Cardiac electrophysiology part ii lecture 4
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Cardiac electrophysiology part ii lecture 4 Cardiac electrophysiology part ii lecture 4 Presentation Transcript

  • Cardiac Electrophysiology Electrocardiogram – Part II April Strader Ph.D Lecture 4
  • Electrical Properties of Different Cardiac Tissues From Table 20-3 Little effect ↑ strength of contraction I ca , I k , I na Expel blood from Ventricles Ventricular Muscle Little effect ↑ strength of contraction I ca , I k , I na Expel blood from Atria Atrial Muscle ↓ pacemaker rate ↑ pacemaker rate I ca , I k , I f, I na Tertiary Pacemaker Rapid conduction of AP Purkinje fibers ↓ conduction velocity and pacemaker rate ↑ conduction velocity and pacemaker rate I ca , I k , I f Secondary Pacemaker AV node ↓ conduction velocity and pacemaker rate ↑ conduction velocity and pacemaker rate I ca , I k , I f Primary Pacemaker SA Node Cholinergic Effects B-adrenergic Effects Major Currents Function Tissue Name
  • Electrical system of the heart Purkinje fibers Bundle of His Sinoatrial node Atrioventricular node 3 possible Pacemakers – Primary – Sinoatrial node, Secondary – Atrioventricular node Tertiary – Purkinje fibers
  • Direction of cardiac muscle depolarization
  • P wave – depolarization of atria QRS complex – depolarization of ventricular muscle T wave – repolarization of ventricular muscle *repolarization of atria lies under QRS The Electrocardiogram What information does the EKG give you? Fig. 20-6 rate, rhythm, tissue health
  • Two cell model of EKG activity Positive deflection Negative deflection isoelectric When wave of depolarization moves towards a positive electrode, the deflection is positive. Fig. 20-9
  • 6 limb leads – define electrical activity in frontal plane 6 precordial leads – define electrical activity in transverse plane Each lead is a single axis in one of the planes 12 Lead EKG The 3 augmented leads compare one limb electrode to the average of the other two. (aVR, aVL, aVF) Leads are made of a combination of electrodes that form imaginary lines in the body along which the electrical signals are measured. Fig. 20-7
  • Electrical axis of the heart is normally between -30 and 90 degrees. Einthoven’s Triangle (6 limb leads) Fig. 20-8
  • Willem Einthoven Nobel prize in 1924 for electrocardiogram (discovered in 1903)
  • Using Einthoven’s Triangle We can estimate the electrical axis of the heart Read p. 498 Fig. 20-11
  • What does the axis tell us? Left axis deviation (between -90 and -30 degrees) -Short and/or obese persons -parallels amount of conductance over tissue Right axis deviation (between 180 and 90 degrees) -Tall and thin persons -parallels amount of conductance over tissue
  • Conduction abnormalities and arrhythmias
  • Conduction Blocks
    • First degree AV block
      • Slowing of conduction from SA to AV
      • Longer P-R intervals
    • Second degree AV block
      • Partial block/intermittent
      • P wave intermittently dissociated from QRS (Mobitz type I and II) (long P-R or absent QRS)
    • Third degree AV block
      • Complete block of impulse – complete AV dissociation.
      • Atria and Ventricles are electrically separate, Purkinje take over
      • P waves and QRS have no relationship
      • Usually requires artificial pacemaker
  • First degree block Second degree block Third degree block Normal WPW Conduction Arrhythmias
  • Re-entry – defect is a unidirectional block -Can cause continuous excitation called “circus movement” -Wave of depolarization travels in an endless circle Requirements 1) Closed conduction loop 2) A region of unidirectional block 3) Slow conduction of action potentials around the loop (to allow for ERP to pass)
  • Wolff-Parkinson-White Syndrome -Common example of accessory conduction pathway (Bundle of Kent) -A common route for a re-entry pathway -Often results in supraventricular tachycardia -Occurs in ~ 0.3-1% of population (Bundle of Kent) Delta wave
  • Cation distubances and the EKG
    • Look at how potassium and calcium regulate the action potential and imagine what effect they have on the EKG pattern.
      • Hypokalemia
      • Hypercalcemia
    http://www.gwc.maricopa.edu/class/bio202/cyberheart/ekgqzr2.htm Good EKG quiz website
  • - decreases amplitude or inversion of the T wave -          increases amplitude of the U wave -          prolongation of the Q-T interval -          Increased amplitude of the P wave, prolongation of the P-R interval -          Widening of the QRS complex HYPOKALEMIA
  • Hyperkalemia