OSCE interpretation

Question 1

What is the normal calibration of an ECG

Answer 1

25 mm/s and 10 mm/1mV

Question 2

Normal adult’s heart rates?

Answer 2

Normal: 60-100 bpm
Tachycardia: > 100 bpm
Bradycardia: < 60 bpm

Question 3

2 methods to calculate HR on ECG

Why might you choose one over the other?

Answer 3

1. 300 / number of large squares
2. 6 x number of QRS in 10 seconds

Only the second option works for irregularly irregular rhythms

Question 4

Normal cardiac axis?

Answer 4

In healthy individuals, you would expect the axis to lie between -30° and +90º
Normally, if the electrical activity is towards a lead then this lead positive. The closer to it, the more positive the lead is.

Question 5

Describe right axis deviation

Answer 5

• Depolarisation is distorted to the right
• Between 90 and 180
• Moves toward leads III, away from lead II and massively away from lead I
• See increased positivity in III, slightly less positivity in II and almost negativity in lead I

Question 6

Describe left axis deviation

Answer 6

• Depolarisation is distorted to the left
• Between - 30 and - 90
• Moves towards aVL, far away from III, and away from II to the other side of I
• Lead III is hugely negative
• Lead II is negative
• Lead I is positive

Question 7

What to look for with P waves

Answer 7

• Are they present?
• Is so, are they each followed by a QRS?
• Do the P waves look normal? Duration, direction, shape
• If P waves are absent, is there any atrial activity?
  o Sawtooth baseline –> flutter waves
  o Choatic baseline –> fibrillation waves
  o Flat line –> no atrial activity at all

Question 8

Normal PR interval

Answer 8

120 - 200 ms (1.2 - 2 s)

3-5 small squares

Question 9

Shortened PR interval causes?

Answer 9

• P wave is originating from somewhere closer to AV node so conduction takes less time - some people have smaller atria, or SA node is not in fixed place
• Atrial impulse is getting to the ventricle via a faster shortcut, e.g. accessory pathway, Wolf-Parkinson White syndrome
• Would see delta waves in WPW syndrome

Question 10

Three things to look at with QRS

Answer 10

• Width
• Height
• Morphology

Question 11

Width of QRS

Answer 11

• Narrow (< 0.12 seconds)

- Broad (> 0.12 seconds)

Question 12

Causes of broad QRS

Answer 12

• Bundle branch block
• Ventricular ectopics
• Ventricular arrhythmias

Question 13

Causes of narrow QRS

Answer 13

• Atrial ectopics

Question 14

Height of QRS

Answer 14

• Small (< 5 mm in limb leads or < 10 mm in chest leads)

- Tall - imply ventricular hypertrophy

Question 15

Morphology problems of QRS

Answer 15

• Delta waves (WPW if with tachyarrhythmias)

- Q waves

Question 16

What are pathological Q waves

Answer 16

> 25% the size of the R wave that follows it
OR
2mm in height and > 40ms in width

Question 17

R and S waves

Answer 17

• In lead V1 the S wave is larger than the R wave
• The transition to R being the larger wave should occur in lead V3 or V4
• If it occurs into V5 or V6 this is poor R wave progression
• Can be a sign of previous MI or in very large people due to poor lead position

Question 18

ST elevation in mm/squares

Answer 18

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

Question 19

ST depression in mm/squares

Answer 19

• > 0.5 mm in > 2 contiguous leads

Question 20

T waves

Tall

Answer 20

> 5 mm in limb leads
AND
10 mm in chest leads

Question 21

T waves
Tall
Height

Answer 21

> 5 mm in limb leads
AND
10 mm in chest leads

Question 22

T waves
Tall
Causes

Answer 22

• Hyperkalaemia

- Hyperacute STEMI

Question 23

T waves
Inversion
Causes

Answer 23

• Ischaemia
• Bundle branch block
• PE
• LVH
• HOCM
• General illness

Question 24

Biphasic T waves

Causes

Answer 24

• Ischaemia

- Hypokalaemia

Question 25

Flattened T waves | Causes

Answer 25

- Ischaemia | - Electrolyte imbalances

Question 26

U waves | What are they?

Answer 26

- > 0.5 mm deflection after the T wave | - Best seen in V2 or V3

Question 27

U waves | Causes

Answer 27

- Electrolyte imbalances - Hypothermia - Secondary to antiarrhythmic therapy (digoxin, amiodarone)

Question 28

What does a small square on an ecg represent

Answer 28

0.04 seconds

Question 29

What does a large square on an ecg represent

Answer 29

0.2 seconds

Question 30

ECG: How many large squares in 1 second

Answer 30

5

Question 31

ECG: How many large squares in 1 minute

Answer 31

300

Question 32

Spirometry Reference ranges

Answer 32

FEV1: >80% predicted FVC: >80% predicted FEV1/FVC ratio: >0.7

Question 33

Spirometry Details that need to be checked

Answer 33

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