A First Look at the ECG Flashcards
The standard limb leads look at events in which plane?
Vertical or frontal plane
A wave of depolarisation approaching a +ve electrode causes what?
An upward going blip
Fast/slow events are transmitted better on ECG?
Faster
What does the PR interval correspond with?
Time from atrial depolarisation to ventricular depolarisation
Due to transmission through AV node
What does the QRS interval correspond to?
Time for whole of ventricle to depolarise
What does the QT interval correspond to?
Time spent while ventricles are depolarised
Why can you not see atrial repolarisation?
As it coincides with ventricular depolarisation
Ventricular depolarisation involves much more tissue depolarising 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 and in different directions
How do the ventricles depolarise?
- IV septum depolarises from R to L
- Bulk of ventricle depolarises from the endocardial to the epicardial surface
- Upper part of IV septum depolarises
Why is the T wave on an ECG positive going?
AP is longer in endocardial cells than in epicardial cells so wave of repolarisation runs in the opposite direction of wave of depolarisation
I.e. wave of repolarisation runs away from recording electrode leading to a positive 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 the recording from the left leg with respect to the right arm
What would happen to the ECG reading if the heart was rotated to the left/developed hypertrophy on the left/atrophy on the right?
Axis deviation might may lead to the R wave being bigger in SLL I
At what plane do the precordial leads look at the heart in?
Horizontal/transverse plane
