invasive tests at 6-monthly intervals.

RESULTS

Forty-three successful dilatations were achieved. The single initial technical failure was due to heavy calcification of a brachiocephalic artery. In the follow-up period restenosis was noted in four patients. All restenosis occurred within 24 months. No restenosis at the angioplasty site was noted on subsequent follow-up of the remaining 39 patients. No perioperative stroke or death was encountered. A surprisingly high mortality rate was noted on follow-up in this group of patients, suggesting the presence of more aggressive and advanced diffuse vascular disease.

CONCLUSION

Retrograde intraoperative angioplasty of the proximal component of a tandem extracranial lesion has in this series proven to be a safe and durable therapeutic option. This technique has an acceptable restenosis rate in a subset of patients who have been demonstrated to have a shortened life expectancy and a high mortality rate in the follow-up period.

Ultrasonographic characterization of carotid plaques

The composition of atherosclerotic plaques in the carotid artery is assumed to be related to the development of neurological symptoms. The echo patterns produced by B-mode ultrasound may be of use in the assessment of the plaques' composition. It is suggested that fibrotic and "stable" plaques are more echogenic than lipid/hemorrhagic and echolucent or "unstable" plaques. B-mode ultrasound procedures were performed 1 day prior to surgery on 46 consecutive endarterectomies. Two observers assessed the plaques according to their echo pattern and echogenicity and sorted them into three categories: 1) predominantly echolucent, 2) heterogeneous, and 3) predominantly echogenic. The intraobserver agreement was moderate (kappa = 0.44) and the interobserver agreement low (kappa = 0.38). Furthermore, subjective categorization of plaque types resulted in type 1 plaques being as fibrotic as type 2 or 3 plaques. We conclude that B-mode ultrasound and subsequent subjective categorization of atherosclerotic plaques cannot adequately determine the volume of fibrosis or lipids within the plaque.

Brachial artery flow pattern and clinical backgrounds in patients with angina pectoris

Blood flow velocity of the brachial artery was measured noninvasively by ultrasound pulsed Doppler technique under the guidance of a B-mode ultrasound image in 56 patients with angina pectoris. There was no significant stenosis along the brachial artery on a B-mode image. The authors investigated seven clinical backgrounds for each patient, ie, age, gender, absence or presence of smoking, hyperlipidemia, diabetes mellitus, hypertension, and the number of significantly stenosed (> or =50%) coronary arteries. Among these variables, the determinants of the brachial artery velocity profile were selected by stepwise multiple regression analysis. Selected variables were the presence of hypertension for peak systolic velocity (R=0.276), age and the number of diseased vessels for peak reverse velocity (R=0.624), and age for peak diastolic velocity (R=0.609). The peak systolic velocity was larger in patients with hypertension than in those without it (0.565+/-0.023 vs 0.490+/-0.013 m/see, P<0.05), and the peak reverse velocity was larger in patients with multivessel disease than those without it (-0.117+/-0.071 vs -0.053+/-0.081 m/sec, P<0.01). Thus, the level of flow velocity of the brachial artery in patients with angina pectoris was partly determined by age, hypertension, and severity of coronary artery disease. The simple measurement of brachial artery flow velocity suggests changes in peripheral vasculature related to atherosclerosis.

Transcranial Doppler ultrasound criteria for hemodynamically significant internal carotid artery stenosis based on residual lumen diameter calculated from en bloc endarterectomy specimens

BACKGROUND AND PURPOSE

Transcranial Doppler (TCD) is often used in conjunction with carotid duplex ultrasonography (CDUS) to evaluate the hemodynamic significance of internal carotid artery (ICA) stenosis. We examined the sensitivity and specificity of TCD criteria for detection of a hemodynamically significant stenosis (residual lumen diameter < 1.5 mm) at the origin of the ICA.

METHODS

We selected patients who underwent carotid end-arterectomy (CEA) and had preoperative TCD data available. Eighty-one patients underwent transorbital evaluation, 49 of whom also had transtemporal TCD performed. The endarterectomy specimens were removed en bloc and sectioned, and the minimal residual lumen diameter calculated by computer analysis.

