Atrial Fibrillation (AFib) is a heart rhythm disorder characterized by rapid and irregular electrical activation of the heart’s upper chambers. The heart’s ability to pump blood effectively is measured by the Ejection Fraction (EF), which represents the percentage of blood leaving the heart with each contraction. Because a normal heart rhythm is necessary for maintaining pumping strength, AFib can significantly affect the Ejection Fraction, often causing a measurable decline in heart function.
The Mechanics of Reduced Ejection Fraction in AFib
Atrial fibrillation impairs the heart’s pumping efficiency through two primary mechanisms that reduce the volume of blood the ventricles can pump out. The first is the loss of the “atrial kick.” In a normal heartbeat, the atria contract just before the ventricles, providing a final surge of blood that contributes up to 30% of the total volume in the left ventricle.
When AFib occurs, the atria quiver chaotically instead of contracting forcefully, causing the loss of this critical atrial kick. The ventricles receive less blood to begin with, resulting in less blood being pumped out with each beat and lowering the Ejection Fraction. This loss of organized filling is particularly impactful for individuals whose ventricles are already stiff.
The second mechanism relates to the sustained, rapid, and often irregular heart rate that frequently accompanies uncontrolled AFib. A persistently fast heart rate, or tachycardia, does not allow the heart muscle enough time to relax and fill completely between beats. Over time, this chronic overworking can exhaust and weaken the heart muscle, leading to tachycardia-induced cardiomyopathy.
This weakening causes the heart muscle fibers to remodel and dilate, making them less effective at contracting and resulting in a chronically reduced Ejection Fraction. This type of cardiomyopathy is often reversible if the underlying rapid heart rhythm is successfully controlled.
Recognizing and Measuring Decline in Pumping Efficiency
A reduction in Ejection Fraction due to AFib often manifests as symptoms associated with heart failure, where the heart cannot pump enough blood to meet the body’s needs. Patients may notice increasing fatigue and weakness, as their muscles and organs are not receiving adequate oxygenated blood. Shortness of breath, particularly during physical exertion or when lying flat, is another common symptom as fluid backs up into the lungs.
Peripheral swelling, known as edema, can also occur, most noticeably in the legs, ankles, and feet. This happens because the weakened heart is less effective at removing fluid from the body’s tissues. Recognizing these symptoms prompts a medical evaluation to determine the extent of the heart’s pumping decline and to measure the Ejection Fraction.
The Ejection Fraction is most commonly measured using an echocardiogram, or “echo.” This non-invasive ultrasound provides a moving picture of the heart chambers, allowing a clinician to calculate the percentage of blood ejected from the left ventricle with each beat. A normal Ejection Fraction is typically 50% to 70%, and a measurement below 40% is often classified as Heart Failure with Reduced Ejection Fraction (HFrEF).
This diagnostic process confirms whether AFib has led to ventricular dysfunction and guides the subsequent treatment approach. The echo is important for both diagnosis and monitoring the heart’s recovery once treatment has begun.
Strategies for Restoring Heart Function
The primary goal of treatment for reduced Ejection Fraction caused by AFib is to stabilize the heart’s rhythm or rate, allowing the heart muscle to recover strength and function. This is accomplished through two main therapeutic strategies: rate control and rhythm control.
Rate control focuses on slowing the rapid ventricular rate to a sustainable pace, typically using medications like beta-blockers or calcium channel blockers. These drugs block chaotic electrical signals from the atria, preventing them from being transmitted too frequently to the ventricles. Slowing the heart rate allows the ventricles more time to fill, which improves the Ejection Fraction and can potentially reverse tachycardia-induced damage.
Rhythm control aims to restore and maintain the heart’s normal sinus rhythm, immediately bringing back the beneficial atrial kick. This strategy often involves antiarrhythmic drugs to help maintain a coordinated electrical pattern. Electrical cardioversion may also be used, delivering a controlled electrical shock to briefly reset the heart back to a normal rhythm.
For a more permanent solution, catheter ablation is a specific procedure used to eliminate the erratic electrical signals causing AFib. During ablation, a physician uses flexible tubes to reach the heart and delivers energy to create small scars that block the abnormal electrical pathways. Successful ablation restores a normal rhythm, which is frequently associated with a significant and lasting improvement in the Ejection Fraction.