Carotid General and Lecture Questions

[Diane]

Hi Steve,
Got a couple of carotid questions,
1) For the ICA/CCA ratio do you use the PROXIMAL ICA PSV or the HIGHEST of the ICA measurements that you take no matter if it is prox, mid or distal. I’ve worked at a couple of places and people say different things.

2) If you are looking at distal ICA and the vessel runs completely vertical do you:
a) Use a completely straight box with a 0 angle
b) Steer the box until you get optimal colour flow with a 0 angle
c) Use a completely straight box OR steer the box and use a 60 degree angle

I always get confused when I have a vertical vessel to use a 0 or 60 degree angle correct. I’ve heard different things from people. I think I would more so use a 0 degree angle if it is a vertical vessel?

3) In your video, you had one of these images (in the attached image) up of the vertebral artery. I was wondering would it be still okay if you had steered the box to the left rather than the right in the picture?
I think I would have been more inclined to steer the box to the left.
Or do you just generally steer the box until you get the best colour flow there is no matter if it is steering to the left or right ?

4) When you’re using your eye ball method of noting down what the diameter reduction of the ICA is, is this more so to be more specific especially for the category 16-49% because it is so broad?
I don’t think I’m confident enough to eyeball diameter stenosis but if I was to put a value on it, could you just take a picture in trans of the diseased ICA, get the diameter measurement of the whole ICA and then just the patient lumen and then work out a percentage?
(I drew a diagram in the attached image)

5) Do you bother with proximal CCA measurements? I was told as trainee to do so but at my current workplace, they don’t put much emphasis on taking proximal CCA measurements, just only distal CCA measurements.

6) When taking subclavian peak systolic velocities, where is it best to take your sample? Proximal, mid or distal artery?

Many thanks!

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[Stephen Bird]

Hi Diane,

For my ICA / CCA ratio I use the PSV in the middle of the CCA.
If you use a proximal PSV it may be influenced by altered haemodynamics generated by the vessel origin. If you use a distal CCA it may be influenced by the beginning of bulb widening.

The CCA mid section I think is the most stable and reproducible reference point.

The debate of should I use 60 degrees always OR should you use the minimum angle possible is as old as I am!

My personal view on this is I like to make everything as optimised as possible at every junction in my scanning.
Hence with steering I use the smallest amount of steering that I require after heel – toeing the transducer as the more steering you use the longer the transmission tissue path and hence the signal to noise ratio will be compromised. So no steering is best (but rarely achievable). Use no steering as your first option but in reality you will need to steer a bit, just steer the minimum amount to give you the desired result.

As for the zero to 60 degrees angle correction debate, I personally go for the lowest angle possible as in theory the lower the angle the more accurate the Doppler equation is at calculating the velocity. So I am happy to use right down to zero, but never go over 60 degrees.

When I steer the box I steer in whatever direction allows me to generate the lowest angle of incidence with the blood flow direction.

So in carotid ultrasound that mostly means you are steering towards the patients head (distally), however there are exceptions when I would steer the other way (towards the patients feet). They would include the proximal CCA, proximal vertebral and sometimes the ICA origin depending on the angle of the bifurcation. The point of steering is to get a lower angle to the vessel, again with zero being best and 90 degrees being hopeless (as you will have a zero Doppler shift). I think in the vertebral image you attached the vessel is curving and you could have steered either way successfully ( I am happy with the image that I have steered correctly).

Yes, with %diameter reduction less than 50% it is important to be more accurate than 16-49% as that range is so broad and the clinical implications are so profound, especially in a younger patient. The diagrams you have attached are correct and that method will generate a reasonable result, however there are some pitfalls. Not many plaques are symmetrical, plaques often contain calcium and shadowing, colour Doppler blooming or bleeding can overestimate the patent lumen etc.
So we have some issues! By all means put a calliper on as you suggest but remember that there are these limitations. Personally I think you can make an estimation by eyeballing the vessel and I am happy to say 10% 20% 30% 40% based on the way it looks. Run a calliper over it and see how close you are.

A proximal CCA interrogation is important as you may detect turbulence or an increased PSV from an origin stenosis. If your first look is in the middle of the CCA you will miss origin pathology.

I don’t do a subclavian PSV measurement as part of a carotid series.
I do them for thoracic outlet syndrome assessment and in this case I do it proximally, adjacent to the head of the clavicle. If I want a representative subclavian PSV I would use the same theory as I described for the CCA, That is pick a spot in the middle of the vessel.

Steve

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