Fractional area change is another one of those echocardiographic parameters that is exactly what it says- it’s the percentage change in area of a chamber between systole and diastole. Let’s look at how it can help in the assessment of the Right Ventricle.
I’d highly recommend looking at our previous articles on TAPSE and S’ before continuing. This is an advanced measurement, get some help and supervision before you embark on it.
WHAT IS FRACTIONAL AREA CHANGE?
Fractional area change is another one of those echocardiographic parameters that is exactly what it says- it’s the percentage change in the area of a chamber between systole and diastole. The precise formula for it is
Fractional area change= Chamber area in diastole- chamber area in systole
Chamber area in diastole
It’s classically measured in the left and right ventricles.
WHY DOES IT MATTER?
Fractional area change may be yet another method of assessing right ventricular function, however, by its nature it provides a more global assessment of RV function than the more commonly used TAPSE and S’. It correlates well with RV ejection fraction as measured on MRI, and has been shown to predict outcomes in patients after myocardial infarction and pulmonary embolism.
YOU’VE SAID THIS BEFORE WITH TAPSE AND S’
Yes, I know! Trust me on this one- you want to see how it’s done.
- SIGH. HOW DO I DO THIS?
RV FAC is classically measured from the four-chamber window- in particular, the RV focused view that we’ve been using for TAPSE and S’. It’s super important to get this view this time and to see the RV free wall.
Once you’ve got the view, you’re going to freeze your image, then trace the RV area in diastole. This is either identified as the point just before tricuspid valve closure, or the midpoint of the QRS complex if you have ECG attached. Be careful not to include trabeculations and the moderator band- you want the myocardium.
Repeat the same process for systole. Systole is either identified as the smallest RV area or the end of the T wave if you have ECG attached.
This is much easier to do away from the patient on your machine/echo workstation software, on a saved loop.
Your machine may have a package for FAC- if not, you can work it out yourself by plugging your end-diastolic and end-systolic areas into the above formula
SO WHAT IS NORMAL FAC?
A FAC of more than 35% is considered normal. <25% is considered severely impaired.
SO WHAT ARE THE ADVANTAGES OF FAC?
The main advantage of FAC over TAPSE and S’ is that it includes the contribution of the RV free wall- so it increases your sensitivity for detecting RV dysfunction.
Remember the examples of RV dysfunction I showed in both the TAPSE and S’ post with preserved longitudinal but impaired radial function? FAC in that case was <25%, correlating with severe RV dysfunction.
WHAT ARE ITS PITFALLS?
Sadly there are a lot.
- You need a REALLY good view of the RV, including the free wall. In critically unwell patients this can be very difficult.
- Because of the need for tracing and a clear view, it means that this measurement is significantly user-dependent- more so than TAPSE or S’.
- Because part of the tracing includes the interventricular septum, a particularly hyperdynamic LV can give a false positive for a well-functioning RV.
- In the same vein, a stunned septum (i.e post-cardiac surgery) can make the RV appear worse than it actually is.
- It doesn’t include the right ventricular outflow tract in its assessment and may miss RV dysfunction localized there.
SO NOW I HAVE 3 TOOLS TO MEASURE THE RV- GREAT! WHAT HAPPENS IF I ASSESS AN RV AND GET NON-MATCHING VALUES?
I’d get a senior echocardiographer to have a look. Either there’s been user error, or you’ve got a very complex RV with dissimilar contraction between segments (post-cardiac surgery, post-infarction, bundle branch block).
- Fractional area change adds (yet) another tool to assess RV function
- It’s defined as the difference between end-diastolic and end-systolic RV areas, divided by end-diastolic area
- It correlates well with MRI measured RV ejection fraction
- It’s measured in an RV Focused apical 4 chamber view, by tracing end-diastolic and end-systolic areas
- Care should be taken to ensure the accuracy of the tracings
- While it improves the sensitivity of RV assessment by including the free wall, it’s highly user-dependent
- Buckland J. 5 things to know about using Fractional Area change (FAC) to assess RV function. https://www.cardioserv.net/rv-function-fac/
- DiLorenzo MP, Bhatt SM, Mercer-Rosa L. How best to assess right ventricular function by echocardiography. Cardiol Young. 2015;25(8):1473-1481. doi:10.1017/S1047951115002255
- Orde, S., Slama, M., Yastrebov, K. et al. Subjective right ventricle assessment by echo qualified intensive care specialists: assessing agreement with objective measures. Crit Care 23, 70 (2019). https://doi.org/10.1186/s13054-019-2375-z