Aortic Stenosis - HD

Introduction

My name is Tia Gordon
and I'll be presenting on aortic stenosis.
I have no disclosures.

Our overview today will be to go over
normal aortic valve structure
and physiology, aortic stenosis, etiology
and pathophysiology, the qualitative
and quantitative assessment of aortic stenosis on echo,
obtaining measurements
and a case study of the right, left and non coronary cusps.

Normal Aortic Valve Structure and Physiology

The cusps are thin and pliable
and is responsible for regulating blood flow from the left
ventricle to the rest of the body.

Aortic Stenosis: Definition

Aortic stenosis is the narrowing of aortic valve opening,
increasing resistance of the blood
to flow from the left ventricle to the aorta.
It is the most common heart disease in the geriatric population.

Etiology of Aortic Stenosis

There are several etiologies,
including degenerative calcification,
congenital malformation, and post-inflammatory processes.

Degenerative Calcification

Degenerative calcification is the most common etiology
of aortic stenosis after the age of 65.
Affecting men more than women,
the valve is usually tricuspid,
but it may be challenging to determine the number
of cusps on echo due
to shadowing artifact from the calcification.

Congenital Malformation

Congenital aortic stenosis is often due
to an abnormal number of cusps, most commonly bicuspid.
Because these valves are abnormal, they are prone
to calcification and due
to their already narrowed orifice area, only a small amount
of calcification can create significant stenosis.

Another congenital malformation is when a membrane grows
across the left ventricular outflow tract,
creating subvalvular aortic stenosis.
In these patients, their aortic valve may look completely
normal, but will have increased flow velocities
in the outflow tract.
That's why it's important to look at valve morphology.
If the valve looks normal,
there is increased flow velocities.
Take a closer look at the LVOT.

Here's an example of a typical bicuspid valve with fusion
of the right and left cusps.
Over time, the valve can accumulate calcification
causing stenosis.
Again, it may be difficult to determine the number
of cusps due to the calcification.

When looking at a calcific steno,
a calcified steno aortic valve, you should have a high index
of suspicion for a bicuspid valve, even in patients
above the age of 65.

Here is a case of subvalvular membrane.
The aortic valve looks completely normal tri leaflet
with thin pliable cusps.
But in the apical five chamber,
we see some aliasing in the left ventricular outflow tract.
On spectral doppler, there is a peak velocity
of nearly three meters per second,
and in the LVOT there are significantly
increased flow velocities.
Looking closer at the LVOT, we can see a small mobile
membrane.

Post-Inflammatory Processes

Post-inflammatory diseases can also cause aortic stenosis.
Rheumatic fever is an inflammatory disease that can develop
as a complication of inadequately treated strep throat
or scarlet fever, typically
affecting children and young adults.
However, it's rarely seen in the United States today.

Other types of post-inflammatory diseases include patients
who have been exposed to radiation on their chest, those
who have a history of endocarditis and a patient.
Patients who have taken medication known to cause stenosis,
medications like Ergotamine that used
to be prescribed for migraines.
More recently, Fen was thought to cause FA falo,
though it's been controversial.

This is an example of rheumatic aortic valve.
On ultrasound, there is increased echogenicity along the
leaflet edges and fusion of the aortic valve commissures.

Pathophysiology

Due to increased resistance, the LV works harder
to meet metabolic needs over time causing left
ventricular hypertrophy.
This progresses to decreased LV compliance,
causing elevated left end dog pressures leading
to left atrial enlargement and eventually heart failure.

Thickened myocardium requires increased blood supply
from coronary arteries.
Blood supply becomes inefficient, resulting in angina
and potentially myocardial ischemia.

If the heart is unable to eject enough blood
to meet the metabolic needs of the body, it can lead
to syncope, cerebral infarct, and even death.

Qualitative Assessment on Echo

Looking qualitatively at aortic stenosis on echo,
we find a chunky aortic valve
with decreased excursion of the cusps.
Left ventricular hypertrophy, left atrial enlargement,
and many times there may be additional calcification on the
annulus of the mitral valve.

To interrogate the morphology of the aortic valve,
the peroneal long and short axis are the best views.
Peral long axis may demonstrate an asymmetrical closure line
typically found in by custody aortic valves
or systolic domine indicative of aortic stenosis.

The stored axis is best view is the best view
to determine the number of cusps and the severity
and location of any calcification
or thickening of the valve.

