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2011-06-17 00:34:26
cardiology defenitions etc


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  1. Repolarization
    Repolarization - Recovery.

    -After depolarization, sodium channels close, calcium channels close, and potassium flows out from the cell.

    • -The sodium-potassium pump restores the cell to its negative state from the outpouring of potassium.
    • Can be stimulated if the impuse is stong enough.
  2. Depolarization
    Depolarization - Stimulation

    Sodium rushes into the cell through fast sodium channeels. Calcium moves into the cells slowly.

    • -Causes the inside of the cell to become more positive.
    • -Contraction begins from the innermost layer (endocardium) to the outermost layer (epicardium).

    Depolarization is an electrical event expected to result in contraction, which is mechanical output, PEA is electrical without output.
  3. Polarization
    Polarization - ready state

    • Resting state when no electrical activity occurs in the heart.
    • More negative on the inside.
    • Waiting and ready for an impulse.
  4. Normal axis (0 to 90 degrees)
    • Lead I - positive
    • Lead aVF - positive
    • Lead II - nil
  5. Left axis deviation (30 to 90 degrees)
    • Lead I - positive
    • Lead aVF - negative
    • Lead II - negative
  6. Right superior axis (-90 to +180 degrees)
    • Lead I - negative
    • Lead aVF - negative
    • Lead II - positive
  7. How to determine positive or negative axis deviation?
    Net QRS voltage = upwards-downward deflection (mm) = a -b = 3 - 2 = 1
  8. Normal variant (0 to -30 degrees)
    • Lead I - positive
    • Lead aVF - negative
    • Lead II - positive
  9. What is axis deviation?
    Major vector of ventricular activiation. Determine if 'net QRS voltage' is positive (>0) in leads I, II, and aVF. Dictates which direction the electricity is moving through the heart.
  10. Right axis deviation (>100 degrees)
    • Lead I - negative
    • Lead aVF - positive
    • Lead II - nil
  11. Chronotropic effects
    Chronotropic effects are those that change the heart rate.

    Chronotropic drugs may change the heart rate by affecting the nerves controlling the heart, or by changing the rhythm produced by the sinoatrial node. Positive chronotropes increase heart rate; negative chronotropes decrease heart rate.

    • Positive Chronotropes - (increases heart rate)
    • Most Adrenergic agonists
    • Atropine
    • Dopamine
    • Epinephrine
    • Isoproterenol

    • Negative Chronotropes - (decreases heart rate)
    • Beta-blockers such as Metoprolol
    • Acetylcholine
    • Digoxin
    • The non-dihydropyridine calcium channel blockers like diltiazem and verapamil
  12. Dromotropic effect
    A dromotropic agent is one which affects the conduction speed in the AV node, and subsequently the rate of electrical impulses in the heart.[1][2]