Atrial fibrillation — an irregular, rapid heartbeat that inhibits blood flow — can occur for no known reason at all, but it is usually related to several common risk factors for cardiovascular disease.

The number one risk factor for AF is age. Most cases occur in people over 60. The average age for patients with atrial fibrillation is 66.8 years for men and 74.6 years for women.

This happens because with advancing age, the heart’s electrical system can simply become worn out, much like the wiring in an old lamp can cause a short circuit.

In addition, as people age they are more likely to develop other risk factors, such as high blood pressure, which causes the heart to work too hard to pump blood. This thickens and weakens the heart muscle, leading to fibrillation.

Yet another factor is congestive heart failure, a condition in which fluid builds up because the heart has become too weak to effectively pump.

In fact, atrial fibrillation often causes congestive heart failure — but the reverse can also happen.

Other factors that can contribute to atrial fibrillation include:

• Damage from a previous heart attack

• Heart surgery

• Diabetes

• Heart valve disease

When you have AF, your heart is functioning at only 75 percent, so it’s not surprising that fatigue is a common symptom.

It’s also important to understand that some people do not have any symptoms at all. This is called “silent atrial fibrillation,” and people who experience it are at as great a risk as those with recognizable symptoms.

Less common causes of atrial fibrillation include:

• Pericarditis (inflammation of the sac that holds the heart)

• Sleep apnea (a common sleep disorder that causes high blood pressure)

• Viral infection

• Medications, such as cough and cold medicine, decongestants, and asthma inhalers

• Chronic lung diseases like asthma and emphysema

One of my patients, Jim, was healthy during most of the year until the season when sugar cane is burned in Florida.

During the burning, particles in the air aggravated his asthma, which in turn put stress on his heart, resulting in atrial fibrillation.