ECG Basics Flashcards
Which direction does repolarisation spread in relation to depolarisation?
The opposite direction, epicardial – endocardial (outside - inside)
Will the signal go up or down if…
a) depolarisation goes away from the electrode
b) depolarisation goes towards the electrode
Therefore, what happens to the signal when repolarisation does the same things?
a) downward signal
b) upward signal
Repolarization does the opposite
Explain what’s seen on an ECG viewing from the apex during ___ and why?
a) atrial depolarization
b) spread through the septum
c) spreading through the ventricular myocardium
d) end of depolarisation
e) ventricular repolarisation ;)
a) Small upward deflection as there is little muscle in the atria and the excitation is moving towards the electrode
b) Small downward deflection: small as not moving directly away (not 180 degrees away), but downward as excitation is technically still moving away
c) Large upward deflection: large as lots of muscle, upward as excitation is moving directly towards the electrode
d) small downward deflection: Downward as moving away, but small as not directly (180 degrees) away
e) Medium upward deflection: upwards as repolarisation moves away from the electrode, and medium as each myocardial cell repolarises on its own (not synchronized)
Where is the electrode in the following leads? (not augmented)
- Lead 1
- Lead 2
- Lead 3
- Views heart from L side
- Apex of heart
- Views heart from the right bottom
What 2 factors determine the amplitude of the signal?
- Muscle mass is proportional to the amplitude
2. Position of electrode in relation to the ‘moving excitation’
What do the following waves represent? P wave: Q wave: R wave: S wave: T wave:
P wave: atrial depolarisation Q wave: septal depolarisation R: main ventricular depolarisation S wave: end of ventricular depolarisation T wave: ventricular repolarisation
What does it mean when the line is on the isometric baseline?
No signal
How does a signal become amplified?
How many leads are amplified?
Amplifiers have one positive and one negative view:
They take in the negative signal, invert it to make it positive and add it to the actual positive input.
Sum up the ‘2 positives’ to create one amplified view
3 leads are amplified
Define a heart lead:
How many cables are there and how many leads in an ECG?
Lead: electrical view of the heart
10 cables, 12 views/leads
How many leads are there in the chest and limbs?
How many limb and chest cables are there?
6 limb leads, 6 chest leads (V1-V6)
6 chest cables
4 limb cables, (black one generates no signal it is the ‘earth electrode’)
How could you calculate an irregular heart rate using an ECG?
- Count the number of peaks in 30 squares (equal to 6 seconds) and multiply that number by 10 to give you bpm
- Count the number of peaks in the bottom segment representing 10 seconds and X by 6
How many seconds is represented in each square on an ECG usually?
What is the normal bpm?
0.2 seconds in each larger square, 0.04 seconds in each little square
Normal bpm is 60-100 bpm
Which wave is absent in atrial fibrillation?
P wave: representing atrial depolarisation
What can be indicated by a broad QRS complex?
It’s taking more time for excitation to pass through the ventricles. Indicates that the AP is being generated from somewhere elsewhere than the SA node (which generates APs quicker), and may be coming from the AV node or bundle of HIS
What does the segment between P-R represent? How many seconds and squares long is it usually and what does it mean if its longer?
It’s the time it takes for an AP to cause ventricular systole, typically 280 ms and the space between P-R should be 3-5 squares. >280 ms indicates a block
