Mitral valvular disease includes basically two entities:
- Mitral insufficiency, which occurs when the valve does not close properly, causing part of the blood volume to return to the left atrium, where it comes from. It occurs because the leaflets do not come together properly when they have to close completely.
- Mitral stenosis, which is defined by an inValvular Prosthesis – Valvular Replacement complete opening of the valve because the orifice has become smaller. Usually, it occurs because the shells are merged into certain sites as a result of an inflammatory process.
Both conditions increase the workload of the heart, and without treatment will cause serious complications.
Before discussing more deeply about mitral regurgitation and its surgical treatment, it is important to know the anatomy and functioning of the mitral valve. This will help us to better understand how the surgical treatment is performed.
Anatomy and Physiology of the Mitral Valve
The mitral valve opens each time the left ventricle relaxes (diastole) by letting the blood flow into the left atrium. When the left ventricle contracts (systole), the increase in pressure within the ventricle produces closure of the mitral valve. This prevents blood flow back into the atrium. The correct valvular function is dependent on the normal functioning of a set of structures: the mitral annulus, the valvular veils and the subvalvular apparatus (formed by the tendinous cords and the papillary muscles). It is, as can be seen, a complex valve.
The mitral valve consists of two veils (the remaining heart valves have three): the anterior veil (which occupies approximately 2/5 of the annular circumference) and the posterior veil. The anterior mitral veil and the non-coronary veil of the aortic valve have common tissue (this is known as the mitro-aortic junction). The posterior veil of the mitral valve is quadrangular in shape and is anchored to 3/5 of the circumference of the mitral annulus. Each of the veils is subdivided, in turn, into 3 segments.
The valvular coaptation area is where the two mitral valve leaflets meet. It is of critical importance for an adequate closure of the valve since if it does not adequately coapt, mitral insufficiency occurs due to a hole where blood returns to the atrium when the left ventricle contracts.
The mitral annulus forms the anatomical junction between the left atrium and the left ventricle. It is the area where the valvular veils are inserted. It is less developed at the level of the posterior veil; As a consequence, this zone of the mitral annulus is the one that is more easily dilated when the atrium or left ventricle dilates. Correction of mitral annulus diameter to restore physiological diameter will, therefore, be an essential part of mitral valve repair.
The tendinous cords are fibrous bands that are anchored to the papillary muscles and to the two leaflets at different points. They play a key role in maintaining the position of the veils during ventricular contraction.
There are two papillary muscles: the anterolateral papillary muscle and the posteromedial papillary muscle. Each papillary muscle sends tendon strings to both mitral veils. The anterolateral papillary muscle is irrigated by two coronary arteries: the anterior descending artery and a branch of the circumflex artery. The posterior (or posteromedial) papillary muscle is irrigated only by one artery, the circumflex artery, or the right coronary artery (differs in each person). For this reason, this muscle has a greater risk of being affected when there is a decrease in the blood supply to the heart.
The insertion of the papillary muscles in the left ventricular wall causes the ventricular wall to influence the function of the valve. When the ventricle dilates, either rapidly or more slowly, a displacement of the papillary muscles occurs. This, in turn, causes the mitral veils to move because of the excess traction exerted by the strings on them.
The mitral valve is surrounded by several anatomical structures of vital importance: the aortic valve (remember the mitral aortic continuity) and the circumflex artery. Such structures must be fully respected during mitral repair surgery to avoid complications.
Most patients with mitral regurgitation remain asymptomatic for long periods of time. The most common symptoms and signs include fatigue, decreased exercise capacity, as well as the feeling of choking (dyspnea) and palpitations. These are associated with arrhythmias such as atrial fibrillation.
Basically, we can distinguish three types of mitral regurgitation according to their origin:
- Degenerative organic mitral regurgitation: the Self disease of the valve leaflets and subvalvular. It is the most frequent type. Mitral valvular prolapse (including Barlow syndrome), calcification of the mitral annulus, rheumatic fever, congenital diseases, etc. are among the diseases that cause it.
- Ischemic mitral regurgitation: when an acute myocardial infarction affecting any of the arteries that supply the papillary muscles occurs. If the artery does not receive enough blood, a papillary muscle can rupture. When the coronary disease is chronic, ischemia (the decrease in blood pressure) causes the anatomy of the ventricle to change and malfunction of the papillary muscle.
- Functional mitral regurgitation occurs when the valve annulus dilates. It can cause any disease that causes a significant dilation of the left ventricle so that when dilating the valve ring the veils do not completely coapt.
The main causes of severe acute mitral regurgitation considered a surgical emergency when mitral insufficiency develops in a short period of time, are infective endocarditis, rupture of a papillary muscle in the context of an acute myocardial infarction, rupture Of a relevant tendinous cord and the traumatisms.
Diagnosis of Mitral Disease
As for the diagnosis and planning of surgery, the basic pillar remains echocardiography. It is essential to determine the mechanism that produces mitral regurgitation, as well as its severity and how it affects ventricular function.
Transesophageal echocardiography (cardiac ultrasound from the esophagus, inserting the ultrasound probe through the mouth) is a very useful complement in confirming the diagnosis and understanding the mechanism of the degenerative disease. The emergence of three-dimensional echocardiography is providing a greater experience and definition regarding the characterization of the mitral valve anatomy and already plays a very significant role in surgical planning today.
What is Mitral Valve repair surgery?
The treatment of choice in patients with the mitral disease is valve repair. Although valvular repair requires expert knowledge and the great experience, the advantages for the patient are very significant, extending their longevity, avoiding oral anticoagulation and, of course, preserving the patient’s own valve.
Surgical repair of the mitral valve, like any valve surgery is performed with extracorporeal circulation, and the same pattern as in other surgeries followed (see the section: During Cardiac Surgery ). Once the heart is stopped, the left atrium must be accessed, but instead of replacing the valve with a prosthesis, the repair will be performed.
One form of mitral valve repair is simple commissurotomy. It is indicated in some cases of mitral stenosis when the commissures (the area where the anterior and posterior veils are touched) are fused, but neither the tendinous chordae nor the papillary muscles are affected. The procedure consists of widening the commissures by an incision along the natural line thereof.
The rupture of the tendinous cords is the valve lesion most susceptible to surgical repair. For this, new tendinous ropes have implanted that anchor the segment of the veil that prolapses as a consequence of the rupture of the cord with the corresponding papillary muscle. The length of the tendinous rope must be the ideal one to avoid that the valve continues prolapsing, but that does not retract. Sometimes it is necessary to use several tendinous ropes to correct the prolapse.
As we have discussed, mitral insufficiency usually influences several factors, and dilation of the mitral annulus is very common. If we imagine that the mitral valve is two gates, the ring would be the frame of both. In order to restore the correct valve function, a mitral annuloplasty is almost always performed, associated or not with other procedures. This usually consists (although there are several possible techniques) in the implantation of a ring semi-rigid prosthetic. This is sutured to the patient’s mitral annulus and has a diameter that allows a correct valvular coaptation, restoring the original shape of the mitral annulus.
In summary, mitral valve repair surgery is complex surgery, which often requires the use of several different techniques, but has been shown to have important advantages over mitral valve replacement. Therefore, it should be tried whenever possible.