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Carotid Artery Triplex Ultrasound (1)

Rationale for Carotid Triplex Ultrasound

Carotid Artery Triplex Ultrasound

The primary role of triplex sonography in assessing patients with suspectedextracranial cerebrovascular disease is to first, detect the presence ofatherosclerotic disease and, second, to determine the degree to which theinternal carotid artery is stenosed. Vascular surgeons and interventionalists relyvery heavily on the results of carotid triplex ultrasound in managing their patientswith carotid disease. It is not uncommon for surgeons to take a patient directly tothe operating room based on the results of a carotid triplex exam from a lab thathas a proven track record and validated results. Magnetic resonanceangiography (MRA) and catheter-angiography also play important roles inworking up a patient with suspected critical carotid artery disease. However,each modality has its limitations and technical pitfalls.

Carotid disease in strokeThere is convincing evidence of a causal association between atherosclerotic

narrowing of the carotid arteries and cerebral infarction. Moderate to severecarotid artery stenosis occurs in approximately 15 to 30 percent of patients withcarotid artery territory (anterior cerebral circulation) stroke, and is associated withan increased risk of recurrent stroke.1 2 As the degree of stenosis increases therisk of stroke also increases and surgical or interventional reduction of moderateto severe ipsilateral carotid artery stenosis reduces the risk of future stroke insymptomatic patients.3 4 By identifying the presence and degree of carotidstenosis, imaging of the carotid arteries aids in the selection of patients who maybenefit from surgical therapy.

In the early 1990s two large-scale clinical trials were conducted that sorted outthe confusing, non-standardized ways that carotid ultrasounds were beingperformed and interpreted in North America. The North AmericanSymptomatic Carotid Endarterectomy Trial (NASCET) compared the efficacyof carotid duplex ultrasound and catheter angiography in identifying patients witha≥70% ICA stenosis who had symptoms of cerebral ischemic events. The study also assessed clinical outcomes in those patients, half of whom were randomizedto surgical treatment (TEA) the other half to medical management. The studyreached some noteworthy conclusions:

o Carotid duplex ultrasound, when performed in accordance with stricttechnical standards, equals or exceeds catheter angiography in detectinga≥70% ICA stenosis.

o The risk of ipsilateral stroke was reduced significantly in patients withcarotid stenosis 50-69% who received carotid endarterectomy.5



Patients with stenosis of 70-99% showed the most significant reduction in therate of ipsilateral stroke.6 7

Role of Carotid Triplex Ultrasound Evaluationo Detect presence of atherosclerotic diseaseo Grade ICA stenoses –significantly affects clinical management of patiento Evaluate plaque morphology- especially surface characteristics that

might suggest plaque ulceration or intraplaque hemorrhageo Presence of collateral flow –associated with altered intracranial

hemodynamics or vertebral/subclavian steal syndrome.o Intimal-medial thickness measurement –used by some physicians in

adjusting pharmacological management of patients with hyperlipidemia,diabetes, hypertension syndrome.

Clinical Indications for Carotid Triplex UltrasoundWhile more patients are requesting and receiving carotid triplex ultrasound

examinations for screening and as part of a complete physical examinationsin senior patients with cardiovascular risk factors, the primary symptomaticclinical indications remain unchanged. They include:

o TIA–Transient Ischemic Attack–(See Chapter–Strokes and TIAs)

o Amaurosis fugax–Amaurosis fugax is a sudden, dramatic loss of visionin one eye caused by a temporary lack of blood flow to the retina. Thevisual loss is frequently described as having a gray orblack “shade pulleddown” or a “camera lens narrowing” over the affected eye. It usually lastsseveral seconds but may last several minutes. Amaurosis fugax frequentlyresults from embolization of thrombus or plaque debris from the carotidbifurcation to the retinal artery. This blocks the artery for a time andcauses loss of vision in that eye for as long as its blood supply is cut off.