RESULTS

For the transorbital approach, the strongest indicators of a residual lumen diameter < 1.5 mm were reversed flow in the ipsilateral ophthalmic artery and a > 50% peak systolic velocity difference between the carotid siphons (distal ICAs) in patients with unilateral ICA origin stenosis. They were 100% specific and 31% and 26% sensitive, respectively. For the transtemporal approach in patients with a unilateral stenosis, a > 35% difference in ipsilateral middle cerebral artery (MCA) peak systolic velocity relative to the contralateral MCA or a > 50% difference in contralateral anterior cerebral artery (ACA) peak systolic velocity relative to the ipsilateral ACA were 100% specific for identifying a residual lumen diameter of < 1.5 mm. Sensitivities were 32% and 43%, respectively. Irrespective of contralateral stenosis, a > 35% difference in ipsilateral MCA peak systolic velocity relative to the ipsilateral posterior cerebral artery had a 100% specificity and a 23% sensitivity for detecting a < 1.5 mm minimal residual lumen diameter.

CONCLUSIONS

Although the TCD sensitivity for detecting a hemodynamically significant stenosis is relatively low, it can be highly specific (up to 100%). We conclude that TCD enhances the specificity of highly sensitive CDUS criteria for detecting a hemodynamically significant ICA stenosis.

Power Doppler imaging of carotid artery stenosis. Comparison with color Doppler flow imaging and angiography

BACKGROUND AND PURPOSE

Power Doppler imaging (PDI) is a new sonographic technique that has recently been introduced for vascular application. Since the technical principles of PDI may provide increased sensitivity to visualize the continuity of blood flow in arterial stenoses, we investigated the diagnostic significance of PDI and the intermethod relationship for the measurement and classification of internal carotid artery (ICA) stenosis in comparison with both color Doppler flow imaging (CDFI) and angiography.

METHODS

One hundred patients with a total of 128 ICA stenoses (50% to 69%, n = 37; 70% to 79%, n = 27; 80% to 99%, n = 64) and 12 ICA occlusions were consecutively investigated by means of PDI, CDFI, and intra-arterial angiography (n = 48). Reduction of the intrastenotic lumen was measured on longitudinal and transverse views of PDI and CDFI for the calculation of the degree of diameter and area stenosis, respectively. Angiographic stenosis was determined with the use of the North American Symptomatic Carotid Endarterectomy Trial (NASCET), European Carotid Surgery Trial (ECST), and common carotid (CC) methods.

RESULTS

PDI provided significantly more excellent or good (92% versus 79%; P < .01) displays of the intrastenotic lumen than CDFI, particularly in complicated high-grade stenosis. While linear regression analysis demonstrated a high overall correlation between PDI and CDFI for diameter (r = .88; P < .001) and area stenosis (r = .79; P < .001), categorization of ICA stenosis revealed best agreement for 80% to 99% area stenoses. Since angiography frequently either underclassified (NASCET method) or overclassified (ECST, CC methods) the degree of ICA stenosis in comparison to both PDI and CDFI, the sonographic-angiographic correlation was only moderate (regression coefficients ranged from .62 to .70; P < .001).

CONCLUSIONS

PDI further improves the assessment of ICA stenosis by providing better visualization of the stenotic vascular lumen than CDFI. Sonographic imaging of the stenotic plaque on both PDI and CDFI provided a direct measurement of the local degree of stenosis, while the angiographic grade of stenosis essentially depended on the method used for evaluation.

New color Doppler technique for detecting turbulent tumor blood flow: a possible aid to hepatocellular carcinoma diagnosis

We created a new imaging technique that detects and emphasizes turbulence, which is a characteristic of blood flow in hepatocellular carcinoma. We devised two indices that determine a characteristic tumor flow, the bi-directional and low-peak indices. In the phantom study, both indices of turbulence caused by a stenosis were much higher. In the clinical study, both indices were significantly higher in tumors than in the portal vein or hepatic vein. A turbulent blood flow was detected in 77% of tumors, whereas such detection seldom occurred in the portal or hepatic vein. This technique has the potential to distinguish turbulence in hepatocellular carcinoma.

The measurement of internal carotid artery stenosis: comparison of duplex with digital subtraction angiography

OBJECTIVES

To compare the subjective (eyeballed) method for measuring internal carotid artery (ICA) stenosis by non-selective intra-arterial digital subtraction angiography (IA-DSA) with objective and duplex methods.

DESIGN

Retrospective study.

MATERIALS AND METHODS

Fifty-three consecutive patients underwent IA-DSA prior to carotid endarterectomy providing 103 carotid angiograms. Objective assessment of ICA stenosis was by the North American Symptomatic Carotid Endarteectomy Trial (NASCET) criterion and the Carotid Stenosis Index (CSI). Duplex estimation of stenosis was derived from peak systolic and diastolic velocities in the ICA and common carotid artery (CCA).

