MITRAL VALVE: anatomy, function and pathologies

Mitral valve

What is the mitral valve

The mitral valve is one of the four valves found within the heart, along with the aortic valve, triscuspid valve, and pulmonary valve. The mitral valve allows the passage of arterial blood from the left atrium to the left ventricle, preventing the reflux towards the atrium and allowing the correct development of the systole-diastole cycle that characterizes every heartbeat.

Anatomy of the heart

Before we focus on the mitral valve, it is necessary to clarify some basic terms and concepts of cardiovascular anatomy:

  • The heart is in effect one muscle, which contracts and releases autonomously and rhythmically, formed by four chambers: two atria, right and left, and two ventricles, right and left, placed under the atria. The atria do not communicate with each other, being separated by a wall (Interatrial septum). The ventricular septum separates the ventricles. In summary, the only possible communication is between the atria and the ventricles, both on the right and on the left.
  • Just as the skeletal muscles contract to express a force and therefore a job (eg lifting an object), the heart muscle also contracts: its job is to impart pressure to the blood contained in it to pump it towards the arteries. The real workers, in the heart, are the ventricles, while the atria serve more to receive blood.
  • They are called arteries all the vessels that carry blood from the heart to the organs.
  • They are called veins all the vessels that carry blood to the heart.
  • There diastole it is the phase in which the blood passes from the atria to the ventricles.
  • Is called systole the phase in which blood passes from the ventricles to the arterial vessels that arise from them (pulmonary artery on the right and aorta on the left).
  • The right atrium receives blood from the Hollow Veins, the largest veins in our body, where blood flows from all organs except the lungs. It therefore receives deoxygenated blood, rich in cellular waste.
  • The right ventricle, by contracting, pumps the blood it has received from the atrium into the pulmonary artery. It goes to the lungs where, through gaseous exchanges between blood and air, carbon dioxide is released and the blood is supplied with oxygen.
  • The Right Heart it is, therefore, composed of atrium and right ventricle: it always flows blood poor in oxygen which is pumped towards the lungs (pulmonary circulation) to be oxygenated.
  • The left atrium receives freshly oxygenated blood from the pulmonary veins. There are four pulmonary veins, two from the right lung and two from the left.
  • The left ventricle pumps the oxygenated blood it has received from the atrium into the aorta.
  • With Left Heart we therefore mean the set of atrium and left ventricle, which receives oxygenated blood and pumps it to all organs except the lungs (systemic circulation).
  • To conclude, one can imagine the bloodstream as if it were a continuous path that passes through these stages: systemic circulation - right heart - pulmonary circulation - left heart - systemic circulation and so on.
Mitral valve

Anatomy of the heart

Anatomy and functions of the mitral valve

Let's now pass to the mitral valve: it is one of the two atrioventricular valves of the heart, together with the tricuspid. It owes its name to its particular shape: being in fact formed by two flaps or cusps (front and rear), when open it recalls the papal miter. The valve is located between the atrium and the ventricle left, while the tricuspid is located between the atrium and the right ventricle.

The cusps they are similar to small sheets, made of very resistant fibrous tissue. These fit on the so-called annulus (ring) fibrous, which surrounds the atrioventricular orifice. Each leaflet has one face facing up, then towards the atrium, and one facing the ventricle. On the latter, tendon cords are attached, which at the other end are attached to small muscles located in the ventricle (papillary muscles). These contract together with the ventricle and tension the cords. Thus the cusps are retained and cannot open towards the atria, preventing blood reflux.

Opening and closing of the mitral valve they are regulated by the pressure gradient between the atrium and ventricle. When the pressure in the first exceeds that in the second, the valve opens, allowing blood to flow from the top (atrium) to the bottom (ventricle). As blood passes into the ventricle, the pressure in this chamber increases, while that in the atrium decreases. As the ventricle begins to contract, the pressure in the ventricle exceeds that in the atrium, and the valve closes.

With mitral valve apparatus we mean the set of: flaps, fibrous ring, tendon cords and papillary muscles. Its function is:

  • Allow blood flow from the atrium to the ventricle
  • Prevent it in the opposite direction.
Mitral valve

Flaps and mitral valve anatomy.

Pathologies of the mitral valve

Pathologies of the mitral valve are divided into two categories: stenosis is insufficiency valve. Each, in turn, is the result of numerous underlying conditions and pathologies.