o Ischemic oculopathy - A condition in which there is ischemia in both theanterior and posterior segments of the eye caused by atheroscleroticcarotid artery disease. Posterior segment abnormalities include ischemicinsults to the retina or optic nerve.8 The most common presentingsymptoms are ocular pain and visual loss, either gradual or abrupt,amaurosis fugax, and afterimages. Loss of visual acuity is the mostfrequently encountered symptom. Atherosclerotic disease of the carotidartery is the most common cause; however, it is an infrequentmanifestation of carotid. Approximately 5% of patients with marked carotidartery stenosis present with manifestations of ischemic oculopathy.9

o Central retinal vein occlusion - A condition caused by thrombosis in thevein draining the retina. The sudden obstruction of the blood flow awayfrom the eye can lead to bleeding in the retina and loss of vision. Thisdisorder is most commonly seen in older individuals who have significantatherosclerosis. In addition, hypertension is a risk factor as well asconditions that make the blood clot more easily. If a small vein is



obstructed, the symptoms may be mild. If a major vein is blocked, thesymptoms are usually rapid and severe. Disorders that increase theviscosity of the blood and make it "more sticky" may lead to retinal veinocclusion. Some conditions which can produce this state are inheriteddisorders, smoking, use of estrogen and polycythemia. Hypertension andatherosclerosis may damage the vessels, making them more subject todeveloping clots. Common symptoms include blurred vision is there isbleeding within the retina or fluid immediately in front of it. If a majordraining vein is obstructed, the retina will become damaged and visualloss will occur over several hours.

o Follow-up to carotid surgery - thromboendarterectomy (TEA or CEA).Patients who have had open surgery for the removal of clot and plaqueand repair of a severely diseased carotid artery should be followed on aregular basis. Many times these patients also have contralateral carotidartery disease which also bears following (watchful waiting).

o Follow-up to carotid stenting–Carotid artery angioplasty withsupportive stent placement is becoming a routine part of vascularinterventional practice. It is usually reserved for patients who are at highrisk for complications from an open surgical procedure under generalanesthesia. It is important to note that stents alter hemodynamic states inthe internal carotid artery. Typically, peak systolic velocities are higher ina stented artery than in a normal carotid artery (PSV >140 cm/sec). Thesonographic criteria for determining normalcy are still being validated.

o Pre-op Coronary Artery Bypass Surgery –Because of the high rate ofassociation between carotid artery disease and coronary artery disease,patients being worked-up for bypass surgery routinely undergo carotidtriplex ultrasound examination. The detection of an occult high-gradelesion in one of the internal carotid arteries might postpone the open-heartprocedure until the neck can be cleaned out. In one study the finding ofcarotid stenosis greater than 75% in patients over 60 years of age wasassociated with occurrence of stroke in 15% of cases. The authorsconcluded that carotid screening is helpful to determine patients atincreased risk of stroke and should be performed in patients greater than60 years10

o Vertigo, dizziness, and syncope are not generally caused by carotidstenosis; patients with these symptoms who are found to have carotidstenosis should be considered "asymptomatic" regarding the stenosis.



ICAVL Standards –Extracranial Cerebrovascular Testing 2005

The Intersocietal Commission on the Accreditation of Vascular Labs (ICAVL)published revised Standards for carotid artery testing in 2005. A complete copyof this document is available at:http://www.intersocietal.org/icavl/apply/standards.htm. A web link can be foundon the Sonography-Related Links page of the ProSono Library.

The following protocol incorporates these widely accepted standards into anexamination process that produces reliable, reproducible results that is easy onboth the sonographer and the patient. General Comments:

o A complete carotid triplex study is bilateral and includes evaluation of thecommon carotid artery (CCA), internal carotid artery (ICA), external carotidartery, vertebral artery (VA), and subclavian artery (SA) on each side.

o Measurements of both arm systolic pressures are recommended to helpidentify vertebral-subclavian steal syndrome or hemodynamicallysignificant subclavian artery stenosis.

o Both imaging and Doppler information are used to identify vessels.o Doppler signals are obtained from each selected site at an angle of 60o or

less with respect to the vessel wall or color-aided flow direction.

Examination Protocol- One of the important aspects of a vascular triplexexamination protocol is that it provides a method for the sonographer to perform,record and report information obtained during a triplex procedure in an efficientand reproducible way. The three components of a triplex ultrasound exam are:

o 2-D High-resolution, gray scale imaging (2D)o Color Doppler imaging (CDI)o Spectral Doppler waveform analysis (SA)

Patient Positiono Supineo Head turned slightlyo Standard ultrasound approach (right side)o Vascular lab approach (from head)

Instrumentationo High frequency (5MHz–15MHz) phased array

transducer.o Range-gated Doppler with the ability to adjust position

of the range gate within the area of interest.o Audio output DopplerAppropriate recording device or digital archiving

capabilities.

