I am just back from a trip to the Middle East, where I was scanning and teaching echocardiography. I got to see some really unusual and challenging cases; in one country I visited, there are no cardiologists, so I was often seeing undiagnosed heart disease, or animals which had received a previous echocardiogram but questions still remained.
I will share some of these cases as I work through them – we also filmed every single scan, so have some interesting case walkthroughs to share as well – but today I am going to share some images from a case that is much more familiar: the small, older dog with a murmur. We hardly need echocardiography to tell us that this is going to be a case of myxomatous mitral valve disease, but we do need echo to stage the patient and decide whether or not the patient should begin treatment (usually pimobendan +/- furosemide).
This topic is one of the core modules of our new course from Professor Luis Fuentes, which you can enrol on now here if you like to pay in GBP, or here if you prefer USD. As one of the world’s top veterinary cardiologists, Virginia is best placed to guide you on what to do once you have performed your echo: how to interpret your results, and how to treat your patient. You can also attend Zoom calls with her to talk through any difficult cases!
I am going to split the following case into three sections: subjective, 2D echo signs for those just getting started with echo; intermediate techniques for more experienced users of cardiac ultrasound; and advanced techniques for those who make it that far!
When you first put your probe on the chest, you want to assess 3 things about everything that you can see:
The most obvious structure you see first of all is the left ventricle. In this dog, is it normal in size? I would say no. Subjectively, it looks dilated. Comparing it with the right ventricle is not a fool-proof method because in advanced stages of mitral valve disease, your patient will often have a dilated right ventricle as well, but in this particular dog, the right ventricle really does look very small in comparison with the left. The interventricular septum pushes into the right ventricle more than usual, giving the left ventricle a slightly more circular shape than a normal canine heart.
Is it normal in function? Yes – the walls of the left ventricle look to be coming in nicely during systole, and in an animal with significant mitral regurgitation (which we are already suspecting from the murmur and the appearance of the mitral valve), left ventricular systolic function should look very good: the heart is working harder than normal, to deal with that extra volume of blood. If left ventricular function looks poor, that would be a really bad sign for your patient, and they would be at the end stages of their disease.
You have probably already noticed that the mitral valve looks thickened. In the second part of the above clip, you might have also noticed that I changed my probe angulation very slightly, in order to cut through the mitral valve commissures differently and visualise the gap. Here’s that angle again, slowed down:
Also notice that the anterior leaflet (or septal; the top one, closest to the septum) closes differently to the posterior (mural) leaflet. Although neither leaflet is totally normal, the posterior leaflet is more correctly positioned, further into the left ventricle, whereas some parts of the the anterior leaflet are closing in line with the plane of the mitral annulus. From just this information, we can tell two things about this dog’s mitral regurgitation:
(1) It is likely to be severe (the left ventricle is dilated, the left atrium is severely dilated, and we can actually see the hole on B-mode imaging!)
(2) It is likely to be posteriorly directed (the anterior leaflet is most severely affected, and parts of it show mild prolapse from some views)
Most importantly, combined with clinical signs (this dog is not showing signs of heart failure now or in the past), the cardiac remodelling we can see tells us this dog is likely to be stage B2.
The short-axis views further confirm what we already know.
If you’re a beginner, you can stop here! Hopefully, you can see how much information you can get from a good right parasternal long axis view. It really is your most important echo view, and well worth investing time in. Once you have mastered this view, you will find that adding additional views into your examination is much less painful, and far more intuitive. Sort of like, since I can already play tennis, I’m pretty confident I’d be half decent at whatever the new fashionable thing the people at my gym are doing when they’re running around swinging their racquets inside a glass box. If you need help with your right parasternal long axis view, email me or book a call with me and we can talk through what you are stuck with, and how you can improve.
Above: visiting an ancient old fort in Bahrain with our amazing videographer, Vincent
Once I have performed my B-mode examination, I then go back and put colour Doppler over all of the valves. I avoid doing this straight away (unless I have a restless patient where time is going to be very limited); I want to form an opinion first, a hypothesis to test, before biasing myself with what my colour Doppler is doing.
