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Yr 3 - Skills & Extras > ECG Interpretation > Flashcards

ECG Interpretation Flashcards

1
Q

Give the order of interpreting an ECG in an OSCE station

A
  1. Confirm date and time of ECG
  2. Confirm patient name & DOB - check it matches ECG
  3. Confirm calibration of ECG
  4. Confirm speed of ECG
  5. Heart rate
  6. Rhythm
  7. Cardiac axis
  8. P waves (morphology and relation to QRS)
  9. QRS complex (wide or narrow)
  10. ST segment (elevated or depressed)
  11. T waves (inversion, flattened, biphasic, tented)
  12. Q wave (pathological or non-pathological)
  13. QT interval
  14. Present findings
  15. Ask for previous ECGs to compare
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2
Q

What is the normal calibration of an ECG?

A

10mm/1mV

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3
Q

What is the normal speed of an ECG?

A

25mm/s

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4
Q

When determining the heart rate, what lead should you look at?

A

Lead II

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5
Q

What is normal heart rhythm called?

A

Sinus rhythm

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6
Q

How can the HR be calculated?

A
  1. Count the number of R waves (tip of QRS complexes) in 10 second rhythm strip
  2. Multiply this number by 6
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7
Q

How can you assess the heart rhythm?

A

Mark out R wave on piece of paper and move it along the rhythm strip → check if subsequent intervals are similar.

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8
Q

What does the cardiac axis describe?

A

Every time the left ventricle contracts it sends out a pulse of electrical activity (the QRS complex). This pulse radiates out from the heart, mostly in one direction.

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

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9
Q

What is the normal QRS axis in a healthy individual?

A

between -30 degrees and +90 degrees

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10
Q

To determine the cardiac axis, what leads need to be looked at?

A

I, II and III

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11
Q

Causes of tachy and bradycardias:

A
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12
Q

If the QRS axis is less than 30 degrees, what does this indicate?

A

Left axis deviation

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13
Q

What is left axis deviation due to?

A

Conduction problems

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14
Q

If the QRS axis is more than 90 degrees, what does this indicate?

A

Right axis deviation

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15
Q

What is the cause of right axis deviation?

A

Right ventricular hypertrophy

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16
Q

In a normal cardiac axis, what are the deflections of all the leads? (of I, II and III)

A

Lead II has the most positive deflection

Lead I and lead III are also positive (i.e. all pointing up)

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17
Q

Describe leads I, II and III in right axis deviation

A

Lead III has most positive deflection

Lead I should be negative

i.e. leads I and III are pointing towards each other

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18
Q

Describe leads I, II and III in left axis deviation

A

Lead I has most positive deflection

Lead II and III are negative

(i.e. lead I and III pointing away from each other)

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19
Q

If lead I and II are pointing towards each other, what does this indicate?

A

Right axis deviation

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20
Q

If lead I and II are pointing away from each other, what does this indicate?

A

Left axis deviation

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21
Q

If lead I and II are pointing the same way what does this indicate?

A

Normal cardiac axis

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22
Q

How are p waves used to determine sinus rhythm?

A

LOOK AT THE P WAVES

  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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23
Q

What is the normal duration of a p wave?

A

<0.12 seconds (3 small squares)

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24
Q

What is the normal amplitude of a p wave?

A

<2.5mm

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25
Q

If a p wave exceeds 2.5mm (0.25mv - two and a half small squares), what does this indicate?

A

Atrial enlargement

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26
Q

What is the normal direction of p waves?

A

upright in leads I, II and aVF but inverted in lead aVR

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27
Q

What would inverted p waves indicate?

A

an ectopic atrial rhythm (not originating from sinus node)

28
Q

What does the PR interval indicate?

A

the time taken for electrical activity to move between the atria and ventricles.

29
Q

What should the duration of the PR interval be?

A

120-200 ms (3-5 small squares)

30
Q

How many s is a prolonged PR interval?

A

>0.2 seconds

31
Q

How many s is a shortened PR interval?

