What does the waveform from the Left Vertebral artery suggest?

The selection of Subclavian steal syndrome as the correct answer suggests that the waveform from the Left Vertebral artery indicates altered flow patterns due to significant stenosis, typically in the subclavian artery on the same side. In this condition, blood flow is diverted from the vertebral artery to supply blood to the arm or other areas, resulting in retrograde flow within the vertebral artery itself. This is often identified by the characteristic waveform seen on Doppler ultrasound, where the flow may appear to be directed toward the heart rather than the brain, reflecting the compensatory physiological response to the obstructed blood flow in the subclavian artery.

In contrast, normal vertebral flow would show a stable waveform directed cranially toward the brain, without significant variation in the shape or direction. Critical stenosis might imply narrowing of the artery, but it does not inherently indicate retrograde flow or subclavian steal. Lastly, retrograde flow would suggest reversal of blood flow direction, but in the context of Subclavian steal syndrome, this flow is specific to the vertebral artery's compensatory response to subclavian obstruction, making it a more accurate descriptor of the condition.