CVS 3 - Mechanical properties of the heart 2

Question 1

What are the two main phases of the heart beat?

Answer 1

Systole - 2 subparts

Diastole - 4 subparts

Question 2

State the phases of the cardiac cycle

Answer 2

(Diastole)
1. Slow filling (of atria and ventricules, AV valves opened)
2. Atrial systole
(Systole)
3. Isovolumetric ventricular contraction -
(unchanged volume, all valves closed isometric contraction)
4. Ventricular ejection - semilunar open
(Diastole) - rapid ejection + reduced ejection
5. Isovolumetric ventricular relaxation
6. Rapid filling then back to reduced filling (step 1)

Question 3

What happens during slow ventricular filling?

Answer 3

Phase: Atria and ventricles relaxed, blood filling ventricles slowly
Valves: AV open, semilunar closed

Question 4

What happens during atrial systole?

Answer 4

Phase: Atria contract, top off ventricles with blood
Valves: AV open, semilunar closed
P wave: atrial depolarisation

S4: Abnormal heart sound

Question 5

What happens during isovolumetric ventricular contraction?

Answer 5

Phase: Contraction of ventricles with no change in volume
Valves: AV closes as pressure in ventricles exceeds atria
QRS: Ventricular depolarisation
S1: “lub” from the closure of the AV valves

Question 6

What happens during ventricular ejection (aka ‘rapid ejection’ + ‘reduced ejection’)?

Answer 6

Rapid ejection:
Phase: Ventricles contract –> pressure within exceeds aortic and pulmonary artery
Valves: Semilunar open –> blood leaves heart
RV contraction pushes tricuspid valve into atrium –> creates wave in jugular vein – “C” wave
The ventricular pressure exceeds the aortic and pulmonary pressures so the aortic and pulmonary valves open and blood rapidly flows out into the aorta and pulmonary artery.

Then reduced ejection:
Phase: Blood flow from ventricles decreases
Valves: SL BEGIN to close because blood starting to flow back from arteries due to lower ventricular pressure
T wave: Ventricular repolarisation
Marks the end of systole. Ventricular pressure begins to fall
T wave on the ECG due to the repolarisation of the ventricles. There are NO heart sounds because none of the valves are shutting.

Question 7

What happens during isovolumetric ventricular relaxation?

Answer 7

Phase: Atria filling with blood
Valves: SL shut, AV shut (Shutting of atrial valve creates dichrotic notch in atrial reading)
S2: “dub” from SL valves closing

Question 8

What happens during rapid ventricular filling?

Answer 8

Phase: Ventricles filling
Valves: AV valve open
S3: Abnormal, due to mitral incompetence

Question 9

What is ejection fraction?

Answer 9

SV/EDV - the proportion of the blood in the heart that is pumped out in one contraction

Question 10

What ECG change is seen in atrial systole?

Answer 10

P wave - atrial depolarisation

Question 11

What abnormal heart sound could be heard during atrial systole and what could it be a result of?

Answer 11

S4 - this could be due to tricuspid incompetence, pulmonary embolism or congestive heart failure

Question 12

How does atrial pressure change during atrial contraction?

Answer 12

Atrial pressure shows a small increase - a wave

Question 13

Describe the pressure and volume changes that take place during isovolumic contraction.

Answer 13

The valves are all closed so there is no change in volume but the pressure increases dramatically.

Question 14

What heart sound will be heard during isovolumic contraction?

Answer 14

S1 - closing of the atrioventricular valves

Question 15

What ECG change is seen during isovolumic contraction?

Answer 15

QRS complex - ventricular depolarisation

Question 16

Describe the electrical activity and heart sound heard during rapid ejection.

Answer 16

There is no electrical activity - isoelectric line on ECG. No heart sounds are heard.
Depolarisation of heart happens before this

Question 17

What is the dichrotic notch and when does it occur?

Answer 17

The dichrotic notch is caused by the elastic recoil of the aorta causing a small rise in aortic pressure once ventricular contraction has ended.

Question 18

What changes in pressure occur during isovolumic relaxation?

Answer 18

The atrial pressure increases due to the filling against closed valves - v wave. Volume of the ventricles does not change. (the AV and SL valves are closed)

Question 19

What heart sound can be heard during isovolumic relaxation?

Answer 19

S2 - this is due to the shutting of the aortic and pulmonary valves

Question 20

What changes in volume and pressure take place during rapid ventricular filling?

Answer 20

There is a gradual increase in ventricular volume but ventricular pressure remains about the same. Atrial pressure decreases. This is just before reduced filling then atrial systole

Question 21

What abnormal heart sound can be heard during rapid ventricular filling and what could it be a result of?

Answer 21

S3 usually abnormal and can signify turbulent ventricular filling
Can be due to severe HT or mitral incompetence

Question 22

What diagram can show all this information?

Answer 22

Wiggers diagram

Question 23

What is the normal pressure in the pulmonary circulation?

Answer 23

25/5 mmHg

Question 24

What do points 1-4 on the pressure-volume loop indicate?

Answer 24

1 - EDV
2 - Aortic pressure encountered –> pressure has been build up but same volume
3 - ESV –> pressure is the same, lower volume
4 - same volume (low) and smaller pressure
Then heart fills again but same pressure and no contraction so this is EDV then contracts blabla pressure increases but same volume (2) etc.
In clinic this is used to see how heart is working, in transplants for example.

Question 25

Which feature of the pressure-volume loop indicates stroke volume?

Answer 25

The length between point 3 and 2 ie between just before contraction so max volume and just after systole - ESV so volume that stayed in ventricles.
pressure is the same and volume has been ejected so the difference in volume in the heart is the volume ejected so stroke volume

Question 26

Which points on the pressure-volume loop indicate preload and afterload?

Answer 26

Afterload is after point 2 as it is when the aortic pressure is encountered
Preload is point 1 as point 1 is EDV

Question 27

What effect do preload and afterload have on pressure-volume loops?

Answer 27

If preload increases, diagram becomes larger on the right –> because SV increases
If afterload increases, diagram becomes thinner on the left –> because SV decreases (point 1 remains the same as EDV is the same)

Question 28

What effect do afterload and preload have on stroke volume?

Answer 28

Afterload decreases SV as the more afterload there is, the greater the pressure you have to work against
Preload increases SV
This will have an effect on CO

Question 29

What is contractility? What is its effect on the pressure volume loop?

Answer 29

It is the contractile capability of the heart.
Measure of contractility is ejection fraction.
Contractility is increased during sympathetic stimulation so during exercise.
This will make the pressure volume loop wider ! (also the fact that EDV changes with exercise because of changes in peripheral circulation - vasoconstriction - venous return is bigger)