Echo Calculators

 

 

  • Summary Page
  • Cardiac Output/Stroke Volume
  • Qp/Qs (Shunt)
  • Aortic Valve Area (Stenosis)
  • Mitral Regurgitation (EROA/PISA)
Click on a tab above to go to the appropriate echo calculator. Each tab has an example to help you better understand what information you need for each calculation, as well as a range of reference values to help interpret the results. Or use this summary page to make a quick calculation.

Qp/Qs Calculator

LVOT diameter: cm
LVOT VTI: cm
RVOT diameter: cm
RVOT VTI: cm

Qp: ml/beat        Qs: ml/beat

Qp:Qs

 

Cardiac Output and Stroke Volume Calculator

Heart Rate: beats/min
LVOT VTI: cm
LVOT diameter: cm

Stroke Volume ml
Cardiac Output L/min

 

Aortic Valve Area Calculator

LVOT diameter: cm
LVOT VTI:
cm
LVOT peak velocity:
meters/s

Aortic Valve VTI: cm
Aortic Valve peak velocity:
meters/s

Valve Area (by VTI): cm^2
Valve Area (by peak velocity)
: cm^2

 

Mitral Regurgitation Severity (PISA method)

PISA radius: cm
Aliasing velocity: cm/s
Peak MR velocity: meters/s
MR VTI: cm

Effective regurgitation orifice area mm^2
Regurgitant Volume: ml

 

 

Cardiac output can be calculated by echo across any structure where one can measure cross sectional area and some information about velocity of blood flow. This could be the aorta, the pulmonic artery, or across any of the valves.

The easiest and least variable place to measure cardiac output is at the left ventricular outflow tract (LVOT). The LVOT diameter changes very little through systole and diastole and is assumed to be constant and closely approximating a circle in shape, however this introduces some error as it is in fact elliptical in many patients.

 

Cardiac Output and Stroke Volume Calculator

Plug in your information below to calculate the cardiac output:

Heart Rate: beats/min
LVOT VTI: cm
LVOT diameter: cm

Stroke Volume ml
Cardiac Output L/min

 

 

 

Details:

The LVOT diameter is measured in the parasternal long axis view in systole. The LVOT velocity time intergral (VTI) provides information regarding blood velocity across the time period of systole and is in the units of cm. Typical values are close to 2 cm.

The LVOT pulsed wave Doppler in either the apical long axis or 5 chamber view and the VTI can be traced out on the ultrasound machine or using digital software offline.

For the cardiac output calculation therefore you need the following:

1) the LVOT VTI, 2) the LVOT diameter and 3) the heart rate.

Recall that:

Cardiac output is = Heart Rate x Stroke Volume 

                               and

Stroke Volume = LVOT area x LVOT VTI

                          = Pi(LVOT diameter/2)^2 x LVOT VTI.

Example:

 

 

 

Heart Rate: 100beats/min

 

 

 

Hence LV stroke volume = 3.14 (2.0cm/2)^2 x 19cm = 60 cm^3  or 60 ml

Cardiac Output = HR x SV = 100 beats/min x 60 ml/beat = 6000 ml/min or 6.0L/min

Pitfalls:

1. The LVOT VTI may not be accurate when the rhythm is irregular as in atrial fibrillation. In this case one should average the VTIs of several beats.

2. The LVOT diameter if off by a little can introduce significant error in output values since the radius is squared. Regardless in the same patient using the same LVOT diameter will give useful information about changes in cardiac output.

 

 

 

 

Echo can be used to estimate the magnitude of a left to right or right to left shunt in cases where they exist due to an atrial septal defect or ventricular septal defect, for example. One usually calculates the ratio of the pulmonic blood flow (Qp) to the systemic blood flow (Qs). Values greater than 1 suggests a left to right shunt, values less then 1 suggests a right to left shunt.

For this one needs an estimation of stroke volume across the left side chambers, usually measured at the left ventricular outflow tract (similar information needed as with cardiac output calculation) and the right side, usually measured at the right ventricular outflow tract.

Calculate your Qp/Qs

LVOT diameter: cm

LVOT VTI: cm

RVOT diameter: cm

RVOT VTI: cm

Qp: ml/beat       Qs: ml/beat

Qp:Qs

Example:

You are asked to calculated the shunt fraction Qp/Qs for a secundum ASD.

For this, you need to obtain the following measurements:

LVOT diameter (parasternal long axis) LVOT velocity (Apical 5 or 3 chamber, PW)
RVOT diameter (PSAX) RVOT VTI (PSAX, PW)

We use the fact that

Flow (Q) = area of the tube in cm^2 x VTI stroke distance in cm

In this case the "tubes" are the LVOT and RVOT. We assume they are circles with the same diameter throughout systole. Since the area of a circle is 2(Pi)radius^2 we can calculate:

Qp = 2(Pi)(RVOT diameter/2)^2 * RVOT VTI

Qs = 2(Pi)(LVOT diameter/2)^2 * LVOT VTI:

  In the example shown above we have:

Qp = 2Pi(2.41/2)^2 X 23
Qs=  2Pi(1.9/2)^2 x 22

= 1.7

Note that for the ratio Qp/Qs the 2(Pi) terms cancel out.

