The Paradox

Adhering to rules gives us a certain sense of confidence. The same is true for echocardiography. We all like guidelines and simple shortcuts and that's fine. But sometimes we have to see the overall picture. Things may be more complex than we think.The following case will illustrate this point.

Quantifying aortic stenosis

Aortic stenosis is severe when the mean gradient exceeds 40 mmHg and the maximum velocity exceeds 4m/s. This is the case when left ventricular function is normal. However, let us see whether this assumption always holds true: Here's an echo of Zlatko - a patient from the Slovak Republic who had very severe untreated hypertension and a systolic murmur:

Four-chamber view. Note the presence of severe left ventricular hypertrophy.

I suppose you will agree that left ventricular function is normal. We determined an ejection fraction of 70%. However, the most striking aspect was the degree of left ventricular hypertrophy. The septum is 20 mm. This must be a consequence of hypertension.

Not so clear after all

Is there something else? Take a look at the following view:

Apical long-axis view of the same patient.

Mitral annular calcification is obvious. The calcification protrudes deeply into the myocardium. But this is not the key feature here. The aortic valve is also calcified and thickened. Based on the 2D images we would presume the patient has aortic stenosis. Unfortunately we were unable to obtain decent images from the parasternal window. This would probably have permitted even better appreciation of the degree of calcification and valve opening. However, this is a real case and we had to rely on what was available. The next step was to measure gradients across the aortic valve with the aid of CW Doppler.

Doppler findings

CW Doppler across the aortic valve.

Some beats show a high velocity of 3.8 m/s across the valve. The mean gradient is approximately 32 mmHg. This was the maximum gradient we achieved. Even the right parasternal window did not provide higher gradients (you should always use several windows to find the maximum gradient). How would you grade aortic stenosis? Well, if you adhere to conventional wisdom you would rate aortic stenosis as being moderate in this case.

A second look

However, there is one additional feature you should note. Go back to the four-chamber view. See how small the ventricle is? The end-diastolic diameter is only 29 mm, and end-diastolic volume is 43 ml. This is very low. It is certainly related to the severity of left ventricular hypertrophy. How does this relate to the degree of aortic stenosis?

A small ventricle cannot provide very high stoke volumes. Sure, the ventricle tries to compensate by increasing contractility. In fact, left ventricular function is hyperdynamic, but there is a limit to this compensatory mechanism. This becomes evident when you look at the velocity time integral on pulsed-wave Doppler investigation of the left ventricular outflow tract, and calculate the stroke volume index (stroke volume/body surface area).

PW Doppler of the LVOT to calculate the stroke volume.

We determined a stroke volume index of just 32 ml, which is rather low. A low small stroke volume affects the gradients. They will be lower than one would expect, and do not reflect the actual severity of aortic stenosis. A very similar condition is observed in patients who have aortic stenosis and poor left ventricular function; they also have a low stroke volume and lower gradients across the valve.

Paradoxical low-flow, low-gradient aortic stenosis

This entity also has a name. It is known as paradoxical low-flow, low-gradient aortic stenosis. It is paradoxical because left ventricular function appears normal, but gradients are still low. You will frequently see this in patients who have disproportionately high left ventricular hypertrophy and a high afterload. In the case of Zlatko, the combination of severe hypertension and aortic stenosis led to this condition. Is this all important? Yes, because it alters treatment. As aortic stenosis is severe and the patient is symptomatic, we should perform aortic valve surgery. A final note: what is the actual quality of the patient's contractile function? Based on the ejection fraction it is good. However, there is another way of looking at myocardial function. It is known as deformation imaging:

Speckle traking echocardiography: Longitudinal strain of the individual segments is depicted in a bulls eye format.

This bulls-eye view shows longitudinal contractile function, derived from speckle tracking. Note that function is normal (red) in the apical segments (center) while it is reduced in the basal segments (outer segments).
That's interesting, isn’t it? What does this tell us? That subclinical myocardial dysfunction is already present. We lack sufficient data to make any clinical decisions in this regard, but the condition might point out to the need for early aortic valve surgery.

The key message:

To summarize: things aren’t always what they seem to be. The same is true in echo. To fully understand the relevance of certain findings, we need to take a close look at hemodynamics. This has been illustrated in several previous posts as well:
The Empty Heart
Fear of Complexity
Butterfly Effect

So what's next?

If you also want to be able to diagnose these types of pathologies and become a true echo experts in just 90 days, then check out our Echo MasterClass which is currently open for registration here.

There's more to come, of course.