ECG Basics

Question 1

What direction are the leads in on the axis circle

Answer 1

Lead I = at the 0° line - straight to the right
Lead II = below I, at the +60°, south-east direction
Lead aVF = to the left of II, at the +90°, straight down at the middle
Lead III = to the left of aVF, at the +120°, south-west direction
Lead aVR = after III, at the -150° line, north-west direction
Lead aVL = after aVR, at the -30° line, north-east direction

Question 2

What are the lead locations (inferior, anterior, lateral)

Answer 2

Inferior = II, III, aVF
Anterior = V3, V4 (represent the LV)
Lateral = I, aVL, V5, V6
V1 and V2 are also technically anterior but they are also Septal and represent the RV

Question 3

What are the associated coronary arteries to the limb leads?

Answer 3

Inferior = RCA
Anterior/Septal = LAD
Lateral = LCX

Question 4

What are the reciprocal lead groupings?

Answer 4

Lateral and inferior are reciprocal to each other
Anterior would be reciprocal to posterior (V8 and V9)

Question 5

What ° range is normal axis, LAD, RAD, and extreme?

Answer 5

Normal axis = -30° to +90°
LAD = 0° to -90°
RAD = +90° to +180°
Extreme axis = +180° to -90°

Question 6

What leads are analysed for axis deviation and what are the indicators?

Answer 6

Leads = I, aVF, and II
Normal = + I + aVF + II OR + I + II - aVF
LAD = + I - aVF - II
RAD = - I + aVF
Extreme = - I - aVF

Question 7

What deflections should QRS in each lead be in a normal healthy adult?

Answer 7

All leads should have positive deflections (QRS), except:
aVR = negative
aVL = positive or biphasic
V3 and V4 = biphasic, V4 may be positive
R-waves progress in amplitude from V1 to V6

Question 8

What deflections should P-waves in each lead be in a normal healthy adult?

Answer 8

All leads should be positive except:
Inferior leads (II, III, aVF) as electrodes are away from atria - negative
V1 = biphasic as depolarisation moves from RA to LA and away from the electrode

Question 9

What steps should be taken when reading an ECG trace?

Answer 9

1. Rhythm
2. Rate
3. Axis
4. P-Waves
5. PR intervals
6. QRS complexes
7. T-Waves
8. ST segments
9. QT intervals
10. U-Waves?

Question 10

Types of rhythm

Answer 10

Regular (normal sinus, brady sinus, tachy sinus)
Regularly irregular
Irregularly irregular

Question 11

How to calculate rate

Answer 11

Ideally → no. small boxes divided by 1,500
If not → no. large boxes divided by 300
If rhythm is irregular → no. R-waves x 6

Question 12

What are R-wave progressions?

Answer 12

R-waves should increase in amplitude (positive QRS deflections) from V1 towards V6 with simultaneous diminishing of S-waves.
This indicates the electrical impulse travelling normally from the SA node down to the AV node, through the bundle of His and Purkinje fibres towards the LV

Question 13

What speed and voltage is an ECG typically set to?

Answer 13

Speed of 25mm/s and voltage of 10mm/mV

Question 14

What is the typical speed and amplitude of each component of the ECG (PQRST)

Answer 14

P-wave = <120ms and <2.5mm
PR interval = 120-200ms
QRS complex = <120ms
QT interval = <440ms in men <460ms in women
T-wave = 120-200ms and <5mm in limb leads <10mm in V leads

Question 15

Normal rate, bradycardia, tachycardia

Answer 15

Normal = 60-100bpm
Brady = <60bpm
Tachy = >100bpm

Question 16

How many mm is 1 small box and 1 large box

Answer 16

1 small box = 1mm
1 large box = 5mm

Question 17

How many seconds is 1 small box and 1 large box

Answer 17

1 small box = 0.04s (40ms)
1 large box = 0.2s (200ms)

Question 18

How many mV is 1 small box and 1 large box

Answer 18

1 small box = 0.1mV
1 large box = 0.5mV

Question 19

Possible ECG artifacts

Answer 19

AC interference, motion artifact, muscle movement, baseline wander