Transcatheter Aortic Valve Replacement: A Sonographer’s Perspective - HD

Introduction

Hello, my name is Tia Gordon
and today I'll be talking about transcatheter aortic valve
replacement, a sonographer's perspective.
I have no disclosures.

Overview of Discussion

Today I will discuss a brief history of the TAVR procedure
and the clinical trials that brought
us to where we are today.
I'll go over the procedure
and more specifically the echo imaging used pre, intra,
and post procedure, including grading
paravalvular leaks.

Brief History of the TAVR Procedure

The TAVR procedure is performed with catheterization
to replace the aortic valve.
The first case
of successful implementation was in April 2002.
The procedure required a transseptal puncture
and the interventionalist would navigate the
stent through the mitral valve, often causing severe MR
to reach the aortic valve.
This was very challenging, not only to navigate
through the anatomy, but the delivery system was rather
large and had minimal steering capabilities.
Over the years, there have been many improvements on valve
design and the delivery system.
Due to these advancements, the procedure can be performed
with different approaches.

Transfemoral Approach

The majority of TAVRs are performed via transfemoral
catheterization where the catheter enters the patient's
groin going up through the aortic arch
and is placed across the aortic valve for deployment.

Alternative Approaches

Many patients who have calcific aortic stenosis will also
have calcification in their arteries.
This can increase the risk of vascular complications
and limit catheter access,
so these patients may require a different approach.
Luckily, there are several other access points used today,
including transaxillary where the catheters enter
through the patient's axillary artery
through cephalic artery into the carotid,
and finally, the aortic arch to reach the aortic valve.
Another is to perform the procedure transapically,
where a small incision is made at the apex of the heart
and the catheters go from the apex to the aortic valve.
Finally, the last approach used is the transaortic,
which is the most invasive with direct access to the aortic.

Clinical Trials for TAVR

PARTNER Trial

There have been three completed trials for TAVR.
The first trial called the PARTNER trial for placement
of aortic transcatheter valves utilized the Sapien balloon
expandable valve and consisted of two groups.
Cohort A consisted of 699 patients who were considered
to be high surgical risk according to the Society
of Thoracic Surgeons or STS score,
and were randomly chosen to either undergo TAVR
or surgical AVR
and cohort B, which consisted of 358 patients
who were considered inoperable
and either were treated with medications or TAVR.
The patients were followed for one year
and those who underwent the TAVR procedure had significant
reduction in symptoms, repeat hospitalizations
and mortality.
Some complications
of the procedure included a higher incidence
of major strokes and vascular complications.
However, TAVR was found to be superior compared
to standard therapy for these patients
and has become the preferred treatment in inoperable
and high risk aortic stenosis patients.

PARTNER 2 Trial

The second trial for TAVR, the PARTNER 2,
again using the Sapien valve, included 2000 patients
who were intermediate surgical risk candidates.
Looking at two year outcomes.
SAVR or surgical AVR
had fewer major vascular complications and
paravalvular leaks.
TAVR, on the other hand had larger aortic valve areas,
lower rates of acute kidney injury, severe bleeding,
new onset AFib, and shorter stays.
In the ICU transfemoral, TAVR had a lower rate of death
or disabling stroke than SAVR.
There were similar mortality rates between TAVR and SAVR,
and the trial concluded that TAVR was found
to be non-inferior to surgical AVR.

SURTAVI Trial

A third trial.
The surgical replacement in transcatheter aortic valve
implantation or SURTAVI was performed
to compare surgical AVR
and the CoreValve self-expanding bioprosthesis, the CoreValve.
The trial consisted of
1,660 patients considered
to be intermediate surgical risk with an STS score
between three and 15%.
These patients were followed for two years
and had similar findings to the PARTNER trials, including
surgical AVRs having a higher rate of acute kidney injury,
AFib and transfusion requirements.
TAVR patients had a higher rate
of residual aortic regurgitation
and need for pacemaker implantation.
However, TAVR resulted in better aortic valve hemodynamics
and was found to be non-inferior to surgical AVR.

