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