Heart form and structure; related to function

Question 1

Functions of the heart

Answer 1

1. Pump - aim is to get blood where it needs to go
2. Receive and deliver blood
3. Pulmonary and systemic circulations

Question 2

R heart vs left wall and trabeculations

Answer 2

R heart more trabeculae and thinner walled

Question 3

Apex movement in contraction

Answer 3

Fixed point over whole of cardiac cycle

Question 4

% wall thickening

Answer 4

40%

Question 5

% longitudinal shortening

Answer 5

20%

Question 6

Degree of rotation at base

Answer 6

clockwise

Question 7

Degree of rotation at apex

Answer 7

anticlockwise

Question 8

Components of pump function

Answer 8

• Atrial component
• LV wall thickening
• LV longitudinal shortening
• LV torsion
• LV rotation

Question 9

What is torsion?

Answer 9

Because there is opposing rotations, you get torsion which is actually a net motion of the heart in one direction. Not routinely measured

Question 10

Net degree of torsion of heart

Answer 10

ANTICLOCKWISE

Question 11

What is EF?

Answer 11

Stroke volume/EDV X 100

Question 12

Assessors of cardiac function

Answer 12

EF!! main one

• Cardiac index
• Dp/dt
• Strain
• MAPSE
• Torsion
• MV E and e’
• CO

Question 13

What is cardiac index

Answer 13

Cardiac index = CO/body surface area

Question 14

What is dp/dt

Answer 14

change in pressure over change in time

• Good way of getting insight into how heart works because heart needs to generate pressure to get blood to leave and also needs to get blood to fill
• Can assess invasively or through echo doppler

Question 15

What is strain?

Answer 15

Way of measuring proportional change in a dimension
- LV gets 40% thicker gives a strain of 0.4
- Longitudinal strain will be -0.2
- Circumferential strain also gets smaller
Can use in cardiac oncology clinic when giving drugs that can be cardiotoxic. If strain is a bit decreased, they may be more suseptible to cardiotoxic effects

Question 16

What is MAPSE?

Answer 16

mitral annular plane systolic excursion

Can measure base moving down from diastole to systole by putting cursor on annulus - is about 12cm at mitral annulus

Question 17

What is MV E and e’?

Answer 17

Gives a sense of filling of the heart

Measuring speed of flow into LV and use tissue doppler to assess annular movement too

Question 18

3 limitations of EF in assessing cardiac function

Answer 18

1. HF with preserved EF: often to do with diastolic because EF tells you about systolic
2. Hypertrophic cardiomyopathy: Have small LV so only need to get a little bit of blood out to get reasonable EF
3. Mitral regurgitation: When you look at EF - it can be misleadingly normal or reassuringly high. This is because you assume that SV is going somewhere useful but with MR - not all of it will go into blood/body. Some of it will go straight through mitral valve and back into the left atrium. Therefore, EF gives a false sense of heart function.

Question 19

Myocyte orientation

Answer 19

Epicardium - left handed helical arrangement
Mesocardium - circumferential
Endocardium - right handed helical arrangement

Question 20

What is laminar structure of myocytes called?

Answer 20

Sheetlets

Question 21

How many bundles form sheetlets?

Answer 21

6-8

Question 22

How much does each myocyte thicken by and how much does wall thicken?

Answer 22

Myocyte - 10%
Wall - 40%
Discrepancy

Question 23

How is discrepancy between myocyte and wall thickening explained?

Answer 23

Sheetlets - In diastole, roughly upright but in systolic phase, they are reorientated to a more perpendicular orientation
- So not only are myocytes getting thicker but sub structures are shearing, sliding, reorientating over one another

Question 24

Sheetlets in HCM

Answer 24

stuck in systolic perpendicular orientation and then they just get a little flatter in diastole so mobility is reduced here
Strain is reduced because they don’t proportionately increase wall thickness that much
But EF is normal
many sarcomere mutations occur so calcium handling becomes abnormal and myocytes are in hypercontracted state

Question 25

Sheetlets in HCM

Answer 25

Able to reorientate themselves to a more wall perpendicular orientation and not able to achieve normal systole

Question 26

Epicardium base and apex rotation viewed from apex

Answer 26

Apex: Anticlockwise
Base: Clockwise

Question 27

Endocardium base and apex rotation viewed from apex

Answer 27

Apex: Clockwise
Base: Anticlockwise

Question 28

Volume pressure loop summary from mitral valve closure

Answer 28

Start at mitral valve closure at ED.
Period of straight up pressure without volume change. Then aortic valve will open and blood will exist so pressure drops. Then you hit point of end systolic pressure volume relationship where aortic valve has closed, volume inside ventricle is at it’s smallest. There is a rapid drop in pressure as not much blood in there. Invite blood to enter venrticle
Takes us on to filling of the heart

Question 29

LVV and LVP over time

Answer 29

ED start and M is for mitral valve closing. Blood has come into LV and will have a period of isovolumic contraction as all valves shut. Causes sharp increase in pressure but no real change in volume.
Then aortic valve will open as pressure in ventricle exceeded pressure on other side of valve and get contractile push. As blood leaves, volume f blood in LV drop.
At a certain point, pressure on other side of valve will exceed ventricle and valve will close. Then period of relaxation - untwist. The valves all shut so isovolumic and then mitral valve opens and get suction effect and will start again