There's currently a third PARTNER trial for patients
with severe aortic stenosis who have a low surgical risk.
Over the years, there not only has been advancements in
valve design, but greater operator experience leading
to shorter times in the cath lab
and better patient outcomes.

Patient Selection for TAVR

Let's take a look at what parameters are needed
for a patient to be a candidate for TAVR.
ECHO is used for patient selection to verify the severity
of aortic stenosis.
This can also include stress testing for those
with low flow, low gradient aortic stenosis
or asymptomatic AS.
Additionally, ECHO allows us
to evaluate the patient's imaging windows.
If they have suboptimal transthoracic windows, a TEE
or transesophageal ECHO should be considered for imaging
during the procedure.
TEE may also be used
for sizing the valve if the patient is unable
to get a chest CT.

Here is an example of a patient
with a severely calcified tricuspid aortic valve
and fair imaging windows.
According to the measurements obtained by the sonographer,
the patient meets all the criteria
for severe aortic stenosis with a peak velocity
of 4.7 meters per second, mean gradient of 53 millimeters
of mercury, a aortic valve area of 0.58 centimeters squared,
and a dimensionless index of 0.21.

Nearly all patients will have a CT for proper valve sizing.
Typical measurements include the cross sectional area
of the aortic annulus, the LVOT and the aortic valve.
The height of the right and left coronary
arteries are also measured, so the prosthesis
or native valve leaflets won't occlude the origin
of the coronaries causing myocardial infarction.
CT can also verify if the native stenotic valve is truly tri
leaflet and can quantify the amount of calcification.
Additionally, the size of the arteries will be measured
to determine vascular access.
If the vessel is too narrow, the TAVR will have
to be placed using a different approach.

The TAVR Procedure

Let's move on to the TAVR procedure.
As I mentioned in the trials, there are two valves
that are used today.

Edwards SAPIEN Valve

Here is the Edwards SAPIEN valve, a balloon expandable valve
that cannot be adjusted.
Once placed on the right is a cine angiogram
of the valve deployment.
You can see the balloon expand inside the valve
and the valve cage expands
until it is anchored into the aortic annulus.

CoreValve

The other valve in use is the CoreValve,
a self expandable valve that can be slightly adjusted
until full deployment.
On the right is a cine of a CoreValve deployment.
The catheter is pulled back
and the valve expands to adhere to the annulus.
And this is what the CoreValve
looks like once fully deployed.

Intra-Procedure Imaging

Under fluoro imaging
during the procedure is mostly done with fluoroscopy.
It's the primary guidance for valve implantation
and it's used for assessing vascular access and injury.
ECHO is used in conjunction to evaluate function
and placement to interrogate the severity
of any paravalvular leaks
and to assess any additional complications
that may arise from the procedure.

During the procedure.
Echo imaging can be performed with either transthoracic
or transesophageal imaging.
When hospitals are new to TAVR, it is strongly recommended
to use transesophageal imaging
until the team has more experience with the procedure
and should still be used in patients receiving general
anesthesia, high risk patients,
and those with poor imaging windows.
It is also critical to have TEE
as a backup in case complications
arise during the procedure.

When performing transthoracic imaging for the procedure,
the sonographer must have ample experience
with TAVR interrogation.
Firstly, because the patient is supine,
a suboptimal position, potentially limiting imaging windows,
so they need to be comfortable with off axis imaging
to get the necessary information.
Secondly, proper evaluation of
the transcatheter heart valve takes a lot
of talent for the sonographer.
Proper angulation
and sweeping through the prosthesis is critical
to find paravalvular leaks.
And thirdly, the sonographer may have
to provide a quick assessment on the severity
of paravalvular leaks to the interventionalist
or let them know of any potential
complications seen on echo.