When evaluating the number of cusps, it's important
to look at the aortic valve in systole
to determine if the valve is bicuspid or tricuspid.
If it is by cuspid.
Seeing the valve on phos allows you
to determine which cusps are fused.

Here is an example of a bicuspid aortic valve with a Rafe
or underdeveloped aortic valve cusp.
In this case, the left coronary cusp is underdeveloped
and infused with the right cusp.
When the valve is closed.
In diastole, it looks similar to a tricuspid valve.
However, when the valve is open in systole,
it clearly shows the football shaped opening
and fusion of the right and left cusp.

Quantitative Assessment

Moving on to quantifying the severity of aortic stenosis.
This is the criteria from the American Society
of Echocardiography in determining the severity
of aortic stenosis.

The peak velocity, peak gradient
and mean gradient all come from measuring the velocity time
integral of the highest velocity across the aortic valve.
The aortic valve area and dimensionless index can be
calculated with just a few additional measurements.

Dimensionless Index

To calculate the dimensionless index,
which is essentially a ratio,
simply divide the velocity time integral of the LVOT
with the VTI of the aortic valve.
You can also use velocity though is less preferred.
If the ratio is under five or under 0.5, there is stenosis.
If it's less than 0.25, it's severe aortic stenosis.
It's a very simple calculation
to get a quick assessment on the severity of stenosis.

Aortic Valve Area (Continuity Equation)

Next, the aortic valve area is calculated using the
continuity equation which follows the law of conservation.
Basically, what goes in must go out.
Therefore the stroke volume of the LVOT
and the stroke volume of the aortic
valve should be the same.
So by calculating the stroke volume of the LVOT
and the maximum flow velocity going
through the aortic valve, we can determine
the aortic valve area.

This is the continuity equation.
To calculate the aortic valve area,
only three measurements are needed.
The LVOT diameter, the L-V-O-T-V-T-I
and the A utic valve VTI,
the cross-sectional area is calculated by PI radius squared.
We get the radius by dividing the diameter by two,
multiply it by the VTI of the LVOT
and divide that by the aortic valve VTI.
If it calculates to less than 1.5 centimeter squared,
there is as if it's less than one centimeter squared,
then there is severe as.

Obtaining Measurements

2D Measurements: LVOT Diameter

First let's talk about the 2D measurements.
In particular the LVOT.
The LVOT diameter should be measured in zoom
with optimized image settings
to clearly define the left ventricular outflow tract.
Measure the diameter with inner edge to inner edge technique
and the caliper should be five to 10 millimeters
below the aortic annulus.
Additionally, it may help to do a lateral to medial sweep
through the valve to make sure the
widest diameter is measured.

At the bottom of the screen is an example
of measuring the widest diameter of the circle.
However, if you aren't in the correct window
and are for shortening the LVOT,
your widest diameter could be shortchanged.

The reason why this particular measurement is so critical is
because it's in the continuity equation,
the diameter is squared.
Let's say for example, we have one patient
and three sonographers.
One sonographer measures the LVOT diameter at
2.2 centimeters.
Plug that into the cross-sectional area calculation
and we get 3.8 centimeters square.
The next sono sonographer measures the LVOT at two
centimeters giving a cross-sectional area
of 3.1 centimeter squared.
The third sonographer measures at 1.8 centimeters
for a cross-sectional area of 2.5 centimeter squared.
So we get it. We go from a difference
of just four millimeters to 1.3 centimeter squared.
Now, 1.3 doesn't sound like too much of a difference,
but if we plug it into the rest of the equation,
you can really see a difference in the valve areas.

So again, we have our three sonographers
with their difference, different LVOT diameters.
We'll pretend they measure the exact same L-V-O-T-V-T-I
of 25 centimeters, an aortic valve VTI of 65 centimeters.
Using the rest of the calculation.
The first sonographer calculates an aortic valve area
of 1.5 centimeter squared sonographer two,
an aortic valve area of 1.2 centimeter squared
and sonographer three, an aortic valve area
of 0.9 centimeter squared.
If we look back at the guidelines for aortic valve area,
this patient can have anywhere from mild
to severe aortic stenosis.
That's the difference of four millimeters.

Continuous Wave Doppler

Let's talk a little more about obtaining these
measurements with the ultrasound.
First we'll start with continuous wave doppler.
Continuous wave doppler is
where the transducer uses two PEO electric crystals, one
that is constantly emitting pulses, another
that is constantly listening for the return signals.
This allows the machine
to record the highest velocities without alia.

