BSI: EKG Interpretation II

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  1. What is the axis?
    • The axis is the mean or general direction of depolarization through the ventricles:
    • - Vector tail is always at the AV node
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    • - Normal Axis is ~ 40 °
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    • - If the heart is displaced, the axis will also be displaced in the same direction
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  2. What will hypertrophy do to the axis?
    Hypertrophy of a ventricle will shift the axis towards the hypertrophy because there is more electrical activity on the hypertrophied side of heart.

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  3. What will myocardial infarction do the axis?
    Myocardial infarction will shift the axis away from it because the infarcted area has no electrical activity.

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  4. What two leads are needed to determine the axis?
    • Lead I
    • Lead AVF

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  5. How do you determine the axis?
    • Lead I
    • - Lead I runs through AV node from left to right and the AV node is center of sphere (see figure)
    • - The left side of the sphere is positive and the right side is negative (left arm is positive and right arm is negative)
    • - If the wave of depolarization through the ventricles is directed towards the left side of the heart (left side of sphere), the QRS in lead I will be positive (upward deflection)—remember: positive charges flowing towards positive electrode will cause positive deflection
    • - If the wave of depolarization through the ventricles is directed towards the right side of the heart (right side of sphere), the QRS in lead I will be negative (downward deflection)

    • Lead AVF
    • - Lead AVF runs through AV node in a vertical line
    • - If draw sphere with the center being the AV node, the top is negative and the bottom is positive (see figure)
    • - If wave of depolarization through the ventricles is directed down, the QRS in Lead AVF will be positive (upward deflection)
    • - If wave of depolarization through the ventricles is directed upward, the QRS in Lead AVD will be negative (downward deflection)

    Therefore, a normal axis (~40 °) will show a positive QRS in leads I and AVF (normal = "two thumbs up!")

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  6. What are the characteristics of an abnormal axis?
    Recall, a normal axis (~40 °) will show a positive QRS in leads I and AVF

    • Abnormal axis:
    • 1) Right axis deviation (RAD): QRS is negative in lead I and positive in lead AVF
    • 2) Extreme right axis deviation: QRS will be negative in lead I and lead AVF
    • 3) Left axis deviation (LAD): QRS will be positive in lead I and negative in lead AVF

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  7. How will ventricular hypertrophy affect the EKG?
    Ventricular hypertrophy of either ventricle will affect the QRS complex.
  8. How do you determine if hypertrophy is present?
    • Right ventricular hypertrophy
    • - Axis will shift to right
    • - Will see positive deflections in V1 and V2 that progressively
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    • Left ventricular hypertrophy
    • - Axis will shift left
    • - QRS complexes will be in normal direction, just amplified
    • - Will see huge QRS complexes in V1-V6
    • - To diagnose, measure depth of QRS in Lead V1 and height of QRS in V5: if > 35 mm there is left ventricular hypertrophy
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  9. What are the three hallmarks of infarction?
    • 1) Inverted T waves
    • - Prolonged depolarization of ventricles during ischemia changes pattern of repolarization
    • - Ventricles repolarize in opposite direction to normal repolarization
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    • 2) Elevated or depressed S-T segments
    • - Sign of acute injury
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    • 3) Presence of significant Q waves
    • - Elevated Q waves present in every lead except Lead AVR
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  10. For infarction, which lead will not show elevated Q waves?
    Every lead except Lead AVR will show elevated Q waves if infarction is present.
  11. Is this a normal EKG? If not, what is wrong?

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  12. Is this a normal EKG? If not, what is wrong?

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  13. Is this a normal EKG? If not, what is wrong?

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67524
Card Set
BSI: EKG Interpretation II
Description
BSI: Spring 2011, EKG Interpretation II
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