The ECG Flashcards
SLL 1
Left arm wrt right arm
SLL2
Left leg wrt right arm
SLL3
Left leg wrt left arm
A wave of depolarisation approaching the LL in SLL II
A positive recording (relative to RA)
A wave of depolarisation going away from LL in SLL II
A negative potential relative to the RA
A wave of repolarisation approaching the LL in SLL II
A negative recording
A wave of repolarisation going away from the LL in SLL II
A positive recording
What causes the P wave
Atrial depolarisation
What causes the QRS complex
Ventricular depolarisation
What causes the T wave
Ventricular repolarisation
what is the PR interval and what length should it be
Time from atrial depolarisation to ventricular depolarisation. Mainly due to transmission through the AV node
0.12-0.2s
how long is the QRS complex
0.08s
QT interval
Time spent while ventricles are depolarised (0.42s at 60bpm)
Why isn’t atrial depolarisation visible on an ECG
It coincides with ventricular depolarisation
Why is the QRS complex so complex
Different parts of the ventricles depolarise at different times in different directions
Timings of ventricular depolarisation
1- interventricular septum depolarises from left to right
2- bulk of ventricle depolarises from endocardial to epicardial surface
3- upper part of interventricular septum depolarises
Why is the T wave positive
Because action potential is longer in endocardial cells than epicardial cells so wave of depolarisation is moving away from recording electrode
Why is the R wave biggest in SLL II?
Main vector of depolarisation is in like with axis of recording
Augmented limb leads
aVR- right arm wrt left leg and arm
aVL- left arm wrt right arm and left leg
aVF- left leg wrt arms
What extra info do the precordial (chest) leads give
Show progression of main vector of depolarisation.
6 leads arranged in front of the heart, allow a horizontal view
What does the rhythm strip tell you
Heart rate
Also if each QRS complex is preceded by a P-wave, if the PR or QT intervals or QRS complexes the right length
One large square on an ECG
0.2s
How to determine heart rate from ECG
Count R waves in 30 large squares (6s) and multiply by 10
STEMI
ST elevated myocardial infarction (worse than non-stemi)
