First look at ECG Flashcards
Standard limb leads look at event in what plane
Vertical/frontal
SLL I
Left arm with respect to right arm
SLL II
Left leg with respect to right arm
SLL III
Left leg with respect to left arm
Fast events
Depolarisation and repolarisation of action potential
Are fast event transmitted
Yes
Slow events
Plateau of the action potential
Are slow events transmitted
No
What causes an upward-going blip
A wave of approaching depolarisation
What is SLL II actually recording
The difference in potential between the left leg and right arm
PR interval
Time from atrial depolarisation to ventricular depolarisation (0.12-0.2s)
QRS period
Time for the whole of the ventricle to depolarise (0.08s)
QT interval
Time spent while ventricles are depolarised (0.42s)
Why is atrial depolarisation not seen
Coincides with ventricular repolarisation, ventricular repolarisation swamps any signal from atrial repolarisation
Q part of QRS complex
Interventicular septum depolarises from left to right
R part of QRS complex
Bulk of the ventricle depolarises from the endocardial to epicardial surface
S part of QRS complex
The upper part of the interventicular septum depolarises
Why is the T wave positive-going
Action potential in endocardial cells longer than epicardial cells, wave of repolarisation runs in opposite direction to wave of depolarisation
Why is R wave bigger in SLl II than SLL I and SLL III
Main vector of depolarisation is in line with the axis of recording from the left leg with respect to the right arm
Height of SLL R wave from higher to lowest
SLL II, SLL III, SLL I
What extra information do augmented limb leads give
3 other perspective on events in the heart
Augmented limb leads
Recording from one limb lead with respect to the other two combined
aVR and aVL waves are
Negative
aVF waves are
Positive
What extra information to precordial leads give
Look at same events but in the horizontal/transverse plane
Where are precordial leads arranged
In front of the heart
V1 - V6
Progression from negative to positive
What timing should the paper rhythm strip run by
25mm/sec
Calibrating pulse is
0.2sec = 1 large square (5mm)
Normal heart rate
60-100bpm
Bradycardia heart rate
<60bpm
Tachycardia heart rate
> 100bpm
What the rhythm strip tells you
Heart rate If each QRS complex is preceded by a P-wave If PR interval too short or long If QRS complex too wide If QT interval too long
Too short PR interval
<0.12s
Too long PR interval
> 0.2s
Too wide QRS complex
> 0.12s
Too long QT interval
> 0.42s (at 60bpm)
STEMI
ST elevated myocardial infarction
STEMI indicates
Something has gone seriously wrong
NSTEMI
Non-ST elevated myocardial infarction
How to measure heart rate from a rhythm strip
Count number of R waves over 30 large squares and multiply by 10
