Electrocardiography. Characteristics of the normal electrocardiogram. Mean electrical axis

Question 1

ECG definition

Answer 1

measurement of electrical activity as the heart beats

(depolarisation + repolarisation)

over time using electrodes + leads

Question 2

function of ECG

Answer 2

• cardiac rhythm disturbances
• electrolyte disturbances
• poor coronary artery bloodflow

Question 3

waves of ECG

Answer 3

P wave
QRS complex
T wave

Question 4

P wave

Answer 4

atrial depolarisation = atrial contraction

positive in lead I,II,avF
duration= 0.12s
amplitude = 2.5mm

Question 5

QRS complex

Answer 5

ventricular depolarisation = ventricular contraction

Q = always negative
R = always positive
S = always negative

0.06-0.1 seconds

Question 6

T wave

Answer 6

ventricular repolarisation = ventricular relaxation

positive in leads I/II + V3-V6

Question 7

intervals on ECG

Answer 7

PR interval
ST segment
QT interval

Question 8

PR interval

Answer 8

time taken for impulse to go from atria to ventricles

0.12-0.20 seconds

Question 9

ST segment

Answer 9

end of S wave
beginning of T wave

ST segment must be isoelectric

Question 10

QT interval

Answer 10

Q wave to T wave
= total time of
- ventricular depolarisation + ventricular repolarisation

Question 11

ecg electrodes types

Answer 11

limb leads
chest leads

Question 12

limb leads

Answer 12

right arm = RED
left arm = YELLOW
right leg = GREEN
left leg = BLACK

Question 13

chest leads

Answer 13

V1-V6

Question 14

standard bipolar leads

Answer 14

LEAD I = RA LA
LEAD II = RA LL
LEAD III = LA LL

neg to pos

Question 15

augumented unipolar leads

Answer 15

aVR = right arm +
avL = left arm +
avF = left leg +

Question 16

chest leads - v1

Answer 16

intercostal space 4
RHS sternal border

RED

Question 17

chest leads - v2

Answer 17

intercostal space 4
LHS sternal border

YELLOW

Question 18

chest leads - v3

Answer 18

inbetween v2-v4

GREEN

Question 19

chest leads v4

Answer 19

midclavicular line
intercostal space 5

BROWN

Question 20

chest leads v5

Answer 20

anterior axillary line
intercostal space 5

BLACK

Question 21

chest lead V6

Answer 21

mid-axillary line
intercostal space 5

PURPLE

Question 22

ECG principle 1

Answer 22

positive deflection
- wave of depolarisation travelling towards positive electrode
- wave of repolarisation towards negative electrode

negative deflection
- wave of depolarisation travelling towards negative electrode
- wave of repolarisation towards positive electrode

no net deflection = dep/rep at perpendicular to electrode axis

Question 23

ECG principle 2

Answer 23

different leads have different shapes/ deflections

• position of electrode
• direction of waves
• mass of tissue experiencing waves

Question 24

ECG preparations

Answer 24

• patient calm/ relaxed/ lying down
• skin with alcohol + electrode gel
• calibrated at 10mm/mV
  at 25mm/s

Question 25

ECG diagram

Answer 25

Question 26

normal ECG

Answer 26

• NORMAL SINUS RHYTHM
• QRS at regular intervals
• before each QRS must be P wave/ after P wave must be QRS
• P wave in avF = positive/ isoelectric
• R-R interval should in regular intervals = heart rate of 60-100bpm

Question 27

mean electrical axis

Answer 27

main direction of ventricular depolarisation

as a 2D vector on frontal plane

using standard limb leads I,II,III

Question 28

mean electrical axis - normal

Answer 28

-30 to +90

Question 29

mean electrical axis - LAD

Answer 29

-30 to -90
- left ventricular hypertrophy

Question 30

mean electrical axis - RAD

Answer 30

+90 to +180
right ventricular hypertrophy

Question 31

mean electrical axis - EAD

Answer 31

-90 to +180
ventricular tachycardia

Question 32

mean electrical axis - step 1

Answer 32

amplitude of QRS waves

Question 33

mean electrical axis - step 2

Answer 33

Question 34

mean electrical axis - step 3

Answer 34