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Yr 3 - Skills & Extras > ECG Interpretation > Flashcards

ECG Interpretation Flashcards

1
Q

Run through the steps of interpreting an ECG in an OSCE station

A
  1. Confirm time and date of ECG
  2. Confirm patient name & DOB - ensure this matches ECG
  3. Check calibration (usually 10mm/1mV)
  4. Check paper speed (usually 25mm/s)
  5. Heart rate
  6. Heart rhythm
  7. Cardiac axis
  8. P waves (morphology & relation to QRS)
  9. PR interval
  10. QRS complex (wide or narrow)
  11. ST segment (elevated or depressed)
  12. T waves
  13. Q wave
  14. QT interval
  15. Present findings & diagnosis
  16. Ask to review previous ECG to compare
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2
Q

What lead should you look at to determine the HR?

A

Lead II

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3
Q

How can the HR be determined on an ECG?

A

Count the number of R waves seen in the 10 second rhythm strip (lead II).

Multiply this x6.

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4
Q

If the HR is regular what is another way the HR can be determined on an ECG?

A
  1. Count the number of large squares present within one R-R interval
  2. Divide 300 by this number to calculate heart rate
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5
Q

How will conducting system problems affect the HR?

A

Bradycardia

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6
Q

How will hypothermia affect the HR?

A

Bradycardia

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7
Q

Causes of tachy/bradycardia

A
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8
Q

How can you determine the heart rhythm on an ECG?

A

Look at lead II (rhythm strip) and mark out each R wave on piece of paper and move it along the rhythm strip to check if subsequent intervals are similar.

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9
Q

Define sinus rhythm.

A

A sinus rhythm is any cardiac rhythm in which depolarisation of the cardiac muscle begins at the sinus node.

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10
Q

How can sinus rhythm be determined on an ECG?

A
  1. Are p waves present?
  2. Are there p waves upright (positive) in lead II?
  3. Are p waves inverted (negative) in aVR?
  4. Is every p wave followed by QRS complex?

If yes → sinus rhythm

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11
Q

What does cardiac axis describe?

A

Cardiac axis describes the overall direction of electrical spread within the heart.

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12
Q

What leads must you look at to determine the cardiac axis?

A

leads I, II and III.

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13
Q

If the cardiac axis is < -30 degrees, what does this indicate?

A

Left axis deviation (due to conduction problems)

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14
Q

If the cardiac axis is > +90 degrees, what does this indicate?

A

Right axis deviation (due to right ventricular hypertrophy)

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15
Q

What is this shape of QRS complex known as?

A

Isoelectric

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16
Q

In right axis deviation, which lead has the most positive defection?

A

Lead III

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17
Q

In left axis deviation, which lead has the most positive defection?

A

Lead I

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18
Q

Describe leads I, II and III in LAD

A

I → positive

II & III → negative

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19
Q

Describe leads I, II and III in RAD

A

I → negative

II & III → positive

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20
Q

What characterises sinus rhythm?

A

the presence of correctly orientated P waves on the electrocardiogram.

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21
Q

When assessing the p waves, what should you look at?

A
  1. Are p waves present?
  2. Is each p wave followed by a QRS complex?
  3. Do the p waves look normal? → check duration, direction and shape
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22
Q

What is the normal duration of a p wave

A

<0.12 seconds (<3 small squares)

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23
Q

The largest p wave deflection should not exceed what?

A

2.5mm

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24
Q

What does an enlarged p wave (>2.5 mm) indicate?

A

Atria enlargement

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25
Q

What lead are p waves inverted?

A

aVR

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26
Q

What do abnormal inverted p waves indicate?

A

An ectopic atrial rhythm, originating from sinus node

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27
Q

What feature of an ECG are seen in AF?

A
  • Tachycardia
  • Irregularly irregular rhythm
  • Absent P waves
  • Narrow QRS complexes
  • Chaotic baseline
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28
Q

What is the PR interval?

A

PR interval is the time taken for electrical activity to move between the atria and ventricles (AV node delay).

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29
Q

What is the normal length of the PR interval?

A

0.12-0.20 seconds (3-5 small squares)

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29
Q

What is the normal length of the PR interval?

A

0.12-0.20 sec (3-5 small squares)

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30
Q

What does a prolonged PR interval (>0.2 seconds) indicate?

A

Presence of an AV block

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31
Q

Describe the PR interval in first degree heart block

A

Involves a fixed prolonged PR interval (>0.2s)

It is the same prolonged PR interval throughout entire length of rhythm strip

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32
Q

Describe the PR interval in second degree heart block (type 1)

A

Progressive prolongation of PR interval until eventually atrial impulse is not conducted and QRS complex is dropped

AV nodal conduction resumes with next beat and sequence of progressive PR interval prolongation (and eventual dropping of a QRS complex) repeats itself

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33
Q

Describe the PR interval in second degree heart block (type 2)

A

In second-degree type 2 block, there are intermittent non-conducted P waves without warning (i.e. intermittent dropping of QRS complexes due to failure of conduction).

Unlike type 1, there is no progressive prolongation of the PR interval; instead, the PR interval remains constant, and the P waves occur at a constant rate with unchanged P-P intervals.

