ECG Theory

Question 1

Where on the chest should V1 be placed?

Answer 1

Right sternal edge, 4th intercostal space

Question 2

Where on the chest should V2 be placed?

Answer 2

Left sternal edge, 4th intercostal space

Question 3

Where on the chest should V3 be placed?

Answer 3

Midway between V2 and V4

Question 4

Where on the chest should V4 be placed?

Answer 4

Mid-clavicular line, 5th intercostal space

Question 5

Where on the chest should V5 be placed?

Answer 5

Anterior axillary line, same level as V4

Question 6

Where on the chest should V6 be placed?

Answer 6

Mid axillary line, same level as V4

Question 7

Which colour of limb lead corresponds to each of the bony prominences?

Answer 7

Right arm red, left arm yellow, left leg green, right leg black

Question 8

One small box on an ECG is equal to what amount of time? One large box is equal to what amount of time?

Answer 8

0.04 secs / 0.2 secs

Question 9

How is the rate calculated from an ECG of a person with a regular pulse?

Answer 9

300 divided by the number of large boxes between two R waves

Question 10

How is the rate calculated from an ECG of a person with an irregular pulse?

Answer 10

The number of QRS complexes in 30 large squares multiplied by 10

Question 11

What 5 questions should you ask yourself to ascertain the rhythm of an ECG?

Answer 11

1. Is there electrical activity present? 2. Is the rhythm regular or irregular? 3. Are P waves present? 4. What is the relationship between the P waves and QRS complexes? 5. What is the QRS duration?

Question 12

How can you tell if the axis of an ECG is normal?

Answer 12

The QRS complex in leads I and aVF will both be positive

Question 13

How can you tell if the axis of an ECG is deviated to the left?

Answer 13

The QRS in lead I will be positive but in aVF will be negative

Question 14

How can you tell if the axis of an ECG is deviated to the right?

Answer 14

The QRS in lead I will be negative but in aVF will be positive

Question 15

What does left axis deviation suggest?

Answer 15

LVH or damage to the right ventricle

Question 16

What does right axis deviation suggest?

Answer 16

RVH or damage to the left ventricle

Question 17

What is the PR interval?

Answer 17

The time from the onset of the P wave to the onset of the QRS complex

Question 18

What does the PR interval represent in the cardiac cycle?

Answer 18

The beginning of atrial depolarisation to the beginning of ventricular depolarisation

Question 19

What is the normal value of the PR interval?

Answer 19

120-200ms (3-5 small squares)

Question 20

The duration of the QRS complex is considered normal when?

Answer 20

It is < 120ms (3 small squares)

Question 21

What is the QT interval?

Answer 21

The beginning of the QRS until the end of the T wave

Question 22

What does the P wave represent in the cardiac cycle?

Answer 22

Atrial depolarisation

Question 23

What does the QRS complex represent in the cardiac cycle?

Answer 23

Ventricular depolarisation

Question 24

What does the T wave represent in the cardiac cycle?

Answer 24

Ventricular repolarisation

Question 25

The T wave should not be more than how high?

Answer 25

Half the height of the QRS

Question 26

Supraventricular rhythms originate where? Describe their QRS complexes?

Answer 26

From the AV node or above / narrow QRS complexes

Question 27

What are the two main features of sinus rhythm?

Answer 27

A P wave for every QRS and QRS for every P wave / PR interval < 200ms (one large box)

Question 28

What is a sinus arrhythmia?

Answer 28

When an ECG meets all the criteria of sinus rhythm, but the rhythm itself is irregular

Question 29

What are the two main features of atrial fibrillation on ECG?

Answer 29

No P waves / Irregularly irregular QRS

Question 30

What causes atrial fibrillation?

Answer 30

Disorganised activity in the atria

Question 31

What causes atrial flutter?

Answer 31

Re-entry circuit within the atria

Question 32

What are the 3 main features of atrial flutter on ECG?

Answer 32

Saw-tooth baseline / F waves / Ventricular rate divisible by 300

Question 33

Retrograde P waves are a sign of what?

Answer 33

Junctional rhythm

Question 34

What causes junctional rhythm?

Answer 34

Electrical impulses originate at the AV node instead of the SA node

Question 35

What are the main features of a supra ventricular tachycardia on ECG?

Answer 35

Regular, narrow complex tachycardia / Often no clear P waves

Question 36

How should a supra ventricular tachycardia be treated?

Answer 36

Vagal manoeuvres, then adenosine if these fail

Question 37

If an ECG shows sinus rhythm with a differing P wave morphology every 3 beats, what does this suggest?

Answer 37

Supraventricular ectopic beats

Question 38

What happens to the QRS complex in ventricular rhythms?

Answer 38

Broad complex

Question 39

Polymorphic ventricular tachycardia is often associated with what ECG feature?

Answer 39

QT prolongation

Question 40

Describe what is meant by aberrancy?

Answer 40

An underlying BBB causes a broad QRS which leads to difficulty diagnosing a supraventricular rhythm

Question 41

What is a good predictor of SVT with aberrancy?

Answer 41

Known pre-existing BBB

Question 42

If in doubt about an ECG with possible aberrancy, should you treat the patient?

Answer 42

Yes, if in doubt treat as VT

Question 43

Describe what happens to an ECG in 1st degree heart block?

Answer 43

Prolonged PR interval

Question 44

Describe what happens to an ECG in Mobitz 1 heart block?

Answer 44

Progressive PR prolongation until the occurrence of a dropped beat

Question 45

Describe what happens to an ECG in Mobitz 2 heart block?

Answer 45

Random beats are missed

Question 46

Describe what happens to an ECG in 3rd degree heart block?

Answer 46

No relationship between the P waves and QRS complex

Question 47

Defibrillation can be used to treat which cardiac arrest rhythms?

Answer 47

VF and VT

Question 48

What is pulseless electrical activity?

Answer 48

Cardiac arrest alongside any rhythm which would normally be associated with a pulse

Question 49

What is asystole?

Answer 49

The total cessation of electrical activity from the heart

Question 50

Leads II, III and aVF correspond to which vascular territory, and which specific artery?

Answer 50

Inferior, right coronary artery

Question 51

Leads I, aVL, V5, V6 correspond to which vascular territory, and which specific artery?

Answer 51

Lateral, left circumflex artery

Question 52

Leads V1-V4 correspond to which vascular territory, and which specific artery?

Answer 52

Anterior, left anterior descending artery

Question 53

What happens to the T wave in ischaemia?

Answer 53

Tall, biphasic, inverted

Question 54

What are the criteria for thrombolysis?

Answer 54

ST elevation > 1mm in two contiguous limb leads OR > 2mm in two contiguous chest leads

Question 55

What is pericarditis? What is it secondary to?

Answer 55

An important cause of ST elevation, usually secondary to an MI or viral infection

Question 56

How should pericarditis be treated if not contraindicated?

Answer 56

NSAIDs

Question 57

As well as ST elevation, what are some other signs of pericarditis?

Answer 57

Widespread changes, PR depression

Question 58

How can you tell if an ECG shows RBBB?

Answer 58

M shape in V1, W shape in V6

Question 59

How can you tell if an ECG shows LBBB?

Answer 59

W shape in V1, M shape in V6

Question 60

Left anterior hemiblock will show what type of axis deviation?

Answer 60

Left axis deviation

Question 61

Left posterior hemiblock will show what type of axis deviation?

Answer 61

Right axis deviation

Question 62

What is a normal QT interval?

Answer 62

< 440ms (11 small boxes, just over 2 large boxes)