Download The 12-Lead EKG Chapter 12

The 12-Lead EKG
Chapter 12
Robert J. Huszar, MD
Instructor
Patricia L. Thomas, MBA, RCIS
Outline
• Electrical Axes and Vectors
• The electrical current, vectors, and the lead
axis
• The hexaxial reference figure
• The QRS axis
• Determination of Axis
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
Magnitude, Direction, and Polarity
Normal Depolarization
Figure 12-2
• Interventricular
Septum 1 & 2
• Right Ventricle 3
• Left Ventricle
(thick lateral
portion) 3
• Left Ventricular
(lateral/posterior/
base) 4
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
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
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)
Practical Method EA
THE END
OF
CHAPTER 12
Hauszar Robert, Basic Dysrhythmias, Interpretation & Management, Third Edition, Mosby, Inc. 2002,
pp. 171-187.
Scheidt, Stephen M.D., Basic Electrocardiography,CIBA-GEIGY Pharmaceuticals, 1986
pp. 3,18,19