A First Look at the ECG Flashcards
What do standard limb leads look at?
Events in the vertical or frontal plane
What causes an upward going blip?
A wave of approaching depolarisation
Which type of events are transmitted better, fast events or slow events?
Fast events
What are the charges found at the right arm?
2 negatives
What are the charges found at the left arm?
1 positive
1 negative
What are the charges found at the left leg?
2 positives
What causes the P wave?
Atrial depolarisation
What causes the QRS complex?
Ventricular depolarisation
What causes the T wave?
Ventricular repolarisation
What does the timing of the PR interval tell you?
Time from atrial depolarisation to ventricular depolarisation is mainly due to transmission through the AV node
What does the timing of QRS tell you?
Time for the whole of the ventricle to depolarise
What does the timing of QT interval tell you?
Time spent while ventricles are depolarised (varies with HR)
Why is atrial repolarisation not seen?
Atrial repolarisation coincides with ventricular depolarisation. Ventricular depolarisation involves much more tissue depolarising much faster so it swamps any signal from atrial repolarisation
Why is the QRS complex so complex?
Different parts of the ventricle depolarise at different times in different directions
What occurs at Q?
The interventricular septum depolarises from left to right
What occurs at R?
The bulk of the ventricle depolarises from the endocardial to the epicardial surface
What occurs at S?
The upper part of the interventricular septum depolarises
Why is the T wave positive going?
The action potential is longer in endocardial cells than in epicardial cells, so the wave of repolarisation runs in the opposite direction to the wave of depolarisation i.e a wave of repolarisation moving away from the recording electrode produces another positive going blip
Why is the R wave bigger in SLL II than in SLL I or 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 would happen if the heart was rotated to the left or developed hypertrophy on the left, or atrophy on the right?
Causes axis deviation
What extra information do the augmented limb leads give you?
-By recording from 1 limb lead with respect to the other 2 combined it gives you 3 other perspective on events in the heart.
What extra information do the precordial leads give you?
- These are arranged in front of the heart and therefore look at the same events, but in horizontal (or transverse) plane
- Because the main vector of depolarisation is as shown by the arrow, it will produce a negative going blip when recorded from V1, a positive going blip from V6 and flip over somewhere around V3 or V4
What do limb leads look at?
Spread of depolarisation and repolarisation from 6 angles in the frontal plane
What do precordial leads look at?
The same events as the limb leads from 6 angles in the transverse plane
What can the rhythm strip tell you?
Heart rate
What is important about the timing of the rhythm strip?
- Paper should run at 25mm/sec
- Calibrating pulse is 0.2 sec= 1 large square/5mm
How is HR measured using a rhythm strip?
Measure the R-R interval and work out how many occur in 60 sec or better
-Count the R waves in 30 large squares which is equal to 6 sec and multiply by 10
What are the parameters of different HR?
- Normal= 60-100 bpm
- Bradycardia= <60 bpm
- Tachycardia= >100bpm
Other than HR, what can the rhythm strip tell you?
- Is each QRS complex preceded by a P wave?
- Is the PR interval too short or too long?
- Is the QRS complex too wide?
- Is the QT interval too long?
What is a STEMI?
ST elevated myocardial infarction
What is a NSTEMI?
Non-ST elevated myocardial infarction
How does the severity of a STEMI compare to a NSTEMI?
STEMI is worse than NSTEMI
