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ESA 2- Cardiovascular System > ECG > Flashcards

Flashcards in ECG Deck (72):
1

What is the myocardium?

A large mass of muscle

2

What is the myocardium undergoing?

Electrical changes, all more or less at the same time

3

What does the electrical changes going on in the myocardium generate?

A large, changing electrical field

4

How can the electrical field produced by the myocardium be detected?

By electrodes on the body surface

5

What do electrodes outside the cell record?

Only changes in membrane potential

6

What do the skin electrodes ‘see’ with each systole?

Two signals, one depolarisation, one repolarisation

7

How does excitation spread over the myocardium?

Due to the interlinking of cardiac myocytes by gap junctions

8

What does the spread of excitation spreading over the myocardium generate?

A changing signal, which the electrodes detect

9

Why do we need gap junctions?

To produce coordinated depolarisation, and therefore coordinated contraction

10

What do gap junctions allow?

A pause before the ventricles contract after the atria contract

11

What is the importance of the pause before ventricles contract?

It allows for a more rapid spread through the myocytes, so more of the tissue is contracting at once

12

How is the ECG explained?

By a combination of the effects of depolarisation and repolarisation, and their spread over the heart

13

What is the starting point in conduction of the heart?

SA node

14

What is the passage of conduction through the heart?

SA node →  internodal tracts →  AV node →  Bundle of His →  Left bundle branch and right bundle branch →  Purkinje fibres

15

Where are the internodal tracts?

Between the nodes

16

What do the internal tracts throw off?

An extra limb of depolarisation by Bachmanns bundle

17

What does Bachmanns bundle allow for?

Smooth contraction of the atria

18

What does the AV node do?

Holds everything for a moment so there is a pause in the signal to allow all of the atria to contract

19

What is the Bundle of His needed for?

Depolarisation to travel through to get the ventricles

20

How are the atria and ventricles related electrically?

They are separate, apart from through the bundle of His

21

What will electrical non-seperation cause of the atria and ventricles cause?

Problems

22

How does the left bundle branch differ from the right bundle branch?

It is fractionally faster

23

Why is the left bundle branch slightly faster than the right bundle?

Because the left ventricle is larger than the right

24

Where does the left bundle branch reach?

The apex of the left ventricle

25

What does the right bundle branch do?

Feeds the signal to the right ventricle

26

What is the result of the left and right bundle branches reaching the apex of heart?

Blood is pumped out from the bottom upwards, so blood is pushed out through large vessels

27

What do Purkinje fibres do?

Feed the rest of the myocardium

28

How long is it before cells begin to repolarise?

About 280ms

29

How does repolarisation spread?

In the opposite direction to depolarisation over the ventricles

30

What repolarises first?

Epicardial (outer) surface

31

How do left ventricles contract?

In a cork screw way

32

How do atria contract?

Like fists

33

What is the advantage of the ventricular method of contraction?

It is more efficient and forceful

34

How many electrodes are attached in the ECG?

10

35

How many leads are there in the ECG?

12

36

In what planes is the heart inspected in the ECG?

Frontal 
Horizontal

37

What are the types of leads in the ECG?

Unipolar 
Bipolar

38

What leads are unipolar?

Chest leads (V1-V6) and augmented leads (AVR, AVL, AVF)

39

How do unipolar leads read?

From labelled positive electrode, and utilise several other electrodes as the negative

40

What are the bipolar leads?

I, II, III

41

What do bipolar leads use?

One positive and one negative electrode from the standard limb leads

42

What makes up Einthoven’s triangle?

Lead I, II and III

43

Where is lead I positioned?

From the negative electrode on the right arm to the positive electrode on the left arm

44

What is the purpose of lead I?

It is the ‘seeing’ electrode- the field of view

45

Where is lead II positioned in Einthovens triangle?

Goes from negative electrode on right arm to positive electrode on left leg

46

Where is lead III positioned in Einthovens triangle?

Goes from positive electrode on left leg to negative electrode on left arm

47

Where does lead III look?

From the left up, looking through the apex of the heart

48

Why is lead III the favourite lead?

Because it looks through the apex of the heart, and therefore good for looking the rhythm of heart

49

Where are limb leads placed?

Can be anywhere along extremities, but best over bones

50

Why are limb leads bess places over bones?

Because less distraction of signals

51

What does depolarisation moving towards an electrode lead to?

Positive deflection from the baseline

52

What does depolarisation moving away from an electrode lead to?

Negative deflection from the baseline

53

What does repolarisation moving towards an electrode lead to?

A negative deflection from the baseline

54

What does repolarisation moving away from an electrode lead to?

Positive deflection from baseline

55

Why does repolarisation cause a negative deflection when it’s moving towards you?

Because repolarisation is negative

56

What happens as an electrode is moved in relation to the heart?

It ‘sees’ a different deflection from the baseline

57

What will be seen if the current is moving directly towards the electrode?

A big spike

58

What will be seen if the current is passing near to the electrode?

There will be a peak/trough, but doesn’t have the same magnitude- will be a small change

59

What happens to deflection as you move the electrode around the heart?

It changes whether there is positive or negative deflection

60

What does the amplitude of a signal depend on?

How much muscle is depolarising 
How directly towards the electrode the excitation is moving

61

How do different portions of the hear give different amplituded waves?

They have smaller or larger amounts of muscle

62

What causes the P wave?

Atrial depolarisation

63

What causes the Q wave?

Septal depolarisation spreading to ventricle

64

Do we always see the Q wave?

No

65

What causes the R wave?

Main ventricular depolarisation

66

What causes the S wave?

End ventricular depolarisation

67

What causes the T wave?

Ventricular depolarisation

68

What are the confounders to ECG readings?

Lead misplacement
Muscle contraction 
Interference
Poor electrode contact

69

How can you tell if leads are placed wrong?

You get a completely wrong picture

70

What may cause confounding muscle contraction?

Movement
Shivering
Talking 
Coughing

71

What can interfere with the ECG?

Alternating current from too close equipment

72

What can cause poor electrode contact?

Sweat
Cable pull
Hair