The Einthoven leads I,II,III

The Einthoven leads measure the ECG in a truly bipolar fashion between two limbs:

  • I = left arm - right arm
  • II = left leg - right arm
  • III = left leg - left arm

In modern ECG machines Einthoven III is usually not measured but calculated from I and II: III = II – I.

next: How to measure the augmented leads aVF, aVR and AVL