Determining The Determining The Heart’s Electrical AxisHeart’s Electrical Axis

Principles To Principles To RememberRemember

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

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

QuadrantsQuadrants

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

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

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

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

Now, How Do We Now, How Do We Determine Axis ?Determine Axis ?

Look at Lead I and aVFLook at Lead I and aVF

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

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

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

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

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

Fine TuningFine Tuning

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

The Tools To Fine TuneThe Tools To Fine Tune

Determine the quadrantDetermine the quadrant Find the smallest QRS Find the smallest QRS

deflection in the six deflection in the six standard leadsstandard leads

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

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

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

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

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

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

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