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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.