How do we calculate electrical axis?

Calculation of electrical axis in the frontal plane (*by inspecting extremity electrodes*)

In leads with biphasic QRS complexes (such as QR or RS) if amplitudes of Q and R waves or

amplitudes of R and S waves are equal, then electrical axis should be perpendicular (with 90 degrees)

to this lead.

If two leads have high R waves with equal amplitudes,

then electrical axis should be in the middle of these two leads.

In daily practice, we do not have to measure the electrical axis precisely.

What we usually need is to determine if there is normal axis, right axis deviation or left axis deviation.

More precise axis measurements are needed during scientific reasearch.

Age-adjusted normal and abnormal values for the electrical axis

Neonate: between +30 and 190 degrees: normal.

Neonate: <+30 to <-90 degrees: left axis deviation.

Neonate: >190 to -90 degrees: extreme right axis deviation.

1 month to 1 year old: +10 to +120 degrees: normal.

1 month to 1 year old: >+120 degrees: right axis deviation.

1 month to 1 year old: <+10 to -90 degrees: left axis deviation.

1-5 years old: +5 to +100 degrees: normal.

1-5 years old: >+100 degrees: right axis deviation.

5-8 years old: 0 to +140 degrees: normal.

5-8 years old: >+140 degrees: right axis deviation.

5-8 years old: <0 degree: left axis deviation.

8-16 years old: 0 to +120 degrees: normal.

8-16 years old: >+120 degrees: right axis deviation.

Adult: -30 to +90 degrees: normal.

Adult: <-30 degrees: left axis deviation.

Adult: -30 to -45 degrees: moderate left axis deviation.

Adult: -45 to -90 degrees: marked left axis deviation.

Adult: +90 to +120 degrees: moderate right axis deviation.

Adult: +120 to 180 degrees: marked right axis deviation.

Reference

Circulation 2009;119:e235-e240.

In leads with biphasic QRS complexes (such as QR or RS) if amplitudes of Q and R waves or

amplitudes of R and S waves are equal, then electrical axis should be perpendicular (with 90 degrees)

to this lead.

If two leads have high R waves with equal amplitudes,

then electrical axis should be in the middle of these two leads.

In daily practice, we do not have to measure the electrical axis precisely.

What we usually need is to determine if there is normal axis, right axis deviation or left axis deviation.

More precise axis measurements are needed during scientific reasearch.

Age-adjusted normal and abnormal values for the electrical axis

Neonate: between +30 and 190 degrees: normal.

Neonate: <+30 to <-90 degrees: left axis deviation.

Neonate: >190 to -90 degrees: extreme right axis deviation.

1 month to 1 year old: +10 to +120 degrees: normal.

1 month to 1 year old: >+120 degrees: right axis deviation.

1 month to 1 year old: <+10 to -90 degrees: left axis deviation.

1-5 years old: +5 to +100 degrees: normal.

1-5 years old: >+100 degrees: right axis deviation.

5-8 years old: 0 to +140 degrees: normal.

5-8 years old: >+140 degrees: right axis deviation.

5-8 years old: <0 degree: left axis deviation.

8-16 years old: 0 to +120 degrees: normal.

8-16 years old: >+120 degrees: right axis deviation.

Adult: -30 to +90 degrees: normal.

Adult: <-30 degrees: left axis deviation.

Adult: -30 to -45 degrees: moderate left axis deviation.

Adult: -45 to -90 degrees: marked left axis deviation.

Adult: +90 to +120 degrees: moderate right axis deviation.

Adult: +120 to 180 degrees: marked right axis deviation.

Reference

Circulation 2009;119:e235-e240.