ECG's Flashcards
How many limb leads are there in an ECG?
3
Lead I
Lead II
Lead III
How many augmented leads are there in ECG?
3
Name the three augmented leads in ECG.
aVR, aVL and aVF
How many chest leads are there in ECG?
6
V1-6
What do standard limb leads look at?
Events in the vertical or frontal plane
Where does standard limb lead one (SLL1) record?
Right arm to left leg
Where does standard limb lead two (SLL2) record?
Left leg to right arm
Where does standard limb lead three (SLL3) record?
Left arm to left leg
Which events are transmitted well and show clearly on ECG?
Fast events- depolarisation and repolarisation of the AP
Which events are transmitted poorly and don’t show up on ECG?
Slow events e.g. the plateau of the AP
In the SLL2, what will a wave of depolarisation approaching the electrode in the left leg do?
Cause a a positive potential relative to the electrode in the right arm.
In the SLL2, what will a wave of depolarisation going away from the electrode in the left leg cause?
A negative potential relative to the electrode in the right arm
In the SLL2, what will wave of repolarisation approaching the electrode in the left leg cause?
A negative potential relative to the electrode in the right arm
In the SLL2, what will a wave of repolarisation going away from the electrode in the left leg cause?
A positive potential relative to the electrode in the right arm.
RECAP- what does the P wave represent?
Atrial depolarisation
RECAP- what does the QRS complex represent?
Ventricular depolarisation
RECAP- what does the T wave represent?
Ventricular repolarisation
What is meant by the PR interval?
Measurement from the start of the P wave to the start of the QRS complex
What does PR interval measure?
Time from atrial depolarisation to ventricular depolarisation
How long is PR interval usually?
0.2 seconds
What is the time taken for the QRS complex used to measure?
Time for the whole of the ventricle to depolarise
What does the QT interval measure?
Time for ventricles to depolarise and repolarise
What is the average QT interval?
0.42 s at 60 bpm but varies with heart rate
Why can’t you see atrial repolarisation on SLL2 ECG?
Because atrial repolarisation coincides with ventricular depolarisation.
->Ventricular depolarisation involves much more tissue depolarising much faster so it swamps any signal from atrial repolarisation.
Okay so what also occurs when ventricular depolarisation occurs?
Atrial repolarisation.
What happens during depolarisation of the ventricle?
Different parts of the ventricle depolarise at different times and at different directions.
Which part of the ventricle depolarises first?
Interventricular septum - from left to right
Which part of the ventricle depolarises second?
Bulk of the ventricle- from the endocardial to the epicardial surface
Which part of the ventricle depolarises third?
Upper part of the interventricular septum
Is the action potential longer in endocardial or epicardial cells?
Endocardial cells
Why is the R wave bigger in SLL II than in SL I or SLL III?
Because the main vector of depolarisation is in line with the axis of recording from the left leg with respect to the right arm.
What extra information do the augmented limb leads give you?
By recording from one limb lead with respect to the other two combined, it gives you 3 other perspective on events in the heart
How is aVR recorded?
Recorded from the right arm with respect to the left arm and the left leg.
How is aVF recorded?
From the left leg relative to the right arm and the left arm.
How is aVL recorded?
From the left arm relative to the right arm and the left leg.
What do precordial chest leads do?
Measure electrical events in the heart but on the transverse plane.
Compare limb leads and precordial chest leads.
Limb leads look at the spread of depolarisation (and repolarisation) from 6 angles in the frontal plane, and the precordial leads look at the same events from 6 angles in the transverse plane.
Which standard limb line does the rhythm strip reading come from?
SLL2
What speed does the paper for an ECG run at?
25 mm/s
How can you check the paper is running at the right speed?
Look at the calibrating pulse
It should be 0.2 seconds (the length of one big square).
What can the rhythm strip be used to calculate?
Heart rate
Describe the two ways you can measure heart rate from the rhythm strip.
Measure the RR interval and work out how many occur in 60 .
OR
Count the R waves in 30 large squares (= 6 s) and multiply by 10
Define bradycardia
HR below 60 bpm
Define tachycardia
HR above 100 bpm
What other questions should you ask yourself when looking at an ECG rhythm strip?
Is each QRS complex preceded by a P wave?
Is the PR interval too short (<0.12 s) or too long (>0.2 s)?
Is the QRS complex too wide (>0.12 s)?
Is the QT interval too long (>0.42 s at 60 bpm)?
What does STEMI stand for?
ST segment elevation myocardial infarction
What does NSTEMI stand for?
Non-ST segment elevation myocardial infarction
What is a myocardial infarction?
A heart attack
What may elevation of the ST segment mean?
Something is seriously wrong.
Indication of how serious the MI was.
Which is more serious- STEMI or NSTEMI?
STEMI
Use this link for a quiz/revision on ECG :)
http://ajames131.wix.com/ecginterp
Which leads of the ECG look at the heart in the frontal plane?
I, II, III, aVR, aVF, aVL
Which leads of the ECG look at the heart in the horizontal plane?
V1-6
