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ESA 2- Cardiovascular System > ECG > Flashcards

Flashcards in ECG Deck (72)
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1

What is the myocardium?

A large mass of muscle

2

What is the myocardium undergoing?

Electrical changes, all more or less at the same time

3

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

A large, changing electrical field

4

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

By electrodes on the body surface

5

What do electrodes outside the cell record?

Only changes in membrane potential

6

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

Two signals, one depolarisation, one repolarisation

7

How does excitation spread over the myocardium?

Due to the interlinking of cardiac myocytes by gap junctions

8

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

A changing signal, which the electrodes detect

9

Why do we need gap junctions?

To produce coordinated depolarisation, and therefore coordinated contraction

10

What do gap junctions allow?

A pause before the ventricles contract after the atria contract

11

What is the importance of the pause before ventricles contract?

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

12

How is the ECG explained?

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

13

What is the starting point in conduction of the heart?

SA node

14

What is the passage of conduction through the heart?

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

15

Where are the internodal tracts?

Between the nodes

16

What do the internal tracts throw off?

An extra limb of depolarisation by Bachmanns bundle

17

What does Bachmanns bundle allow for?

Smooth contraction of the atria

18

What does the AV node do?

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

19

What is the Bundle of His needed for?

Depolarisation to travel through to get the ventricles

20

How are the atria and ventricles related electrically?

They are separate, apart from through the bundle of His

21

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

Problems

22

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

It is fractionally faster

23

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

Because the left ventricle is larger than the right

24

Where does the left bundle branch reach?

The apex of the left ventricle

25

What does the right bundle branch do?

Feeds the signal to the right ventricle

26

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

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

27

What do Purkinje fibres do?

Feed the rest of the myocardium

28

How long is it before cells begin to repolarise?

About 280ms

29

How does repolarisation spread?

In the opposite direction to depolarisation over the ventricles

30

What repolarises first?

Epicardial (outer) surface