Instead of writing mushy-mushy post. I thought might as well write something useful. This post might be relevant to medical & allied heath students and junior doctors who want to know more about echocardiogram. And I’m sure a general public could understand echo after reading this post.
Just like scanning babies, all we do is place the probe on the chest. And we get ourselves an echocardiogram. See everyone is happy. It’s a girl, Mom!
Let me tell you what I feel about echocardiogram. Echocardiogram is the new stethoscope. I recommend all medical students & junior doctors to get use of holding the probe and start scanning. It will take time to be good at it. Gee, I’m still learning everyday. Only when you start doing your own scanning that you would be able to appreciate what need to be measured and why they are important.
Yup, something like this. By using the ultrasound probe, we ‘slice’ the heart into many images from different direction. This guy looks like that Prison Break guy.
In brief, I will tell you how we use echo to understand the heart and its function. To keep it simple, every echo machine has 3 main modalities:
- M-Mode (motion)
And Doppler has 3 types:
- Colour Doppler
- Pulse wave Doppler (PW)
- Continuous wave Doppler (CW)
We use 2D echo to see the heart structures, and measure the distance, the length, area, even volumes. For example in the picture below, we use 2D mode to measure the distance of the LVIDD (Left ventricle inner diameter in diastole), IVS (Interventricular septal wall), LV posterior wall, among other things. This is important as this is how we tell if the heart chambers are dilated (cardiomyopathy) or has thickened wall (hypertrophic).
This is 2D. Reliable, but get that dotted line perpendicular to the LV long axis and cut the plane through the tip of the mitral valve.
Whereas, M-Mode looks at ‘motion’ (hence M) and is able to calculate length/distance more precisely as you freeze frame the structure along a single line over time (see pic), but you still measure the same stuff as in 2D.
Good old M-Mode, among the first echo technology to be developed in the 70’s. Along with bell bottom jeans & pop yeh-yeh.
Okay now Doppler. We use colour Doppler to look at regurgitant flow and turbulence jet. And believe it or not colour is essentially a form of pulse wave Doppler. To see video example of Colour Doppler, click here: Beni Facebook.
Color Doppler from TEE, look at that ‘beautiful’ mitral regurgitant jet from the LV into the LA. You can measure additional sort of stuff here like the vena contracta (VC), and PISA to get the EROA and MR volume. This is how we tell if the regurgitation is mild, moderate or severe.
Okay now Pulse & Continuous Wave Doppler. They look scary at first, but trust me, it’s FUN. This is where you apply your high-school physics. So to begin with, we mostly want to know the pressure. So by using Doppler we can estimate pressure. But, since we are using an ultrasound machine… all we could measure is velocity. Remember, echocardiogram is a study of SPEED (velocity) & PRESSURE. Now lemme get into my red Mustang while flexing my Vin Diesel biceps.
We use Pulse Wave to find a velocity of blood (or tissue) at a specific depth. For example if you wanna know the pressure inside the LVOT (left ventricle outflow tract), all you need to do is place your sample volume inside the LVOT and hit pulse. It will give you a spectral Doppler. Either you want to measure the VTI (or TVI depending on which side of the Atlantic you live) or just the maximum velocity (Vmax). Then you use the modified Bernoulli Equation (P = 4 x V squared) and convert Vmax into Peak Pressure. Eureka!
Remember to place your Doppler cursor (sample volume) exactly at where you want to measure! In this case, the LVOT. An important info when you want to use continuity equation to calculate stroke volume. 好料, seehh!
Whereas, we use Continuous Wave to find the highest velocity along the Ultrasound beam. This is how we know pressure gradient across a valve – say the Tricuspid valve. Now you might ask why on earth we want to measure the pressure gradient across the Tricuspid. Well, the answer to that: “that’s how we estimate the pressure inside the Pulmonary artery or the PASP (Pulmonary artery systolic pressure)”. An important disease that unfortunately under-diagnosed (or under-recognised) is PULMONARY HYPERTENSION. Your patient is breathless, help her.
Spectral Doppler from Continuous wave, in this example we measure the Tricuspid valve maximum velocity (Vmax), here the Vmax is 2.6 m/s.. So we could gauge the pressure gradient between the RA and the RV (after using the Bernoulli formula we get 28 mmHg).
Beside measuring blood velocity, we could also measure tissue velocity by ‘pulsing’ the tissue, remember PW here, not CW. We measure tissue velocity to assess myocardial tissue function (e.g: example at the mitral septal or lateral annulus). This info will tell us how good the heart muscle in relaxing (psst! Diastolic function, yup E/e’ and e’ velocity). Coz’ in echo all we are interested is how the heart looks (anatomy) and whether the heart function is normal (physiology).
Tissue Doppler, we use Pulse wave TDI to measure how fast the myocardial tissue moves. Notice here, we place the sample volume at the tricuspid annulus.
BONUS: We don’t talk much about 3D, but technically we use 3D volumetric dataset. And currently common features are Live 3D, 3D zoom and Full Volume (for a higher volume rate, notice we don’t use 2D lingo like frame rate). And this is useful when we want to interrogare the valves better and understand what causes it to be abnormal – think mitral valve prolapse, endocarditis et cetera. What the heck, just take a look at the 3D image. You savvy, aye?
3D Image of Mitral valve, looking down at Mitral from left atrium, the so called En face view or the surgeon’s view.
NOTE: If you guys find this useful, please leave comment & feedback. So I could do this again 🙂 Until then study hard.
ps: hm, I tried posting some videos but WordPress no longer allows me to upload videos as they want me to upgrade my account to premium version. Cit!