Introduction

As we learned in the first course on Aortic Regurgitation (AR), it is a heart condition characterized by the leaking of blood backward through the aortic valve into the left ventricle. This happens because the aortic valve does not close properly, allowing blood to flow back into the LV during diastole. Echocardiography is vital to assessing the severity, for devising a treatment plan, and for surgical timing. There are multiple measurements and equations that are used in the assessment of AR, so this course will dive into the more complex equations and how to accurately make these measurements.

Figure 10.1 Drawing of aortic regurgitation within the heart

Review of Aortic Regurgitation Part 1:

In the first course on aortic regurgitation, we discussed the intricacies of the aortic valve anatomy along with the physiology, signs, and symptoms of aortic regurgitation. Echocardiography provides a non-invasive means to assess the severity of the condition and visualize the structure and function of the heart valves. Doppler echocardiography, in particular, is instrumental in quantifying the regurgitant flow and pressure gradients across the aortic valve.

Furthermore, echocardiography aids in identifying any associated complications, such as left ventricular enlargement and dysfunction, which are common in advanced chronic cases. This information is crucial for treatment planning as well as monitoring the progression of the condition.

Figure 10.2 Review of parameters and findings used to assess the severity of AR

Review of Methods used to assess the severity of aortic regurgitation with echocardiography:

2D Imaging: This is used to analyze the aortic valve for any structural abnormalities that can affect the need for treatment and surgical intervention. It is also used to assess the LV size and function, along with if there are any other abnormalities.
Color Doppler Imaging: In aortic regurgitation, color shows the regurgitant blood flowing back into the left ventricle during diastole. The size and shape of this jet can offer initial insights into the severity of the regurgitation. You can use color to visually assess the size of the jet in comparison to the LVOT and AV area.
- How to adjust your color Doppler for accuracy:
  - Color gain should be turned up to just below clutter noise level (otherwise, the jet is underestimated)
  - Nyquist limit should be between 50-70 cm/sec. As the Nyquist limit is lowered, the jet will appear larger.
Continuous Wave Doppler: Tracing the AR signal gives you the peak velocity and velocity time integral (VTI) of blood flow through the aortic valve. It helps to quantify the regurgitant volume of the regurgitant jet, which is a key parameter in estimating the severity of the regurgitation.
Pulsed-Wave Doppler: This technique is used to measure the velocity time integral (VTI) of the AV used to calculate the stroke volume. It is also used to assess if there is holodiastolic flow reversal seen in the abdominal and descending aorta.
Pressure Half-Time (PHT): This method estimates the time taken for the pressure in the aorta to drop by half during diastole.
Vena Contracta Width: This measures the narrowest portion of the regurgitant jet near the orifice. A wider vena contracta indicates more severe regurgitation.
Regurgitant Volume, Fraction, and EROA: These are calculated using various measurements. They provide quantitative measures of the volume of blood regurgitated and the percentage of blood that regurgitates back into the left ventricle. These methods will be explained in more detail later in the course.

Types of Aortic Regurgitation:

Now let’s look at the different types of aortic regurgitation as each has its own characteristics and underlying causes. Here are the main types:

Acute Aortic Regurgitation: This type develops suddenly and progresses rapidly. It is usually caused by aortic dissection, infective endocarditis, or trauma.
- Infective Endocarditis: This is an infection of the heart valves, including the aortic valve, usually caused by bacteria. It can lead to acute aortic regurgitation from the perforated cusp.
- Traumatic Aortic Regurgitation: This is a rare form of aortic regurgitation caused by trauma to the chest, often from a severe blow or impact.
- Pathophysiology to note for acute AR:
  - It creates a sudden, large regurgitant volume, which will significantly elevate the left ventricular end-diastolic volume and pressure.
  - The decrease in forward stroke volume can cause cardiogenic shock, which requires urgent intervention such as Nitroprusside/Inotropic agent, surgical repair, or replacement.
Chronic Aortic Regurgitation: This type progresses slowly over time. It is most commonly caused by conditions such as aortic valve degeneration, rheumatic heart disease, or a congenital bicuspid aortic valve.
- Rheumatic Aortic Regurgitation: This is a type of chronic aortic regurgitation that results from rheumatic fever, an inflammatory disease that can affect the heart valves with calcification.
- Bicuspid Aortic Valve Regurgitation: This is a congenital condition where the aortic valve has only two leaflets instead of the normal three. It can lead to regurgitation and/or stenosis over time. (Significant premature valve disease occurs with a bicuspid aortic valve – aortic regurgitation in 40% and aortic stenosis in 30%).
Aortic Valve Prolapse: This occurs when the aortic valve leaflets do not close properly and bulge back into the left ventricle. It is most clearly visualized on PLAX or TEE at 120 degrees. This can happen from:
- Myxomatous or Congenital Abnormality
- Decreased Commissural Support
- Partial Cusp Tear due to Trauma
Aortic Root Dilation: Enlargement of the aortic root, which can be caused by conditions like Marfan syndrome, can lead to aortic regurgitation.
Functional Aortic Regurgitation: This occurs due to abnormalities in the structure or function of the aortic valve, often secondary to other heart conditions such as dilated cardiomyopathy.

