A few words about carotid interpretation:
Interpreting the carotid criteria can be tricky. There is more than one way to classify a stenosis. There’s the PSV, EDV, and ICA/CCA ratio findings to consider.
When it comes to the 50-59% criteria. The PSV holds a lot of influence. You’ll notice that other conditions involve an EDV of 40-100 cm/s and a ratio of >2; but it’s not uncommon to have only 2 of the 3 criteria. When this happens, we still call it a 50-69% stenosis. Of course this only counts when there is visualization of pathology in the vessel along with post stenotic turbulence.
We all know that there’s such thing as compensatory flow, which is increased flow as a result of a significant stenosis or occlusion in another vessel. In this case you will have increased flow without the visualization of significant plaque accompanied by post stenotic turbulence.
When it comes to the 70-79% and the 80-99% stenosis, we rely heavily on the EDVs. When a stenosis becomes more severe, we tend to see a dramatic increase in the EDV as well as the PSV. So an increased EDV is more of an accurate indicator of these high-grade stenoses.
It’s safe to say that an 80-99% stenosis must have an EDV>140 cm/s.
When it comes to the 70-99% stenosis, it’s very rare to have that without the EDV>100 cm/s as well as the ration >4.0; however if you encounter a ratio of >4.0 without an EDV> 100cm/s (but close), still consider it a 70-99% stenosis. This is because velocities can be affected by so many factors outside of the stenosis itslef; and ratios help us to see what the velocities may miss. Essentially, there is really no way to have and ICA/CCA ratio of >4.0 (which is really high) without the stenosis being very significant.
Below is the most recent criteria: