In most prehospital cardiac monitors, there are 4 wires that make up the ECG monitoring cable. For 12-Lead ECGs an additional 6 wires are added. So this gives us 10 wires, which gives you 12 leads.
A lead is considered one angle view of the heart primarily a view of the left ventricle. Limb leads are identified as Leads I, II, III, aVR, aVL and aVF | | | | | |
