ECG made easy

Question 1

Why is it best to electrically consider the heart to be just two chambers?

Answer 1

As the atria contract together and the ventricles contract together

Question 2

What is the normal electrical conduction path in the heart?

Answer 2

Depolarisation begins in the sinoatrial node –> atrioventricular node (which slows conduction) –> bundle of his –> right/left bundle branch –> purkinje fibres

Question 3

What is normal/sinus rhythm?

Answer 3

60-100bpm

Question 4

What does the P wave represent?

Answer 4

Atrial contraction

Question 5

What does the QRS complex represent?

Answer 5

Ventricular contraction

Question 6

Why is the p wave smaller than the QRS complex?

Answer 6

As there is more ventricular muscle mass

Question 7

What does the t wave represent?

Answer 7

Ventricular repolarisation

Question 8

What is a u wave? Who might have one?

Answer 8

Repolarisation of papillary muscles
Only present in some individuals
If preceded by normal T wave –> physiological
If preceded by flattened t wave –> pathological

Question 9

What is the standard rate that ECGs run at?

Answer 9

25mm/s

Question 10

How much time does 1 large square represent?

Answer 10

0.2s

Question 11

How much time does 1 small square represent?

Answer 11

0.04s

Question 12

How many large boxes are equal to 1 minute?

Answer 12

300

Question 13

How many large squares represent 1 second?

Answer 13

5

Question 14

How can you calculate HR from an ECG?

Answer 14

300/no. of large boxes between the R-R interval

Question 15

What is the PR interval?

Answer 15

Time between start of p wave and start of QRS complex

Question 16

What is a normal PR time?

Answer 16

120-200ms (3-5 small squares)

Question 17

What can a short PR interval mean?

Answer 17

Depolarisation occurring too close to AV node/abnormally fast conduction from atria to ventricles

Question 18

What does the QRS duration represent?

Answer 18

How long ventricular contraction takes

Question 19

What is the normal QRS duration?

Answer 19

120ms (3 small squares) or less

Question 20

What things may cause a prolonged QT interval?

Answer 20

Electrolyte abnormalities

Drugs

Question 21

What can a prolonged QT lead to?

Answer 21

Ventricular tachycardia

Question 22

Define a prolonged QT interval

Answer 22

Greater than 450ms

Question 23

What surface of the heart do leads I, II and VL look at?

Answer 23

Left lateral surface

Question 24

What surface of the heart do leads III and VF look at?

Answer 24

Inferior surface

Question 25

What lead looks at the right atrium?

Answer 25

VR

Question 26

What plane do the chest leads look at the heart in?

Answer 26

Horizontal plane

Question 27

What part of the heart do leads V1 and V2 look at?

Answer 27

Right ventricle

Question 28

What part of the heart do leads V3 and V4 look at?

Answer 28

Interventricular septum

Question 29

What part of the heart do leads V5 and V6 look at?

Answer 29

Anterior and lateral walls of left ventricle

Question 30

When the ECG machine detects a wave of depolarisation towards it does it cause an upwards or downwards deflection on the ecg?

Answer 30

Upwards

Question 31

When the ECG machine detects a wave of depolarisation away from it does it cause an upwards or downwards deflection on the ecg?

Answer 31

Downwards

Question 32

What does it mean if the QRS is mainly upwards?

Answer 32

The depolarisation is moving towards that lead

Question 33

What does it mean if the QRS is mainly downwards?

Answer 33

The depolarisation is moving away from that lead

Question 34

What pattern of QRS do you see when the wave of depolarisation is moving at right angles to the lead?

Answer 34

R and S wave are of equal size

Question 35

Which two leads look at the heart from opposite directions?

Answer 35

II and VR