Chapters Transcript Video Low-Flow, Low-Gradient Aortic Stenosis Matt Summers reviews the testing and non-invasive valve hemodynamics used in diagnosis of severe aortic stenosis. so another hot topic. Not a new topic but uh something that's coming up that increasing frequency it seems is this concept of low flow or abnormal flow eric stenosis. Um So I wanted to spend some time talking about that in the current context of current uh tavern tavern uh management of severe aortic stenosis. So the definitions have changed somewhat but the concepts have remained the same over the past 20 to 30 years has been recognized um initially and surgical patients obviously. But really when we're talking about low flow low gradient A. S. We're talking about the presence of truly cyanotic severely cyanotic aortic valves with either discordant valve thermodynamics or an underestimation of those valve thermodynamics because of abnormal flow. And that's really what it boils down to. But the reason this is important is because differentiating whether a patient has true severe aortic stenosis or um a non severe aortic stenosis. With another reason for for having low flow is very very important. Patients with severe aortic stenosis obviously will benefit from aortic valve replacement and the patients without it uh may not. And as paul mentioned starting that clock potentially too early on replacing the aortic valve when the valve is not truly cyanotic uh leads to earlier to general degeneration and more complex decisions on the back end. And so when I when I think about these really the reason that you would have abnormal flow is because you have abnormal cardiac stroke volume. And as we all know that's dependent on three factors uh contract Illini pre load after load. One that we historically uh label is low flow low gradient is that patients with low contract ili or E. F. Production patients with cardiomyopathy. These uh that can't generate enough stroke volume to actually generate a hemo dynamic that's quantified as significant. I mean great inter peak philosophy but some of the more esoteric uh concepts within local gradient s are pre load after load um are abnormal. So these are the small L. V. Chambers such as wild type amyloidosis, restrictive cardiomyopathy. Smaller ladies with L. V. H. That have um small chambers and have a different stroke alignment as relation to hypertension. Um The prevalence is estimated very very high. So uh some studies have estimated that up to one half of patients with small A. B. A. S. So truly small offices have some component with low flow low gradient. Um It seems to be the predominant uh subtypes are the classic local low gradient which reduced the f. Um Those occurring up to 15% of patients. Um but when this is evaluated and the partner trials it can be up to 25% of patients have abnormal flow in this paradoxical fashion with preserved the f. When I think about this and I think how most of us think about this we lump aortic stenosis into traditional or normal flow aortic stenosis and then abnormal flow. And so we all recognize the normal flow aortic stenosis and we all recognize these severity thresholds. I listed them in order of the more commonly used and variables that are less likely to be affected by technical errors or pitfalls with measurements. We generally rely on the peak velocity of over four and then I mean great and over 40 I'll talk a little bit about dimensional index which uh maybe a little less prone to measurement errors. And then the one that's traditionally the reason for referral Eric area, less than one. Talk about some of the pitfalls with that. When we're looking at this subset, that is the topic of this abnormal flow, um We generally have three different categories. There's 1/4 that I won't go into too much detail but reduced ejection fraction is historically called classical low flow low gradient. People with uh cardiomyopathy um typically normal yet for the paradoxical low flow, an entity that's recently been uh looked at quite a bit uh severe mitral regurgitation, lack of forward stroke volume and its contributions to underestimation of the severity of aortic stenosis. But all of these are quantified currently and the guidelines and literally by an aortic valve area of less than one. So whenever we're getting these discordant data, when we see a valve that severely narrowed visually or calcified valve that isn't opening. Um And we're getting discordant valve thermodynamics. The first thing to do is to look at measurement errors. I don't want to belabor this too much because it gets down into physics but the reason that we when we are reviewing, reviewing these patients in valve conference, we look at certain numbers is because the accuracy of these numbers can be variable depending on how they're acquired. This is a concept with all uh ultrasound uh Doppler equation. So your your velocity, peak velocity, which is probably our most accurate measure, is highly dependent on the incident angle of the beam. So if you get over 15° Uh regulation and where the blood is traveling versus where you're sampling it, you can be off by 25-30%. Um as far as your your estimation of the peak velocity, it's important that when you're looking at the numbers, not just look at the number that's red reported on the report, but look at how that was acquired, making sure it's not being a first step to this data. The mean grading over 40 is also dependent on beam angles. So there's pitfalls with that but also a measurement and tracing of the velocity time integral dimensional index is probably the one that's least prone to errors and measurements. Just the ratio of the Lv outflow track uh B T I versus the L B T I, which is effectively measuring the ratio of the total amount of flow to the velocity of the flow through that and then the one that's most commonly used, common reason for referrals. Aortic valve area. This as you can see on the right when