Physiology - ECG Theory and Practice

Question 1

What direction does depolarisation in the ventricles travel?

Answer 1

Endocardium through to epicardium. Slide 3

Question 2

What is an electrocardiogram and what does it do?

Answer 2

It is the recording of potential changes and can show cardiac rate, rhythm, chamber size, electrical axis of the heart and can assess for an MI or infarction. Slide 4

Question 3

What components make up an electrical vector in the cardiac dipole?

Answer 3

Magnitude and direction.

Slide 7

Question 4

If the depolarisation moves towards the electrode which records what does it appear like on the ECG?

Answer 4

It has an upwards deflection. Slide 8

Question 5

If there is no movement of the depolarisation towards or away from the recording electrode what does it appear like on the ECG and what is the special name for it?

Answer 5

A flat line, isopotential. Slide 9

Question 6

What are the 12 leads in the 12 lead ECG?

Answer 6

Limb leadds: Leads I, II, III
Augmented voltage leads: aVR, aVL, aVF
Chest leads: V1-V6. Slide 10

Question 7

Which leads picture the heart on the frontal and transverse plane?

Answer 7

Frontal: Limb leads and augmented voltage leads.
Transverse: Chest leads. Slide 10

Question 8

What is Einthoven’s Triangle?

Answer 8

The triangle the standard limb leads make. Slide 11

Question 9

In lead II how can the P wave be created??

Answer 9

As lead II sees the heart from an inferior angle, when the atria depolarise the potential moves in an inferior direction: towards the recording electrode. So the P wave is the first small deflection positively. Slide 12

Question 10

How is the QRS complex created with lead II?

Answer 10

Q: Ventricular depolarisation starts at the interventricular septum and goes from left to right which means it goes away away from the recorder and creates a dip.
R: Then the main walls of the ventricles contract which flow towards the recorder, created a positive deflection.
S: The base of the ventricles then depolarise and move from apex to base so it moves away from the recorder creating a negative dip. Slide 13

Question 11

What does the T wave represent on an ECG and why is it a positive deflection?

Answer 11

It represents ventricular repolarisation which is when the ventricles become more negative. As the repolarisation moves away from the recorder then its the same as the negative moving towards the recorder so it results in a positive wave. Slide 14

Question 12

What can the PR interval show clinically?

Answer 12

If the PR interval is increased then it can suggest that the conduction of the AV node is decreased and there is a longer delay. Slide 16

Question 13

What is the hexaxial reference system?

Answer 13

View of the heart on the frontal plane, have 6 views in total. Slide 18

Question 14

What leads have a lateral and inferior view on the heart on the frontal plane?

Answer 14

Lateral: Leads I and aVL
Inferior: Leads II, III and aVF. Slide 19

Question 15

What are each chest lead looking at in the heart?

Answer 15

V1+V2 = 'Look' at the interventricular septum.
V3+V4 = Anterior of the heart
V5+V6 = lateral aspect (left V) of heart. Slide 21

Question 16

What is the relationship between the R wave and the S wave through V1 to V6?

Answer 16

Through V1 to V6 the R wave increases in size and the S wave decreases in size. Slide 21

Question 17

How do you work out the heart rate from an ECG?

Answer 17

300/ number of large squares between beats. Slide 27

Question 18

What are the 6 steps to analysing an ECG?

Answer 18

Verify patient details
Check date and time ECG was taken
Check calibration of ECG
Determine the axis
Workout the rhythm 
Look at the individual leads for changes. Slide 34