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)
What is aVF?
L leg wrt the left and right arm (SLL I)
Why is the R wave (QRS) negative in aVR?
Travels in opposite direction to main vector of depolarisation
Why is the R wave (QRS) the smallest blip in aVL compared to all of the augmented and standard limb leads?
Travels at a right angle to the main vector of depolarisation
What plane do the precordial (chest) leads look at events in?
Transverse plane
What extra information do the precordial leads provide?
They’re arranged in front of the heart and therefore look at the same events, but in the transverse plane
Explain the concept of progression in the precordial leads
It is the change in the R waves from V1 to V6 - a negative blip is recorded in V1, a positive blip in V6 and a flip over somewhere around V3/4
What can the rhythm strip tell you?
Heart rate - count R waves in 30 large square and multiply by 10
How fast does an ECG run?
25mm/sec
How long is the calibrating pulse and how many squares does it take up?
0.2s = 1 large square (5mm)
What are the boundaries for normal HR and abnormal?
60-100 normal
> 100 tachycardia
< 60 bradycardia
What to look out for on the rhythm strip
Is QRS followed by P wave?
Is PR too short (<0.12s) or too long (>0.2s)?
Is QRS too long (>0.12s?
Is the QT too long (>0.42s at 60bpm)?
What does STEMI stand for?
ST elevated myocardial infarction
What does NSTEMI stand for?
Non-ST elevated myocardial infarction
Is STEMI or NSTEM worse?
STEMI is worse
