Normal Heart Rhythm
The primary function of the heart is to pump oxygen-rich blood throughout the body. The oxygen is used by the body's tissues to perform their normal work. A by-product of this process is carbon dioxide; the blood carries this waste back to the heart and then into the lungs where it is expelled. The lungs also replenish the blood with oxygen. The oxygen-rich blood then returns to the heart and is again pumped throughout the body to meet the tissue's needs. A healthy heart will beat approximately 100,000 times each day and pump over 1,800 gallons of blood throughout the body's circulatory system.
Your heart is approximately the same size as your fist. Inside, the heart is divided into right and left sides by a thick muscular wall called a septum. The right and left sides are divided into upper chambers called the atria and lower chambers called the ventricles. The heart's right side (consisting of an atrium and a ventricle) receives blood from the body and sends the blood to the lungs where it is replenished with oxygen. After leaving the lungs, the blood travels into the left atrium and then through the left ventricle where it is pumped out to the rest of the body.
As you exercise or become excited, your body will demand more oxygen and the heart may pump more rapidly to accommodate this need. On the other hand, the heart will pump less frequently when your body is at rest (that is, when there is less demand for oxygen).
The rate that your heart beats is normally controlled by an electrical impulse that originates in a small mass of muscle tissue within the upper right chamber of your heart. This specialized tissue is the sinoatrial node (or S-A node), the heart's "natural pacemaker".
The S-A node will send an electrical signal through the heart's special conduction pathway (found in the atria and ventricles) that will cause the heart muscle to contract, thus pumping blood throughout the body. The normal heart rate ranges between 60 and 100 beats per minute.
From the S-A node, the electrical impulse is relayed along the heart's conduction or wiring system. It spreads throughout both the right and left atria causing them to contract. The impulse also reaches the atrio-ventricular node. This special region transmits the heart's signal to the ventricles causing them to contract and pump blood.
Arrhythmia - a disturbance of normal heart rhythm
An arrhythmia is any deviation from or disturbance of the normal heart rhythm. The basic rhythm of the heart is a tightly regulated phenomenon designed to insure maximal efficiency and optimal performance. It is a dynamic phenomenon that changes according to the metabolic needs of the body. The cardiac rhythm involves several different microscopic and macroscopic structures within the normal heart.
The Sino-Atrial Node
The heart's normal or intrinsic pacemaker is called the sino-atrial node. It is located in the upper right chamber (right atrium). A signal or impulse is emitted to trigger the heart beat. At times the heart may be slower, such as during sleep, or faster as during activity or stress. This impulse travels across the upper chambers of the heart. However, in order to trigger the pumping or lower chambers (the ventricles) the impulse must cross the specialized electrical (conduction) system.
This connection between the upper and lower chambers of the heart is in a central area called the septum. Here a series of specialized tissues take the impulse from the top chamber, slow its progression down a bit, and then pass it on to specialized fibers that transmit the impulse across the pumping chambers to signal the muscles within these chambers to contract and pump. With the next heart beat, the process starts again.
Arrhythmic Disturbances
An arrhythmia may occur when any portion of this sequence is interrupted or disturbed. Among arrhythmic disturbances are the failure of the pacemaker or electrical system to trigger appropriately and conduct impulses properly. Other arrhythmias occur when abnormal foci within the heart interrupt the normal sequence of electrical stimulation and temporarily, or for prolonged periods of time, initiate the electrical sequence.
Arrhythmias may be benign, symptomatic, life threatening or even fatal. Their consequences depend not only on their manifestation but on the presence of important abnormal structural conditions of the heart.
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Arrhythmia Conditions