Inferring right-heart pressures with echocardiography using tricuspid regurgitation
Measuring the velocity of the tricuspid regurgitation jet can help you estimate the systolic pressure in the right ventricle. How do you get a reliable measurement in patients with atrial fibrillation? In this video, Cristiana Monteiro—a cardiac physiologist from the University of Oxford—provides answers and explains the underlying physics of this right-heart pressure measurement.
Measuring the velocity of the tricuspid regurgitation jet can help you estimate the systolic pressure in the right ventricle. How can you distinguish between tricuspid regurgitation and a valve click on a continuous wave Doppler trace? How do you get a reliable measurement in patients with atrial fibrillation? In this video, Cristiana Monteiro—a cardiac physiologist from the University of Oxford—provides answers and explains the underlying physics of this right-heart pressure measurement.
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At the end of this Medmastery lesson, you will be able to make use of tricuspid regurgitation to estimate the systolic pressures in the right heart and pulmonary artery. The pressures in the right heart are lower than in the left heart, because blood leaving the right ventricle only has to travel as far as the lungs. In addition, blood flows from the atria into the ventricles due to a pressure gradient between the chambers. A very similar process happens during regurgitation.
Regurgitation jets can only happen if the pressure in the chamber they originate from, in this case the right ventricle, is higher than the pressure in the chamber receiving the flow, in this case the right atrium. This means that by measuring the pressure of a tricuspid regurgitation shift and adding it to the right atrium pressure, we will be able to estimate the pressure in the right ventricle. Let's look at this in practice. Start by placing your cursor across the tricuspid valve seen here as a dashed line.
Here we have an example of a parasternal short axis view. But this can be done in any view where you can see the tricuspid valve. If tricuspid regurgitation is visible, there will appear as a predominantly blue jet below the tricuspid valve during systole. Now we are looking at a four chamber apical view focus on the right heart. As before, place your cursor across the tricuspid valve and watch for regurgitation, to ensure you are looking at the right phase of the cardiac cycle, this regurgitant jet will appear when your ECG is somewhere between the QRS and the end of the T wave.
Now, hit the continuous wave Doppler button on the echo console. The continuous wave Doppler will produce a spectral trace that looks like this. Now be careful. The bright high velocity near instantaneous signal highlighted here is just a result of valve motion. It is called the valve click and it does not relate to blood flow, it should not be measured. Tricuspid regurgitation will show as a broader signal that lasts longer than the valve click. And if you can see two traces as we see here, the first peak will be a valve click and the second peak will be true tricuspid regurgitation.
Because the right ventricle is at the top of the screen and the right atrium at the bottom, when viewing the heart in the four chamber apical view, tricuspid regurgitation will be moving away from the right ventricle. This is visually represented on the trace as a peek below the graph line. This means the maximum velocity of any regurgitation jet is the furthest measured point below this axis. Here is an example of a good signal.
This patient is in sinus rhythm, demonstrated by irregular heart rate. In this case, you only need to measure the peak of one of the regurgitation jets like this one. This peak indicates the maximum velocity shown in this trace, your Echo machine will automatically measure this and calculate the pressure of this regurgitation jet.
The valve clicks are slightly more subtle, but still noticeable as brief, intense and bright signals at the onset of the regurgitation jet. In this example, the patient is in atrial fibrillation with a variable heart rate. Despite the patient's condition, the principle for calculating tricuspid valve regurgitation is the same. The exception to the rule is atrial fibrillation, where you should measure at least five regurgitation jets to get a reliable average maximum velocity.
If we go back to our example, you may notice I was only able to capture four heartbeats in this image. In this case, it is best practice to capture the fifth peak on a second image. I'll try to get a screen with a total of five heartbeats or more. Now for a bit of theory. We know that the difference in pressure will initiate flow and that a solution flows from an area of high pressure to an area of low pressure, we also know that blood moves from the right atrium to the right ventricle through the tricuspid valve.
So if blood is flowing from the right ventricle into the right atrium through the tricuspid valve, it is because the pressure in the right ventricle is higher than there in the right atrium. The pressure of the tricuspid regurgitation shift reflects the pressure difference between the right ventricle and the right atrium. And although you are measuring the velocity of regurgitation jet, the echo machine will automatically calculate the equivalent pressure for you. Let's look at an example of how a tricuspid regurgitation jet can be used to determine right sided pressures in the heart.
Here, the right ventricle has a pressure of 20 millimeters of mercury, and the right atrium has a pressure of five millimeters of mercury. The difference in pressure between the two chambers is 15 millimeters of mercury. This is the pressure of the tricuspid regurgitation jet. In much the same way, if you add the pressure of the right atrium to the pressure exerted by the tricuspid regurgitation jet, you can estimate the Right Ventricular Systolic pressure, in this case, five millimeters of mercury plus 15 millimeters of mercury indicates that the right ventricle exerts 20 millimeters of mercury during systole.
Now, this is important, the systolic pressure in the right ventricle and the pulmonary artery are equal. Therefore, measuring the velocity of the tricuspid regurgitation jet, and estimating systolic pressure of the right ventricle can give you an indirect measurement of the systolic pressure in the pulmonary artery. In our previous example, we use the systolic pressure of the right atrium and the tricuspid regurgitation jet to estimate the systolic pressure of the right ventricle, 20 millimeters of mercury.
This would indicate that systolic pressure in the pulmonary artery is also 20 millimeters of mercury. This relationship is important when determining whether a patient has pulmonary hypertension, a condition whether blood pressure in the lung arteries is increased causing significant shortness of breath. This is unless there is pulmonary stenosis. The thicken leaflets and narrowed valve opening characteristic of pulmonary stenosis will cause the blood flow in the pulmonary artery to have higher velocity and pressure than the blood flow in the right ventricle. But we know pulmonary stenosis is rare, so it's nothing you should really worry about.
When using the pulmonary artery systolic pressure, or PASP to assess for pulmonary hypertension, be sure to check your national echocardiography guidelines for the correct estimation of right atrial pressure when assessing a patient and what degree of pulmonary hypertension these pressures suggest. In this example, the maximum tricuspid regurgitation pressure is 41 millimeters of mercury. The estimated right atrial pressure for this patient, according to the guidelines, is 10 millimeters of mercury. When added together these pressures provide a right ventricular and pulmonary artery systolic pressure, 51 millimeters of mercury. Fantastic. You now understand how to use tricuspid regurgitation to calculate the pulmonary artery systolic pressure.