A

<0.12 seconds

32
Q

What is the major differential of a shortened PR interval?

A

Wolff-Parkinson White Syndrome

33
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.

34
Q

What wave is seen in WPW syndrome? Why?

A

Delta wave (slurred upstroke of QRS) → these are associated with accessory pathways

35
Q

What ECG feature is associated with an accessory pathway?

A

Delta wave

36
Q

What are the 2 possible mechanisms behind a shortened PR interval?

A
  1. The p wave is originating from somewhere closer to the AV node so conduction takes less time (the SA node is not fixed in place and some people’s atria are smaller than others)
  2. The atrial impulse is getting to the ventricle by a faster shortcut instead of conducting slowly across the atrial wall → accessory pathway
37
Q

What does a prolonged PR interval suggest?

A

An atrioventricular delay (AV block)

38
Q

What are the 3 types of heart block?

A
  • 1st degree
  • 2nd degree (type 1 or type 2)
  • 3rd degree
39
Q

How can first degree heart block be determined by the PR interval?

A

Fixed prolonged PR interval → i.e. same prolonged PR interval throughout entire length of rhythm strip

40
Q

Does type 1 or type 2 of second degree heart block involve a prolonged PR interval?

A

Type 1 i.e. Mobitz type 1 (Wenckebach)

41
Q

How can second degree heart block (type 1) be determined by the PR interval?

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
42
Q

What is the most severe type of heart block?

A

Third degree

43
Q

How can a third degree heart block be determined by the PR interval?

A

Prolonged PR intervals but these are varied (shorter then longer etc - random!)

44
Q

Where does first degree heart block occur?

A

Occurs between the SA node and AV node (i.e. within the atrium

45
Q

Where does second degree type 1 heart block 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)

46
Q

Where does second degree type 2 heart block occur?

A

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

47
Q

Where does 3rd degree heart block occur?

A

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

48
Q

What is considered to be a wide QRS complex?

A

>0.12 seconds (3 small squares)

49
Q

What is considered to be a wide QRS complex?

A

>0.12 seconds (3 small squares)

50
Q

What is considered to be a narrow QRS complex?

A

<0.12 seconds (3 small squares)

51
Q

Is a wide or narrow QRS complex normal?

A

Narrow (<0.12 seconds)

52
Q

What does a wide QRS complex indicate?

A

A slower spread of ventricle depolarisation

53
Q

When assessing a QRS complex, what characteristics should you pay attention to?

A
  1. Width
  2. Height
  3. Morphology
54
Q

What type of QRS complex does a bundle branch block produce?

A

Wide (>0.12s)

55
Q

How does a BBB lead to a broad QRS?

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

56
Q

How would a ventricular ectopic affect the QRS?

A

Wide QRS → impulse spreads slowly across the myocardium from a focus in the ventricle

57
Q

How would an atrial ectopic affect the QRS? Why?

A

Narrow QRS → as it would conduct down the normal conduction system of heart

58
Q

Differentials for a wide QRS?

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)
59
Q

What is a pathological Q wave?

A

A Q wave where it is not meant to be

60
Q

In which leads should Q waves NEVER be seen?

61
Q

Give 3 criteria for a pathological Q wave:

A
  1. >40 ms (0.4s) (1mm) wide OR
  2. Q wave is >25% the size of the R wave that follows it OR
  3. Q wave is >2mm in height from isoelectric line to peak of Q wave
62
Q

What can pathological Q waves be a sign of?

A

Pathological Q waves are a sign of previous myocardial infection → are the result of absence of electrical activity

Can also be a sign of an acute MI

63
Q

When are Q waves pathological?

A

1) > 40 ms (1 mm) wide

2) > 2 mm deep

3) > 25% of depth of QRS complex

4) Seen in leads V1-3

64
Q

What do pathological Q waves usually indicate?

A

current or prior myocardial infarction.

Yr 3 - Skills & Extras (7 decks)

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