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The 12-Lead EKGChapter 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 DepolarizationFigure 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 ENDOF
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