The ECG (die) Flashcards
What is the P wave representative of?
Depolarisation spreading across the atria
Describe the pattern of spread of excitation across the heart
Starts at the SA node
Spreads over atria to the AV node
Excitation spread half way down the septum then out across the axes of the heart
Through ventricular muscle along an axis slightly left of septum towards base of ventricles
Repolarisation spreads from epicardial through the ventricular myocardium
Explain the shape of the P wave
Small because there is little muscle
Upward deflection because moving towards the electrode
Explain shape of the Q part
Small because not moving directly away from the electrode
Downwards because moving away
Explain R
Large deflection because there is lots of muscle and is moving towards the electrode
Upwards because moving towards the electrode
Explain S
Small and downwards because depolarisation is moving away from the electrode but not directly
Explain T
Upwards because moving away from electrode but repolarisation
Medium because timing in different cells is dispersed
What does P show?
Atrial depolarisation
What does Q show?
Septal depolarisation towards the ventricle
What does S show?
End ventricular depolarisation
What does R show?
Main ventricular depolarisation
What does T show?
Ventricular repolarisation
Where do each of the electrodes go which are coloured?
Ride Your Green Bike
Red = right arm Yellow = left arm Green = left leg Blue = right leg
Where do V1 and V2 go?
V1 = 4th rib space on RHS V2 = 4th rib space LHS
Where does V3 go?
Further left and inferior in 4th rib space compared to V2
Where does V4 go?
Mid clavicular line in 5th rib space
Where does V5 go?
Anterior axillary line
Where does V6 go?
Mid axillary line in 6th rib space
What is a lead?
An electrical view of the heart
Where are the different lead views from?
I - LHS
II - views heart towards apex
III - views heat from the bottom
How many leads are there altogether? Give all the leads
12
I, II, III
aVR, aVL, aVF
Six chest leads V1-V6
How many squares are there per minute?
300
What indicates atrial fibrillation?
No P wave
What does the PR interval show?
The time taken for the impulse to reach the ventricles
How long should the PR interval be?
3-5 squares
200 ms
What is bundle branch block?
Damage to conducting pathways which determine the route of spread of depolarisation.
What can be seen in bundle branch block?
Lengthened QRS complex
What is heart block caused by?
A communication problem between atria and ventricles
What is first degree heart block?
Conduction delay through the AV node but all electrical signals reach the ventricles
What is seen in first degree heat block?
Elongated PR interval
What is type 1 second degree heart block?
Some, but not all, atrial beats get to the ventricle
What is seen in type 1 second degree heart block?
PR interval is erratic
PR interval elongates until eventually a QRS complex is dropped. The system is then reset.
What is type 2 second degree heart block?
Electrical excitation sometimes fails to pass through the AV node/bundle of His
What is seen in type 2 second degree heart block?
Constant PR interval
Not all atrial contractions are followed by ventricular contraction
What is third degree heart block?
No electrical conduction to the ventricles so ventricles use an ectopic pacemaker.
What is seen in third degree heart block?
No consistency in PR interval
What is seen in ventricular ectopic beats?
QR wave is often higher and taller.
Ectopic beats can occur every 3rd/4th etc
Or in couplets, triplets etc.
What are ventricular ectopic beats?
Occurs when ventricular cells gain pacemaker activity. Causes ventricular contraction before normal depolarisation.
