ECG

Question 1

Describe the parts of the conducting system in order of flow

Answer 1

SA node

AV node

Bundle of His

Bundle branches

• right bundle branch
• left bundle branch (-> anterior + posterior fascicles)

Purkinje fibres

Question 2

What is the order for describing an ECG?

Answer 2

Patient details

Calibration

Rate

Rhythm

Conduction intervals

Axis

P wave

PR interval

QRS complex

ST segment

T wave

Question 3

What represents atrial depolarisation?

Answer 3

P wave

Question 4

How much time is a small sqaure?

Answer 4

0.04s

Therefore, large square = 0.2s

Question 5

What should always precede a QRS complex?

Answer 5

A p-wave

Question 6

What is the normal length of a p wave?

Answer 6

Less than 0.12s

Question 7

What is the PR interval?

Answer 7

The time taken for the conduction to be passed from the SAN to the ventricles

Question 8

What represents ventricular depolarisation?

Answer 8

QRS complex

Question 9

What is the normal length of a QRS complex?

Answer 9

Less than 0.12 seconds

Question 10

What is classed as a prolonged PR interval?

Answer 10

Greater than 0.2 seconds

Question 11

What does the QT interval represent?

Answer 11

Time taken to depolarise and repolarise the ventricular myocardium

Question 12

What represents ventricular repolarisation?

Answer 12

The ST segment

Question 13

What does the T wave represent?

Answer 13

It is a low amplitute deflection after ventricular repolarisation

Question 14

How much voltage is one small square?

Answer 14

0.1mV

Question 15

What are the standard limb leads on an ECG?

Answer 15

Lead 1 - R arm to L arm (lateral view)
Lead 2 - R arm to L leg (inferior view)
Lead 3 - L arm to L leg
Lead aVR - (L arm and L leg) to R arm
Lead aVL - (R arm and L leg) to L arm
Lead aVF - (R arm and L arm) to L leg

Question 16

How should heart rate be calculated?

Answer 16

300 / (no. of large squares between RR interval) = beats per minute