What it is
Left-ventricular fractional shortening (FS) is the percentage change in the LV cavity diameter between end-diastole and end-systole, measured by M-mode echocardiography. It is the quickest, most reproducible bedside index of LV systolic function — a single number that says how much the ventricle’s short axis contracts with each beat.
The method
FS = (LVEDD − LVESD) / LVEDD × 100
- LVEDD = LV end-diastolic diameter (mm)
- LVESD = LV end-systolic diameter (mm)
The end-systolic diameter must be smaller than the end-diastolic diameter (the tool rejects the reverse as a measurement error).
Severity bands
- ≥ 28% — normal (typical pediatric range ~28–44%)
- 25–27% — borderline
- 15–24% — reduced
- < 15% — severely reduced
When to use it
Use FS for a fast, focused assessment of LV systolic function: PICU/NICU haemodynamic evaluation, monitoring cardiotoxic chemotherapy (e.g. anthracyclines), screening for cardiomyopathy, or trending a known patient. Its strength is reproducibility from a single M-mode sweep — handy when a full ejection-fraction quantification is impractical.
Worked example
LVEDD 42 mm, LVESD 30 mm:
- FS = (42 − 30) / 42 × 100 = 12 / 42 × 100 = 28.6%
That clears the 28% cut-off → normal systolic function.
Pitfalls and caveats
- FS is load-dependent. Tachycardia, high afterload, or hypovolaemia shift it independently of true contractility — interpret it alongside the clinical loading conditions.
- It samples one short-axis slice, so it is unreliable with regional wall-motion abnormality or abnormal septal motion (post-cardiac-surgery, conduction abnormality, RV pressure/volume overload, paced rhythm). In those settings, correlate with a volumetric ejection fraction.
- Measurement geometry matters — off-axis M-mode or oblique cursor placement distorts both diameters and therefore the ratio.
- The ~28–44% range is broad and partly age-dependent in children; read FS against age-appropriate reference values, not a single adult threshold.
Run it: Left Ventricular Fractional Shortening (FS)
Decision support for qualified clinicians only — verify against current primary guidelines and your clinical judgement.