Examination Protocol



Coronal section throughcarotid bifurcationshowing a large,

heterogeneous plaque atthe origin of the ICA.

Transverse sectionthrough CCA showing

a focal soft plaque.

Gray Scale ImagingThe ultrasound examination begins with brief real-time survey of the neck vasculature. The goal ofthe initial survey is to:o Evaluate anatomyo Get a “lay of the land”o Observe and note presence of pathology

In a sagittal (coronal) plane of section thesurvey begins with the transducer placed on antero-lateral neck using the sternocleidomastoid muscleas a built-in “standoff”. After identifying the CCA, the transducer is moved cephalad from the clavicleto the angle of mandible. At the bifurcation, subtleangling of the transducer anteriorly and posteriorlyand rotation to obtain a longitudinal image of thevessels, the ICA and ECA can be imaged.

Representative 2D images are obtained and documented of the:o CCAo ICAo ECAo Carotid bifurcation

In a transverse (axial) plane of section, the carotidsystem is evaluated from the clavicle to the angle ofthe mandible. Again, the sternocleidomastoid muscleis used as a window and representative images areobtained and copied of the:

o CCAo Carotid bifurcation

Identifying and Differentiating Neck VesselsCorrect differentiation between the ICA and the ECA at the bifurcation is of

critical importance. Since the ECA provides blood to the face and scalp,structures that are easily and adequately perfused by collateral circulation in theevent of a complete occlusion, the presence and extent of disease in this vesselis of little, if any, clinical importance. The ICA, however, is the main conduit forblood to the anterior and middle circulation to the brain. Disease in the ICA is ofimmense clinical importance and assessment of presence and severity is theprimary reason for performing carotid. While the ECA typically lies anterior andmedial to the ICA, variations in anatomic configuration of the neck vasculature,particularly vessel tortuosity, can complicate acquisition of spectral Doppler.Also, changes in resistivity in the cerebral circulation and some types of cardiaccomorbidity can alter the spectral waveform appearance.



ECA–early branching isseen in the neck. Flowtoward the transducer is

demonstrated in the superiorthyroidal artery at its takeoff

from the ECA

ECA– “temporal tapping”. Transmitted oscillation from

tapping the temporal artery justanterior to the pinna of the earare seen during diastole in the

ECA.

The following table provides helpful hints in correctly identifying thebifurcation vessels.

Table I. Carotid Bifurcation Vessel Triplex Characteristics

ICA ECA

Lateral and posterior (lots of variation) Medial and anterior (lots of variation)

No branches present in neck Branches early in neck–superior thyroidalartery

Low-resistance waveform High-resistance waveform

No response to “temporal artery tapping” Alterations waveform during temporal arterytapping

“Temporal artery tapping” is a simple technique to help differentiate the ECA from the ICA. Using CDI to guide the spectral Doppler range gate, it is placedthe vessel to be interrogated. While watching the spectral display and listeningto the audio output, the temporal artery, as it passes just anterior to the pinna ofthe ear, is lightly tapped with the free hand. Since the temporal artery is aproximate branch of the ECA, the tapping is transmitted into the ECA and isdisplayed as an oscillation on the spectral display. It can also be heard onaudio output. If there is no alteration of the Doppler signal during the tapping,then the vessel being interrogated is most likely the ICA.

Doppler Protocol –General Commentso Accurate Doppler findings are critical to correct diagnosis and grading.o Color Doppler provides global display of hemodynamic conditions present.o Color Doppler directs acquisition of spectral information.o Spectral Doppler provides flow velocities–(quantified data.)

This data is the foundation for grading ICA stenoses.