RESULTS

The coefficient of repeatability was poorest for NASCET stenosis estimates (40%), whilst the improved values for CSI (20%) were consistent with the lower variability recorded for measuring the CCA diameter. Correlation and agreement levels between subjective (r = 0.80, -41% to +33%) or objective assessments and duplex (NASCET: r = 0.76; -52 to +28%; CSI: r = 0.72; -27 to +39%) showed similar values.

CONCLUSIONS

We conclude that the inter-observer variability for assessing angiograms obtained by arch injection is considerable and precludes high agreement when IA-DSA is compared with other methods. As the agreement of duplex ultrasound with IA-DSA is similar to the agreement between DSA methods, duplex can be offered as the first stage assessment of ICA stenosis, with the proviso that the duplex assessment is performed consistently by an experienced operator.

Evaluation and characterization of carotid plaque

Doppler sonography, combining high-resolution imaging and Doppler spectrum analysis, has proven to be the best choice for safe, noninvasive, low-cost screening for the etiology of stroke. With high-resolution imaging, plaque can be characterized relative to the risk for intraplaque hemorrhage, thought by many to be the precursor of plaque ulceration. Using high-resolution ultrasound, heterogeneous plaque has been shown to be associated with intraplaque hemorrhage. Criteria for distinguishing heterogeneous from homogeneous plaque are discussed, as are techniques for characterizing plaque. Several published articles strongly suggest that, when heterogeneous plaques are identified, the incidence of neurological symptoms and stroke on follow-up increases, relative to patients with homogeneous plaques. Additional long-term follow-up studies of heterogeneous plaque are needed. Most recently, carotid wall thickness has been evaluated as a physiological marker for atherosclerotic disease and as a gauge of the effectiveness of medical therapies. It is likely that carotid wall thickness will become important in the diagnosis and management of atherosclerosis. Radiologist are encouraged to learn this new form of ultrasound examination, which is reviewed briefly in this article.

Transcranial Doppler ultrasound battery reliably identifies severe internal carotid artery stenosis

BACKGROUND AND PURPOSE

There is a clinical imperative for noninvasive tests for carotid disease that have high sensitivity. Previous studies have shown that transcranial Doppler ultrasound (TCD) can identify intracranial collateral flow patterns and other hemodynamic consequences of carotid occlusion. We hypothesized that a battery of such TCD findings would have a greater sensitivity than any one TCD finding alone and would have clinical utility in identifying carotid disease.

METHODS

We determined the prevalence of seven TCD findings in patients with various degrees of carotid stenosis as measured by a blinded observer on 138 cerebral angiograms. We further determined the sensitivity and specificity of any one finding or any single abnormality in the TCD battery (the combination of all seven findings) for identifying severe (> or = 70%) carotid stenosis by angiography.

RESULTS

The following four individual TCD findings were associated (P < .001) with > or = 70% carotid stenosis on cerebral angiography: ophthalmic and anterior cerebral artery flow reversal and low middle cerebral artery flow acceleration and pulsatility. The presence of any single abnormality in the TCD battery had a similar association (P < .001) with > or = 70% carotid stenosis. The individual TCD findings had sensitivities of 3% to 83% and specificities of 60% to 100% for identifying > or = 70% carotid stenosis. The TCD battery had a sensitivity of 95% and specificity of 42% for identifying > or = 70% carotid stenosis.

CONCLUSIONS

A battery of TCD findings that can be routinely measured reliably identified patients with > or = 70% angiographic internal carotid artery stenosis with high sensitivity.

Defining the limitations of measurements from Doppler spectral recordings

PURPOSE

The purpose of this study was to determine whether Doppler measurements of peak velocity and four other quantitative measures of spectral shape are affected significantly by the site of the Doppler recording in relation to the location of the maximum stenosis.

METHOD

Continuous-wave and pulsed Doppler recordings were made distal to a 70% (area reduction or 45% diameter reduction) asymmetric stenosis in an in vitro flow model under steady and pulsatile flow conditions. Recordings were taken at six different locations proximal and distal to the stenosis. A photochromic dye technique was used to visualize the actual flow field in the model.

