L5: The Cardiac Cycle

Question 1

What is the primary pacemaker of the heart?

Answer 1

Sinoatrial node (SA node)

Question 2

Where is the SA node located?

Answer 2

Top corner of the right atrium

Question 3

Function of the SA node

Answer 3

Generates an AP that causes the upper part of the heart to contract

Question 4

Define intrinsic pacemaker activity

Answer 4

Beats with a clock-like function & does not require any external stimulus to generate an AP

Question 5

What happens after the impulse arrives at the AV node?

Answer 5

Spreads down the specialist conducting tissue called Bundle of His

Question 6

Function of Bundle of His

Answer 6

Brings excitation to the top of the septum & through

Question 7

Name two branches in the Bundle of His

Answer 7

1) Right bundle branch
2) Left bundle branch

Question 8

Name of fibres that branch from the apex

Answer 8

Purkinje Fibres

Question 9

What does purkinje fibres do ?

Answer 9

Radiate out through the ventricular wall

Question 10

When does the heart not have its own intrinsic activity?

Answer 10

When excitation arrives at the muscle of the heart (atrium & ventricles)

Question 11

How is the atrial & ventricular AP characterised?

Answer 11

Having a flat stable resting membrane potential in between beats

Question 12

Which node of the heart has the fastest intrinsic rate?

Answer 12

SA node

Question 13

Define intrinsic rate

Answer 13

Rate at which the heart beats when all cardiac, neural & hormonal inputs are removed

Question 14

Role of SA node for being the fastest

Answer 14

Determines the rate of all other structures within the heart

Question 15

2nd fastest intrinsic rate

Answer 15

AV node

Question 16

3rd fastest intrinsic rate

Answer 16

Bundle of His

Question 17

Slowest intrinsic rate

Answer 17

Purkinje Fibre

Question 18

Define cardiac arrhythmias

Answer 18

When structures starts firing off at faster rates or at abnormal intervals

Question 19

Why is conduction from SA to the AV nodes relatively slow?

Answer 19

No specialised conducting pathways linking them

Question 20

What happens when the wave of excitation arrives at the AV node?

Answer 20

‘AV PAUSE’

Question 21

2 Importances of the AV pause

Answer 21

1) Prevents high heart rates being transmitted into the ventricles
2) Allow ventricles to fill before wave of excitation is passed from atria down to ventricle

Question 22

What happens in conditions like atrial fibrillation (AF)?

Answer 22

Atria beating too fast, resulting in ventricles not pumping properly

Question 23

Why do people live happily if they have lethal arrhythmia?

Answer 23

AV node filters out high frequencies because of AV pause, prevents high rates being transmitted from right atrium through to ventricles

Question 24

What does ECG stand for?

Answer 24

The Electrocardiogram

Question 25

Name the triangle that connects the shoulders to the groin?

Answer 25

Einthpoven's Triangle

Question 26

What does the ECG measure?

Answer 26

Electrical activity of the heart

Question 28

What is the first thing that is recorded in the ECG?

Answer 28

Wave of excitation arising in the SA node, the atrial depolarisation

Question 29

What happens after atrial depolarisation?

Answer 29

Wave of excitation moves down Hiss Bundle into the right/left bundle branches

Question 30

What happens during depolarisation of the septum (towards the atria)?

Answer 30

Wave of depolarisation moves down the Hiss Bundle into the right & left bundle

Question 31

Stage after depolarisation of the septum?

Answer 31

Depolarisation of the ventricles (towards apex)

Question 31

What happens during the depolarisation of the ventricles (towards apex) R STAGE ?

Answer 31

Wave of excitation moves down towards the apex of the heart & depolarises ventricular muscle

Question 32

What happens to the reading during R: depolarisation of the ventricles?

Answer 32

QR gives a big upward ascend

Question 32

Define isoelectric line

Answer 32

Baseline of an ECG tracing & denotes resting membrane potential

Question 33

What happens after the depolarisation of ventricles (towards apex)?

Answer 33

Depolarisation of ventricles (towards atria)

Question 34

What happens during the depolarisation of ventricles (towards atria) S PHASE ?

Answer 34

Wave of excitation turns around the tip of the apex & spreads back up the walls of right + left ventricle

Question 35

After the wave shoots to R, what does the S stage denote?

Answer 35

Wave coming down to the isoelectric line

Question 36

What happens after the depolarisation of the ventricles (towards atria) S STAGE ?

Answer 36

Repolarisation of the ventricles (towards endocardium)

Question 37

What happens during the repolarisation of the ventricles (towards endocardium) T STAGE ?

Answer 37

Wave of repolarisation brings a wave of negativeness through ventricle to give the repolarisation of the ventricle

Question 38

What is the duration of ventricular AP determined from?

Answer 38

Time of ventricular depolarisation to the end of the AP (T-wave)

Question 39

Why do we not see a wave of atrial repolarisation?

Answer 39

Atria repolarises when ventricular cells depolarises, so it is hidden & lost

Question 40

What does the PQ interval tell us?

Answer 40

How fast the wave of excitation spreads from the SA node to the AV node

Question 41

What is the PQ interval a measure of ?

Answer 41

Atrial conduction & AV nodal delay

Question 42

What is AV nodal delay?

Answer 42

Delays signal to ensure atria is empty of blood before contraction

Question 43

What is the AV block ?

Answer 43

If impulse is not passing through AV node properly

Question 44

What does QRS duration tell us ?

Answer 44

How fast wave of depolarisation spreads from top of ventricle down through ventricles

Question 45

What does it mean when the QRS duration is long?

Answer 45

Wave of excitation takes long to spread through ventricle

Question 46

Define ventricular conduction velocity

Answer 46

Speed at which electrical signal travels through heart muscle

Question 47

What does the QT interval useful for?

Answer 47

Index of AP duration

Question 48

Define diastole

Answer 48

Gap in between beats

Question 49

Define systole

Answer 49

Contractile phase

Question 50

Define isovolumic contraction

Answer 50

Contraction of a closed ventricle without a change in volume, pressure rises in ventricle

Question 51

Define ventricular ejection

Answer 51

When volume of blood is ejected out of LV

Question 52

Define dichotic notch

Answer 52

When aortic valve snap shuts when LV pressure is lower than aortic pressure

Question 53

When does mitral valves open?

Answer 53

When LV pressure is lower than LA pressure