Medically reviewed in June 2022
In a healthy heart, an electrical signal at the top of the heart prompts it to contract, squeezing blood from the two upper chambers (the atria) into the two lower ones (the ventricles). As the signal travels down your heart, it then prompts the ventricles to contract, pushing blood to the rest of your body. Once empty, the ventricles relax until another signal starts the process again. This constant contracting and relaxing of your heart is your heartbeat, or heart rhythm.
But what happens if the signal doesn’t travel through the heart in a steady, organized fashion?
Then you have a heart rhythm problem—or an arrhythmia. There are several types, such as premature (extra) beats. This is most common type of arrhythmia, and it doesn’t usually pose a worrisome health risk. It typically feels like a skipped beat or a fluttering in the chest. But sometimes the signals go haywire, causing potentially serious problems. If left unchecked, atrial fibrillation (AFib) can lead to a stroke and even heart failure. Knowing more about the heart’s electrical system will help you understand the causes, symptoms and risks of AFib, and how your healthcare provider might choose to treat it.
The heart’s electrical system
“The heart’s electrical system is a very organized, synchronous, very smart system,” says Guru Mohanty, MD, a cardiac electrophysiologist with Chippenham Hospital in Richmond, Virginia. “Think of it as a room with a switch that lights up the room.”
The switch of the heart is a cluster of cells known as the sinoatrial (SA) node, he says. Normally the SA node sends one signal down throughout the heart. “With AFib, the system becomes disorganized and irregular,” Dr. Mohanty says. The signals come from somewhere other than the SA node. “It’s like there are hundreds of switches at the top flipping on and off and not talking to each other,” he says. “It gets a signal from one spot and beats, from another spot and beats. When all these signals come in, they make the heart beat irregularly.”
The net effect of this irregular heartbeat is that the atria don’t empty properly. The blood that remains pools in the upper chambers and becomes static, making it possible for blood clots to form. Clots in turn can break off and block blood flow to the brain, causing stroke.
Causes and symptoms
The risk of developing AFib increases with age, and it’s often found with other heart diseases.
Some of the more common causes of AFib include chronic high blood pressure, heart attacks and heart failure, and it’s sometimes a complication of heart surgery. Other non-heart-related causes can include sleep apnea, emphysema and other lung diseases, and an overactive thyroid. A study of more than 14.3 million people published in January 2017 in the Journal of the American College of Cardiology found that people who abused alcohol were at more than double the risk of afib as people who didn't.
Sometimes AFib has no symptoms, and sometimes symptoms can be mild or severe. Mild symptoms can include mild chest discomfort, heart palpitations or a rapid heartbeat, lightheadedness and mild shortness of breath. Chest discomfort and shortness of breath can also be more severe, and people with AFib can faint or feel confused due to reduced blood flow to the brain.
Diagnosis and treatment
Mohanty says that the electrocardiogram, or EKG, is the tool that doctors use to diagnose AFib. The EKG reads the electrical signals the heart puts out and can tell the speed, rhythm and strength of the signals.
Knowing when AFib started can be important. Healthcare providers can shock the heart back to its normal rhythm with a process known as electrical cardioversion. If you know AFib started within the last 48 hours, it’s safer to assume there are no blood clots in the area, which could be dislodged with cardioversion.
Drugs known as anti-arrhythmics can also get the heart back to a normal rhythm, says Mohanty. Healthcare providers often prescribe blood thinners to prevent stroke when they discover AFib. A minimally invasive surgical process called catheter ablation, which burns or freezes certain heart cells to stop the abnormal rhythm, can also help, according to Mohanty.
“Unfortunately, none of these treatments are cures,” says Mohanty. “But they can be highly effective and can suppress the atrial fibrillation for a long time.” Mohanty also points out that although a healthy diet and exercise don’t impact AFib specifically, both are important for overall heart health and to reduce the risk of some possible causes of afib. “Exercising regularly, not smoking and eating well are all important for cardiovascular health and wellbeing,” he says.
