Left ventricular (LV) fractional shortening (FS) is a valuable echocardiographic parameter used to assess left ventricular systolic function. While ejection fraction (EF) is more commonly employed, FS offers a complementary perspective and can be particularly useful in specific clinical scenarios. This article provides a detailed overview of LV fractional shortening, including its calculation, normal ranges, comparison with ejection fraction, and its role in diagnosing and managing cardiovascular diseases.
Understanding Fractional Shortening: What is it and how does it differ from Ejection Fraction?
Fractional shortening (FS) quantifies the percentage change in LV internal dimension during systole. It directly reflects the degree of LV contraction and shortening during ejection. In contrast, ejection fraction (EF) represents the percentage of blood ejected from the LV with each contraction. Both parameters assess systolic function, but they do so through different metrics. EF focuses on the volume of blood ejected, while FS focuses on the change in linear dimensions of the LV.
What is Fractional Shortening 2D?
Two-dimensional echocardiography (2D-echo) is the primary imaging modality used to measure fractional shortening. The technique involves acquiring images of the LV in the parasternal long-axis view (PSLAx) during both diastole (end-diastole) and systole (end-systole). These images are then used to measure the internal LV dimensions at these two time points.
How to Calculate Fractional Shortening?
The calculation of fractional shortening is relatively straightforward:
FS (%) = [(LVIDd - LVIDs) / LVIDd] x 100
Where:
* LVIDd: Left Ventricular Internal Dimension during Diastole (end-diastole) – this is the largest internal dimension of the LV during the cardiac cycle.
* LVIDs: Left Ventricular Internal Dimension during Systole (end-systole) – this is the smallest internal dimension of the LV during the cardiac cycle.
These measurements are typically obtained from the parasternal long-axis view (PSLAx) of the echocardiogram, where the LV is optimally visualized. The measurements are taken at the level of the papillary muscles. Accuracy in measuring LVIDd and LVIDs is crucial for obtaining a reliable FS value. Careful attention should be paid to the endocardial borders to avoid inaccuracies caused by poor image quality or artifacts.
LV Fractional Shortening: PLAX View
The parasternal long-axis (PLAX) view is the preferred view for measuring LV fractional shortening. This view provides an optimal visualization of the LV from apex to base, allowing for accurate measurement of the internal dimensions. Other views, such as the apical views, can be used in certain circumstances, but the PLAX view remains the gold standard. It's important to note that measurements taken from different views might show slight variations.
LV Fractional Shortening vs. Ejection Fraction:
While both FS and EF assess LV systolic function, they provide different information. FS is a measure of the *linear* shortening of the LV, while EF is a measure of the *volume* of blood ejected. In most cases, both parameters correlate well, with reduced FS indicating reduced EF. However, there are situations where they may diverge. For example, a patient with a dilated LV may have a normal or even elevated FS despite a reduced EF, as the large LV chamber size can lead to increased linear shortening even with impaired ejection. Conversely, conditions affecting the geometry of the LV, such as hypertrophic cardiomyopathy, can influence FS disproportionately compared to EF.
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