Understanding ECGs

Question 1

what type of activity does an ECG show?

Answer 1

electrical activity
(not mechanical ie wont see valves closing etc)

Question 2

what is the name of the recording of potential differences in the heart?

Answer 2

electrocardiogram

Question 3

what is the name for the separation of charge one after the other?
(depolarisation and then hyperpolarisation)

Answer 3

dipole

Question 4

what do electrodes record?

Answer 4

the difference in potential between two points

Question 5

when will the net potential measured by the electrodes be 0mV?

Answer 5

when the lead (ie imaginary line between 2 electrodes) is perpendicular to the dipole

Question 6

what is the leading charge and what is the lagging charge of the cardiac dipole?

Answer 6

leading charge: positive

lagging chard: negative

Question 7

what limb lead is the most parallel to the cardiac dipole?

Answer 7

lead II

Question 8

how does a lead look at the moving charge?

Answer 8

looks from the positive electrode to the wave coming towards it from the negative electrode

Question 9

what direction does the depolarisation have to move in order for an upwards deflection?

Answer 9

depolarisation needs to be moving towards positive electrode

ie positive electrode is looking at wave coming towards it

Question 10

what are PR, ST and TP intervals flat on an ECG?

Answer 10

because there is no moving wave

ie no change in potential at that time

Question 11

how are augmented limb leads formed?

Answer 11

1 of the limb electrodes acts as the positive recording electrode and the other 2 are coupled together as teh negative reference electrode

Question 12

what limb electrodes make up aVR?

Answer 12

positive electrode: RA

negative electrode: LA+LL

Question 13

what limb electrodes makes up aVL?

Answer 13

positive electrode: LA

negative electrode: LL+RA

Question 14

what limb electrodes make up aVF?

Answer 14

positive electrode: LL

negative electrode: LA+RA

Question 15

why is the aVR recordings downwardly deflecting?

Answer 15

because the wave is manly moving away from the positive electrode

Question 16

why is the limb lead II particularly good for looking at electrical activity?

Answer 16

because the wave is parallel to the lead axis and so has a great net potential difference so has well resolved waves

Question 17

why is limb III not too good for looking at electrical activity?

Answer 17

because the wave is almost perpendicular to the lead axis so has a very small net potential difference so has poorly resolved waves

Question 18

how many chest electrodes are there?

Answer 18

6

Question 19

where is chest electrode 1 and what lead does it form?

Answer 19

1: 4th intercostal space, R of sternum

lead = V1

Question 20

where is chest electrode 2 and what lead does it form?

Answer 20

2: 4th intercostal space, L of sternum

lead = V2

Question 21

where is the chest electrode 3 and what lead does it form?

Answer 21

3: between 2 and 4

lead = V3

Question 22

where is the chest electrode 4 and what lead does it form?

Answer 22

4: 5th intercostal space midclavicular line

lead = V4

Question 23

where is the chest electrode 5 and what lead does it form?

Answer 23

5: 5th intercostal space anterior axillary line

lead = V5

Question 24

where is the chest electrode 6 and what lead does it form?

Answer 24

6: 5th intercostal space mid-axillary line

lead = V6

Question 25

what gives the negative reference electrode for the chest leads?

Answer 25

all 3 limb leads combines

roughly the ecentre of the heart

Question 26

what happens to the limb leads if chest leads arent working?

Answer 26

nothing

Question 27

what happens to the chest leads if the limb leads aren’t working?

Answer 27

chest leads don’t work either

Question 28

what plane do the limb leads show?

Answer 28

frontal plane

Question 29

what plane do the chest leads show?

Answer 29

horizontal plane

Question 30

how long should the P wave be?

Answer 30

0.08- 0.10 seconds

between 2/3 small boxes

Question 31

how long should the PR interval be?

Answer 31

0.12 - 0.2s

between 3/5 small boxes

Question 32

what should the normal callibration of ECG be?

Answer 32

paper speed = 25mm/sec

10mm amplitude = 1mV

Question 33

what is one small square on ECG paper?

Answer 33

1mm, 0.04s

Question 34

what is one big square on ECG paper?

Answer 34

5mm, 0.2s

Question 35

how many big squares and little squares are there per second?

Answer 35

5 big squares per second

25 small squares per second

Question 36

how do you figure out the heart rate?

Answer 36

300/

no.of big squares between QRS complexes

Question 37

what is the ECG rhythm strip?

Answer 37

a prolonged recording of lead 2 which allows you to detect rhythm distrubances

Question 38

what is the step by step approach to analysing an ECG rhythm strip?

Answer 38

1. clarify patient
2. date/time of ECG
3. check calibration of the machine
4. is electrical activity present?
5. is the rhythm irregular or irregular?
6. what is the heart rate?
7. are there P waves present?
8. is the PR interval normal?
9. is each p wave followed by a QRS complex
10. is QRS duration normal
11. look for individual leads for changes

Question 39

how would you tell if the cardiac rhythm is regular or irregular from a rhythm strip?

Answer 39

if rhythm is regular, QRS complexes occur at regular intervals

Question 40

how can you calculate the heart rate from a rhythm strip if the rhythm is irregular?

Answer 40

count number of QRS complexes within 30 big squares and times that by 10

Question 41

what can it mean if the PR interval is too long?

Answer 41

problem with AV conduction

Question 42

what does it mean if each P wave is followed by a QRS complex?

Answer 42

sinus rhythm

Question 43

how long should a QRS complex be?

Answer 43

less than 0.10 seconds

less than 3 small boxes