First look at the ECG

Question 1

What does ECG stand for

Answer 1

Electrocardiogram

Question 2

What are the main groups of leads used in an ECG?

Answer 2

Standard limb leads

Augmented limb leads

Precordial (chest) leads

Question 3

What do the standard limb leads do?

Answer 3

look at events in the vertical, or frontal, plain

Question 4

What possible pairs of electrodes can be recorded using standard limb leads?

Answer 4

SLL 1 - left arm with respect to right arm

SLL 2 - Left leg with respect to right arm

SLL 3 - left leg with respect to left arm

Question 5

What are standard limb leads good/bad at measuring?

Answer 5

Fast events, eg depolarisation and repolarisation of the AP, are transmitted well

Slow events, eg the plateau of the AP, are not

Question 6

In a standard limb lead test

A wave of approaching depolarisation causes what to show up?

Answer 6

Upward-going blip

Question 7

SLL readings are basically to do with the difference in potential between the two electrodes

Describe how a difference in potential is created & measured in an SLL 2 reading

Answer 7

Main wave of depolarisation passes down the ventricles and through the body fluids towards the electrode on the left leg

Downwards moving depolarisation creates a positive potential relative to the electrode on the right arm

Question 8

A wave of depolarisation moving away from one electrode will cause what reading on the other?

What shaped ‘blip’ will this create?

Answer 8

Positive potential

The shape of the blip will depend on which electrode is measuring with respect to the other

^so you cant tell whether the blip will be up or down

Question 9

In basics

What ‘charge’ is depolarisation and repolarisation?

Answer 9

Depolarisation is Negative

Repolarisation is positive

Question 10

A wave of repolarisation will cause what potential at the opposite electrode?

Answer 10

Negative potential

Question 11

What are the different waves on an ECG?

Answer 11

P wave

QRS complex

T wave

Question 12

What causes the P wave?

Answer 12

Atrial depolarisation

Question 13

What causes the QRS complex?

Answer 13

Ventricular depolarisation

Question 14

What causes the T wave?

Answer 14

Ventricular repolarisation

Question 15

What is the PR interval?

Answer 15

Time from atrial depolarisation to ventricular depolarisation

Question 16

What node is associated with the PR interval?

Answer 16

Atrioventricular

Question 17

What is the normal value for the PR interval?

Answer 17

0.12 - 0.20 sec

Question 18

What does the QRS value tell you?

Answer 18

Time for the whole pf the ventricle to depolarise

Question 19

What is a normal value for the QRS time?

Answer 19

0.08 s

Question 20

WHat is the QT interval?

Answer 20

Time spent when ventricles are depolarised

Question 21

At 60 bpm, what is the normal value for the QT interval?

Answer 21

0.42 s

Question 22

Why isnt atrial repolarisation visible on the ECG?

Answer 22

coincides with ventricular depolarisation

VD has a much larger amount of tissue depolarising faster so gives a big boi wave

Question 23

Explain what causes the individual peaks on the QRS complex

Answer 23

Q - the interventricular septum depolarises from left to right

R - the bulk of the ventricle depolarises from the endocardial to the epicardial surface

S - the upper part of the interventricular septum depolarises

Question 24

If the T wave is caused by ventricular repolarisation

Why is it positive going?

(in SLL 2)

Answer 24

Action P is longer in ENDOcardial cells than in EPIcardial cells

Wave of repolarisation runs in opposite direction to the Depol wave - it moves AWAY from the recording electrode

Repol wave moving AWAY = positive blip

Question 25

What is the main difference between an SLL 1, 2 & 3 graph?

Answer 25

SLL 2 has the largest waves

Its a more jaggy line

Question 26

What causes the difference in R-wave size in SLL 2, compared to SLL 1 & 3?

Answer 26

In an SLL 2, the main vector of depolarisation is in line with the axis of recording from the left leg with respect to the right arm.

Basically, the wave is shot directly at the electrode in the left leg

Question 27

What extra information does augmented limb leads give you?

Answer 27

By recording from one limb lead with respect to the other two combined, it gives you 3 other perspectives on events in the heart

Question 28

What is the benefit of using both standard LLs and augmented LLs?

Answer 28

recordings from SLLs I, II, III and aVR, aVL, aVF give you 6 different
views of events occurring in the frontal (or vertical) plane

Question 29

What is the function of precordial leads?

Answer 29

These are arranged in front of the heart and therefore look at the same events, but in the horizontal (or transverse) plane

Question 30

How many chest leads are used in precordial measurement?

Answer 30

6

V1, 2, 3 etc - 6

Question 31

Explain what causes ‘Progression’ in precordial chest lead measurement?

Answer 31

Chest leads arranged in front of heart

Main vector of depol wave travels to V6

This causes a +ve blip at V6 and a -ve blip at V1

As you progress through the individual electrodes, there will be a point (V3/V4) where the blip flips

Question 32

What plane do the limb leads measure in?

Answer 32

Frontal

Question 33

What plane do chest leads measure in?

Answer 33

Transverse

Question 34

Describe how the Rhythm strip should ‘run’

Answer 34

25mm/sec

Calibrating pulse is 0.2 sec = 1 large square (5mm)

Question 35

What is the name for an abnormally low heart rate?

Answer 35

Bradycardia

< 60 bpm

Question 36

What is the name for an abnormally rapid heart rate?

Answer 36

Tachycardia

> 100 bmp

Question 37

What is STEMI?

Answer 37

ST elevated myocardial infarction

Question 38

What is NSTEMI?

Answer 38

Non-ST elevated myocardial infarction

Question 39

What does STEMI look like on an ECG?

Answer 39

ST portion abnormally high

QRS goes up then only comes down a little bit

Question 40

Which is worse, STEMI or NSTEMI?

Answer 40

STEMI is worst