Echo Imaging During the Procedure

Let's talk a little more about echo imaging.
During the TAVR procedure,
the sonographer should interrogate the shape
and location of the aortic valve using the parasternal long
and short axis views.
Looking at the shape of the stent,
it should be completely circular
and the circumference of the stent should be fully
opposed to the annulus.
If it's not completely circular
or if there's space between the stent
and the aortic annulus, the valve may be undersized,
which may not treat the patient's aortic stenosis
or the valve may not be fully expanded.
Leading to potential paravalvular leaks.

To evaluate valve placement, look
for any impingement on the mitral valve
or if it's above the aortic annulus.
If any of these situations occur, there is an increased risk
for the valve to migrate either down into the left ventricle
or up through the aorta.

Here is an example of a valve
that is smaller than the aortic annulus
and may need to be expanded.
Further. Looking at the parasternal long axis, it's important
to recognize proper placement of the valve using TEE.
The image on the left demonstrates a valve
that was placed too low impinging on the anterior mitral
valve leaflet, whereas the image on the right is placed too
high, the valve is above the aortic valve.
These scenarios can lead to serious complications including
valve migration, a critical problem during the procedure
that's typically only treated with open heart surgery.

Assessing Paravalvular Leaks

Next, it's crucial to look for any paravalvular leaks.
There is a high mortality rate in TAVR patients
with even mild paravalvular regurgitation.
Regurgitant jets are typically eccentric,
irregularly shaped,
and often multiple, so sweeping through the plane
of the aortic valve in multiple views is critical.
Acoustic shadowing from native valve
or bioprosthesis can make it challenging
to find paravalvular leaks, especially those posterior
to the valve in the short axis view.
This is why it's important
to use all possible views of the aorta.
To interrogate the posterior side of the valve
of the long axis views can be very useful.
Scanning the parasternal long axis, the apical five
and the apical three chambers can provide the proper
angulation to evaluate the entire
posterior side of the valve.
For paravalvular leaks, again, sweeping completely
through the valve in each view is a must.

Here is an example of sweeping
through the aortic valve in the parasternal long axis.
The transducer sweeps from a lateral angle
to a medial angle, making sure
to go across the entire aortic valve.
By performing the sweep, you can start
to appreciate the paravalvular leak anterior to the valve.

The parasternal short axis view is crucial in assessing the
number and severity of paravalvular jets.
It's again important to sweep
through the entire valve plane.
In the short axis, the transducer should sweep superior
to inferior going above the valve down through the LVOT.
In this view, we can appreciate that there are multiple jets
of regurgitation. And again, the apical five
and three chambers should be used to interrogate
for posterior paravalvular leaks.

In addition, patients who have more challenging
or lower imaging windows, you may want
to try the subcostal short axis
to have a better look at the aortic valve.
Try to think outside of the box when interrogating,
like using the right sternal border
to get a different angle on the aortic valve.

Grading the Severity of Paravalvular Leaks

Let's talk a little bit more about how to grade the severity
of paravalvular leaks.
While echo is the most frequently used modality
to evaluate the presence
and severity of paravalvular leaks,
there is some ambiguity in how to grade them.
This has become a high priority for patient outcomes
because patients with just mild paravalvular leaks
have a high mortality rate.
The Valve Academic Research Consortium 2
or VARC 2 criteria is a consensus on grading the severity
of paravalvular leaks in patients.
We'll go through each of these parameters.

Circumferential Extent

First is the circumferential extent
or the percent of the circumference the paravalvular leak
occupies to grade estimate the angle that contains the jet.
For example, in this case, the angle is estimated
to be 30 degrees, then divided
by the full circumference 360 degrees,
and you'll calculate the percent
of the circumferential extent of the jet.
In this case, it's 8%, which would be classified
as a mild paravalvular leak.
If there are multiple jets,
the circumferential extent should include the sum
of all the angles of each regurgitant jet
and not any spaces in between the jets.
Be cautious of eccentric jets.
If you calculate the circumferential extent
and the imaging plane is above
or below the vena contracta of the paraleak, you may
overestimate the severity of the jet.