RESULTS

Distal to the stenosis, the flow visualization results demonstrated a strong radial and axial variation of the velocity field and thus explained why the Doppler measurements of peak frequency and spectral broadening were strongly dependent on the recording site. The peak frequency was maximum within the throat of the stenosis and returned to the prestenotic value five tube diameters distal to the stenosis. Other measurements of spectral broadening and spectral shape varied greatly depending on the location of the recording site in the poststenotic region. Higher order spectral moments such as the coefficient of kurtosis were found to exhibit large temporal variability, which makes them inappropriate as diagnostic indicators.

CONCLUSIONS

Because of the complex nature of the poststenotic flow field, these results clearly demonstrate that no single Doppler measurement can accurately quantify the severity of a stenosis. Of the Doppler measurements only peak velocity is related to the severity of stenosis. Reproducible peak velocity measurements are obtained only if the Doppler sample volume is positioned at or very near the throat of the stenosis and at an appropriate radial site that may not necessarily be at the center of the vessel.

History of ultrasonic duplex scanning

Ultrasonic duplex scanning was developed and introduced into clinical practice by the combined efforts of engineers and physicians. The instrumentation represents a marriage of B-mode imaging and Doppler technology. Since its introduction in 1974, numerous modifications and upgrading of the technology have taken place. The modern duplex scanner can be used to study vascular disease wherever it is found in the body.

Performance of carotid ultrasound in evaluating candidates for carotid endarterectomy is optimized by an approach based on clinical outcome rather than accuracy

BACKGROUND AND PURPOSE

The best method of selecting endarterectomy candidates for cerebral angiography is controversial. Carotid duplex ultrasound (CDUS) is widely used, but its performance varies across institutions. The clinical utility of CDUS could be improved with test criteria based on patient outcome rather than test accuracy.

METHODS

In 155 carotid bifurcations studied by CDUS and cerebral angiography, the degree of angiographic stenosis was measured by a reader, blinded to CDUS, using the North American Symptomatic Carotid Endarterectomy Trial (NASCET) method. We calculated accuracy, sensitivity, and specificity for predicting > or = 70% angiographic carotid stenosis of different peak systolic frequencies (PSF) measured by CDUS and generated a receiver operator characteristic (ROC) curve. We used NASCET outcome data and published data on angiographic complications to define relative "costs" of false-positive and false-negative CDUS, and we determined the point on the ROC curve representing the CDUS criterion with the highest clinical utility. We compared projected morbidity and mortality rates for 1000 hypothetical endarterectomy candidates resulting from the use of the most accurate CDUS criterion versus the CDUS criterion with the highest clinical utility by ROC analysis.

RESULTS

While PSF > or = 8 kHz had the highest CDUS accuracy (93%), its projected stroke and death rate due to CDUS error was 10.4/1000. On the other hand, PSF > or = 7 kHz, defined by ROC analysis to have the highest clinical utility, had a lower morbidity and mortality rate of 6.8/1000.

CONCLUSIONS

The use of ROC analysis and available outcome data can improve the performance of CDUS in selecting endarterectomy candidates for cerebral angiography.

Angiographic and duplex grading of internal carotid stenosis: can we overcome the confusion?

The stroke risk reduction benefit of surgical intervention in carotid occlusive disease has been validated in multicenter trials for various angiographically defined lesion severity categories. The two divergent angiographic grading methods used for internal carotid artery stenosis in these trials have caused confusion in the clinical application of their recommendations. Moreover, while today's highly accurate carotid duplex scanning can obviate the need for preoperative angiography in many cases, the duplex criteria must be tailored to achieve sufficiently reliable results on which therapeutic decisions can be made. This review offers a clarification of the discrepancies between the angiographic grading techniques and how their measurements of percent stenosis correlate to the duplex criteria needed to support the treatment decision-making process for carotid obliterative disease.

A transputer-based physiological signal processing system. Part 1--System design

This paper, the first of two, details the design and in-vitro testing of a transputer-based physiological signal processing system. The heart of the system is a transputer-based digital signal processing (DSP) board which can act as a stand-alone spectrum analyser, designed to operate in the audio-frequency band up to 25 kHz. The board comprises a T800 processor, two A100 transversal filters, 12 bit A-D circuitry capable of sampling up to 48 kHz, memory and address mapper. The initial application of the system is for the detection of early arterial disease. For this the DSP board is harnessed to the front end of a multigate pulsed Doppler ultrasound scanner operating at 4.8 MHz insonation frequency and incorporating a vessel wall tracking unit. The complete system performs a Fourier transform on the backscattered signals, providing spectral information on discrete areas of flow (0.6 mm3) across the vessel lumen in real time. This first paper describes the hardware, and the second describes the performance testing of the system on the bench and an assessment of its ability to detect low grade stenoses during steady flow.

