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Cardiovascular System > ECGs > Flashcards

ECGs Flashcards

1
Q

Where is the SA node located?

A

Top right hand corner of right atrium

near junction of SVC and right atrium

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2
Q

Why is the SA node specialised?

A

Myocytes do not contract
They spontaneously depolarise
to generate action potentials

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3
Q

What is the SA node known as?

A

Pacemaker of heart

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4
Q

Why is the SA node the pacemaker of the heart?

A

Beause it spontaneously depolarises faster than other parts of the electrical conducting system
So it sets the rhythm of the heart beat

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5
Q

What is it called when the SA node sets the rhythm of the heart beat?

A

Sinus rhythm

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6
Q

What happens after the SA node generates an action potential?

A

Wave of depolarisation spreads across internodal pathways and atrial myocytes, downwards and to left

Depolarised atrial myocytes contract

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7
Q

Where is the AV node located?

A

Interatrial septum

Above the tricuspid valve

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8
Q

What happens during depolarisation of the atrial myocytes and their contraction?

A

Action potential is held up at AV node

AV node delay

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9
Q

What is the purpose of AV node delay?

A

To allow time for all the atria to depolarise and contract

Emptying the atria, filling the ventricles

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10
Q

Wher doere does the AV node conduct the action potential to?

A

Down the bundle of His

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11
Q

Where is the bundle of His located?

A

Beginning of the interventricular septum

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12
Q

What is the only electrical conducting pathway between the atria and ventricles?

A

The bundle of His

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13
Q

Why is the bundle of His the only electrical conducting pathway between the atria and ventricles?

A

Because of fibrous rings between the atria and ventricles

non-conductive tissue

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14
Q

What does the bundle of His divide into?

A

Right bundle branch

Left bundle branch

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15
Q

Where do the right and left bundle branches lie?

A

Interventricular septum

sub-endocardially - just beneath endocardium

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16
Q

Where do the right and left bundle branches carry the action potential to?

A

Down the interventricular septum

to the apex

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17
Q

How does the interventricular septum depolarise?

A

From left to right

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18
Q

What carries the action potential from the apex of the heart?

A

Purkynje fibres

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19
Q

Where are the purkinje fibres located?

A

Walls of ventricles

sub-endocardially

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20
Q

Where do the purkinje fibres carry the action potential to?

A

Up the ventricular walls, to the base of the ventricles

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21
Q

How does the myocardium of the ventricles depolarise? Why?

A

From endocardium to epicardium

since bundle branches, His purkinje system lie sub-endocardially

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22
Q

What is an important feature of the His-purkinje system?

A

Carry action potentials extremely fast, almost simultaneously
So ventricular myocytes depolarise and contract in a synchronised way

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23
Q

What is the overall direction of depolarisation?

A

Towards the apex of the heart

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24
Q

What is the order of contraction in the heart?

A 
Atrial myocytes
Septum - left to right
Apex
Walls of ventricles - endocardium to epicardium
Base of ventricles
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25
Q

What is the order by which cardiomyocytes repolarise?

A

The opposite to the order by which they depolarised

Base of ventricles
Walls of ventricles - epicardium to endocardium
Apex
Septum - right to left

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26
Q

What does an ECG record?

A

Changes occurring on extracellular surface of cardiomyocytes during depolarisation and repolarisation

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27
Q

How is the ECG set up?

A

Electrodes placed on skin

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28
Q

If wave of depolarisation is moving towards a positive electrode, how does this show on an ECG?

A

Positive complex

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29
Q

If wave of depolarisation is moving away from a positive electrode, how does this show on an ECG?

A

Negative complex

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30
Q

If wave of repolarisation is moving towards a positive electrode, how does this show on an ECG?

A

Negative complex

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31
Q

If wave of repolarisation is moving away from positive electrode, how does this show on an ECG?

A

Positive complex

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32
Q

Why do deflections eventually return to the baseline?

A

Change takes over more than half of cardiomyocytes

Becoming more similar, change decreasing

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33
Q

What does a flat line on an ECG mean?

