CVS - Cardiac Cycle

Question 1

What does the myocardium consist of?

Answer 1

Individual specialised cells joined by low electrical resistance connections

Question 2

What is the contraction on each cell produced by?

Answer 2

Action potential - A rise in intracellular calcium triggered by an all or none electrical event in the cell membrane

Question 3

What produces the action potential in the heart? And where is it located?

Answer 3

Sino-atrial node - specialised pacemaker cells

Right atrium

Question 4

What is the period when the myocardium is contracting and relaxing?

Answer 4

Contracting - systole (1/3rd of time)

Relaxation between contractions = diastole (2/3rd of time)

Question 5

What is the cardiac cycle? How many stages are there?

What is the total duration?

Answer 5

Sequence of pressure flow changes and valve operations that occur with each heartbeat
7 stages
0.9 seconds

Question 6

What are the valves between the atrium and ventricle?

Answer 6

Right side = Tricuspid

Left side = Mitral

Question 7

Name the outflow valves

Answer 7

Aortic and pulmonary valves

Question 8

What is cardiac output?

Answer 8

Volume pumped per minute by the left heart

Pumping is intermittent it is the product of the volume ejected per cardiac cycle (stroke volume) and number of cycles per minute (heart rate).

Question 9

What is stroke volume?

What is it on an average person?

Answer 9

How much each ventricle pumps at rest

70ml blood per beat

Question 10

What do cells contract in response too?

Answer 10

Action potential in membrane which causes rise in intracellular calcium

Question 11

What do the valves open or close dependent on?

Answer 11

Pressure on each side

Question 12

What do valves have to prevent back flow?

Answer 12

Cusps

Question 13

What prevents inversion of valves on systole?

Answer 13

Cusps of mitral and tricuspid valves attach to papillary muscles via chordae tendineae

Question 14

How long is the delay after the action potential reaches the atrioventricular node?

Answer 14

120 ms

Question 15

What direction does the action potential spread in the ventricular myocardium?

What direction does the ventricle contract from?

Answer 15

Endocardial (inner) to epicardial (outer)

Apex up forcing blood through outflow valves

Question 16

What is a wiggers diagram?

Which side of heart is it typically plotted for?

Answer 16

Allows us to plot changes that occur in pressure with time

Typically plotted for left side of heart

Question 17

What is the A wave in cardiac cycle?

Answer 17

Atrial pressure rising due to atrial systole

Question 18

Describe the pressure and volume changes in atrial contraction.

What valves are open/closed?

Answer 18

Atrial pressure increase
Ventricular volume increase

Provides the last 10-20% of blood to fill ventricles

Tricuspid/mitral valve - open
Aortic/pulmonary valve - closed

Question 19

What does the P wave in an ECG represent?

Answer 19

Onset of atrial depolarisation

Question 20

What happens in phase 2 of cardiac cycle, isovolumetric contraction (ventricle start to contract?

Answer 20

Mitral valve closes. Closing of mitral valve = C wave
Isometric volume (no change in volume) as all valves closed
Rapid rise in ventricular pressure

Question 21

What does the first heart sound signify?

Answer 21

Closing of mitral and tricuspid valves

Question 22

What signifies the onset of ventricular depolarisation in ECG?

Answer 22

QRS complex

Question 23

What happens during rapid ejection? Phase 3 of cardiac cycle

What are the state of the valve?

Answer 23

Intraventricular pressure exceeds that of aorta causing aortic valve to open
Atrial pressure initially decreases as atrial base pulled downward as ventricle contracts (X descent)
Rapid decrease in ventricular volume

Mitral/tricuspid - closed
Aortic/pulmonary - open

Question 24

Why does the rate of ejection fall in the ventricles during ‘reduced ejection’ phase 4?

What wave on ECG depicts ventricle reploarisation?

What happens to atrial pressure?

Answer 24

Ventricle is repolarised which leads to decline in tension and rate of ejection begins to fall

T wave

Gradually rises due to continued venous return (V wave).

Mitral/tricuspid valve - closed
Aortic/pulmonary valve - open

Question 25

What halogens in phase 5 of cardiac cycle isovolumetric relaxation?

Are valves open/closed?

Answer 25

Intraventricular pressure falls below aortic pressure, brief back flow of blood which causes aortic valve to close

Rapid decline in ventricular pressure. Volume remains constant since all valves are closed

Mitral/tricuspid - closed
Aortic/pulmonary - closed

Question 26

What causes the dicrotic notch in aortic pressure curve?

Answer 26

Valve closure

Question 27

How do you calculate end stroke volume?

Answer 27

End diastolic volume - end systolic volume

Typically 70/80ml

Question 28

What gives you the second heart sound?

Answer 28

Closure of aortic and pulmonary valves

Only CLOSURE of valves gives heart sounds

Question 29

What causes the Y descent in atrial pressure during phase 6 of cardiac cycle. Rapid filling stage.

What must occur for mitral valve to open?

Answer 29

Fall in atrial pressure that occurs after mitral valve has opened

Intraventricular pressure must fall below atrial pressure and ventricle begins to fill

Mitral/tricuspid valve - open
Aortic/pulmonary valve - closed

Question 30

What is the third heart sound occasionally heard?

Answer 30

Filling of ventricles - which is normally silent

Children - normal
Adults - can be a sign of pathology

Question 31

What is phase 7 of cardiac cycle?

Answer 31

Reduced filling - rate of ventricular filling slows down (diastasis) as ventricle reaches inherent relaxed volume
Further filling driven by venous pressure
Ventricles are 90% full by end of phase 7

Mitral/tricuspid valve - open
Aortic/pulmonary valve - closed

Question 32

Where does the right and left heart pump blood to?

Answer 32

Right - Lungs (pulmonary circulation)

Left - Body (systemic circulation)