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Stage 2: Supporting Life > Arrhythmias > Flashcards

Arrhythmias Flashcards

1
Q

What is an arrhythmia (dysrhythmia)?

A

A disturbance of the normal rhythmic beating of the heart, usually due to an ectopic (out of place) pacemaker

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2
Q

What features can the aberrant rhythm have?

A
  • Too fast or too slow
  • Regular or irregular
  • Intermittent or permanent
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3
Q

How do you diagnose specific types of arrhythmias?

A

ECG

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4
Q

What are the main symptoms of arrhythmias?

A
  • Palpitations (sensation of pounding heart)
  • Breathlessness
  • Dizziness, faintness, syncope
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5
Q

What are 4 important types of arrhythmias?

A

1) Complete heart block
2) Atrial fibrillation
3) Ventricular fibrillation
4) Ventricular tachycardia

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6
Q

What do all regions of the conducting system have the capacity to be?

A

Pacemakers

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7
Q

What is the phase 4 funny current?

A

A mixed sodium and potassium inward current

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8
Q

What is the effective refractory period?

A

When cells cannot fire another AP during most of an existing AP

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9
Q

What are 3 ways that arrhythmias are classified?

A

1) By rate
2) By location
3) By cause

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10
Q

What are the two classifications of arrhythmias by rate?

A

1) Inappropriate bradyarrhythmia (<60bpm)

2) Inappropriate tachyarrhythmia (>100bpm)

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11
Q

What are the two classifications of arrhythmias by location?

A

1) Supraventricular (atrial or AV nodal origin

2) Ventricular (ventricular origin)

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12
Q

Which type of arrhythmia (by location) is more dangerous and more difficult to treat?

A

Ventricular

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13
Q

What are the two classifications of arrhythmias by cause?

A

1) Disorders of impulse generation

2) Disorders of impulse conduction

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14
Q

How do bradycardia arrhythmias occur?

A

1) SAN slows down

2) impulse from SAN is blocked, slower distal pacemaker takes over

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15
Q

How do tachycardia arrhythmias occur?

A

1) Disorders of impulse generation → afterdepolarisations

2) Disorders of impulse conduction → re-entry

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16
Q

What is complete (third degree) heart block?

A

Blocked electrical connection between atria and ventricles

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17
Q

What are 3 causes of complete heart block?

A

1) Idiopathic bundle branch fibrosis
2) Atherosclerotic coronary heart disease
3) Dilated cardiomyopathy

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18
Q

What is the effect on cardiac rhythm of complete heart block?

A

1) Heartbeat is slow (doesn’t stop bc of distal pacemakers) → degree of slowing depends on location of block
2) Heart rhythm is driven by ‘escape beats’ originating from the distal pacemaker just below the block

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19
Q

What is a distal pacemaker?

A

A latent pacemaker in the conduction system becoming active

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20
Q

What happens when the AVN takes over from the SAN?

A

1) When the AVN is free of dominance from the SAN, it will take over
2) However, its pacemaker activity is intrinsically slower so the HR becomes slower

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21
Q

What happens to the HR when the bundle branches take over?

A

It slows down for the left bundle branch and then even slower for the right

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22
Q

Why does the HR slow down when the bundle branches take over?

A

Bc they have less channels involved in funny current further away from SAN

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23
Q

Why are all parts of the conduction system potential/latent pacemakers?

A

Bc they have the ion channels required for phase 4 depolarisation

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24
Q

Why does the intrinsic automaticity of the conduction system normally remain latent?

A

Bc of overdrive suppression by the SAN (the fastest pacemaker dominates)

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25
Q

What happens when latent pacemakers take over?

A
  • If the conduction system is blocked between the atria and ventricles the heart will generally continue to beat more slowly
  • The region of the pacemaker just distal to the block will take over from the SAN
  • It paces the heart more slowly since its rate of intrinsic depolarisation is slower than that of the SAN
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26
Q

What symptoms occur when a latent pacemaker takes over (complete heart block)?

A
  • Temporary syncope → as the heart stops bc it takes a few seconds for the latent pacemaker to take over
  • Followed by recovery, with breathlessness, fatigue and possible chest pain, especially on effort
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27
Q

Why can chest pain occur in complete heart block?

A

CO drops with HR and if this is sufficient it can lead to chest pain

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28
Q

What is the prognosis of complete heart block?

