Ejection Fraction (EF) is a measurement that provides a percentage of how efficiently the heart is pumping blood. This metric is obtained through imaging tests and assesses the strength of the heart muscle, particularly the left ventricle. A reduced EF value signals compromised function, often leading to a diagnosis of heart failure. Monitoring this percentage allows medical professionals to track the progression of heart conditions and evaluate treatment effectiveness.
How the Heart Calculates Ejection Fraction
The ejection fraction reflects the difference between the volume of blood the ventricle holds and the volume it successfully pushes out. During the heart’s resting phase (diastole), the chamber fills to its maximum capacity, called the End-Diastolic Volume (EDV). When the heart contracts (systole), it expels blood, but some volume remains behind, known as the End-Systolic Volume (ESV). The volume ejected with each beat is the Stroke Volume (SV), calculated by subtracting ESV from EDV.
The ejection fraction is derived by comparing the Stroke Volume to the initial End-Diastolic Volume. Although both ventricles have an EF, the Left Ventricular Ejection Fraction (LVEF) is the standardized and most commonly cited measurement. This is because the left side pumps oxygenated blood to the entire body, while the right side pumps deoxygenated blood only to the lungs.
Interpreting Ejection Fraction Values
The specific numerical ranges of the LVEF categorize the heart’s pumping function and guide clinical diagnosis. A normal, healthy LVEF generally falls between 50% and 70%, indicating that the heart is ejecting at least half of the blood within the main pumping chamber with each contraction.
A mildly reduced value is often in the range of 41% to 49%, which may indicate early dysfunction and is classified as Heart Failure with Mid-Range Ejection Fraction (HFmrEF). When the LVEF drops to 40% or lower, it is considered significantly reduced and is used to diagnose Heart Failure with Reduced Ejection Fraction (HFrEF). The lower the percentage, the more severely compromised the heart’s pumping ability is.
Diagnostic Methods for Measurement
Measuring the ejection fraction requires specialized imaging techniques to precisely calculate the blood volumes within the heart chambers. The most widely used method is the echocardiogram, or “echo,” a non-invasive ultrasound of the heart. This test uses sound waves to create moving images of the heart’s structure and blood flow, providing a reliable estimate of the LVEF.
For the highest level of accuracy, Cardiac Magnetic Resonance Imaging (CMR) is considered the gold standard for EF measurement. CMR provides exceptionally detailed three-dimensional images of the heart, allowing for a more exact calculation of the ventricular volumes. Alternative methods include Nuclear Scans, such as the Multigated Acquisition (MUGA) scan, which uses a small amount of radioactive tracer to track blood and calculate the EF.
Underlying Conditions That Reduce Ejection Fraction
A reduction in ejection fraction indicates that the heart muscle has been weakened or damaged, impairing its ability to contract forcefully. The most common cause is a prior myocardial infarction (heart attack), where a blockage starves the muscle of oxygen, leading to scarring and permanent loss of contractile tissue. This damaged muscle cannot participate effectively in the pumping action, which lowers the overall EF.
Chronic, uncontrolled high blood pressure (hypertension) is another frequent cause of reduced EF. The heart must work against high resistance, causing the muscle to stretch and weaken, often resulting in dilated cardiomyopathy. Other causes include valvular heart disease, which strains the muscle, and certain chemotherapy drugs or long-standing diabetes that cause direct toxicity to the heart muscle cells.