1. Robert J. Huszar, MD Instructor Patricia L. Thomas, MBA, RCIS
The 12-Lead EKG Chapter 12
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

5. Magnitude, Direction, and Polarity

6. Normal Depolarization Figure 12-2
Interventricular Septum 1 & 2
Right Ventricle 3
Left Ventricle (thick lateral portion) 3
Left Ventricular (lateral/posterior/base) 4

8. The Hexaxial Reference Figure
Composite of the two triaxial reference figures (limb leads+ augmented leads)
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 lead axes

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

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.
5. Determine location (normal, RAD or LAD)

14. Practical Method EA

15. THE END OF CHAPTER 12
Hauszar Robert, Basic Dysrhythmias, Interpretation & Management, Third Edition, Mosby, Inc. 2002, pp
Scheidt, Stephen M.D., Basic Electrocardiography,CIBA-GEIGY Pharmaceuticals, 1986
pp. 3,18,19