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Electrophysiology of the Heart

Explore the intricate workings of the heart's electrophysiological properties, from excitability to automaticity, conductivity, and the effects of Adrenergic and Cholinergic stimulation on pacemaker activity. Learn about the major cardiac membrane currents in different phases of action potentials. Delve into refractory periods, rhythmicity, and factors affecting resting membrane potential in cardiac myocytes. Discover the role of time-dependent and voltage-dependent currents, and how conductivity varies in different cardiac tissues.

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Electrophysiology of the Heart

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  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

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

  7. Major Cardiac Membrane Currents

  8. 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

  9. Refractory Periods

  10. 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

  11. Rhythmicity/Automaticity

  12. Major Cardiac Membrane Currents

  13. 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

  14. Principle Time Dependent and Voltage Dependent Currents

  15. Effect of Adrenergic and Cholinergic Stimulation on Pacemaker Activity

  16. Conductivity

  17. Conduction Velocities in Different Cardiac Tissue

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