Electrocardiogram

Question 1

Label the parts of the cardiac conduction system on the diagram

Answer 1

Question 2

Describe the normal ECG trace

Answer 2

Question 3

What does each waveform correlate with?

Answer 3

P wave = Atrial systole causing increase in ventricular volume

PR interval = Time taken for current to pass from SA node to AV node

QRS segment = Isovolumic ventricular contraction which initiates ventricular systole

T wave = ventricular repolarisation

Question 4

What is the frontal QRS axis?

Answer 4

The direction of the vector sum (average direction of the electrical depolarisation as it spreads through the ventricles during a single cardiac cycle).

Defined graphically by the QRS deflections of the frontal leads

Question 5

Where are the precordial leads placed?

Answer 5

V1: 4th intercostal space just to right of sternum

V2: 4th intercostal space just to the left of sternum

V3: In between V2 and V4

V4: 5th intercostal space in mid clavicular line

V5: In same horizontal plane as V4, in anterior axillary line

V6: In same horizontal plane as V4 and V5 in the mid axillary line

Question 6

Which surfaces of the heart to V1-V6 view?

Answer 6

V1-V2: Septal

V3-V4: Anterior/septal

V4-V5: Lateral

(V1-V4 extensive anterior)