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Semester 2 > CVS Session 7 > Flashcards

CVS Session 7 Flashcards

0
Q

Why do electrodes outside the cell ‘see’ two signals with each systole?

A

Can only ‘see’ changing membrane potential therefore one signal for depolarisation and one for repolarisation

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1
Q

In which direction does the large changing electrical field generated by the myocardium travel?

A

Radiating away from the myocytes through the body to the skin

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2
Q

What does an ECG show?

A

Effects of depolarisation
Effects of repolarisation
Spread of electrical field alteration over the heart

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3
Q

How does conduction spread over the atria?

A

Starts at SAN
Spreads over atria to AVN
AVN delays conduction for 120 ms

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4
Q

How does spread of excitation cause ventricular depolarisation?

A

Activity spread down septum then out over ventricular myocardium
Endocardial –> epicardial

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5
Q

What causes depolarisation to spread in the epicardial direction?

A

A uniform thin layer of depolarisation in the endocardial surface

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6
Q

Where does the last signal seen originate from?

A

Activity of cells at base of valves

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7
Q

How does repolarisation occur?

A

After 280 ms it spreads in the opposite direction to depolarisation

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8
Q

Why does repolarisation occur in the opposite direction to depolarisation?

A

To unravel the fibres arranged in a figure of eight pattern that have twisted during depolarisation

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9
Q

What is a view in relation to an ECG?

A

Imaginary direction in which you are looking at the heart depending on the position of the electrode relative to the spread of activity

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10
Q

What creates an upward signal on an ECG?

A

Depolarisation moving towards the electrode

Repolarisation moving away from the electrode

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11
Q

What causes a downward signal on an ECG?

A

Depolarisation moving away from the electrode

Repolarisation moving towards the electrode

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12
Q

What does the amplitude of the signal depend on?

A

How much muscle is depolarising

Vector of movement of excitation

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13
Q

Considering the apex view, why does atrial depolarisation cause a small upwards deflection?

A

Small amount of muscle

Moving towards electrode but not directly

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14
Q

How does excitation spread from the septum?

A

Spreads ~1/2 down septum then out across the axis of the heart

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15
Q

What restricts the amplitude of the signal caused by spread from the septum given that a large amount of muscle is depolarising?

A

Its relative direction

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16
Q

How does excitation spread through the ventricular myocardium?

A

Through ventricular muscle along an axis slightly to the left of the septum

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17
Q

Why does the epicardium repolarise first?

A

Cells in epicardium happen to spontaneously repolarise first

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18
Q

Why is the area under the R wave equal to that under the T wave?

A

Same cells are involved

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19
Q

What does the QRS complex show?

A

Spread of excitation to endocardium and subsequent spread across ventricles

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20
Q

What does the P wave show?

A

Atrial systole

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21
Q

What does the Q wave show?

A

Septal depolarisation spreading to ventricle

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22
Q

What does the R wave show?

A

Main ventricular depolarisation

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23
Q

What does the S wave show?

A

End of ventricular depolarisation

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24
Q

What does the T wave show?

A

Ventricular depolarisation

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25
Q

Why is atrial repolarisation not seen on an ECG?

A

It is lost in the QRS complex as the signal is small and swamped by ventricular changes

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26
Q

Starting from the apex view, as you move the view clockwise around the heart, what happens to the R wave?

A

Amplitude decreases –> becomes -ve –> becomes more -ve –> neutral –> small +ve –> large +ve

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27
Q

How does the amplifier in an ECG utilise a +ve and -ve electrode?

A

Invert -ve electrode

Add signal to +ve input making signal detectable

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28
Q

In which direction does lead I look from?

A

Left side

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29
Q

In which direction does lead II view the heart?

A

Towards apex

30
Q

In which direction does lead III view the heart?

A

From the bottom

31
Q

In which plane do the augmented leads measure electrical activity?

A

Vertical

32
Q

Using clock positions, what views do the augmented leads have of the heart?

A 
aVL = 2 o' clock
aVF = 6 o' clock
aVR = 10 o' clock
33
Q

Which plane do the chest leads give views in?

A

Horizontal

34
Q

Where are the electrodes for V1-3 placed?

A 
V1 = 4th intercostal space, right eternal edge
V2 = 4th intercostal space, left eternal edge
V3 = 5th rib b/w V2 and V4
35
Q

Where are the electrodes for V4-V6 placed?

