ECG I

Question 1

What are leads?

Answer 1

visual representation of cardiac activity from a given perspective (coronal/horizontal plane)
different lead = different view of heart so change in ECG indicated location of damage

fixed cathode (+ve) and fixed anode (I,II,III) or virtual anode (avF, avL, avR, V1-6)

Question 2

What is a cardiac vector?

Answer 2

magnitude and direction of waves of depolarisation measured using ECG

Question 3

What does the isoelectric line represent?

Answer 3

no net V change, vector perpendicular to lead

Question 4

What does downward deflection (negative) mean?

Answer 4

toward anode (-)

Question 5

What does upward deflection (positive) mean?

Answer 5

toward cathode (+)

Question 6

What does the steepness of the line, width of deflection mean?

Answer 6

steepness of line - denote velocity of action potential

width of deflection - duration of event

Question 7

How to calculate the velocity of waveforms?

Answer 7

ECG amplitude/time

Question 8

What are the measurements on an ECG?

Answer 8

0. 04s wide, 0.1mV high

0. 2s wide, 0.5mV high

Question 9

What is lateral?

Answer 9

left circumflex artery

Question 10

What is anterior/inferior?

Answer 10

right coronary artery

Question 11

What is septal?

Answer 11

left anterior descending

Question 12

What is Einthoven’s triangle?

Answer 12

3 limb leads

heart at centre represents 0 potential when voltages summed together

Question 13

What are leads 1, 2, 3 ?

Answer 13

1 - RA to LA
2 - RA to LL
3 - LA to LL

Question 14

Describe the placing of...
V1
V2
V3
V4
V5
V6 

polarity?
plane?

Answer 14

1 - right sternal border, 4th intercostal space
2 - left sternal border, 4th intercostal space
3 - halfway between 2/4
4 - mid clavicular line, 5th intercostal space
5 - anterior axillary line (armpit crease), level of V4
6 - mid axillary line, level of V4

unipolar
horizontal

Question 15

What is the cathode and anode for V1-V6?

Answer 15

virtual anode (Wilson's Central Terminal) - composite pole of 1/3(RA + LA + LL)
cathode = chest lead

Question 16

Views of V1-6?

Answer 16

1-2 = septal
3-4 = anterior
5-6 = lateral
each measure activity of different region of heart

Question 17

Describe leads 1-3?

Answer 17

bipolar
coronal plane
1 cathode = LA, anode = RA LATERAL
2 cathode = LF, anode = RA INFERIOR
3 cathode = LF, anode = LA INFERIOR

Question 18

Describe leads avR, L and F?

Answer 18

unipolar (virtual anode)
coronal
avR cathode = RA, anode 1/2(LA+LF) - 
avL cathode = LA, anode 1/2(RA+LF) LATERAL
avF cathode = LF, 1/2(RA + LA) INFERIOR

Question 19

P wave duration

Answer 19

80ms

Question 20

PR interval duration

Answer 20

120-200ms

Question 21

QRS duration

Answer 21

<120ms

Question 22

QT interval duration

Answer 22

420ms

Question 23

T wave duration

Answer 23

160ms

Question 24

RR interval duration

Answer 24

0.6-1.2s

Question 25

Why is QT interval corrected?

Answer 25

reported to correct interval according to breathing rate

Question 26

How to calculate cardiac axis?

if 2 cycles given

Answer 26

use 2 leads with 90 degree separate view of each other
calculate value of angle relative to 0

find average angle of the two
lead II most commonly used single leads

Question 27

What is the cardiac axis?

Answer 27

net vector of R wave
(largest electrical event because most muscle)
range -30 to +90 degrees

Question 28

Positive deflection?

Answer 28

towards positive electrode

Question 29

Negative deflection ?

Answer 29

towards negative electrode

Question 30

How do deflection rules change for repolarisation?

Answer 30

reverse process

positive deflection is away from positive electrode

Question 31

Why does lead 3 show a negative deflection?

Answer 31

lead is oriented more normally to direction of depolarisation in the heart

Question 32

What are augmented leads?

Which show positive and negative deflections?

Answer 32

average voltage of 2 points on skin as -ve pole and 3rd reading from +ve electrode
positive = avL/F
negative = avR

Question 33

What do the 6 chest and limb leads measure?

Answer 33

limb - depolarisation in frontal plane of heart

chest - measure depolarisation in horizontal plane of heart

Question 34

How to determine if heart is on the correct side?

Answer 34

same deflection of avL up and down

Question 35

Describe respiratory sinus arrhythmia

Answer 35

breathing cycle affects heart beat
RR interval smaller during inspiration so HR increases and longer during expiration so HR decreases

resting HR controlled by PNS and during inspiration inhibition removed so HR increases little between 70 –> 110bpm