Learning Module 1: Cardiac Physiology

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Learning Module 1Cardiac Physiology
Clark J. Cotton
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What is Your Heart Rate?

• To take your pulse, place your fingers on your
  wrist and count heart beats.
• Alternatively, place your fingers over your neck
  and count beats.
• Your pulse is the number of beats in 15 seconds
  multiplied by 4.

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What is a Heart?

• The heart is composed of contractile muscle,
  similar to our skeletal muscle.
• The heart acts as a pump for our bodies blood
  supply.
• Blood is pumped to the lungs via the right
  ventricle to pick up oxygen.
• Blood is pumped to the tissue via the left
  ventricle to distribute oxygen throughout the
  body.

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Basic Heart Anatomy

• Heart consists of 4 chambers (2 atria 2
  ventricles).
• Atria are smaller than ventricles, left ventricle
  bigger than right ventricle.
• Blood flows in the following order
• 1. Right atria
• 2. Right ventricle
• 3. Lungs
• 4. Left atria
• 5. Left ventricle
• 6. Rest of Body

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What is an Action Potential?

• Normally, our cells maintain a membrane potential
  of -55mV.
• During an action potential, the membrane
  potential quickly reaches 5mV for a short time.
• The large spike in membrane potential is due to
  an influx of positive Na and Ca2 ions.

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What Causes a Heart Contraction?

• There are several areas of the heart that
  rhythmically fire action potentials generating a
  wave of electrical energy. This electrical
  signal is what causes the heart muscles to
  contract.
• The S-A node depolarizes at the fastest rate and
  is therefore the pacemaker for the heart. The
  rest of the nodes transfer the electrical signal
  of the SA-node to the other chambers of the
  heart, stimulating them to contract in turn.

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Electrocardiograms (ECGs)

• Because a large number of cells in the heart
  rhythmically depolarize, with each contraction,
  we can record the electrical changes on our body
  surface.
• This electrical trace is known as an
  electrocardiogram.

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Electrocardiogram and Heart Rate

• The SA-node is the first part of the heart to
  show electrical activity.

ECG
Heart
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Electrocardiogram and Heart Rate

• Shortly after the SA-node fires, both atria of
  the heart depolarize (P-wave) followed closely by
  atrial contraction.

ECG
Heart
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Electrocardiogram and Heart Rate

• There is a brief pause, and then the AV-node,
  Bundle of HIS, and Purkinje fibers fire in
  succession (QRS complex).

ECG
Heart
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Electrocardiogram and Heart Rate

• There is a brief pause, and then the AV-node,
  Bundle of HIS, and Purkinje fibers fire in
  succession (QRS complex).

ECG
Heart
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Electrocardiogram and Heart Rate

• There is a brief pause, and then the AV-node,
  Bundle of HIS, and Purkinje fibers fire in
  succession (QRS complex).

ECG
Heart
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Electrocardiogram and Heart Rate

• There is a brief pause, and then the AV-node,
  Bundle of HIS, and Purkinje fibers fire in
  succession (QRS complex).

ECG
Heart
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Electrocardiogram and Heart Rate

• Following Ventricular depolarization, the
  ventricles contract and repolarization
  (T-wave) occurs.

ECG
Heart
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How Does the Electrical Signal Travel Throughout
the Heart?

• The electrical signal from pacemaker cells
  spreads to nearby cells via gap junctions.
• Gap junctions are channels that are shared by two
  adjacent cell membranes.
• When one heart cell fires an electrical signal,
  the signal quickly spreads to neighboring cells.

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Concept Maps

• Concept maps are a great way to organize complex
  material in an easy to understand manner.
• For example, consider the concept of a farm. To
  describe a farm, you might use the following
  terms
• Farm, Farmer, Banker, Hired Help, Livestock,
  Land, Machinery, Crops, Manure.
• A concept map provides a useful framework in
  which to visualize these terms.

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Concept Maps

• Concept maps are a great way to organize complex
  material in an easy to understand manner.
• For example, consider the concept of a farm. To
  describe a farm, you might use the following
  terms
• Farm, Farmer, Banker, Hired Help, Livestock,
  Land, Machinery, Crops, Manure.
• A concept map provides a useful framework in
  which to visualize these terms.

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Cardiac Physiology Concept Map

• Construct a concept map of cardiac physiology
  using the following terms
• Atria, Ventricles, gap junctions, action
  potentials, p-waves, QRS complex, t-wave,
  arteries, veins, systole, diastole, pacemaker,
  SA-node, AV-node, Bundle of HIS, Purkinje fibers,
  electrocardiogram.