Mean Electrical Axis Calculation

Question 1

What is the mean electrical axis?

Answer 1

Orientation of the cardiac dipole during the most intense phase of ventricular contraction (R wave)

• Clinical indicator of whether depolarization is proceeding over normal pathways
• Reported in degrees according to the axial reference system convention

Question 2

What is the mean electrical axis?

Answer 2

Orientation of the cardiac dipole during the most intense phase of ventricular contraction (R wave)

• Clinical indicator of whether depolarization is proceeding over normal pathways
• Reported in degrees according to the axial reference system convention

Question 3

What is a normal axis deviation?

Answer 3

-30 - +90

Question 4

What is a right axis deviation?

Answer 4

> +90deg

• Physical displacement of the heart to the right
• Right ventricular hypertrophy
• Loss of electrical activity to the left ventricle

Question 5

What is the first way to calculate mean electrical axis?

Answer 5

Find the lead with the largest R wave and follow that dipole. Remember if the wave is negative, then the dipole is in the opposite direction!

Question 6

What is the second way to calculate mean electrical axis?

Answer 6

Equiphasic Approach:

• Determine which lead contains the most equiphasic QRS
• Determine which lead lies 90deg away from the most equiphasic lead and look at tracing
• -If QRS complex is predominantly positive, then the direction of this lead is approximately the QRS axis
• -If the QRS complex is predominantly negative, then the QRS axis is 180deg away from the direction of this lead

Question 7

What is a left axis deviation?