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Determining The Hearts Electrical Axis

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Principles To Remember l 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.

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l 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.

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

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

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

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

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

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

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

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l 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)

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l 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)

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l 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)

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Fine Tuning l 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.

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

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

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

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

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l 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.

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

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

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l 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.

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