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34
Q

What occurs in 3rd degree (complete) heart block

A
  • No electrical communication between the atria & ventricles due to a complete failure of conduction
  • Presence of P waves and QRS complexes that have no association with each other (atria & ventricles functioning independently)
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35
Q

Where does 1st degree heart block occur?

A

Between the SA and AV node (i.e. within the atrium)

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36
Q

Where does 2nd degree heart block type I occur?

A

Occurs in the AV node (this is the only piece of conductive tissue in the heart which exhibits the ability to conduct at different speeds).

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37
Q

Where does 2nd degree heart block type II occur?

A

Occurs AFTER the AV node in the bundle of His or Purkinje fibres

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38
Q

Where does 3rd degree heart block occur?

A

Occurs at or after the AV node, resulting in complete blockade of distal conduction

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39
Q

A shortened PR interval (<0.12s) can mean one of two things. What could it indicate?

A
  1. P wave is originating from somewhere closer to the AV node → conduction takes less time
  2. Atrial impulse is getting to the ventricle by a faster shortcut (accessory pathway)
40
Q

What is Wolff Parkinson White Syndrome?

A

A relatively common heart condition that causes the heart to beat abnormally fast for periods of time. This is caused by an extra electrical connection in the heart between the atria and ventricles.

41
Q

What ECG feature is characteristic of WPW syndrome?

A

A delta wave → slurred upstroke of the QRS complex

42
Q

What is the normal length of a QRS complex?

A

<0.12s / <3 small squares within the QRS complex (i.e. narrow)

43
Q

Give a cause of a broad QRS (>0.12s) with a regular pulse

A

Ventricular tachycardia

44
Q

Give a cause of a broad QRS (>0.12s) with a irregular pulse

A

Ventricular fibrillation

45
Q

When assessing the QRS complex, what characteristics should you look at?

A
  1. Width
  2. Height
  3. Morphology
46
Q

What causes a narrow QRS complex?

A
  • A narrow QRS complex occurs when the impulse is conducted down the bundle of His and the Purkinje fibres to the ventricles
  • This results in a well organised synchronised ventricular depolarisation → NORMAL
47
Q

What causes a wide (>0.12s) QRS complex?

A

A slower spread of ventricle depolarisation caused by:

  • ventricular ectopic (where the impulse spreads slowly across the myocardium from a focus in the ventricle)
  • bundle branch block
48
Q

How can a bundle branch block lead to a broad QRS complex?

A

as the impulse gets to one ventricle rapidly down the intrinsic conduction system then has to spread slowly across the myocardium to the other ventricle

49
Q

Give some differentials for a wide QRS complex

A
  • Bundle branch block
  • Hyperkalaemia
  • Ventricular tachycardia (wide QRS, regular rhythm, tachycardia)
  • Wolff Parkinson White syndrome
  • Paced rhythm e.g. pacemaker
  • Medications (Tricyclic antidepressant overdose)
50
Q

An overdose of which drug can cause wide QRS complexes?

A

Tricyclic antidepressants

51
Q

Normal height of a QRS complex?

A

<5mm in limb leads, <10mm in chest leads

52
Q

Give some causes of a tall QRS (>5mm in the limb leads or >10mm in the chest leads)

A
  • Ventricular hypertrophy
  • Body habitus e.g. tall, slim people
53
Q

What is a delta wave?

A

A slurred upstroke in the QRS complex.

54
Q

Cause of a delta wave?

A

Extra pathway conducting electricity from the atria to the ventricles.

I.e. a sign the ventricles are being activated early than normal from a point distant to the AV node

55
Q

Does the presence of a delta wave diagnose WPW syndrome?

A

No → this requires evidence of tachyarrhythmias AND a delta wave

56
Q

What can pathological Q waves indicate?

A

MI (old or recent) → are the result of the absence of electrical activity

57
Q

describe the normal depth of Q in relation to R

A

Q depth should be less than the height of R in that lead

58
Q

Give 3 features that would make a Q wave pathological

A
  • >40 ms (0.4s) (1mm) wide (remember this is the Q wave NOT the QRS complex)
  • Q wave is >25% the size of the R wave that follows it (peak of QRS complex)
  • Q wave is >2mm in height from isoelectric line to peak of Q wave
59
Q

What is the ‘j point’ segment?

A

Where the S wave joins the ST segment

60
Q

What is the most common, ‘normal’ ECG variant?

A

High take off / benign early repolarisation

This point can be elevated, resulting in the ST segment that follows it also being raised (this is known as ‘high take off’)

61
Q

When looking at the ST segment, what are you assessing?

A

If there’s any ST elevation or depression

62
Q

Describe the shape of a healthy ST segment

A

Should be isoelectric line (neither elevated nor depressed).

63
Q

What must be present to define ST elevation?

A

ST elevation of 1mm above the isoelectric line in 2 continuous leads (except V2-V3)

64
Q

What must be present to define ST depression?

A

ST depression of 0.5mm below the isoelectric line in 2 continuous leads

65
Q

When is ST elevation significant?

