The heart is a hollow organ consisting of 4 chambers which pumps blood throughout the body. The upper chambers are the atria and lower chambers are called the ventricles and the chambers are separated by a thin muscular wall called the septum. The right atriums and ventricles move deoxygenated blood to the lungs, while oxygen-rich blood is circulated in the heart through the coronary arteries and the left atriums and ventricles pump it out of the heart through the aorta.
The heart muscle cells generate, conduct and respond to electrical impulses spontaneously. Cardiac contraction is stimulated by impulses from the Sinoatrial node or SA node, which is the pacemaker of the heart, located in the right atrium. Once the SA node stimulates the impulse it travels between the atrium and ventricles, where the Atrioventricular node or AV node is located. Here the impulse stays for a few seconds before it travels to the purkinje fibers and these fibers trigger the ventricles to contract. The electrical activity of the heart is graphed in a wave pattern on an electrocardiogram (ECG/EKG). The electrocardiogram is a test that checks the conduction of the heart and any problems associated with it. It helps locate the cause of chest pain which may be due to inflammation, heart attack or angina. It can help find the cause of symptoms of heart diseases as well as show if medications are working effectively. To understand the pathology on an ECG it is important to know how a normal sinus rhythm works.
As the heart conducts, one heartbeat is a group of waves called P-QRS-T deflections. The P wave is the electrical activity of the atria. When the atrium is stimulated, the impulse is recorded as a P wave. The QRS-T complex shows the electrical activity of the ventricles. The QRS complex shows the depolarization of the ventricles and the T wave shows the repolarization of the ventricles. The PR interval shows the time the impulse takes to travel from SA node to AV node. It is a good measure of any cardiac problems related to the AV node function.
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