Electrophysiology of the Heart

1. Electrophysiology of the Heart J.M. Cairo, Ph.D. Telephone: 568-4246 Email: jcairo@lsuhsc.edu

2. Electrophysiological Properties of the Heart • Excitability • Ability of the heart to respond to a stimulus • Rhythmicity (Automaticity) • Ability of the heart to initiate a depolarization in the absence of external stimuli • Conductivity • Ability of the heart to propagate an impulse once it has been initiated

3. Other terms… • Chronotropy • Relates to heart rate: a positivechronotropic agent will increase heart rate; a negativechronotropic agent will decrease heart rate • Dromotropy • Relates to conduction velocity: a positivedromotropic agent will increase the conduction velocity of an impulse through the heart; a negativedromotropic agent will slow the conduction velocity of the impulse

4. Effect of Adrenergic and Cholinergic Stimulation

5. Excitability

9. Factors Affecting Resting Membrane Potential in Cardiac Myocytes • Macromolecules • Diffusible ions (Na+, K+, Ca++, Cl-) • Electrochemical gradients • Sodium-Potassium ATPase pump

12. Major Cardiac Membrane Currents

14. Membrane Currents for the Various Phases of the Ventricular Myocyte Action Potential • Phase 0 (Rapid Upstroke) • INaand ICa • Phase 1 (Early Repolarization) • Inactivation of INa and ICa, and IK (minor contribution) • Phase 2 (Plateau) • Continued entry of Na and Ca through major channels and minor membrane current due to Na-Ca exchanger • Phase 3 (Repolarization) • IK • Phase 4 (Diastolic period) • IK and Na-K pump

15. Refractory Periods

16. Refractory Periods • Absolute Refractory Period • Beginning of phase 0 to the beginning of phase 3 • Refractory to all stimuli • Relative Refractory Period • Beginning of phase 3 to the beginning of phase 4 • A stronger than normal stimulus will result in an AP that is less than a normal AP

17. Rhythmicity/Automaticity

19. Major Cardiac Membrane Currents

21. Membrane Currents for the Various Phases of the SA node and AV node Action Potentials • Phase 0 (Slow Upstroke) • INaand ICa • Phase 3 (Repolarization) • IK • Phase 4 (Diastolic depolarization) • IK, ICa, If

22. Principle Time Dependent and Voltage Dependent Currents

24. Effect of Adrenergic and Cholinergic Stimulation on Pacemaker Activity

26. Conductivity

27. Conduction Velocities in Different Cardiac Tissue