Diastolic Flow Reversal

The second parameter to grade the severity
of paravalvular leak is to interrogate the aortic arch for diastolic flow reversal.
Severe flow reversal is a dense holodiastolic waveform
and may even be seen in the abdominal aorta.

Regurgitant Volume

Third is the regurgitant volume.
The stroke volume should be the same across
all valves in the heart.
However, if a valve becomes insufficient,
the stroke volume across that valve increases to keep up
with metabolic needs.
Therefore, if we calculate the stroke volume
of the aortic valve that has regurgitation
and subtract it with the stroke volume of a competent valve,
in this case, the mitral valve,
then we would calculate the regurgitant volume
or the extra volume that passes through the aortic valve.
So for example, in this case,
we'll use the right ventricular outflow tract
to calculate the regurgitant volume. To calculate the
stroke volume of the RVOT, we take the diameter,
which is 1.9 and the VTI where we pulse wave through the
outflow tract, and we get 14 centimeters
for our velocity time integral.
To calculate the volume,
we do the cross-sectional area times the VTI
and we get 39.6 milliliters.
We perform the same calculation for the LVOT,
which we get a diameter of two centimeters
and a VTI of 24 calculating to an LV stroke volume
of 75.3 milliliters.
To calculate the regurgitant volume,
we'll subtract the stroke volume of the LVOT, again,
75.3 milliliters by the stroke volume
of the RVOT 39.6 milliliters,
and the difference is 35.7 milliliters.
So a regurgitant volume
of 35.7 milliliters is considered moderate regurgitation.

Regurgitant Fraction

Once you've calculated the regurgitant volume,
calculating regurgitant fraction is fairly simple.
We only need the regurgitant volume,
which we just calculated,
and that will be divided by the LV stroke volume.
Here we get a regurgitant fraction of 47%, again consistent
with moderate regurgitation.

Effective Regurgitant Orifice

The last parameter in the VARC 2 criteria is
to calculate the effective regurgitant orifice.
For this measurement, we'll measure the PISA radius at the
and the peak velocity of the regurgitant jet
to perform PISA.
Depending on the angle of the jet, the apical five
and apical three chamber is typically used,
shift the baseline towards the flow.
In this case, regurgitation in this view is red,
so the baseline should be moved up
to approximately 40 centimeters per second.
Measure the maximum PISA radius.
Here we're getting a radius of 5.5 millimeters.
Next, with continuous wave doppler,
we measure the peak velocity of the aortic regurgitation.
In this case, it's 3.5 meters per second.
To quantify the ERO,
we'll use the calculation 2 pi r squared
with the radius we measured of 0.5 centimeters is equal
to 1.5 square centimeters, which is then multiplied
by the aliasing velocity, which should be close
to 40 centimeters per second.
In our case, it was 38 centimeters per second,
giving us a total of 60.
We then divide that by the peak velocity
of the regurgitation, which was 3.5 meters per second,
converting to centimeters,
it would be 350 centimeters per second,
and we get an effective regurgitant orifice
of 0.17 centimeters squared consistent
with moderate paraleak.

Valve Function and Complications

In addition to placement and any paravalvular leaks,
it's important to evaluate the valve
for function if it's functioning properly,
was the AS treated
or is there still a gradient across the aortic valve?
This doesn't mean to only look from an
aortic stenosis standpoint.
Here is a case where the valve used to have happened
to have a frozen leaflet causing valvular regurgitation
leading to placement of a second valve.

