electrocardiography

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

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For more information on electrocardiography, visit Britannica.com.

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

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

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

• Procedures - EKG: electrocardiogram
• Abbreviations - EKG: electrocardiogram