What are the causes of Mitral Valve Prolapse?
Mitral valve prolapse (MVP) is the most common valvular heart disorder. In order to better understand this condition, a brief review of the heart’s anatomy is in order.
The heart consists of 2 sides: right and left. The right side of the heart receives blood from the rest of the body and circulates it through the lungs to make it oxygenated. Oxygenated blood from the lung then enters the left side of the heart, first the left atrium and then the left ventricle.
The left ventricle is the main pumping chamber of the heart since it is responsible for pushing blood through the rest of the circulatory system. Between the left ventricle and the left atrium lies the mitral valve. This valve performs a very important function. When the left ventricle contracts, blood must flow out to the rest of the body rather than back to the left atrium. By closing when the left ventricle contracts, the mitral valve prevents a backup of blood into the left atrium.
The mitral valve is made up of two thin leaflets of tissue that line the internal walls of the base portion of the left ventricle. The opening and closing of these leaflets is controlled by blood flow and two attached muscular bands called chordae. Mitral valve prolapse occurs when the mitral valve leaflets and attached chords undergo a process called myxomatous (mix-o-ma-tous) change, or degeneration.
This process leads to a change in the structural proteins of the leaflets and chords, such that the mitral valve leaflets become billowed and floppy. This floppiness interferes with the typical perfect closure of the mitral valve leaflets that should occur when the ventricles contract. The leaflets, in essence, prolapse in on themselves due to forceful blood flow in the contracting ventricle.
This prolapse accounts for the characteristic “mid-systolic click” that doctors can hear when they listen to an MVP heart with the stethoscope. While the “click” sound used to be the accepted measure to diagnose MVP, now ultrasonic (echocardiographic) imaging of the heart to directly visualize the myxomatous and prolapsing leaflets is the norm.
Usually, MVP is not so severe to cause seriously concerning symptoms. However, with time, MVP can progress and lead to a mitral valve that fails to close normally during ventricular contraction. This causes mitral regurgitation (as in blood regurgitating back into the left atrium from the left ventricle), which if severe enough can cause over a period of years or decades progressive left atrial dilation and heart failure (thus, the reason for periodic follow up physician visits among individuals with MVP).
In addition, MVP can increase an individual’s risk for bacterial infections of the heart valve whenever bacteria are exposed to the bloodstream (as occurs during most medical or dental procedures). This is the reason why antibiotics might be prescribed for individuals with MVP whenever they undergo a medical or dental procedure.
MVP occurs in 5-10 percent of all people, more frequently affecting females between teenage and middle age years, and is strongly influenced by genetics. The exact causes are poorly understood. MVP may associate with other conditions, including palpitations and abnormal heart rhythms, anxiety, panic attacks and migraines. The conditions suggest that individuals with MVP may have some imbalance in their autonomic nervous system.
Finally, MVP occurs in individuals with connective tissue disorders such as Marfan’s Syndrome. Fortunately, given that many researchers are studying MVP, it is hopeful that improved understandings of this disorder will be known in the future.