The axis of the heart is the major direction of overall electrical activity. It is measured in two different planes: The coronal (vertical) plane and the transverse (horizontal) plane. The P wave axis and the QRS axis reflect electrical activity during depolarization. The T wave axis reflects electrical activity during ventricular repolarization.
CORONAL (VERTICAL) PLANE:
-Assess the P wave axis, the QRS axis, and the T wave axis.
-P wave axis: 0 to +75 degrees.
-QRS axis: -30 to +90 degrees.
-T wave axis: 0 to +90 degrees (within 45 degrees of the QRS axis).
-Normal: -30 to +90 degrees.
-Left axis deviation: -30 to -90 degrees.
-Right axis deviation: +90 to +180 degrees.
-Superior axis (Extreme right axis) deviation: -90 to -180 degrees.
TRANSVERSE (HORIZONTAL) PLANE:
-Referred to as Transition.
-Normal transition is in leads V3 and/or V4.
-Transition point before lead V3:
-Early transition (previously referred to as counterclockwise rotation).
-Transition point after lead V4:
-Late transition (previously referred to as clockwise rotation).
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