ECG

Question 1

What causes an upward deflection on ECG?

Answer 1

When depolarisation moves towards the recording electrode, it generates an upward deflection on the ECG

Question 2

What causes a downward deflection on ECG?

Answer 2

When depolarisation moves away the recording electrode, it generates a downward deflection on the ECG

Question 3

What causes an area of a flat line on the ECG?

Answer 3

If there is no movement towards or away from the recording electrode, there is no deflection on the ECG (it is isopotential)

Question 4

What does the P wave represent in an ECG?

Answer 4

The P wave represents atrial depolarisation

Question 5

What is a Q wave in an ECG?

Answer 5

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

Question 6

What is an R wave in an ECG?

Answer 6

A deflection upwards (positive) is called an R wave, irrespective of whether, or not, it is proceeded by a Q wave.

Question 7

What is an S wave in an ECG?

Answer 7

A downward (negative) deflection following an R wave is called an S wave

Question 8

What does the QRS complex represent in an ECG?

Answer 8

The QRS complex represents ventricular depolarisation.

Question 9

What is the typical duration of the QRS complex in an ECG?

Answer 9

Normally has a duration of 0.1 s (100 ms), or less.

Question 10

What is the T wave on an ECG?

Answer 10

The T wave represents ventricular repolarisation

It is an upward (positive) deflection because the wave of repolarisation is spreading away from the recording electrode

Question 11

What is the P wave?

Answer 11

Atrial depolarisation moving towards the recording electrode

Question 12

What is the Q wave?

Answer 12

Left to right depolarisation of the interventricular septum moving slightly away from the recording electrode

Question 13

What is the R wave?

Answer 13

Depolarisation of the main ventricular mass moving towards the recording electrode

Question 14

What is the S wave?

Answer 14

Depolarisation of ventricles at the base of the heart moving away from the recording electrode

Question 15

What is the T wave?

Answer 15

Ventricular repolarisation moving in a direction opposite to that of depolarisation accounts for the usually observed upward deflection

Question 16

What is the PR interval and it’s typical time duration?

Answer 16

The PR interval is from the start of the P wave to the start of the QRS complex and reflects the time for the SA node impulse to reach the ventricles, normally 0.12 – 0.2 s (120 - 200 ms).

Question 17

What is the ST segment?

Answer 17

The ST segment is from the end of the QRS complex to the start of the T wave. It is normally isoelectric

Question 18

What is the QT interval?

Answer 18

The QT interval is from the start of the QRS complex to the end of the T wave.

It primarily reflects the time for ventricular depolarisation and repolarisation.

Need to be corrected for heart rate. Normally approximately 0.36 - 0.44 s at a heart rate of 60 beats per min

Question 19

What are the components of the 12 lead ECG?

Answer 19

Three standard limb leads (I, II and III) – these are termed bipolar

Three augmented voltage (aV) leads [aVR (right), aVL (left) and aVF (foot)] – these are termed unipolar

Six chest leads (V1 – V6) (aka precordial leads)

Question 20

What is the purpose of the 12 leads in the ECG?

Answer 20

Collectively, the 12 leads provide a comprehensive ‘picture’ of the heart in different directions and planes

vertical (or frontal, coronal) - leads I,II, III, aVR, aVL and aVF

horizontal (or transverse) - leads V1 – V6

Question 21

One lead recorded over a period of time is enough to workout the heart rate and rhythm so why are 12 leads required?

Answer 21

The 12 leads look at the heart from different directions allowing you to:

Determine the axis of the heart in thorax

Look for any ST segment or T wave changes in relation to specific regions of the heart. This is crucial e.g. in diagnosing Ischaemic Heart Disease

Look for any voltage criteria changes. This is crucial e.g. in diagnosing chamber hypertrophy

Question 22

What areas of the heart do the chest leads look at?

Answer 22

V1 Septal view of the heart
V2 Septal view of the heart
V3 Anterior view of the heart
V4 Anterior view of the heart
V5 Lateral view of the heart
V6 Lateral view of the heart

Remember: SSAALL

Question 23

What areas of the heart do the other chest leads look at?

Answer 23

Lead I Lateral view (calculated by analysing activity between the RA and LA electrodes)

Lead II Inferior view (calculated by analysing activity between the RA and LL electrodes)

Lead III Inferior view (calculated by analysing activity between the LA and LL electrodes)

aVR Lateral view (calculated by analysing activity between LA+LL -> RA)

AVL Lateral view (calculated by analysing activity between RA+LL -> LA)

aVF Inferior view (calculated by analysing activity between RA+LA -> LL)

Question 24

Leads II, III and aVF correspond to?

Answer 24

View: Inferior

Blood supply:
Right coronary artery (90%)
Left circumflex artery (10%)

Question 25

Leads I, aVL, V5 and V6 correspond to?

Answer 25

View: lateral

Blood supply:
Left circumflex artery (leads I and aVL)

Question 26

Leads V3 and V4 correspond to?

Answer 26

View: anterior

Blood supply:
Distal left anterior descending (LAD) artery

Question 27

Leads V1 and V2 correspond to?

Answer 27

View: septal

Blood supply:
Proximal left anterior descending (LAD) artery