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Cardiovascular System > Session 6 - ECG > Flashcards

Session 6 - ECG Flashcards

1
Q

What is the function of pacemaker cells?

A

Spontaneously generate action potentials that initiate the cardiac cycle

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2
Q

Where are the primary cardiac pacemaker cells located?

A

Sinoatrial node in right atrium

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3
Q

What do action potentials propagate through?

A

Gap junctions

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4
Q

What are 3 parts of the heart that makes up the conduction system?

A

Sinoatrial node
Atrioventricular node
Left and right bundle branch

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5
Q

What is the function of sinoatrial node?

A

Sets heart rate and rhythm as it has the fastest rate of depolarization, suppressing other pacemakers

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6
Q

What is the function of the atrioventricular node?

A

Slows conduction, giving time for atria to contract before ventricles

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7
Q

What is the function of LBB and RBB?

A

Electrical conducting system cells can fire but not typically manifested

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8
Q

How does electrical activity spread through the heart in the atria?

A

SA node initiates, depolarizer right atrium and left atrium, hits AV node and slightly slows conduction down, conduction travels through Bundle of His, travels through annulus fibrosus

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9
Q

Where is the SA node located?

A

Top right atrium

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10
Q

Where is the AV node located?

A

Inter atrial septum near tricuspid valve

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11
Q

How does electrical activity spread through the heart in the ventricles?

A

Through bundle of His, enters the inter-ventricular septum where it divides into right and left bundle branch, which terminate in Purkinje fibres which conduct depolarisation wave through the ventricles

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12
Q

Where is the right bundle branch located?

A

Along right side of inter ventricular septum

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13
Q

Where is the left bundle branch located?

A

Along left side of inter ventricular septum

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14
Q

How many electrodes are involved in recording the ECG and where should they be placed?

A

10 - 4 on limbs 6 on chest

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15
Q

What does limb lead 1 measure?

A

Voltage difference between RA and LA

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16
Q

What does limb lead II measure?

A

Voltage difference between RA and LL

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17
Q

What does limb lead III measure?

A

Voltage diff between LA and LL

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18
Q

What does aVR measure?

A

Voltage difference between right arm and average of left arm and left foot

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19
Q

What does aVL measure?

A

Voltage difference between left arm and average of right arm and left foot

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20
Q

What does aVF measure?

A

Voltage difference between left leg and average of right arm and left arm

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21
Q

What are the 3 types of chest leads?

A

Septal
Anterior
Lateral

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22
Q

How do you determine the shape of the deflection?

A

Height of deflection depends on how directly depolarisation wave is coming towards or away from positive electrode and the number of cells generating the signal

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23
Q

How will the QRS complex appear if depolarisation wave comes directly towards + electrode?

A

Tall and positive

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24
Q

How does QRS complex appear if wave comes obliquely towards electrode?

A

Smaller but positive

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25
Q

How does QRS complex look like if wave comes at 90 degrees to electrode?

A

No complex

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26
Q

How does QRS wave look like when depolarisation wave goes directly away from electrode?

A

Deep -ve

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27
Q

How is SA node depolarisation represented on the ECG?

A

Nothing bc insufficient signal to register

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28
Q

How does atrial depolarisation appear on ECG?

A

Small upward deflection bc it spreads along atrial muscle fibers and internodal pathways towards the AV node which is downwards and to the left

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29
Q

What wave does atrial depolarisation generate?

A

P wave

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30
Q

How long does atrial depolarisation last?

A

80-100ms

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31
Q

How does the delay at AV node appear on the ECG?

A

Isoelectric segment - flat line on ECG after p wave

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32
Q

How does the spreading of depolarisation from atrium to ventricle appear on the ECG?

A

Isoelectric flat segment

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33
Q

How long does depolarization from atrium to ventricle take?

A

120-200ms

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34
Q

How does depolarisation of interventricular septum appear on the ECG?

A

Small downward deflection because moving obliquely away to the sides

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35
Q

What wave does depolarisation of the interventricular septum cause?

A

Q wave

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36
Q

How does depolarisation of apex and free ventricular walls appear on the ECG?

A

Upward and large deflection

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37
Q

What wave does depolarisation of apex and free ventricular walls generate?

A

R wave

38
Q

What does the depolarisation to base of ventricles appear on the ECG?

A

Small downward deflection

39
Q

What wave does depolarisation to the base of the ventricles generate?

A

S wave

40
Q

How long does ventricular muscle depolarization take?

A

80-120ms

41
Q

How does ventricular repolarization appear on the ECG?

A

Medium upward deflection

42
Q

What type of wave does ventricular repolarisation generate?

A

T wave

43
Q

What does the p wave represent?

A

Atrial depolarisation

44
Q

What does the QRS complex represent?

A

Ventricular depolarisation

45
Q

What does the T wave represent?

A

Ventricular repolarisation

46
Q

What are the 2 limb leads used to look at the left side of the heart?

A

I and aVL

47
Q

What 3 limb leads should be used to look at the inferior surface of the heart?

A

II III AVF

48
Q

What 4 chest leads face the septum and anterior surface of ventricles?

A

V1 V2 V3 V4

49
Q

Which 2 chest leads face the lateral surface of the ventricles?

A

V5

V6

50
Q

How much time does one small square on the ECG paper represent?

A

0.04s

51
Q

How many squares represent one second on the ECG?

A

5 large squares

52
Q

What are the 2 types of intervals needed to know to determine the type of rhythm?

