Systolic Function: Ejection Fraction Methods, Fractional Shortening & Strain

Ejection Fraction: The Core Formula

Ejection fraction (EF) describes the fraction of end-diastolic volume ejected with each systole:

EF (%) = (EDV − ESV) ÷ EDV × 100

EDV and ESV can come from 2D biplane volumes, 3D volumes, or (historically) single-dimension linear estimates. The method used to obtain EDV and ESV determines the formula's accuracy and its current guideline status.

Simpson Biplane Method (Modified Simpson's Rule)

The biplane method of discs, also called modified Simpson's rule, is the ASE-recommended 2D method for calculating LV volumes and EF. The endocardial border is traced at end-diastole and end-systole in both the apical 4-chamber and apical 2-chamber views. The software divides the traced LV cavity into a stack of parallel discs of equal height between the mitral annular plane and the apex, sums the disc volumes, and averages the two biplane estimates. Because it does not assume a fixed LV shape (unlike single-dimension formulas), it remains reliable in dilated, foreshortened, or asymmetrically remodeled ventricles, which is why it is the current standard of care.

Severity partitions for LVEF are also sex-specific:

Teichholz Method

Before biplane discs became standard, LV volume was often estimated from a single M-mode LVID measurement using a geometric formula assuming a prolate-ellipsoid shape:

LV volume (mL) = [7.0 ÷ (2.4 + D)] × D³

where D is the LV internal diameter in centimeters, applied separately at end-diastole (using LVIDd) and end-systole (using LVIDs) to obtain EDV and ESV, from which EF is then derived using the standard EF formula. Because this method depends entirely on one linear dimension and a fixed geometric assumption, it becomes inaccurate whenever the ventricle is not uniformly shaped — regional wall motion abnormalities, aneurysms, or asymmetric hypertrophy all invalidate the assumption. Current ASE guidance explicitly states that the Teichholz (and Quinones) method is no longer recommended for clinical LV volume or EF measurement, though the formula still appears on the AE exam blueprint and candidates must be able to calculate it correctly and recognize its limitations.

Fractional Shortening

Fractional shortening (FS) is a simpler, single-dimension linear index of systolic function derived directly from the LV internal diameters:

FS (%) = (LVIDd − LVIDs) ÷ LVIDd × 100

A widely used normal range for FS is approximately 25–45%, which broadly corresponds to a normal EF range. Like the Teichholz method, FS relies on a single M-mode dimension measured at the LV base and is therefore only representative of global function in a symmetrically contracting ventricle; it should not be relied upon when regional wall motion abnormalities are present, since the base may contract normally while a distal segment does not.

Global Longitudinal Strain (GLS)

Strain quantifies the percentage deformation (shortening or lengthening) of myocardium relative to its baseline length, most commonly assessed by 2D speckle-tracking echocardiography (STE):

Strain (%) = (Lₜ − L₀) ÷ L₀

Global longitudinal strain (GLS) averages this deformation across all myocardial segments in the standard apical views as the LV shortens along its long axis during systole. Because the myocardium shortens, GLS is reported as a negative number — a more negative value indicates better systolic function.

GLS by speckle tracking is angle-independent, unlike tissue Doppler-derived indices, and has demonstrated incremental prognostic value over LVEF in a wide range of cardiac conditions, including valve disease, cardiomyopathy, and cancer-therapy cardiotoxicity surveillance. Because GLS values vary meaningfully between vendors and software versions, serial comparisons in an individual patient should use the same equipment and software each time. Acquisition begins with the apical long-axis view (to visualize aortic valve opening and closing clicks for accurate timing), followed by the 4- and 2-chamber views; results are commonly displayed as a color-coded 17-segment "bull's-eye" map alongside the numeric peak GLS value.

Technique Pitfalls That Affect Accuracy

All apical-view volumetric and strain measurements share the same acquisition pitfalls, and the AE exam frequently tests recognition of these errors rather than the formulas alone. Apical foreshortening — failing to capture the true long axis and apex — systematically underestimates LV length and therefore underestimates EDV, ESV, and can spuriously alter EF. Endocardial dropout, common in patients with poor acoustic windows, can be corrected with contrast enhancement (LV opacification) when two or more contiguous endocardial segments are not well visualized, per ASE indications for contrast use. For GLS specifically, when regional tracking quality is suboptimal in more than two myocardial segments in a single view, the calculation of that view's contribution to global strain should be avoided altogether rather than reported with reduced confidence.

Choosing the Right Method

On the AE exam, expect scenario-based questions that require recognizing which EF method is appropriate: biplane discs for routine and serial clinical assessment (the current ASE-recommended 2D standard), 3D echocardiography when available and image quality permits (more accurate and reproducible than 2D, without geometric assumptions), GLS as a complementary, more sensitive marker of subclinical systolic dysfunction that can be abnormal even when EF is still preserved, and Teichholz/FS recognized primarily as legacy single-dimension techniques with well-defined geometric limitations rather than current first-line tools.