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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
How does QRS complex look like if wave comes at 90 degrees to electrode?
No complex
26
How does QRS wave look like when depolarisation wave goes directly away from electrode?
Deep -ve
27
How is SA node depolarisation represented on the ECG?
Nothing bc insufficient signal to register
28
How does atrial depolarisation appear on ECG?
Small upward deflection bc it spreads along atrial muscle fibers and internodal pathways towards the AV node which is downwards and to the left
29
What wave does atrial depolarisation generate?
P wave
30
How long does atrial depolarisation last?
80-100ms
31
How does the delay at AV node appear on the ECG?
Isoelectric segment - flat line on ECG after p wave
32
How does the spreading of depolarisation from atrium to ventricle appear on the ECG?
Isoelectric flat segment
33
How long does depolarization from atrium to ventricle take?
120-200ms
34
How does depolarisation of interventricular septum appear on the ECG?
Small downward deflection because moving obliquely away to the sides
35
What wave does depolarisation of the interventricular septum cause?
Q wave
36
How does depolarisation of apex and free ventricular walls appear on the ECG?
Upward and large deflection
37
What wave does depolarisation of apex and free ventricular walls generate?
R wave
38
What does the depolarisation to base of ventricles appear on the ECG?
Small downward deflection
39
What wave does depolarisation to the base of the ventricles generate?
S wave
40
How long does ventricular muscle depolarization take?
80-120ms
41
How does ventricular repolarization appear on the ECG?
Medium upward deflection
42
What type of wave does ventricular repolarisation generate?
T wave
43
What does the p wave represent?
Atrial depolarisation
44
What does the QRS complex represent?
Ventricular depolarisation
45
What does the T wave represent?
Ventricular repolarisation
46
What are the 2 limb leads used to look at the left side of the heart?
I and aVL
47
What 3 limb leads should be used to look at the inferior surface of the heart?
II III AVF
48
What 4 chest leads face the septum and anterior surface of ventricles?
V1 V2 V3 V4
49
Which 2 chest leads face the lateral surface of the ventricles?
V5 | V6
50
How much time does one small square on the ECG paper represent?
0.04s
51
How many squares represent one second on the ECG?
5 large squares
52
What are the 2 types of intervals needed to know to determine the type of rhythm?
PR interval | QRS interval
53
How long is a normal PR interval?
Less than 1 large box
54
What does a prolonged PR interval represent?
Delayed conduction through AV node and bundle of His
55
How long should a QRS interval be?
Less than 3 small box
56
What does a widened QRS complex mean?
Depolarisation arising in ventricle but not spreading via the rapid conducting His-Purkinje system
57
How do you diagnose ventricular rhythm?
>120ms
58
What does normal sinus rhythm refer to?
Pacemaking impulses arises from SA node and are transmitted to ventricles via AV node and His-Purkinje system
59
What are 5 characteristics of a normal sinus rhythm?
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
What is definition of heart block?
Delay or failure of conduction of impulses from atria to ventricles via AV node and Bundle of His
61
What are 4 causes of heart block?
Degeneration electrical conducting system with age Acute myocardial ischemia Medications Valvular heart diseases
62
What does first degree heart block refer to?
Partial block in AV node
63
How do you recognize a first degree heart block on ECG?
PR interval is more than 0.2s
64
What does second degree Mobitz type 1 refer to?
Block between SA node and AV node
65
How do you recognize second degree Mobitz type 1 block on ECG?
Successively longer PR intervals until one QRS is dropped
66
What does second degree Mobitz type 2 block refer to?
Block at AV node between node and Bundle of His or at bilateral bundle branches
67
How do you recognize second degree Mobitz type 2 block on ECG?
PR intervals do not lengthen, suddenly dropped QRS with irregular ventricular rhythm
68
What does third degree block refer to?
Atria and ventricles depolarize independently as AV conduction completely fails
69
How do you recognize a third degree heart block on ECG?
Escape rhythm is very slow at 20-40 bpm | Usually wide QRS complex
70
What does bundle branch block refer to?
Delayed conduction within the bundle branches - can be right or left
71
How to recognize bundle branch block on ECG?
P wave and PRI normal | Wide QRS complex
72
What are 3 parts of the heart that supraventricular arrhythmias can arise from?
Sinus node Atrium AV node
73
How to differentiate supraventricular and ventricular arrythmias on ECG?
Supraventricular QRS complex is normal | Ventricular QRS complex is wide and bizarre
74
What is atrial fibrillation caused by?
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
How do you recognize atrial fibrillation on ECG?
No p waves Wavy baseline Irregular RR intervals
76
What are the haemodynamic effects of atrial fibrillation?
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
What are premature ventricular ectopic beats?
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
What is ventricular tachycardia?
Run of more than or 3 consecutive premature ventricular contractions
79
What is ventricular fibrillation?
Abnormal, chaotic, fast ventricular depolarisation due to impulses from numerous ectopic sites in ventricle, no coordinated contraction, ventricles are quivering
80
What is myocardial ischaemia?
Lack of perfusion but no muscle necrosis so no cardiac troponins in blood
81
What is a myocardial infarction?
Muscle necrosis present so cardiac troponins present in blood
82
What is STEMI caused by?
Complete occlusion of coronary artery
83
How to see which part of the heart has STEMI?
Leads facing daffected area has ST segment elevation
84
What is a q wave?
Any negative deflection that precedes a R wave
85
Why does myocardial necrosis and scar tissue from evolving and old infarcts lead to pathological Q waves?
No electrical activity on dead tissue so no action potentials, but ECG picks up electrical forces from opposite side of infarct Ed heart
86
How do you differentiate non STEMI and ischaemia if they have the same ECG?
Blood test for myocytes necrosis
87
How do you recognize Non-STEMI and ischaemia from an ECG?
ST segment depression and T wave inversion,
88
How much potassium level is considered to be hypokalaemia?
<3.5mmol/L
89
What happens during hypokalaemia?
Decreased extracellular potassium causes myocardial hyperexcitability
90
What are the ECG changes during hypokalaemia?
``` Increased amplitude and width of P wave PRI prolonged T wave flattened and inversion ST depression Prominent U waves ```
91
What happens during hyperkalaemia?
Resting membrane potential becomes less negative, in activates some voltage gated Na+ channels, heart becomes less excitable, conduction problems occur
92
What are the ECG changes during hyperkalaemia?
Tall tented T waves Loss of P wave Widening QRS

Cardiovascular System (11 decks)

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