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Lec50) Lec50) Presentation Transcript

  • Learning Modules
    The Conduction System
    ECG Basics
    How to Analyze a Rhythm
    Normal Sinus Rhythm
    Heart Arrhythmias
    Advanced 12-Lead Interpretation
  • Generating rhythmical electrical impulses to cause rhythmical contraction of the heart muscle
    (2) Conducting these impulses rapidly through the heart
    The Conduction System
  • Depolarization and Impulse Conduction
    Heart is autorhythmic
    Depolarization begins in sinoatrial (SA) node
    Spread through atrial myocardium
    Delay in atrioventricular (AV) node
  • Depolarization and Impulse Conduction
    Spread from atrioventricular (AV) node
    AV bundle
    Bundle branches
    Purkinje fibers
  • Specialized Excitatory and Conductive System of the Heart
    Sinoatrial node
    Internodal pathways
    AV node
    A-V Bundle (Bundle of His)
    Bundle Branches
    Purkinje fibers
  • Sinoatrial (also called sinus or S-A node, in which the normal rhythmical impulse is generated
    Internodal pathwaysthat conduct the impulse from the sinus node to the atrioventricular (A-V) node
    A-V node, in which the impulse from the atria is delayed before passing into the ventricles
  • A-V bundle, which conducts the impulse from the atria into the ventricles
    Left and right bundle branches of Purkinje fibers, which conduct the cardiac impulse to all parts of the ventricles
  • The impulse reaches the A-V node about 0.03 second after its origin in the sinus node
    Then there is a delay of another 0.09 second in the A-V node
    A final delay of another 0.04 second occurs mainly in penetrating of the A-V bundle
  • The total delay in the A-V nodal and A-V bundle system is about 0.13 second. This, in addition to the initial conduction delay of 0.03 second from the sinus node to the A-V node
    This makes a total delay of 0.16 second before the excitatory signal finally reaches the contracting muscle of the ventricles
  • The total time for transmission of the cardiac impulse from the initial bundle branches to the last of the ventricular muscle fibers in the normal heart is about 0.06 second.
  • The Spread of the Cardiac Impulse Through the Heart
    • The impulse spreads through the atria but is delayed more than 0.1 second in the A-V nodal region before appearing in the ventricular septal A-V bundle
    • Once it has entered this bundle, it spreads very rapidly through the Purkinje fibers to the entire endocardial surfaces of the ventricles
    • Then the impulse spreads through the ventricular muscle to the epicardial surfaces
  • Pacemakers of the Heart
    SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.
    AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.
    Purkinje fibers- Back-up pacemaker with an intrinsic rate of 20 - 45 bpm.
  • Atrial Muscle (Nodal) Action Potential
    Outward K+ current (repolarization)
    Inward Na+ and Ca++ ions (depolarization)
    Threshold
    Slow spontaneous Inward Na+ ions
    Automaticity - a pacemaker cell’s ability to spontaneously depolarize, reach threshold, and propagate an AP
  • Self-Excitation of Sinus Nodal Fibers
    Sodium ions from outside the fibers tend to leak to the inside Influx of positively charged sodium ions causes a slow rise in the resting membrane potential in the positive direction
    Sodium- Calcium channels become activated and causing the action potential
    Influx of sodium and calcium ions then ceases while large quantities of positive potassium ions diffuse out of the fiber
  • Normal Electrocardiogram
    The electrocardiogram (EKG) is a representation of the electrical events of the cardiac cycle
    The electrical potentials generated by the current can be recorded; the recording is known as an electrocardiogram
    It is most valuable diagnostic tools for the recognition of large variety of cardiac disorders