A
  • >1mm (1 small square) in 2 or more contiguous limb leads OR
  • >2mm in 2 or more chest leads
66
Q

Give some differentials for ST elevation

A
  • STEMI → most common
  • Benign early repolarisation
  • Pericarditis
  • Vasospasm
  • Pulmonary embolism
  • LV aneurysm
  • LV hypertrophy
  • Left bundle branch block
67
Q

When is ST depression significant?

A

ST depression >/= 0.5mm in >/= 2 contiguous leads

68
Q

Give some differentials for ST depression

A
  • NSTEMI
  • Posterior MI
  • LBBB
  • Digoxin toxicity
  • Reciprocal changes
69
Q

When assessing the T waves, what are you looking for?

A

Morphology → inversion, flattening, biphasic, tented etc

70
Q

What defines a ‘tall’ T wave in limb and chest leads?

A
  • >5mm in limb leads AND
  • >10 mm in chest leads
71
Q

Give 2 differentials for tall T waves

A
  • Hyperkalaemia
  • Hyperacute STEMI
72
Q

Inversion of T waves in which leads are normal?

A
  • T waves are normally inverted in V1
  • Inversion in lead III is a normal variant
73
Q

Give some differentials for inverted T waves

A
  • T wave inversion in aVL → inferior wall MI
  • Raised intracranial pressure
  • PE
  • Bundle branch blocks (V4-6 in LBBB and V1-V3 in RBBB)
  • Left ventricular hypertrophy (in lateral leads)
  • Hypertrophic cardiomyopathy (widespread)
  • General illness
74
Q

What are biphasic T waves?

A

Biphasic waves have two peaks

75
Q

Give 2 differentials for biphasic T waves

A
  1. Ischaemia
  2. Hypokalaemia
76
Q

What are flattened T waves a non-specific sign of?

A

Are a non-specific sign that may represent ischaemia or electrolyte imbalance.

77
Q

what are hyperacute T waves?

A

Hyperacute T waves are a sign of an early stage STEMI (often precede appearance of ST elevation and Q waves).

Features → broad based, symmetrical

78
Q

What is a U wave?

A

The U wave is a small (0.5 mm) deflection immediately following the T wave, usually in the same direction as the T wave.

79
Q

What are u waves classically seen in?

A
  • These become larger the slower the bradycardia:
  • Classically seen in various electrolyte imbalances, hypothermia and 2ary to antiarrhythmic therapy (e.g. digoxin, procainamide or amiodarone).
80
Q

Rhythm problems:

81
Q

What condition does this ECG show? What characteristics lead you to this diagnosis?

A

First degree heart block

  • Each P is followed by QRS
  • Prolonged PR interval (>0.2s)
  • Bradycardia
82
Q

What is 2nd degree heart block type 1 also called?

A

Wenckebach

83
Q

What condition does this ECG show? What characteristics lead you to this diagnosis?

A

2nd degree (Mobitz) type 1 heart block

  • PR interval gets longer
  • Each P wave is followed by QRS complex until a QRS is dropped
  • Cycle starts again
84
Q

What condition does this ECG show? What characteristics lead you to this diagnosis?

A

Second degree heart block type 2

  • Every P wave is NOT followed by a QRS (intermittently dropped)
  • Pattern here is 2:1 but can be variable
  • PR interval is consistent
85
Q

Give some symptoms of 2nd degree heart block type 2

A
  • Lethargy/fatigue
  • Faint/LOC
  • SOB
  • Heart failure
  • Angina
86
Q

What condition does this ECG show? What characteristics lead you to this diagnosis?

A

Complete/3rd degree heart block

  • There are regular P waves
  • There are regular QRS complexes
  • There is no relationship between the two
87
Q

When there is no signal from the atria, pacemakers in the ventricles take over (e.g. ventricular ectopic). How does this affect the QRS complex?

A

Wide (>0.12s)

88
Q

How does a bundle branch block affect the QRS?

A
  • If one of the bundles stops working, the ventricles will contract out of sync
  • This will produce a wide QRS The patterns are different for left and right BBB
89
Q

Which leads do you look at to diagnose bundle branch block?

90
Q

Describe QRS complexes in V1 and V6 in left BBB

A

WiLLiaM

V1 → w shaped (i.e. widened and downward deflecting)

V6 → m shaped

91
Q

Describe QRS complexes in V1 and V6 in right BBB

A

MaRRoW

V1 → m shaped

V6 → w shaped

92
Q

Describe the rate and rhythm in atrial flutter

A

Tachycardia, regular rhythm

93
Q

Atrial arrhythmias:

94
Q

Describe the typical atrial beat in atrial flutter

A

Around 300 bpm

95
Q

In 2:1 conduction in atrial flutter, what will the HR be if the atrial beat is 300bpm?

96
Q

What causes ventricular tachycardia?

A

Ventricular tachycardia is just a series of regular fast ectopics from a ventricular pacemaker

97
Q

Who is benign early repolarisation commonly seen in?

A

commonly seen in young, healthy patients < 50 years of age - also known as ‘high take off’ or ‘j point elevation’

Yr 3 - Skills & Extras (7 decks)

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