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Atrial fibrillation and heart disease

What is normal heart rhythm?

The heart has four chambers, or areas. During each heartbeat, the upper chambers (atria) contract, followed by the two lower chambers (ventricles). This action is directed by the heart's electrical system.

The electrical impulse begins in an area called the sinus node, located in the upper part of the right atrium. When the sinus node fires, an impulse of electrical activity spreads through the right and left atria, causing them to contract, forcing blood into the ventricles.

Then the electrical impulses travel in an orderly manner to another area called the atrioventricular (AV) node and HIS-Purkinje network. The AV node is the electrical bridge that allows the impulse to go from the atria to the ventricles. The HIS-Purkinje network carries the impulses throughout the ventricles. The impulse then travels through the walls of the ventricles, causing them to contract. This forces blood out of the heart to the lungs and the body. The pulmonary veins empty oxygenated blood from the lungs to the left atrium. A normal heart beats in a constant rhythm -- about 60 to 100 times per minute at rest.

What is atrial fibrillation?

Atrial fibrillation (AF) is the most common type of irregular heartbeat. It affects up to 500,000 people in the UK and becomes more likely with increasing age.

If you have AF, the impulse does not travel in an orderly fashion through the atria. Instead, many impulses begin simultaneously and spread through the atria and compete for a chance to travel through the AV node.

The firing of these impulses results in a very rapid and disorganised heartbeat. The rate of impulses through the atria can range from 300 to 600 beats per minute. Luckily, the AV node limits the number of impulses it allows to travel to the ventricles. As a result, the pulse rate is often less than 150 beats per minute, but this is often fast enough to cause symptoms. 

What are the symptoms of atrial fibrillation?

You may have atrial fibrillation without having any symptoms at all. If you have symptoms, they may include:

  • Heart palpitations (a sudden pounding, fluttering, or racing feeling in the chest).
  • Lack of energy; feeling over- tired.
  • Dizziness (feeling faint or light-headed).
  • Chest discomfort (pain, pressure, or discomfort in the chest).
  • Shortness of breath (difficulty breathing during normal activities or even at rest).

What causes atrial fibrillation?

Atrial fibrillation is associated with many conditions, including:

  • High blood pressure
  • Coronary artery disease (narrowing of the heart arteries)
  • Heart valve disease
  • Having undergone heart surgery
  • Chronic lung disease
  • Heart failure
  • Cardiomyopathy (disease of heart muscle that causes heart failure)
  • Congenital (present at birth) heart disease
  • Pulmonary embolism (blood clot in lungs)
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