Benjamin Freed, MD, on Speckle Tracking Echo for Managing PH

In this podcast, Benjamin Freed, MD, talks about what speckle tracking echo is, how to use it to manage pulmonary hypertension, and the challenges associated with its use.

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Benjamin H Freed, MD, FACC, FASE, is assistant professor of medicine in the Division of Cardiology at Northwestern Medicine in Chicago, Illinois.



Benjamin Freed:  My name is Ben Freed. I am the assistant professor of medicine at Northwestern Memorial Hospital. I am a cardiologist who specializes in cardiovascular imaging.

In this podcast today, I will be talking about right ventricular strain and how to use speckle‑tracking echo strain in patient management, primarily for patients with pulmonary hypertension, but for a variety of cardiovascular diseases as well.

The overview of this talk, we'll be starting with how important the right ventricle is in pulmonary hypertension, and a variety of different cardiovascular conditions. For a while, the right ventricle wasn't thought of as being all that important. But we know now that it is particularly important in diseases like pulmonary hypertension, where the response of the right ventricle to the increasing afterload determines a patient's symptoms and ultimately their outcomes.

We need a better way to measure right ventricular function during our clinical practice. We have two-dimensional echo, obviously, as one of the first imaging modalities to take a look at the right ventricle. However, given the complex shape of the right ventricle, the two‑dimensional echo isn't conducive to measuring function of the right ventricle. We do have some parameters that we use, such as TAPSE, such as prime, or fractional area change. These measures all have a lot of limitations. A lot of them don't give accurate measures of right ventricular function, which is so important to know.

That's when we consider something like speckle‑tracking strain, which we have found over the last couple years to be relatively accurate as well as reproducible in measuring RV function on 2D echo, and potentially even more accurate and reproducible than some of the other markers that we use on a daily basis.

Speckle‑tracking strain, what exactly is it? It's important to understand the fact that the myocardium, the muscle of the heart, is one large band that's wrapped around and sort of this helical shape. It contains myocardial fibers that run in a lot of different directions. In the right ventricle, the orientation of these fibers is primarily in the longitudinal direction.

The majority of the subendocardial fibers at the right ventricle run in this longitudinal direction. Then there's a smaller subset of myocardial fibers in the epicardial layer of the right ventricle that run in the circumferential direction.

When we measure right ventricular strain, what we're doing is measuring the deformation of these myocardial fibers in the longitudinal direction. Strain is the percent change in length during relaxation and contraction. The more deformation of the myocardial fiber, the better the strain.

The value turns out to be a negative number. The more negative that strain value, the better the strain, the better the myocardial deformation. Specifically, when we talk about speckle‑tracking strain, this is a type of strain where we're measuring the acoustic markers within the actual myocardium on 2D echo.

There are a lot of different software programs out there that measure this speckle‑tracking strain. These programs will track these acoustic markers throughout the cardiac cycle and, through an algorithm, give you a percent strain. This method, the speckle‑tracking method, is a lot less angle‑dependent and a lot more reproducible than some of the other methods for calculating strain.

After we obtain a 2D image on our echo of the right ventricle, preferably in apical focus for chamber view, we enter it into the software, manually trace the endocardium. The algorithm records six regional, either peak‑systolic or end‑systolic strain measurements.

Then we can average all of these six regional strains for global RB strain, or we can average just the three free wall measurements for RV free wall strain. Nowadays, most of the literature uses just the free wall strain rather than the global strain, because the idea is that the free wall strain stays away from the septum, which contains a lot of left ventricular fibers.

Since we're just focused on right ventricular function, we just focus on the RV free wall strain. We use RV strain then in a variety of different ways, specifically when we are concerned or we're looking at patients who have pulmonary hypertension. For starters, as I mentioned earlier, RV strain is one of the best ways to assess RV function on 2D imaging.

It has been shown in some other studies, when comparing directly with measures such as TAPSE, such as prime or fraction area change, as I mentioned, to be more accurate, as correlated with MRI‑derived RV ejection fraction and more reproducible than markers such as fractional area change.

