What is Atrial Fibrillation?

On average, over the course of a lifetime, the human heart beats more than two billion times. With each beat, an electrical impulse passes through the electrical system of the heart, causing its four chambers to contract. During each heartbeat, the two upper chambers – the atria – contract, followed by the two lower chambers – the ventricles.

heart illustration

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Each electrical impulse begins in the sinoatrial (SA) node in the upper part of the right atrium. When the SA node fires, the impulse spreads through the right and left atria, causing them to contract and forcing blood into the ventricles. The impulse then travels to the atrioventricular (AV) node – an electrical bridge that allows impulses to go from the atria to the ventricles. As the ventricles contract, blood is forced out of the heart and into the lungs and the body.

At rest, a normal heart beats 60 to100 times per minute. This normal rhythm is known as sinus rhythm. At some point in our lives, each of us feels a skip of a beat or a rapid pulse. This is a normal response to excitement or stress; however, some people develop an ongoing pattern of quick, disorganized heartbeats. The heart’s electrical impulses are irregular and rapid and as a result, so are the heartbeats. The most common type of irregular heartbeat or arrhythmia, is called Atrial Fibrillation or AF.

During Atrial Fibrillation, the upper chambers of the heart beat 300 to 600 times per minute, making them appear to quiver (fibrillate). This makes it difficult for the chambers to empty because the atria beat so quickly that they are unable to fully contract and pump blood properly. When blood is not pumped completely out of the atria, it may pool and clot. Even the smallest blood clots can cause strokes if they dislodge and travel to the brain.

Who is affected by AF?
Atrial Fibrillation is the world’s most common cardiac arrhythmia, affecting more than 2.2 million Americans1 and millions of people worldwide. Each year, approximately 160,000 people in the U.S. are diagnosed with AF.

AF is a progressive disease – its prevalence increases markedly with age, from less than 1 percent for those younger than age 60, to roughly 1 in every 10 persons aged 80 years or older. In the U.S., AF affects 2.3 percent of people older than 40 years of age and 5.9 percent of persons over age 65. The median age of individuals with AF is 75 years old.

AF also occurs in as many as 53 percent of patients undergoing cardiac operations,2 often causing a permanent condition.

Studies have shown that men have a higher risk of developing Atrial Fibrillation than women, and Caucasians have a higher prevalence than African Americans 1. AF accounts for one fourth of all strokes in the elderly and in the US alone, Atrial Fibrillation is estimated to be responsible for more than 70,000 strokes each year.3

Approximately 1 in 10,000 otherwise healthy young adults have AF without underlying heart disease. This type of AF, called Lone AF, is usually intermittent but can become chronic in about 25 percent of the cases. Stress, alcohol consumption, tobacco use or the use of stimulants may play a role in causing Lone AF.

Types of AF

Paroxysmal AF
This type of AF often comes on suddenly and ends spontaneously. The irregular heart rhythm may last for a few seconds, minutes, hours or longer before the heart returns to a normal rhythm on its own. It is sometimes called Lone AF and symptoms can range from mild to severe.

Persistent AF
This type of AF persists unless it is treated. Common treatment options include medications and lifestyle changes related to smoking, alcohol consumption, and caffeine or stimulant use. When medications do not work to correct or control AF, procedures such as electrical cardioversion, catheter ablation, pulmonary vein isolation, ablation of the AV node or device therapy may be recommended.

Permanent AF
Sometimes called chronic AF, this type of irregular heart rhythm is diagnosed when the regular rhythm of the heart cannot be restored. Medications are usually taken to control the heart rate and reduce the risk of clotting; however, permanent AF is frequently resistant to drug therapy. In some cases, physicians may recommend ablation – elimination of the heart tissue responsible for the irregular rhythm –to address the arrhythmia.

Risks and implications

Stroke
Studies show that the risk of stroke for people with AF is five to seven times greater than for those without it.4 The American Heart Association reports that in the U.S., AF is estimated to be responsible for more than 70,000 strokes each year.3  

During AF, the heart muscle does not contract normally to force the heart valves open. When blood is not pumped completely out of the atria, it may pool and clot. Even small blood clots can cause problems if they leave the heart and travel to other parts of the body. They may clog arteries or disrupt blood supply to vital organs. If a blood clot moves to an artery in the brain – which often occurs in cases of AF – a stroke can occur.

The risk of stroke caused by AF is increased for those who are over age 60 or have:

  • already had a stroke.
  • high blood pressure.
  • diabetes.
  • heart failure.

Heart Failure
Because AF can decrease the heart’s ability to pump blood by as much as 25 percent, Atrial Fibrillation, combined with a rapid heart rate over a long period of time, can lead to heart failure. When the heart is unable to pump enough blood, the body begins to compensate by retaining fluid. Fluid accumulates in the lower legs (edema) and the lungs (pulmonary edema). Pulmonary edema makes breathing more difficult and reduces the ability of the lungs to add oxygen to and remove carbon dioxide from the blood. This life-threatening complication is called heart failure.

Damaged or stretched heart muscles often result from heart failure, which can impair the electrical system that controls the normal, steady rhythm of the heartbeat. This may change the patterns of contraction and relaxation of the heart muscle, a condition known as electrical remodeling.

Reduced quality of life
Atrial Fibrillation is associated with a lack of energy, dizziness, chest discomfort and/or shortness of breath. With untreated AF, it is often difficult to be active, which can have an adverse effect on one’s quality of life.

Published: January 1, 2007

 

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