We’ve all been in this situation…. our patient appears to have a very tight, calcified aortic valve which visually appears to be moderate to severe aortic stenosis. As we scan through our protocol, we obtain a peak aortic valve velocity of 3.3 m/s and mean pressure gradient (PG) of 23.6 mmHg. The calculated AVA is showing 0.7cm², but the obtained velocity values do not add up to the severely indicated AVA? What could be causing this? Is this correct? Does the patient have moderate or severe AS?
It is important as clinicians to understand the hemodynamics and methodology of calculating the aortic valve area using the continuity equation. It is common to experience discordant values that do not match the textbook explained method. This blog is going to discuss two situations that commonly occur: low-flow, low-gradient aortic stenosis with reduced and preserved LV EF.
First, let’s cover the basic parameters for severe aortic stenosis:
Any one of these parameters can suggest severe aortic stenosis, however there should be concordance between all parameters!
There are situations where our severity cut-off parameters do not match up like we wish they would….
What do we do when the gradient/velocity do not correlate with the AVA severity parameters….. FURTHER INVESTIGATION!
The first and most important part is to rule out potential measurement errors! This includes all parameters involved in the continuity equation:
After you are able to confirm there are no errors in the measurements, then we can move forward to considered other types of aortic stenosis:
What is the hype about these two? What makes the outcome different based on the ejection fraction? Let’s talk this through….
The stroke volume is low (< 35 mL/m²), velocity/gradients are low ( <4 m/s & <40 mmHg), but the AVA is displaying as SEVERE (< 1.0 cm²). Depending on the ejection fraction (reduced vs. preserved) will guide us to different questions.
If the EF is preserved (> 50%) , we need to look at a few potential factors contributing to these findings:
A lot of times when we have elderly (>70 years old) small bodied patients, they commonly have small LV cavities (low volumes) and LVH (commonly due to chronic hypertension). This will cause a decrease in the gradient/velocities because of the low flow volumes and not much volume to pump out of the thickened small chamber.
In this situation, the ASE guideline paper recommends using an integrated approach to determining the true severity of the stenosis.
First and most important part….. velocity & gradients are FLOW DEPENDENT! In other words, if the EF is decreased then that will affect the velocities and gradients!
In situations where we calculate an AVA of < 1.0 cm² with low gradient/velocities (< 4 m/s & < 40 mmHg), low flow status (< 35 mL/m²) and a REDUCED EF (<50%) = we MUST take further investigative steps to determine the cause of low flow status with severely calculated AVA!
If the EF is reduced (<50%), then we need to determine if the decrease in valve opening (AVA) is due to true severe AS or LV dysfunction? Low flow status hinders the ability of force applied for the leaflet cusps to open = cause decrease in AVA. What would the gradient/velocity be if the myocardium was functioning at a normal state?
The answer is 3 simple words ….. Dobutamine Stress Echo ! This test allows us to evaluate the heart as if it were function at an increased EF by giving dobutamine! We want to look for:
We can end up with 2 main outcomes…
Of course there is always the 3rd outcome of no change in stroke volume (absence contractile reserve). These patients have a high mortality rate due to the myocardium not being viable.
We all have those patients where our measurements do not all correspond to the severity reference charts. It is vital in these situations we take additional steps to further investigate the reason behind these discordant values.
Incorporating these investigation questions helps provide the best patient care we all strive to provide our patients!
Check out our past blogs on aortic stenosis!
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Andrea Fields MHA, RDCS
Baumgartner, H., Hung, J., Bermejo, J., Chambers, J. B., Edvardsen, T., Goldstein, S., . . . Otto, C. M. (2016). Recommendations on the echocardiographic assessment of aortic valve stenosis: A focused update from the European Association of Cardiovascular Imaging and the American Society of Echocardiography. European Heart Journal – Cardiovascular Imaging, 18(3), 254-275. doi:10.1093/ehjci/jew335
Nakatsuma, K., Taniguchi, T., Morimoto, T., Shiomi, H., Ando, K., Kanamori, N., . . . Kimura, T. (2017). Prognostic Impact of Peak Aortic Jet Velocity in Conservatively Managed Patients With Severe Aortic Stenosis: An Observation From the CURRENT AS Registry. Journal of the American Heart Association,6(7). doi:10.1161/jaha.117.005524