cardiac electrophysiology part ii lecture 4

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  • 1. Cardiac Electrophysiology Electrocardiogram Part II April Strader Ph.D Lecture 4

2. Electrical Properties of Different Cardiac Tissues From Table 20-3 Little effect strength of contraction I ca , I k , I na Expel blood from VentriclesVentricular 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 PrimaryPacemaker SA Node Cholinergic Effects B-adrenergic Effects Major Currents Function Tissue Name 3. 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 4. Direction of cardiac muscle depolarization 5. P wave depolarization of atria QRScomplex 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 6. Two cell model of EKG activity Positivedeflection Negativedeflection isoelectric When wave of depolarization moves towards a positive electrode, the deflection ispositive. Fig. 20-9 7. 6 limb leads defineelectrical activity infrontal plane 6 precordial leads define electrical activity intransverse plane Each lead is a single axis in one of the planes 12 Lead EKG The 3 augmented leads compare one limb electrode to theaverage 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 8. Electrical axis of the heart is normally between -30 and 90 degrees.Einthovens Triangle (6 limb leads) Fig. 20-8 9. Willem EinthovenNobel prize in 1924 for electrocardiogram (discovered in 1903) 10. Using Einthovens Triangle We can estimate the electrical axis of the heart Read p. 498 Fig. 20-11 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 tissueRight axis deviation (between 180 and 90 degrees) -Tall and thin persons -parallels amount of conductance over tissue 12. Conduction abnormalities and arrhythmias 13. 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

14. First degree block Second degree block Third degree block Normal WPWConduction Arrhythmias 15. 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 ofaction potentials around the loop (to allow for ERP to pass) 16. 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 17. 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 18. -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 19. Hyperkalemia