In the case of this dog, I am expecting to see severe mitral regurgitation, posteriorly directed. Just as when I was imaging the valve itself, I make subtle adjustments to the angulation of my probe, so that I am cutting through different sections of the valve. I don’t want to underestimate the severity of the regurgitation because I happen to be slicing through a relatively unaffected part of the valve.
If I see a clear vena contracta (the narrowest part of the colour map, which should correlate with the size of the gap), I will measure it from here, where I am taking advantage of my machine’s axial resolution. I can measure a vena contracta from my apical views too, but this will be limited by my lateral resolution, which is always going to be poorer. Measuring vertically is always more precise than measuring horizontally.
The below video shows colour Doppler over the mitral valve and left atrium in this dog. Notice also the swirling of colour in the left atrium, which is another indication of severity. Blood is coming backwards into the left atrium, hitting the back wall, and swirling back on itself.
Colour over the short axis view at mitral valve level confirmed that the leak is quite extensive, filling up most of the closure point between the two leaflets.
From the apical 4 chamber view you can see again how thickened the mitral valve leaflets are – particularly the anterior leaflet – and we can get another view of the vena contracta and flow convergence zone. This area, or ‘PISA’, is not measurable in this dog from this view, but if you are interested in PISA then it is addressed in the advanced section below.
Mitral inflow Pulse Wave Doppler also showed E wave velocities of almost 1.5m/s, as another piece of evidence that this leak is severe. Finally, a continuous wave Doppler trace through the mitral valve was quite dense – another qualitative piece of evidence. Remember, a high velocity CW Doppler trace through the regurgitant jet does not correlate with severity, and is, in fact, a good sign for your patient. The velocity of this backward flow is influenced by left ventricular systolic function, not severity of regurgitation, so high velocities = good systolic function!
Any examination of a dog with myxomatous mitral valve disease is not complete without a thorough check of the right heart. In this dog, right ventricular systolic function was good (as assessed visually, and quantified by TAPSE and S’), and there is no evidence of elevated pulmonary pressures.
All of this extra work is, of course, to say that our initial staging of this dog as likely B2 based off history, symptoms, and B-mode imaging from the right parasternal views, is further supported.
In patients with very severe mitral regurgitation, you can measure a PISA – proximal isovelocity surface area – without adjusting anything, but in most, you will need to give your colour Doppler a helping hand. You do this by maximising your scale (PRF), and then reducing your baseline in order to promote aliasing. Only go as low as you need to, to see a measurable PISA. Zoom in over the mitral valve to make it clearer and easier to see and measure.
If you are quoting a PISA radius alone and not a full PISA calculation, always quote your aliasing velocity alongside it. For example: “PISA radius of 0.42cm (aliasing velocity set at -45.9cm/s)”, otherwise it is meaningless.
If you want to learn more about how PISA works, and how to combine your radius measurement with your continous wave Doppler trace for an estimate of the regurgitant orifice area, please let me know that you are interested. You can, technically, calculate a regurgitant volume as well, but in my opinion, that’s pushing the ultrasound voodoo a step too far. There are so many caveats to a PISA measurement in dogs (too many to go into here), and I would always interpret any PISA-derived values with a pinch of salt and be sure that it matches the rest of your echocardiographic examination. For me, it’s a supporting measure, but never an independently diagnostic one.
If you are measuring manually, you would normally measure to the top of the PISA (upward); on the Vinno D10, it draws a hemisphere for you, which is directed downward.
Below, an online trace of the continuous wave Doppler trace through the mitral regurgitation jet, to combine with my PISA measurement above. Taken on the impressive Vinno D10 ultrasound machine.
Whatever stage you are at with echocardiography, I hope you enjoyed this case walkthrough, and got some useful points from it. For those of you on the Confidence in Echocardiography programme, this case (and several others) have been filmed and talked through in detail, and will be hitting your training portals over the next few months as we edit them. There is no additional charge for this and you will be able to access these new training videos automatically.
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