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4 — The Extracranial Duplex Ultrasound Examination
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flow may be elevated. In complex cases where one or both of the carotid arteries (particularly the ICA) are compromised, Doppler flow velocities will be elevated through the vertebral arteries to compensate through collateral pathways involving the circle of Willis.
The use of ultrasound in the diagnosis of extracranial carotid disease has become a standard tool used by clinicians. The combination of real-time B-mode imaging, spectral Doppler analysis and color Doppler imaging has proven to be highly ac- curate and reproducible. Multiple studies have lead to reliable criteria by which to grade stenosis. Atherosclerotic disease can be easily detected and monitored with ultrasound techniques in order to prevent serious consequences such as stroke.
Critical Thinking Questions
1. Your initial B-mode and Doppler evaluation of the left carotid system suggests that there may be occlusion of the internal carotid artery. What key features will help to confirm an occlusion of this vessel?
2. A carotid–vertebral artery duplex examination has been requested on a pa- tient who is in the cardiac intensive care unit awaiting a cardiac transplanta- tion. The patient has an intra-aortic balloon pump (IABP). Doppler waveform contour is markedly altered, and there is an arrhythmia. What is the best way to approach this duplex examination in terms of interpreting the Doppler velocities and flow patterns and application of other diagnostic criteria?
3. During a carotid–vertebral artery duplex examination, you document high- grade, 80% to 99% stenosis of the left proximal internal carotid artery. There is minimal plaque visible in the right proximal internal carotid artery (and through the carotid bifurcation), yet the peak systolic velocity is diffusely increased at 165 cm/s. Is this a 50% to 79% stenosis? What may account for the elevated Doppler flow velocities contralateral to the 80% to 99% stenosis? How would you describe this in the vascular laboratory report?
4. Brachial systolic pressures are asymmetrical: right 􏰃 86 mm Hg, left 􏰃
138 mm Hg. As you begin the carotid–vertebral artery duplex, you find an abnormal, dampened, and hesitant Doppler waveform contour through the right proximal common carotid artery. What do you expect the remainder of the carotid–vertebral artery duplex examination to reveal?
REFERENCES
1. Barber FE, Baker DW, Nation AWC, et al. Ultrasonic duplex echo-Doppler scanner. IEEE Trans Biomed Eng. 1974;21(2):109–113.
2. Beach KW. D. Eugene Strandness, Jr., MD, and the revolution in noninvasive vascular diag- nosis. Part 1: foundations. J Ultrasound Med. 2005;24(3):259–272.
3. Fell G, Breslau P, Knox RA, et al. Importance of noninvasive ultrasonic Doppler testing in the evaluation of patients with asymptomatic carotid bruits. Am Heart J. 1981;102(2): 221–226.
4. Fell G, Phillips DJ, Chikos PM, et al. Ultrasonic duplex scanning for disease of the carotid artery. Circulation. 1981;64:1191–1195.
In cases where one vertebral artery is congenitally or pathologically small in caliber, the contralateral vertebral artery will often dilate and carry increased flow to compensate. In the case of severe ipsilateral subclavian steal, the contralateral vertebral artery
SUMMARY