The heart moves blood throughout the body in a continuous, rhythmic loop known as the cardiac cycle. This cycle consists of two primary phases: systole and diastole. Systole represents the active contraction and ejection phase when the heart chambers squeeze to push blood out to the lungs and the rest of the body. Diastole is the subsequent phase of relaxation and filling, where the chambers expand to receive blood returning from circulation. Systolic function refers specifically to the force and effectiveness of the heart’s contraction, determining the amount of blood successfully pumped with each beat.
The Mechanics of Heart Contraction
Systolic function begins when an electrical signal sweeps across the ventricles, the heart’s lower pumping chambers. This signal triggers the ventricular muscle fibers to contract simultaneously, generating immense pressure. When this pressure exceeds the pressure in the upper chambers, the mitral and tricuspid valves—which separate the atria from the ventricles—snap shut, preventing backflow.
The pressure continues to rise until it surpasses the pressure in the major arteries. The semilunar valves (the aortic and pulmonary valves) are then forced open, initiating the ejection phase. Blood is forcefully propelled out of the ventricles into either the aorta (to the body) or the pulmonary artery (to the lungs).
The left ventricle’s systole is particularly forceful, as it must overcome high systemic pressure to pump oxygenated blood to the entire body. The right ventricle pumps deoxygenated blood to the nearby lungs, which requires a much lower pressure. The total volume of blood ejected by the ventricle with a single contraction is known as the stroke volume.
Quantifying Systolic Function: Ejection Fraction
Medical professionals quantify the heart’s pumping efficiency using the Ejection Fraction (EF). This percentage represents the amount of blood pumped out of a ventricle relative to the total amount of blood present just before contraction. The Left Ventricular Ejection Fraction (LVEF) is the primary measurement used because the left ventricle powers systemic circulation.
A healthy LVEF generally falls within the range of 50% to 70%, indicating the heart is effectively pumping out at least half of the blood in its main chamber during systole.
LVEF Ranges
When the LVEF drops to between 41% and 49%, it is categorized as a mildly reduced or mid-range function. An EF that is 40% or lower is considered significantly reduced, indicating substantial impairment in the muscle’s ability to contract and eject blood.
Measurement Methods
Echocardiography, or a heart ultrasound, is the most common and non-invasive method used to calculate the LVEF. Other imaging techniques, such as cardiac Magnetic Resonance Imaging (MRI) or nuclear scans, can also provide a precise measurement of the EF. These tests allow doctors to visualize the heart’s chambers and calculate the volume difference between the filling phase and the volume remaining after contraction.
Understanding Systolic Heart Failure
A severely reduced systolic function is the defining characteristic of Systolic Heart Failure, or Heart Failure with Reduced Ejection Fraction (HFrEF). This diagnosis is applied when the Left Ventricular Ejection Fraction is measured at 40% or less. In this condition, the heart muscle is weakened and cannot contract with sufficient force to push an adequate volume of blood to the body’s tissues.
The reduced pumping efficiency means the body receives less oxygen and fewer nutrients, which can lead to chronic fatigue and weakness. When the left ventricle cannot effectively eject blood, fluid can back up into the lungs, causing shortness of breath, particularly during exertion or when lying flat. Other signs include swelling (edema) in the legs, ankles, or abdomen, as the body struggles to manage fluid balance.