ECG

Question 1

What is the myocardium?

Answer 1

A large mass of muscle

Question 2

What is the myocardium undergoing?

Answer 2

Electrical changes, all more or less at the same time

Question 3

What does the electrical changes going on in the myocardium generate?

Answer 3

A large, changing electrical field

Question 4

How can the electrical field produced by the myocardium be detected?

Answer 4

By electrodes on the body surface

Question 5

What do electrodes outside the cell record?

Answer 5

Only changes in membrane potential

Question 6

What do the skin electrodes ‘see’ with each systole?

Answer 6

Two signals, one depolarisation, one repolarisation

Question 7

How does excitation spread over the myocardium?

Answer 7

Due to the interlinking of cardiac myocytes by gap junctions

Question 8

What does the spread of excitation spreading over the myocardium generate?

Answer 8

A changing signal, which the electrodes detect

Question 9

Why do we need gap junctions?

Answer 9

To produce coordinated depolarisation, and therefore coordinated contraction

Question 10

What do gap junctions allow?

Answer 10

A pause before the ventricles contract after the atria contract

Question 11

What is the importance of the pause before ventricles contract?

Answer 11

It allows for a more rapid spread through the myocytes, so more of the tissue is contracting at once

Question 12

How is the ECG explained?

Answer 12

By a combination of the effects of depolarisation and repolarisation, and their spread over the heart

Question 13

What is the starting point in conduction of the heart?

Answer 13

SA node

Question 14

What is the passage of conduction through the heart?

Answer 14

SA node → internodal tracts → AV node → Bundle of His → Left bundle branch and right bundle branch → Purkinje fibres

Question 15

Where are the internodal tracts?

Answer 15

Between the nodes

Question 16

What do the internal tracts throw off?

Answer 16

An extra limb of depolarisation by Bachmanns bundle

Question 17

What does Bachmanns bundle allow for?

Answer 17

Smooth contraction of the atria

Question 18

What does the AV node do?

Answer 18

Holds everything for a moment so there is a pause in the signal to allow all of the atria to contract

Question 19

What is the Bundle of His needed for?

Answer 19

Depolarisation to travel through to get the ventricles

Question 20

How are the atria and ventricles related electrically?

Answer 20

They are separate, apart from through the bundle of His

Question 21

What will electrical non-seperation cause of the atria and ventricles cause?

Answer 21

Problems

Question 22

How does the left bundle branch differ from the right bundle branch?

Answer 22

It is fractionally faster

Question 23

Why is the left bundle branch slightly faster than the right bundle?

Answer 23

Because the left ventricle is larger than the right

Question 24

Where does the left bundle branch reach?

Answer 24

The apex of the left ventricle

Question 25

What does the right bundle branch do?

Answer 25

Feeds the signal to the right ventricle

Question 26

What is the result of the left and right bundle branches reaching the apex of heart?

Answer 26

Blood is pumped out from the bottom upwards, so blood is pushed out through large vessels

Question 27

What do Purkinje fibres do?

Answer 27

Feed the rest of the myocardium

Question 28

How long is it before cells begin to repolarise?

Answer 28

About 280ms

Question 29

How does repolarisation spread?

Answer 29

In the opposite direction to depolarisation over the ventricles

Question 30

What repolarises first?

Answer 30

Epicardial (outer) surface

Question 31

How do left ventricles contract?

Answer 31

In a cork screw way

Question 32

How do atria contract?

Answer 32

Like fists

Question 33

What is the advantage of the ventricular method of contraction?

Answer 33

It is more efficient and forceful

Question 34

How many electrodes are attached in the ECG?

Answer 34

10

Question 35

How many leads are there in the ECG?

Answer 35

12

Question 36

In what planes is the heart inspected in the ECG?

Answer 36

Frontal  | Horizontal

Question 37

What are the types of leads in the ECG?

Answer 37

Unipolar  | Bipolar

Question 38

What leads are unipolar?

Answer 38

Chest leads (V1-V6) and augmented leads (AVR, AVL, AVF)

Question 39

How do unipolar leads read?

Answer 39

From labelled positive electrode, and utilise several other electrodes as the negative

Question 40

What are the bipolar leads?

Answer 40

I, II, III

Question 41

What do bipolar leads use?

Answer 41

One positive and one negative electrode from the standard limb leads

Question 42

What makes up Einthoven’s triangle?

Answer 42

Lead I, II and III

Question 43

Where is lead I positioned?

Answer 43

From the negative electrode on the right arm to the positive electrode on the left arm

Question 44

What is the purpose of lead I?

Answer 44

It is the ‘seeing’ electrode- the field of view

Question 45

Where is lead II positioned in Einthovens triangle?

Answer 45

Goes from negative electrode on right arm to positive electrode on left leg

Question 46

Where is lead III positioned in Einthovens triangle?

Answer 46

Goes from positive electrode on left leg to negative electrode on left arm

Question 47

Where does lead III look?

Answer 47

From the left up, looking through the apex of the heart

Question 48

Why is lead III the favourite lead?

Answer 48

Because it looks through the apex of the heart, and therefore good for looking the rhythm of heart

Question 49

Where are limb leads placed?

Answer 49

Can be anywhere along extremities, but best over bones

Question 50

Why are limb leads bess places over bones?

Answer 50

Because less distraction of signals

Question 51

What does depolarisation moving towards an electrode lead to?

Answer 51

Positive deflection from the baseline

Question 52

What does depolarisation moving away from an electrode lead to?

Answer 52

Negative deflection from the baseline

Question 53

What does repolarisation moving towards an electrode lead to?

Answer 53

A negative deflection from the baseline

Question 54

What does repolarisation moving away from an electrode lead to?

Answer 54

Positive deflection from baseline

Question 55

Why does repolarisation cause a negative deflection when it’s moving towards you?

Answer 55

Because repolarisation is negative

Question 56

What happens as an electrode is moved in relation to the heart?

Answer 56

It ‘sees’ a different deflection from the baseline

Question 57

What will be seen if the current is moving directly towards the electrode?

Answer 57

A big spike

Question 58

What will be seen if the current is passing near to the electrode?

Answer 58

There will be a peak/trough, but doesn’t have the same magnitude- will be a small change

Question 59

What happens to deflection as you move the electrode around the heart?

Answer 59

It changes whether there is positive or negative deflection

Question 60

What does the amplitude of a signal depend on?

Answer 60

How much muscle is depolarising  | How directly towards the electrode the excitation is moving

Question 61

How do different portions of the hear give different amplituded waves?

Answer 61

They have smaller or larger amounts of muscle

Question 62

What causes the P wave?

Answer 62

Atrial depolarisation

Question 63

What causes the Q wave?

Answer 63

Septal depolarisation spreading to ventricle

Question 64

Do we always see the Q wave?

Answer 64

No

Question 65

What causes the R wave?

Answer 65

Main ventricular depolarisation

Question 66

What causes the S wave?

Answer 66

End ventricular depolarisation

Question 67

What causes the T wave?

Answer 67

Ventricular depolarisation

Question 68

What are the confounders to ECG readings?

Answer 68

Lead misplacement Muscle contraction  Interference Poor electrode contact

Question 69

How can you tell if leads are placed wrong?

Answer 69

You get a completely wrong picture

Question 70

What may cause confounding muscle contraction?

Answer 70

Movement Shivering Talking  Coughing

Question 71

What can interfere with the ECG?

Answer 71

Alternating current from too close equipment

Question 72

What can cause poor electrode contact?

Answer 72

Sweat Cable pull Hair