we're measuring ele bot diameter can be highly variable requires an eco tech to pinpoint two locations in the L. V. Outflow track And use that number in an equation called the continuity equation that solved for an aortic valve area. So it's highly prone to measurement errors but it's the most commonly reported um assessment of aortic valve uh severity and it's also the one that's used in commonly in all these low floor abnormal flow aortic stenosis patients. Then we get down into the concepts of if you look through your echo and patient clinically suspect have aortic stenosis aortic stenosis but there's discordance and measurements um excluded all of these pitfalls and measurements. Then it's trying to differentiate between true low flow low gradient S. And these concepts have been around for a while but but really what it amounts to is they have similar measures severe low flow low gradient A. S. Is a. S. With abnormal low forward flow and pseudo stenosis, abnormal baseline low flow without severe aortic stenosis basically have lack of enough stroke volume to open the valve. The valve itself is not severely cyanotic like a severe patient. Those measures are very similar identical and aortic valve area, less than one ingredient of less than 40 stroke index. Strike index of less than 35 there you're getting the discordance and and data with an A. V. A less than one but I mean gradient it's less than 40 I mentioned the reasons causes why that might be present. Starting with the classic low flow low gradient historically. And in the guidelines still there's to a recommendation to um suppose these patients to the beauty means stress echoes. But really that's based on historical data from the Sabra literature where assessing whether someone has contract our reserve which stroke volume, august 20% is prognostic lee important in those patients less so in Taber patients. And some of the current data that's out. Um But what you're trying to do is augment the stroke volume to see if the gradient change or the aortic valve area changes pseudo stenosis. If you give them low doses of you mean your main gradients will not change your aortic valve area will go up because you're generating enough pressure and flow um to open the valve and that's the opposite and classic local low gradient. What's important to note is that less than 50% of low flow low gradient A. S. Patients have contracted reserve. You get a negative result doesn't mean that you don't have severe low local low gradient A. S. Means you don't have contract. I'll reserve could have either of the two. The other. The other way to test for this is with valve scoring which is becoming increasingly more common. Um It's quantification of what we see visually when we're looking at a patient with aortic stenosis. The first thing we look at is what the valve looks like. Is it opening and closing. Is it heavily sclerotic scarred. Um And that's this is providing objective measure of what we're seeing visually. Probably a little less prone as well to over gaining and things like that on the echocardiogram. Um But we use that in the context of other clinical variables to assess whether a patient has talk about cardiac cath here in a minute. The concept once you have a normal yeah what we call paradoxical, even more complex. But it's just as prevalent as the classic form, controversial as well but it's it's highly related to pre loaded after patients come in with high blood pressure. Um In the guidelines there's a class one recommendation to reevaluate their valve area when the blood pressure is is improved. And that's because of this concept of after load mismatch contributing to an underestimation of the aortic valve grading. Um Preloaded is another issue. These are the, like I mentioned, the amyloid patients with low stroke falling related to just a small change. You can get underestimation of the aortic valve area, the transfer of the gradient based on that. And so in these uh checking blood pressure, making sure it's not through the roof, making sure the data is acquired under normal conditions. It's almost possible uh is what the guidelines recommend. But really it comes down to and I'll show you in the guidelines for treatment um Clinical diagnosis of whether you suspect the symptoms that the patient is experiencing are related to severe, There's things you can do in the cath lab that are very very rarely done to sort of affect this after load mismatch. Um But one of the increasingly commonly recognized features of this is that a large amount of these patients with paradoxical low flow, low gradient aortic stenosis have a wild type amyloid um when they undergo nuclear testing. And then my trophy regurgitation is something we look at commonly here we know that when there's M. Are present of intermediate or severe quantification by E. R. O. A. The stroke volume decreases for about 70 down to a little under 50. And that along with that results in the mean gradient decreased from 57 to 33. Peak velocity goes down significantly. Native valve area and dimensions index are unchanged. And so it's important to recognize when you're reading these echoes and see discordant thermodynamics. If there's the presence of moderate or severe mitral regurgitation, how that may be contributing to the estimation of the trans popular gradients. Back to the guidelines again, the only class one in the guidelines is to normalize blood pressure and re measure everything else stress, echo dimensional index. Ct scoring all recommendations. But in practice I think things tend to be a little bit different. We very rarely used in stress echoes because only 50% of those patients typically have contracted our reserve where we'd expect a different result with me when we treat um we are looking at symptoms due to a s there's an entire column in the in the guideline algorithm for patients with low flow, low gradient aortic stenosis and E. F. Less than or greater