Electrocardiogram - ECG - recording

An ECG represents a composite recording of all the action potentials generated by all cardiac muscle cells during each heartbeat. To record an ECG, 12 metal electrodes are positioned on the arms, legs, and chest. These electrodes detect the heart electric activity and transmit it to the electrocardiograph, which amplifies and records the signals.

The twelve electrodes, or leads, are placed on the body to obtain 6 limb leads and 6 chest leads. Together, these leads provide a 3-dimensional representation of the heart electric activity. Each lead is analogous to a video camera recording the same event, atrial and ventricular depolarization, and repolarization from a different angle. Therefore, each limb or chest lead record slightly different electric activity of the heart. This results in the electrocardiograph producing 12 different tracings.

By comparing these recordings with one another, and with normal tracings, physicians can detect heart abnormalities, including the presence of arrhythmia, enlargement of left ventricle, abnormalities in the cardiac conduction system, and damage to certain regions of the heart.

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