Color Doppler ProtocolColor Doppler imaging (CDI) provides a global display of hemodynamic

patterns in the area being examined. It can focus the examiner’s attention on variations in the laminar arterial flow patterns seen in normal, non-diseasedcarotid arteries. Using the CDI display as a guide, the sonographer canquickly and accurately obtain spectral Doppler waveforms in the areas ofinterest. The hemodynamic parameters displayed by CDI include:o Presence of flow–system sensitivity and gain controls must be optimized.o Direction of flow–relative to the transducer position.o Relative velocities within the CDI display area.o Flow characteristics in such as:

1. Laminarity2. Turbulence3. High velocity jets

CDI is also of great value in identifying the presence and direction of flowin the vertebral arteries as they pass through the ossified cervical vertebrae.Detection of a short segment of a vertebral artery in an intervertebral spacemakes acquisition of spectral Doppler waveforms fast and accurate. Again,system sensitivity and gain settings must be optimized for adequatedetection.

Spectral Doppler ProtocolSpectral Doppler waveforms provide the foundation for grading carotid

artery stenoses. While 2D and CDI images offer a wealth of information onthe morphologic status of the extracranial carotid arteries, it is the spectralDoppler information that allows determination of the extent of hemodynamicsignificance of an ICA atherosclerotic lesion.11 12 Since hemodynamicsignificance of a carotid lesion is usually the determining factor in patientmanagement, acquisition of adequate and accurate spectral Dopplerwaveforms is essential in a carotid triplex examination.

Using CDI as guide, range-gated samples of flow patterns are obtainedfrom various sites within the neck arteries. At a minimum, these sites shouldinclude:

Hemodynamic flow characteristics as displayed with Color Doppler imaging (CDI).LEFT: normal laminar–normal flow pattern with increasing velocities toward central lumen.MIDDLE: turbulent flow –multi-directional flow distal to a stenosisRIGHT: high velocity jet–stenosis profile with a high-velocity jet at point of maximum

stenosis



When carotid disease is present, additional documentation should be made ofany abnormal Doppler findings. When a stenosis is present, spectral Dopplerwaveforms should be obtained proximal, at and distal to the area of maximumstenosis. PSV and EDV measurements should be made and recorded.

Triplex sonography has been used in the evaluation of carotid artery diseasesince the introduction of the technology in the late 1970s. Technologicaladvances in digital imaging, image processing, and Doppler display formats havebeen accompanied by an increased accuracy in clinical assessment. Manyauthors over the years have published broadly validated data, however, thediagnostic criteria used in their protocols has varied and has madestandardization of examination methods and outcomes difficult.

Three major developments in the standardization of triplex sonography as itrelates to the diagnosis and management of patients with carotid atheroscleroticdisease have occurred in the past decade: the North American symptomaticCarotid Endarterectomy Trial (NASCET), the Asymptomatic CarotidAtherosclerosis Study (ACAS), and the report from the Society of Radiologists inUltrasound Consensus Conference.

Site Recorded Samples Demonstrating:

CCA 2 sites Mid and distal PSV*, direction of flowICA 2 sites Proximal and mid PSV and EDV*–highest

values, direction of flowECA 1 site PSV, direction of flowVA 1 site Presence and direction of flowSA 1 site Presence and phasicity (triphasic normal)

PSV = peak systolic velocity EDV–end diastolic velocity

Standardized Interpretation Protocol

Triplex demonstration of a very tight (80-99%) stenosisin the proximal ICA. The color column is narrowed bymural plaque. CDI demonstrates increased velocitiesat and just beyond this narrowing with turbulent flowdownstream. This is a classic “stenosis profile”.

Spectral Doppler waveforms demonstrate extremelyhigh PSVs (~450 cm/sec) and an elevated

EDV (~150 cm/sec).



Society of Radiologists in Ultrasound Consensus Conference.

In 2003, a panel of radiologists, neuroimaging specialists, vascularsurgeons and vascular technologists met to establish criteria for theinterpretation of carotid triplex examinations. Their recommendations:

o All ICA examinations should be performed with grayscale, color Dopplerand spectral Doppler ultrasound.

o Categories of disease:1. Normal2. < 50% stenosis.3. 50 to 69% stenosis.4. ≥70% stenosis to near occlusion.

o Peak systolic velocity (PSV) in the ICA and the presence of plaque are theprimary diagnostic criteria.

o Stratification Criteria:

Diameterreduction

%Plaquing PS V

0 No plaque present <125 cm/s

< 50 Plaque present <125 cm/s

50-69 Plaque present 125 - 230 cm/second

≥70% Plaque present >230 cm/second

Near occlusion Markedly narrow lumen on color Doppler images

Total occlusion No detectable patent lumen on grayscale and no flowdetected with spectral power and color Doppler