Mitral insufficiency

Mitral regurgitation is the second most common valve defect after aortic stenosis. It involves the regurgitation of blood from the ventricle to the left atrium, with two fundamental consequences:

  • Overloading of the atrium and left ventricle: if a little blood returns to the atrium with each ventricular beat, it is inevitable that it will be overloaded. In addition, at the next diastole, the usual amount of blood will reach the ventricle, to which must be added the amount regurgitated during the previous systole, with consequent overload of the ventricle as well.
  • Decrease in the amount of blood pumped into the circulation (systolic output), as some will go to the atrium instead of the aorta.

At the beginning the heart implements compensations that make the situation stable even for a long time. In fact, insufficiency is one of the defects best tolerated by the patient, who can live with the disease for a long time unknowingly. In fact, both the atrium and the ventricle dilate, and this allows to maintain normal upstream and downstream pressures for a long time. However, if the situation is not improved, these mechanisms will become insufficient, and the patient will begin to experience typical symptoms:

  • Tiredness, especially in relation to activities that previously performed without problems
  • Difficulty in breathing (dyspnea), especially during exertion
  • Sometimes the appearance of arrhythmias, especially Atrial Fibrillation, favored by the dilation of the atrium.

Insufficiency can be the result of several conditions:

  1. The cusps open and close normally: the regurgitation is due to the perforation of a cusp (eg for an infection, Endocarditis) or due to the enlargement of the annulus, therefore of the implantation base of the cusps. The latter is possible in all cases in which the ventricle dilates (eg in the course of congenital dilated cardiomyopathy, aortic insufficiency, myocardial infarction ...)
  2. The movement of the cusps is reduced, so they only partially close during systole. This can happen either because the cusps pull the cusps excessively (for example in the case of ventricular dilation, in which the papillary muscles move away from the valve, putting the cords in more traction) or because the cusps themselves are rigid and retracted (eg. of rheumatic disease, today almost completely eradicated in the West; however, it remains as a result of chronic inflammatory diseases, autoimmune, exposure to radiation).
  3. The movement of the cusps is excessive, and in systole they are partially reversed into the atrium. The causes can be the rupture of the papillary muscles (during a heart attack, the death of the cells of the papillary muscles can cause the dreaded acute mitral insufficiency) or the thickening of the cusps. The latter occurrence is common in young women (often with particular chest conformations and low body weight) and is called "Mitral prolapse": a condition that recognizes a hereditary component, caused by the thickening of the cusps with an increase in the force necessary to hold them during systole. The cusps increase in weight and thickness because there is the accumulation of proteoglycans, molecules capable of binding large quantities of water, as if they were sponges. And just as a water-soaked sponge weighs much more, soaked cusps are both thickened and heavier. This has the effect of making the cusps difficult to be held by the tendon cords: in fact, the image of the "flaps to hammock“, Precisely because they overflow towards the atria, assuming a hammock or crescent or dome shape, with concavity facing the ventricle. If the weight becomes excessive, there will be incomplete closure of the two flaps, with the appearance of insufficiency. It must therefore be emphasized that prolapse it does not necessarily mean insufficiency: this is usually only true in advanced stages. In reality, more than for the insufficiency, this condition is fearful for the onset of arrhythmias: this is because the cords, put in excessive traction, "stretch" the papillary muscles to which they are attached, activating anomalous electric currents: one of the symptoms of prolapse is in fact the heart-pounding, or the unpleasant perception of the heartbeat in the chest. Another, more rare, symptom may be the so-called cordialgia, or pain in the chest at the level of the heart, is thought to be due to the excessive tensioning of the tendon cords. The doctor will therefore suspect the presence of prolapse based mainly on the symptoms listed above reported by the patient, and on the fact that on auscultation of the chest a noise (called click) in mid / late systole will be appreciable, which is typical of this condition, and is generated by excessive movement of the flaps during ventricular contraction. Sometimes, the suspicion is reinforced by the presence of slight changes on the ECG. Confirmation of suspicion will be obtained with Echocardiogram, through which we can appreciate both the presence of the alteration and its extent (how thick the flaps are) and the possible presence of overt valve insufficiency. Sometimes, the echocardiogram does not have the expected response: sometimes in fact, the symptoms reported by the patient are the result of psychological (eg anxiety) rather than cardiac disorders.

