ECG

Question 1

What do the standard limb leads of an electrocardiogram look at?

Answer 1

Events in the vertical (frontal) plane

Question 2

What does a wave of approaching depolarisation approaching the electrode cause on the ECG?

Answer 2

An upward-going blip

Question 3

Are fast or slow events better transmitted on an ECG?

Answer 3

Fast events transmitted better

Question 4

How do augmented limb leads give you extra information from an ECG?

Answer 4

By recording from one limb lead with respect to the other two combined, you gain three perspectives on events in the heart

Question 5

What do precordial leads look at?

Answer 5

The same events as limb leads but in the horizontal (transverse) plane

Question 6

What do the limb leads and precordial leads look at?

Answer 6

The limb leads look at the spread of depolarisation and depolarisation from 6 angles in the frontal plane, the precordial leads look at the same events from 6 angles in the transverse planes

Question 7

Changes in the spread of depolarisation affect the ECG in what manner?

Answer 7

A predictable manner

Question 8

What does the P wave of an ECG correspond to?

Answer 8

Atrial depolarisation

Question 9

What does the QRS complex of an ECG correspond to?

Answer 9

Ventricular depolarisation

Question 10

What does the T wave of an ECG correspond to?

Answer 10

Ventricular repolarisation

Question 11

Why can atrial repolarisation not be seen on an ECG?

Answer 11

It coincides with ventricular depolarisation, but ventricular depolarisation involves much more tissue depolarising much faster and so swamps any signal from atrial repolarisation

Question 12

Why is the T wave positive-going?

Answer 12

The action potential is longer in endocardial cells than in epicardial cells so the wave of repolarisation runs in the opposite direction to the wave of depolarisation

Question 13

Why is the R wave bigger in standard limb lead I than in II or III?

Answer 13

Because main vector of depolarisation is in line with the axis of recording

Question 14

What is the PR interval and what is its normal range?

Answer 14

PR interval is the time taken from atrial depolarisation to ventricular depolarisation, and is mainly due to transmission through the AV node
Normal range is 0.12-0.2 seconds

Question 15

What is the usual time taken for the whole of the ventricle to depolarise (QRS complex)?

Answer 15

0.08 seconds

Question 16

What is the order and pattern of depolarisation of the different parts of the ventricle?

Answer 16

First - interventricular septum depolarises from left to right
Second - bulk of the ventricle depolarises from the endocardial to the epicardial surface
Third - upper part of interventricular septum depolarises

Question 17

What is the QT interval? What does this vary with and what is the normal value?

Answer 17

Time spent while ventricles are depolarised
Varies with heart rate
Normally about 0.42 seconds at a heart rate of 60 bpm

Question 18

How can you calculate the heart rate from the rhythm strip of an ECG?

Answer 18

Measure R-R interval and work out how many occur in 60 seconds
or
Count the R waves in 30 large squares (6 seconds) and multiply by 10

Question 19

What are the things to look for in the rhythm strip of an ECG?

Answer 19

Is each QRS complex preceded by a P wave?
Is the PR interval too short or too long (<0.12 or > 0.2 seconds)?
Is the QRS complex too wide (>0.08 seconds)?
Is the QT interval too long (>0.42 seconds at 60bpm)?

Question 20

What is the normal heart rate and what are bradycardia and tachycardia?

Answer 20

Normal is 60-100bpm
Bradycardia < 60bpm
Tachycardia > 100bpm

Question 21

What is the difference between STEMI and NSTEMI?

Answer 21

STEMI shows elevation of ST segment of the ECG and seems to be an indication of a more severe myocardial infarction (worse than NSTEMI)