It is also used to help distinguish between Atrial Fibrillation with a Rapid Response and that of Atrial Flutter.
In a Lewis Lead, the negative electrode is placed on top of the manubrium and the positive electrode in the 5th inter-costal space right sternal border.
Place your monitor selector switch on Lead I and move your right arm electrode to the manubrium. Next place your left arm electrode on the 5th inter-costal space right parasternal border.
The left leg electrode is placed over the right rib margin. The negative electrode goes on top of the manubrium and the positive electrode goes over the 5th inter-costal space parasternal order.
If your monitor is always in the lead II setting, then the positive electrode would be the left leg electrode (red) and the negative electrode would be the right arm (white).
Then you would place the negative electrode, (right arm -white)) on top of the manubrium and the positive electrode, (left leg -red)) on the 5th inter-costal space right parasternal border. The left arm electrode (black) would then be placed over the right rib margin.
Remember when placing your electrodes on patients, it is important to know what lead your monitoring in and especially where you place the electrodes on the patient. It should be based on where you want your positive and negative electrode and what you are monitoring for...