ECG generation Flashcards

1
Q

what is the resting membrane potential in cardiac cells

A

-90 mV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

how is a normal ECG produced

A
  • depolarisation an repolarisation of cells produce an electrical current in oposite directions
  • dipoles exist within the myocardium (currents flow between poles as consequence of ion movement
  • ## a minimum of 2 leads (usually 3) on the blimbs of patient measures the electric charge and compares them to give an ECG
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is magnitude of deflection and what is it determined by

A

height or depth of the waves
determined by:
- direction of depolarisation
- amount of muscle mass that is depolarising (i.e. atria have less deflection than ventricles b/c have less muscle mass)
- which lead you are using or where the electrodes are connected
- other factors such as insulation (fluid or fat surrounding the heart)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

where do you want to place ECG leads on dogs/cats

A
  • left forelimb (below elbow)
  • right forelimb(“ “)
  • left hindlimb (above hock)

rarely placed on the chest unless trying to pick up more subtle details (diagnostic for DCM)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

where do you place ECG leads on horses/cows

A

typically just use a base-apex lead arrangement

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

why dont you see atrial repolarisation in an ECG

A

magnitude of deflection is determined by muscle mass
- since atrial mass is less than ventricular mass, dont see because ECG picks up ventricular, but would be somewhere between QRS

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

what does the P wave indicate

A

depolarisation of the atria.
the direction of the resulatant vector is normally such that the P wave is positive
- direction of resultant vector is normally such that the P wave is positive and points to the left side of the animal during depolarisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

how do you calculate HR from an ECG

A

the number of small boxes on the ECG paper between two R waves can be counted and divided into 3,000 (for a paper speed of 50 mm/s) or 1500 (25 mm/s).
(i.e 1500/# of boxes between 2 R waves)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does the QRS complex indicate

A

depolarisation of the ventricles

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

what does the ECG tell us

A

the electrical activity that intiates contractions NOT contractions themselves

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

why is it possible to produce an ECG from surface electrode monitoring (why can we pick up electircal impulses produced in the heart in the skin of the limbs)

how are electircal impulses produced in the heart picked up in skin

A

because a large number of cells are electrically active simultaneously, the extracellular currents become so strong that it is possible to record voltage differences between electrodes on the surface of the body (electrical currents spread into tissues surrounding the heart)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does the QRS complex indicate

A

depolarisation of the ventricles
depolarisation wave is propogated from the atria, through the AV node and onto the vntricles
- depolarisation of the AV node occurs between the P wave and the beginning of the QRS complex
- the Q wave: the septum is the first part of the ventricles to depolarise resulting in the vector being small and the deflection being negative
- the R wave: from the septum, the depolarisation wave spreads through the prukinje fibres to the inside of the myocardium. during most of the the depolarisation, the resultant vector points downwards from right to left and the deflection is therefore positive
- The S wave: the base of the left ventricle is the last part of the ventricles to depolarise. the direction of the resultant vecotr results in a negative deflection

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does the T wave indicate

A

ventricular repolarisation
biphasic - could be positive or negative, both normal. (would be abnormal in humans, be careful about googling)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what can different sizes of ECG complexes tell you about heart size

A
  • P-wave may be taller with right atrial enlargement
  • Pwave may be wider with left atrial enlargement
  • R wave may be taller with left ventricular enlargment
  • S wave may be deeper with right ventricular enlargement
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

what does paroxysmal tachycardi mean

A

heart rate increases abruptly

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

how do wide and bizarre complexes happen

A
  • can happen is conducting system is damaged
  • damage to one bundle branch of conduction system (BBB bundle branch block)
  • p wave initiated but impulse not conducted normally
17
Q

which lead is usually the most informative

A

lead 2