Electrocardiogram Learning - An Overview of Leads and Electrodes

To properly use the electrocardiogram (EKG) machine, one must appreciate the principles behind its function, which is to provide a window into the heart’s rhythmic and conductive activities. As shown in this EKG tutorial, cardiac electrical impulses are detected through the EKG electrodes, and understanding how these work is the key to successful EKG learning. Normally, each electrode is color-coded and transmits electrical signals from a specific location of the heart.


The electric currents generated in the heart partially leak into the surrounding tissues. A small amount of electrical activity reaches the skin surface and can be measured.

Electrodes attached to the skin can pick up these electric currents, making registration of cardiac electrical activity or electrocardiography possible. The currents measured on the skin are very weak and have to be amplified for adequate recording. Furthermore, disturbances in measuring these currents (such as disturbances caused by nearby electrical devices) have to be filtered out before amplification to obtain a clear and accurate image of cardiac electrical activity.

Placing electrodes at different sides of the body (on the right and left arms, for example) allows for measurement of the difference in electrical charges between these sides. This represents the difference in electrical charges between the corresponding areas of the heart.


A lead is composed of a several electrodes which are simultaneously used to measure electrical activity. An ECG tracing is used to obtain information about the electrical activity of the different areas of the heart. Thus, leads are placed at different angles and on different areas of the body including both arms, the left leg, and on the thorax.

Armed with adequate knowledge of the physiology behind these leads and electrodes, one can proceed with more confidence in EKG learning. This skill is especially useful to physicians, nurses and emergency care givers who encounter life-threatening cardiac conditions on a regular basis. No EKG tracing becomes too difficult to interpret when the basic mechanisms have been mastered. The Medical-ELearning.com website offers a step-wise approach to learning the EKG for beginners as well as those with advanced training.