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Cardiology > ECG - Arrythmia Diagnosis > Flashcards

ECG - Arrythmia Diagnosis Flashcards

1
Q

What is the inherent rate of depolarisation of the SA node?

A

60-100 bpm

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2
Q

What is the intrinsic rate of depolarisation of the AV node?

A

45-50 bpm

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3
Q

What is the intrinsic rate of the bundle branches?

A

45-50 bpm

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4
Q

What is the intrinsic rate of depolarisaiton of atrial cells?

A

55-60 bpm

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5
Q

What is the intrinsic rate of depolarisation of the ventricular myocardium?

A

30-35 bpm

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6
Q

What are ectopic beats?

A

Tissue outside the SA node discharging and causing a coordinated contraction. Type of contraction depends on locus

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7
Q

What is a premature atrial ectopic?

A

Ectopic that has a focus of depolarisation outside the SA node but within the atria. P-wave axis is often altered depending on locus of discharge, and ventricular contraction occurs in an irregular pattern relative to normal contraction of the heart

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8
Q

What is the duration of the QRS complex in an atrial ectopic?

A

Normal - < 3ss due to conduction through the ventricles being normal

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9
Q

What is a ventricular premature ectopic?

A

Focus of depolarisation in the ventricles. Ventricular conduction outside bundle branches is slow, resulting in characteristically broad QRS complex with bizarre morphology. Repolarisation is also bizarre, resulting in lack of concordance of T-wave

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10
Q

What can occur following a ventricular ectopic?

A

Compensatory pause - indicates that ectopic has had no effect on SA node. Atria still contract at same rate, but P-waves become lost in ventricular ectopic waveform

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11
Q

Do the atria continue to contract normally with a ventricular ectopic?

A

Yes - p-wave rate remains constant, but atrial depolarisation that occurs during ectopic beat is not conducted into ventricles due to either depolarisation or repolarisation of the ventricles. This leads to p-waves becoming buried within ectopic beats

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12
Q

What can happen follwoing an atrial ectopic?

A

Non-compensatory pause - due to atrial contraction outwith normal SA automaticity, leading to the SA node being “re-set”. This leads to a pause of variable duration, and can lead to alteration in HR following the pause

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13
Q

What can the PR interval in an atrial ectopic indicate in terms of proximity to the AV node?

A

Shorter the PR interval, closer the proximity

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14
Q

How are tachycardias defined in terms of location?

A

SVT and VT

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15
Q

What defines a ventricular tachycardia?

A

Tachycardia with a depolarisation focus below the bundle of His

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16
Q

In terms of QRS complex, are ventricular tachycardias broad or narrow complex?

A

Broad complex

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17
Q

In terms of the QRS complex, are supraventricular tachycardias broad or narrow?

A

Narrow

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18
Q

Where do SVTs originiate from?

A

SA node or Atrial Focus

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19
Q

Which area in the atria is regarded as very arrythmogenic?

A

Area around AV node and bundle of His

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20
Q

What is the junctional region?

A

Locus of tissue in the area of the atrioventricular node, the “junction” between atria and ventricles

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21
Q

What are the three main supraventricular zones which SVTs originate from?

A
  • SA node
  • Junctional Region
  • Atrial focus - other than SA node/junctional region
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22
Q

What direction will atrial contraction spread in a junctional depolarisation?

A

Superiorly into atrium from junction, and inferiorly through bundle of his

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23
Q

What are features of a junctional tachycardia?

A
  • Regular, narrow complex tachycardia
  • P-wave changes
    • Significantly shortened PR interval - varies depending on focus
    • Inverted p-waves in inferior leads
    • P-waves may be absent - buried in QRS
    • P-waves may follow QRS
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24
Q

What are the main criteria for diagnosis of AF on ECg?

A
  • Irregularly irregular rhythm
  • No P-waves
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25
Q

What is the pathophysiology of AF?

A

Multiple sites in atria depolarise independently, but fail to fully depolarise atria due to other areas being in a refractory state, producing small depolarisation events (wavelets). These are conducted into ventricles at variable intervals, leading to the irregularly irregular rate

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26
Q

What determines whether atrial depolarisation in AF is conducted into the ventricles?

A

Intranodal refractory foci block conduction. When these foci complete their refractory period, the wavelets find a path of conduction through the node and into bundle of his

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27
Q

What is a HR < 100bpm in AF known as?

A

Controlled AF

28
Q

What is the difference between coarse and fine AF?

A

Isoelectric line is more distorted in Coarse AF, whereas fine is less distorted. Fine AF represents more atrial depolarisation foci than coarse.

29
Q

What occurs in the atria during atrial flutter?

A

Re-entrant loop created in RA in a clockwise fashion which then discharges into LA. This occurs at about 300 pm.

30
Q

What protects the ventricles from conducting every flutter wave in atrial flutter?

A

AV node - healthy node conducts at a rate of about 2:1

31
Q

How is atrial depolarisation conducted into the AV node in a normal individual?

A

Conducting tract through non-conducting tissue

32
Q

In those who experience AVNRT, what structural anomaly put them at risk of developing AVNRT?

A

Two tracts into the AV node through the non-conducting tissue

33
Q

In terms of conduction characteristics, what is the difference between normal conduction pathway into the AV node and aberrant conduction pathway into the AV node in those with AVNRT?

A
  • Normal pathway - Normal depolarisation/repolarisation
  • Aberrant pathway - Slow depolarisation, rapid repolarisation
34
Q

Why can the aberrant pathways in the AV node in AVNRT predispose to AVNRT being triggered by atrial ectopics?

