11- Understanding The Ecg

Question 1

What can ecgs be used for

Answer 1

achyarrhythmias
•Bradyarrhythmias
•Myocardial infarction
•Myocardial ischaemia
•Cardiomyopathy
•Assessment of pacing
•Electrolyte disturbances

Question 2

Where do the 3 true bipolar leads run from

Answer 2

1: RA to LA
2: RA to LL
3: LA to LL

Question 3

Where do the 3 augmented lead run from

Answer 3

AVL: mid to LA
AVR: mid to RA
AVF: mid to LF

Question 4

What are the angles of the different leads

Answer 4

L1: 0
L2: +60
L3: +120
aVL: -30
aVF: +90
aVR: +210

Question 5

How do you calculate QRS axis

Answer 5

Looking at the ecg you add the change in voltage of L1 and of aVF
To calculate theta tan-1( aVF/ L1), use CAST if necessary

Question 6

How do you know the deviation of the QRS axis

Answer 6

Less than -30 is left axis

More than +90 is right axis

Question 7

Where are the 6 precordial leads placed?

Answer 7

V1 4th Intercostal space to the right of the sternum
V2 4th Intercostal space to the left of the sternum
V3 Midway between V2 and V4
V4 5th Intercostal space at the midclavicular line
V5 Anterior axillary line at the same level as V4
V6 Midaxillary line at the same level as V4 and V5

For each lead, the chest lead is positive pole
•The negative pole is Wilson’s central terminal (composite pole of right arm, left arm and left leg (average potential across the body)

Question 8

What are the polarities of the 4 limb electrodes

Answer 8

RA negative
LA negative/ positive
RL neutral
LL positive