# Determining The Heart’s Electrical Axis

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Determining The Heart’s Electrical Axis

Principles To Remember
Principle # 1 : When a positive sensing electrode sees an electrical impulse as coming head on, it will write the highest amplitude deflection on the EKG paper.

Principle # 2 : When the positive sensing electrode sees an electrical impulse crossing it on a perpendicular path, it will write the smallest amplitude deflection on the EKG paper.

Quadrants If the electrical axis of the heart is between + 0 & +90 degrees, the axis is said to be in the normal quadrant

If the electrical axis of the heart is between -0 & -90 degrees, it is said to be in left axis deviation

If the electrical axis of the heart is between +90 and +180 degrees, it is said to be in right axis deviation

If the electrical axis of the heart is between -180 and -90 degrees, it is said to be in extreme right axis deviation

Now, How Do We Determine Axis ?
Look at Lead I and aVF

Step #1 : Determine if the overall QRS complex deflection is grossly positive or grossly negative in Leads I and aVF

Step #2 : If the QRS are both positively deflected, then the electrical axis is in the normal quadrant (up,up)

If the QRS complex for Lead I is positively deflected but the QRS in avF is negatively deflected, then the electrical axis is said to be left axis deviated (up,down)

If the QRS complex in Lead I is negatively deflected but the QRS in aVF is positively deflected, then the electrical axis is said to be right axis deviated (down,up)

If the QRS in Lead I and in aVF are both negatively deflected, the electrical axis is said to be extreme right axis deviated (down,down)

Fine Tuning It is not enough to merely determine the quadrant. It is better to be able to determine where in the quadrant the axis is located.

The Tools To Fine Tune Determine the quadrant
Find the smallest QRS deflection in the six standard leads

Rotate 90 degrees from the smallest electrode into the quadrant that Lead I & aVF said the axis would be located.

Determine if the QRS complex of the smallest deflection is grossly positive or negative.

If the R wave to S wave difference is 0-1 mm, make no fine adjustments in the axis degree setting.

If the R wave to S wave difference is between 2-3 mm, then adjust the axis 10 degrees towards the + or - pole of the smallest QRS.

If the smallest QRS deflection is grossly negative, the fine adjustment of 10 degrees is swung toward the negative pole of that lead.

If the smallest QRS deflection is grossly positive, the fine adjustment of 10 degrees is swung toward the positive pole of that lead.

If the R wave to S wave difference is between 4-5 mm, then adjust the axis 15 degrees towards the + or - pole of the smallest QRS.