9.2 Mitral-Valve Anatomy, Motion, and Mechanisms

Treat the mitral valve as an apparatus

The mitral valve functions through the coordinated annulus, anterior and posterior leaflets, chordae tendineae, anterolateral and posteromedial papillary muscles, and supporting LV myocardium. The annulus is dynamic and saddle shaped rather than a flat ring. Its anterior portion is in fibrous continuity with the aortic root; its posterior portion is more prone to dilation. Ventricular contraction, papillary position, chordal tension, leaflet tissue, and left-atrial or ventricular remodeling can therefore produce regurgitation even when no leaflet is torn.

The anterior leaflet is broad and relatively tall; the posterior leaflet is narrower radially and divided by indentations into P1, P2, and P3 scallops. The corresponding anterior regions are called A1, A2, and A3. In the surgeon's view from the left atrium with the aortic valve superior, A1/P1 are toward the anterolateral commissure and left atrial appendage, A3/P3 toward the posteromedial commissure, and A2/P2 central. Primary chordae attach near the free edge, secondary chordae to the ventricular leaflet surface, and basal or tertiary chordae mainly to the posterior leaflet. Chordal rupture can free an edge; papillary displacement can tether an otherwise normal leaflet.

Sweep to localize pathology

A single 2-D plane cannot identify every scallop reliably. The usual parasternal long-axis plane crosses A2 and P2, but an off-axis window changes the sampled segments. Parasternal short axis shows both commissures and all posterior scallops when the imaging level is correct. Apical four-, two-, and long-axis sweeps reveal coaptation, annular motion, chordae, papillary muscles, and the direction of associated regurgitation. TEE multiplane sweeps, biplane imaging, and 3-D en-face views are especially useful when TTE cannot define a significant lesion.

Prolapse means the leaflet edge moves beyond the annular plane into the LA during systole. Billowing describes displacement of the leaflet body while the free edge may still coapt on the ventricular side. A flail leaflet has an everted free edge that points into the LA because chordal or papillary support is lost. Use multiple frames and views; annular nonplanarity makes a single flat reference line misleading. Color-jet direction can support localization—an incompetent posterior leaflet often produces an anteriorly directed jet—but jets can be central, multiple, deflected, or altered by combined lesions. Direction is a clue, not proof.

Describe motion with a functional classification

Type identifies motion, while etiology identifies the disease and mechanism explains how malcoaptation occurs. A perforated leaflet and a dilated annulus can both have type I motion but require different management. Mixed mechanisms are common: degenerative prolapse may coexist with annular dilation, and a rheumatic valve may be both stenotic and regurgitant. Report every important component rather than forcing one label.

Primary MR originates in the leaflet or chordal apparatus, as with prolapse, flail, rheumatic damage, endocarditis, cleft, or calcification. Secondary MR results from ventricular or atrial remodeling despite initially normal leaflets. Ventricular secondary MR commonly shows apical tethering, increased tenting, reduced closing force, and regional or global LV dysfunction. Atrial functional MR is associated with LA and annular enlargement, often with AF, and less ventricular tethering. Annular calcification can restrict the posterior leaflet, distort the orifice, create shadowing, and contribute to both stenosis and regurgitation.

Acquire anatomy that answers a structural question

When repair or transcatheter therapy is considered, the examination becomes a geometric map. Record the involved scallops, commissural extension, flail or prolapse width, coaptation location and gap, leaflet length and mobility, calcification in the grasping or surgical zone, clefts or perforations, chordal density, annular dimensions, baseline mitral area and gradient, number and location of jets, and LV/LA response. Three-dimensional TEE and multiplanar reconstruction help communicate en-face location, but gain-related dropout can invent a cleft and blooming can fuse tissue. Confirm with source 2-D planes and color.

Suitability is procedure and device specific and belongs to the multidisciplinary heart team. The sonographer's role is to acquire complete, labeled, reproducible anatomy and state limitations. Do not declare a valve suitable from a single central jet, and do not omit baseline stenosis because the referral says regurgitation. Current structural guidance emphasizes communication across 2-D, biplane, 3-D, and MPR formats; every displayed orientation needs landmarks. Mechanism, lesion location, hemodynamic severity, and chamber consequence together create an actionable study.

Motion, disease, and severity are different answers

Carpentier type describes leaflet motion. Etiology names the disease, mechanism explains malcoaptation, and Doppler integration grades severity; one label cannot substitute for the others.