than 50%. So that second column is our paradoxical low flow low gradient es And the first column is our classic low flow low gradient S. Still recommended. W means stress echo to differentiate the classic. But if you see on the paradoxically it's ultimately coming down to whether you think is most likely the most likely and cast. So this is this is a thing that commonly gets brought up. Um Should across the valve and measures were still prone or susceptible to the same measurement errors. Um And issues with low stroke volume. When you take a patient the cath lab across the valve. If you're getting low flow on an echo at rest should expect low flow and low gradients on a calf at rest. You can do provocative testing um But you're still prone to the same effects of lack of contract. I'll reserve or not important. Part of this is that when you look at patients that have their valves crossed and diagnostic cast, not significant uh increase perfusion deficits you see on M. R. I. So it's not a benign thing just to cross the valve and measure it really should be used in patients where there's inconclusive noninvasive testing or discrepancy and symptoms in relationship dynamics and how do these patients end up so classic local, low gradient S. Is why it's important to differentiate if they don't get treatment. So if it's unrecognized or there's a strict adherence to to uh region definitions of valve severity, the five year mortality. Uh No treatment is 91% versus 43% of students. So it is important to differentiate these Paradoxical is pretty similar to normal flow S but but it's significantly uh decreased and then sudo stenosis when you match them to heart failure. Patients without aortic stenosis have a very similar. So, to summarize uh does my patient have severe aortic stenosis? I think we all are comfortable dealing with that in the vast majority of cases where uh the valve thermodynamics are important with the patient's symptoms and the valve appearance, but it really, and the other half of the patients requires a thorough evaluation of the T. T. Not just reading the report. Um You're relying on these measures that I mentioned, essentially looking at the quality of each of those measures mentioned, this index is probably that was the most reliable as far as being less thrown to measurement errors. Um But you should recognize the caveats to aortic valve area measurements in the condo the equation. If you do not have um concordance between the valve appearance and the aerodynamics? That's when you're looking at, are there technical errors? Is the abnormal? Is there M. R. It's not any of those things, then, is there the presence of a low small cavity or any reason to be after load mismatch. And then you should consider additional testing and mentioned that stress echo isn't commonly used anymore. It's not benign to take a patient with a very or just give them to you. I mean um they can develop atrial fibrillation that can decompensate. It's not an uncommon thing for that to occur. The calcium scoring really is is quantifying what we're looking at visually. We're looking at valves all day. I think we got a good sense for which which patients have a significant calcium score or not. But quantifying that with the T. Is important will be increasingly important in differentiating these. But ultimately this is a clinical diagnosis. There's a lot of pitfalls in addition to just waiting for a main gradient to get over 40. There's a lot of patients uh that won't generate a gradient of 40 and there's several reasons, as I mentioned why that would be the case. But it's looking at the entire picture in the context of the aortic valve and your assessment of the visual severity in relation to human dynamics this case from yesterday that I wanted to highlight this. This guy that came in last week, 88 year old had a newly reduced the f 12%. Um And he came in and over to be compensated. Heart failure? You can see on the left and along his aortic valve is opening very well zoomed in up here heavily calcified for leaflet mobility and the short axis you see this as well. Some two different views. The first thing you notice is that the ejection fraction is very low. Some of these measures looks like we have at least moderate M. R. And some of the other views that looked a little bit worse. Um When we're looking at beam angle there is a little bit of an angular ation but not too bad. But what you'll notice here is that even though the valve is severely narrowed at least an appearance, we're only getting a mean grading of 19. And people ask you 2.9 if we look at the dimensional index in the aortic valve area, they're very very low dimensional indexes this velocity and this velocity in a ratio. You can see right away L. V. O. T. V. T. I. Which is a rough estimation of your stroke volume should be 20 to 25. It's under 10 here. So we're seeing the manifestation of that reduced ejection fraction and its ability to generate the gradients that we typically hang our hat on for processing the valve on C. T. It's heavily calcified which fits with what we are visually seeing on the echocardiogram. This patient had disease suppressors. Um and was uh failure when he came in last week. Got diary's for a V. A. V. P. C. I. Um And he did well came off. Oppressors was improving considerably, but he still had similar gradients afterwards. He really was to help facilitate getting the intel in. And then yesterday we did a transferrable tavern and he did well with that. So he's currently in the hospital recovering. Um, but he is a typical patient that I think paul and I and the and the rest of the team, uh, see, um, where there's reasons that the valve appearance don't necessarily match what we're seeing on, on gradient estimations. Published September 23, 2022 Created by Related Presenters Matthew Summers, M.D. Sentara Cardiology Specialists View full profile
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