A

PR interval

QRS interval

53
Q

How long is a normal PR interval?

A

Less than 1 large box

54
Q

What does a prolonged PR interval represent?

A

Delayed conduction through AV node and bundle of His

55
Q

How long should a QRS interval be?

A

Less than 3 small box

56
Q

What does a widened QRS complex mean?

A

Depolarisation arising in ventricle but not spreading via the rapid conducting His-Purkinje system

57
Q

How do you diagnose ventricular rhythm?

A

> 120ms

58
Q

What does normal sinus rhythm refer to?

A

Pacemaking impulses arises from SA node and are transmitted to ventricles via AV node and His-Purkinje system

59
Q

What are 5 characteristics of a normal sinus rhythm?

A

Regular rhythm = 60-100bpm
Each QRS complex is preceded by a P wave
P wave is upright in I and II, inverted in aVR
PR interval is constant
QRS complex <100ms

60
Q

What is definition of heart block?

A

Delay or failure of conduction of impulses from atria to ventricles via AV node and Bundle of His

61
Q

What are 4 causes of heart block?

A

Degeneration electrical conducting system with age
Acute myocardial ischemia
Medications
Valvular heart diseases

62
Q

What does first degree heart block refer to?

A

Partial block in AV node

63
Q

How do you recognize a first degree heart block on ECG?

A

PR interval is more than 0.2s

64
Q

What does second degree Mobitz type 1 refer to?

A

Block between SA node and AV node

65
Q

How do you recognize second degree Mobitz type 1 block on ECG?

A

Successively longer PR intervals until one QRS is dropped

66
Q

What does second degree Mobitz type 2 block refer to?

A

Block at AV node between node and Bundle of His or at bilateral bundle branches

67
Q

How do you recognize second degree Mobitz type 2 block on ECG?

A

PR intervals do not lengthen, suddenly dropped QRS with irregular ventricular rhythm

68
Q

What does third degree block refer to?

A

Atria and ventricles depolarize independently as AV conduction completely fails

69
Q

How do you recognize a third degree heart block on ECG?

A

Escape rhythm is very slow at 20-40 bpm

Usually wide QRS complex

70
Q

What does bundle branch block refer to?

A

Delayed conduction within the bundle branches - can be right or left

71
Q

How to recognize bundle branch block on ECG?

A

P wave and PRI normal

Wide QRS complex

72
Q

What are 3 parts of the heart that supraventricular arrhythmias can arise from?

A

Sinus node
Atrium
AV node

73
Q

How to differentiate supraventricular and ventricular arrythmias on ECG?

A

Supraventricular QRS complex is normal

Ventricular QRS complex is wide and bizarre

74
Q

What is atrial fibrillation caused by?

A

Ectopic atrial foci causes depolarisation and generates rapid chaotic impulses, they reach AV node at rapid irregular rate and not all conducted, but when conducted, ventricles still depolarize normally so QRS complex is normal

75
Q

How do you recognize atrial fibrillation on ECG?

A

No p waves
Wavy baseline
Irregular RR intervals

76
Q

What are the haemodynamic effects of atrial fibrillation?

A

Atria doesn’t contract, it quivers, so heart rate and pulse are irregularly irregular, no contraction = increased blood stasis esp in left atrium, clots can form, so can cause ischaemic stroke secondary to emboli

77
Q

What are premature ventricular ectopic beats?

A

Ectopic focus in ventricle muscles, impulses don’t spread via fast His-Purkinje system so depolarization slower = wider QRS complex, premature because occurs earlier than expected

78
Q

What is ventricular tachycardia?

A

Run of more than or 3 consecutive premature ventricular contractions

79
Q

What is ventricular fibrillation?

A

Abnormal, chaotic, fast ventricular depolarisation due to impulses from numerous ectopic sites in ventricle, no coordinated contraction, ventricles are quivering

80
Q

What is myocardial ischaemia?

A

Lack of perfusion but no muscle necrosis so no cardiac troponins in blood

81
Q

What is a myocardial infarction?

A

Muscle necrosis present so cardiac troponins present in blood

82
Q

What is STEMI caused by?

A

Complete occlusion of coronary artery

83
Q

How to see which part of the heart has STEMI?

A

Leads facing daffected area has ST segment elevation

84
Q

What is a q wave?

A

Any negative deflection that precedes a R wave

85
Q

Why does myocardial necrosis and scar tissue from evolving and old infarcts lead to pathological Q waves?

A

No electrical activity on dead tissue so no action potentials, but ECG picks up electrical forces from opposite side of infarct Ed heart

86
Q

How do you differentiate non STEMI and ischaemia if they have the same ECG?

A

Blood test for myocytes necrosis

87
Q

How do you recognize Non-STEMI and ischaemia from an ECG?

A

ST segment depression and T wave inversion,

88
Q

How much potassium level is considered to be hypokalaemia?

A

<3.5mmol/L

89
Q

What happens during hypokalaemia?

A

Decreased extracellular potassium causes myocardial hyperexcitability

90
Q

What are the ECG changes during hypokalaemia?

A 
Increased amplitude and width of P wave 
PRI prolonged 
T wave flattened and inversion 
ST depression 
Prominent U waves
91
Q

What happens during hyperkalaemia?

A

Resting membrane potential becomes less negative, in activates some voltage gated Na+ channels, heart becomes less excitable, conduction problems occur

92
Q

What are the ECG changes during hyperkalaemia?

A

Tall tented T waves
Loss of P wave
Widening QRS

Cardiovascular System (11 decks)

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