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Updated: Mar 14 2019

Spread of Excitation

Images conduction.jpg
  • Snapshot
    • A 30-year-old man presents to the emergency room for palpitations and a syncopal episode. His blood pressure is 140/95 mmHg, pulse is 180/min, and respirations are 20/min. An electrocardiogram is ordered and reveals a supraventricular tachycardia. Vagal maneuvers are attempted with no effect. An intravenous medication that slows conduction through the atrioventricular node is started. (Adenosine)
  • Introduction
    • Two types of muscle cells exist in the heart
      • contractile cells
        • working cells of the heart that contract
      • conducting cells
        • tissues
          • sinoatrial (SA) node
            • generate action potentials spontaneously
          • atrioventricular (AV) node
          • atrial intermodal tracts
          • bundle of His
          • Purkinje system
        • rapidly spread action potentials
        • except for the SA node, all other tissues’ ability to generate action potentials are suppressed
  • Spread of Excitation
    • SA node → atrial intermodal tracts → left and right atria → AV node → bundle of His → Purkinje system → ventricles
    • SA node
      • serves as the pacemaker, generating the action potential
    • AV node
      • slows conduction velocity
        • ensures ventricles have enough time to relax and fill with blood before contraction
        • rapid conductions through AV node can lead to decreased stroke volume and cardiac output
    • His-Purkinje system is very rapid
      • low-resistance pathways
      • essential for efficient contraction
    • Relative conduction velocities
      • Purkinje fibers > atria > ventricles > AV node
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