Ejection fraction

An ejection fraction (EF) is the fraction of blood ejected from a ventricle of the heart with each heartbeat. It is calculated by dividing the stroke volume by the end-diastolic volume, and is an inherent measure of the pumping efficiency of the heart. Hearts that beat busily but do not succeed in expelling much blood are said to be in heart failure. Left ventricular ejection fraction is a measure of the efficiency of pumping into the systemic circulation, whereas right ventricular ejection fraction is a measure of the efficiency of pumping into the pulmonary circulation.

Ejection fraction is commonly measured by an echocardiogram and serves as a general measure of a person's cardiac function. Ejection fraction is typically low in patients with the systolic form of congestive heart failure. In contrast, one way that ejection fraction can be normal and yet heart failure can still exist is if the end-diastolic volume is too small; if there is not much blood in the ventricle to begin with, then no matter how much of it you eject, stroke volume is still small and therefore so is cardiac output. Thus SV and CO are absolute measurements, whereas EF is inherently a relative measurement (as is any fraction, ratio, or percentage).

Medical uses

Ejection fraction is an important determinant of the severity of systolic heart failure. Causes of systolic heart failure include coronary artery disease, congenital heart disease, valvular heart disease, conduction disease, infectious disease, and granulomatous disease among others.

Unlike heart rate, which can be high or low in a healthy person and can vary over the course of the day, a low ejection fraction is always associated with disease.

Measurement

Ejection fraction is commonly measured by echocardiography, in which the volumes of the heart's chambers are measured during the cardiac cycle. Ejection fraction can then be obtained by dividing the volume ejected by the heart (stroke volume) by the volume of the filled heart (end-diastolic volume).

Ejection fraction can also be measured by computed tomography (CT scan), magnetic resonance imaging (MRI), ventriculography, gated SPECT and radionuclide angiography (MUGA) scanning. A MUGA scan involves the injection of a radioisotope into the blood and detecting its flow through the left ventricle. Historically, the gold standard for measurement of the ejection fraction is ventriculography.

Physiology

Normal values

Ventricular volumes
Measure	Right ventricle	Left ventricle
End-diastolic volume	144 mL (± 23 mL)	142 mL (± 21 mL)
End-diastolic volume / body surface area (mL/m2)	78 mL/m2 (± 11 mL/m2)	78 mL/m2 (± 8.8 mL/m2)
End-systolic volume	50 mL (± 14 mL)	47 mL (± 10 mL)
End-systolic volume / body surface area (mL/m2)	27 mL/m2 (± 7 mL/m2)	26 mL/m2 (± 5.1 mL/m2)
Stroke volume	94 mL (± 15 mL)	95 mL (± 14 mL)
Stroke volume / body surface area (mL/m2)	51 mL/m2 (± 7 mL/m2)	52 mL/m2 (± 6.2 mL/m2)
Ejection fraction	66% (± 6%)	67% (± 4.6%)
Heart rate	60–100 bpm	60–100 bpm
Cardiac output	4.0–8.0 L/minute	4.0–8.0 L/minute

In a healthy 70-kilogram (150 lb) man, the stroke volume is approximately 70 mL and the left ventricular end-diastolic volume (EDV) is 120 mL, giving an ejection fraction of 70⁄120, or 0.58 (58%).

Right ventricular volumes being roughly equal to those of the left ventricle, the ejection fraction of the right ventricle physiologically matches that of the left ventricle within mathematically narrow beat-to-beat limits.

Healthy individuals typically have ejection fractions between 50% and 65%. However, normal values depend upon the modality being used to calculate the ejection fraction, and some sources consider an ejection fraction of 55% to 75% to be normal. Damage to the muscle of the heart (myocardium), such as that sustained during myocardial infarction or in atrial fibrillation or a plurality of etiologies of cardiomyopathy, compromises the heart's ability to perform as an efficient pump (ejecting blood) and, therefore, reduces ejection fraction. This reduction in the ejection fraction can manifest itself clinically as heart failure. A low ejection fraction has its cutoff below 40% with symptomatic manifestations constant at 25%. In the USA, a chronically low ejection fraction less than 30% is qualifying support for eligibility of disability benefits from the Social Security Administration.

Healthy older adults favorably adapt as the ventricles become less compliant and are routinely echocardiographically proven to have an EF from 55–85% with the help of good genetics and a healthy lifestyle. Compliance, defined as

${\frac {d(volume)}{d(pressure)}}$

is a property of the heart that allows contractility. Encyclopedic documentation of the commonly documented "hyperdynamic" ventricle remains sparse.

The ejection fraction is one of the most important predictors of prognosis; those with significantly reduced ejection fractions typically have poorer prognoses. However, recent studies have indicated that a preserved ejection fraction does not mean freedom from risk.

The QT interval as recorded on a standard electrocardiogram (EKG) represents ventricular depolarazation and ventricular repolarazation and is rate-dependent.

Physics

In mathematics allowed by medical imaging, EF is applied to both the right ventricle, which ejects blood via the pulmonary valve into the pulmonary circulation, and the left ventricle, which ejects blood via the aortic valve into the cerebral and systemic circulation.

EF is essentially a ratio; a mathematical expression of forward movement of blood out of the heart contrasted to the amount retained in a single cardiac cycle. One important mathematical expression involves easily reproduced volumetrics.

By definition, the volume of blood within a ventricle immediately before a contraction is known as the end-diastolic volume (EDV). Likewise, the volume of blood left in a ventricle at the end of contraction is end-systolic volume (ESV). The difference between EDV and ESV represents a ratio between the ventricles full and emptied. This ratio allows many variables such as stroke volume (SV) and Cardiac Output (CO). SV describes the volume of blood ejected from the right and left ventricles with each heartbeat. Ejection fraction is the fraction of the end-diastolic volume that is ejected with each beat; that is, it is stroke volume (SV) divided by end-diastolic volume (EDV):

$E_{f}(\%)={\frac {SV}{EDV}}\times 100$

Where the stroke volume is given by:

$SV=EDV-ESV$

History

As a mathematical term, ejection fraction is an extension of well documented work by Adolph Fick entitled cardiac output. Fick's theory gradually merged to fit the precision of wall motion mathematics first defined by Laplace. This led to the application of compliance or delta V (volume)/ delta P (pressure) to the required mathematics. Myocardial compliance represents a variable ratio between pressure and volume. Applied to the heart, this appreciation led to further progress represented by length-tension constructs I.e. the Frank–Starling law of the heart. Youngs' Modulus lent itself to elasticity, another important ratio of stress and strain. The gathered mathematics eventually birthed medical imaging, gradually followed by cardiac imaging.