Page 69 - Libro 2
P. 69
4 — The Extracranial Duplex Ultrasound Examination
49
of a progressive proximal subclavian artery stenosis, changing pressure gradients at the origin of the ipsilat- eral vertebral artery can change the ratio of antegrade to retrograde flow in the vertebra to the point where flow is entirely in the retrograde direction—a “com- plete” steal. In this setting, it is important to determine
the flow direction based on the color Doppler and spec- tral Doppler settings. Abnormal steal patterns can also develop in the presence of a brachiocephalic artery ste- nosis or occlusion. Blood flow can be affected in the carotid distribution (Fig. 4-19A) as well as within the subclavian and vertebral arteries (Fig. 4-19B).
A
B
Figure 4-19 Duplex images demonstrating brachiocephalic artery occlusion. A: Abnormal Doppler arterial flow through the carotid distribution. B: Abnormal Doppler flow through the subclavian and vertebral distribution.