Short-stay carotid endarterectomy is safe and cost-effective

BACKGROUND

Carotid endarterectomy (CEA) is conventionally performed following a contrast arteriogram, under general anesthesia, and with postoperative admission to an intensive care unit (ICU). We investigated whether any of these traditional adjuncts to CEA is necessary.

PATIENTS AND METHODS

Eighteen consecutive patients had CEA performed according to a protocol of duplex scanning only, operation under regional anesthesia, and admission to the ICU only in cases of a proven need for services unique to the ICU (group I). Utilization of preoperative arteriography, admission to the ICU, postoperative complications, total hospital length of stay, and hospital charges were calculated for this group and results were compared with a group of 178 patients undergoing conventional CEA (arteriography, general anesthesia, routine ICU admission) during the same period (group II).

RESULTS

In group I, 1 patient (6%) underwent preoperative arteriography and 4 patients (22%) were admitted to the ICU after CEA. Most group II patients (114 of 178, or 64%) underwent preoperative arteriography and virtually all (175 of 178, or 98%) were admitted to the ICU. Compared with group II, the average hospital length of stay for group I was significantly shorter (1.3 +/- 0.1 versus 3.1 +/- 0.3 days, P = 0.03) and hospital charges were significantly reduced ($5,861 +/- 229 versus $11,140 +/- 729, P = 0.02).

CONCLUSIONS

This pilot study suggests that CEA can be safely performed without routine preoperative carotid arteriography; that routine ICU admission is unnecessary for the majority of cases; and that elimination of routine arteriography and ICU admission can reduce hospital charges for CEA by nearly one half.

Clinical outcome in patients with mild and moderate carotid artery stenosis

PURPOSE

The natural history of incidentally discovered asymptomatic mild (< 50%) and moderate (50% to 79%) carotid artery stenosis is not known. The carotid artery duplex ultrasound surveillance program at the University of Washington Department of Vascular Surgery has serially evaluated patients with carotid artery disease for more than a decade and provides data on the progress and management of this disease.

METHODS

Patients with asymptomatic carotid artery bruits who had carotid artery disease causing less than 80% lumen diameter narrowing at their initial visit were identified. At each return visit (6 months, 1 year, and annually thereafter) a clinical questionnaire was completed, and bilateral carotid artery duplex sonography was performed.

RESULTS

Two hundred thirty-two patients (136 men and 96 women) were monitored for up to 10 years with sufficient data for a 7-year life-table analysis. Progression in the degree of stenosis was noted in 23% of patients during follow-up, and nearly half of these progressed to severe stenosis (80% to 99%) or occlusion. The risk of progression to severe stenosis and occlusion was significantly greater for those patients with moderate initial stenosis than mild initial stenosis (p < 0.01). The cumulative stroke risk for patients with mild initial stenosis (6%) was half of that for patients with moderate initial stenosis (11%) after 7 years. Carotid endarterectomy was performed in 27 patients during follow-up; in 13 the indication was an event ipsilateral to the stenosis, and in 14 there was asymptomatic progression to high-grade stenosis.

CONCLUSIONS

Regular monitoring of mild to moderate carotid artery stenosis shows how these lesions progress over time, permitting a realistic appraisal of their potential for producing an ischemic cerebrovascular event.

Carotid artery duplex scanning in preoperative assessment for coronary artery revascularization: the association between peripheral vascular disease, carotid artery stenosis, and stroke

PURPOSE

The purpose of this study was to identify high-risk populations for severe carotid artery disease (SCD) and neurologic events (NE) after nonemergency isolated coronary artery bypass graft procedures (CABG).

METHODS

Between February 1989 and July 1992, 387 patients underwent preoperative carotid artery duplex scanning as part of a preoperative assessment for nonemergency cardiac procedures. Of these patients, 376 had isolated CABG, and 11 had combined carotid endarterectomy (CEA) and CABG. Patient demographics, risk factors, and preoperative neurologic symptoms were recorded and analyzed. Severe carotid artery disease was defined as a 80% or greater stenosis of either internal carotid artery by carotid artery duplex scanning. Patients were evaluated for neurologic events (cerebrovascular accident, transient ischemic attack, amaurosis fugax, or reversible ischemic neurologic deficits) during the in-hospital postoperative period.

