ECG theory and practice

Question 1

Where does depolarisation spread?

Answer 1

From the endocardium to the epicardium

Question 2

Where does repolarisation spread?

Answer 2

From the epicardium to the endocardium

Question 3

What is an ECG?

Answer 3

The ECG is a recording of potential changes, detected by electrodes positioned on the body surface, that allows the electrical activity of the heart to be monitored in a manner that is simple to perform

Question 4

What is needed to generate detectable potential changes?

Answer 4

Large masses of cardiac tissue

Question 5

What is extracellular current?

Answer 5

What generates the changes in potential which we can record on the body surface

Question 6

What is an electrical vector?

Answer 6

the separation of charge with particular direction

Question 7

Where does the wave of depolarisation spread in terms of the AV node?

Answer 7

Away from the AV node. Spreading to the left of the heart

Question 8

What allows us to approximate the electrical axis of the heart?

Answer 8

The direction of the vector

Question 9

What are the components of the electrical vector?

Answer 9

Magnitude and direction

Question 10

What defection on the ECG does depolarisation generate moving towards the recording electrode?

Answer 10

upward deflection

Question 11

What deflection on the ECG does depolarisation generate moving away from recording electrode?

Answer 11

downward deflection

Question 12

What is the lead axis?

Answer 12

The imaginary line between two electrodes

Question 13

What deflection on the ECG does depolarisation generate when there is no movement away or from recording electrode?

Answer 13

no deflection. Isopotential

Question 14

What does the 12 lead ECG comprise of?

Answer 14

• three standard limb leads
• three augmented voltage leads
• six chest leads

Question 15

Which plane of the heart is seen in chest leads?

Answer 15

horizontal

Question 16

What plane of the heart is see in limb and augmented leads?

Answer 16

vertical

Question 17

What is lead I

Answer 17

RA to LA

Question 18

What is lead II

Answer 18

RA to LL

Question 19

What is lead III

Answer 19

LA to LL

Question 20

How is the P wave formed?

Answer 20

Atrial depolarization spreads from the SA node inferiorly and to the left - depolarization is moving towards the recording electrode (+ve) in lead II producing a (normally) upward deflection in this lead – the P wave

Question 21

What is a Q wave?

Answer 21

a downward (negative) deflection preceding an R wave is called a Q wave

Question 22

What is an R wave?

Answer 22

a deflection upwards (positive) is called an R wave, irrespective of whether, or not, it is proceeded by a Q wave – this can be confusing

Question 23

What is an S wave?

Answer 23

a downward (negative) deflection following an R wave

Question 24

How is a Q wave formed?

Answer 24

ventricular depolarization starts in the interventricular septum and spreads from left to right causing the small and narrow Q wave

Question 25

How is an R wave formed?

Answer 25

subsequently the main free walls of the ventricles depolarize causing a tall and narrow R wave

Question 26

How is an S wave formed?

Answer 26

finally, the ventricles at the base of the heart depolarize, producing a small and narrow S wave

Question 27

How is a T wave formed?

Answer 27

It is an upward (positive) deflection because the wave of repolarization is spreading away from the recording electrode (think of it as negative charge moving away from the recording electrode which is the equivalent of positive charge moving towards it!)

Question 28

What is a T wave?

Answer 28

ventricular repolarisation

Question 29

What is the normal length for the PR interval?

Answer 29

0.12-1.2 s

Question 30

What is the PR interval strongly influenced by?

Answer 30

the delay in conduction through the AV node. If conduction from AV node is fast, the PR interval decreases and vice versa

Question 31

True/False. the ST segment is normally isoelectric

Answer 31

True

Question 32

What is the normal length for the QT interval?

Answer 32

0.44 in males and 0.46 in females

Question 33

What is the recording electrode in augmented leads?

Answer 33

One recording lead other two linked.

Question 34

How mamy views of the heart do we have with a 12 lead ECG?

Answer 34

12 views, 6 from limbs and augmented and 6 from chest

Question 35

What are V1 and V2 looking at?

Answer 35

interventricular septum

Question 36

What are V3 and V4 looking at?

Answer 36

anterior of the heart

Question 37

What are V5 and V6 looking at?

Answer 37

lateral aspect (left ventricle) of the heart

Question 38

What is the first positive deflection in the QRS complex in V1?

Answer 38

R wave immediately followed by an S wave

Question 39

What happens to the R ad S wave as you move from V1 to V6?

Answer 39

progressive increase in R wave and progressive decrease in S wave

Question 40

How long does the P wave last?

Answer 40

0.08-0.1 s

Question 41

How long does the QRS complex last?

Answer 41

less than 0.1 s

Question 42

What is the ECG rhythm strip?

Answer 42

Prolonged recording of one lead. Usually lead II. It allows you to detect rhythm disturbance

Question 43

What are the 6 steps in analysing the ECG?

Answer 43

``` 1- verify patients name and DOB 2-check time and date when ECG was taken 3-Check the calibration of the ECG paper 4- determine the axis if possible 5-work out the rhythm 6- look at individual leads for voltage criteria changes or any ST or T wave changes ```

Question 44

What are the 7 steps in determining rhythm?

Answer 44

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

Question 45

true or False. Always use ECG over clinical judgement

Answer 45

False clinical judgment comes first