A
  • Episodes of syncope tend to get longer and exhale beats slow
  • Most patients die within 2 months unless treated, some die immediately if distal pacemaker doesn’t take over
  • Risk depends on location of block → more distal block = slower rhythm = greater risk of asystole
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29
Q

What is asystole?

A

Heart stopping

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30
Q

How is complete heart block treated?

A
  • Implantation of a permanent pacemaker to generate the cardiac rhythm (unless risk is low or block is likely to be temporary)
  • If risk of asystole is high, may need immediate temporary pacemaker as well
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31
Q

Describe the ECG in complete (3rd degree) heart block

A
  • Hallmark = QRS complex becomes dissociated from the P wave (atrioventricular dissociation)
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32
Q

What causes the ECG pattern in 3rd degree heart block?

A
  • QRS is generated by a distal pacemaker which has its own rhythm so the P wave happens more frequently than the QRS complex
  • Atria and ventricles beat independently
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33
Q

What is a tachyarrhythmia?

A

Rapid HR generally caused by re-entry

34
Q

What causes tachyarrhythmias?

A

1) The impulse from the SAN is delayed/trapped in one region of the heart
2) Therefore the SAN is working but not driving HR, meanwhile the adjacent tissue finishes depolarising and is no longer refractory
3) The delayed impulse then re-enters the adjacent tissue and spreads throughout the heart
4) This can occur once, creating a premature beat, or indefinitely generating a sustained tachycardia

35
Q

What is the cause of the most serious arrhythmias?

A

Re-entry/tachyarrhythmias

36
Q

When do tachyarrhythmias tend to occur and why?

A

During/after an MI → after an MI, there are scars so different areas of myocardium have different conductivity

37
Q

Where can tachyarrhythmias occur?

A

Wherever adjacent areas of myocardium have different conduction rate and refractoriness

38
Q

What are causes of tachyarrhythmias?

A

1) Ischaemia
2) Myocardial scarring
3) Certain congenital conditions

39
Q

What often triggers tachyarrhythmias?

A

Premature impulses arising from triggered automaticity

40
Q

What are the 2 basic requirements for re-entry?

A

1) A conducting pathway with a non-excitable core around which the impulse can cycle
2) Zones of differential conductivity or refractoriness within the path

41
Q

Describe what happens in re-entry

A

1) Unidirectional block in conduction system with slowed retrograde conduction
2) Impulse can’t go through the block, but instead comes round to the distal ends and starts again
3) Wave of depolarisation spreads out into the whole heart faster than the SAN
4) Re-entrant rhythm can persist as long as the cycling impulse continues to re-enter non refractory tissue

42
Q

How do you stop re-entry?

A

1) Convert the unidirectional block to a bidirectional block by suppressing conduction
2) Prolong the refractory period so the retrograde impulse cannot re-enter conducting myocardium

43
Q

How else can re-entry occur?

A

Without a defined anatomical pathway = functional re-entry

44
Q

When does functional re-entry typically occur and why?

A

During or after an MI → cardiac conduction is slowed in some regions of the heart and therefore becomes spatially heterogenous

45
Q

What happens in functional re-entry?

A

1) Interaction of waves of depolarisation with obstacles or zones of impaired conduction leads to breaking up the waves and formation of spiral waves of excitation (rotors)
2) These may give rise to chaotic electrical activity of the myocardium, leading to fibrillation

46
Q

What can initiate re-entry?

A

Triggered automaticity

47
Q

What can cause abnormal electrical activity?

A

Early or delayed afterdepolarisations (EAD/DAD)

48
Q

What happens in EAD?

A

AP becomes prolonged as potassium channels are inhibited

49
Q

What causes EADs?

A

Stimuli that increase the calcium current or AP duration e.g. hypoxia, catecholamines, sotalol (anti-arrhythmic)

50
Q

What are DADs caused by?

A

Excessive increases in calcium concentrations due to catecholamines or digoxin

51
Q

What is atrial fibrillation?

A

A chaotic atrial rhythm with rapid and irregularly irregular ventricular rhythm (pulse)

52
Q

How do you describe the rhythm in atrial fibrillation?

A

Irregularly irregular

53
Q

What is the cause of atrial fibrillation?

