Electrocardiogram

A recording of the electrical activity of the heart. An electrocardiogram is a simple, non-invasive procedure. Electrodes are placed on the skin of the chest and connected in a specific order to a machine that, when turned on, measures electrical activity all overaround the heart. Output is usually in the form of a long scroll of paper displaying a printed graph of activity. Newer models output the data directly to a computer and screen, although a print-out may still be made.To take a specific situation, the initial diagnosis of a heart attack is usually made by a combination of clinical symptoms and characteristic electrocardiogram (EKG) changes. The EKG can detect areas of muscle ischemia (muscle deprived of oxygen) and/or dead tissue in the heart.

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Graphic record of the heart's integrated action currents obtained with the electrocardiograph displayed as voltage changes over time. [electro- + G. kardia, heart, + gramma, a drawing]

- concordant changes e. the presence of more than one waveform change, each in the same direction (polarity).

- discordant changes e. the presence of more than one waveform change, each in a different direction (polarity).

- scalar e. (skal′ar) electrocardiographic lead output that can be displayed on one plane of the body in contradistinction to vector e. in which the display is on two or more planes.

- unipolar e. an e. taken with the exploring electrode placed on the chest overlying the heart or upon a single limb, the indifferent (“zero” potential) electrode being the central terminal.

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elec·tro·car·dio·gram -'kärd-ē-ə-.gram n the tracing made by an electrocardiograph also the procedure for producing an electrocardiogram

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n.

a recording of the electrical activity of the heart on a moving paper strip. The ECG tracing is recorded by means of an apparatus called an electrocardiograph (see electrocardiography). It aids in the diagnosis of heart disease, which may produce characteristic changes in the ECG.

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elec·tro·car·dio·gram (e-lek″tro-kahrґde-o-gram″) [electro- + cardiogram] a graphic tracing of the variations in electrical potential caused by the excitation of the heart muscle and detected at the body surface. The normal electrocardiogram is a scalar representation that shows deflections resulting from atrial and ventricular activity as changes in the magnitude of voltage and polarity (positive and negative) with time. The first deflection, the P wave, is due to excitation of the atria; the QRS complex of deflections, to excitation (depolarization) of the ventricles; and the T wave, to recovery of the ventricles (repolarization). Abbreviated ECG or EKG. See also lead² and see terms under wave, complex, and interval.

Normal electrocardiogram.