Ejection fraction

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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.

Overview[edit]

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):[1]

E_f (\%) = \frac{SV}{EDV}\times100

Where the stroke volume is given by:

SV = EDV - ESV

Normal values[edit]

Measure Typical value Normal range
end-diastolic volume (EDV) 120 mL[2][non-primary source needed] 65–240 mL[2][non-primary source needed]
end-systolic volume (ESV) 50 mL[2][non-primary source needed] 16–143 mL[2][non-primary source needed]
stroke volume (SV) 70 mL 55–100 mL
ejection fraction (Ef) 58% 55–70%[3]
heart rate (HR) 75 bpm 60–100 bpm[4]
cardiac output (CO)oo 5.25 L/minute 4.0–8.0 L/min[5]

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 70120, 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%.[6] 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%.[7] In the USA, a chronically low ejection fraction less than 30% is qualifying support for eligibility of disability benefits from the Social Security Administration.[8]

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.[9][non-primary source needed][10][non-primary source needed]

The QT interval as recorded on a standard electrocardiogram (EKG) represents ventricular depolarazation and ventricular repolarazation and is rate-dependent.[11][non-primary source needed]

Measurement[edit]

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.

Improving EF[edit]

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.[12]
  • 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.[13]

Treating low EF[edit]

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).[14] 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.[14] In these studies, survival rates were significantly higher for people with ICDs compared to those that received traditional medical care.[14]

Medication intervention[edit]

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.[15]
  • 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.[15]
  • 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.[15]

See also[edit]

References[edit]

  1. ^ Morton Kern 5th edition page 180
  2. ^ a b c d Schlosser, Thomas; Pagonidis, Konstantin; Herborn, Christoph U.; Hunold, Peter; Waltering, Kai-Uwe; Lauenstein, Thomas C.; Barkhausen, Jörg (2005). "Assessment of Left Ventricular Parameters Using 16-MDCT and New Software for Endocardial and Epicardial Border Delineation". Am J Roentgenol 184 (3): 765–773. doi:10.2214/ajr.184.3.01840765.  Values:
    • End-diastolic volume (left ventricular) – average 118 and a range of 68 – 239mL and
    • End-systolic volume (left ventricular) – average 50.1 and range, 16 – 143 mL:
    • 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.
  3. ^ O'Connor, Simon (2009). Examination Medicine (The Examination). Edinburgh: Churchill Livingstone. p. 41. ISBN 0-7295-3911-3. 
  4. ^ Normal ranges for heart rate are among the narrowest limits between bradycardia and tachycardia. See the Bradycardia and Tachycardia articles for more detailed limits.
  5. ^ Edwards Lifesciences LLC > Normal Hemodynamic Parameters – Adult 2009
  6. ^ Kumar, Vinay; Abbas, Abul K; Aster, Jon. (2009). Robbins and Cotran pathologic basis of disease (8th ed.). St. Louis, Mo: Elsevier Saunders. p. 574. ISBN 1-4160-3121-9. 
  7. ^ "Heart2008;94:426-428 doi:10.1136/hrt.2007.123877". 
  8. ^ "Ejection fraction and SSA disability benefit eligibility.". 
  9. ^ Owan TE, Hodge DO, Herges RM, Jacobsen SJ, Roger VL, Redfield MM (July 2006). "Trends in prevalence and outcome of heart failure with preserved ejection fraction". N. Engl. J. Med. 355 (3): 251–9. doi:10.1056/NEJMoa052256. PMID 16855265. 
  10. ^ Bhatia RS, Tu JV, Lee DS, et al. (July 2006). "Outcome of heart failure with preserved ejection fraction in a population-based study". N. Engl. J. Med. 355 (3): 260–9. doi:10.1056/NEJMoa051530. PMID 16855266. 
  11. ^ Bazett, H. C. (1920). "An analysis of the time-relations of electrocardiograms". Heart 7: 353–370. 
  12. ^ Zile MR (May 2003). "Heart failure with preserved ejection fraction: is this diastolic heart failure?". Journal of the American College of Cardiology 41 (9): 1519–22. doi:10.1016/S0735-1097(03)00186-4. PMID 12742292. 
  13. ^ Heart Rhythm Society. "Ejection Fraction". Retrieved 23 March 2013. 
  14. ^ a b c http://www.medterms.com/script/main/art.asp?articlekey=7520
  15. ^ a b c http://www.cpmc.org/services/heart/tx/ejtreatment.html