Figure 10.3 Diagram of types and causes of aortic regurgitation

Aortic Regurgitation Jet Directions:

After reviewing the types of AR, it is also important to note the direction of the AR jet, which can provide important information about the severity and etiology of the regurgitation. It can also aid in determining when surgical intervention is needed. Here are the main directions of AR jets:

Central Jet: This is the most common direction for the regurgitant flow. The jet is directed toward the center of the left ventricle and is indicative of regurgitation originating from the middle portion of the aortic valve.
Posterior eccentric Jet: This jet is directed towards the posterior wall of the left ventricle and anterior mitral valve leaflet.
Anterior eccentric Jet: This jet is directed towards the septum in the left ventricle.
Multiple Jets: In some cases, there may be more than one regurgitant jet, which can indicate complex valve pathology.

Figure 10.4 Demonstration of the direction the AR jet can travel

Aortic Regurgitation Jet Severity:

Figure 10.5 Example of the severity of AR based on how far the jet travels within the left ventricle. Since this example is based on the jet being central, keep in mind that eccentric jets may not have the same distance it will travel into the LV to still be significant.

PISA Quantification of Aortic Regurgitation:

The Proximal Isovelocity Surface Area (PISA) method is a valuable technique used to assess the severity of aortic regurgitation. It involves the calculation of the regurgitant flow based on the hemispheric shape of the regurgitant jet. With PISA, proper technique, and accurate measurements are essential for reliable results. Additionally, PISA assessment is often used in conjunction with other echocardiographic parameters for a comprehensive evaluation. PISA calculation will give you an EROA, regurgitant volume, and fraction. The PISA calculation method is most commonly used in mitral regurgitation assessment but can be done in aortic regurgitation as well.

Here’s an overview of the PISA assessment for aortic regurgitation:

Principle:
- The PISA method is based on the concept of flow convergence. When blood flows through a regurgitant orifice, it forms a hemispheric region of flow convergence around the orifice.
- The flow convergence region is termed the Proximal Isovelocity Surface Area (PISA).
Image Acquisition: PISA requires 4 measurements from 2 images: CW Doppler of AR jet and color on zoomed AV with adjusted baseline.
- Color Doppler image:
  - Zoom on the AV and optimize the image. Turn on the color Doppler to visualize the regurgitant jet (this is most commonly done from the apical window; however, in eccentric jets, PLAX might be an option as well).

Figure 10.6 Eccentric AR from PLAX view

Adjust the color aliasing velocity in the direction of the regurgitant flow (in apical, this will be up; from parasternal, this will be down) to around 40 cm/s. Lowering the aliasing velocity too much can overestimate the radius.
- The aliasing velocity (Nyquist limit) is the maximum velocity at which the color Doppler signal can be accurately measured. It’s an important parameter in the calculation of regurgitant flow.
Pan through the valve to find the largest radius. The goal is to obtain a clear, well-aligned image of the jet for accurate measurements. If it’s difficult to see a radius because of a calcified valve, try turning down the 2D gains in order to reduce shadowing over the color that calcification can cause.

Figure 10.7 PISA measurement with an example of machine calculations shown

CW Doppler image of AR:
- Align the cursor parallel to the regurgitant jet and turn on CW. Most often, this will be from an apical window, but can also be attempted from PLAX with posterior-directed eccentric jets, as seen in Figure 10.6.
- Again, pan through the valve to ensure the most accurate, dense Doppler signal. Adjust the Doppler scale above the baseline to at least 4 m/s.
- Trace the CW signal to get both the peak velocity and TVI of the AR signal (Figure 10.8).
  - When arrhythmia is present, you may have to measure multiple signals and average them.

