Are there different types of mitral valve prolapse?
Yes. Prolapsing mitral valves are categorized as either classic or nonclassic by medical professionals. Classic mitral prolapse is associated with a high risk of symptoms and complications, while a non-classic prolapse generally is not.
Depending on the affected mitral leaflet’s thickness, as well as the degree of displacement and how the leaflet connects to the mitral valve annulus, MVP can also be grouped into further sub-types, namely symmetric, asymmetric, flail, and non-flail.
How does the mitral valve work? What does it look like?
When trying to understand the various mitral valve prolapse types that exist, it helps to be familiar with the anatomy of the mitral (aka bicuspid) valve…
The bicuspid valve has two leaflets or cusps, which are the anterior cusp and the posterior cusp. Each of the mitral cusps has three tissue layers. These are known as the spongiosa, the fibrosa, and the atrialis. The mitral annulus, which is a fibrous, saddle-shaped ring, surrounds and connects to these leaflets, helping them close when the left ventricle contracts. The annulus is not a perfect ring. Its size changes with leaflet position, contracting as the mitral valve closes and then dilating again.
Collagen tendon ‘strings’ of varying thickness and length known as the chordae tendineae (or tendinae) connect the undersides of the leaflets to the walls of the left ventricle chamber by way of the papillary muscles. When the ventricle contracts, the reduced pressure in the left atrium tugs on the leaflets, pulling them upwards. The chordae tighten to hold them in place and prevent prolapse.
What are the different mitral valve prolapse types?
Echocardiography may deliver the following diagnoses:
Classic MVP: In classic mitral prolapse, there is often too much connective tissue in the valve leaflets, thickening the spongiosa layer. This causes collagen in the fibrosa layer to separate, creating enlarged and weakened cusps. A thickness of five millimeters or more justifies a diagnosis of classic mitral valve prolapse, particularly if the leaflets extend more than two millimeters beyond the mitral annulus ring into the left atrium chamber. The extra thickness can also cause the chordae tendinae to elongate or rupture, augmenting prolapse.
Note: In addition to thicker leaflets, some definitions of classic MVP mention a prolapse of five millimeters or more. Compared to patients with a nonclassic prolapse, those with the classic form tend to be diagnosed at earlier ages, experience greater symptoms, and have other disorders.
Non-classic MVP: Patients receive a diagnosis of nonclassic mitral prolapse when thickening of the leaflet/s measures less than five millimeters and leaflet displacement measures less than two. Less thickness generally means a lower risk of complications. Depending on the measurement, non-classic prolapse is sometimes considered a normal variation in the valve’s anatomy.
Symmetric MVP: When classic prolapse is present, it may be further classified as symmetric in nature. This indicates that the two mitral leaflet tips attach evenly to the mitral annulus, coapting or meeting at the exact same point. This classification is less serious than the next sub-type, as there is generally a lower risk of blood regurgitation and other MVP complications.
Asymmetric MVP: This type of classic MVP results when mitral leaflet tips don’t attach evenly to the annulus. One cusp is positioned further toward the atrium. Lesions may play a part in this type of displacement. Patients with asymmetric MVP can develop severe regurgitation, which can lead to greater degeneration of the valve, ruptured chordae tendinae, and a flail leaflet.
Flail MVP: With flail displacement, which is asymmetric and can be mild or severe, the leaflet’s tip turns outward or upward, becoming concave in relation to the atrium. It can also cause valve deterioration and chordae tendinae rupture. Flail displacement leaves the leaflet flapping or flailing, compared to the normal closed position, so patients tend to have regurgitation.
Non-flail MVP: Patients with non-flail displacement do not have outwardly turned mitral valve leaflets. They avoid some of the risks for complications (and unpleasant symptoms) that those with flailing leaflet are typically subject to. However, the non-flail determination does come after being both classic and asymmetric, so it can still be considered a serious condition.
Note that the displacement measurements above apply to adults only.