1. Guyton 2011 pages 115-120 Berne 2008 pages 302-309

2. Excitatory and Conductive System of the Heart Natural Excitation of The Heart To cause rhythmical contraction of the heart muscle Conducting impulses rapidly through the heart. Is susceptible to damage by heart disease, especially by ischemia of the heart tissues

3. SA Node = normal pacemaker Natural Excitation of The Heart Have two cell type RMP is much less negative Lack the i Kl, then the ratio of g K to g Na during phase 4 is much less Pacemaker Cells (Small, round cells having few organelles and myofibril) Conductor Cells (Slender, elongated cells)

4. SA Node = normal pacemaker Natural Excitation of The Heart Change the slope of Phase 4 Change the RMP Change threshold Potential Change the Heart Rate Normal rhythm = 70 – 80 beats/min

5. SA Node = normal pacemaker Depolarization and repolarization is slower in slow responses Na, Ca Ca K Natural Excitation of The Heart

6. Internodal Pathways Natural Excitation of The Heart

7. AV Node Natural Excitation of The Heart Regions AN region (transitional zone) N region (mid portion) NH region Cause of the Slow Conduction Mainly by diminished numbers of gap junctions One-way conduction Normal rhythm = 40 – 60 beats/min

8. Purkinje fibers Natural Excitation of The Heart Cause of the Rapid Conduction mainly by increased numbers of gap junctions Normal rhythm = 15– 40beats/min

9. Summary of the Spread of the Cardiac Impulse Through the Heart (second) Natural Excitation of The Heart

10. Conduction Rate (m/s)Tissue 0.05SA node 1Internodal Pathways 0.05AV node 1Bundle of His 2Left and Right Bundles 4Purkinje System 1Ventricular Muscle Impulse Velocity in Different Part of the Heart

11. Natural Excitation of The Heart Points Overrdrive Suppression Stokes - Adams Syndrome Ectopic Pacemaker

12. Natural Excitation of The Heart Effect of ANS of cardiac rhythmicity

13. Natural Excitation of The Heart Parasympathetic division Sympathetic division Mainly innervates nodes Acetylcholine Increased permeability to K Increases the overall activity of the heart Norepinephrine Increased permeability to Na and Ca Innervates all areas Decreases Heart Rate

14. Reentry Phenomenon Natural Excitation of The Heart

15. Reentry Mechanisms Natural Excitation of The Heart Pathway around the circle is too long Like cardiac dilation Velocity of conduction becomes decreased Blockage of the Purkinje system, Ischemia of the muscle, High blood potassium levels The refractory period of the muscle shortened in response to various drugs, such as epinephrine or after repetitive electrical stimulation

16. Global Reentry Natural Excitation of The Heart

17. The End

18. Early afterdepolarizations More likely to occur when the prevailing heart rate is slow; a rapid heart rate suppresses EADs Induced by the addition of cesium in an isolated Purkinje fiber preparation. More likely to occur in cardiac cells with prolonged action potentials than in cells with short action potentials. Early afterdepolarizations More likely to occur when the prevailing heart rate is slow; a rapid heart rate suppresses EADs Induced by the addition of cesium in an isolated Purkinje fiber preparation. More likely to occur in cardiac cells with prolonged action potentials than in cells with short action potentials. Triggered activities When action potentials are sufficiently prolonged, some Ca++ channels that were activated at the beginning of the plateau have sufficient time to recover from inactivation

19. Delayed afterdepolarizations The amplitudes of the DADs are increased by interventions that raise intracellular Ca ++ concentrations. Increasing the extracellular [Ca ++ ] Administering toxic amounts of digitalis glycosides. Delayed afterdepolarizations The amplitudes of the DADs are increased by interventions that raise intracellular Ca ++ concentrations. Increasing the extracellular [Ca ++ ] Administering toxic amounts of digitalis glycosides. Triggered activities