4 Most Common Errors We Make In Evaluating Aortic Valve Velocity In Echocardiography

I don’t know about you, but aortic stenosis cases seem to be my bread and butter.  It seems like I see more patients with aortic stenosis than any other pathology.

Granted, some of that may be attributed to the the region where my echo lab is located of course. Regardless, aortic stenosis plays a huge role in all of our scanning lives as a cardiac sonographer.

Unfortunately, with the recent trend of being asked to see more patients in less time, all of us are prone to making errors when evaluating the aortic valve. This is especially true  if that unfortunate trend continues.

In this post, we’ll take a look at some of the most common errors all of us make when measuring the aortic valve velocity during our AS cases.

Introduction

Fact is, even if our patients don’t have aortic stenosis, we still evaluate aortic valve velocities on everyone we see (at least we should be!)

With the machines we use today, there are many tools at our disposal that we can use to accurately evaluate the maximum aortic valve velocities with echocardiography.

Those tools include:

• 2D Ultrasound
• Color Doppler
• Spectral Doppler

In our routine echo exams, we use all three of these tools to evaluate the structure and the function of the aortic valve.  

But it’s the spectral Doppler that we use to measure the aortic valve peak velocities.  

Unfortunately, there are some very easy to make errors that can cause us to either underestimate or overestimate those gradients.

Here are the top 4:

Top 4 Errors When Measuring Peak Aortic Valve Velocity

1. Increased Doppler Angle

An incorrect Doppler angle is by far one of the most common pitfalls we as cardiac sonographers encounter when attempting to measure the aortic valve peak gradient.

Remember learning about the Doppler equation and cosine theta? Say what!?  Yeah, you might need to reach way back into the recesses of your mind.  But I know it’s in there!

In short, we must keep our ultrasound beam parallel to the direction of blood flow. We’ve got about a 20 degree window to work within before things start going south real fast. It’s always best to strive for 0 degrees, because any angle other than zero will begin to give an underestimated measurement.

The more of an angle you have to the direction of blood flow, the less accurate the measurement of the peak aortic velocity will be.  And just so you know, that error is always going to be an underestimation.

But what about the angle correction feature on the echo machine?

All of our ultrasound machines have this feature, but is it something we should be using? In short, no. The reason is, because blood flows in three dimensions, and the angle correct cursor only functions in 2 dimensions.

So, while the angle correct cursor does artificially give the echo machine a Cosine theta of 0, it’s only an approximation, because there’s no way of knowing which direction the blood is flowing in that third dimension.

Because of this, the American Society of Echocardiography does not recommend using the angle correction cursor in evaluating the aortic valve gradient measurements.

Things You Can Do To Improve Doppler Angle

• Roll the patient farther onto their side.  If this doesn’t improve the angle, try rolling the patient back.
• Move down one intercostal space. Often times this will open up the LVOT and offer up a nice direct line that is parallel to the blood flow.
• Do not report peak aortic valve velocities using angle correction.  Utilize the angle correction feature only as a tool to inform yourself of what the minimum peak velocities could possibly be. But again, do not report these measurements.

2.  Not Fully Opening Up The LVOT

This is a common error for new cardiac sonographers or experienced sonographers who just simply are moving through their exam too fast.

In this case, the cursor is thrown up on the current 2D image and continuous wave Doppler is turned on. Then the first Doppler signal that’s displayed is assumed to be the correct one. The sonographer might even take 2 or 3 measurements of these erroneous Doppler signals.

The problem is that not all patients will offer up an open LVOT that’s perfectly open and parallel to the ultrasound beam.  This is especially true in short elderly patients with aortic stenosis. Over the years, remodeling of the heart can take place making the LVOT almost perpendicular to the ultrasound beam.

As you can imagine, measurements taken like this can be way off.  I’ve even experienced circumstances where patients had severe aortic stenosis but only mild gradients were ever recorded…with differences of over 2 m/sec! Those are significant differences.

Just a reminder to really pay attention to making sure that the LVOT is fully open as much as possible when assessing aortic valve velocities.

3. Measuring Artifact

This is one of the most  common errors we’re tempted to do when measuring the peak TR gradient.  But it’s also a common error in measuring the peak aortic valve Doppler tracing.

Essentially, what happens is that we overestimate the aortic valve velocity by including the light, wispy Doppler signal that extends past the true peak velocity as part of the aortic tracing.

This is simply just artifact and has nothing to do with the true aortic blood flow.  So be careful not to include these artifacts.

What Can You Do To Avoid Measuring Aortic Velocity Artifact?

• Decrease the overall Doppler gain and compression settings. This will often times eliminate much of that wispy artifact.
• Decrease the Doppler scale.  Not only will this help you make measurements that are significantly more accurate, but it also gives you a much better chance at distinguishing between what’s artifact and what’s the real aortic valve spectral Doppler tracing.
• Measure multiple aortic valve Doppler waveforms.  If in doubt, make multiple measurements to help validate your findings.

4. Measurements The Just Don’t Make Sense

Pay close attention to whether or not the measurements you’re recording actually make sense.  

What I mean is, think about what the aortic valve looks like in 2D.  Does the valve look stenotic? Is it thickened? Do the aortic valve leaflets open, or are they fixed?

If the aortic valve appears to be abnormal, then you should go into your Doppler exam expecting to have abnormal spectral Doppler tracings.

This common error amongst echocardiographers goes hand in hand with the error of not fully opening up the LVOT.  If the tech were to observe that the valve is abnormal, yet the Doppler tracings of the peak aortic valve velocity are close to normal, then something is not adding up, and it’s time to figure out what it is and how to fix it.

This holds true in every aspect of your echocardiogram examination. Always look at your measurements, both 2D and Doppler and check to see if they make sense.

Tips For Making Measurement That Make Sense

• Always look at each and every measurement you make. This is true for 2D measurements as well as for Doppler measurements.
• If things don’t add up, figure out what is wrong and fix it.  Then make the measurement again.

Conclusion

Measuring the peak aortic valve gradient is not just something we do with patients who have aortic stenosis. It’s something we should do on every patient.  You may find that the patient has a subaortic membrane that’s causing an LVOT obstruction that you didn’t notice.

For patients who do have aortic stenosis, take the extra time to ensure that you’re not only obtaining the absolute maximum velocity, but that you’re also tracing the true spectral Doppler tracing.  

Key Takeaways:

• Maintain an ultrasound beam that’s as close to parallel to the blood flow as possible.
• Open up the LVOT and aortic valve as much as you can.
• Decrease Doppler gain and the spectral Doppler scale to help avoid measuring artifact.
• Always look at your measurements and ask yourself if they make sense compared to what you’re seeing with your own eyes.

Related Articles

1. How To Calculate Aortic Valve Area Using The Continuity Equation

2. The Pedoff Probe: Become a Pro At Blind Continuous Wave Doppler

3. Spectral Doppler : What It Is And How’s It Used In Ultrasound!

Resources:

1. Cardioserv.net
2. Echocardiography: A Journal of Cardiovascular Ultrasound and Allied Techniques Vol. 21 Number 2 2004
3. American Society Of Echocardiography