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4 — The Extracranial Duplex Ultrasound Examination
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Figure 4-32 Duplex images demonstrating various normal vertebral artery Doppler waveform contours.
In the next phase toward a complete steal, this notch extends below the baseline progressing toward alter- nating (to-and-fro) flow. Vertebral artery flow direc- tion will be fully retrograde in the case of a complete subclavian steal (Fig. 4-34).
Reactive Hyperemia
Reactive hyperemia is a provocative noninvasive test that can be used to augment a subclavian steal from
the “latent” stage to the “complete” stage. Reactive hyperemia testing begins with a blood pressure cuff on the upper arm. The cuff is inflated to a pressure that is more than systolic pressure for 3 to 5 minutes, and duplex scanning is performed to continuously monitor the vertebral artery. At the end of the infla- tion period, the cuff is rapidly deflated while the ip- silateral vertebral artery flow is observed. The test is considered positive when flow in the vertebral artery completely reverses direction.
Figure 4-33 Abnormal, resistive, and blunted ver- tebral artery Doppler waveform contour, which in- dicates distal (versus intracranial) severe stenosis or occlusion.
