Heart form and structure; related to function Flashcards
Functions of the heart
- Pump - aim is to get blood where it needs to go
- Receive and deliver blood
- Pulmonary and systemic circulations
R heart vs left wall and trabeculations
R heart more trabeculae and thinner walled
Apex movement in contraction
Fixed point over whole of cardiac cycle
% wall thickening
40%
% longitudinal shortening
20%
Degree of rotation at base
clockwise
Degree of rotation at apex
anticlockwise
Components of pump function
- Atrial component
- LV wall thickening
- LV longitudinal shortening
- LV torsion
- LV rotation
What is torsion?
Because there is opposing rotations, you get torsion which is actually a net motion of the heart in one direction. Not routinely measured
Net degree of torsion of heart
ANTICLOCKWISE
What is EF?
Stroke volume/EDV X 100
Assessors of cardiac function
EF!! main one
- Cardiac index
- Dp/dt
- Strain
- MAPSE
- Torsion
- MV E and e’
- CO
What is cardiac index
Cardiac index = CO/body surface area
What is dp/dt
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
What is strain?
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
What is MAPSE?
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
What is MV E and e’?
Gives a sense of filling of the heart
Measuring speed of flow into LV and use tissue doppler to assess annular movement too
3 limitations of EF in assessing cardiac function
- HF with preserved EF: often to do with diastolic because EF tells you about systolic
- Hypertrophic cardiomyopathy: Have small LV so only need to get a little bit of blood out to get reasonable EF
- 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.
Myocyte orientation
Epicardium - left handed helical arrangement
Mesocardium - circumferential
Endocardium - right handed helical arrangement
What is laminar structure of myocytes called?
Sheetlets
How many bundles form sheetlets?
6-8
How much does each myocyte thicken by and how much does wall thicken?
Myocyte - 10%
Wall - 40%
Discrepancy
How is discrepancy between myocyte and wall thickening explained?
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
Sheetlets in HCM
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
