ECGs Flashcards
What are the rough steps to reading an ECG (in an OSCE)?
- Check this is the right ECG
- Rate
- Rhythm
- Cardiac Axis
- P waves
- P-R interval
- QRS complexes
- S-T segment
- T waves
- U waves
- Summarise what you have identified and what it might suggest
What should you check for in the first step of reading the ECG?
- patient ID (name and DoB)
- age
- presentation (e.g. chest pain)
- the date and time the ECG was performed
How do you count the heart rate?
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
What’s a normal adult heart rate?
Normal = 60 – 100 bpm
Tachycardia > 100 bpm
Bradycardia
How long is a small square in an ECG?
0.04 seconds
How long should the P-R interval be?
0.12 - 0.2 secs (3-5 small squares)
How long should the QRS complex be?
0.08 - 0.12 secs (2-3 small squares)
What is the normal:
- Width of the QRS?
- Height of the QRS?
- 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
- 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)
How big does ST elevation have to be to become significant?
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.
What does ST depression show?
ST depression ≥ 0.5 mm in ≥ 2 contiguous leads intidcates myocardial iscaemia
T waves are tall if they are…
- > 5 small squares in the limb leads AND
- > 10 small squares in the chest leads
What do tall T-waves indicate?
- Hyperkalaemia (“Tall tented T waves”)
- Hyperacute STEMI
In which leads is T wave inversion normal?
- V1
- lead III
What do biphasic T waves indicate?
- ischaemia
- hypokalaemia
Causes of LBBB
- myocardial infarction
- diagnosing a myocardial infarction for patients with existing LBBB is difficult
- hypertension
- aortic stenosis
- cardiomyopathy
- rare: idiopathic fibrosis, digoxin toxicity, hyperkalaemia
What is the ECG change on 1st degree heart block?
Consistently prolonged PR interval
What is the ECG change on second degree heartblock:
- Mobitz 1
- Mobitz 2
- Progressively increasing PR interval followed by dropped QRS (long, long, drop)
- Regularly dropped QRS complexes in ratio of normal:dropped e.g. 3:1
What are the ECG features in hypokalaemia?
- 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)
What does VT look like?
Fast, broad complex
What does ventricular flutter look like?
- 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)
