There are multiple types of ECGs. Typically, there are three lead ECGs, or more, with electrodes placed at different parts of the body, as shown in the slide. The right leg is typically used as the reference, and the three electrodes will be placed at the left leg, the right arm, and the left arm. These three electrodes form what is known as the ECG Einthoven Triangle, which was defined in 1907. Based on these electrodes, there are three leads that can be derived. More than three leads can be derived, depending on how many more electrodes are placed on the body.