Figure 10.8 CW trace of aortic regurgitation

Now for the Measurements:
- The next step is to measure the radius of the PISA from the images optimized from a zoomed color of AV.
  - Measure the radius in the direction of the AR flow (this will help eliminate underestimation on eccentric jets)

Figure 10.9 Example of measuring PISA radius on a posterior directed eccentric jet

Measure the radius along the diastolic phase of the EKG tracing
Tip: To get the most accurate PISA radius, measure at the same point in the cardiac cycle as the CW max velocity.
From the CW Doppler image, trace the AR signal, which will give you both a peak velocity and VTI, which are used in the calculation as explained below.

Calculations:

Regurgitant Flow Calculation:
- The first thing is to calculate the regurgitant flow rate using the PISA radius and the aliasing velocity measurements.
- Equation: Regurgitant Flow = 6.28 x (PISA Radius)2 x Alias Velocity
EROA calculation:
- The next part of the equation is used to calculate the effective regurgitant orifice area (EROA) and uses the regurgitant flow, calculated in the previous step, along with the peak AR CW velocity
- Equation: ERO= AR flow/ peak AR velocity
Regurgitant Volume calculation:
- Lastly, use the calculated ERO and the TVI from the AR trace to calculate the AR regurgitant volume.
- Equation: Regurgitant Volume= ERO x TVI of AR CW jet
Severity Grading:
- The obtained regurgitant volume and EROA are used to determine the severity of aortic regurgitation, usually classified as mild, moderate, or severe based on established criteria seen in figure 10.10.

Figure 10.10 Severity grading chart of AR

Figure 10.11 PISA calculation overview of images and measurements needed and equations used

Pitfalls of PISA:

Not zooming enough to accurately measure the radius
- A 10% error in the radius measurement leads to a 21% error in flow calculation
Adjusting the color baseline too high or too low to obtain an optimal hemispheric flow convergence for PISA radius measurement
Not measuring the PISA radius to coincide with the peak AR CW timing on EKG
Can be technically challenging as it requires multiple measurements and views

Quantification of Aortic Regurgitation using the Continuity method:

The continuity method is based on the “what goes in, must go out” theory, meaning the blood passing through the mitral valve should be equal to the volume passing through the aortic valve. By calculating both of these volumes and subtracting them from each other, the resulting volume is the amount of regurgitant volume still in the LV. Similar to the PISA method, the continuity method requires multiple views and measurements. The calculation will give you a regurgitant volume, ERO, and regurgitant fraction.

First, calculate the LVOT stroke volume
1. From the PLAX zoomed view of the AV, measure the LVOT diameter
2. From the apical window, place the cursor sample volume in the LVOT, and using PW Doppler, trace the LVOT signal for TVI
3. Equation: LVOT Stroke Volume = 0.785 (LVOT diameter)2 x LVOT TVI
Next, calculate the MV stroke volume
1. From a 2D apical zoomed view of the MV, measure the annulus during diastole.
2. Place the PW sample volume at the mitral annulus (not leaflet tips as used in diastolic function assessment). Trace the MV inflow from the PW Doppler signal. Trace the middle of the Doppler signal (modal velocity) instead of the outside border, which is done with CW MV inflow trace.
  1. Modal velocity is found to be the most accurate for calculating volumetric flow and is less gain-dependent.
3. Equation: MV Stroke Volume = 0.785 (MV diameter)2 x MV TVI at annulus
To calculate the AR volume, subtract the LVOT stroke volume from the MV stroke volume, and this will give you the AR regurgitation volume.
1. Equation: AR regurgitant Volume (cm3)= LVOT SV – MV SV
Calculate the regurgitant Fraction (RF)
1. Equation: RF = AR volume (cm3)/ LVOT stroke volume (cm3)
Next, calculate the Effective Regurgitant Orifice (ERO) (cm2).
1. Equation: ERO = AR regurgitant volume (cm3)/ AR TVI (cm)

Figure 10.12 Continuity method for calculation of aortic regurgitation

Pitfalls:

If the MV annular measurement is not accurate, the error is squared
- This can be especially hard to measure if there is annular calcification
Not placing the sample volume at the MV annulus
If the Doppler alignment is not parallel to the flow, measurements will be underestimated
Not tracing the modal velocity in MV PW Doppler signal
If there is mitral regurgitation more than mild, this method for AR can be inaccurate
If there is a-fib or any arrhythmia that makes each signal different in size, then 5 measurements of each should be done and averaged.

Figure 10.13 Continuity equation breakdown for AR

If there are still questions on the severity of the AR, there are other options for evaluation, like TEE 3D color analysis, as demonstrated in Figure 10.14.

