The Left Ventricular Ejection Fraction (LVEF) is a calculation that serves as a fundamental measure of the heart’s overall pumping capacity. Expressed as a percentage, LVEF represents the efficiency with which the heart’s main chamber expels blood with each contraction. Physicians rely on the LVEF to assess the functional health of the heart muscle and to guide diagnosis, risk stratification, and treatment decisions for a variety of cardiovascular conditions.
Understanding Left Ventricular Ejection Fraction
The left ventricle is the largest and strongest of the heart’s four chambers, responsible for pumping oxygen-rich blood into the aorta for distribution to the entire body. Its action is a two-part cycle: the diastole phase, where the muscle relaxes and the chamber fills with blood, and the systole phase, where the muscle contracts and ejects blood. The LVEF is a direct measurement of the heart’s performance during this contraction phase.
The ejection fraction is mathematically derived as the stroke volume—the amount of blood pumped out in one beat—divided by the total volume of blood in the ventricle just before the contraction, known as the end-diastolic volume. This ratio is then multiplied by 100 to express the result as a percentage. For example, if the left ventricle contains 100 milliliters of blood at the end of diastole and pumps out 60 milliliters, the LVEF would be 60%. It is physically impossible for the ventricle to expel all the blood it contains; a portion must remain to maintain pressure and chamber integrity.
The Clinical Significance of LVEF 55
An LVEF of 55% falls squarely within the established normal range for a healthy adult heart, generally accepted to be between 50% and 70%. This reading indicates that the left ventricle is contracting efficiently and is able to maintain adequate blood flow to meet the body’s metabolic demands.
A reading of 55% is considered normal. LVEF values help categorize heart function: 41% to 49% is classified as mildly reduced, and a measurement of 40% or less is considered reduced. The precise LVEF value is used to differentiate types of heart failure, such as heart failure with preserved ejection fraction (HFpEF, where the LVEF is \(\geq\)50%), from heart failure with reduced ejection fraction (HFrEF, where the LVEF is \(\leq\)40%).
While 55% is a healthy finding, it sits near the lower boundary of the normal range (50%). This low-normal position may prompt a clinician to review the patient’s overall cardiovascular risk profile, especially if risk factors like hypertension or diabetes are present. Some studies suggest that LVEF readings in the 50% to 55% range may be associated with a slightly increased future risk for developing heart failure compared to individuals with a higher LVEF.
Diagnostic Tools Used to Measure LVEF
The most common and widely accessible method used to obtain the LVEF measurement is transthoracic echocardiography, often simply called an echo. This non-invasive ultrasound procedure uses sound waves to create moving images of the heart’s chambers and valves. The LVEF is typically calculated using the modified Simpson’s rule, or the biplane method of disks.
This method involves tracing the inner border of the left ventricle in two different image planes, capturing the volume at the end of the filling phase (end-diastole) and the end of the pumping phase (end-systole). The software then mathematically divides the ventricle into a series of small, stacked disks to estimate the total volume at these two points in time.
Other imaging techniques are used to confirm or provide more precise LVEF measurements, especially when echocardiogram images are unclear. Cardiac Magnetic Resonance Imaging (CMR) is considered the “gold standard” because it provides highly detailed, three-dimensional images without relying on geometric assumptions. Nuclear ventriculography (MUGA scan) is another technique that labels red blood cells with a small amount of radioactive tracer, allowing a specialized camera to track the blood volume during contraction and relaxation.
Medical Conditions That Influence Ejection Fraction
A decrease in LVEF below the normal range is often the result of underlying medical conditions that damage or weaken the heart muscle, impairing its ability to contract forcefully. One of the most common causes is Coronary Artery Disease (CAD), where blockages in the heart’s arteries limit blood flow and oxygen supply to the muscle. A heart attack, the acute manifestation of CAD, permanently damages a section of the muscle, causing scar tissue that cannot contract and lowering the overall LVEF.
Cardiomyopathies, or diseases of the heart muscle, represent another significant category of influence. Dilated cardiomyopathy, for example, causes the left ventricle to stretch and become thin, drastically reducing the muscle’s contractility and resulting in a low LVEF. Conversely, Hypertrophic Cardiomyopathy causes the muscle wall to thicken, often resulting in a preserved LVEF, but the stiff muscle impairs the heart’s ability to fill completely during the relaxation phase.
Chronic high blood pressure, or hypertension, forces the left ventricle to pump against persistently elevated resistance, known as afterload. This chronic strain causes the muscle wall to thicken, leading to Left Ventricular Hypertrophy (LVH). Initially, this thickening helps maintain a normal LVEF, but over time, the stiff, thickened muscle can fail to relax fully, leading to heart failure with preserved ejection fraction. Eventually, the muscle may fail completely, causing the LVEF to drop.
Valvular Heart Disease also profoundly affects the LVEF by creating either a flow obstruction or a backflow of blood. Aortic stenosis (narrowing of the aortic valve) increases the resistance the ventricle must overcome to eject blood, similar to hypertension. Mitral regurgitation (a leaky mitral valve) causes blood to flow backward into the left atrium, placing a significant volume overload on the left ventricle and leading to a reduced LVEF.