Mitral valve stenosis (MVS) is a condition where the heart’s mitral valve, located between the left atrium and left ventricle, becomes narrowed. This narrowing impedes the normal flow of oxygen-rich blood from the left atrium into the left ventricle. When restricted, the heart must work harder to push blood through, potentially leading to complications.
Rheumatic Fever: The Primary Culprit
Rheumatic fever is the most frequent cause of mitral valve stenosis. This inflammatory disease develops as a complication of an untreated Streptococcus pyogenes infection, commonly known as strep throat. The body’s immune system mistakenly attacks healthy tissues, including heart valves, triggering inflammation within the heart.
Over time, this inflammation leads to scarring, thickening, and stiffening of the mitral valve leaflets. The leaflets can fuse together, reducing the valve’s opening. Prompt and effective treatment of strep throat with antibiotics is crucial to prevent this long-term heart damage.
Other Contributing Factors
While rheumatic fever is the predominant cause, several other factors can contribute to mitral valve stenosis. Some individuals are born with an abnormally formed mitral valve, a condition known as congenital mitral stenosis. This structural abnormality can lead to a narrowed valve opening from birth or predispose it to narrowing over time.
As people age, the mitral valve can undergo calcification, where calcium deposits accumulate on its leaflets and supporting structures. This age-related calcification causes the valve to stiffen and become less flexible, leading to stenosis. Radiation therapy directed at the chest area can also damage heart valves. This damage can result in scarring and stiffening of the mitral valve, with symptoms potentially appearing many years after treatment.
Certain autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis, can also cause inflammation and scarring of the mitral valve. These conditions involve the immune system attacking the body’s own tissues, which can extend to the heart valves and lead to their thickening and dysfunction.
How These Factors Damage the Valve
Regardless of the initial cause, the underlying mechanism of mitral valve stenosis involves progressive changes to the valve’s structure. Inflammation, whether from an infection like rheumatic fever or an autoimmune condition, initiates tissue damage. This leads to the formation of scar tissue, causing the valve leaflets to thicken and lose their flexibility.
Over time, the edges of the valve leaflets, known as commissures, can fuse together, reducing the valve’s opening. Calcium deposits may accumulate, making the valve more rigid. These combined changes obstruct the flow of blood from the left atrium to the left ventricle, causing blood to back up and increasing pressure within the left atrium. This increased pressure can impact other parts of the heart and lungs.