Tag Archives: carotid doppler

Pulsatile Internal Jugular Vein

The right internal jugular vein drains blood down from the brain into the superior vena cava and then into the right atrium of the heart. By examining the neck, doctors can see the fullness of the vein and use that to estimate central venous pressure. Elevated venous pressure is one sign of volume overload (essentially a back up of fluid) that can occur with heart failure.

The internal jugular vein runs right next to the common carotid artery so we look at it during every carotid duplex Doppler study. Normally, in transverse view it is nice and flat (as in the image below) or partially filled into an oval like appearance.

The internal jugular vein is fully collapsed atop the common carotid artery. The white outline shows its approximate location.

The internal jugular vein is fully collapsed atop the common carotid artery. The white outline shows its approximate location.

With volume overload, it can puff up like a balloon due to all the blood that is essentially backed up waiting to go through the heart.

The internal jugular vein is filled in the setting of heart failure and volume overload.

The internal jugular vein is filled in the setting of heart failure and volume overload.

Now look at this clip. The internal jugular vein is bounding as it fills and collapses. It is pulsatile (profoundly so).

So what is going on to cause this? I’ll give you a hint: there is something wrong with one of the heart valves. As always, let me know your thoughts.

Subclavian Steal

This first picture is a normal vertebral artery waveform. Compared to the next one (which is abnormal) it is easy the see a difference. In the abnormal one, the flow dips down to baseline immediately after systole. The pattern created is called a “bunny waveform” for resembling a crouched rabbit as viewed from the side.

Normal vertebral artery waveform. Sharp upstroke and a good amount of diastolic flow typical for an artery feeding a low resistance vascular bed (the brain).

Normal vertebral artery waveform. Sharp upstroke and a good amount of diastolic flow typical for an artery feeding a low resistance vascular bed (the brain).

After the systolic peak, there is a severe drop in flow velocity. The resultant waveform resembles a crouched rabbit from the side - head to the right.

After the systolic peak, there is a severe drop in flow velocity. The resultant waveform resembles a crouched rabbit from the side – head to the right.

How does this happen? The left vertebral artery takes off from the left subclavian artery just after its origin. A stenosis in the origin of the subclavian artery is the culprit. A stenosis (narrowing) accelerates blood flow. In order to keep the same amount of blood flowing through a smaller opening everything has to move faster. By Bernoulli’s principle, higher velocity flow has a lower pressure and as we have discussed in prior posts, blood always flows toward the low pressure/low resistance vascular beds. To bring it all together, just at the peak of systole, blood flow is fastest through subclavian stenosis and pressure is lowest – low enough in fact to cause blood to flow backward from the vertebral artery into the low pressure zone. In other words, blood is stolen from brain into the arm.

In mild subclavian stenosis, the pressure differential is only great enough at peak systole, when velocity is highest, to elicit a dip in flow in the vertebral artery. The post systolic dip, as I call it, or the “bunny” waveform as others call it is formed.

As subclavian stenosis worsens, the pressure differential grows larger and lasts longer through the cardiac cycle. Flow reversal becomes more and more prominent making forward flow during systole and reversed flow in diastole (so called “to and fro” flow). Eventually, there is constant reversed flow when the subclavian artery is occluded.

A more significant steal. Blood from drops and then reverses in the vertebral artery during most of systole.

A more significant steal. Blood flow velocity drops and then reverses in the vertebral artery during most of systole.

What does all this mean for patients? First and foremost, as a clinical effect of atherosclerosis, it defines people at higher risk for things like stroke and heart attack. And, as discussed previously, those patients may benefit from treating their vascular risk factors of smoking, diabetes, cholesterol, blood pressure with medication, diet and exercise. We suspect that most patients with mild subclavian stenosis and bunny waveforms in the vertebral artery never notice it.

In uncommon situations the blood that is stolen from the brain through the vertebral artery can cause neurological symptoms such as vertigo, passing out, blurry vision or slurred speech. Usually for this to happen there has to be something else affecting blood flow to the brain such as an occluded carotid artery or very low blood pressure from shock, dehydration or sepsis.

Interestingly, I have seen patients with subclavian steal who developed neurological symptoms while on dialysis. Can anyone explain why?

Carotid Spectral Doppler Waveform in Heart Failure

The hemodynamics of advanced heart failure are quite complex. In this post, I present a visual demonstration of some of these changes by looking at the carotid artery spectral Doppler waveform in advanced heart failure.

To begin let’s look at normal. The brain maintains a continuous supply of blood throughout the cardiac cycle. Thus, there is forward flow through systole and diastole in the carotid arteries. The spectral waveforms in the image below show this well. The brain does this by maintaining a low vascular resistance. Just like water finding the easiest path down hill, blood finds the easiest path to follow in the body. The brain makes it very easy for blood to flow into it; probably because it considers itself a vital organ.

