Electrocardiogram
(Also called Resting EKG and Resting ECG)

Overview

The Heart's Electrical Conduction System
The heart is, in the simplest terms, a pump made up of muscle tissue. Like all pumps, the heart requires a source of energy in order to function. The heart's pumping energy comes from an intrinsic electrical conduction system.

An electrical stimulus is generated by the sinus node (also called the sinoatrial node, or SA node), which is a small mass of specialized tissue located in the right atrium (right upper chamber) of the heart. The sinus node generates an electrical stimulus periodically (60 to 100 times per minute under normal conditions). This electrical stimulus travels down through the conduction pathways (similar to the way electricity flows through power lines from the power plant to your house) and causes the heart's chambers to contract and pump out blood. The right and left atria (the two upper chambers of the heart) are stimulated first and contract a short period of time before the right and left ventricles (the two lower chambers of the heart). The electrical impulse travels from the sinus node to the atrioventricular (AV) node, where it stops for a very short period, then continues down the conduction pathways via the bundle of His into the ventricles. The bundle of His divides into right and left pathways to provide electrical stimulation to both ventricles.

This electrical activity of the heart is measured by an electrocardiogram. By placing electrodes at specific locations on the body (chest, arms, and legs), a graphic representation, or tracing, of the electrical activity can be obtained. Changes in an EKG from the normal tracing can indicate one or more of several heart-related conditions.

Many medical conditions can cause changes in the EKG pattern, including, but not limited to, the following:

• ischemia - decreased blood flow to the heart muscle due to clogged or partially clogged arteries.
  
  
• heart attack (Also called myocardial infarction, or MI.) - damage to the heart muscle due to insufficient blood supply.
  
  
• conduction disorder - a dysfunction in the heart's electrical conduction system, which can make the heart beat too fast, too slow, or at an uneven rate.
  
  
• electrolyte disturbance - an imbalance in the level of electrolytes, or chemicals, in the blood, such as potassium, magnesium, or calcium.
  
  
• pericarditis - an inflammation or infection of the sac which surrounds the heart.
  
  
• valve disease - malfunction of one or more of the heart valves that may cause an obstruction of the blood flow within the heart.
  
  
• enlarged heart - a condition caused by various factors, such as valve disorders, high blood pressure, congestive heart failure, conduction disturbances, etc.
  
  
• chest trauma - blunt trauma to the chest, such as a motorist hitting the steering wheel in an automobile accident.

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