A

No significant electrical activity occurring in heart

No change on surface of caridomyocytes

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34
Q

If a wave of depolarisation is travelling directly towards a positive electrode, how does show on an ECG?

A

Tall positive complex

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35
Q

If a wave of depolarisation is travelling at an angle towards a positive electrode, how does this show on an ECG?

A

Shorter positive complex

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36
Q

If a wave of depolarisation is travelling perpendicularly towards a positive electrode, how does this show on an ECG?

A

Small biphasic complex - positive then negative

or no complex

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37
Q

How does depolarisation of the SA node show up on an ECG? Why?

A

Flat line, baseline

Insufficient electrical activity to be picked up by ECG

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38
Q

How does depolarisation of the atria show up on an ECG? Why?

A

Produces small positive complex

Because wave of depolarisation is moving towards positive electrode at apex, at an angle

Shows up because is large muscle mass depolarising

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39
Q

What is the ECG wave corresponding to atrial depolarisation?

A

P wave

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40
Q

How does the AV node delay show up on an ECG?

A

Flat line, baseline

called segment 1b

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41
Q

How does depolarisation of the His-purkinje system show up on an ECG?

A

Flat line, baseline

still segment 1b

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42
Q

How dows depolarisation of the interventricular septum show on an ECG? Why?

A

Short negative complex

Because moving away from positive electrode at apex, at an angle

Shows up because is large muscle mass depolarising

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43
Q

What does depolarisation of the interventricular septum correspond to on an ECG?

44
Q

How does depolarisation of the apex and ventricular wall show up on an ECG?

A

Tall positive complex

Because depolarisation moving directly towards positive electrode at apex
Also because large muscle mass is depolarising

45
Q

Which wave on an ECG corresponds to depolarisation of the apex and ventricular walls?

46
Q

In LV hypertrophy, how is the R wave different? Why?

A

Taller

due to larger muscle mass depolarising

47
Q

How does depolarisation of the base of the ventricles show up on an ECG?

A

Short negative complex

Because moving away from positive electrode at apex, but at an angle

48
Q

Which wave on an ECG corresponds to depolarisation of the base of the ventricles?

49
Q

How does ventricular repolarisation show up on an ECG?

A

Medium positive complex

Because repolarisation is moving away from positive electrode at apex
at an angle

50
Q

Which wave on an ECG corresponds to repolarisation of the ventricles?

51
Q

How many electrodes are placed on the skin in an ECG?

52
Q

What are the ten ECG electrodes divided into?

A

Four on the limbs

Six on the chest

53
Q

Where are each of the four limb electrodes placed?

A

Right arm - red
Left arm - yellow
Left leg - green
Right leg - black

54
Q

What is a lead?

A

Refers to view of the heart

55
Q

How many views do the four limb leads give?

56
Q

What can the six limb lead views be divided into?

A

Unipolar leads

Bipolar leads

57
Q

What are the unipolar leads?

58
Q

What are the bipolar leads?

A

Lead 1
Lead 2
Lead 3

59
Q

What are the positive and negative poles with the unipolar limb leads?

A

Positive pole is one electrode, see from here

Negative pole is average of other two electrodes, ends up being heart

60
Q

What does avF look at?

A

Heart from left leg

its inferior surface

61
Q

What does avR look at?

A

Heart from right arm

62
Q

What does aVL look at?

A

Heart from left arm

its left lateral surface

63
Q

What are the degrees of aVF, aVL, aVR?

A 
aVF = 90degrees
aVR = -150degrees
avL = -30degrees
64
Q

What are the positive and negative poles with the bipolar limb leads?

A

Positive pole is one electrode

Negative pole is another electrode

65
Q

What are lead 1’s poositive and negative poles?

A

Left arm is positive pole

Right arm is negative pole

66
Q

What are lead 2’s positive and negative poles?

