How to calculate rate on ECG ?
QRS complexes x 6
What condition has a sawtooth appearance on ECG ?
Atrial flutter
What does the p wave represent ?
Atrial depolarisation
What does the flat line between the p wave and qrs complex represent ?
Delay of stimulus in the bundle of his to allow atria enough time to pump all the blood into the ventricles
What does the QRS complex represent ?
Ventricular contraction
- changing direction of electrical stimulus as it passes through the hearts conduction system
What does the Q wave represent ?
Depolarisation in the septum
- whilst electrical stimulus passes through the bundle of his, and before it separates down the two bundle branches, it starts to depolarise the septum from left to right
What does the R wave represent ?
Electrical stimulus as it passes through the main portion of ventricular walls
(Hence the bigger wave)
What does the S wave represent ?
Depolarisation of purkinje fibres
- purkinje fibres spread through ventricles from top to bottom and then back up through ventricle walls
What does the T wave represent ?
Ventricular repolarisation
Normal duration of PR interval ?
0.12-0.20 s (3-5 small squares)
Normal duration of QRS complex ?
0.08-0.12 (2-3 small squares)
Normal duration of QT interval ?
0.35-0.43s (~9-11 small squares)
What does a U wave represent ?
Repolarisation of purkinje fibres
T= AV node and bundle branches specifically
What is the characteristic sign of Supraventricular tachycardias on ECG ?
- narrow QRS (defines its Supraventricular origin)**
- regular rapid pattern
- rate 170-230 (too fast to likely be sinus tachy)
Appearance of AF on ECG .
- chaotic rhythm with recognisable QRS
- absent p waves **
- fibrillation baseline
- irregular distances between QRS complexes
Appearance of atrial flutter on ECG ?
- flutter rate 250-350
- 2:1 or 4:1 response (I.e. Every 4th impulse goes to ventricles)
- saw tooth baseline
ECG findings of ventricular fibrillation ?
- chaotic irregular deflections of varying amplitude
- no p waves, QRS or T waves
- rate 150-500bpm
ECG findings in ventricular tachycardia ?
- very broad QRS (>160ms)**
- extreme axis deviation (QRS +ve in aVR and -ve in I and aVF)
- AV dissociation
How many seconds does a big square represent on ECG ?
0.2s
Which leads do you look at on ECG to determine axis ?
I and III
- if both point up = normal
How can you tell if someone has left axis deviation on ECG ?
QRS positive in lead I and negative in lead III
- as they are Leaving each other so Left axis deviation
- not significant until lead II also predominant negative too
How can you tell if someone has right axis deviation on ECG ?
If QRS is negative in lead I and positive in lead II
- aRRiving so Right axis deviation
Cause of left axis deviation
Usually due to conduction defect NOT left ventricular hypertrophy:
- left anterior fascicular Block
- inferior MI
- normal variant in obese people
- WPW
Causes of right axis deviation ?
- normal variant in children and tall thin adults
- RVH
- chronic lung disease
- antero-lat MI