Mitral stenosis

Mitral stenosis it represents the least frequent valve defect ever. Several conditions can cause incomplete opening of the valve during diastole, with incomplete emptying of the atrium and residual blood inside it. This valve defect is the only one to spare the left ventricle, which obviously is not overloaded. However, the constant residue of blood has two consequences:

  • Decreased cardiac output, which is expressed by asthenia (disproportionate fatigue) and in the most severe cases cyanosis (purplish color of the skin), pallor, loss of hair at the extremities.
  • Pressure increase in the left atrium, which affects the pulmonary circulation upstream. This causes a worsening of gas exchange, resulting in dyspnea (labored breathing), initially from exertion and then at rest. In severe cases, it can lead to pulmonary edema, a medical emergency as it puts the patient at risk of death.

The main causes are:

  • Degeneration of the connective tissue with deposit of calcifications at the level of the cusps or annulus (valvular sclerosis).
  • Autoimmune diseases (for example Lupus or Rheumatoid Arthritis).
  • Radiation exposure.
  • Endocarditis.

Diagnosis of Mitral Valve Disorders

Both conditions are recognized on clinical examination by the presence of a murmur on cardiac auscultation, due to the passage of blood through a narrow orifice (stenosis) or reflux (insufficiency).

  • In case of stenosis we will have a murmur during diastole, therefore between the second and first tone.
  • In case of insufficiency, the murmur will be during systole, so between the first and second tone.

The definitive diagnosis, however, is made through Doppler echocardiography, often abbreviated with the term echocardiogram or simply echocardium.

Therapies and interventions 

Unlike aortic valve defects, mitral valve defects are almost never treated with valve replacement surgery, but rather by repair or plastic. This is because it has been seen that keeping the valve apparatus intact, especially the tendon cords, results in greater success.

Therapeutic options:

  • Replacement: it is basically carried out only in case of Endocarditis with destruction of the flaps or in case of rheumatic disease with calcification and retraction; that is, only in those situations in which repair is absolutely not possible. The damaged valve is removed and replaced with a biological prosthesis (which has the disadvantage of having a limited duration of 10-20 years) or mechanical (which has the disadvantage of requiring oral anticoagulant therapy for life and not being able to be used in case of endocarditis because it is more easily colonized by bacteria).
  • Mitral clip: in case of insufficiency with excessive movement of the flaps. This technique, which does not require thoracic incisions as it is percutaneous, is usually reserved for elderly patients who are not in a condition to allow a proper surgery. It consists in fixing the central part of the flaps by means of a suture. This creates a double lumen, shaped like an 8 (with the risk of future stenosis) but a decrease in regurgitation.
  • Repair with pericardial patch: in case of perforation (for example during uncomplicated endocarditis).
  • Minimally invasive annuloplasty: repair of the annulus, carried out with a beating heart.
  • Balloon valvuloplasty, percutaneous technique that allows to widen the annulus in case of stenosis, inflating a balloon placed at the tip of the catheter which is inserted at the level of a peripheral vein and led to the heart.
  • Replacement of tendon cord (Neo-chord technique), innovative, minimally invasive intervention, carried out with a beating heart. It involves the replacement of a damaged rope with an artificial one.
  • Resection of the flap in case of rupture of the tendon cord: in this case the portion of the flap that gave attachment to the cord is resected, and the remaining portions are sutured together.
  • In case of mitral prolapse, which is almost always of the posterior flap, a triangular resection is performed: a small portion of the flap, at the base, of triangular shape is cut and removed. If both flaps prolapse, the rear is entirely removed and its cords are transferred to the front.

Repairs are nowadays carried out in almost all cases with technique minimally invasive, which has a considerably reduced impact on the patient in the post-operative period as it does not require a median sternotomy (which consists in opening the chest at a median level, cutting the sternum and thus "disturbing" the tissues that are interposed between it and the heart causing inflammation and adhesions), but a small incision (usually about 5-6 cm) in the right chest. Indeed, in some cases (for example for the mitral clip or balloon annuloplasty, as mentioned) the lateral thoracic incision is also avoided and everything is done with percutaneous endovascular: the valve is reached by inserting catheters into a peripheral vein (usually femoral) capable of traveling along the venous system to the heart, and there they can be used to repair or suture the valve with various methods. Interventions in median sternotomy therefore, due to the negative effects that this entails and that we have previously mentioned (inflammation, adhesions, greater post-operative pain and bleeding, presence of means for reducing the surgical fracture of the sternum ...), in addition to the need to operate stopping the heart (using the so-called CEC or extra-corporeal circulation after blocking the heart with a particular solution called cardioplegic, obviously only for the time necessary for the operation), are now reserved for a few specific cases.

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