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## The 12Lead EKG Chapter 12

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Title: The 12Lead EKG Chapter 12

1
• Robert J. Huszar, MD
• Instructor
• Patricia L. Thomas, MBA, RCIS

2
Outline
• Electrical Axes and Vectors
• The electrical current, vectors, and the lead
axis
• The hexaxial reference figure
• The QRS axis
• Determination of Axis

3
Electrical Axes Vectors
• Instantaneous cardiac vector-the electrical
current generated by the depolarization or
repolarization of the atria or ventricles at any
given moment
• Graphically as an arrow that has magnitude,
direction, and polarity
• Length of the shaft of the arrow represents the
magnitude of the electrical current
• Orientation or position of the arrow indicates
the direction of flow of the electrical current
• The tip of the arrow represents the positive pole
of the electrical current
• The tail is the negative pole

4
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5
Magnitude, Direction, and Polarity
6
Normal DepolarizationFigure 12-2
• Interventricular Septum 1 2
• Right Ventricle 3
• Left Ventricle (thick lateral portion) 3
• Left Ventricular (lateral/posterior/base) 4

7
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8
The Hexaxial Reference Figure
• Composite of the two triaxial reference figures
• Purpose is to determine the direction of the QRS
axis
• Each - pole is assigned a degree number 00 to
1800
• The top are given numbers
• The bottom are given numbers
• NOT TO BE CONFUSED WITH the - poles of the

9
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10
Electrical Axis Calculation
• Plotting of the net direction or the electrical
axis
• QRS axis is most important it is correlates with
the anatomy of the heart
• Pathophysiology causes a shift in the axis

11
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12
Calculate the Axis
• 1. Calculate the algebraic sum of QRS in Leads I
III
• 2. Plot the vector results on a triaxial
reference system
• 3. Draw the perpendicular until Lead I III
cross.
• 4. Draw a separate line from the center to the
intersection of the two perpendiculars gives the
electrical axis.

13
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14
Practical Method EA
15
THE ENDOFCHAPTER 12
• Hauszar Robert, Basic Dysrhythmias,
Interpretation Management, Third Edition,
Mosby, Inc. 2002, pp. 171-187.
• Scheidt, Stephen M.D., Basic Electrocardiography,C
IBA-GEIGY Pharmaceuticals, 1986
• pp. 3,18,19