Introduction

Question 1

In sinus rhythm, where are the acton potentials generated

Answer 1

SA node (pacemaker)

Question 2

Describe where the action potential travels after being generated in the SA node

Answer 2

SA node > rapidly through the atria (atrial contraction) > relatively slowly through the AV node > very rapidly through the bundle of His and left and right bundle branches > rapidly through the Purkinje fibres (ventricular contraction)

Question 3

True or false - an ECG lead is the wire that connects the electrode to the recording device

Answer 3

FALSE - it is the imaginary line, the lead axis, between two (or more) electrodes

In a lead one electrode acts as the recording (positive) electrode. (Think of it as the ‘seeing electrode’).

Question 4

When depolarization moves towards the recording electrode, it generates a(n) UPWARD/ DOWNWARD deflection on the ECG

Answer 4

upward

(and when depolarization moves away from the recording electrode, it generates a downward deflection on the ECG

Question 5

What happens if there is no movement towards or away from the recording electrode

Answer 5

there is no deflection on the ECG (it is isopotential)

Question 6

Describe what the different leads are called in a 12 lead ECG

Answer 6

Three standard limb leads (I, II and III)
Three augmented voltage (aV) leads [aVR (right), aVL (left) and aVF (foot)]
Six chest leads (V1 – V6) (aka precordial leads)

Question 7

Collectively, the 12 leads provide a comprehensive ‘picture’ of the heart in different directions and planes

Which leads represent the
- vertical
- horiztonal
Direction

Answer 7

Vertical: I,II, III, aVR, aVL and aVF
Horiztonal: V1-V6

Question 8

Which lead is often used as the rhythm strip?

Answer 8

II (one of the standard limb leads)

Question 9

The three limb leads for a triangle called what?

Answer 9

Einthoven’s triangle (equilateral triangle where the heart is at the centre)

Question 10

Draw Einthoven’s triangle

Answer 10

look it up (inc which end it -ve and which is +ve)

Question 11

Depolarization moving towards the recording (+ve) electrode gives an _____ deflection on the ECG, whereas away from it causes a _____ deflection

Answer 11

1) upward

2) downward

Question 12

What is the p wave and how long should it be?

Answer 12

depolarisation of atrial muscle (<0.12s)

Question 13

What is the QRS complex and how long should it be?

Answer 13

Ventricular activation/ depolarisation (≤0.1s)E

Question 14

What is the t wave?

Answer 14

Ventricular repolarisation

Question 15

state which each aspect of the QRS complex represents

Answer 15

Q wave: depolarisation of the IV septum
R wave: depolarisation of the main free walls of the ventricles
S wave: depolarisation of ventricles at the base of the heart

Question 16

What is the PR interval and how long should it last?

Answer 16

Start of the P wave -> start of the QRS complex

Reflects the time for the SA node impulse to reach the ventricles, largely caused by AVN delay (0.12 – 0.2s)

Question 17

what is the ST segment?

Answer 17

end of the QRS complex - start of the T wave.
Normally isoelectric
Ventricular systole

Question 18

What is the QT interval and how long should it be?

Answer 18

Start of the QRS complex - end of the T wave.
Ventricular depolarization and repolarization, (0.44s in males, 0.46s in females)
Prolongation predisposes to disturbances of cardiac rhythm – drugs may be causative

Question 19

What are aVL, aVR and aVF called?

Answer 19

augmented limb leads (unipolar)

Question 20

name the lateral leads

Answer 20

I and aVL - each has the recording electrode on the left arm and views the heart from the left

Question 21

name the inferior leads

Answer 21

II, III and aVF - each has the recording electrode on the left foot and views the heart from an inferior direction

Question 22

state which view of the heat the precordial leads have

Answer 22

V1 and V2: septal (coming from the right ‘looking’ at the IV septum)
V3 and V4: anterior
V5 and V6: lateral (left ventricle)

Question 23

describe the placement of the precordial leads

Answer 23

V1: 4th IC space, immediately right of the sternum 
V2: same on left
V3: between V2 and 4
V4: 5th IC space, midclavicular line
V5: 5th IC space, anterior axillary line
V6: 5th IC space, mid axillary line

Question 24

normal ECG calibration

Answer 24

25mm/sec

Question 25

how to calculate HR from the rhythm strip?

Answer 25

300/ no. of large squares between R waves
OR
No. of R waves x 6

Question 26

in normal calibration, how many squares is 1 second, 0.2s, 0.04s

Answer 26

5 large squares = 1 s
1 large square = 0.2s
1 small square = 0.04s

Question 27

6 key steps when analysing an ECG

Answer 27

1) Patient details: Name and date of birth
2) Date + time taken
3) Calibration of the ECG paper
4) axis
5) rate and rhythm
6) individual lead inspection for voltage criteria changes or any ST/ T-wave changes

Question 28

for step 5 of analysing an ECG (work out the rate and rhythm) what 7 questions should you ask?

Answer 28

5. 1 Is electrical activity present?
6. 2 Is the rhythm regular or irregular?
7. 3 What is the heart rate?
8. 4 P-waves present?
9. 5 What is the PR interval?
10. 6 Is each P-Wave followed by a QRS complex?
11. 7 Is the QRS duration normal?