The ECG Flashcards
What are the SLLs?
SLL I - right arm to left arm.
SLL II - right arm to left leg.
SLL III - left arm to left leg.
Looks at events in the frontal plane.
What events of an action potential are transmitted?
Depolarisation and repolarisation.
Depolarisation = upward blip.
What is the recording from SLL II?
The main wave of depolarisation passes down through the ventricles and bodily fluids towards the electrode on the left leg.
As the wave of depolarisation passes, the electrode on the left leg creates a positive potential relative to the electrode on the right arm.
What are waves of repolarisation like in SLL II?
Towards left leg - negative potential.
Towards right arm - positive potential.
What is the PR interval?
The time taken from atrial depolarisation to ventricular depolarisation, mainly due to transmission through the AVN (~0.2s).
What is the QRS complex?
The time taken for the whole of the ventricle to depolarise (~0.08s).
What is the QT interval?
The time taken for the ventricles to depolarise and repolarise (varies with HR, ~0.42s at 60bpm).
How is atrial repolarisation explained on an ECG?
Coincides with ventricular depolarisation (which involves much more tissue depolarising much faster, swamping any repolarising signal).
What causes the QRS complex shape influenced by?
Different parts of the ventricle depolarising at different times, in different directions.
Interventricular septum - left and right.
The bulk of the ventricle - endocardial to epicardial surface.
The upper part of the interventricular septum.
Why is the T wave positive?
The AP is longer in endocardial cells than in epicardial cells.
The wave of repolarisation runs in the opposite direction to the wave of depolarisation (the R blip). A wave of repolarisation moving away from the recording electrode produces another positive blip.
Why is the R wave biggest in SLL II, compared to SLL I and 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 are the augmented limb leads?
Recording from one limb lead, with respect to the other two.
aVR - to right arm, negative.
aVF - to left leg, positive.
aVL - to left arm, weird.
What are the precordial chest leads?
In front of the heart and looks at the same events, but in the transverse plane.
V1 - negative.
V3/4 - flips signs.
V6 - positive.
‘Progression’ occurs.
How can you calibrate pulse and HR on an ECG?
Paper - 25mm/s.
Pulse = 0.2s = 5mm (1 big square).
HR = counting the number of R waves in 30 big squares and x10.
<60 - bradycardia.
60-100 - normal.
>100 - tachycardia.
What is STEMI?
ST segment elevation MI.
Elevation of the ST segment can identify and classify MI severity.
