This is a normal ECG of a 2 year old boy. What is the heart rate?

• 100 bpm

• 114 bpm

• 128 bpm

• 190 bpm

Answer explanation

There are 19 R waves on the rhythm strip.

Because the horizontal division of this ECG is normal (25 mm/s), the rhythm strip is a 10 second reading.

To get the heart rate we compute 19 x 6 = 114 bpm

What is the normal range for the net direction of the depolarisation wave? (Normal heart axis)

• -90° to 30°

• -30° to 60°

• -30° to 90°

• -60° to 30°

Answer explanation

The correct answer is -30° to 90°. If the net depolarisation is outside of these ranges, it will be referred to as either LAD or RAD.

Which lead is usually shown as the rhythm strip?

• I

• II

• III

• aVF

Answer explanation

Lead II is shown as it most accurately represents the characteristic ECG trace, since it measures across the direction of net depolarisation.

What is the normal horizontal division on an ECG?

• 20 mm/s

• 20 cm/s

• 25 mm/s

• 25 cm/s

Answer explanation

The correct answer is 25 mm/s. This means each small box represents 0.04 s, and each large box represents 0.2s.

What is the normal vertical division on an ECG?

• 1 mV/cm

• 10mV/cm

• 1mV/mm

• 1V/cm

Answer explanation

The correct answer is 1 mV/cm.

This is standardised and you will see a 1 mV calibration 'box' on each strip.

What does the P wave correspond to physiologically?

• Atrial depolarisation

• The depolarisation wave slowly passes the AV node

• Repolarisation of atrium

• Atrioventricular conduction

Answer explanation

What does the PR interval correspond to physiologically?

• Repolarisation of atrium

• Represents atrial depolarisation & atrioventricular conduction

• Ventricular depolarisation

• Depolarisation of Purkinje fibres

Answer explanation

What does the QRS complex correspond to physiologically?

• Repolarisation of atrium

• Ventricular depolarisation

• Septal depolarisation

• Depolarisation of the SA node

Answer explanation

What does the T wave correspond to physiologically?

• Ventricular repolarization

• Electrical diastole

• Septal depolarization

• Depolarization of Purkinje fibres

Answer explanation

What does this ECG show?

• VF

• AF

• RBBB

• LBBB

Answer explanation

Correct answer: LBBB

Conduction to the left ventricle is delayed, causing a characteristic W-shaped QRS complex in V1 and a M-shaped QRD complex in V5 or V6