The other thing that speckle‑tracking strain has over these other markers is that it can help divide RV function into mild, moderate, and severe, which is something that these measures such as TAPSE and fractional area change are really not able to do. They just cut off, either it's normal or abnormal. RV strain has that advantage as well.

One of the other uses of RV strain is that because it's so good at measuring RV function on 2D echo, we can use it to measure strain over time. Particularly in patients who have pulmonary hypertension, after we start therapy, such as pulmonary vasodilator therapy, we can measure strain at the beginning, and then measure it at some time point afterwards. There have been studies showing that there is an increase in RV strain. Some studies report up to 5% at even 6 months. To have this improvement of 5% strain in 6 months is a really good predictor of outcomes.

One of the reasons to use this measure over some of the other measures is not only is it more accurate and reproducible, but it is a quite sensitive marker too in detecting improvements, RV function after starting therapy.

One of the biggest uses of RV strain and what's most in the literature is the prognostic power of RV strain. Particularly in pulmonary hypertension, there are a variety of studies showing that RV free wall strain in particular is very strong prognostic marker in these patients.

One recent study showed that by adding RV free wall strain to parameters such as age, sex, and PA systolic pressure, that provides the highest C‑statistic above and beyond just the PA systolic pressure alone.

There was a larger study of almost 600 patients out of Mayo from a couple years ago that showed that RV free wall strain predicts outcomes after 16.5 months. There's a one and a half times increased risk of death per every 7% decrease in RV strain. Again, a very powerful predictor of outcomes.

So there are a variety of challenges when using a speckle‑tracking strain, particularly looking at RV strain. For starters, for both RV and LV strain, but primarily for RV strain, there's very little normative data. This is primarily because most of the data that we have comes from single‑center studies with a very small amount of patients. We don't have that database of what actually constitutes as a normal value for RV strain.

The most recent American Society of Echocardiography guidelines, which was published in 2015, states that RV free wall strain greater than or equal to negative 20% is considered normal. That's more negative than negative 20% is considered normal. However, that's based on very little data as I mentioned.

The other challenge, particularly with the right ventricle, is the quality of the 2D image that you obtain. It's already difficult to visualize the right ventricle in many patients with cardiovascular disease, particularly involving the right ventricle, but you need quality 2D image that includes a really nice look at the RV free wall in order to apply strain, and to put it in the software, and manually trace and allow the algorithm to calculate strain. If you don't have a quality 2D image, the accuracy of the strain measurement is going to be decreased.

Another challenge is intervendor variability. There are a lot of different software companies out there that allow us to calculate strain for both the left ventricle and the right ventricle. The problem is that these companies all have different algorithms within their software that calculates the strain. And so several years ago, when they looked at a number of these vendors and they calculated strain for the same left ventricle and right ventricle, they got very different values.

It's obviously not because the right ventricle or the left ventricle is different at all in terms of their function, but it's more because of the algorithms that they use. There is currently a task force out of the American Society of Echocardiography, looking to standardize these measurements across different vendors. The vendors are also included on this task force. So, a whole group of people are working together to get all these algorithms similar so that we can get similar measurements across the board and not have to worry about using different software companies to measure strain.

The last challenge here is just the workflow. A lot of particularly busy clinics don't perform strain at all in their echo lab. That's because it does take some time to do as well as teaching the sonographers ‑‑ the people who take the images ‑‑ how to perform the strain and as well as the echocardiographers. All of this can take some time, so working out the key in some of these software programs so that it can be very easy to make it just a standard part of the workflow.

The overall key take‑home message for pulmonologists is that it is incredibly important to get an idea of RV function in a variety of cardiovascular diseases, particularly pulmonary hypertension.

As I mentioned earlier, RV function is critical, because it is RV failure that is one of the biggest causes of death in these patients. We need a measure such as RV strain in order to get a better assessment of RV function.

We should make every attempt to apply RV strain when we perform echo on these patients so that we can better understand what the function is of the right ventricle at baseline and be able to follow the function over time.

Thank you for listening to this podcast today. For more information, feel free to click on the links below.