# Fractional shortening for estimation of ejection fraction

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## Fractional shortening (FS) for estimating systolic function

Fractional shortening (FS) is calculated by measuring the percentage change in left ventricular diameter during systole. It is measured in parasternal long axis view (PLAX) using M-mode. The end-systolic and end-diastolic left ventricular diameters are measured. The following formula is used to calculate fractional shortening:

FS (%) = (LVEDD – LVESD / LVEDD) • 100

Fractional shortening is a rather poor measure of left ventricular systolic function. This is due to the following reasons:

- Left ventricular geometry must be normal.
- There must not be regional differences in contractile function. Otherwise, the point of measurement may not be representative.
- Ventricular activation must be normal. For example, in the setting of left bundle branch block (LBBB), fractional shortening is not representative of ventricular function, since the activation proceeds abnormally.

### Normal value for fractional shortening (FS)

Normal FS, M-mode | >25% |

Normal FS, 2D measurement | >18% |

### Advantages of fractional shortening

If ventricular geometry is normal and there are no regional wall motion abnormalities, then fractional shortening correlates strongly with ejection fraction. Similar to ejection fraction, fractional shortening is affected by preload and afterload. It possible to calculate fractional shortening using measurements in 2D.