In cardiovascular physiology, ejection fraction (EF) represents the volumetric fraction of blood pumped out of the left and right ventricle with each heartbeat or cardiac cycle. In finite mathematics allowed by medical imaging, EF is applied to both the right ventricle, which ejects blood via the pulmonary valve into the pulmonary circulation, or the left ventricle, which ejects blood via the aortic valve into the cerebral and systemic circulation.
Imaging of the physiology of the mammalian heart is the art that allows meaningful mathematical expression defining EF. Noninvasive cardiac imaging has become a worldwide utility enabling study of cardiac performance reproducibly and inexpensively. Simplified, ejection fraction is a mathematical product allowed by cardiac imaging. As a volumetric mathematical term, ejection fraction is an extension of the work of Adolph Fick in cardiac output. Dedicated technology such as echocardiography, computed tomography (CT scan), magnetic resonance imaging (MRI) and radionuclide angiography (MUGA) scanning have definitively allowed clinically relevant mathematics regarding a diversity of myocardial diseases such as ischemia, congenital heart disease, conduction disease, infectious disease, granulomatous disease and resulting heart failure as a sequelae to the original insult which damaged the forward pumping ability of the heart.
|This section does not cite any references or sources. (March 2013)|
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). SV describes a volumetric measurement 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:
|Measure||Typical value||Normal range|
|end-diastolic volume (EDV)||120 mL[non-primary source needed]||65–240 mL[non-primary source needed]|
|end-systolic volume (ESV)||50 mL[non-primary source needed]||16–143 mL[non-primary source needed]|
|stroke volume (SV)||70 mL||55–100 mL|
|ejection fraction (Ef)||58%||55–70%|
|heart rate (HR)||75 bpm||60–100 bpm|
|cardiac output (CO)oo||5.25 L/minute||4.0–8.0 L/min|
In a healthy 70-kilogram (150 lb) man, the SV is approximately 70 mL and the left ventricular 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 changevolume /changepressure 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.[non-primary source needed][non-primary source needed]
|This section does not cite any references or sources. (March 2013)|
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 stroke volume by end-diastolic volume as described above.
Accurate volumetric measurement of performance of the right and left ventricles of the heart is inexpensively and routinely echocardiographically interpreted worldwide as a ratio of the dimension between the ventricles in systole and diastole. For example, a ventricle in greatest dimension could measure 6 cm while in least dimension 4 cm. Measured and easily reproduced beat to beat for ten or more cycles, this ratio may represent a physiologically normal EF of 50-60%. Mathematical expression of this time-dependent ratio can then be interpreted as the greater half as cardiac output and the lesser half as cardiac input.
Other methods of measuring ejection fraction include cardiac MRI, fast-scan cardiac computed axial tomography (CT) imaging, ventriculography, gated SPECT, and the MUGA scan. A MUGA scan involves the injection of a radioisotope into the blood and detecting its flow through the left ventricle. The historical gold standard for the measurement of ejection fraction is ventriculography.
Depending on the burden of systolic heart failure, a physician may make recommendations to help improve EF. Medication for systolic heart failure is commonly prescribed under several ongoing protocols. Other things that could be done to improve how well the heart pumps include:
- Limiting salt – Limiting salt (sodium) to 2,000 mg a day is an important part of maintaining a healthy heart and treating heart failure. With a low EF, the kidneys get less blood than they should. This makes them unable to rid the body of excess water and salt. Eating too much salt can lead to even more fluid buildup. It also increases blood pressure, which makes an already-weakened heart work harder.
- Fluid management – With a low EF, blood can back up in the lungs and force fluid into the breathing spaces. The fluid then builds up, making it difficult to breathe. Excess fluid can also cause weight gain and swelling. Depending on the EF, a doctor may limit the amount of daily fluid intake.
- Physical activity – Exercise can help strengthen the heart and improve how well it pumps blood to the rest of the body. All it takes is 30 minutes a day of activity, even if that activity is walking. It is always recommended that patients consult their doctors about an exercise program that is right for them.
Treating low EF
Many people having survived a heart attack can benefit from a medical device called an implantable cardiac defibrillator (ICD). An ICD is a pacemaker-like device that treats ventricular fibrillation (VF), the deadly heart rhythm that causes sudden cardiac arrest (SCA). Several large clinical studies have been conducted in recent years to see whether ICDs could help prevent SCA in those people whose heart muscle, and its pumping ability, is damaged by a heart attack. People in the studies had an EF of 40 or below. In these studies, survival rates were significantly higher for people with ICDs compared to those that received traditional medical care.
Certain medications help reduce the heart's workload, increase blood flow, widen vessels or eliminate excess water from the body, all of which may help treating low ejection fraction. Prescribed medications may include:
- Inotropes (such as digoxin): Helps the heart to contract more vigorously and effectively, and helps to reduce symptoms.
- Angiotensin II receptor antagonists: Similar to ACE inhibitors, these medications reduce the stress on the heart muscle and may benefit patients with diabetes and heart disease. The medication protects the kidneys from diabetes-related complications.
- Beta blockers: These medications may improve symptoms by slowing the heart's contraction rate and reducing its pumping action, thus lessening the heart's workload.
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- Also, ejection fraction was estimated in this study to be average 59.9% ± 14.4%; range, 18 – 76%, but secondary source (see above) is used in this article instead.
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