The Heart Conduction System

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The Heart Conduction System

• Prepared by
• Eric Johannesen
• Iowa-Grant High School

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The Heart Conduction System

• The rate at which the heart beats is controlled
  by the nervous system.
• The actual beat begins within the heart itself
  and will begin without any nerve supply
• The cells that begin the heartbeat are called
  pacemaker cells.
• The pacemaker system is important in maintaining
  the hearts regular rhythm.
• The system must also function to make the heart
  contract in a high organized manner.
• The atria must contract so that blood is
  efficiently pumped out of the heart.

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The Pacemaker System

• Called the sinoatrial node (SA)
• Special group of muscle cells found in the right
  atrium
• The electrical signal allows the pulse to spread
  across the atria. The atria contracts and forces
  blood into the two ventricles.

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Cardiac Cycle

• The Cardiac Cycle included one complete
  contraction and a following relaxation phase
• During relaxation, the atria fill with blood in
  preparation for the next contraction.
• Contraction phase is called Systole and the
  relaxation phase is called Diastole
• Blood pressure measurements are taken during both
  phases of the cardiac cycle
• The higher of the two numbers represents the
  systolic phase (Contraction of the heart) and the
  diastolic occurs when the heart relaxes.
• In humans, a typical number is 120/75

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Electrocardiogram

• The flow of ions that allows the cardiac muscle
  to contract causes a small electrical current.
• An ECG (Electrocardiogram) is the electronic
  instrument that measures this small activity.

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Sinus Rhythm-Normal Rate
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Sinus TachycardiaHeart Rate Faster Than Normal
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Sinus BradycardiaHeart Rate is Slower Than Normal
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Atrial FibrillationThe SA node no longer acts as
the pacemaker.
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Ventricular FibrillationThe ventricles fire
uncontrollably. Very serious condition. The
heart muscle quivers. Shockable rhythm.
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AsystoleFlat Line Non-Shockable Rhythm
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Lub-Dub

• The sound of Lub-Dub
• Lub is created when the ventricles contract
• Dub occurs when the ventricles relax

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What effects heart rates?

• Elevated stress
• Illness
• Activity
• Cardiac Event
• Heart Murmurs
• Defective Valve or valves