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ESA 2- Cardiovascular System > ECG > Flashcards

ECG Flashcards

1
Q

What is the myocardium?

A

A large mass of muscle

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2
Q

What is the myocardium undergoing?

A

Electrical changes, all more or less at the same time

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3
Q

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

A

A large, changing electrical field

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4
Q

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

A

By electrodes on the body surface

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5
Q

What do electrodes outside the cell record?

A

Only changes in membrane potential

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6
Q

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

A

Two signals, one depolarisation, one repolarisation

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7
Q

How does excitation spread over the myocardium?

A

Due to the interlinking of cardiac myocytes by gap junctions

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8
Q

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

A

A changing signal, which the electrodes detect

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9
Q

Why do we need gap junctions?

A

To produce coordinated depolarisation, and therefore coordinated contraction

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10
Q

What do gap junctions allow?

A

A pause before the ventricles contract after the atria contract

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11
Q

What is the importance of the pause before ventricles contract?

A

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

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12
Q

How is the ECG explained?

A

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

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13
Q

What is the starting point in conduction of the heart?

A

SA node

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14
Q

What is the passage of conduction through the heart?

A

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

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15
Q

Where are the internodal tracts?

A

Between the nodes

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16
Q

What do the internal tracts throw off?

A

An extra limb of depolarisation by Bachmanns bundle

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17
Q

What does Bachmanns bundle allow for?

A

Smooth contraction of the atria

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18
Q

What does the AV node do?

A

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

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19
Q

What is the Bundle of His needed for?

A

Depolarisation to travel through to get the ventricles

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20
Q

How are the atria and ventricles related electrically?

A

They are separate, apart from through the bundle of His

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21
Q

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

A

Problems

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22
Q

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

A

It is fractionally faster

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23
Q

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

A

Because the left ventricle is larger than the right

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24
Q

Where does the left bundle branch reach?

A

The apex of the left ventricle

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25
Q

What does the right bundle branch do?

A

Feeds the signal to the right ventricle

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26
Q

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

A

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

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27
Q

What do Purkinje fibres do?

A

Feed the rest of the myocardium

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28
Q

How long is it before cells begin to repolarise?

A

About 280ms

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29
Q

How does repolarisation spread?

A

In the opposite direction to depolarisation over the ventricles

30
Q

What repolarises first?

A

Epicardial (outer) surface

31
Q

How do left ventricles contract?

A

In a cork screw way

32
Q

How do atria contract?

A

Like fists

33
Q

What is the advantage of the ventricular method of contraction?

A

It is more efficient and forceful

34
Q

How many electrodes are attached in the ECG?

A

10

35
Q

How many leads are there in the ECG?

A

12

36
Q

In what planes is the heart inspected in the ECG?

A

Frontal

Horizontal

37
Q

What are the types of leads in the ECG?

A

Unipolar

Bipolar

38
Q

What leads are unipolar?

A

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

39
Q

How do unipolar leads read?

A

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

40
Q

What are the bipolar leads?

A

I, II, III

41
Q

What do bipolar leads use?

A

One positive and one negative electrode from the standard limb leads

42
Q

What makes up Einthoven’s triangle?

A

Lead I, II and III

43
Q

Where is lead I positioned?

A

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

44
Q

What is the purpose of lead I?

A

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

45
Q

Where is lead II positioned in Einthovens triangle?

A

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

46
Q

Where is lead III positioned in Einthovens triangle?

A

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

47
Q

Where does lead III look?

A

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

48
Q

Why is lead III the favourite lead?

A

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

49
Q

Where are limb leads placed?

A

Can be anywhere along extremities, but best over bones

50
Q

Why are limb leads bess places over bones?

A

Because less distraction of signals

51
Q

What does depolarisation moving towards an electrode lead to?

A

Positive deflection from the baseline

52
Q

What does depolarisation moving away from an electrode lead to?

A

Negative deflection from the baseline

53
Q

What does repolarisation moving towards an electrode lead to?

A

A negative deflection from the baseline

54
Q

What does repolarisation moving away from an electrode lead to?

A

Positive deflection from baseline

55
Q

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

A

Because repolarisation is negative

56
Q

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

A

It ‘sees’ a different deflection from the baseline

57
Q

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

A

A big spike

58
Q

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

A

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

59
Q

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

A

It changes whether there is positive or negative deflection

60
Q

What does the amplitude of a signal depend on?

A

How much muscle is depolarising

How directly towards the electrode the excitation is moving

61
Q

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

A

They have smaller or larger amounts of muscle

62
Q

What causes the P wave?

A

Atrial depolarisation

63
Q

What causes the Q wave?

A

Septal depolarisation spreading to ventricle

64
Q

Do we always see the Q wave?

A

No

65
Q

What causes the R wave?

A

Main ventricular depolarisation

66
Q

What causes the S wave?

A

End ventricular depolarisation

67
Q

What causes the T wave?

A

Ventricular depolarisation

68
Q

What are the confounders to ECG readings?

A

Lead misplacement
Muscle contraction
Interference
Poor electrode contact

69
Q

How can you tell if leads are placed wrong?

A

You get a completely wrong picture

70
Q

What may cause confounding muscle contraction?

A

Movement
Shivering
Talking
Coughing

71
Q

What can interfere with the ECG?

A

Alternating current from too close equipment

72
Q

What can cause poor electrode contact?

A

Sweat
Cable pull
Hair

ESA 2- Cardiovascular System (18 decks)

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