Ejection fraction
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The ejection fraction (EF) or, more correctly, left-ventricular ejection fraction (often abbreviated LVEF) is a measure of how much blood the left ventricle of the heart pumps out with each contraction. The normal left ventricle has an average volume of 100ml and with each heart beat ejects approximately 70 ml, the stroke volume. Therefore the ejection fraction can be calculated as the volume ejected during ventricular systole divided by the volume of blood in the left ventricle at the end of filling i.e. the end diastolic volume (LVEDV). In this case the calculation is easy and can be expressed as the ratio 0.7 or more commonly as a percentage 70%. Evidently any damage to the muscular wall of the heart, due for instance to myocardial infarction or cardiomyopathy, will lead to a reduced efficiency of action and a reduction in the EF. This manifests itself clinically as heart failure. This fraction may be severely reduced, even down to below ten per cent. The EF is a very important measure in cardiology as it is closely linked to prognosis. Those with a significantly reduced EF have a poor prognosis.
The most commonly used method to measure the ejection fraction is echocardiography. Other methods include cardiac MRI, fast scan cardiac computed axial tomography (CT) imaging, ventriculography 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 current gold standard for the measurement of ejection fraction is ventriculography.