Important Points

1) This ratio is highly sensitive to errors in measurement of the LVOT and RVOT diameter, since both of these values are halved and then squared.

2) Measuring the RVOT diameter can be challenging without adequate echo windows. The Diameter should be measured at the RVOT, proximal to the pulmonic valve, which is where the VTI measurement takes place.

3) This formula only works well in cases where there is pure left to right or shunting. It does not work with bidirectional shunting.

 

 

 

Aortic Stenosis is graded as follows:
Category
Mild AS
Moderate AS
Severe AS
Valve Area (cm^2)
>1.5
1.0-1.5
<1.0
Peak Jet Velocity (m/s)
<3
3-4
>4
Mean Gradient (mmHg)*
<25
25-40
>40
Source: ACC/AHA guidelines 2006. Guidelines for the Management of Patients With Valvular Heart Disease. Circulation 2006;114;450-527
*beware of low gradients in cases of severe aortic stenosis with diminished LV function Additional testing is needed to assess severity.
Aortic Stenosis Calculator (by continuity equation)
Input the following: (either VTIs or peak velocity can be used)
LVOT diameter: cm
LVOT VTI:
cm
LVOT peak velocity:
meters/s
Aortic Valve VTI: cm
Aortic Valve peak velocity:
meters/s
Aortic Valve Area (by VTI): cm^2
Aortic Valve Area (by peak velocity)
: cm^2

 

Description and Example:

To calculate Aortic Valve Area by the continuity equation you need the following:

1) LVOT diameter from the PLAX view (in most people this is near 2 cm). This is assumed to be constant throughout systole.

2) LVOT velocity and/or VTI from the 5 chamber or apical long axis view.

3) The velocity of VTI at the aortic valve from the 5 chamber or apical long axis view.

 

LVOT diameter from PLAX view LVOT VTI from Apical Long axis or 5 chamber view
Aortic VTI from Apical long axis or 5 chamber view  
 
By the continuity Equation: Area1xVTI1 = Area2x VTI2
LVOT Area x LVOT VTI = AV Area x AV VTI 3.14(2.0cm/2)2 x 19cm = AV Area x 82.1cm
AV Area = 0.72cm^2, which is consistent with severe aortic stenosis.

 

 

Criteria For MR severity*
Criteria
Mild MR
Severe MR
Regurgitant Volume
< 30 cc
> 60 cc
Regurgitant Fraction
< 30 %
> 50 %
EROA
< 0.20 cm^2
> 0.40 cm^2
 
*Moderate MR has values considered in between those of mild and severe both.
Mitral Valve Regurgitation Calculation (PISA method)
PISA radius: cm
Aliasing velocity: cm/s
Peak MR velocity: METERS/s
MR VTI: cm
Optional input (to calculate regurgitant fraction):

LVOT diameter: cm
LVOT VTI: cm

Effective regurgitation orifice area (EROA) : cm^2
Regurgitant Volume: ml
Forward LV Stroke Volume: ml
Regurgitant Fraction: %
 

 

The Proximal Isovelocity Surface Area (PISA) method for MR severity assumes that there is flow convergence in systole around one and only one leaking orifice of the mitral valve. We assume blood flow converges in a hemispherical shape as it goes from the left ventricle toward the left atrium (see figure below).
We use the continuity equation (flow on one side must equal flow on the other) with the area of the hemisphere of flow convergence and its velocity to calculate the area of the effective regurgitant orifiace area (EROA). This is possible since we know the peak mitral regurgitant velocity.
The mitral regurgitant volume is obtained from the EROA by multiplying it by the MR VTI . This principle is illustrated below along with a sample calculation at the bottom of the page.
Method:
Step 1) Get a good apical view of the MR jet in color, zoom in if possible around the hemispherical flow convergence in the LV near the mitral valve.
Step 2) Decrease the aliasing velocity in the direction of the MR (lower velocity scale in TTE and upper velocity scale in a TEE) to around 40cm/s
Step 3) Freeze frame the video clip in a frame that shows a nice hemispherical color shell with a rim of the aliasing color (here shown in light blue). Measure the hemisphere's radius (PISA radius)
Step 4) Use CW across the mitral valve to get the peak mitral velocity and VTI.
Step 5) Calculate the EROA and Regurgiation volume as shown to the right with the continuity equation.

 

Example Calculation:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Here is a sample calculation from a real example:

 Important Points:

1. It is important to shift the color baseline to get a lower aliasing velocity in order to get an adequate hemispherical flow convergance profile. An aliasing velocity around 40cm/s is recommended.

2. Whether you are doing TEE or TTE a simple rule of thumb is to shift the baseline in the direction of the MR jet (this means changing the lower velocity in TTE apical views and the upper aliasing velocity in the mid esophageal TEE views.)

3. This method is only reliable for quantifying a single centrallly directed jet. In patients with multiple MR jets, or those which are eccentric the PISA method is not reliable.