ECGs

Question 1

What are the rough steps to reading an ECG (in an OSCE)?

Answer 1

1. Check this is the right ECG
2. Rate
3. Rhythm
4. Cardiac Axis
5. P waves
6. P-R interval
7. QRS complexes
8. S-T segment
9. T waves
10. U waves
11. Summarise what you have identified and what it might suggest

Question 2

What should you check for in the first step of reading the ECG?

Answer 2

• patient ID (name and DoB)
• age
• presentation (e.g. chest pain)
• the date and time the ECG was performed

Question 3

How do you count the heart rate?

Answer 3

If REGULAR:

• Count the number of large squares present within one R-R interval
• Divide 300 by this number to calculate the heart rate

If IRREGULAR, this won’t work. Instead:

• Count the R waves in the whole strip (=10 seconds)
• Multiply by 6

Question 4

What’s a normal adult heart rate?

Answer 4

Normal = 60 – 100 bpm

Tachycardia > 100 bpm

Bradycardia

Question 5

How long is a small square in an ECG?

Answer 5

0.04 seconds

Question 6

How long should the P-R interval be?

Answer 6

0.12 - 0.2 secs (3-5 small squares)

Question 7

How long should the QRS complex be?

Answer 7

0.08 - 0.12 secs (2-3 small squares)

Question 8

What is the normal:

1. Width of the QRS?
2. Height of the QRS?

Answer 8

1. QRS can be described as

• narrow (<0.12s / 3small squares) - normal
• wide (<0.12s / 3 small squares) - sign of abnormal depolarisation sequence (e.g. ventricular ectopic) or BBB

2. QRS can be described as

• small < 5 small squares in the limb leads or < 10 small sqares in the chest leads
• tall - imply ventricular hypertrophy (can be due to habitus ie. in tall slim people)

Question 9

How big does ST elevation have to be to become significant?

Answer 9

ST elevation is significant when it is greater than 1 mm (1 small square) in 2 or more contiguous limb leads or >2mm in 2 or more chest leads.

Question 10

What does ST depression show?

Answer 10

ST depression ≥ 0.5 mm in ≥ 2 contiguous leads intidcates myocardial iscaemia

Question 11

T waves are tall if they are…

Answer 11

• > 5 small squares in the limb leads AND
• > 10 small squares in the chest leads

Question 12

What do tall T-waves indicate?

Answer 12

• Hyperkalaemia (“Tall tented T waves”)
• Hyperacute STEMI

Question 13

In which leads is T wave inversion normal?

Answer 13

• V1
• lead III

Question 14

What do biphasic T waves indicate?

Answer 14

• ischaemia
• hypokalaemia

Question 15

Causes of LBBB

Answer 15

• myocardial infarction
  
  • diagnosing a myocardial infarction for patients with existing LBBB is difficult
• hypertension
• aortic stenosis
• cardiomyopathy
• rare: idiopathic fibrosis, digoxin toxicity, hyperkalaemia

Question 16

How do you differentiate LBBB from RBBB?

Answer 16

William LBBB and Marrow RBBB

in leads V1 and V6

Question 17

Causes RBBB

Answer 17

• Right ventricular hypertrophy / cor pulmonale
• Pulmonary embolus
• Ischaemic heart disease
• Rheumatic heart disease
• Congenital heart disease (e.g. atrial septal defect)
• Myocarditis
• Cardiomyopathy

Question 18

What is the ECG change on 1st degree heart block?

Answer 18

Consistently prolonged PR interval

Question 19

What is the ECG change on second degree heartblock:

1. Mobitz 1
2. Mobitz 2

Answer 19

1. Progressively increasing PR interval followed by dropped QRS (long, long, drop)
2. Regularly dropped QRS complexes in ratio of normal:dropped e.g. 3:1

Question 20

What is the ECG change on 3rd degree heart block

Answer 20

No relation between P wave and QRS complexes

AND often very bradycardic

Question 21

What are the ECG changes in hyperkalaemia?

K>5.5

Answer 21

Early: Tall tented T-waves

>6.5 K: P wave widening and flattening until disappeared, PR segment lengthens

>7: wide QRS and bradycardia +/- conduction blocks

>9 sine wave

Question 22

What are the ECG features in hypokalaemia?

Answer 22

• Increased P wave amplitude
• Prolongation of PR interval
• Widespread ST depression and T wave flattening/inversion
• Prominent U waves (best seen in the precordial leads V₂-V₃)
• Apparent long QT interval due to fusion of T and U waves (= long QU interval)

Question 23

What are the ECG changes with pericarditis?

Answer 23

Very similar to STEMIs just EVERYWHERE

• Widespread concave ST elevation (rather than tombstone) and PR depression throughout most of the limb leads (I, II, III, aVL, aVF) and precordial leads (V2-6)
• Reciprocal ST depression and PR elevation in lead aVR (± V1)
• Sinus tachycardia is also common in acute pericarditis due to pain and/or pericardial effusion

Question 24

What does VT look like?

Answer 24

Fast, broad complex

Question 25

What does ventricular flutter look like?

Answer 25

• Chaotic irregular deflections of varying amplitude
• No identifiable P waves, QRS complexes, or T waves
• Rate 150 to 500 per minute
• Amplitude decreases with duration (coarse VF –> fine VF)

Question 26

If a patient in VT is haemodynamically STABLE what do you give?

Answer 26

Drug therapy

• amiodarone: ideally administered through a central line
• lidocaine: use with caution in severe left ventricular impairment
• procainamide

Question 27

What do you do if someone in VT is haemodynamically unstable?

Answer 27

electrical cardioversion

Question 28

What is the management of atrial fibrillation?

Answer 28

Rate control:

• b-blockers
• CCBs if asthmatic
• digoxin if they don’t work

Rhythm control:

• Cardioversion (amiodarone or electrical) if new / indicated

Stroke risk:

CHADSVASC for DOAC use

Question 29

What is the management of STEMI?

Answer 29

MONA

+ PCI

: will need clopidogrel + unfractionated heparin