Causes

To understand the causes of A-fib, it may be helpful to know how the heart typically beats.

The typical heart has four chambers — two upper chambers (atria) and two lower chambers (ventricles). Within the upper right chamber of the heart (right atrium) is a group of cells called the sinus node. The sinus node is the heart's natural pacemaker. It produces the signal that starts each heartbeat.

In a regular heart rhythm:

• The signal travels from the sinus node through the two upper heart chambers (atria).
• The signal passes through a pathway between the upper and lower chambers called the atrioventricular (AV) node.
• The movement of the signal causes your heart to squeeze (contract), sending blood to your heart and body.

In atrial fibrillation, the signals in the upper chambers of the heart are chaotic. As a result, the upper chambers shake (quiver). The AV node is then bombarded with signals trying to get through to the lower heart chambers (ventricles). This causes a fast and irregular heart rhythm.

The heart rate in atrial fibrillation may range from 100 to 175 beats a minute. The normal range for a heart rate is 60 to 100 beats a minute.

Causes of atrial fibrillation

Problems with the heart's structure are the most common cause of atrial fibrillation. Possible causes of atrial fibrillation include:

• Coronary artery disease
• Heart attack
• Heart defect that you're born with (congenital heart defect)
• Heart valve problems
• High blood pressure
• Lung diseases
• Physical stress due to surgery, pneumonia or other illnesses
• Previous heart surgery
• Problem with the heart's natural pacemaker (sick sinus syndrome)
• Sleep apnea
• Thyroid disease such as an overactive thyroid (hyperthyroidism) and other metabolic imbalances
• Use of stimulants, including certain medications, caffeine, tobacco and alcohol
• Viral infections

Some people who have atrial fibrillation have no known heart problems or heart damage.