Causes of mitral valve prolapse

Depending on the cause, primary mitral valve prolapse (idiopathic, hereditary, congenital) is distinguished, which is an independent pathology not associated with any disease and caused by genetic or congenital failure of connective tissue. Mitral valve prolapse in differentiated TSDS (Marfan syndrome, Ehlers-Danlos syndrome (types I-III), osteogenesis imperfecta (types I and III), elastic pseudoxanthoma, increased skin extensibility (cutis laxa)) is currently classified as a variant of primary mitral valve prolapse.

Secondary mitral valve prolapse develops as a result of some 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
• Ischemic heart disease.
• Primary pulmonary hypertension.
• Left ventricular aneurysm.
• Heart injury.
• Hematological diseases (von Willebrand disease, thrombocytopathy, sickle cell anemia).
• Mixed with the left atrium.
• Myasthenia gravis.
• Thyrotoxicosis syndrome.
• "Sporty" heart.
• Primary gynomastia.
• Hereditary diseases (Klinefelter syndrome, Shereshevsky-Turner, Noonan).

Based on the presence of structural changes in the mitral valve leaflets, the following are distinguished:

• classic mitral valve prolapse (leaflet displacement >2 mm, leaflet thickness >5 mm);
• non-classical PMC (sash displacement >2 mm, sash thickness <5 mm).

By localization of mitral valve prolapse:

• PMC of the anterior sash;
• PMC of the rear sash;
• PMC of both flaps (total PMC).

According to the degree of prolapse:

• prolapse of the 1st degree: deflection of the valve by 3-5 mm;
• prolapse grade II: deflection of the valve by 6-9 mm;
• prolapse grade III: deflection of the valve by more than 9 mm.

According to the degree of myxomatous degeneration of the valve apparatus:

• myxomatous degeneration grade 0 - there are no signs of myxomatous lesion of the mitral valve;
• myxomatous degeneration grade I - minimal. Thickening of the mitral leaflets (3-5 mm), arcuate deformation of the mitral orifice within 1-2 segments, no disturbance of leaflet closure;
• myxomatous degeneration grade II - moderate. Thickening of the mitral leaflets (5-8 mm), elongation of the leaflets, deformation of the contour of the mitral orifice over several segments. stretching of the chords (including single ruptures), moderate stretching of the mitral ring, disruption of the closure of the leaflets;
• myxomatous degeneration grade III - pronounced. Thickening of the mitral cusps (>8 mm) and elongation, maximum depth of cusp prolapse, multiple chord ruptures, significant expansion of the mitral annulus, no closure of the cusps (including significant systolic separation). Multivalvular prolapse and dilation of the aortic root are possible.

According to hemodynamic characteristics:

• without mitral regurgitation;
• with mitral regurgitation.

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

Causes of Primary Mitral Valve Prolapse

The occurrence of primary mitral valve prolapse is caused by myxomatous degeneration of the mitral cusps, as well as other connective tissue structures of the mitral complex (fibrous ring, chords) - a genetically determined defect in collagen synthesis, leading to disruption of the architectonics of fibrillar collagen and elastic structures of connective tissue with accumulation of acidic mucopolysaccharides (hyaluronic acid and chodroitin sulfate) without an inflammatory component. A specific gene and chromosomal defect that determines the development of PVP has not yet been identified, but three loci associated with PVP have been identified on chromosomes 16p, 11p and 13q. Two types of inheritance of myxomatous degeneration of the valvular apparatus of the heart have been described: autosomal dominant (in MVP) and, more rare, linked to the X chromosome (Xq28). In the second case, myxomatous disease of the heart valves develops (A-linked myxomatous valvular dystrophy, sex-linked valvular dysplasia). In MVP, increased expression of the Bw35 antigen of the HLA system is noted, which contributes to a decrease in interstitial magnesium and disruption of collagen metabolism.

[ 14 ], [ 15 ], [ 16 ]

Pathogenesis of mitral valve prolapse

In the development of mitral valve prolapse, the leading role is given to structural changes in the cusps, fibrous ring, chords associated with myxomatous degeneration with subsequent disruption of their sizes and relative positions. With myxomatous degeneration, there is a thickening of the loose spongy layer of the mitral cusp due to the accumulation of acidic mucopolysaccharides with thinning and fragmentation of the fibrous layer, reducing its mechanical strength. Replacement of the elastic fibrous tissue of the valve cusp with a weak and inelastic spongy structure leads to bulging of the cusp under blood pressure into the left atrium during left ventricular systole. In a third of cases, myxomatous degeneration extends to the fibrous ring, leading to its expansion, and the chords with their subsequent lengthening and thinning. The main role in the development of mitral regurgitation in mitral valve prolapse is attributed to the constant traumatic effect of the turbulent regurgitant flow on the altered cusps and dilation of the mitral annulus. Dilation of the mitral fibrous ring by more than 30 mm in diameter is characteristic of myxomatous degeneration and serves as a risk factor for the development of mitral regurgitation, which occurs in 68-85% of individuals with MVP. The rate of progression of mitral regurgitation is determined by the degree of expression of the initial structural and functional disorders of the components of the mitral valve apparatus. In case of minor prolapse of unchanged or slightly changed mitral valve leaflets, 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 leaflets, including tendinous chords and papillary muscles, the development of mitral regurgitation is progressive. The risk of developing hemodynamically significant mitral regurgitation over 10 years among individuals with MVP with a virtually unchanged structure is only 0-1%, while an increase in the area and thickening of the mitral valve leaflet >5 mm increases the risk of mitral regurgitation to 10-15%. Myxomatous degeneration of the chords can lead to their ruptures with the formation of "floating" acute mitral regurgitation.

The degree of mitral valve prolapse also depends on some hemodynamic parameters: heart rate and left ventricular EDV. With an increase in heart rate and a decrease in EDV, the mitral valve cusps come closer together, the diameter of the valve ring and the tension of the chords decrease, leading to an increase in valve prolapse. An increase in left ventricular EDV reduces the severity of mitral valve prolapse.