ECG reading

Question 1

A small square on an ECG graph represents how many seconds?

Answer 1

40ms (0.04 seconds)

Question 2

One large square on an ECG graph represents how many seconds?

Answer 2

200ms (0.2 seconds)

Question 3

What does the ‘P’ wave represent?

Answer 3

Atrial contraction

Question 4

What does the ‘QRS’ complex represent?

Answer 4

Ventricular contraction

Question 5

What does the ‘T’ wave represent?

Answer 5

Ventricular relaxation

Question 6

What does a broad QRS complex indicate?

Answer 6

Left and right ventricles aren’t contracting at the same time

Question 7

Which ECG leads are measuring the inferior region of the heart? (3)

Answer 7

Leads II, III and AVF

Question 8

Which ECG leads are measuring the anterior region of the heart? (4)

Answer 8

Leads V1, V2, V3 and V4

Question 9

On an ECG, 5 large squares represent how much time?

Answer 9

1 second

Question 10

Heart rate can be measured by the number of large squares between R - R intervals. What does 1 large square equate to in terms of heart rate?

Answer 10

300bpm

Question 11

If there are 3 squares in the R - R interval, what is the heart rate?

Answer 11

100bpm

Question 12

What is the normal time of the PR interval?

Answer 12

120-200ms (3-5 small squares)

Question 13

Where should the chest leads V1 and V2 attach on the body?

Answer 13

VI on the (patients) right hand side, 4th intercostal space sternal edge
V2 on the (patients) left hand side, 4th intercostal space sternal edge

Question 14

Where should chest leads V3 and V4 attach on the body?

Answer 14

V4 should attach on the patients left hand side, 5th intercostal space in the midclavicular line
V3 should attach in between V2 and V4 (on the 4th rib)

Question 15

Where should chest leads V5 and V6 be placed on the body?

Answer 15

V6 should be in the mid axillary line along from V4

V5 should be in between V4 and V6.

Question 16

To work out if the cardiac axis is in the normal direction, which leads parts of the ECG should be used?

Answer 16

I, II and III.

Question 17

Which part on the ECG recording will indicate the cardiac axis?

Answer 17

QRS complex

Question 18

In an ECG reading with a normal cardiac axis, which QRS complex should be most positive?

Answer 18

II

Question 19

In a right axis deviation, which QRS complex is most positive?

Answer 19

III (this is the right inferior-lateral region of the heart, which makes sense for right axis deviation as it is generally caused by right ventricular hypertrophy).

Question 20

How does left axis deviation occur on an ECG reading in leads II and III?

Answer 20

Both have negative QRS complexes.

Question 21

What would first degree heart block look like on an ECG reading?

Answer 21

1. P-R interval prolonged = 360ms
2. One P wave per QRS complex
   (essentially just prolonged P - R interval)

Question 22

What pathologies can first degree heart block signify?

Answer 22

1. Coronary artery disease
2. Acute rheumatic carditis
3. Digoxin toxicity
4. Electrolyte disturbances

Question 23

What are the two types of second degree heart block?

Answer 23

Type 1 Mobitz - AKA Wenckebachs

Type 2 Mobitz

Question 24

What will the ECG reading look like in Wenckebachs second degree heart block?

Answer 24

There is a progressive lengthening of the P-R interval, for example it could go; 260ms, 280ms, 320ms. A QRS complex will then be dropped, and another P wave will come along, and the progressive lengthening recommences.

Question 25

What happens in type 2 Mobitz second degree heart block?

Answer 25

The ‘P-R’ interval of the conducted beats is constant, but there is a dropped QRS complex, often in a pattern of for example 2:1 or 3:1. Meaning after 3 normal cycles, a QRS complex is dropped. There is sometimes no pattern though.

Question 26

There is another type of second degree heart block, called 2:1, what does this refer to?

Answer 26

There are two P waves for every QRS complex. The anomaly/initial P wave may be disguised in the T wave or S wave.

Question 27

What is third degree heart block?

Answer 27

Atrial contraction is normal, but no beats are conduced to the ventricles. The ventricles natural pacemaker which is a lot slower, than takes over. The ECG reading will show regular P waves, but they have no relation to the random QRS complexes.

Question 28

Why might third degree heart block have occurred?

Answer 28

In patients with an MI or it may be a chronic state due to fibrosis of the bundle of His.

Question 29

If the P wave is tall on an ECG, what can this indicate?

Answer 29

P pulmonale - right atrial hypertrophy (most commonly due to tricuspid stenosis)

Question 30

If the P wave is broad on an ECG, what can this indicate?

Answer 30

P mitrale - left atrial hypertrophy (most commonly due to mitral stenosis)