Understanding the ECG through its history

Einthoven placed electrodes on the left arm and leg (because the heart is on the left), the right arm, and therefore had to use the right leg as the grounding electrode.

His ECG's therefore consisted of 3 strips:-
- Lead I which was the signal difference between the arms.
- Lead III which was the signal difference on the left
And Lead II was calculated by the machine by adding Lead I to Lead III.

It took another 30 years for the remaining leads to be invented, and this was done by Wilson in Michigan.
He made leads for the right arm, left arm, and left leg.
He then made leads for the chest.
The rule of the limb leads is that if you add all the P's, QRS's and T's then you will get a flat line. If you don't, then there has been lead misplacement.

The only thing to remember about the chest leads is that you start at the 4th interspace, and end at the 5th interspace.

Other rules to follow:-
AVL and I should look the same.
AVR and II should look reversed.
AVF and III should look the same.