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An arrhythmia is defined as any variation from the normal rhythm in the heartbeat. When the heart beats, the electrical impulses that cause it to contract follow a specific pathway through the heart. Heart arrhythmias occur when the electrical impulses that control the heartbeat do not work properly, causing the heart to beat either too fast, too slow, or irregularly.
The heart is divided into four compartments, two top compartments (also known as atria) and two lower compartments (known as ventricles). During a normal heartbeat, the atria contract and squeeze blood down into the ventricles. This contraction is triggered by a small group of cells in the right atrium, called the sinus node. When the sinus node sends its electrical impulse across the atria, it causes the atria to contract and pump blood down into the ventricles. From the atria, this electrical impulse goes to the center of the heart to another node that is situated between the atria and ventricles. From here, the electrical impulse travels down the ventricles, causing them to contract and pump blood to the lungs and throughout the rest of the body. In a healthy heart, the heart usually beats between sixty and one hundred beats per minute. People who are more physically active have a slower resting heart rate than someone who is more sedentary because their hearts beat much more efficiently.
Heart arrhythmias are often harmless; in fact most people have occasional irregular heartbeats that may feel like a fluttering or racing heart. However, some cardiac arrhythmias are caused by a weak or damaged heart and may cause bothersome, sometimes life-threatening, signs and symptoms. Noticeable signs and symptoms do not always indicate a serious problem. Some people who feel an irregularity in their heartbeat do not have a serious problem; while others who have life-threatening arrhythmias may have no symptoms at all and only become aware of their condition from a routine visit with their doctor.
Cardiac arrhythmias are classified based on where they originate, either the atria or ventricle, and also by the speed of the heart rate they cause. There are two general terms used to describe the speed of the heart rate, tachycardia and bradycardia. Tachycardia refers to a very fast heartbeat, with a resting heart rate of over one hundred beats per minute. The opposite, bradycardia, is defined as a slow heartbeat. Bradycardia is a heart rate of less than sixty beats per minute. There are more tachyarrhythmias than there are bradyarrhythmias. The common tachyarrhythmias are atrial fibrillation, atrial flutter, supra-ventricular tachycardia, Wolff-Parkinson-White syndrome, ventricular tachycardia, ventricular fibrillation, and Long QT syndrome. The major two bradycardias are Sick Sinus syndrome and Conduction Block syndrome.
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