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 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

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 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

6. 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

7. 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

8. Electrical axis of the heart is normally between -30 and 90 degrees. Einthoven’s Triangle (6 limb leads) Fig. 20-8

9. Willem Einthoven Nobel prize in 1924 for electrocardiogram (discovered in 1903)

10. Using Einthoven’s 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 tissue Right axis deviation (between 180 and 90 degrees) -Tall and thin persons -parallels amount of conductance over tissue

12. Conduction abnormalities and arrhythmias

14. First degree block Second degree block Third degree block Normal WPW Conduction 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 of action 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

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