Atrial fibrillation symptoms: Why they're easy to miss

The hallmark sign of atrial fibrillation (afib) — a racing, irregular heartbeat — usually comes and goes. During an episode, people may notice a fluttering, pounding sensation in their chest and become lightheaded, dizzy, and breathless. However, at least a quarter of people with afib don’t feel any symptoms, a condition known as silent afib.

“We don’t really know why some people with afib feel symptoms while others do not,” says Dr. Shaan Khurshid, assistant professor of medicine at Harvard Medical School and a cardiac electrophysiologist at Massachusetts General Hospital. Some people notice only heart-related symptoms, others experience only dizziness or shortness of breath, and some people feel a combination. “I’ve had people say they can tell exactly when their afib starts and stops, and others who say they feel absolutely nothing,” he says.

What is atrial fibrillation?

Afib occurs when the heart’s electrical system goes awry. Instead of the heart’s natural pacemaker creating a steady beat, the heart’s upper chambers (atria) quiver rapidly — up to hundreds of times per minute. Most of the electrical impulses telling the lower chambers (ventricles) to contract don’t get through. But many do, causing the heart rate to become irregular and soar to 175 beats per minute (bpm) or higher. A normal heart rhythm is a steady rate between 60 and 100 bpm. Episodes of afib may occur for occasional, brief periods or much longer — even permanently in some people (see “Afib: How long, how often?”).

About one in 11 people ages 65 and older have afib, which is also more common in people with high blood pressure, heart disease, obesity, and sleep apnea.

Common atrial fibrillation symptoms

During a bout of afib, people often say they feel as though their heart is racing, fluttering, pounding, or flip-flopping. Because the ventricles don’t have time to fill normally, less oxygen-rich blood reaches the muscles and tissues, which can make people feel tired and weak. Fluid may build up in the lungs, which can cause breathlessness. Insufficient blood flow to the brain can lead to dizziness, lightheadedness, or fainting. Finally, the rapid heart rate strains the heart, which can further contribute to fatigue.

“A lot of people with afib just say they feel very tired. But some people describe a vague feeling that something’s wrong and can’t be more specific,” says Dr. Khurshid. Another less-discussed symptom that some people experience during afib episodes is feeling as though they need to urinate. “When the atria fibrillate, they stretch and release a hormone called atrial natriuretic peptide,” Dr. Khurshid explains. This hormone signals the kidneys to get rid of excess fluid in the body.

Afib symptoms may be more pronounced during exercise or even everyday activities such as walking or climbing stairs. But people can also become more aware of their irregular heartbeat when they’re quiet and still — for example, when they lie down to sleep at night.

How is afib diagnosed?

Because bouts of afib are often short-lived and sometimes symptomless, diagnosing it can be challenging. The definitive test is an electrocardiogram (ECG), a record of the heart’s electrical activity. But a routine ECG done during an annual checkup lasts only about 10 seconds, so it may not pick up afib that occurs only sporadically.

As a result, diagnosing afib often requires wearing a heart monitor, which uses electronic sensing devices placed on the chest to continuously check the heart’s rhythm. One option is a Holter monitor, a device worn in a pocket or elsewhere on the body with wires connected to several electrodes on the chest. It records an ECG for one to two days. But cardiologists are increasingly using wireless patch monitors, which are about the size of a large band-aid and can record an ECG for up to 14 days.

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