Mitral Valve

Anatomy

The mitral apparatus consists of 3 elements: a ring, a veil made up of 2 valves and a under-valvular apparatus composed of the ropes and pillars.

the mitral ring :

The two mitral valves are fixed on a fibrous ring, of which the former part (the third of its circumference) corresponds to the insertion of the large valve, under the aortic ring and the posterior part (two thirds of its circumference) with insertion of the small valve. This last portion is mobile and corresponds to the part being able to dilate at the time of the cardiac diseases comprising a dilation of the left ventricle and that of the ring.

the valves :

The mitral valve comprises two valves: the large valve (or septal valve, or former layer) very mobile and the small valve (or parietal valve or posterior layer) which being used of butted for the large valve to ensure the coaptation and to allow the continence at the time of the contraction (Systole) ventricular. Two faces are distinguished: the higher or auricular face (i.e., giving on the left auricle) and the lower or ventricular face.

the under-valvular apparatus :

It consists of 2 muscular pillars and ropes . The elastic fabric ropes, made up (nonmuscular) connect the top of the pillars to the 2 valves. The primary education ropes fit on the free edge of the valves and the secondary ropes on the face lower (or ventricular) of the valves.

At the time of the diastole, in opened position, the mitral valve has an aspect of funnel, with a diameter of 32 mm on the level of the ring and of 26 mm on the level of the top of the valves.

Normal mitral surface is from 4 to 6 cm ² in the adult.

Physiology

The Diastole (or relaxation, in opposition to the systole=contraction) ventricular is separate in three phases according to the variation of its volume: successively, there is a short phase of isovolumetric relieving (ventricle of constant and minimal volume), a passive phase of filling of the ventricle and an active phase of filling by contraction of the auricles.

During the phase of isovolumic relieving, the valves aortic and mitral are closed: the pressure in the ventricle falls quickly. As soon as this pressure becomes lower than the auricular pressure, the mitral valve opens. The ventricle then fills quickly whereas the auricle is at rest (passive ventricular filling at the time of the diastole), then the filling slows down and finally occurs the contraction (systole) auricular (active filling).

This auricular systole all the more contributes to the filling that the heart rate is high. Its role is particularly important in the event of obstacle with the flow of blood flow between the auricles and the ventricles as at the time of the mitral contracting. In this last case, the mechanical obstacle is translated on the plan hemodynamic by the appearance of a gradient of diastolic pressure more important between the auricle and the left ventricle. This gradient is all the more high as valvular surface is low and all the more high as the flow crossing the sténosé opening is high the measurement of this difference in pressure between the left auricle and the left ventricle lasting the diastole thus allows to estimate the surface of the mitral valve by the Formule of Gorlin.

Roles of the mitral valve

The mitral valve with two quite distinct roles:

It ensures the permeability and the continence between the left auricle and the left ventricle at the time of the various movements of the cardiac revolution (Systole and Diastole).

It takes an active part in the left ventricular contraction thanks to the action of the muscular pillars and the ropes. Thus at the time of the contraction of the left ventricle, the muscular pillars prolonged by the ropes take support on the valves what increases the contractile effectiveness of the cardiac muscle.

The mitral valve ensures a role of non-return valve between the left auricle and the left ventricle, imposing an one way on the blood circulation. Thus on the level of the left heart at the time of a cardiac revolution, blood can normally pass from the left auricle towards the left ventricle then left ventricle towards the aorta.

A mitral valve normally functioning with thus for role to ensure the permeability and the auriculo-ventricular continence:

At the time of the ventricular Diastole (passive filling) then of the auricular systole (active filling), it must allow, by opening sufficient, the passage of the blood flow of the left auricle towards the left ventricle.

At the time of the ventricular Systole, it must prevent, while being closed again correctly, blood to pass in a retrograde way of the ventricle towards the auricle. The blood contained in the left ventricle having to be to expel towards the aorta through the aortic valve.

Techniques of exploration

The mitral valve is a fine and mobile structure and requiring consequently an important space-time definition for good being analyzed.

the Radiographie of the thorax does not make it possible to visualize the valves except if they are calcified. It makes it possible to see the repercussion of a valvular attack on the size of the cardiac cavities (modification of the size of the heart or its contours).
the Angiographie, by injection of a product of contrast directly in the left ventricle, is a invasive Examen. It does not make it possible to visualize the valve directly but makes it possible to detect and quantify an escape on the latter.
the angiography can be coupled to a hemodynamic exploration: measure pressures in the cavities and measures flow. The measurement of the pressure of the left ventricle does not present a theoretical difficulty: a hollow and flexible probe is brought by retrograde way until in the left ventricle under radiological control. This probe is coated connected to a pressure pick-up. The access of the left auricle is much more complex: it cannot be approached by retrograde left way (by going up the flow of the blood current), the opening of the mitral valve being with close to 180° of the opening of the aortic valve. One is generally satisfied to measure the pressure on the level of the pulmonary capillary, the catheter being pushed by right way in the right auricle, the ventricle right, then in the pulmonary artery until his distality. The pressure obtained is then superposable with the pressure of the left auricle.
the key examination remains the echocardiography. It is about a simple technique of imagery by ultrasounds. This examination makes it possible to visualize the two valves (small and large), to analyze the aspect and mobility of it. The cardiac Doppler, by analyzing the speed of blood through the valvular opening, makes it possible to evaluate the surface of its opening of it, to visualize an escape, to analyze its mechanism of it and to obtain an approximate quantification from it. in certain cases, the examination can be to supplement by a echography transœsophagienne: the probe of echography is then located at the end of a flexible Endoscope which the patient swallows. The definition of the image is then much better.
the Imagery by magnetic resonance or the cardiac scanner does not have a temporal definition sufficient for analyzing the valve well.

Diseases

Congenital

Acquired

The mitral valve is at the origin of certain diseases (the mitral valvulopathy S) when it does not provide any more its various functions.

the mitral contracting, secondary with a acute Rheumatoid arthritis, is a disease become rare. It is defined by a mitral surface lower than 2 cm ², from which appear hemodynamic modifications. It thus creates a stopping with the filling of the left ventricle.

the mitral insufficiency is an attack much more frequent and has many causes of which the Prolapsus of the mitral valve.

Random links: