ECG (Cardiovascular)

Question 1

Where in the layers of the heart does repolarisation spread from?

Answer 1

The epicardium to the endocardium.

Question 2

Why can potential changes only be detected from atrial and ventricular muscle?

Answer 2

Only large masses of cardiac tissue generate sufficient current to be detected at the body surface.

Question 3

What information can an ECG provide us with?

Answer 3

Info about cardiac rate and rhythm, chamber size, the electrical axis of the heart, assess for myocardial ischaemia and infarction.

Question 4

What is the device that records the ECG called?

Answer 4

The electrocardiograph.

Question 5

What determines the magnitude of an electrical signal in an ECG?

Answer 5

The mass of cardiac muscle involved in generation of the signal.

Question 6

What is an ECG lead?

Answer 6

The imaginary line (lead axis) between 2 or more electrodes.

Question 7

Is the recording electrode positive or negative?

Answer 7

Positive.

Question 8

What deflection will movement towards and away from the recording electrode cause?

Answer 8

Towards: upward deflection. Away from: downwards deflection.

Question 9

What are the 12 leads of the ECG?

Answer 9

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

Question 10

What limbs do the limb leads go from/to?

Answer 10

I: RA (-ve) to LA (+ve). II: RA (-ve) to LL (+ve). III: LA (-ve) to LL (+ve).

Question 11

What is a downward deflection preceding an R wave called?

Answer 11

A Q wave.

Question 12

Do R waves always have to be preceded by a Q wave?

Answer 12

No

Question 13

What is a downward deflection following an R wave called?

Answer 13

An S wave.

Question 14

What does the PR interval represent and why is it diagnostically important?

Answer 14

Time for SA node impulse to reach ventricles. It is strongly influenced by delay in conduction through the AV node.

Question 15

What does the QT interval represent and what does prolongation
of it predispose to?

Answer 15

Disturbances in cardiac rhythm (drugs may be causative).

Question 16

Are the waves positive or negative in aVR?

Answer 16

Negative.

Question 17

What are the lateral leads and where do they view the heart from?

Answer 17

I and aVL - from the left.

Question 18

What are the inferior leads and where do they view the heart from?

Answer 18

II, III and aVF - inferior direction.

Question 19

What forms the reference electrode for the precordial leads and where is this?

Answer 19

Links all 3 limb electrodes, effectively at the centre of the heart.

Question 20

What are V1/2, V3/4 and V5/6 looking at in the heart?

Answer 20

V1/2 - interventricular septum. V3/4 - anterior. V5/6 - lateral aspect (LV) of heart.

Question 21

What happens to the R and S waves as you move from lead V1-V6?

Answer 21

R wave - progressively increases. S wave - progressively decreases.

Question 22

What are the locations of the 6 chest electrodes?

Answer 22

V1 - 4th intercostal space immediately right of sternum.
V2 - 4th intercostal space immediately left of sternum.
V3 - midway between V2 and V4.
V4 - 5th intercostal space mid-clavicular line.
V5 - same horizontal level as V4 anterior axillary line.
V6 - mid-axillary line.

Question 23

What is the standard paper speed of an ECG?

Answer 23

25mm/sec.

Question 24

What do the large and small boxes represent?

Answer 24

Large - 0.2s of time and 5mm of amplitude. Small - 0.04s of time and 1mm of amplitude.

Question 25

How do you calculate the heart rate on an ECG?

Answer 25

300/number of large squares between R waves.

Question 26

What are the 6 key steps in analysing an ECG?

Answer 26

1. Verify patient details: name and DOB.
2. Check date/time taken.
3. Check paper calibration.
4. Determine axis if possible.
5. Work out the rhythm (7 questions).
6. Look at individual leads for voltage criteria changes or any ST or T-wave changes.

Question 27

What are the 7 questions you need to ask about rhythm?

Answer 27

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?

Question 28

What can an ECG not exclude?

Answer 28

MI (may or may not cause ST elevation/depression), intermittent rhythm disturbance (ambulatory ECG recording for 24hrs/7days), stable angina (exercise ECG).

Question 29

How long should each P wave, QRS complex and PR interval be?

Answer 29

P wave - 0.08-0.1s.
QRS complex - <0.1s.
PR interval - 0.12-0.2s.

Question 30

What part of the ECG is systole and what part is diastole?

Answer 30

ST segment systole, TP interval diastole.

Question 31

How can you tell if there is left axis deviation or right axis deviation?

Answer 31

Left - aVF is downwards, lead I is upwards.

Right - aVF is upwards, lead I is downwards.

Question 32

If the heart rate is irregular, how do you calculate the heart rate?

Answer 32

Count the number of QRS complexes in 30 large squares and multiply by 10.

Question 33

What do tall QRS complexes indicate?

Answer 33

Hypertrophy.

Question 34

How large does the ST segment elevation have to be for it to be a STEMI?

Answer 34

2mm rise in 2 adjacent leads, or 1mm in 2 associated leads.