A

Most often an ectopic focus located in the cardiac muscle layer surrounding a pulmonary vein

54
Q

What are risk factors for AF?

A

Atrial dilation, heart failure, hypertension, excessive alcohol intake, old age

55
Q

What is the effect of AF on cardiac rhythm?

A
  • No organised atrial beating due to chaotic electrically activity (quivering) → depolarising chaotically with small depolarisations which can cause random QRS waves
  • Ventricular excitation occurs when atrial depolarisations are sufficient to be conducted through the AVN
56
Q

What are symptoms of AF?

A

Palpitations, breathlessness, dizziness, syncope

57
Q

What is the prognosis of AF?

A
  • Typically progression is paroxysmal → persistent → permanent
  • Associated with progressive electrical and structural remodelling of the atria which promotes more complex and refractory forms of re-entry
58
Q

What is AF a major risk for?

A

Stroke

59
Q

How can AF lead to stroke?

A

Lack of organised atrial beat causes stasis of blood → thrombi can form esp. in the left atrium appendage, and then embolise to the cerebral circulation

60
Q

What is the hallmark on a AF ECG?

A

Lack of P waves due to chaotic electrical activity

61
Q

Describe the ECG in AF

A
  • Lack of P waves
  • Baseline shows small fibrillatory (f) waves of varying amplitude (ripples of depolarisation
  • Irregularly irregular high frequency QRS complexes cause fast irregular tachycardia (>150 bpm)
  • With time, f waves become smaller and QRS complexes occur less frequently, so HR slows down
62
Q

What other features can AF lead to?

A

Fast irregular tachycardia (>150bpm)

63
Q

What is ventricular tachycardia?

A

A run of rapid (typically 120-200bpm) successive ventricular beats caused by an ectopic site in one of the ventricles

64
Q

What are 4 causes of ventricular tachycardia?

A

1) Cardiac scarring after MI
2) Dilated cardiomyopathy
3) Congenital e.g. Brugada syndrome, LQT syndrome
4) Some anti-arrhythmic drugs
(1 and 2 most common)

65
Q

What is the mechanism of cause of ventricular tachycardia?

A

Almost always due to re-entry

66
Q

What is the effect of VT on cardiac rhythm?

A
  • Tachycardia

- Rhythm may be regular (monomorphic VT) or irregular (polymorphic VT)

67
Q

What are symptoms of VT?

A

Chest pain, SoB, syncope

68
Q

What is the prognosis of VT?

A
  • Depends on cause

- If persistent, may compromise cardiac pumping, leading to HF and death

69
Q

What is the hallmark on a VT ECG?

A

Broad (QRS) complex rhythm

70
Q

Describe the ECG in VT

A
  • Broad complex rapid rhythm
  • Complexes can be of regular (monomorphic) or varied shape (polymorphic)
  • Atria usually beat more slowly and independently of the ventricles (AV dissociation)
  • P waves don’t ‘capture’ the ventricles
71
Q

Why do P waves not ‘capture’ the ventricles?

A

Bc when they get through the AV node, the conduction system is usually refractory, since it’s being depolarised so frequently by the ventricular ectopic pacemaker

72
Q

Why is the QRS complex broad on a VT ECG?

A

Initiation of AP in the ventricles means the ectopic site sends AP out through cardiac muscle of the ventricles which is slower than the conduction system

73
Q

What are the notches on a monomorphic (one shape) VT ECG due to?

A

The SAN

74
Q

What is polymorphic otherwise known as?

A

Torsades de pointes |||iii|||

75
Q

What is ventricular fibrillation?

A

Chaotic and disorganised electrical activity of the heart

76
Q

What are the causes of VF?

A

1) MI
2) Ischaemic heart disease
3) Cardiomyopathy
4) Idiopathic

77
Q

What is the effect of VT on cardiac rhythm?

A

No organised ventricular beat so no CO

78
Q

What is the symptom and prognosis of VF?

A

Unconsciousness within seconds, death occurs rapidly

79
Q

What is the ECG hallmark of VF?

A

Disorganised electrical activity which fades as the heart dies

80
Q

What is the most important bradycardia?

A

Complete heart block

81
Q

Describe the most clinically important tachyarrhythmias

A

Caused by re-entry and in the context of myocardial changes associated with coronary heart disease

Stage 2: Supporting Life (30 decks)

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