As a sonographer, it's important to keep the angle
of your cursor as parallel to flow as possible.
Poor doppler angles can underestimate the peak velocity.
The velocities can be interrogated in the apical five
and three chambers due to the importance
of being parallel to flow.

The non-imaging transducer should be used in patients
who have an aortic prosthesis,
who have higher flow velocities or who have a thickened
and calcified valve.

The typical windows used
for non-imaging transducer include the apical window,
the supra sternal notch, and the right sternal border.

Additional windows to use
for the non-imaging transducer include the right
supraclavicular where you place the probe
to the right of the patient's neck.
Many times you might find flow of the SBC.
Luckily, the aortic valve is just the left.
So between sliding
or angling the transducer,
you'll be able to find the velocity.

Another view is the subcostal window.
For this one, it can be very challenging to find
and may need to use additional pressure
for proper angulation.
The narrow opening of the aortic valve creates a smaller jet
to find, and it's not always in the center of the valve.
It helps to use some off axis imaging
to really find the highest velocities.
So be adventurous and think outside the box with positioning
and angulation of the non-imaging transducer.

Here is an example of a sonographer using the subcostal
short axis view to doppler the aortic valve
to obtain the highest velocity
that is thinking outside the box.

Again, obtaining the highest flow velocity is important.
This will calculate the peak velocity, peak gradient,
and me gradient as well as the velocity time integral.

If it's very challenging
to find the velocity using an imaging,
using an imaging enhancer may help to bring out the signal.
The whole word of caution it
to not measure feathering in the doppler signal
and to optimize your spectral doppler display.
One is because it will make the patient's pathology worse
and possibly send them to surgery before they need it.
The second reason, these patients are typically followed
closely with serial echoes,
so the next stenographer is going
to be pulling their hair out to try
and match a false measurement.

Last thing to keep in mind
with using continuous wave doppler, especially
with a non-imaging probe.
If the patient has mitral regurgitation in addition
to their their aortic stenosis, be careful not
to mix up the two signals both the current systo
and flow in the same direction.

To differentiate, it may be helpful
to measure the ejection time.
The aortic velocity will have a shorter ejection time than
the mitral regurgitation
because mitral regurgitation occurs during
isovolumic contraction time, systole
and isovolumic relaxation time until the mitral valve opens
as only occurs during systole.

Additionally, look at the shape of the waveform.
Mitral regurgitation has a parabolic flow profile, whereas
as looks more triangular
and patients with hypertrophic cardiomyopathy will have a
light peaking dagger shape waveform
all are very different pathologies
and should not be confused with one another.

Pulse Wave Doppler

The final important parameter is the pulse
wave Doppler assessment.
For an accurate cross-sectional area calculation,
the velocity of the LVOT should be sampled from
where the LVOT diameter was measured.

This can be a bit difficult
because the measurement is made in the peroneal long axis
and the LVOT velocity is sampled in the apical
five or three chambers.
So as a guide, it may be helpful
to place the sample volume at the aortic valve
and move it apically until there is no more aine.

A great indicator for a good pulse wave sample volume
placement is if there is a closing click
on the spectral wave form.
However, for patients with aortic stenosis,
the flow velocities near the aortic valve tend
to be increased, so the sample volume may have
to be moved slightly more apically
to minimize falsely increased flow velocities.

So how can you tell if your pulse wave sample is too
close to the aortic valve?
If you have a high velocity across the aortic valve,
but a large aortic valve area,
your pulse wave sample may be too close to the aortic valve.

Some things to check on your echo is the accuracy
of the LVOT diameter.
Another is to look at the overall
hemodynamics of the patient.
Was there significant aortic regurgitation
or is the patient in a high output state?
If none applies, the pulse wave sample is too close.

Patients where you might get a higher flow of velocity,
but relatively normal aortic valve area may
be in a high output state.
Is your patient obese or pregnant?
Do they have kidney or liver disease?
These can lead to falsely increased flow velocities.

On the other hand, what about if your pulse wave sample is
too far from the aortic valve?
If you have a lower velocity across the aortic valve,
but a small aortic valve area,
your pulse wave sample may not be close
enough to the aortic valve.

Still check your LVOT diameter
or again, look at the hemodynamics of the patient.
Are they in a low output State?
Patients in low output states include those
with poor left ventricular systolic function,
a small cardiac chamber,
or if they have mitral valve disease.
If done apply, your pulsive sample is too far
from the aortic valve.

