Determining The Hearts Electrical Axis

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Determining The Hearts Electrical Axis
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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.

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• 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

• 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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• 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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• 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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• 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 ?

• Look at Lead I and aVF

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

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

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• 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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• 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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• 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

• 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

• Determine the quadrant
• Find the smallest QRS deflection in the six
  standard leads

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

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

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• 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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• 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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• 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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• 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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• 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.