Electrical Properties of the Heart

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Electrical Properties of the Heart

• Physics of circulation and
• Respiration
• Instructor Prof. Dr. Ir. J.Spaan
• By Derbe Ejere

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Out line

• Electrical Conduction System of The Heart
• The Electrocardiogram
• The Cardiac Arrhythmia

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I Electrical Conduction
System of The Heart
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• Cardiac cells
• A. Myocardial Cells
• ? Make up the mechanical activity of the
  heart
• B. Specialized Cells
• ? Make up the hearts electrical conduction
  system
• ? Have the following properties
• Automaticity
• Excitability
• Conductivity
• Contractility

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http//butler.cc.tut.fi/
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• II
• The Electrocardiogram (ECG)

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A. Heart as a Dipole

• Current flow b/n adjacent depolarized and
  polarized regions ? dipole
• The magnitude of the dipole
• - The mass
• - Charge difference
• Recording dipole ? Electrocardiogram (ECG)
• Why Electrocardiogram? ? Information about
• - Sequence of activation (rhythm)
• - Quantity of tissue activated (hypertrophy)
• - Healthiness of tissue (Ischemia,Infarction)

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B. Electrogenesis of ECG

• ECG waves
• P wave
• QRS Complex
• - Q wave
• - R wave
• - S wave
• T wave

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• 2. ECG Segments
• P-R
• S-T
• 3. ECG Intervals
• P-R
• QRS
• Q-T
• S-T

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C. ECG Leads

• Limb leads ? Electrical activity on frontal plane
• i) Standard leads ? Einthovens triangle
• ? Bipolar
• I
• II
• III
• ii) Augmented leads ?
• Unipolar
• aVR
• aVL
• aVF

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• 2. Precordial (chest) leads
• V1 ?Right bundle branch system
• V2 ?Right anterior surface
• V3 ?Right anterior septal surface
• V4 ?Left anterior surface
• V5 ?Left ventricle
• V6 ?Lateral surface

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• III. The Cardiac Arrhythmias

http//www.sjm.com/
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• 1. Premature Atrial Contraction
• - Atrium depolarizes earlier ?contracts earlier
• - QRS is normal
• - P-Q time is shorter ? S-A is not pacemaker
• - beats originate in parts of the atrium
• 2. Premature Ventricular Contraction
• - Ectopic pacemaker is in ventricle ? early
  contraction
• - QRS complex is inverted ? depolarization wave
  propagates in the opposite direction of the
  normal
• 3. Sinus-bradycardia
• - Normal rhythm (S-A is pacemaker) but slow (lt
  60bpm)

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• 4. Ventricular fibrillation
• - Ventricular tissue randomly generates action
  potentials from many different regions
• - No organization to contraction
• - No P waves, no QRS complex
• 5. Atrial flutter
• - P wave is saw tooth
• - high frequency contraction of Atrium
• - p wave can be transmitted only when the AV
  node and/or Purknjes fibers and/or heart muscle
  cells are depolarized

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• 6. Atrial fibrillation
• - Atrial tissue randomly generates action
  potentials from many different regions
• - No organization to contraction
• 7. Sinus-tachycardia
• - Normal P wave ?S-A is the pacemaker
• - Faster beat than normal
• 8. Ventricular-tachycardia
• - Ectopic pacemaker in the ventricle

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