A 
V4 = 5th intercostal space, mid-clavicular line
V5 = 5th intercostal space, b/w V4 and V6
V6 = 5th intercostal space, mid axillary line
36
Q

What standard rate do all ECG machines run at?

A

300 squares per minute

37
Q

How can heart rate be calculated?

A

300/ squares of RR interval

~12 beats present normally

38
Q

How do you asses the rhythm of a heart trace?

A

Choose lead where relevant components are most visible to see if R waves are regular/irregular

39
Q

How is the axis determined?

A

Estimate the direction of arrow that generates the R wave by looking at the most positive leads

40
Q

When are P waves absent?

A

Atrial fibrillation

41
Q

How long should a normal PR interval be?

A

~120 ms

42
Q

What 3 different PR interval abnormalities can be seen and what do they indicate?

A

Prolonged = first degree heart block
Erratic = second degree heart block
No relationship b/w P and R = third degree heart block

43
Q

What is heart block?

A

Something that prevents transmission b/w atria and ventricles

44
Q

What type of damage can the QRS complex be used to identify?

A

Ventricular

45
Q

What does the QT interval indicate?

A

Length of systole

46
Q

What is the T wave examined for?

A

To see if repolarisation is in the right direction

47
Q

Why are intervals between R waves irregular in atrial fibrillation?

A

Pacemaker other than SAN is controlling contraction at a slower than usual rate

48
Q

Why is atrial fibrillation dangerous if the heart continues to function?

A

Pooling occurs in corners of atria which increases the risk of a clot being pumped into the arteries

49
Q

If the R waves are further apart than the P waves, what does this indicate?

A

Atria are contracting more frequently than ventricles

50
Q

How is the P wave seen in third degree heart block?

A

Normal shape but not related to the QRS complex

51
Q

What causes natural axis deviation?

A

Size of person

52
Q

Why is the normal axis of the heart a single vector pointing slightly left?

A

Combination of R and L ventricular depolarisation with thicker ventricle wall on left pulling net arrow left

53
Q

How do the limb leads appear in right axis deviation?

A 
I = -ve
II = small
III = +ve
54
Q

How do the limb leads appear in left axis deviation?

A 
I = +ve
II = small
III = -ve
55
Q

If the net deflection is 0, what does this tell you about the axis?

A

At right angles to that view

56
Q

What causes bundle branch block?

A

Damage to conducting pathways altering route of spread of depolarisation

57
Q

What changes are detected on an ECG of a patient with bundle branch block?

A

QRS complex changes shape - almost always increased width

‘Bunny ears’ may be present

58
Q

What causes ‘bunny ears’ in bundle branch block?

A

Spread of depolarisation turns around and moves back along path it has just taken due to block –> two R waves generated

59
Q

How is damage to the myocardium identified on an ECG?

A

Changes to the ST segment

60
Q

When does damage to the myocardium occur?

A

If there are problems w/perfusion to the myocardium - if it is stressed, dying or dead

61
Q

What does damage to the myocardium affect?

A

Spread of electrical activity during systole

62
Q

What do extra ST signals indicate?

A

Extra electrical current generated in systole due to stressed/dying/dead myocardium

63
Q

What does ST depression indicate?

A

Transient hypoxia

64
Q

Why will the heart rate often be high on an ECG displaying ST depression?

A

It is investigated by exercise test

65
Q

What does ST elevation indicate?

A

Dying tissues generate injury currents due to lack of oxygen

66
Q

What three ECG changes may be identified during myocardial infarction?

A

ST elevation (sometimes)
Pathological Q waves
Inverted T waves

67
Q

What causes pathological Q waves in MI?

A

Dead myocardium replaced by fibrous tissue that electrical activity has to flow around

68
Q

How are pathological Q waves identitified on an ECG?

A

> 0.04s wide (1 small square)

69
Q

How would the ECG of someone who has not presented with an Mi show that they had in fact suffered a previous MI?

A

Pathological Q waves - they persist after other changes are resolved

70
Q

In myocardial infarction, what does the view with the most prominent abnormality help identify?

A

Which coronary artery is blocked

Whether full/partial ventricular wall thickness affected

71
Q

What type of MI are pathological Q waves seen in?

A

Full thickness

72
Q

Which leads most commonly show the most prominent abnormality in an MI?

A

Chest leads

Semester 2 (45 decks)

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