Topic 24 - Electrocardiogram; analysis of ECG

Question 1

Words to include

Answer 1

• Eelectrocardiography (ECG)
  
  • Electric activity
  • Myocyte
  • Eintholen’s triangle
    
    • mV
    • Bipolar leads
    • Lead 1
      
      • RA
      • LA
    • Lead 2
      
      • RA
      • LL
    • Lead 3
      
      • LA
      • LL
    • Refrence electrode
    • Investigating electrode
  • Heart as a dipole
    
    • Working fibers
    • Action potential
    • Membrane
    • Three-dimentional vector
    • Oscillogram
    • Depolarization
    • Plateu
    • Isoelectric line
    • Repolarization
    • Downward deflection
    • Total repolarization
  • Potential differences (U)
    
    • Electrode
• Electrocardiogram
  
  • Graphic pattern
  • Potential changes
  • Rhytmic cardiac activity
  • Ultrasound
• ECG curve
  
  • Waves
  • Segment
  • Intervals / complexes
  • P-wave
    
    • Atrial depolarization
  • PQ-segment
    
    • Isolectric line
    • Atrial depolarization
  • QRS-complex
    
    • Ventricular depolarization
    • Atrial repolarization
  • Q-wave
    
    • Bundle of His
    • Downward deflection
  • R-wave
    
    • Ventricular depolarization
  • S-wave
    
    • Right ventricle depolarization
    • Endocardium
    • Epicardial surfaces
  • ST-segment
    
    • Isoelectric line
    • Ventricular depolarization
  • T-wave
    
    • Ventricular repolarization
  • TP-segment
    
    • Resting phase
    • Full repolarization
    • Myocytes
• Oscilloscope
  
  • Asymmetrical
• Unipolar
  
  • Right arm
  • Left arm
  • Left leg
  • 0 Potential refrence point
• His bundle ECG
  
  • SA node
  • AV node
  • Conduction system
  • Septum
• Esophageal ECG
  
  • SA node
  • AV node
  • Conduction system
• Vectorcardiography
  
  • Anatomy
• Vector loop
• Echocardiography
  
  • Ultrasound examination
  • Anatomy
  • Doppler (blood flow)

Question 2

1. Define electrocardiogram
2. Define ECG

Answer 2

1. Electrocardiogram: The graphical pattern representing the potential changes during rhythmic cardiac activity
2. Electrocardiography (ECG): Electric activity of the whole heart
   
   • Electrocardiography is the process of producing an electrocardiogram

Question 3

How are potential differences measured?

Answer 3

• Potential differences (U) are measured between the pairs of electrodes
  
  • During rest: the sum of the potential differences around the dipole (integral vector) is always zero

Question 4

The heart as a dipole

Answer 4

• All single working fibers can be looked at as a dipole as the different phases of the AP travel alongside its membrane
• The dipole can be characterized by a three-dimensional vector which has direction, measure and polarity

1. In rest no AP, the oscillogram is at isoelectric line
2. If depolarization happens under the refrence electrode, there is an upstroke on oscillogram
3. At total depolarization (plateu) we are back at isoelectric line
4. When repolarization begins, there is a downward deflection on depolarization
5. At total repolarization, no potential difference, so isoelectric line in rest

Question 5

Einthoven’s triangle

Answer 5

• Einthoven invented a device to detect slight electric changes (mV)
  
  • Pairs of electrodes are placed around the heart as dipole – creating the Einthoven’s Triangle
• Einthoven’s standard bipolar leads are the potential differences measured between two of the three electrodes placed onto the surface of the body around the heart at the points of a uniform triangle

1. Lead 1​
   
   1. ​Refrence electrode: RA
   2. Investigating electrode: LA
2. Lead 2
   
   1. ​​Refrence electrode: RA
   2. Investigating electrode: LL
3. Lead 3
   
   1. ​​Refrence electrode: LA
   2. Investigating electrode: LL

Question 6

Analysis of ECG curves

Answer 6

• Waves: Deflections on the ECG curve
• Segment: The part of the line that falls between waves
• Intervals / complexes: Large parts that may contain one or more waves and segments
• ​Divided into:
  
  • P-wave
    
    • ​Positive deflection
    • Beginning of atrial depolarization
  • PQ-segment
    
    • ​On the isoelectric line
    • Total atrial depolarization
  • QRS-complex (beginning of ventricular depolarization and atrial repolarization)
    
    • ​Q-wave
      
      • ​Transmission of the excitation from the bundle of His to the ventricular muscles
      • Downvard deflection
    • R-wave
      
      • ​Max ventricular depolarization
      • The stimulus runs from the endocardium to pericardium and from base to apex
    • S-wave
      
      • ​Right ventricle depolarization from the endocardium close to the apex towards the epicardial surfaces of the base of the heart
  • ST-segment
    
    • ​Isoelectric line on the oscilloscope
    • Ventricular depolarization
  • T-wave
    
    • ​Beginning of ventricular repolarization
  • TP-segment
    
    • ​Resting phase, following full repolarization
      
      • ​Oscilloscope is at the isoelectric line
    • Myocytes:
      
      • ​Outside: positive +
      • Inside: negative ÷

Question 7

How can we measure ECG?

Answer 7

• By an oscilloscope, the asymmetry of the heart makes measurable the total electric activity of it
• ECG can only be measured because the heart is an asymmetrical object of changing wall thickness

Question 8

Give the different types of ECG

Answer 8

1. Unipolar
   
   • RA, LA and LL connected to each other via high resistance forming 0 potential reference point
   • The potential difference between 0-point and different points on the surface are detected
2. His bundle ECG
   
   • Electrode goes up to the septum through vein catheter
   • Analysis of SA, AV node and the conduction system
3. Esophageal ECG
   
   • Electrode through esophagus close to the heart
   • Analysis of SA, AV node and the conduction system
4. Vectorcradiography
   
   • Information about the anatomy of the heart
5. Vector loop
   
   1. Provides info about the functioning of certain territories
6. Echocardiography
   
   • Ultrasound examination
   • Provides more detailed picture about the anatomy of the heart and about the blood flow (Doppler)