The mitral valve is naturally bicuspid, meaning it is formed by two flaps, or leaflets. This valve is situated between the left atrium and the left ventricle, serving as a one-way gate for oxygenated blood moving through the left side of the heart. Its function is to permit blood flow from the atrium to the ventricle. It prevents any backward leakage when the ventricle contracts to pump blood to the body.
The Normal Bicuspid Structure of the Mitral Valve
The mitral valve consists of two distinct leaflets: the anterior leaflet, which is larger and thicker, and the posterior leaflet. The posterior leaflet attaches to a greater portion of the valve’s circumference. The leaflets are attached to a fibrous ring called the mitral annulus that provides structural support.
These two leaflets open during the heart’s resting phase, known as diastole, allowing blood to fill the left ventricle from the left atrium. During the contraction phase, or systole, the leaflets must close tightly to create a complete seal. This tight closure is maintained by a network of thin, fibrous cords called the chordae tendineae.
The chordae tendineae anchor the leaflets to the walls of the left ventricle. They connect to two muscular projections inside the ventricle, known as the papillary muscles. The synchronized contraction of the papillary muscles and the tension exerted by the chordae prevent the leaflets from bulging backward into the left atrium during ventricular contraction. This backward bulging is a condition known as prolapse.
Differentiating Mitral Valve Structure from the Aortic Valve
The mitral valve’s normal, healthy structure is bicuspid. The other three valves—the tricuspid, pulmonary, and aortic valves—are typically tricuspid, meaning they have three leaflets. The aortic valve, which controls blood flow from the left ventricle into the aorta, is usually formed of three cusps.
Confusion often arises because a condition known as a bicuspid aortic valve (BAV) is the most common congenital heart defect. This is an abnormality where the aortic valve is born with only two cusps instead of the usual three. A bicuspid mitral valve is the standard, healthy anatomy. Conversely, a bicuspid aortic valve represents a structural defect that can cause problems over time.
Common Functional Problems of the Mitral Valve
When the components of the mitral valve system fail to work in harmony, two primary types of dysfunction can occur: mitral regurgitation and mitral stenosis. Mitral regurgitation is a leaky valve where the leaflets fail to close completely during systole. This incomplete closure allows blood to flow backward from the high-pressure left ventricle into the left atrium.
This backward flow forces the heart to re-pump the same blood, increasing the workload on the left ventricle. A common cause of regurgitation is mitral valve prolapse, where one or both leaflets bulge excessively into the atrium during contraction. Regurgitation can also result from a damaged valve apparatus due to conditions like a heart attack or advanced degeneration.
Mitral stenosis is the opposite problem, involving a narrowing or stiffening of the valve opening. This makes it difficult for blood to pass from the left atrium to the left ventricle during the filling phase, or diastole. The resistance to forward flow causes pressure to build up in the left atrium, which can subsequently cause fluid to back up into the lungs. The most frequent cause of mitral stenosis is a history of rheumatic fever, which can lead to the fusion and scarring of the valve leaflets over time. Both stenosis and severe regurgitation can strain the heart muscle and lead to serious issues, including heart failure and irregular heart rhythms.
Monitoring and Lifestyle Considerations
Individuals with known mitral valve conditions benefit from regular medical monitoring to track the stability or progression of the condition. A key diagnostic tool is the echocardiogram, an ultrasound of the heart, which provides clear images of the leaflets and measures blood flow through the valve. Asymptomatic individuals with minimal disease may undergo an echocardiogram every three to five years. Those with thickening leaflets or moderate disease may require annual checks.
Maintaining a heart-healthy lifestyle is essential for managing valve health. This includes controlling blood pressure, as high blood pressure increases the strain on the compromised valve and can worsen regurgitation. A diet low in saturated fats and sodium also helps manage overall cardiovascular health and fluid retention, especially in individuals with developing heart failure symptoms.
Regular physical activity is encouraged for most patients, often recommending at least 150 minutes of moderate aerobic exercise weekly. Furthermore, individuals with certain valve conditions or those who have had a valve replacement must be diligent with dental hygiene to prevent bacterial infections. These infections, called infective endocarditis, can settle on the valve tissue and cause rapid, severe damage.