Figure 10.14 3D color TEE image of severe AR

Putting it All Together and Grading the Severity

Case Study 1

While this case may not have the most beautiful images, it is an example of what most sonographers have to deal with every day in the echo lab. The goal of this case study is to help identify the severity of AR with an eccentric jet.

Patient Information:
- This is a 78-year-old female with a medical History of hypertension, asthma, dyspnea on exertion, and a new onset of chest pain.
Echocardiographic Evaluation:
- She originally had an echo in July of 2022, which showed normal EF, and sclerotic AV with mild AR.
- Because of a change in symptoms and it had been a year since her last echo, another echo was ordered, which showed:

As you can see from the videos, the AR jet is eccentric posteriorly directed. These cases can be very difficult to determine the severity. Here are a few images that can help determine the amount of AR:

Figure 10.16 Color m-mode

Figure 10.17 Color doppler of the aortic valve in an apical 3-chamber

As seen in this still image of color from apical 3ch, the eccentric jet might not go very far back into the ventricle compared to if it was a central jet.

Figure 10.18 Color doppler of the aortic valve in an apical 5-chamber

Another still image from apical 5ch with color. In this image, you can see that the regurgitant jet is going farther into the LV compared to the previous image.

Figure 10.19 CW of the aortic valve

Because of how eccentric the jet is, the CW attempt is not parallel to flow, so is not very helpful in the assessment.

Figure 10.20 PISA attempt of aortic regurgitation

In this PISA attempt, can you spot the issue?
The biggest issue is the color baseline was moved in the wrong direction. It should be moved in the direction of the regurgitant flow, and this was moved down, away from the flow. Also, the valve was not zoomed on, making the rate of error when measuring higher. This measurement cannot be used to accurately assess the amount of AR.

Figure 10.21 PISA of aortic regurgitation after adjusting the color baseline in the correct direction and zooming on the aortic valve

After adjusting the color baseline up in the direction of the flow and zooming on the valve, the PISA measurement was more accurate. Even though we were not able to get a good CW AR trace for PISA calculation, you can still use the radius measurement to estimate the amount of regurgitation. As long as the aliasing velocity is around 40, a PISA radius of .7 will calculate out to moderate AR. A radius of .8 is more moderate to severe, and .9 to 1.0 will be severe.

Diagnosis and Severity Assessment:
- Based on the information, the aortic regurgitation severity in this patient was called moderate. Not being able to see the previous images to compare, it’s hard to know if the previous echo under called the AR due to it being eccentric and harder to assess or if this did increase from mild to now moderate in severity. While this patient does not yet need surgery, she will be closely monitored with echocardiograms to assess the progression.

Case Study 2

Patient Information: This is a 56 y/o male who was referred to a cardiologist by his primary care physician due to elevated blood pressure. He had no significant symptoms and was even doing training for a long-distance road bike race.
Vitals: 6ft, 178lbs, BMI 24.1, BP 148/86 mmHg, pulse 76 bpm.
Cardiologist Assessment:
- During the clinical assessment, the cardiologist had an EKG done in the office, which showed a right bundle branch block but no other abnormalities. By auscultation, there was a murmur heard, so an echocardiogram was ordered to assess further:

Even from this first video, it is clear there is something abnormal with the aortic valve.

Color on the PLAX view showed that there is significant aortic regurgitation.

Figure 10.22 Vena contracta of aortic regurgitation

Figure 10.23 shows the aortic root measured 3.9 cm and the ascending aorta measured 5.5 cm

Figure 10.24 Color Doppler of aortic regurgitation in an apical 3 chamber

Figure 10.25 CW of aortic regurgitation

CW signal of aortic regurgitation. The PHT does not measure severe, but if we look at the AV CW signal (below), there was also aortic stenosis, making the PHT not as reliable.

Figure 10.26 AV CW trace shows aortic stenosis.

The cardiologist read this as severe AR with mild AS and a bicuspid AV. Because of the severity of the aortic regurgitation and aneurysm of the ascending aorta, this patient is being referred to a surgeon and will also have a chest/abdomen CT to visualize more of the aorta to see how far the aneurysm extends.

Multiple Pathology Effects on Measurements

What happens when there is more than one valve abnormality present?
- The chart below goes over the limitations of measurements of AR when other pathology is present and what to watch out for.

Figure 10.27 Effects that other valve pathology can have on AR calculation

Aortic Regurgitation Part 2: Quantification

Chapter 1