A graphic recording of the electrical activity of the heart, used to evaluate cardiac function and to diagnose arrhythmias and other disorders.♦ An electrocardiograph is the apparatus used to generate electrocardiograms. The machine functions as a portable set of galvanometers that measure electric potentials at different anatomic sites on the chest and extremities, and contains internal circuitry for computing calculations based on these measurements. Twelve electrodes act as transducers to pick up the electrical signals. Various combinations of signals from the electrodes can be selected for output, each of which provides information about electrical activity in the heart from a different anatomical perspective. For example, electrodes placed on the right arm, left leg and left arm record variations in potential in the frontal plane of the heart. The signals are converted to waveform tracings that are recorded and printed for diagnostic interpretation.

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