Introduction to the ECG

Question 1

What does the P wave correspond to?

Answer 1

Atrial depolarisation

Question 2

What does the QRS complex correspond to?

How long should it take?

Answer 2

Ventricular depolarisation

Less than 0.12s

Question 3

What does the T wave correspond to?

Answer 3

Ventricular depolarisation

Question 4

What does the PR interval correspond to?

How long should it take?

Answer 4

Time from atrial depolarisation to ventricular depolarisation
0.1-0.2s

Question 5

Which points does the PR interval occur between?

Answer 5

The start of the P wave and the start of the QRS complex (Q)

Question 6

What does the QT interval correspond to?

Answer 6

Time spent during which ventricles are depolarised

About 0.42s at 60bpm

Question 7

Which points does the QT interval occur between?

Answer 7

Start of the QRS complex (Q) to the end of the T wave

Question 8

Which points does the ST segment occur between?

Answer 8

The end of the QRS complex (S) and the start of the T wave

Question 9

Which points does the PR segment occur between?

Answer 9

The end of the P wave and the start of the QRS complex (Q)

Question 10

What is the significance of the ST segment?

Answer 10

If elevated in myocardial infarction indicates MI more severe

Question 11

How is depolarisation represented on an ECG?

Answer 11

Upward going blip

Question 12

Are fast or slow events transmitted better?

Answer 12

Fast events

Question 13

What plane are standard limb leads in?

Answer 13

Frontal/vertical

Question 14

What does SLL 1 represent?

Answer 14

Left arm with respect to right arm (

Question 15

What does SLL 2 represent?

Answer 15

Left leg with respect to right arm (

Question 16

What does SLL 3 represent?

Answer 16

Left leg wrt left arm (^I)

Question 17

Is depolarisation towards a lead positive or negative?

Answer 17

Positive

Question 18

Is depolarisation away from a lead positive or negative?

Answer 18

Negative

Question 19

Is repolarisation towards a lead positive or negative?

Answer 19

Negative

Question 20

Is repolarisation away from a lead positive or negative?

Answer 20

Positive

Question 21

Why is there a downward going blip towards Q?

Answer 21

The interventricular septum is being depolarised from LEFT to RIGHT so depolarisation is away from the lead.

Question 22

Why is there an upward going blip towards R?

Answer 22

The bulk of the ventricle is depolarised from endocardium from epicardium from right to left so depolarisation is towards the lead

Question 23

Why is there a downward going blip towards S

Answer 23

Because the upper ventricular system is depolarised from left to right so depolarisation is away from the lead

Question 24

Why is the R wave biggest on SLL 2?

Answer 24

Because the main vector is depolarisation is in line with axis recording from the left leg to the right arm

Question 25

What would left heart hypertrophy or right heart atrophy cause on an ECG?

Answer 25

Right axis deviation

Question 26

What are augmented limb leads?

Answer 26

Recording from 1 lead with respect to 2 other leads. Giving 3 perspectives and 6 in total of frontal and vertical plane.

Question 27

What is aVR?

Answer 27

Right arm with respect to left arm and left leg

Question 28

What is aVL?

Answer 28

Left arm with respect to right arm and right leg

Question 29

What is aVF?

Answer 29

Left leg with respect to left arm and right arm

Question 30

What are the precordial chest leads? | What direction to the move in in what plane?

Answer 30

Move from right to left ventricle in transverse plane

Question 31

How does the direction of the QRS complex change as the precordial chest leads move across the chest?

Answer 31

Negative going blip from V1 but flips to a positive going blip at V3 or V4

Question 32

How fast does the paper run on the rhythm strip?

Answer 32

25mm/s

Question 33

What is the calibrating pulse of the rhythm strip? | How does this correspond to boxes?

Answer 33

0.2sec (5mm) = 1 large box

Question 34

How do you calculate HR from an ECG?

Answer 34

Count the R waves over 30 large squares (6 seconds) and multiply by 10.

Question 35

List the key points that the rhythm strip tells you

Answer 35

Whether each QRS complex is preceded by a P wave Whether the PR interval is to short (<0.12s) or long (>0.2sec) Whether the QRS is too wide (>0.12s) Whether the QT interval is too long (>0.42s at 60bpm)