2. Anatomy of the normal mitral valve
The whole valve is like an apparatus, made up
of two leaflets suspended by about 120
chordae tendinae to two papillary muscles.
The valve is located between the LA and LV and
projects into the LV.
It is essential to note that the whole apparatus
should function properly in order that the valve
functions properly.
3. It is a bicuspid valve.
There are two leaflets- anterior mitral
leaflet(AML) and posterior mitral leaflet(PML).
The PML has 3 scallops and are named P1,P2,
and P3.
The corresponding areas of the AML are known
as A1,A2 and A3, though they do not have any
scallops.
5. The normal valve has an orifice of 4-6 square
cms.
The valve functions as a door, allowing the entry
of blood into the left ventricle during diastole
and closing appropriately during systole to
prevent the back flow of blood.
6. In mitral stenosis, the valve orifice becomes less
than the normal size.
Minimal mitral stenosis is valve orifice>2.5 sq cm
Mild- 1.4-2.5sq cm
Moderate- 1.0-1.4 sq cm
Severe- <1.0 sq cm
7. So when the valve orifice is stenosed,there is
obstruction to flow of blood from the LA to the
LV.
Whenever there is stenosis in the valves, there
is development of a hemodynamic entity
called pressure gradient.
What is pressure gradient?
8. In stenosis the pressure in the upstream
chamber(LA) is really higher than the pressure
in the downstream chamber(LV) during flow of
blood from LA to LV because the LA tries very
hard to empty its blood into the LV.
This is called a pressure gradient.
The mitral valve orifice area and the pressure
gradient are inversely related to each other.
So if valve area decreases, the pressure
gradient increases and if valve area increases,
the pressure gradient decreases.
9. The pressure gradient also depends on the flow
rate of blood through the chamber.
For a normal valve, as the flow rate increases(as
in tachycardia due to exercise) the pressure
gradient also increases, but only to a little extent.
However in a stenosed valve, the pressure
gradient increases to a greater degree with the
increase in the flow rate, and in severe stenosis,
a pressure gradient may be present even at rest.
10. Diastolic pressure gradient(mm hg)
Flow rate
ml/sec
The
numbers
0.5,1,2,3,4
and 6
indicate
the area of
the mitral
valve
orifice in sq
cm.
Hashed
area
shows
normal
flow rate.
11. In the previous slide a graphical
representation has been shown to describe
the relation between the pressure gradient
and flow rate.
It can be easily seen that for the valve having
area 6 sq cm, changes in flow rate have a
very mild effect on the pressure gradient.
However for the valve having area 0.5,even a
normal flow rate produces an appreciable
pressure gradient.
For valves having areas about 2-4sq cm, only
increase in the flow rate(exercise) produces a
significant increase in the pressure gradient.
12. Now due to the development of a pressure
gradient, the LA has to work really hard to keep
on pumping the blood and hence the LA pressure
gradually increases.
In the initial stages it might be only on exertion,
but later it might be elevated even at rest.
13. The elevated left atrial pressure is reflected on the
pulmonary veins resulting in pulmonary venous
hypertension and later pulmonary artery
hypertension.
Pulmonary artery hypertension can be of two
types, passive pulmonary hypertension(passive
backward transmission of the LA pressure) or it
can be of the reactive type, in which there is
reflex constriction of the pulmonary arterioles in
response to the elevated pulmonary vein pressure
and the LA pressure.
14. What are the consequences of this pulmonary
hypertension?
The main result is that it poses a great load to the
RV because it has to now, pump blood against
tremendous pressure continously, and hence after
some time the RV undergoes hypertrophy and
finally dilation.
15. What will happen if dilation occurs?
Normally the heart is elliptical in shape with a well
defined apex. This shape contributes a lot to the
contractile ability of the heart.
When dilation occurs, the shape of the heart
becomes more spherical and the apex is lost.
The apical shape of the heart allows maximum
shortening and lengthening of the muscle fibres
and allows maximum contraction. So if this shape
is lost contractile efficacy will be lost.
16. It is usually the spiral arrangement of the muscle
fibres that gives the blood a real push towards the
opposite side.
However when the original shape is lost, the
muscle fibres become more transverse and hence
the spiral shape is lost and so the ability of the
heart to push blood in a specific direction is
further decreased.
17. Can mitral stenosis cause tricuspid regurgitation?
Yes , sometimes due to RV dilation, the tricuspid
ring also gets dilated, due to the movement of the
papillary muscle towards the lateral wall of the
heart.
This type of regurgitation is called functional
regurgitation.
18. What about the LA?
LA undergoes dilation, and that is why it is more
prone to, atrial fibrillation and due to blood stasis,
it is prone to develop thrombi.
19. Will any problem arise with the LV?
The ejection fraction will reduce because there is
less amount of blood coming into the LV( there is
a decrease in the preload).
20.
21. The previous slide shows a flow chart of the
pressures of the various chambers of the heart.
In the first panel, there is no abnormality in the
valve and all the pressures are normal.
In panel2 the person has mitral stenosis and
passive pulmonary hypertension but no reactive
hypertension.
In panel3 the person has the same amount of
mitral stenosis as in panel2 but here reactive
pulmonary hypertension has developed.
