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Module 103: The Heart, Lungs and Blood > Theme 3: Lecture 6 - Introduction to the ECG > Flashcards

Theme 3: Lecture 6 - Introduction to the ECG Flashcards

1
Q

What is a syncytium

A

one large “cell” having many nuclei that are not separated by cell membrane

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2
Q

What is a functional syncytium

A

Many cells functioning as one

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3
Q

What are the three types of cardiac myocytes

A
  • Pacemaker cells – for setting heart’s rhythm
  • Conducting cells – for transmitting rhythm throughout the heart
  • Contractile cells – for contracting to that rhythm (most numerous)
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4
Q

What is the speed of propagation for the different cardiac myocytes

A
  • Contractile - atrial and ventricular myocytes 0.3-0.5 m/s
  • Conducting system (modified cardiomyocytes), Purkinje fibres up to 5 m/s (fastest neurons ~100 m/s)
  • AV node 0.05 m/s
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5
Q

How are cardiac myocytes linked

A

by low resistance pathways associated with gap junctions at the intercalated discs

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6
Q

What are gap junctions

A

They directly connect the cytoplasm of two cells, which allows various molecules, ions and electrical impulses to directly pass through a regulated gate between cells

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7
Q

What are intercalated discs

A

A lot of gap junctions located together

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8
Q

Describe the fibrous skeleton

A
  • Electrical insulator located between the atria and ventricles
  • Important as it means that for electrical impulses to be transported from the atria to the ventricles, they have to go through the AV node
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9
Q

Where do electrical impulses go once entering the AV node

A
  • Bundle of His then
  • Left and right bundle branches then
  • Purkinje fibres
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10
Q

How are impulses conducted from the SA node to the AV node

A

by internodal bundles

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11
Q

Why are impulses conducted from SA node to AV node conducted by the internodal bundles

A
  • Bundles ensure synchronous contraction of the atria

- Conducting via atrial muscle would be slow (0.3-0.5 m/s), conducting via bundles is much faster (1.0 m/s)

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12
Q

How many specialised bundles are in the atria

A

4

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13
Q

What do the specialised bundles in the atria contain

A

Purkinje like cells (cardiomyocytes modified to conduct) that are in direct contact with atrial muscle

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14
Q

Why does the AV node delay wave of excitation from atria to ventricles by 0.1 - 0.2 s

A

The electrical delay means that ventricles contract after atria to permit longer and more effective ventricular filling

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15
Q

How is the AP conducted very slowly in AV node (0.05 m/s)

A
  • AV node composed of small modified myocytes which makes them slower in conducting
  • Electrical connection between adjoining cells is weaker
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16
Q

What are Purkinje fibres

A

very large myocytes - transmit the impulse faster because bigger diameter cells conduct faster due to lower resistance

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17
Q

What do Purkinje fibres do

A
  • Purkinje fibres transmit the impulse rapidly to the main mass of the ventricles from the Bundle of His
  • From there, slower conduction between contractile myocytes can occur
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18
Q

When are different area of the ventricles depolarised

A
  • First part of ventricular wall to be depolarised is septum, then apex
  • Last part is atrioventricular groove
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19
Q

What is the ECG

A
  • Electrocardiogram

- The ECG is a gross electrical measurement of the heart

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20
Q

How can the ECG detect a current when the individual currents of cardiac myocytes are tiny (nano amps)

A

because the heart is a “functional syncytium” in which large groups of cells all make electrical changes simultaneously

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21
Q

What can the ECG diagnose

A

Rate (but so can the pulse):

  • Holter monitor (ECG) allows 24/7 rate determination
  • Esp. useful when Atrial rate ≠ Ventricular rate

Many Subtleties:

  • Not a one-stop-diagnosis
  • Patient Hx essential for interpretation
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22
Q

What is a Holter monitor

A

a type of portable electrocardiogram (ECG). It records the electrical activity of the heart continuously over 24 hours or longer

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23
Q

What is a lead in an ECG

A
  • a configuration of electrodes (usually consisting of a positive electrode, a negative electrode, and sometimes a ground).
  • 2/3 electrodes placed on the body in standardised positions
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24
Q

What does what you see on an ECG depend on

A

Where you put the leads

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25
Q

Describe a 12 lead ECG

A

looks at the heart from 12 different angles, creating measurements for 12 leads, using 10 separate electrodes.

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26
Q

Describe lead II

A

Lead II has the positive electrode on left leg, negative electrode on right arm, and the ground electrode on the right leg (although the ground could be almost anywhere).

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27
Q

What are the 12 standard leads of an ECG

A
  • 3 bipolar leads
  • 3 augmented leads
  • 6 precordial
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28
Q

What are the 3 bipolar leads

A

I, II, III

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29
Q

What plane do the bipolar leads view the heart in

A

frontal

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30
Q

What are bipolar leads

A

they have a positive and a negative electrode at opposite ends of the heart

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31
Q

What does the P wave show

A
  • Depolarisation of the atria in response to SA node triggering
  • So small it’s never normally seen on an ECG
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32
Q

What does the PQ segment show

A

Delay of AV node to allow filling of the ventricles

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33
Q

What does the QRS complex show

A

Depolarisation of ventricles, triggers main pumping contractions

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34
Q

What does the ST segment show

A
  • Beginning of ventricle repolarisation

- Should be flat and at the same level as before the P wave and during the PQ segment

35
Q

What does the T wave show

A

Ventricular repolarisation

36
Q

What does a wide or misshapen QRS complex show

A
  • Abnormal ventricular conduction

- E.g from ectopic pacemakers or bundle branch block

37
Q

What are large (deep) Q waves a sign of

A

dead tissue (old MI)

