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electrocardiography

 
(i¦lek·trō′kärd·ē′äg·rə·fē)

(medicine) The medical specialty concerned with the production and interpretation of electrocardiograms.


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Britannica Concise Encyclopedia:

electrocardiography

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Method of tracing the electric current of a heartbeat to provide information on the heart. Electrocardiograms (ECGs) are made by applying electrodes, usually to the arms, legs, and chest wall, attached to an electrocardiograph, which records the tiny heart current. Upward and downward movements on the tracing reflect contractions of the atria and ventricles. Deviations from a standard point to a possible heart disorder and its site, as well as to possible high blood pressure and other diseases.

For more information on electrocardiography, visit Britannica.com.

Gale Encyclopedia of Public Health:

Electrocardiography

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The electrocardiogram (ECG) displays important information about the heart, including the occurrence of a heart attack or lack of oxygen, whether conduction of the heartbeat is disturbed, or its rate or rhythm altered. It is useful as a rapid indicator of the diagnosis and it is easy, painless, and inexpensive to record. The record made in healthy people at rest, or undergoing an exercise test, helps predict risk of future heart problems. It is also used to monitor severely ill patients.

The electrocardiograph was invented by Wilhelm Einthoven in Leiden, the Netherlands, around 1900. Einthoven measured the small differences in electrical potential between the arms and legs by amplifying the tiny current passing through the body with each heartbeat. In the twenty-first century, data about heart function are recorded from the chest wall and the limbs with the electrocardiograph and displayed on paper or TV screens as the ECG, an electrical recording, or tracing, of the heartbeat. This tracing is interpreted by physicians or technicians and, in digital form, is analyzed automatically with computers.

(SEE ALSO: Atherosclerosis; Cardiovascular Diseases; Coronary Artery Disease)

— HENRY BLACKBURN



Columbia Encyclopedia:

electrocardiography

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electrocardiography (ĭlĕk'trōkärdēŏg'rəfē), science of recording and interpreting the electrical activity that precedes and is a measure of the action of heart muscles. Since 1887, when Augustus Waller demonstrated the possibility of measuring such action, physicians and physiologists have recorded it in order to study the heart's normal behavior and to provide a method for diagnosing abnormalities. Electrical current associated with contraction of the heart muscles passes through the various tissues and reaches the surface of the body. What is actually recorded is the change in electrical potential on the body surface. The first practical device for recording the activity of the heart was the string galvanometer developed by William Einthoven in 1903. In this device a fine quartz string is suspended vertically between the poles of a magnet. The string is deflected in response to changes in electrical potential and its movement can be optically enlarged and photographed, or, if an immediately visible record is desired, the string's movement can be recorded on a sheet of paper. A more sophisticated form of the electrocardiograph employs a vacuum-tube amplifier. The greatly amplified current from the body deflects a mirror galvanometer that causes a beam of light to move across a light-sensitive film. When an electrocardiograph is taken, electrodes (leads) are attached to the extremities and to the left chest. The recordings obtained in this manner are called electrocardiograms, or more simply EKG's or ECG's. A normal EKG shows a sequence of three waves arbitrarily labeled P, QRS, and T. The P wave is a small, low-amplitude wave produced by the excitation of the atria of the heart. It is followed by a resting interval that marks the passage of electrical impulses into the ventricles. Following this interval comes the QRS wave, a rapid, high-amplitude wave marking ventricular excitation, and then a slow-building T wave denoting ventricular recovery. Abnormalities may be noted from deviation in wave form, height, direction, or duration. The type of abnormal wave may sometimes indicate the type of heart disorder. Usually the physician must associate the EKG with other clinical observations to determine the cause of the abnormality. See also stress test.


Saunders Veterinary Dictionary:

electrocardiography

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The graphic recording from the body surface of the potential of electric currents generated by the heart, as a means of studying the action of the heart muscle.
With the modern electrocardiograph, the current that accompanies the action of the heart is amplified 3000 times or more, and it moves a small, sensitively balanced lever in contact with moving paper. The pattern of heart waves that is traced on the paper indicates the heart's rhythm and other actions.
The normal electrocardiogram is composed of a P wave, Q, R and S waves known as the qrs complex, or QRS wave, and a T wave. The P wave occurs at the beginning of each contraction of the atria. The QRS wave occurs at the beginning of each contraction of the ventricles. The T wave seen in a normal electrocardiogram occurs as the ventricles recover electrically and prepare for the next contraction. There is a refractory period after each P wave and QRS complex during which the muscle is inexcitable; this period is usually about 0.30 second.
The electric impulses in the heart muscle are picked up and conducted to the electrocardiograph by electrodes or leads connected to the body by small metal plates or other methods. The metal plates are moistened with a conductive paste and attached to the limbs and chest (cardiac area) of the animal.

Electrocardiography: Normal lead II ECG complex. By permission from Morgan RV, Bright R, Swartout M, Handbook of Small Animal Practice, Saunders, 2002
Mosby's Dental Dictionary:

electrocardiography

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n

A method of recording electrical activity generated by the heart muscle.

Random House Word Menu:

categories related to 'EKG'

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Random House Word Menu by Stephen Glazier
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McGraw-Hill Science & Technology Dictionary. McGraw-Hill Dictionary of Scientific and Technical Terms. Copyright © 2003, 1994, 1989, 1984, 1978, 1976, 1974 by McGraw-Hill Companies, Inc. All rights reserved.  Read more
Britannica Concise Encyclopedia. Britannica Concise Encyclopedia. © 1994-2012 Encyclopædia Britannica, Inc. All rights reserved.  Read more
$copyright.smallImage.alttext Gale Encyclopedia of Public Health. Encyclopedia of Public Health. Copyright © 2002 by The Gale Group, Inc. All rights reserved.  Read more
Columbia Encyclopedia. The Columbia Electronic Encyclopedia, Sixth Edition Copyright © 2012, Columbia University Press. Licensed from Columbia University Press. All rights reserved. www.cc.columbia.edu/cu/cup/ Read more
Saunders Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.  Read more
Mosby's Dental Dictionary. Mosby's Dental Dictionary. Copyright © 2004 by Elsevier, Inc. All rights reserved.  Read more
Random House Word Menu. © 2010 Write Brothers Inc. Word Menu is a registered trademark of the Estate of Stephen Glazier. Write Brothers Inc. All rights reserved.  Read more

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