Cardiac Conduction

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  1. Conduction system:
    • SA node
    • AV node
    • Bundle of His
    • Purkinje Fibers
  2. Electrical impulses cause the heart to
    depolarize as the heart chambers contract
  3. SA: Paces
  4. AV: Paces
  5. Bundle of His: Paces
  6. Depolarization
  7. Repolarization
    relaxation, return to normal resting stage of the cell
  8. The SA node is the
    Dominant pacemaker

    “Sinus Rhythm”

    Similar to “pebble dropped in water” sending ripple effects starting with atria contraction
  9. “P” Wave
    Atrial depolarization

    Time when atrium is contracting
  10. “PR” interval
    Impulse travel through the conduction system

    impulse is traveling through the conduction
  11. QRS Complex
    After the electrical activity passes through the AV node, bundle branches and Purkinje Fibers then depolarization of the ventricles occur

    The filaments of the Purkinje fibers distribute the depolarization stimulus to the ventricular myocardial cells

    Depolarization of the ventricles produces the QRS complex

    Measured from the beginning of the Q Wave until the end of the S wave.
  12. “Q” wave
    First downward deflection

    Not always present
  13. R wave
    Upward wave
  14. S wave
    Follow R wave

    Downward stroke

    Should return to baseline
  15. “ST” segment
    Represent early ventricular repolarization

    Normally isoelectric line
  16. ST elevations or depression can be caused by
    myocardial injury, ischemia, infarction etc.
  17. T wave tells whether you are having an
  18. “T” wave
    Low broad hump

    Rapid phase of ventricular repolarization

    Repolarization of the ventricles begin immediately after the QRS complex and persists until the end of the T wave
  19. Artifact
    Interference seem on rhythm strip or monitor

    Looks like fuzzy baseline

    Caused by patient moving, loose electrodes,

    Can mimic lethal rhythms – check patient!

    • Can look like an arrythmia. Chieck pt if , if pt is
    • stable could be leads or pt is moving
  20. EKG tracing paper
    Each smallest block is 1mm by 1mm

    Each small block is 0.04 sec.

    Between the heavy black lines are 5 small squares totaling 0.2sec.
  21. Counting rate:
    Usually from R wave to R wave

    Several methods

    -“big block method” – most accurate

    -“6 second strip” – quick method least accurate

    -“Memory method”
  22. What does th p wave in an ECG represent
    atrial depolarization
Card Set
Cardiac Conduction
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