Wednesday, April 8, 2015

Thank God for Khan Academy: EKG III--Lead II, An Explanation of Normal Sinus Rhythm

"Normal Sinus Rhythm" on an EKG by KhanAcademyMedicine

  • Your typical EKG P-QRS-T complex figure is a Lead II EKG.  It records electrical activity from the SA node towards the bottom left part of your heart (your left leg, actually).
  • Tiny boxes=0.04sec
  • AV node cells are narrow=slow conduction.
  • Sodium channels are FAST at depolarizing.
  • ST segment=no net current =/= not active--it's when the ventricles are fully contracted--remember, the EKG is the electrical map and it actually precedes the actual contraction.
  • The PR wave is measured instead of the PQ wave because sometimes the Q doesn't show up.
  • The direction of which the waves and peaks go dictate whether it is the endocardium or epicardium depolarizes and repolorizes first.  (Cool--but not really necessary to understand.)

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