Page 68 - Libro 2

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PART 2 — CEREBROVASCULAR
Figure 4-17 Abnormal, resistive Doppler arterial flow through the common carotid artery in the setting of an internal carotid artery occlusion.
“Steal” Waveform Contours
Another spectral waveform abnormality is the “steal” phenomenon. This describes the situation where one vascular bed draws blood away or steals from anoth- er, which tends to occur when two runoff beds with different resistances are supplied by a limited source of inflow. The degree of arterial steal depends on the severity of the stenosis and the resistance offered by the various downstream vascular beds.
A “latent” steal describes flow that is beginning to show signs of reversal, but is not yet completely retro- grade. There are progressing stages of abnormal flow, which indicate an impending steal. “Hesitant” wave- forms possess a deep flow reversal notch when flow pauses before progressing cephalad (Fig. 4-18). When the deep notch in the Doppler waveform extends below the baseline, with a portion of the flow fully retrograde during part of the cardiac cycle, these waveforms are described as “alternating” or bidirectional. In the case
Figure 4-18 Duplex images of abnormal “hesitant” Doppler vertebral artery flow, indicating latent subclavian steal phenomenon.