The ECG Flashcards
What does SLL stand for?
Standard Limb Leads
Which plane do standard limb leads view events?
Vertical/Frontal
Where are SLL 1 connected?
Left arm with respect to the right arm
Where are SLL 2 connected?
Left leg with respect to the right arm
Where are SLL 3 connected?
Left leg with respect to the left arm
What do the standard limb leads measure?
The difference in potential between the two limbs that are being recorded
When measuring from the electrode on the left leg, would the potential be positive or negative in relation to the right arm?
Positive
Would a wave of repolarisation approaching the left leg cause a positive or negative potential relative to the right arm?
Negative
Would a wave of depolarisation going away from the left leg cause a positive or negative potential relative to the right arm?
Negative
What does the P wave on an ECG represent?
Atrial Depolarisation
What does the QRS complex on an ECG represent?
Ventricular Depolarisation
What does the T wave on an ECG represent?
Ventricular Repolarisation
What is the PR interval?
The time from atrial depolarisation to ventricular depolarisation
What is the normal value for the PR interval?
0.12-0.2 seconds
What is the QRS?
The time taken for the whole of the ventricle to depolarise
What is the normal value for QRS?
0.08 seconds
What is the QT interval?
The time spent while ventricles are depolarised
What is the normal value for the QT interval?
It varies with heart rate but is normally about 0.42 seconds at 60bpm
Why isn’t atrial repolarisation visible on an ECG?
Because atrial repolarisation coincides with ventricular depolarisation which involves much more tissue depolarising much faster and so swamps any signal from atrial repolarisation
What does the Q part of the QRS complex represent?
The interventricular septum depolarising from left to right
What does the R wave of the QRS complex represent?
The bulk of the ventricle depolarising from the endocardial to the epicardial surface
What does the S wave of the QRS complex represent?
The upper part of the interventricular septum depolarises
Why is the R wave bigger in SLL 2 than in SLL 1 or 3?
Because the main vector of depolarisation is in line with the axis of the recording from the left leg with respect to the right arm
Why is the T wave positive?
Because the wave of repolarisation is moving away from the recording electrode
