### Description

The limb leads in a standard 12-lead electrocardiogram can be calculated if the values in 2 of the 6 leads are known.

(1) I

(2) II

(3) III

(4) aVL

(5) aVF

(6) aVR

Einthoven's Law and Augmented Lead Relationships

I + III = II

aVR + aVF + aVL = 0

aVR = - 1/2 * (I + II)

aVL = I - (1/2 * II)

aVF = II - (1/2 * I)

All possible combinations for 2 limb leads known: 6 * 5 = 30

Combinations if 2 original or 2 augmented limb leads are known

(1) I and II

(2) I and III

(3) II and III

(4) aVF and aVL

(5) aVF and aVR

(6) aVL and aVR

I and II Known

III = II - I

aVR = - 1/2 * (I + II)

aVL = I - (1/2 * II)

aVF = II - (1/2 * I)

I and III Known

II = I + III

aVR = -1/2 * ((2 * I) + III)

aVL = 1/2 * (I - III)

aVF = III + (1/2 * I)

II and III Known

I = II - III

aVR = 1/2 * (III - (2 * II))

aVL = 1/2 * (II - (2 * III))

aVF = 1/2 * (II + III)

aVF and aVL Known

I = 2/3 * ((2 * aVL) + aVF)

II = 2/3 * (aVL + (2 * aVF))

III = 2/3 * (aVF - aVL)

aVR = -aVF - aVL

aVF and aVR Known

I = -2/3 * (aVF + (2 * aVR))

II = 2/3 * (aVF - aVR)

III = 2/3 * ((2 * aVF) + aVR)

aVL = -aVR - aVF

aVL and aVR Known

I = -2/3 * (aVR - aVL)

II = -2/3 * ((2 * aVR) + aVL)

III = -2/3 * (aVR + (2 * aVL))

aVF = -aVL - aVR