A

Left leg is positive pole

Right arm is negative pole

67
Q

What are lead 3’s positive and negative poles

A

Left leg is positive pole

Left arm is negative pole

68
Q

What does lead 1 look at?

A

Heart from left arm

its left lateral surface

69
Q

What do leads 2 and 3 look at?

A

Heart from left leg

its inferior surface

70
Q

What are the degrees of Leads 1, 2, and 3?

A

Lead 1 = 0 degrees
Lead 2 = 60 degrees
Lead 3 = 120 degrees

71
Q

The limb leads view the heart in what plane?

A

Coronal plane - vertical

72
Q

Where are each of the six chest electrodes placed?

A

V1 - 4th intercostal space, right sternal border
V2 - 4th intercostal space, left sternal border
V3 - between V2 and V4
V4 - 5th intercostal space, mid-clavicular line
V5 - between V4 and V6
V6 - 5th intercostal space, mix-axillary line

73
Q

What are V1 and V2 called?

A

The septal leads

74
Q

What do leads V1 and V2 look at?

A

Right ventricle and septum

75
Q

What are V3 and V4 called?

A

The anterior leads

76
Q

What do V3 and V4 look at?

A

Anterior wall of ventricles

apex

77
Q

What are V5 and V6 called?

A

Lateral leads

78
Q

What do V5 and V6 look at?

A

Left ventricle

79
Q

Why do each of the chest leads produce different ECGs?

A

At different angles to heart

Waves of depolarisation, repolarisation occur at different angles to each of them

80
Q

What plane do the chest leads view the heart in?

A

Transverse plane - horizontal

81
Q

If one of the chest leads is abnormal, what does this mean?

A

Damaged myocardium

in the area that the chest lead looks at

82
Q

What is the size of one small square on an ECG?

83
Q

How long is one small square on an ECG?

84
Q

What is the size of one large square on an ECG?

85
Q

How long is one large square on an ECG?

86
Q

What is the horizontal axis on an ECG?

87
Q

What is the vertical axis on an ECG?

A

Voltage (mV)

88
Q

How many squares is 1s on an ECG?

A

25 small squares

5 large squares

89
Q

How many squares is 1m on an ECG?

A

300 large squares

90
Q

How is a heart rate calculated if the rhythm is regular?

A

Count number of boxed between two R waves

Do 300/n

91
Q

What is a regular rhythm?

A

Same amount of time between cardiac cycles, one wave to next

92
Q

How is heart rate calculated if the rhythm is irregular?

A

Count number of R waves in 6 seconds, 30 large squares

Multiple by 10

93
Q

What is an irregular rhythm?

A

Different amounts of time between cardiac cycles, one wave to next

94
Q

What is the PR interval?

A

Beginning of P wave

To beginning of Q wave

95
Q

How long is a normal PR interval? How many squares?

A

0.12 - 0.20 seconds

3-5 small squares

96
Q

What is a QRS interval?

A

Beginning of Q wave

To end of S wave

97
Q

How long is a normal QRS interval? How many squares?

A

Less than 0.12 seconds

Less than 3 small squares

98
Q

What is the QT interval?

A

Beginning of Q wave

To end of T wave

99
Q

Does the QT interval vary with heart rate? Why?

A

Yes

Because time in diastole varies with heart rate

100
Q

How long is the normal QT interval? How many squares?

A

Males - 0.45s

Females - 0.47s

11-12 small squares

101
Q

What is sinus rhythm?

A

Depolarisation initiated by SA node

102
Q

What are the criteria of sinus rhythm?

A

Regular rhythm

Heart rate 60-100bpm

P waves

  • upright in leads 2 and 3
  • followed by QRS

Normal PR interval
Normal QRS interval

103
Q

What is sinus bradycardia?

A

Heart rate below 60bpm

104
Q

When is sinus bradycardia physiologically normal?

A

Sleeping

Athletes

105
Q

What is sinus tachycardia?

A

Heart rate above 100bpm

106
Q

When is sinus tachycardia physiologically normal?

Cardiovascular System (22 decks)

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