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Cardiology Teaching Package

A Beginners Guide to Normal Heart Function, Sinus Rhythm & Common Cardiac Arrhythmias

Unipolar Leads

But, wait a minute. That gives us nine wires and it is a 12-lead ECG. Where are the other 3?

Well, so far we have nine wires. They all look directly at the heart with tunnel vision. They only give information based on what is immediately in front of them. These nine wires are known as "unipolar leads".

The three active peripheral leads are AVr, AVL, and AVf.

The "AV" stands for "Augmented Vector". The last letter refers to position, which are as follows:

table displaying the label of the bipolar lead, its meaning and its location on the body
Label Meaning of label Position of lead on body
AVrAugmented vector rightRight wrist
AVLAugmented vector leftLeft wrist
AVfAugmented vector footLeft foot

These 3 leads create a triangle with the heart in the middle, as below. The lines into the centre indicate the line of sight of these leads.

Image: Line of site of the unipolar leads

Diagram showing the line of site of the unipolar leads
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