RESULTS

The prevalence of SCD was 8.5% (33 patients). The 33 patients with SCD were significantly older (65.6 +/- 6.5 years vs 62.5 +/- 10.4 years, p = 0.02), had previous CEA (27.3% vs 2.0%, p = 0.00001), had preoperative neurologic symptoms (21.2% vs 5.9%, p = 0.002), and had peripheral vascular disease (PVD) (63.6% vs 16.9%, p = 0.00001). The sensitivity of PVD for SCD is 63.6% (n = 21/33) (specificity 83.1%, positive predictive value 25.9%, negative predictive value 96.1%). In patients undergoing CABG alone, those who had postoperative NE were older (69.6 +/- 6.7 years vs 62.5 +/- 10.3 years, p = 0.036) and more likely to have PVD (50% vs 19.7%, p = 0.034), SCD (40% vs 4.9%, p = 0.001) and previous CEA (40% vs 2.7%, p = 0.0002). The incidence of postoperative NE in patients with SCD was 18.2% vs 1.7% in patients without SCD (p = 0.001). The sensitivity of SCD for NE was 40% (n = 4/10) (specificity 95.1%, positive predictive value 18.2%, negative predictive value 98.3%).

CONCLUSIONS

PVD may be helpful to identify patients at high risk for severe carotid artery stenosis. Postoperative NE in patients with CABG are associated with increasing age, carotid artery stenosis greater than 80%, previous CEA, and PVD.

Critical carotid artery stenosis: diagnosis, timing of surgery, and outcome

PURPOSE

Patients with critical carotid artery stenoses have been considered to be at high risk for carotid artery occlusion necessitating urgent or emergency endarterectomy once the stenosis is identified. Included in this group of patients are those with carotid string sign or atheromatous pseudoocclusion (APO). This review was conducted to determine the impact of the severity of stenosis including APO on the treatment and outcome of patients undergoing carotid endarterectomy.

METHODS

The records of 203 consecutive carotid endarterectomies performed in 197 patients were reviewed in detail. Patients were stratified into a critical stenosis group (80% to 99% diameter) and noncritical stenosis group based on noninvasive vascular laboratory and carotid arteriography results. Comparisons were performed of demographic data, atherosclerotic risk factors, carotid artery disease presentation, interval between arteriography and endarterectomy, operative details, and surgical results between the critical and noncritical groups and between patients in the critical group with and without APO.

RESULTS

Carotid endarterectomies were performed on 91 critical carotid artery stenoses and 112 noncritical stenoses. The groups did not differ significantly with regards to demographics, risk factors, carotid artery disease presentation, mean back pressure, and operative use of shunt or patch closure. For the critical group the interval between arteriography and endarterectomy was 8.63 +/- 2.38 days compared with 9.64 +/- 2.14 days for the noncritical group (mean +/- SEM, p = 0.75). No patient in either group progressed to occlusion in the interval between arteriography and endarterectomy. Perioperative strokes occurred in two patients (2%) in the critical group and four patients (3.6%) in the noncritical group (p = 0.09). Likewise, no significant difference was demonstrated in these variables when comparing patients with critical carotid artery stenosis and APO with those without APO.

CONCLUSIONS

The presence of a critical carotid artery stenosis including APO did not impact on the treatment or outcome of patients requiring endarterectomy nor did it imply the need for emergency intervention to prevent thrombosis. Surgical intervention can proceed after evaluation and optimization of comorbid conditions without undue concern for interval thrombosis.

An absent ophthalmic artery or carotid siphon signal on transcranial Doppler confirms the presence of severe ipsilateral internal carotid artery disease

