ECG Basics

Question 1

What is the purpose of an ECG?

Answer 1

It is a graphical representation of the electrical activity of the heart.

Question 2

What is depolarisation?

Answer 2

Depolarisation occurs when the membrane potential gets smaller and the overall charge on the inside of the becomes more positive than the overall charge outside of the cell.

Question 3

Which ion is involved in propagating the wave of depolarisation in phase 4?

Answer 3

Ca2+ ions via gap junctions.

Question 4

Which is the major channel/ion is involved in rapid depolarisation of the cell membrane in phase 0?

Answer 4

Na2+

Voltage-gated sodium channels

Question 5

Which ion/channel is responsible for stimulating the initial repolarisation of the cell membrane in phase 1?

Answer 5

K+

voltage-gated potassium channels

Question 6

Which phase is referred to as the “plateau phase?

Answer 6

Phase 2

Question 7

Which ion is responsible for maintaining the plateau aspect of depolarisation in phase 2?

Answer 7

Ca2+

Question 8

How many electrodes are placed on the body during a 12-lead ECG?

Answer 8

10 electrodes

Question 9

How many chest electrodes are there?

Answer 9

6

Question 10

Where, anatomically, should you place each of the chest electrodes (V1-V6)?

Answer 10

V1: Right 4th intercostal space, sternal border

V2: Left 4th intercostal space, sternal border

V3: midway between V2 and V4

V4: 5th intercostal space, in the mid-clavicular line

V5: 5th intercostal space, in the left anterior axillary line (on the same horizontal plane as V4)

V6: left mid axillary line (same horizontal plane as V4 and V5)

Question 11

What does the P wave represent?

Answer 11

Atrial depolarisation/contraction

Records the wave of depolarisation travelling from the SA node towards the AV node.

Question 12

What is represented by the PR segment?

Answer 12

Ventricular filling

Slow spread of depolarisation/conduction at the AV node

Question 13

What does the Q wave represent?

Answer 13

Depolarisation of the inter-ventricular septum

Question 14

What does the R wave represent?

Answer 14

Ventricular depolarisation

Question 15

What does the PR interval represent?

Answer 15

The time taken for the depolarisation to spread from the SA node across the atrium and down to the ventricular muscle via the bundle of His

Question 16

What does the S wave represent?

Answer 16

Depolarisation at the base of the ventricles

Question 17

What does the QRS complex represent?

Answer 17

Represents the whole ventricular depolarisation

Question 18

What does the T wave represent?

Answer 18

Ventricular repolarisation

Question 19

What does the ST segment represent?

Answer 19

The interval between ventricular depolarisation and repolarisation: the interval in which the entire ventricular myocardium is now depolarised.

Question 20

Name the views of the heart provided by the chest leads

Answer 20

V1: Septum view
V2: Septum view
V3: Anterior wall of ventricles
V4: Anterior wall of ventricles
V5: Lateral/left view
V6: Lateral/left view

Question 21

Names the views of the heart provided by the limb leads

Answer 21

I: Lateral view
II: Inferior view
III: Inferior view

aVF: inferior view
aVL: Lateral view
aVR: lateral view

Question 22

Which leads have an inferior view of the heart?

Answer 22

I, III and avF

Question 23

Which leads have a lateral view of the heart?

Answer 23

I, aVL, aVR, V5, V6

Question 24

Which leads have an anterior view of the heart?

Answer 24

V3, V4

Question 25

Which leads have a septal view of the heart?

Answer 25

V1, V2