Mitral Valve Anatomy
The mitral valve (MV) separates the left atrium (LA) and left ventricle (LV). It’s a bileaflet valve composed of an anterior and posterior leaflet, each with three “scallops” designated A1, A2, A3, P1, P2, and P3. The A3-P3 interface tapers into the posteromedial commissure whereas the A1-P1 interface becomes the anterolateral commissure.
The mitral valve leaflets are tethered to the anterolateral (typically one large structure) and posteromedial (1-3 heads) papillary muscles by string-like bands called chordae tendineae. Both papillary muscles send chordae to both mitral leaflets, so pathology of either papillary muscle (namely a rupture) can affect either mitral valve leaflet.
With echocardiography (especially 3D TEE), we can view each scallop of the mitral valve in more than one plane. This allows us to localize pathology like a flail leaflet, regurgitant jet, or vegetation with great accuracy. Additionally, echo lets us calculate measurements like mean pressure gradients and valve areas to assess stenosis and regurgitation.
Normally, the mitral valve area is 4.0 – 6.0 cm2, but this area is reduced with stenosis of varying severity: mild (1.5 – 2.5 cm2), moderate (1.0 – 1.5 cm2), and severe (< 1.0 cm2).
Similarly, the normal mean pressure gradient in normal sinus rhythm at a rate of ~60-80 bpm is < 2 mmHg but this increases with stenosis: mild (2-6 mmHg), moderate (6-12 mmHg), and severe (>12 mmHg).