Ventricular Ejection Fraction
Ejection Fraction (EF) is the fraction of blood ejected by the ventricle relative to its end-diastolic volume. Therefore, EF is calculated from:
EF = (SV / EDV) ⋅ 100
where SV = stroke volume, EDV = end-diastolic volume
Ejection fraction is most commonly measured using echocardiography. This non-invasive technique provides good estimates of end-diastolic (EDV) and end-systolic volumes (ESV), and stroke volume (SV = EDV-ESV). Normally, EF is >60%. For example, if the SV is 75 ml and the EDV is 120 ml, then the EF is 63%. During exercise in highly conditioned individuals, the increased stroke volume (caused primarily by increased inotropy), can result in the EF exceeding 90%.
In heart failure, particularly in dilated cardiomyopathy, EF can become very small as SV decreases and EDV increases. In severe heart failure, EF may be 20% or less. EF is often used as a clinical index to evaluate the the inotropic status of the heart. However, it is important to note that there are circumstances in which EF can be normal, yet the ventricle is in failure. One example is diastolic dysfunction caused by hypertrophy in which filling is impaired because of low ventricular compliance and stroke volume is therefore reduced. In this case, both SV and EDV can be reduced such that EF does not change appreciably. For this reason, low ejection fractions are generally associated with systolic dysfunction rather than diastolic dysfunction.