The human heart has two upper chambers and two lower chambers. The upper chambers are called the left atrium and the right atrium - the plural of atrium is atria. The two lower chambers are the the left ventricle and the right ventricle. When the two upper chambers - the atria - contract at an excessively high rate, and in an irregular way, the patient has atrial fibrillation.
The term atrial fibrillation comes from the Latin words atrium, meaning "hall", fibrilla, meaning "small fiber", and atio, meaning "process".
According to Medilexicon's medical dictionary, atrial fibrillation is "fibrillation in which the normal rhythmic contractions of the cardiac atria are replaced by rapid irregular twitchings of the muscular wall; the ventricles respond irregularly to the dysrhythmic bombardment from the atria."
Atrial fibrillation is the most common arrhythmia - problems with the speed or rhythm of the heartbeat. Arrhythmias are caused by a disorder in the heart's electrical system.
The walls of the atria and ventricles are made of virtually 100% pure muscle. A heartbeat is caused by the tightening of these muscles. When the muscles tighten the chambers squeeze closed and push out the blood which is inside them.
Heartbeat control begins with the sinoatrial node - a small clump of muscle cells located in the right atrium. This is the heart's natural pacemaker; it sends electrical impulses to the atrioventricular node which exists between the atria and ventricles. The atrioventricular node determines how much the ventricles contract. Our pulse rate is caused by the contraction of the left ventricle.
When the atrioventricular node receives too many impulses - more than it is able to conduct - atrial fibrillation occurs. The result is irregular contractions of the ventricles. That is why a patient with atrial fibrillation has an irregular and high pulse rate.
Put simply - during atrial fibrillation the contractions of the two upper chambers of the heart are not synchronized with the contractions of the two lower chambers. Atrial fibrillation is a rapid and irregular heart rate. It frequently causes poor blood flow to the body.
Atrial fibrillation currently affects almost 7 million people in the USA and Europe. Incidence is expected to double within the next forty years.
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