38
Q

Describe sinus rhythm

A
  • When the heart rhythm is generated from the Sino-Atrial Node
  • Each P wave is followed by a QRS complex
  • Each QRS complex is preceded by a P wave
  • When PR interval is always normal (3-5 little boxes)
39
Q

Describe sinus tachycardia on an ECG

A
  • a tachycardia driven by the SA node beating too quickly
  • It has normal PR intervals, and each P matched with a QRS therefore looks normal apart from the frequency of waves being too fast on the ECG but this is still an abnormal rhythm
40
Q

What is the PR interval

A

from start of P wave to start of QRS complex

41
Q

What is the PR segment

A

From end of P wave to start of QRS complex

42
Q

What is the QT interval

A

from start of QRS complex to end of T wave

43
Q

What is the ST interval

A

from end of QRS complex to start of T wave

44
Q

What is a normal PR interval duration

A

120-200ms (3-5 little boxes)

45
Q

What is a normal QRS complex duration

A

80-120ms (2-3 little boxes)

46
Q

What is a normal QT interval duration

A

360-460ms (9-11.5 little boxes)

47
Q

What is 1 second on an ECG trace

A

5 big boxes

48
Q

How long is one little box on an ECG trace

A

40ms

49
Q

What are the 2 types of receptor that the parasympathetic nervous system mainly uses

A

muscarinic and nicotinic cholinergic receptors

50
Q

What is Atropine and what does it do

A
  • Muscarinic antagonist
  • Causes parasympathetic withdrawal to the heart
  • So increases heart rate, contractility and conduction velocity
51
Q

How does sympathetic input get to the heart

A

Via stellate nerves

52
Q

What is the parasympathetic input to the heart

A

Vagus nerve

53
Q

What is heart block

A
  • A type of dysrhythmia
  • any kind of impulse conduction block of the heart
  • Includes AV block, Bundle Branch Block, etc
54
Q

What is AV heart block

A

a delay or failure of atria signal stimulating ventricle

55
Q

What are the causes of heart block

A
  • Ischaemia of AV node or AV bundle
  • Compression of AV bundle by scar or calcified tissue
  • Inflammation of the AV node or bundle
56
Q

What are the symptoms of heart block

A
  • Can be asymptomatic
  • Palpitations
  • Hypotension-like: Dizziness, Malaise, Syncope
  • Risk of Sudden Death
57
Q

What is first degree heart block

A
  • Delayed AV node transition
  • When PR interval > 5 little boxes (200 ms) (Normal PR < 5 little boxes)
  • But all P’s followed by QRS
58
Q

Symptoms of first degree heart block

A

almost always asymptomatic

59
Q

Who does first degree heart block occur in

A

young people

60
Q

How is first degree heart block treated

A

rarely treated

61
Q

What is second degree heart block

A

Some P waves are blocked and are not followed by QRS – Some QRS complexes are “”missing”

62
Q

Describe Mobitz type I second degree heart block

A
  • AKA Wenckeback

- PR interval gets longer until QRS wave fails to follow P wave

63
Q

What causes Mobitz type I second degree heart block

A

Likely AV node damage

64
Q

What is the treatment for Mobitz type I second degree heart block

A

Usually no treatment given

65
Q

Describe Mobitz type II second degree heart block

A
  • AKA hay block
  • Some P waves are blocked and are not followed by QRS
  • PR interval remains the same
  • High risk and can progress to third degree heart block
66
Q

What causes Mobitz type II second degree heart block

A

Likely problem in bundle of His

67
Q

Treatment for Mobitz type II second degree heart block

A

Implant pacemaker

68
Q

Describe third degree heart block

A
  • Atrial signals consistently fail to arrive at ventricles
  • Ventricular rate is consistent but slow as the ventricles decide to contract on their own when they don’t get a signal from the atria
  • Time between atrial beats and ventricular beats is variable.
  • PR interval varies radically – sometimes > 12 boxes
  • Atrial beats are consistent
69
Q

What are premature beats

A
  • Individual beats that aren’t normal
  • Early
  • Triggered by irritable tissue
70
Q

What are escape beats

A
  • Individual beats that aren’t normal
  • Late
  • Triggered by natural rhythmicity of non-atrial tissue
  • Occur when the atrial signal is very delayed or prevented
71
Q

Where are premature and escape beats often triggered

A

In ventricular tissue or by AV node

72
Q

What are premature and escape beats known as

A

Ectopic beats

73
Q

What do premature ventricular contractions look like on an ECG

A
  • Unusually wide and weird looking ventricular electrical activity
  • No S wave, instead a wide negative dip where the T wave should be
74
Q

What are premature ventricular contractions

A
  • Often beat triggered in middle of myocardium
  • The two ventricles will be electrically unsynchronised
  • So delayed and inefficient conduction (non-Purkinje)
75
Q

What is atrial fibrillation

A

disorganised electrical activity in atria

76
Q

Who is AF common in

A

The elderly

77
Q

What does atrial fibrillation look like on an ECG

A
  • No P wave. Instead, flat line OR wiggly line instead of P

- Ventricular rate is fast & irregular due to many signals reaching AV node

78
Q

Why can atrial fibrillation lead to thrombus formation in atrium

A

due to slow flow of blood because atria aren’t beating properly

79
Q

What is respiratory sinus arrhythmia

A
  • heart beat is slightly faster during inspiration, slightly slower during expiration
  • Normal
80
Q

Who is respiratory sinus arrhythmia seen in

A

children and athletes

81
Q

What is respiratory sinus arrhythmia

A

respiratory centres in brain’s medulla

82
Q

What is ST segment elevation a sign of

A

Acute MI

83
Q

Iso electric baseline

A

The line on the ECG trace that runs from the end of T to the next P

Module 103: The Heart, Lungs and Blood (51 decks)

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