First Look at the ECG Flashcards
(41 cards)
What events do the standard limb leads look at
The vertical or frontal plane
SLL I
Left arm to right arm
SLL II
Left leg to right arm
SLL III
Left leg to left arm
What events are transmitted well
Fast events such as depolarisation and repolarisation of the AP
What events are not transmitted well
Slow events such as the plateau of the AP
What does a wave of approaching depolarisation cause
Upward-going blip
What is measured between the standard limb leads
The potential difference
SLL II: A wave of depolarisation approaching the left leg will cause a
Positive potential relative to the right arm
A wave of depolarisation going away from the left leg will cause a_____ relative to the right arm
Negative potential
A wave of repolarisation approaching the left leg will cause a
negative potential relative to the right arm
A wave of repolarisation going away from the left leg will cause a
positive potential relative to the right arm
P wave
Caused by atrial depolarisation
QRS complex
Caused by ventricular depolarisation
T wave
Caused by ventricular repolarisation
PR interval
Time from atrial depolarisation to ventricular depolarisation (0.12-0.2 sec)
QT interval
time spent while ventricles are depolarised (0.42 sec at 60bpm)
Why can’t you see atrial repolarisation:
Atrial repolarisation coincides with ventricular depolarisation. Ventricular depolarisation involved much more tissue depolarising much faster so it swamps any signal from atrial repolarisation
Why is the QRS complex so complex?
Different parts of the ventricle depolarise at different times in different directions
In which order do the different parts of the ventricle depolarise
- Interventricular septum (L to R)
- Bulk of the ventricle (endocardial to epicardial)
- The upper part of the interventricular septum
Why is the T-wave positive going?
The action potential is longer in the endocardial cells than in the epicardial cells so the wave of repolarisation runs in the opposite direction to the wave of depolarisation
This produces another positive-going blip
Why is the R-wave bigger in SLL II than in SLL I or SLL III?
The main vector of depolarisation is in line with the axis of recording from the left leg with respect to the right arm
• What happens if the heart was rotated to the left or developed hypertrophy on the left or atrophy on the right
Axis deviation
What extra information do augmented limb leads give you
3 other perspectives on events in the heart
