ECG Level 1 Tutorial: Basic Electric Stuff
Tutorial: Basic Electric Stuff
This module will teach the basics of electrical physiology in the heart.
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Tutorial: Basic Electric Stuff The Precordial leads
Times Practiced
Cases Completed
1h 24m
Total Time spent
1m 24s
Average Time
The Precordial leads
In the last lesson, we discussed the limb leads. In this lesson, we will discuss the precordial leads.

The precordial leads function in the exact same manner as do the limb leads. There are 2 primary differences, however:
  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.
Precordial leads showing the "ground" electrode as the circle with the blue dotted line
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.

The axial plane measures in a left-right (or right-left) direction as well as a front-back direction

To summarize the limb leads (previous lesson) vs. the precordial leads:
 - limb leads: up-down and right-left directions
 - precordial leads (V1 to V6): front-back and right-left directions

Note that "right-left" direction means right to left, or left to right, in both diections. The same applies for "front-back".