Intro to ECG Flashcards
What is SLLI?
Standard limb lead 1 - left arm right arm
What is SLLII?
Standard limb lead 2 - left leg wrt right arm
What is SLLIII?
Standard limb lead 3 - left leg wrt left arm
What plane do SLL look at events in?
Frontal plane
A wave of depolarisation moving from left leg to right arm will show what sort of blip on a SLL II ECG?
Negative
A wave of depolarisation moving from right arm to left leg will show what sort of blip on a SLL II ECG?
A positive blip - as it travels in the same wave of depolarisation
A wave of repolarisation moving from the left leg to the right arm will show what on a SLL II ECG?
A positive blip
A wave of repolarisation moving from the right arm to the left leg will show what on a SLL II ECG?
Negative
What does each wave on ECG correspond for?
P - atrial depolarisation
QRS - ventricle contraction
T - ventricle repolarisation
Where does the main wave of depolarisation travel to?
Down the atria, ventricles and through the body fluids to the electrode of the left leg (SLLII)
What is the PR interval and how long should it last?
Time from atrial depolarisation to ventricular depolarisation (transmission through AV node)
0.12-0.2s
What is the QRS and how long should it last?
Time for ventricular depolarisation <0.12s (~0.08s)
What is the QT interval and how long should it last?
Time for ventricular depolarisation and depolarisation
0.42s
Why isn’t atrial depolarisation recorded on the ECG?
As it coincides with ventricular depolarisation and as it involves much more tissue depolarising much faster, it overpowers signal from atrial depolarisation
What events are transmitted better on an ECG?
Faster events
What are the different events that occurs in the QRS complex?
Q - IV septum depolarises L to R
R - depolarisation from endocardial to epicardial surface
S - the upper part of the IV septum depolarises
Why are Q and S wave negative in the QRS complex?
Negative as they travel away from main vector of depolarisation - go towards to right arm
Why is the T wave a positive blip?
The AP is longer in endocardial cells than in epicardial cells, so the wave of depolarisation runs in the opposite direction of wave of depolarisation
Why is the R wave (QRS) in SLL II larger than the two other SLL?
As the main vector of depolarisation is inline with the axis of recording from the left leg wrt the right arm
What would happen if heart was rotated to left or develop L hypertrophy or R atrophy?
Causes axis deviation - so blip in SLL I will be larger than the blips in SLL II and III, which will be smaller
What extra information do the augmented limb lead give you?
By recording from one limb lead wrt to the two combined, it gives you 3 other perspectives on events in the heart
What are the augmented limb leads?
aVR
aVL
aVF
What is aVR?
R arm wrt the left arm and left leg (SLL III)
What is aVL?
L arm wrt the left leg and right arm (SLL II)