Final reports should include specific velocity and grayscale findings with studylimitations noted when they exist.13 14

University Of Washington Criteria15

The Department of Vascular Surgery at the University of WashingtonMedical Center has long been the leader in acquiring, analyzing andvalidating spectral Doppler data. It is assumed, of course, that plaque ispresent on 2D imaging in all except the 0% diameter reduction category. Thefollowing table summarizes their interpretive algorithm:



ICA:CCA Ratio16

A variety of interpretative schema use several ratios obtained fromcarotid artery spectral Doppler waveforms. The most common are the:

o ICA to CCA peak systolic ratio (IC:CC - PSV)o ICA to CCA end diastolic ratio (IC::CC–EDV)

Vertebral and Subclavian Interpretation

Subclavian steal phenomenon (SSP) refers to a benign condition in whichhemodynamically significant narrowing of the proximal subclavian arteryresults in flow reversal in the ipsilateral (same side) vertebral artery. It is notan uncommon finding during carotid triplex ultrasound evaluation and hasbeen documented to occur in about 6% of patients undergoing testing.17 SSPis asymptomatic and refers to retrograde flow in the vertebral artery only.Subclavian steal syndrome (SSS), on the other hand, describes a conditioncharacterized by flow reversal in the vertebral artery associated with transientneurological symptoms related to cerebral ischemia.

The primary lesion causing vertebral artery flow reversal is proximalsubclavian artery stenosis or occlusion, resulting in decreased blood pressurein the arm distal to the stenosis. A pressure reduction occurs in the arm thatcauses the collateral network in the Circle of Willis to kick in and shunt blooddown the ipsilateral vertebral artery to the compromised vascular territory.When symptoms are present they typically are related to vertebrobasilar andposterior cerebral circulation ischemia. Specifically, symptoms may include:dizziness, unsteadiness, vertigo, and visual changes. In chronic, severeSSS, arm ischemia occurs, causing arm claudication and rest pain.18

Diameterreduction

%

Peaksystolicvelocity

Enddiastolicvelocity

Spectralcharacteristics

0 <125 cm/s Normal spectral window

1-15 <125 cm/s Spectral broadening in systolicdeceleration

16-49 <125 cm/s Spectral broadening throughoutsystole

50-79 >125 cm/s < 140 cm/s Extensive spectral broadening

80-99 >125 cm/s >140 cm/s Extensive spectral broadening

Occluded Absent signals Dampened signal in CCA

IC: CC ratio > 4.0 = >70% stenosis(Sensitivity: 91%; specificity: 90%; PPV = 87%; NPV=94%)



Diagnostic criteria include:o Brachial systolic pressure >20 mmHG lower than contralateral side.o Diminished or absent radial pulse.o Supraclavicular bruit present on auscultation.o Flow reversal in vertebral artery.o SA spectral Doppler waveform monophasic.

o Technical Considerations

The primary sonographic finding in diagnosing subclavian steal is thedemonstration of flow reversal in the vertebral artery. Having obtainedbilateral brachial artery systolic pressures prior to beginning the ultrasoundprotocol, the examiner will be alerted to pay particular attention tovertebral flow direction if one arm pressure measures more than 20 mmHglower than the other arm. A diminished or absent pulse and monophasicDoppler signals in the radial artery are further clinical evidence that ahemodynamically significant stenotic lesion is present somewherebetween the heart and the wrist.

Triplex ultrasound readily reveals the presence of flow reversal in thevertebral artery on both CDI and spectral Doppler waveform display. Itgoes without saying that, to be able to detect flow reversal, the operatormust be thoroughly familiar with how directional information is displayedon his/her system. A review of the underlying physical principles ofdirectional Doppler display see Chapter 11: Doppler Instrumentation :

http://www.jimbaun.com/11._doppler_instrumentation___rev4.1.pdf

A practical recommendation for validating CDI demonstration ofvertebral artery flow direction is to compare color flow in the vertebral tocolor flow in the CCA and internal jugular vein (IJV). Rarely is flow in theCCA reversed and flow reversal in the IJV is unheard of. In a normalhemodynamic state, then, color hue should be the same in the VA and theCCA. In a steal state, color hue in the VA will be the same as in the IJV.

