Noninvasive Vascular Diagnostic Laboratory. Cerebrovascular Disease
CEREBROVASCULAR DISEASE
3. Which noninvasive tests should be used to diagnose extracranial carotid artery disease?
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Duplex ultrasound has a sensitivity of 97% in detecting carotid artery disease and an accuracy of 95% in correctly classifying carotid stenoses as > 50% reduction in diameter. No other noninvasive test has comparable accuracy.
4. What is duplex ultrasound?
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Duplex ultrasound uses both image and velocity data (hence the name duplex) in a nearly simultaneous presentation of ultrasound echo images (B-mode ultrasound) and blood velocity waveforms obtained by Doppler ultrasound. The Doppler signals are obtained from a single small region of the blood vessel. Average velocities can be estimated for multiple such regions over a large area of the vessel. By assigning colors to the velocities, blood flow can be visually represented. Such a presentation, called colorflow duplex ultrasound, aids the duplex examination but cannot replace the information obtained from the Doppler velocity waveform.
5. Why is blood velocity important in assessing the degree of carotid artery stenosis?
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It is often difficult to measure accurately the arterial lumen on a B-mode ultrasound image because the acoustic properties (and hence the image) of noncalcified plaque, thrombus, and even blood may be similar. Arterial narrowing forces blood through a narrower channel, which increases the blood velocity. This velocity can characterize the degree of arterial narrowing. Current practice classifies the degree of internal carotid stenosis based exclusively on the Doppler velocity data.
6. What are the velocity criteria and categorical ranges of carotid artery stenosis?
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The criteria developed at the University of Washington (Table 73-1) are the most widely accepted. Note that progressive carotid stenosis increases the flow velocity signal as the volume of blood is squeezed through a smaller and smaller orifice. The category > 80% has been termed critical stenosis because of the high rate of disease progression and high incidence of neurologic symptoms for patients in this category.
Table 73-1. UNIVERSITY OF WASHINGTON CRITERIA
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Stenosis
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Criteria
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0%
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Peak systolic velocity < 125 cm/sec and no velocity disturbance
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1-15%
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Peak systolic velocity < 125 cm/sec with turbulence during systolic deceleration
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16-49%
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Peak systolic velocity < 125 cm/sec with turbulence in the entire cardiac cycle
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50-79%
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Peak systolic velocity > 125 cm/sec and diastolic velocity < 140 cm/sec
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80-99%
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Diastolic velocity > 140 cm/sec
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100%
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Absent flow velocity signal
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Abernathy’s Surgical Secrets, Updated Edition (Book w / Student Consult)
Author / s: Harken Alden H., Abernathy Charles, Moore Ernest Eugene
Year: 2004
Pages: 473
Publishers: Elsevier Mosby; 5th Bk & Acc edition
ISBN: 0323034160
