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Module title = Tutorial: Axis
Lesson title = Remember the Vector
This is lesson 1 of 5 in this module
This module assumes you have completed all modules on introduction to ECG and have successfully completed the ECG Rhythm Practice modules.
This module will teach about the electrical axis. This topic causes confusion for many learners, so if you find some parts confusing, please click on the
Feedback
button (top right of screen) to let us know how to improve the lessons.
In the module "Tutorial: Basic Electric Stuff", we covered the topic of
vectors
. That lesson is a pre-requisite for this module.
Remember that a vector represents the size and direction of movement of an electric charge. The QRS vector is sum of all the little cellular charges that occur during ventricular depolarization. There are vectors for the P wave and T wave as well but we will not discuss those here.
If you understand the concept of vectors, then the concept of axis is not very different.
Axis is the "average" vector direction.
If the electrical activity is MOSTLY moving in one direction, then that direction will be the axis.
So how do we determine the direction of the axis? The answer is by analyzing the QRS complex in different ECG leads. Note that we have 12 leads and
the 6 limb leads
measure in a
right-left and head-toe direction
and therefore defines a plane, called the coronal plane:
Remember that these are the 6 limb leads:
Lead 1 Lead II Lead III
Lead aVR Lead aVL Lead aVF
If we draw each of these leads all at the same time and you will see that each lead is
30 degrees different
than the one next to it.
Numerical values have been arbitrarily assigned to the ECG leads.
Lead 1 is zero degrees
and points straight to the patient's left.
Moving
clockwise
, values are positive. For example, Lead aVR is
positive
30 degrees.
Moving
counter-clockwise
from lead I, the values become
negative
. Lead aVL is
negative
30 degrees
Lesson 1 of 5
That was the last lesson!
