An ejection fraction (EF) is the fraction of blood ejected from a ventricle of the heart with each heartbeat. EF is readily compared with the ancient term Systole, long understood as a "gathering" of the heart's fibers, and now known as: "to contract" the heart muscle. It is calculated by dividing the stroke volume by the end-diastolic volume, and is a volumetric measure of the pumping efficiency of the heart. A heart muscle that is old or stiff or beating busily without control and is pumping insufficient blood volume manifests as heart failure; it will usually produce a reduced ejection fraction. An EF at or below 25% will present constant symptomatic manifestations. The EF of the left heart, or left ventricular ejection fraction (LVEF), is a measure of the efficiency of pumping into the systemic circulation. The EF of the right heart, or right ventricular ejection fraction (RVEF), is a measure of the efficiency of pumping into the pulmonary circulation (the lungs).
Stroke volume (SV) and cardiac output (CO) are absolute measurements, where EF is inherently a relative measurement--as is any fraction, ratio, or percentage. EF is commonly measured by an echocardiogram and serves as a general measure of a person's cardiac function. It is typically low in patients with the systolic form of congestive heart failure. However, heart failure can exist even as EF presents as normal if the end-diastolic volume (EDV) is too small: that is, if, at the end of diastole, blood volume in the ventricle is reduced, then regardless of how large a fraction is ejected during systole, stroke volume, and therefore cardiac output, can be dangerously low.
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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.
Echocardiogram Congestive Heart Failure Video
Measurement
Ejection fraction is commonly measured by echocardiography, in which the volumes of the heart's chambers are measured during the cardiac cycle. EF is yielded by the product of forward flow (LVEF) and reversed flow (RVEF). 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
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%). Healthy individuals typically have ejection fractions between 50% and 65%.
Notably, some sources consider an ejection fraction of 55% to 75% to be normal; and normal values depend upon the modality being used to calculate the ejection fraction.
Damage to heart muscle, the (myocardium), such as occurring during myocardial infarction, atrial fibrillation, or any of the etiologies of cardiomyopathy compromises the heart's performance as an efficient pump and usually reduces ejection fraction. Such reduction in the EF can manifest itself as heart failure. A low ejection fraction reaches cutoff for sustainable performance below 40%; an EF at or below 25% will present constant symptomatic manifestations. A chronically low ejection fraction less than 30% is qualification for eligibility for disability benefits in the USA. (Right ventricular volumes are roughly equal to those of the left ventricle; thus, beat-to-beat, the EF of the right ventricle usually matches that of the left ventricle within narrow limits.)
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 change in volume over change in pressure:
is a property of the heart that allows contractility. Encyclopedic documentation of the commonly documented "hyperdynamic" ventricle remains sparse. Gerontologists would likely mention a subset of healthy females >70 years with an EF>65%. This is a beneficial adaptation of seemingly pathologic pressure/volume relationships.
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 depolarization and ventricular repolarization 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 (RVEF), and the left ventricle, which ejects blood via the aortic valve into the cerebral and systemic circulation (LVEF).
EF is essentially a ratio; a mathematical expression of forward movement of blood out of the heart opposed to the volume retained in a single cardiac cycle. This ratio has fixed variables of ESV and EDV and unfixed variables of heart rate and stroke volume.
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):
Where the stroke volume is given by:
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 essential 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. Appreciation of fixed variables of End Systolic Volume (ESV) and End Diastolic Volume (ESV) allows unfixed variables of Heart Rate and Stroke Volume in definition of EF. The gathered mathematics eventually birthed medical imaging, followed by cardiac imaging.
Source of the article : Wikipedia
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