Transcranial Doppler ultrasound provides a useful adjunct to extracranial ultrasound in the diagnosis of carotid bifurcation disease. Previous studies have shown that collateral flow patterns and diminished flow velocities in the ipsilateral middle cerebral artery correlate with hemodynamically significant carotid disease. In a series of 7,054 carotid duplex and transcranial Doppler examinations, 12.5% (95% confidence interval [CI]: 8.7, 16.4) of 287 ophthalmic arteries ipsilateral to an apparent carotid occlusion had no detectable flow signal, compared with 0.5% (95% CI: 0.3, 0.7) of 6,767 ophthalmic arteries ipsilateral to a non-occluded carotid artery (p < 0.001). Carotid siphon signals were not detectable in 24.4% (95% CI: 19.4, 29.4) of arteries ipsilateral to the carotid occlusion, versus 1.0% (95% CI: 0.8, 1.3) ipsilateral to nonoccluded carotid arteries (p < 0.001). A significant number of absent ophthalmic artery and carotid siphon signals (5.7 and 8.7%, respectively) were also found in patients with 80 to 99% extracranial carotid stenosis. A subset of 216 studies with angiographic correlation confirmed the high association of these transcranial Doppler findings with severe stenosis or occlusion of the internal carotid artery. Primary ophthalmological disease or siphon occlusion did not explain these findings. An absent ophthalmic artery or carotid siphon signal on transcranial Doppler examination is believed to represent a failure to detect slow flow distal to severe carotid bifurcation lesions. As a sign of ipsilateral carotid occlusion, the sensitivities of absent ophthalmic artery and carotid siphon signals are quite low (12.5 and 24.4%, respectively). The high specificities of 99.5 and 99.0%, however, make these findings useful in confirming the diagnosis of presumptive carotid occlusion by carotid duplex ultrasound.

Signal processors in duplex sonography: in vitro comparison between analog and digital methods

Using a new flow-test phantom, which respects the acoustic properties of real blood as well as the proximal and distal impedances of body circulation, we assessed the performance of two duplex sonography signal processors on blood-flow measurements. With both the analog and the dynamic signal processor (Fast Fourier Transform), the correlation between duplex sonography and quantitative flow measurements was high (0.96-0.99) for different dynamic conditions (steady or pulsatile blood flow, varying heart rate, blood pressure, and hematocrit) and for different mechanical conditions (silicon tube or animal vessel). The real blood flow was overestimated by duplex sonography; the over-estimation was more pronounced with the analog processor (factor 1.87-4.20) than with the digital processor (factor 1.22-1.64, P < 0.05). Applied to the study of asymmetric stenoses, the digital processor was not superior to the analog processors described in the literature.

Neurologic deficits following noncarotid vascular surgery

Neurologic events following noncarotid vascular surgery (NCVS) are considered unpredictable. To test this hypothesis, we reviewed our vascular registry for a 3-year period and identified all patients with new postoperative focal neurologic events (stroke, hemispheric transient ischemic attack [TIA]) within 2 weeks of a category I or II vascular procedure as defined by the American Board of Surgery, exclusive of carotid surgery and arterial trauma. Thirteen of 1,390 NCVS procedures (0.9%) in 13 patients were associated with focal neurologic events. There were 2 TIAs, 10 anterior circulation strokes, and 1 posterior circulation stroke. Twenty-seven percent of strokes were fatal. The neurologic deficit developed in the immediate postoperative period in 31%, more than 4 hours but less than 72 hours postoperatively in 54%, and within 3 to 14 days postoperatively in 15%. Patients with anterior circulation events (group A, n = 12) were compared for variables potentially influencing postoperative stroke with case controls who were selected using a table of random numbers (group B, n = 12). Controls were derived from a pool of all category I or II NCVS procedures recorded in our vascular registry sequentially during the same time period and who were without new neurologic deficits postoperatively. Using Fisher's exact test, comparisons between groups A and B revealed that new anterior circulation neurologic events in vascular surgical patients tended to be associated with intra-abdominal procedures (p less than 0.05), perioperative hypotension (p less than 0.05), and the presence of a greater than or equal to 50% internal carotid artery stenosis ipsilateral to the neurologic event (p less than 0.001). Such information may prove useful in the management of selected patients prior to arterial reconstruction and in operated NCVS patients with postoperative neurologic events.

The effect of averaging cardiac Doppler spectrograms on the reduction of their amplitude variability

The effect of averaging cardiac Doppler spectrograms on the reduction of their amplitude variability was investigated in 30 patients. Beat-to-beat variations in the amplitude of Doppler spectrograms were also analysed. The quantification of amplitude variability was based on the computation of the area under the absolute value of the derivative function of each spectrum composing mean spectrograms. Fast Fourier transform using a Hanning window was used to compute Doppler spectra. Results obtained over systolic and diastolic periods showed that the reduction of amplitude variability followed an exponentially decreasing curve characterised by the equation f (r) = 100 e-beta(r-1), where r is the number of cardiac cycles, beta the exponentially decreasing rate, and 100 the normalised variability for r = 1. In systole, the decreasing rate beta was 0.165, whereas in diastole it was 0.225. Reductions of the variability in systole for a number of cardiac cycles of 5, 10, 15, and 20 were 48, 77, 90 and 96 per cent, respectively. In diastole, reductions of the variability for the same numbers of cardiac cycles were 59, 87, 96 and 99 per cent, respectively. Based on these results, it can be concluded that no significant improvement in the reduction of amplitude variability may be obtained by averaging more than 20 cardiac cycles.

