Causes of mitral valve prolapse

Depending on the cause, the primary prolapse of the mitral valve (idiopathic, hereditary, congenital) is isolated, which is an independent pathology that is not associated with any disease and is caused by genetic or congenital insufficiency of the connective tissue. The proliferation of the mitral valve with differentiated STD (Marfan, Ehlers-Danlos syndrome (I-III types), imperfect osteogenesis (types I and III), elastic pseudo-xanthoma, increased skin extensibility (cutis lacha)) is currently attributed to the variants of the primary prolapse of the mitral valve .

Secondary prolapse of the mitral valve develops as a result of any diseases and accounts for 5% of all cases of valve prolapse.

[1], [2], [3], [4], [5], [6], [7]

Causes of secondary mitral valve prolapse

• Rheumatic diseases.
• Cardiomyopathy.
• Myocarditis
• Cardiac ischemia.
• Primary pulmonary hypertension.
• Aneurysm of the left ventricle.
• Injury of the heart.
• Hematologic diseases (von Willebrand's disease, thrombocytopathy, sickle-cell anemia).
• Mix of the left atrium.
• Myasthenia gravis.
• Syndrome of thyrotoxicosis.
• "Athletic" heart.
• Primary ginomastia.
• Hereditary diseases (Klinefelter's syndrome, Shereshevsky-Turner, Noonan).

According to the presence of structural changes in mitral valve flaps, there are:

• classic prolapse of the mitral valve (wing displacement> 2 mm, leaf thickness> 5 mm);
• non-classical PMC (slide displacement> 2 mm, leaf thickness <5 mm).

By localization of prolapse of the mitral valve:

• PMK of the front leaf;
• PMK of the posterior leaf;
• PMK of both valves (total PMC).

By degree of prolapse:

• prolapse of the I degree: deflection of the valve by 3-5 mm;
• prolapse of II degree: deflection of the valve by 6-9 mm;
• prolapse III degree: deflection of the leaf more than 9 mm.

By the degree of myxomatous degeneration of the valve apparatus:

• Myxomatous degeneration of the 0th degree - there are no signs of myxomatous involvement of the mitral valve;
• Myxomatous degeneration of the first degree is minimal. Thickening of mitral valves (3-5 mm), arcuate deformation of the mitral orifice within 1-2 segments, absence of ligament obstruction;
• Myxomatous degeneration of II degree - moderate. Thickening of mitral valves (5-8 mm), lengthening of valves, deformation of contour of mitral orifice during several segments. Stretching chords (including single gaps), moderate stretching of the mitral ring, dislocation of the valves;
• Myxomatous degeneration of the third degree - pronounced. Thickening of the mitral valves (> 8 mm) and elongation, maximum depth of prolapse of the valves, multiple ruptured chords, significant expansion of the mitral ring, no folding of the valves (including significant systolic separation). Multiple valve prolapse and dilatation of the root of the aorta are possible.

By hemodynamic characteristics:

• without mitral regurgitation;
• with mitral regurgitation.

[8], [9], [10], [11], [12], [13]

Causes of primary mitral valve prolapse

The origin of the primary prolapse of the mitral valve is due to myxomatous degeneration of the mitral valves, as well as other connective tissue structures of the mitral complex (fibrous ring, chords), a genetically determined defect in collagen synthesis, which leads to a violation of the architectonics of fibrillar collagen and elastic structures of connective tissue with accumulation of acid mucopolysaccharides (hyaluronic acid and Hopdroitin sulfate) without an inflammatory component. A specific gene and chromosomal defect that determines the development of PMC is not currently detected, however, three loci associated with PMC on chromosomes 16p, 11p and 13q have been identified. Two types of inheritance of myxomatous degeneration of valvular heart apparatus are described: autosomal dominant (with PMC) and, more rarely, linked to X-chromosome (Xq28). In the second case, myxomatous heart valve disease develops (A-associated myxomatous valvular dystrophy, valve-associated dysplasia linked to the floor). With PMK, increased expression of the Bw35 antigen of the HLA system was noted, which helps reduce interstitial magnesium and impair the metabolism of collagen.

[14], [15], [16]

The pathogenesis of mitral valve prolapse

In the development of mitral valve prolapse, the structural changes in the valves, fibrous ring, chords, associated with myxomatous degeneration, with subsequent disruption of their size and relative location, are assigned the leading role. With myxomatous degeneration, there is a thickening of the loose spongiosal layer of the mitral valve due to accumulation of acid mucopolysaccharides with thinning and fragmentation of the fibrous layer, reducing its mechanical strength. Replacing the elastic fibrous tissue of the valve leaf with a weak and inelastic spongy structure results in the swelling of the valve under pressure of the blood into the left atrial cavity during left ventricular systole. In a third of cases, myxomatous degeneration extends to the fibrous ring, leading to its widening, and the chord, with subsequent lengthening and thinning. The main role in the occurrence of mitral regurgitation in mitral valve prolapse is attributed to the permanent traumatic effect of the turbulent flow of regurgitation on altered valves and dilatations of the mitral ring. Expansion of the mitral fibrous ring more than 30 mm in diameter is characteristic for myxomatous degeneration and is a risk factor for the occurrence of mitral regurgitation, occurring in 68-85% of patients with PMP. The rate of progression of mitral regurgitation is determined by the degree of severity of the initial structural and functional disorders of the components of the mitral valve apparatus. In the case of a slight prolapse of unchanged or slightly altered mitral valve flaps, a significant increase in the degree of mitral regurgitation may not be observed for a long time, while in the presence of sufficiently pronounced changes in the valves, including tendon chords and papillary muscles, the development of mitral regurgitation is progressive. The risk of formation of hemodynamically significant mitral regurgitation for 10 years among persons with PMC with an almost unchanged structure is only 0-1%, while an increase in the area and a thickening of the mitral valve leaf> 5 mm increases the risk of mitral regurgitation to 10-15%. Mikksomatous degeneration of chords can lead to their rupture with the formation of "flotating" acute mitral regurgitation.

The degree of prolapse of the mitral valve also depends on some hemodynamic parameters: heart rate and left ventricular BWW. With an increase in the heart rate and a decrease in BWW, the mitral valve flaps approach, the diameter of the valve ring and the chord tension decrease, leading to a proliferation of valve flaps. An increase in the left ventricular BWW reduces the severity of the prolapse of the mitral valve.