What Is Atrial Fibrillation?

A racing heartbeat is familiar to anyone who has had to run up a flight of stairs or has been in a frightening situation. But for the estimated 2.6 million Americans who suffer from atrial fibrillation (AF or AFib), that sensation of a fast, irregular, and chaotic heartbeat all too often becomes a way of life. Moreover, for many, it severely impairs their quality of life and may put their health at risk. Recent studies have reported a link between AF and dementia.

AF is remarkably common. It is found in approximately 1 percent of the general population, and it’s the most common cardiac arrhythmia seen by doctors today. Men and women over age 40 have a one in four lifetime risk of developing AF. The ailment becomes more likely with age. AF is rare before age 50, but by age 80, 10 percent of individuals will have AF. It’s estimated that 70 percent of all AF patients are between the ages of 65 and 85. By the year 2050, some 12 million Americans are expected to have AF due to an aging population as well as the obesity epidemic, with more than half of people affected by AF expected to be over the age of 80.

How AF affects the heart

The heart beats close to 100,000 times a day. That’s about 70 beats per minute, every minute, every hour, every day, every year. However, for some people, the rhythmic lub-dub, lub-dub, lub-dub of the heart is not as precise as a Rolex. For some reason, the heart’s electrical system goes haywire, leading to less efficient blood circulation and an irregular and chaotic pulse. That’s because the heart’s atria (upper chambers) quiver rather than contract forcefully, which then leads to an irregular—and often rapid—beating of the lower heart chambers, called the ventricles.

The sinoatrial (SA) node (also referred to as the sinus node), which is located in the upper right atrium, acts as a natural pacemaker that governs the heart’s rate and rhythm. Special muscle fibers in the heart then conduct these electrical messages through the chambers. When a normally functioning SA node controls heart rhythm, it’s called “normal sinus rhythm.”

However, the specialized cells of the SA node are not the only ones capable of controlling electrical stimulation; the millions of heart muscle cells all have the ability to create their own electrical signals, disrupting the normal sinus rhythm in the process.

If these cells misfire, the heart may race from a normal resting rate of 60 to 90 beats per minute (bpm) up to 200 bpm, then slow down after a few moments. This irregularity may occur hundreds of times a day, or only in several short episodes a year.

These misfirings can result in what are called premature or ectopic beats—that is, coming from a source other than the SA node. If there is a so-called “run” of premature beats in the atria, the heart rhythm can go into what’s called atrial fibrillation. This fibrillation—the multiple or rapid firing of electrical signals from different areas of the atria rather than the SA node—alters the movement of blood through the atria.

In cases where a person’s heartbeat is extremely fast—as high as 190 beats per minute after getting out of bed or rising from a chair—symptoms such as shortness of breath, dizziness, weakness, palpitation, or chest pain may occur, and can range from mild to severe. Some people complain that it feels as if “my heart is going to jump out of my chest.”

AF, by far the most common sustained arrhythmia, can last for minutes, hours, days, or weeks. While it’s not always possible—or even necessary—to restore the heart to normal rhythm, most physicians attempt to restore the normal tempo of a healthy heart for those who have symptoms and an impaired quality of life.

AF and stroke

Contrary to popular belief, AF itself is not usually life threatening. However, the presence of AF increases the risk of blood clots (embolisms) forming in the heart, and if a clot travels to the brain, a stroke will result. The stroke risk in patients with AF is up to seven times that of the general public—and the incidence of stroke attributable to AF increases with age, dramatically so after age 80.

Upward of 24 percent of all ischemic strokes (strokes caused by a blood clot blocking a narrowed artery or a clot that travels to the brain from somewhere else in the body) are due to AF. Moreover, strokes related to AF are often major strokes that have worse outcomes than non-AF strokes, with a greater likelihood of significant disability or death.

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HealthAfter50 was published by the University of California, Berkeley, School of Public Health, providing up-to-date, evidence-based research and expert advice on the prevention, diagnosis, and treatment of a wide range of health conditions affecting adults in middle age and beyond. It was previously part of Remedy Health Media's network of digital and print publications, which also include HealthCentral; HIV/AIDS resources The Body and The Body Pro; the UC Berkeley Wellness Letter; and the Berkeley Wellness website. All content from HA50 merged into Healthcentral.com in 2018.