Module title = Tutorial: Basic Electric Stuff

Lesson title = The Precordial leads

1. The first difference is location. See the diagram below to see how they are arranged.
2. The second difference is that these leads only use 1 electrode.

The limb leads are called bipolar leads. Because precordial leads have only 1 electrode, they are called unipolar leads.

However, the precordial leads do have a second electrode: it is the sum of the 3 electrodes used for limb leads and functions like an electrical "ground". Think of this other lead as existing in the middle of the chest. In the diagram above, this is represented by the blue dotted circle. Each black arrow represents each of the 6 precordial leads and the direction of the arrow indicates the positive direction.

As a result of the "location" of the ground lead being in the center of the chest, the precordial leads measure electrical activity that is moving in a front-back (or back-front) direction and/or a right-left (or left-right) direction. Unlike the limb leads, they do not measure any signals in the up-down (head-toe) direction. This is called the axial plane, shown in image below.