Normal CCA spectral waveform. The flow continues throughout the cardiac cycle (from beat to beat) and never goes below the baseline (never reverses).

Normal CCA spectral waveform. The flow continues throughout the cardiac cycle (from beat to beat) and never goes below the baseline (never reverses).

In sharp contrast to normal shown above, in advanced heart  failure we can see a reversal of flow immediately after systole that is striking in appearance if you are accustomed to the normal waveforms.

The flow reversal is marked in this image. The triphasic waveform resembles peripheral vascular flow.

The flow reversal is marked in this image. The triphasic waveform resembles lower extremity peripheral vascular flow.

The post-systolic dip is still evident in the internal caroid artey; although there is no longer any significant flow reversal.

The post-systolic dip is still evident in the internal carotid artery; although there is no longer any significant flow reversal.

chf waveforms vert16_cropped

Not surprisingly, the post-systolic dip and flow reversal are present in the vertebral artery as well.

So, why do we see this waveform in advanced heart failure? Frankly, I don’t know for sure. I suspect it is a combination of effects including increased vascular stiffness and aortic valve dysfunction in dilated cardiomyopathy. Regardless, it is a good visual example of the altered hemodynamics of heart failure. I welcome your thoughts and ideas.

 

 

Aortic Dissection

While working in the lab one day, my tech calmly told me he needed to stop the carotid exam he was performing as the patient was having chest pain. I looked up from my desk to see this loop playing on the machine.

Aortic dissection is not often discovered during a carotid duplex. However, in one series, 40% of aortic arch dissections enter the CCA Stroke 1988;19:970-6. In this case, the patient was being evaluated for chest pain and referred for a right carotid bruit – aortic dissection had not been suspected at that time. Upon seeing an acute appearing dissection of the common carotid artery, we worry it may originate from the aorta and urgently have the patient evaluated for aortic dissection.

We informed the primary team and they arranged urgent CT, cardiothoracic surgery consultation and operative repair the next morning with, thankfully, good outcome.

In this recent review of common carotid artery dissection 46 cases were found in the literature since 1960. Of those, 25% originated from the aortic arch. “The most common presenting neurologic symptoms were hemiparesis, decreased consciousness, headache or neck pain, aphasia and monocular vision loss.”  Journal of Stroke and Cerebrovascular Diseases 2012;21:52-60. Our patient presented with chest pain.

Direction of Flow

A patient came to see me for a second opinion about “backward flow in my vertebral artery”.  I had diagnosed flow reversal previously and now after a follow up study elsewhere, he was being told he did not have it. How can we get to the bottom of this?

Color flowcolor barspectral flow

It is important to understand how flow direction is indicated in vascular ultrasound. First, a color (red/orange or blue/green) can be assigned by the software to indicate flow. Flow toward the probe has positive Doppler shift and away has negative Doppler shift. The color bar with red/orange at one end and blue/green at the other serves as the reference point. Flow that is toward the probe is assigned the top color and flow away the bottom color. The tech is free to flip the “color bar” or change probe direction (by steering the color box) at any time.

The second method is spectral flow. A positive value indicates a positive Doppler shift and thus flow in a direction toward the probe. A negative value is given if there is flow away from the probe. Like the color box, the tech is free to flip the positive and negative scale around the baseline or change the spectral Doppler (probe) direction at any time.

This sounds potentially confusing and prone to error. To help avoid this, a few conventions are used to determine how flow should be displayed. To begin with, the head is to the left of the image. Arterial flow in a physiologic direction is shown by the color red/orange with the spectral flow displayed above the baseline. Reversed arterial flow should be shown by the color blue with a waveform that deflects below the baseline. The same principles apply to venous flow. Physiologic flow is displayed in blue with a spectral waveform below the baseline and above the baseline in red if reversed.

Techs are truly fantastic at what they do and get this right all the time – however, the job of the interpreter is to be absolutely sure it is correct. To do this, keep in mind the variables that cannot be changed (i.e. the constants): the software assigns flow toward the probe the top color and a positive flow value. Flow away is assigned the bottom color and a negative flow value.

Now, with that background in place, does our patient have retrograde flow in the left vertebral artery? Which is the correctly documented image for our patient?

Case1_aCase1_b

 

Yes, she does have flow reversal – both images provide the information necessary to determine this but only the first image correctly documents it. The flow is toward the probe (blue and positive) and thus away from the head (reversed). The second image, in not using the conventions, leads the interpreter to the incorrect impression that flow is in the normal direction.