What Causes Atrial Fibrillation?

Atrial Fibrillation affects millions of people. Most are over the age of 65 years and have other underlying conditions that put them at a higher risk such as high blood pressure, hyperthyroidism, lung problems, diabetes, alcoholism, or drinking high levels of caffeine. It may, in some cases, occur in otherwise healthy individuals, where these conditions do not exist.

To pump blood, your heart muscles must contract and relax in a coordinated rhythm. Contraction and relaxation are controlled by electrical signals that travel through your heart muscles.

Your heart consists of four chambers – two upper chambers (atria) and two lower chambers (ventricles). Within the upper right chamber of your heart (right atrium) is a group of cells called the sinus node. This is your heart’s natural pacemaker. The sinus node produces the impulse that starts each heartbeat.

Normally, the impulse travels first through the atria, then through a connecting pathway between the upper and lower chambers of your heart called the atrioventricular (AV) node. As the signal passes through the atria, they contract, pumping blood from your atria into the ventricles below. A split second later, as the signal passes through the AV node through the right and left bundle branches to the ventricles, the ventricles contract, pumping blood out to your body.

In atrial fibrillation, the upper chambers of your heart (atria) experience chaotic electrical signals. As a result, they quiver. The AV node – the electrical connection between the atria and the ventricles – is overloaded with impulses trying to get through to the ventricles. The ventricles also beat rapidly, but not as rapidly as the atria. The reason is because the AV node is like a highway on-ramp – only so many cars can get on at one time. The result is an irregular and fast heart rhythm. The heart rate in atrial fibrillation may range from 100 to 175 beats a minute or sometimes more. The normal range for a heart rate is 60 to 100 beats a minute.

Possible Causes
Abnormalities or damage to the heart’s structure is the most common cause of atrial fibrillation. Diseases affecting the heart’s valves or pumping system are common causes, as is long-term high blood pressure. However, some people who have atrial fibrillation don’t have underlying structural heart disease, a condition called lone atrial fibrillation. In lone atrial fibrillation, the cause is often unclear. Serious complications are usually rare in lone atrial fibrillation.

Possible causes of Atrial Fibrillation include:

  • High blood pressure
  • Heart attacks
  • Sleep apnea
  • Previous heart surgery
  • Abnormal heart valves
  • Congenital heart defects
  • An overactive thyroid or other metabolic imbalance
  • Exposure to stimulants, such as medications, caffeine or tobacco, or to alcohol
  • Sick sinus syndrome – this occurs when the heart’s natural pacemaker stops functioning properly
  • Emphysema or other lung diseases
  • Viral infections
  • Stress due to pneumonia, surgery, or other illnesses