Normal vertebral artery flow pattern.

The VA demonstrates flow toward the head(red = flow away). The vertebral veinimmediately above it demonstrates flowtoward the heart (blue–flow away). Thespectral Doppler waveform obtained from theVA is plotted under the x-axis indicating flowaway.



1 Lindgren A, Roijer A, Norrving B, et al. Carotid artery and heart disease in subtypes of cerebralinfarction. Stroke 1994. 25:2356-62.2 Bogousslavsky J, Van Melle G, Regli F. The Lausanne Stroke Registry: analysis of 1,000consecutive patients with first stroke. Stroke 1988. 19:1083-92.3 Barnett HJ, Taylor DW, Eliasziw M, et al. Benefit of carotid endarterectomy in patients withsymptomatic moderate or severe stenosis. North American Symptomatic Carotid EndarterectomyTrial Collaborators. N Engl J Med 1998. 339:1415-25.4 Anonymous. Randomised trial of endarterectomy for recently symptomatic carotid stenosis: finalresults of the MRC European Carotid Surgery Trial (ECST). Lancet 1998. 351:1379-87. (9113):

5 Yao-Jen Chang, BA; Alexandra J. Golby, BS, et al. Detection of Carotid Stenosis: FromNASCET Results to Clinical Practice. Stroke. 1995;26:1325-13286 Ferguson GG, Eliasziw M, Barr HW, et al. The North American Symptomatic CarotidEndarterectomy Trial: surgical results in 1415 patients. Stroke. 1999 Sep;30(9):1751-8.7 Morgenstern LB, Fox AJ, Sharpe BL, et al. The risks and benefits of carotid endarterectomy inpatients with near occlusion of the carotid artery. North American Symptomatic CarotidEndarterectomy Trial (NASCET) Group. Neurology. 1997 Apr;48(4):911-5.8 Young LH, Appen RE. Ischemic oculopathy. A manifestation of carotid artery disease. ArchNeurol. 1981 Jun;38(6):358-6.9 http://www.myelectronicmd.com/get_reference.php?Id=994.10 Faggioli GL, Curl GR, Ricotta JJ. The role of carotid screening before coronary artery bypass.Vasc Surg. 1990 Dec;12(6):724-9; discussion 729-31.11 Eliasziw M, Rankin RN, Fox AJ, et al. Accuracy and prognostic consequences ofultrasonography in identifying severe carotid artery stenosis. North American SymptomaticCarotid Endarterectomy Trial (NASCET) Group. Stroke.1995 Oct;26(10):1747-52.12 Staikov IN, Arnold M, Mattle HP, et al. Comparison of the ECST, CC, and NASCET gradingmethods and ultrasound for assessing carotid stenosis. European Carotid Surgery Trial. NorthAmerican Symptomatic Carotid Endarterectomy Trial. J Neurol. 2000 Sep;247(9):681-6.13 Grant EG, Benson CB, Moneta GL, Carotid artery stenosis: grayscale and Doppler ultrasounddiagnosis--Society of Radiologists in Ultrasound consensus conference. Ultrasound Q. 2003Dec;19(4):190-8.

15 Moneta GL, Edwards JM, Chitwood RW, Correlation of North American Symptomatic CarotidEndarterectomy Trial (NASCET) angiographic definition of 70% to 99% internal carotid arterystenosis with duplex scanning. J Vasc Surg. 1993 Jan;17(1):152-7; discussion 157-9.16 Hwang CS, Liao KM, Tegeler CH.J A multiple regression model of combined duplex criteria fordetecting threshold carotid stenosis and predicting the exact degree of carotid stenosis.Neuroimaging. 2003 Oct;13(4):324-9.17 Kliewer MA, Hertzberg BS, Kim DH, et al: Vertebral artery Doppler waveform changesindicating Weak or absent radial and ulnar pulse in the presence of ipsilateral reduced bloodpressure (change is >20 mm Hg) when compared to the contralateral arm suggests SSS. Am JRoentgenol 2000 Mar; 174(3): 815-9.18 Gosselin C, Walker PM: Subclavian steal syndrome: existence, clinical features, diagnosis andmanagement. Semin Vasc Surg 1996 Jun; 9(2): 93-7.

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