Flashcards in Understanding ECGs Deck (43)
what type of activity does an ECG show?
(not mechanical ie wont see valves closing etc)
what is the name of the recording of potential differences in the heart?
what is the name for the separation of charge one after the other?
(depolarisation and then hyperpolarisation)
what do electrodes record?
the difference in potential between two points
when will the net potential measured by the electrodes be 0mV?
when the lead (ie imaginary line between 2 electrodes) is perpendicular to the dipole
what is the leading charge and what is the lagging charge of the cardiac dipole?
leading charge: positive
lagging chard: negative
what limb lead is the most parallel to the cardiac dipole?
how does a lead look at the moving charge?
looks from the positive electrode to the wave coming towards it from the negative electrode
what direction does the depolarisation have to move in order for an upwards deflection?
depolarisation needs to be moving towards positive electrode
(ie positive electrode is looking at wave coming towards it)
what are PR, ST and TP intervals flat on an ECG?
because there is no moving wave
(ie no change in potential at that time)
how are augmented limb leads formed?
1 of the limb electrodes acts as the positive recording electrode and the other 2 are coupled together as teh negative reference electrode
what limb electrodes make up aVR?
positive electrode: RA
negative electrode: LA+LL
what limb electrodes makes up aVL?
positive electrode: LA
negative electrode: LL+RA
what limb electrodes make up aVF?
positive electrode: LL
negative electrode: LA+RA
why is the aVR recordings downwardly deflecting?
because the wave is manly moving away from the positive electrode
why is the limb lead II particularly good for looking at electrical activity?
because the wave is parallel to the lead axis and so has a great net potential difference so has well resolved waves
why is limb III not too good for looking at electrical activity?
because the wave is almost perpendicular to the lead axis so has a very small net potential difference so has poorly resolved waves
how many chest electrodes are there?
where is chest electrode 1 and what lead does it form?
1: 4th intercostal space, R of sternum
lead = V1
where is chest electrode 2 and what lead does it form?
2: 4th intercostal space, L of sternum
lead = V2
where is the chest electrode 3 and what lead does it form?
3: between 2 and 4
lead = V3
where is the chest electrode 4 and what lead does it form?
4: 5th intercostal space midclavicular line
lead = V4
where is the chest electrode 5 and what lead does it form?
5: 5th intercostal space anterior axillary line
lead = V5
where is the chest electrode 6 and what lead does it form?
6: 5th intercostal space mid-axillary line
lead = V6
what gives the negative reference electrode for the chest leads?
all 3 limb leads combines
(roughly the ecentre of the heart)
what happens to the limb leads if chest leads arent working?
what happens to the chest leads if the limb leads aren't working?
chest leads don't work either
what plane do the limb leads show?
what plane do the chest leads show?