ECG

Question 1

How does an ECG detect the excitation of the heart?

Answer 1

The wave of depolarisation and repolarization moves across the heart and sets up electrical currents which can be detected by surface electrodes

Question 2

What is an ECG a record of?

Answer 2

Depolarisation and repolarisation cycle of cardiac muscle obtained from skin surface, the potential differences between distant sites on the body surface are detected by electrodes and coupled to the electrocardiograph

Question 3

What are the 3 limb leads?

Answer 3

• lead I RA-LA
• lead II RA-LL
• lead III LA-LL

Question 4

What is the P wave?

Answer 4

Atrial depolarisation

Question 5

What is the QRS complex?

Answer 5

Ventricular depolarisation (masks atrial repolarisation)

Question 6

What is the T wave?

Answer 6

ventricular repolarisation

Question 7

What is the PR interval?

Answer 7

Largely AV node delay

Question 8

What is the ST segment?

Answer 8

Ventricular systole

Question 9

What is the TP interval?

Answer 9

diastole

Question 10

When do the atria contract?

Answer 10

between the P wave and QRS complex

Question 11

What is the difference between the electrocardiograph and the electrocardiogram?

Answer 11

The electrocardiograph is the machine which the electrodes are coupled to and the electrocardiogram is the recording of the potential differences

Question 12

What is meant by a dipole?

Answer 12

charges which are separated - a vector with components of magnitude and direction

Question 13

What information is provided by an ECG?

Answer 13

information on:
cardiac rate 
cardiac rhythm
chamber size
the electrical axis of the heart 
- main test for myocardial ischaemia and infarction

Question 14

How is the magnitude of the electrical vector determined?

Answer 14

by the mass of cardiac muscle involved in the generation of the signal

Question 15

How is the direction of the electrical vector determined?

Answer 15

the overall activity of the heart at any instant in time and varies over the cardiac cycle

Question 16

What does the word lead refer to in an ECG?

Answer 16

an imaginary line between 2 or more electrodes, one of which electrodes is the recording (+ve) or seeing electrode

Question 17

What happens on the electrocardiogram when the depolarisation moves towards the recording electrode?

Answer 17

Deflection is upwards

deflection downwards when depolarisation moves away

Question 18

What 12 leads comprise a 12 lead ECG?

Answer 18

3 standard limb leads (I, II, III) these are bipolar
3 augmented voltage (aV) leads (aVR, aVL and aVF) these are unipolar
6 chest leads (V1 - V6) the precordial leads

Question 19

What view of the heart do the precordial leads provide?

Answer 19

A horizontal view

Question 20

What view of the heart do the limb leads and augmented voltage leads provide?

Answer 20

A vertical view

Question 21

In lead I which electrode is which?

Answer 21

RA is negative

LA is positive (recording)

Question 22

In lead II which electrode is which?

Answer 22

RA is negative

LL is positive (recording)

Question 23

In lead III which electrode is which?

Answer 23

LA is negative

LL is positive (recording)

Question 24

What direction does lead II see the heart from?

Answer 24

it looks at the heart from the inferior left position so is well placed as the depolarisation of the heart moves in this direction as well

Question 25

What is the normal duration of the P wave?

Answer 25

less than 0.120s

Question 26

What is the downward deflection before the R wave?

Answer 26

The Q wave

Question 27

What is the large upwards deflection?

Answer 27

R wave

Question 28

What is the downward deflection following the R wave?

Answer 28

S wave

Question 29

What is the T wave?

Answer 29

The wave of re polarisation moving away from the recording electrode

Question 30

What does the PR interval indicate?

Answer 30

From start of P wave until start of QRS time for the SA node impulse to reach the ventricles 0.12-0.2s is normal duration

Question 31

What is the ST segment?

Answer 31

end of QRS to start of T wave should be isoelectric

Question 32

What does the QT interval indicate?

Answer 32

from start of QRS to end of T wave primarily reflects time for ventricular depolarisation and repolarisation

Question 33

How do augmented limb leads observe the heart?

Answer 33

there is one positive electrode viewing the others which are linked as -ve, the augmented leads see the heart from different angles than just the standard limb leads

Question 34

What is the hexaxial reference system?

Answer 34

The 6 different views of the heart seen in the vertical plane in a 12 lead ECG

Question 35

Where is the -ve electrode for the precordial leads?

Answer 35

Due to the way the electrodes on the precordium link up the -ve electrode is essentially in the centre of the heart

Question 36

What view do V1 and V2 look at the heart from?

Answer 36

from the right at the interventricular septum

Question 37

What view do V3 and V4 look at the heart from?

Answer 37

anterior view

Question 38

What view do V5 and V6 look at the heart from?

Answer 38

look at the lateral aspect - left ventricle

Question 39

Where do you position the chest leads?

Answer 39

V1 - 4th intercostal space, right sternal edge V2 - 4th intercostal space, left sternal edge V3 - midway between V2 & V4 V4 - 5th intercostal space, midclavicular line V5 - same horizontal position as V4, anterior auxillary line V6 - same horizontal level as V4, mid auxillary line

Question 40

What cardiac event is indicated by the ST segment?

Answer 40

ventricular systole

Question 41

What cardiac event is indicated by the TP segment?

Answer 41

Ventricular diastole

Question 42

Why are 12 leads used when 1 lead can determine rate and rhythm?

Answer 42

it allow us to determine the axis of the heart in the thorax look at ST segment and T wave changes in relation to specific heart regions look at voltage criteria changes - to diagnose chamber hypertrophy

Question 43

6 steps to looking at an ECG

Answer 43

1. Verify patient details: name and date of birth 2. Check date and time ECG was taken 3. Check the calibration of the ECG paper 4. Determine the axis (if possible) 5. Workout the rate and rhythm 6. Look at individual leads for voltage criteria changes OR any ST or T-wave changes

Question 44

What are the 7 questions to workout rate and rhythm from the rhythm strip of the ECG?

Answer 44

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