Stroke Volume and Cardiac Output

Another tool is
to calculate the stroke volume in cardiac output.

The good news to figuring out a patient's stroke volume is
the work is mostly done.
If you've already calculated the aortic valve area,
stroke volume is simply the cross-sectional area multiplied
by the LVOT velocity time integral.

A good practice would be
to compare your doppler derived stroke volume
with the biplane stroke volume
where you subtract the end diastolic volume from
the end systolic volume.
It's rare. These will be the same,
however, they should be in the same ballpark.

To calculate cardiac output,
simply multiply the stroke volume
by the patient's heart rate.

According to the American Society of Echocardiography,
these are the normal values
for stroke volume and cardiac output.

If your patient has a cardiac output greater than eight
liters per minute, they're considered
to be in a high flow state.
The patient is in a low output state,
their stroke volume index
where you take the calculated stroke volume
and divide it by the patient's BSA, you would,
would be less than 35 milliliters per meter square.

It's a lot of math, but putting it into context
with a case study may help make more sense.

Case Study

So here's a patient with an LVOT diameter
of 1.9 centimeters in a bicuspid aortic valve.
Looking at the aortic waveform alone, we get a peak velocity
of 3.7 peak gradient of 53 millimeters of mercury
and a mean grain of 23 millimeters of mercury,
all suggesting there is moderate aortic stenosis.

Let's dig a little deeper.
We've measured the an L-V-O-T-V-T-I of 14.7 and
therefore can calculate the aortic valve area dimensionless
index and stroke volume.

So let's put it together. Let's start
with dimensionless index.
We will simply take the ratio of the L-V-O-T-V-T-I
and the aortic valve VTI.
It's essentially the continuity equation.
Without the R-V-L-V-O-T diameter, we get a ratio
of 14.7 over 73.5,
and our dementias index is 0.2.
This is consistent with severe aortic stenosis.

Let's look at aortic valve area.
We'll take the cross-sectional area of the LVOT,
which is 2.8, multiply that by 14.7,
the L-V-O-T-V-T-I, and we get 41.6.
We divide that by the aortic valve VTI of 73.5
and get an aortic valve area of 0.57.
Again, consistent with severe aortic stenosis.

So we seem to have discrepant values.
The velocity ingredients across the aortic valve suggest
only moderate stenosis while the aortic valve area
and dementia index suggest severe aortic stenosis.
Why would we have these dis discrepancies?

Let's look at the patient's stroke volume
to see if we can determine the patient's flow state.
To get the stroke volume,
we'll multiply the cross-sectional area of 2.8
and multiply it by 14.7.
We get a stroke volume of 41.6,
which is below the normal range.

We can even take it a step further
and calculate the stroke volume index.
We'll take the patient's stroke volume
and divide it by their body surface area,
and we get it 26, which is below the cutoff,
and the patient is considered to be in a low flow state.

So what may cause a patient to be in a low flow state
Here is the AP L four chamber, AP L four,
and two chamber views of the patient.
The patient's ejection fraction is severely depressed,
therefore causing the low flow state.

So what do we go by?
The velocities or the aortic valve area and dementias index?
Because the flow through the aorta is dependent on the flow
of state of the patient, it's more accurate
to follow the aortic valve area
and dementias index calculations.

Types of Aortic Stenosis

There are four types of aortic stenosis.
The usual one with we think of is
the normal flow high gradient aortic stenosis.
We just reviewed a case that was a patient
with low flow high gradient aortic stenosis.

There's also low flow, low gradient aortic stenosis
where the patient is in a low flow state
and they have low flow velocities.
Essentially, the ventricle cannot produce enough force
to cause severe A as.

And finally, the normal flow, low grade
and ES where the patient is in a normal flow state
but does not have high flow velocities.

Take Home Points

Some take home points on aortic stenosis are
to carefully interrogate the aortic valve morphology
and look for supporting evidence of aortic stenosis.
On echo. Remember the values
and important equations used
to determine aortic stenosis severity.

Be adventurous with that.
The non-imaging transducer
to find the highest velocity across the aortic valve.

Check to make sure if your measurements make sense.
If not, if not, look at the bigger picture,
what else is going on with the patient.

Lastly, I wanted to emphasize the importance
of the echo exam to properly interrogate aortic stenosis.
Echo is the standard for aortic stenosis evaluation
over cardiac cath.
Therefore, we play a major role in deciding if
these patients go to surgery.

Thank you.