Aortic Valve Imaging & Clinical Considerations

Podcast Transcript

Announcer:

Welcome to the Talking Tall Rounds series, brought to you by the Sydell and Arnold Miller Family Heart Vascular and Thoracic Institute at Cleveland Clinic.

Leonardo Rodriguez, MD:

So, Brian mentioned the fact that this patient is a small frame, also small annulus, and one of the fears that if you put a valve, this valve will be too small for the patient. And this is actually the definition we’ve had for many years of what is a patient-prosthetic mismatch, and it's essentially a valve that is too small for the patient, and that's what is in many ways related to the size of the patient. And although this definition is based on the size of the orifice, really we detect this patient, we suspect this patient, based on an elevated gradient on echocardiography. And in the true cases of mismatch, these gradients occur early on, even after the first echocardiogram after the intervention, then these gradients are already elevated.

Implicit in this definition, but not clearly said, is the fact that the valve has to be normal. So this becomes in some cases an exclusion diagnosis because we have to be sure that the valve is otherwise normal. This is easy when the gradients are early after surgery because the valve is, or after an intervention, it's fresh and unlikely that it is structurally abnormal. But we often see these patients a little bit after the surgery and this aspect is less clear.

The patient size is important and lately there have been different criteria for the severity of mismatch based on body size. You can see here some of the definitions if the patient is less than 30 or more than 30 in terms of BMI. And you can see, at least in the severe, that is a little bit of a difference. And this has been important because has refocused a little bit, because that was penalizing the more obese patients in terms of mismatch and there is some degree of correction here that I think was appropriate, given this problem.

The incidence, as you can see in this slide, varies widely. But I think the important thing is the severe, which seems to be the more clinically relevant, is relatively uncommon, and lately, serious is actually very uncommon. And I think this is something that is very promising for the future of valvular interventions. Again, the incidence varies and depending on what you look at, this is a very large series of patients with percutaneous transcatheter valve. You can see at least at this time, that was a few years ago, the incidence was around 10 to 12% of severe prosthesis mismatch, although the total population with some degree of mismatch is larger.

But why are we interested in that? First of all is the question when you see a patient that the gradients are high, if this is actually a structural failure of the valve, or if just the valve is small for these particular patients. Secondly, in patient with true mismatch after intervention, maybe the symptoms are not relieved completely. And there has been interest in what is the long-term impact of this mismatch, in terms of symptoms and quality of life. There is definitely an increase in reinterventions, either redo surgeries or other valve-in-valve, in these cases. And again, the question if the mortality in these patients, the long term is also increased in this group of patients.

And how is this calculated? And this is where the imaging is very important, is essentially we do a continuity equation and calculate the valve area, and this valve area is again corrected by surface area. And you can measure the LVOT either by echo, which is a more common way to do that, or you can use a hybrid approach that use the diameter of the area by CT, and then use the rest of the continuity equation to calculate the area.

So this is what we call the measured valve area and the measured patient-prosthetic mismatch. There is also a predicted one, which is another method and there are no measurements. You just go to a table that is either provided by the manufacturer or for historical measurements of normal valves, and then you predict in advance, like in this case that is being shown. If you say that the valve is going to be a 19, you know the area, you divide by body surface area, and you have an idea of if the patient is going to develop patient-prosthetic mismatch. This is important because, depending on how you measure either directly or you predict the valve area, the results are quite different.

So this is an example of the echocardiographic measurements, this is a parasternal long axis. And the proposed method is to use the LVOT diameter just distant to the frame of the, in this case a percutaneous valve, and self-expandable and balloon-expandable valves. Or you can use a CT scan in this case and you can planimeter the area. You see this example is actually there is not even a contrast, and then use this planimeter area for the calculation. In the one label by C you can see the shape is not circular but oval, and therefore a single measurement also introduce another source of discrepancy or error.

This has been again, used and there are several publications in that regard, where the imaging is used for calculation but also again for the ruling out of other morphological characteristics. In this case in particular, for instance, you can see there is a little bit of thrombosis of the valve, and therefore when you have structural damage or involvement of the valve, then the term shouldn't be used. Instead of mismatch, you should just call directly the pathology. In this case, maybe some thrombosis on the leaflet. But again, very important to use this technique properly. It's now a standard of care that if you have a prosthetic valve with elevated gradients, that at some point you'll get a CT scan to look more carefully at the leaflets.

Again, these two measurements can produce significant results. This is a patient with measure by echo, showing a significant mismatch, but when you use the predicted area by the manufacturer, this patient has no mismatch.

This has been all over the literature. Again, depending on if you measure or you predict it, you see the wide variability in terms of diagnosis, and how by echo the presence of severe mismatch is usually higher than when you use the predicted values. Again, this is several cohort, either surgical or by catheter valve. It seems the problem of this variability with technique is more common with the surgical valve, probably related to the fact that it is maybe more difficult for us to do the proper measurements of these valves.

What are the predictors? The case that was presented has several of those. Female patients usually because again, they are a small frame. Also the valve size that is supposed to be implanted, based on the annulus, that may be a 20, and therefore has two criteria when this patient may develop a mismatch. It's also very important.

In terms of what is the prognosis, there have been several papers in that regard. You can see also depending what the definition is, and how big the series, and how long these patients are followed, [results] could be from nothing to significantly reduced functional capacity, and in some cases increased mortality. Largest series I think too are consistent, or most of them are consistent. The mild to moderate mismatch is probably not that important, but those few patients that have severe prosthetic mismatch tend to have worse prognosis overall, either heart failure or rehospitalization, re-interventions, or mortality. Again in multiple series, either surgical or percutaneous, these few cases with severe prosthesis mismatch are important to identify, because again, they may need an intervention or at least follow closely because they have increased complications. In the surgical literature, again, you can see 6% in this particular series, which is within the range that we expect of severe mismatch. You can see that heart failure in these patients, over time, increases depending on the severity of the mismatch. In blue, in this case, is severe mismatch.

Luckily for us, it seems that the incidence or the prevalence of this problem has been decreasing over years, and this is consistent both in the percutaneous and the surgical literature. This may be due to multiple factors. We're much better now to identify a structural failure, and those patients that we use to catalog as mismatch, are now properly diagnosed with thrombosis, calcification, or pannus based on a combination of ultrasound and CT. And also the awareness by the surgeons that this small valve may be problematic, and better techniques in terms of enlarging the annulus, and better design on the valves, which have much better hemodynamic profile. You can see over time, again, based on this series of factors, either definitions or better techniques, these problems seem to be fading. Fortunately for us, because it's a difficult problem to deal with. Again, I want to emphasize that nowadays it is a diagnosis of exclusion. You have to exclude other structural morphologies before making this diagnosis.

Just to finalize, this is a complex diagnosis when definitions vary, and you have to be consistent when you look at literature which definition would you use. You need to use a variety of criteria, clinical, echo, I would say CT scan, and in some cases invasive. The prevalence varies widely depending on the technique or the methodology that you use. It doesn't seem that mild to moderate has major long-term clinical implications, but I think it's important to identify the severe cases because they may have increased mortality and heart failure. And hopefully with more advances and more use of low-profile transcatheter valves, this problem probably will disappear. Thank you.

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