A

Due to rapid repolarisation of aberrant tract, it means that if an atrial ectopic occurs, it arrive at a time where the aberrant tract has repolarised, while the rest of the node is still repolarising. This means the aberrant tract can conduct the ectopic wave.

Due to repolarisation sequence that occurs following this, a re-entrant loop is set up. For each re-entrant loop that occurs, discharge is sent into the bundle of his and thus the ventricles. It also releases depolarisation into atria, which maintains the re-entrant circuit.

35
Q

What maintinas the re-entrant circuit created in AVNRT?

A

Depolarisation conducted down normal pathway back into atria, which then depolarises the atria which is then conducted into aberrant pathway, creating a loop

36
Q

What HR does AVNRT normally produce?

A

>130 Bpm

37
Q

What heart rate indicates a junctional tachyarrythmia?

A

100-140 Bpm

38
Q

What can be assumed if a tachycardia originating in the junctional region exceeds 140 Bpm?

A

Almost certainly AVNRT

39
Q

What assumption can be made about a tachyarrythmia originating in the junctional region if the HR was < 130 Bpm?

A

Junctional tachycardia

40
Q

What clinical features would suggest that a tachycardia is AVNRT?

A
  • Signs on ECG
  • Paroxysmal episodes
  • Normal Resting ECG
41
Q

What are features of AVNRT on ECG?

A
  • Pseudo S waves in lead II, III or AVF - absence in normal ECG
  • HR > 140 Bpm
  • Narrow complex tachycardia
42
Q

Why do pseudo s waves occur in AVNRT?

A

Due to atrial depolarisation away from junctional region (changed p-wave axis) after ventricular depolarisation. Sometimes these waves can occur within the QRS complex

43
Q

What is the following rhythm?

A

AVNRT

44
Q

What are characteristic features of ventricular tachycardias?

A

Broad complex tachcardia

45
Q

Why does re-entry cause VT?

A

Most common cause is due to re-entrant circuits being created within the ventricular myocardium. For example, necrosed myocardial tissue following an MI may still have small tracts of viable conducting tissue within the necrosed area, creating potential for re-entrant loops to be created. Premature Ventricular ectopics can set off these re-entrant circuits, and cause VT.

46
Q

What are the criteria for diagnosis of sustained VT?

A

VT for >30 seconds or requiring iintervention

47
Q

What are criteria for non-sustained VT?

A

>3 beats of Broad complex QRS at >100 Bpm for < 30 seconds

48
Q

What are the 3 main mechanisms that can cause VT?

A
  • Re-entry
  • Abnormal automaticity
  • Triggered Activity
49
Q

What is the most common mechanism that causes VT?

A

Re-entry - following MI

50
Q

How does abnormal automaticity cause VT?

A

Accelerated abnormal impulse generation by a region of ventricular cells, leading to sustained ventricular contraction at faster rate

51
Q

What are the main features of VT?

A
  • Rapid heart rate (> 100 bpm)
  • Very broad complexes (>160ms).
  • AV dissociation
52
Q

In VT, what is a capture beat associated with?

A

AV dissociation

53
Q

Why do capture beats occur in VT?

A

As in VT the focus of depolarisation is within the ventricles, the majority of atrial depolarisaiton (which continues normally in VT) is not conducted, either due to the ventricles being in a depolarised/repolarising state. However, some atrial depolarisation meet the AV node at the point where the ventricle is at rest, and thus the conduction can pass through into ventricles

54
Q

Why do capture beats signify AV dissociation?

A

As majority of atrial depolarisation is not conducted due to rapid ventricular depolarisation, this is AV dissociation. Capture beats demonstrate the rare point where atrial depolarisation does conduct all the way through - it is an indirect indicator of AV dissociation

55
Q

Why do fusion complexes occur in VT?

A

Atrial depolarisation is conducted into the ventricles just as ventricular depolarisation occurs. These two depolarisation vectors meet within the ventricles, causing a fusion complexes.

56
Q

What is the following?

A

Fusion complex - represents AV dissociation in VT, with two sources of ventricular depolarisation (one Supraventricular and one ventricular) meeting in the ventricles

57
Q

What are the main features of AV dissociation in VT?

A
  • Capture Beats
  • Fusion Complexes
  • Dissociated P-waves
58
Q

What are the following in VT?

A

Dissociated P-waves

59
Q

What does the heart rate range between in VT?

A

140-200 Bpm

60
Q

What are escape rhythms?

A

Inherent rhythms which occur during a pause in an area of the cardiac conduction system. For example, atrial escape rhythms can occur during a sinus pause

61
Q

What is the key factor in determining an escape beat from a premature ectopic?

A

It’s timing - ectopics occur earlier than the next expected beat, escape beats occur when there is a pause in cardiac conduction, therefore after next expected beat

62
Q

What is the general rule about the heart rate created by ectopic sites as you move further away from SA node?

A

Gets inherently slower

63
Q

What would an escape rhythm below the bundle of his present as on ECG?

A

Broad complex

64
Q

How would you determine an atrial escape rhythm from a junctional escape rhythm?

A

Look at the p-waves and the PR interval

  • PR normal/slightly shortened, p-waves inverted - Atrial
  • PR very short/absent P-waves - Junctional
65
Q

If a bradycardia had broad complexes and AV disocciation, what type of escape rhythm would be occuring?

A

Ventricular escape rhythm

66
Q

If an atrial or junctional rhythm was sitting between 60-99 Bpm, how would you describe it?

A

Accelerated Atrial/junctional rhythm

67
Q

Outline the different nomneclature for atrial (outside SA node), junctional and ventricular tachy/normo/bradycardias

A

Cardiology (29 decks)

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