Expansion
Three bipolar limb leads forming a triangle around the heart
Expansion
The three bipolar limb leads:
- Lead I - right arm (negative) to left arm (positive), at 0 degrees
- Lead II - right arm (negative) to left leg (positive), at +60 degrees
- Lead III - left arm (negative) to left leg (positive), at +120 degrees
Einthoven’s law: I + III = II.
The three augmented unipolar leads fill in the gaps:
- aVR at -150 degrees
- aVL at -30 degrees
- aVF at +90 degrees
Together the six leads survey the frontal plane at 30 degree intervals, while the six chest leads survey the horizontal plane. The right leg electrode is a neutral reference and contributes no lead.
A negative P wave and inverted complex in lead I, with a normal appearance in the chest leads, suggests arm lead reversal rather than pathology.