8. ECG

Question 1

In what direction do the ventricles depolarise? What does this enable?

Answer 1

Endocardium to epicardium

Coordinated contraction of atria and ventricles

Question 2

Where in the heart has the fastest rate of depolarisation?

Answer 2

Sinoatrial node

Question 3

Depolarisation occurs from the SA node, through atria, AV node, bundle of his, purkinje system from apex to base of ventricles. What order does repolarisation occur in?

Answer 3

Reverse order

Question 4

What does an ECG record?

Answer 4

Changes on the extracellular surface of cardiac myocytes during wave of depolarisation and repolarisation

Question 5

If depolarisation is moving directly towards the electrode, what is seen on an ECG tracing?

Answer 5

Tall positive complex

Question 6

If depolarisation is moving at 90 degrees to the electrode, what is seen on an ECG tracing?

Answer 6

Biphasic or no complex

Question 7

If depolarisation is moving directly away from the electrode, what is seen on an ECG tracing?

Answer 7

Deep negative complex

Question 8

If repolarisation is moving directly towards the electrode, what is seen on an ECG tracing?

Answer 8

Deep negative complex

Question 9

If repolarisation is moving directly away from the electrode, what is seen on an ECG tracing?

Answer 9

Tall positive complex

Question 10

Do you see SA node depolarisation on an ECG?

Answer 10

No, is insufficient signal to register on surface ECG

Question 11

What happens in atrial depolarisation? What wave does this produce on an ECG?

Answer 11

Spreads along atrial muscle fibres and intermodal pathways, towards AV node.
P wave

Question 12

What is the AV node

Answer 12

Fibrous ring between atria and ventricles, which is only crossed by the bundle of His

Question 13

What is seen on an ECG in depolarisation of the AV node?

Answer 13

Isoelectric (flat line) segment

Question 14

In what direction does the septum depolarise? So what does this produce on an ECG?

Answer 14

Left to right

Small downward deflection, Q wave

Question 15

What is seen on an ECG during depolarisation of the apex and free ventricular wall?

Answer 15

Tall positive complex - R wave

Question 16

What will happen to the R wave on an ECG if the LV is hypertrophied

Answer 16

R wave will be correspondingly taller

Question 17

What happens at the end of depolarisation? What does this produce on an ECG?

Answer 17

Depolarisation spreads up towards the base of the ventricles

Small downward deflection, S wave

Question 18

What happens in ventricular repolarisation? What is seen on an ECG tracing?

Answer 18

Begins on epicardial surface in opposite direction of depolarisation.
Upward wave as repolarisation is moving away from electrode, T wave

Question 19

What components of an ECG may not be seen in all leads?

Answer 19

QRS

Question 20

What 3 views in the vertical place (limb leads) look at the inferior surface of the heart? What are they best to detect?

Answer 20

II, III and aVF

Problems in inferior heart surface eg muscle necrosis due to inferior MI

Question 21

What 2 views in the vertical plane (limb leads) look at the left side of the heart?

Answer 21

I and aVL

Question 22

What 1 view in the vertical place (limb leads) looks at the right side of the heart?

Answer 22

aVR

Question 23

What do the V1 and V2 chest leads (horizontal plane) look at?

Answer 23

RV and septum

Question 23

What do the V3 and V4 chest leads (horizontal plane) look at?

Answer 23

Apex and anterior ventricle walls

Question 24

What do the V5 and V6 chest leads (horizontal plane) look at?

Answer 24

LV

Question 25

How much time does one large square on an ECG represent?

Answer 25

0.2 seconds

Question 26

How much time does one small square on an ECG represent?

Answer 26

0.04 seconds

Question 27

How would you calculate the heart rate if the rhythm is irregular on an ECG?

Answer 27

Count number of QRS complexes in 6 seconds (30 large squares) and then multiple by 10

Question 28

How long should the PR interval (time from start of P to R) normally be?

Answer 28

0.12-0.2 seconds

Question 29

How long should the QRS interval normally be?

Answer 29

Less than 0.12 seconds

Question 30

How long should the QT interval normally be on an ECG?

Answer 30

Depends on heart rate, approx 0.45 seconds

Question 31

What should you think about when considering if an ECG shows normal sinus rhythm?

Answer 31

``` Regular? HR? P waves? Are they upright in leads I and II? PR normal? Every P followed by a QRS? Every QRS preceded by a P? QRS normal? ```

Question 32

What is sinus bradycardia?

Answer 32

Sinus rhythm with rate less than 60/min

Question 33

What is sinus tachycardia?

Answer 33

Sinus rhythm with rate over 100/min