ECG generation

Question 1

Describe the generation of the normal ECG?

Answer 1

• Cardiomyocytes are electrically-excitable
• Can generate action potentials
• Waves of depolarisation and repolarisation
• Responsible for rhythmic pumping
• Many cells involved
  
  • Functional syncitium
• Conducted to surface
• Recorded as the ECG
• Electrical activity of the heart can be read off the surface of the skin.

Question 2

What is the normal membrane potential?

Answer 2

-70— 90.

Question 3

Discuss dipoles?

Answer 3

Dipoles exist within the myocardium

• Current flows between poles of these dipoles as a consequence of ion movement
• When we record surface ECG we measure all activity in the ventricular myocytes as the electricity travels through the heart.

Question 4

Show how the wave is generated from placement of the leads and electrical activity?

Answer 4

Question 5

Look at this normal ECG in a dog?

Answer 5

Question 6

Where is the isoelectric baseline?

Answer 6

Question 7

Which are the fastest pacemakers?

Answer 7

SA node is fastest pacemaker > AV node> ventricular pacemakers.

Question 8

Where is AVN conduction in the PQRST complex?

Answer 8

Question 9

Show how ECGs are generated

Answer 9

Question 10

How are wide and bizzare complexes generated?

Answer 10

Passive spread

“wide and bizarre” complexs are generated by rogue pacemaker somewhere in the ventricle generating spontaneous electrical activity not going through the conducting system.

Below you can see these complexes have no P wave

Question 11

What are the two reasons for passive spread and wide and bizarre complexes?

Answer 11

Two reasons for fault:

1. )Electrical activity is coming from ventricle or
2. )conducting system is damaged.

Or both.

Damage to both there will be no conduction to ventricle at all.

Question 12

Show wide and bizarre complexes generated by a conducting abnormality?

Answer 12

P wave is normal but no normal positive upright QRS complex because this animal has damage to its conducting system.

Question 13

Show wide and bizarre complexes caused by electrical activity coming from ventricle?

Answer 13

Wide and bizarre complexes Passive spread Origin is from ventricles

We know this because we have some P waves being generated but the ventricle is being driven by a focus in the ventricles which is generating this wide bizarre complex in the QRS complex.