Mitral Valve Prolapse and Regurgitation

Mitral Valve Anatomy and Function

This is Dr. Cal Shipley at Trial Image with the review of mitral regurgitation due to a flail segment. Let’s take a look first at the anatomy of the mitral valve and how it functions. Mitral valve facilitates movement of blood between the left atrium and left ventricle of the heart. Anatomically, it is located between the left atrium and left ventricle as shown here.

Diastole

During the relaxation phase of the left ventricle, also known as diastole, the mitral valve opens permitting flow of blood from the left atrium into the left ventricle. This action allows refilling of the left ventricle with blood in preparation for the next contraction.

Systole

During the contraction phase of the left ventricle, also known as systole, the mitral valve closes, preventing back flow of blood into the left atrium and facilitating the ejection of blood from the left ventricle into the aorta and the systemic circulation.

With each heartbeat, the valve opens and closes as part of the cardiac cycle, thousands of times a day. The mitral valve is composed of two flaps or leaflets. The leaflets are composed of a very flexible material.

Papillary Muscles

Yet another example of the body’s amazing design, papillary muscles are attached to the inner wall of the left ventricle, and then to the leaflets of the mitral valve.

During systole, the papillary muscles contract preventing ballooning or prolapse of the mitral valve leaflets into the left atrium. Viewing the valve from above, we can see the two leaflets anterior at the bottom and posterior at the top. From a functional point of view, each leaflet is further subdivided into several segments corresponding to the attachment of the papillary muscle tendons. For the purposes of today’s discussion, we are going to focus on the middle or P2 segment of the posterior leaflet of the valve. As the valve opens and closes during the cardiac cycle, we can see the attachment of the papillary tendons to the posterior leaflet.

Proper functioning of the papillary muscles prevents prolapse of the mitral valve leaflets during left ventricular contraction and insures one way flow of blood only from the atrium into the ventricle each cycle. Let’s zoom in a little bit here and take a closer look at the attachments of the tendons of the papillary muscle to the posterior valve leaflet.

Mitral Valve Flail Segment

Under a variety of circumstances, including prolonged mitral valve prolapse trauma, inflammation of the interior of the heart, also known as endocarditis,  and less commonly in the setting of heart attack, also known as myocardial infarction.

The tendons attaching the papillary muscles to the valve leaflets may rupture. This often results in what is known as a flail segment, with the affected portion of the leaflet prolapsing severely up into the left atrium with each contraction of the left ventricle. Viewed from above, it can be seen that the flailed valve segment prevents proper closure of the valve during left ventricular contraction.

The flailed valve now allows for an abnormal two-way flow of blood, with blood flowing from the left atrium into the left ventricle during diastole, but then flowing from the left ventricle back into the left atrium during systole. Depending on the degree of severity, this mitral regurgitation of blood during systole can lead to a marked decrease in the efficiency of the heart’s pumping action, and over time, can have disastrous consequences. The blood jet created by the mitral regurgitation may be seen on echocardiogram.

Cal Shipley, M.D. copyright 2020