A first look at the ECG Flashcards
What are your standard limb leads?
What does an approaching wave of depolarisation cause?
Upward going blip
Which events are better transmitted, fast or slow?
Fast
What is the PR interval and how long does it usually last?
Time from atrial depolarisation to ventricular depolarisation - mainly due to transmission through the AV node (normally about 0.1-0.2 sec)
Should really be called P - Q interval
What is the QRS interval?
Time for the whole of the ventricle to depolarise
(normally about 0.08 sec)
What is the QT interval?
Time spent while ventricles are depolarised (varies with heart rate, but normally about 0.42 sec at 60 bpm)
Why can’t you see atrial repolarisation?
Because atrial repolarisation coincides with ventricular depolaristion. Ventricular depolarisation involves much more tissue depolarising much faster so it swamps any signal from atrial repolarisation.
How do you explain the three stages of the QRS complex?
Different parts of the ventricle depolarise at different times and also in different directions
- The interventricular septum depolarises from left to right
- The bulk of the ventricle depolarises from the endocardial to
the epicardial surface – travels towards the electrode on the left leg – hence the upwards spike
- The upper part of the interventricular septum depolarises
Why is the T - wave positive?
Because the action potential is longer in endocardial cells than in epicardial cells, so the wave of repolarisation runs in the opposite direction to the wave of depolarisation. ie a wave of repolarisation moving away from the recording electrode produces another positive-going blip
Why is the R-wave bigger in SLL II than in SLL I or SLL II?
Because the main vector of depolarisation is in line with the axis of recording from the left leg with respect to the right arm.
What are the augmented limb leads?
What extra information do the augmented limb leads give you?
A. By recording from one limb lead with respect to the other two combined, it gives you 3 other perspective on events in the heart
ie recordings from SLLs I, II, III and aVR, aVL, aVF give you 6 different
views of events occurring in the frontal (or vertical) plane
Can you correctly label the vectors to the correct limb leads?
Should AVR be positive or negative?
Negative, travels away from the heart
Which wave is:
- aVL
- aVF
- aVR
What extra information do the precordial (chest) leads give you?
A.These are arranged in front of the heart and therefore look at the same events, but in the horizontal (or transverse) plane
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Because the main vector of depolarisation is as shown by the arrow, it will produce a negative going blip when recorded from V1, a positive going blip from V6, and flip over somewhere around V3 or V4. “Progression”
Look
On which plane is the spread of depolarisation measured when using:
- Limb leads
- Precordial leads
- Frontal
- Transverse
What does the rhythm strip tell you?
Paper should run at 25mm/sec
Calibrating pulse is 0.2 sec = 1 large square (5mm) (5 arge squares per second)
Then you can determine the heart rate:
Measure the R-R interval and work out how many occur in 60 sec, or better ..
Count the R waves in 30 large squares (= 6 sec) and multiply by 10
60-100 beats per min = normal
Below 60 beats per minute = bradycardia
Above 100 beats per minute = tachycardia
What does STEMI or NSTEMI stand for?
ST elevated myocardial infarction or non-ST elevated myocardial infarction.
ST should be flat because the cells are in their refractory state – st elevation is an indication of how severe the heart attack is. More dead tissue means more elevation. Don’t know why it is elevated though – don’t need to know.