Measurement variability in duplex scan assessment of carotid atherosclerosis

BACKGROUND AND PURPOSE

The reproducibility of duplex scan measures of carotid atherosclerosis was evaluated as part of a study assessing the prevalence of carotid disease in elderly adults.

METHODS

Doppler measures of blood flow velocity were used to evaluate disease severity, and extent of carotid plaque was scored from the B-mode image. A reader assigned a grade from 0 to 3 to each of seven segments in the carotid system, based on the number and size of lesions present. Reproducibility data were obtained from 30 study participants who underwent a repeat scan by a second sonographer. Each scan was then scored by two readers.

RESULTS

Doppler measures of blood flow velocity were found to be highly reproducible, with intraclass correlation coefficients of 0.81 for the common carotid artery, 0.84 for the internal carotid artery, and 0.77 for the internal carotid artery velocity to common carotid artery velocity ratio. Reproducibility of plaque grade was evaluated using segment as the unit of analysis, and both sonographer and reader variation were analyzed. When readers differed perfect agreement was achieved in 84% of the segments (K = 0.67), and when sonographers differed perfect agreement was obtained in 78% of the segments (K = 0.56). When both sonographer and reader differed, perfect agreement was obtained in 77% of the segments (K = 0.53). The plaque index, created by summing plaque grades from selected segments, was highly reproducible, with an intraclass correlation coefficient of 0.86.

CONCLUSIONS

The duplex scan protocol described here provides reliable measures of both extent and severity of carotid disease that are appropriate for use in cross-sectional studies.

Role of arteriography in the preoperative evaluation of carotid artery disease

This retrospective study was undertaken to determine the role of arteriography in the treatment of patients being considered for carotid endarterectomy. The results of preoperative classification of disease severity by duplex ultrasound and arteriography were compared, and the impact of arteriography on patient management was ascertained. We reviewed the records of 83 patients who had carotid surgery planned on the basis of their clinical history and duplex scan results and who then underwent arteriography. Duplex scan results agreed with the classification of stenosis by arteriography in 87% of evaluated sides and were within one category in 98%. In 87% of the cases reviewed, the clinical presentation and duplex scan findings were sufficient for appropriate patient management. In the instances that arteriography was useful (13%), the need for arteriography was evident when the duplex scan (1) was technically inadequate or equivocal; (2) showed an unusual distribution of disease, atypical anatomy, or a recurrent lesion; or (3) demonstrated an internal carotid artery with diameter-reducing stenosis of less than 50% in a patient with hemispheric neurologic symptoms despite antiplatelet therapy.

Evaluation of the carotid artery bifurcation: comparison of magnetic resonance angiography and digital subtraction arch aortography

Thirty-four carotid artery bifurcations were examined using both magnetic resonance angiography (MRA) and digital subtraction arch aortography to determine their accuracy when compared to selective carotid angiography. The sensitivity of MRA was 73% and its specificity was 91% when compared with selective carotid angiography. The sensitivity of arch aortography was 27% and its specificity was 100%.

Accurate noninvasive method to diagnose minor atherosclerotic lesions in carotid artery bulb

In a prospective study using a multigate pulsed Doppler system, minor (less than 30% diameter reduction) carotid artery lesions were diagnosed by detecting not only abnormalities in the blood flow pattern, but also local changes in artery wall distensibility. For the diagnosis of more severe lesions, additional information was obtained from disturbances in the Doppler audio spectrum. Biplane arteriography was used as a reference. The observed agreement, sensitivity, and specificity were 86.6%, 90.3%, and 88.6%, respectively, for all lesions and 85.7%, 82.1%, and 88.6%, respectively, when only minor lesions were considered. kappa (a chance-corrected measure of agreement) was 81.7%. If only blood flow abnormalities were used to detect minor lesions, 43.5% would be missed. Our results indicate that minor carotid artery lesions can be diagnosed noninvasively more accurately when both local blood flow irregularities and local changes in vessel wall distensibility are taken into account.