The heart is a two stage electrical pump. The upper chambers of the heart, the atria, (single=atrium) collect blood from the body and pump it into the lower chambers, or ventricles. There is a little delay for the ventricles to fill, and then they pump the blood out of the heart and back to the body. For this to happen in a coordinated fashion, the heart has its own electrical system
Specialized electrical cells imbedded into part of the muscles in the atrium generate the electricity and act as a pacemaker for the heart. About 60-80 times a minute this pacemaker (the sinoatrial or SA node) fires and sends electrical signals to all of the atrial muscle cells allowing them to fire at once, generating the first half of a heart beat. Electricity also travels to the ventricles but is held up for a split second in the junction between the atrium and ventricle at the atrio-ventricular (AV) node to allow the ventricles to fill with blood. The signal then travels through electrical bundles to allow all the muscle cells of the ventricles to fire at once, causing the second half of the heart beat. This pumps blood out to the body. After the heart pumps, there is another split second when the electrical system resets itself to get ready for the next electrical impulse cycle. This allows blood to return and fill the heart, getting ready for the next heartbeat.
Palpitations is a term that describes the feeling that occurs when a person can feel an abnormality in the normal beating of the heart. These palpitations can be an isolated extra beat, or they can run together and last for prolonged periods of time. Each part of the heart has the potential to be irritable and cause an extra beat to occur. As well, short circuits in the electrical conduction system of the heart can cause "runs" of abnormal firing.
Every muscle cell in the heart has the potential to generate an electrical signal that can spread outside the normal electrical pathways and bundles to try to generate a heart beat. If the SA node fails, then other cells in the atrium try to take over. If they fail, then the AV node can take over but at a lower rate of about 40 beats per minute. And as the final backup, the ventricle itself can generate electricity but at a much slower rate of about 20 beats per minute.
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