There are several serious complications that can occur
during the procedure, so it's important
to look at the whole heart in addition to the function
of the transcatheter heart valve.
If a pericardial effusion is noted, look carefully
to rule out aortic dissection, perforation
or annular rupture, all
of which are life-threatening situations.
Myocardial infarction can occur if the stent
or native valve includes the coronary artery
or if there's embolization of calcification
and look for any new or worse mitral regurgitation possibly
due to impingement of the anterior mitral valve leaflet.
There are lots of things the sonographer has
to pay attention to and requires a high skill level,
so it's important to have an experienced
sonographer scanning the procedure.

Follow-Up TAVR Interrogation

Moving on to the follow up TAVR interrogation,
echo is the primary means
of follow up TAVR assessment and cardiac function.
CMR can also be utilized to confirm the severity
of paravalvular leaks.

Follow up imaging is similar to procedural imaging
where it's important to perform sweeps across the valve
with color doppler to determine the number
and severity of paravalvular leaks.
If the left ventricle has increased in size
or decreased in function, it can be a sign
that there are significant paravalvular leaks
that may need to be treated.
Also, performing serial echoes to interrogate the patency
of the valve because over time, like any other prosthesis,
it can become stenotic and lead to additional treatment.

Finally, because these patients typically have small fixed
and stiff hearts, it's important to look for effusions
because even small effusions are poorly tolerated.

Measuring LVOT in Follow-Up

When looking at an echo of a patient who has a TAVR,
it can be challenging to determine where
to measure the LVOT diameter
and where to place the pulse wave sample volume.
These are both very important parameters
to measure the patency of the valve
for calculating the effective orifice area
and stroke volume.

According to the 2012 expert consensus article from the
Journal of Thoracic and Cardiovascular Surgery
on transcatheter aortic valve replacements, it's recommended
to measure the LVOT diameter immediately proximal
to the stent identified by the orange line instead
of at the base of the prosthetic valve leaflets identified
by the blue line for several reasons.
First is that there is less intra
and inter observer variability in the measurement,
making it more reproducible.
This is more likely due
to the precise anatomic landmarks used
to determine the location of the prosthesis instead
of using the base of the prosthetic valve leaflets
where it can be challenging
to determine the precise location of the cusps due
to reverberations and acoustic shadowing.

Second, there is flow acceleration in the subvalvular
portion of the stent. Transcatheter heart valves have
approximately five millimeters
between the leaflets and the base of the stent.
Therefore, to avoid flow acceleration,
the pulse wave sample volume should be placed just
proximal to the stent as well.
This method for measuring the LVOT diameter
and VTI have better prosthesis patient
mismatch and correlated better
with trans prosthetic gradients.

Looking at the figure
B demonstrates optimal placement
of the pulse wave sample volume.
C demonstrates the flow acceleration within the stent
proximal to the leaflets,
and D is placed at the level of the leaflet cusps,
so pay particular attention to placement
because it can drastically change the calculated stroke
volume in effective orifice area and dimensionless index.

Take Home Points

Lastly, some take home points.
TAVR is here to stay with newer valve designs
and greater operator experience
and improved patient outcomes.
TAVR will become as commonplace as surgical
AVR. ECHO is one imaging modality
that can be used throughout the process of getting a TAVR.
It can determine if the patient fits
the criteria for valve replacement
to interrogate the transcatheter aortic valve placement
and function during the procedure,
and for surveillance of valve
and cardiac function after the procedure.

It's important to have experienced sonographers perform the
transthoracic imaging during the procedure
to properly interrogate the valve
and watch for any potential complications, making sure
to sweep through the valve in all imaging windows
throughout, or quantify the severity of any paravalvular leaks, and it's important
to carefully measure the LVOT diameter
and VTI on follow-up exams.

In addition to looking at overall function of the heart,
various complications can occur
after the procedure such as pericardial effusions,
endocarditis, and restenosis of the valve.
It's our priority to evaluate any complications
so they can properly be treated in a timely manner.
Thank you for your time
and I hope this helps provide some guidance into Echo
imaging for TAVRs.