First look at the ECG Flashcards
What does ECG stand for
Electrocardiogram
What are the main groups of leads used in an ECG?
Standard limb leads
Augmented limb leads
Precordial (chest) leads
What do the standard limb leads do?
look at events in the vertical, or frontal, plain
What possible pairs of electrodes can be recorded using standard limb leads?
SLL 1 - left arm with respect to right arm
SLL 2 - Left leg with respect to right arm
SLL 3 - left leg with respect to left arm
What are standard limb leads good/bad at measuring?
Fast events, eg depolarisation and repolarisation of the AP, are transmitted well
Slow events, eg the plateau of the AP, are not
In a standard limb lead test
A wave of approaching depolarisation causes what to show up?
Upward-going blip
SLL readings are basically to do with the difference in potential between the two electrodes
Describe how a difference in potential is created & measured in an SLL 2 reading
Main wave of depolarisation passes down the ventricles and through the body fluids towards the electrode on the left leg
Downwards moving depolarisation creates a positive potential relative to the electrode on the right arm
A wave of depolarisation moving away from one electrode will cause what reading on the other?
What shaped ‘blip’ will this create?
Positive potential
The shape of the blip will depend on which electrode is measuring with respect to the other
^so you cant tell whether the blip will be up or down
In basics
What ‘charge’ is depolarisation and repolarisation?
Depolarisation is Negative
Repolarisation is positive
A wave of repolarisation will cause what potential at the opposite electrode?
Negative potential
What are the different waves on an ECG?
P wave
QRS complex
T wave
What causes the P wave?
Atrial depolarisation
What causes the QRS complex?
Ventricular depolarisation
What causes the T wave?
Ventricular repolarisation
What is the PR interval?
Time from atrial depolarisation to ventricular depolarisation
What node is associated with the PR interval?
Atrioventricular
What is the normal value for the PR interval?
0.12 - 0.20 sec
What does the QRS value tell you?
Time for the whole pf the ventricle to depolarise
What is a normal value for the QRS time?
0.08 s
WHat is the QT interval?
Time spent when ventricles are depolarised
At 60 bpm, what is the normal value for the QT interval?
0.42 s
Why isnt atrial repolarisation visible on the ECG?
coincides with ventricular depolarisation
VD has a much larger amount of tissue depolarising faster so gives a big boi wave
Explain what causes the individual peaks on the QRS complex
Q - the interventricular septum depolarises from left to right
R - the bulk of the ventricle depolarises from the endocardial to the epicardial surface
S - the upper part of the interventricular septum depolarises
If the T wave is caused by ventricular repolarisation
Why is it positive going?
(in SLL 2)
Action P is longer in ENDOcardial cells than in EPIcardial cells
Wave of repolarisation runs in opposite direction to the Depol wave - it moves AWAY from the recording electrode
Repol wave moving AWAY = positive blip
What is the main difference between an SLL 1, 2 & 3 graph?
SLL 2 has the largest waves
Its a more jaggy line
What causes the difference in R-wave size in SLL 2, compared to SLL 1 & 3?
In an SLL 2, the main vector of depolarisation is in line with the axis of recording from the left leg with respect to the right arm.
Basically, the wave is shot directly at the electrode in the left leg
What extra information does augmented limb leads give you?
By recording from one limb lead with respect to the other two combined, it gives you 3 other perspectives on events in the heart
What is the benefit of using both standard LLs and augmented LLs?
recordings from SLLs I, II, III and aVR, aVL, aVF give you 6 different
views of events occurring in the frontal (or vertical) plane
What is the function of precordial leads?
These are arranged in front of the heart and therefore look at the same events, but in the horizontal (or transverse) plane
How many chest leads are used in precordial measurement?
6
V1, 2, 3 etc - 6
Explain what causes ‘Progression’ in precordial chest lead measurement?
Chest leads arranged in front of heart
Main vector of depol wave travels to V6
This causes a +ve blip at V6 and a -ve blip at V1
As you progress through the individual electrodes, there will be a point (V3/V4) where the blip flips
What plane do the limb leads measure in?
Frontal
What plane do chest leads measure in?
Transverse
Describe how the Rhythm strip should ‘run’
25mm/sec
Calibrating pulse is 0.2 sec = 1 large square (5mm)
What is the name for an abnormally low heart rate?
Bradycardia
< 60 bpm
What is the name for an abnormally rapid heart rate?
Tachycardia
> 100 bmp
What is STEMI?
ST elevated myocardial infarction
What is NSTEMI?
Non-ST elevated myocardial infarction
What does STEMI look like on an ECG?
ST portion abnormally high
QRS goes up then only comes down a little bit
Which is worse, STEMI or NSTEMI?
STEMI is worst
