1. BACKGROUND

1.1. Definition

Mitral valve disjunction (MVD) is the atrial displacement (>1 mm) of the mitral valve leaflets hinge point to the atrioventricular (AV) junction.

Fig 1: Perazzolo Marra, Martina, et al. "Morphofunctional abnormalities of mitral...

It is measured from the top edge of the ventricular wall to the hinge of the leaflet from the left atrial wall, at end-systolic phase (in which the ventricular lumen is smallest).

Fig 2: Diagram and 3C view of mitral valve disjunction. It is measured from the top of...

1.2. Pathology

Alteration of the anatomical relationship between the wall of the left atrium, the mitral annulus and the myocardium of the left ventricle (LV).

Fig 3: 2C view of mitral valve. Image 1 shows a normal anatomical relationship between...

The normal mitral annulus is a complex three-dimensional saddle-shaped, D-shaped structure. The mitral leaflets are asymmetric and the anterior leaflet attaches to approximately one-third of the annulus, but covers most of the valve orifice and forms part of the left ventricular outflow tract.

Fig 4: Image shows normal anterior (A1, A2, A3) and posterior (P1, P2, P3) mitral...

In MVD, the annulus is functionally decoupled from the LV, and paradoxical annular dynamics occur, as the annulus moves in concert with the left atrium during the cardiac cycle and not with the LV. it conditions: 

A. Loss of mechnical coupling to the LV

• Tethering of the mitral annulus to left atrial wall motion: 

  Conditions paradoxical systolic flattening: Left ventricular contraction is thought to cause structural reorganization of the annulus (which lacks contractile fibers) during systole by "pulling" adjacent mechanically coupled segments.

  Annular expansion at end-systole phase: The geometry and function of the mitral annulus are altered with the loss of systolic contraction. In early stages, early systolic contraction is affected, showing paradoxical annular expansion; but in advanced stages, there are no significant diastolic-systolic changes in annular diameter.

  

  Fig 5: Images 1 and 2: 3C TTE showing annular expansion at end -systole phase, going...
   

• Loss of “Saddle-shaped annulus" morphology 

  The normal saddle shape defines the insertion of the valve leaflets and the boundary between the Left atrium (LA) and LV. The loss of the usual systolic accentuation of the "saddle-shaped" morphology is secondary to the discontinuity between the left ventricular myocardium and the left atrial-annular continuum.

  

  Fig 6: Image 1: Degree of saddle defined as the ratio of annular height (H) to...
   

  As the valve flattens, subvalvular tension forces increase. 

• Valve hypermobility and chordae tendineae deformation. 

  Hypermobility, with a ”curling" of the annulus outward at high velocity during mid-systole. "Curling" is associated with increased posterolateral ventricular myocardium, hypertrophy (dancer’s foot sign) and fibrosis.

  

  Fig 7: Images 1 and 2 showing the appearance of the dancer’s foot. Image 3: MRI 3C...
   

B. Papillary muscle fibrosis and myxomatous degeneration of the leaflets

• Mechanical traction forces induce papillary muscle and inferolateral ventricular wall fibrosis

  The presence of disjunction generates traction forces that induce fibrosis of the papillary muscle and posterolateral ventricular wall.

  

  Fig 8: Figure 1: Global longitudinal strain (GLS) in a patient with mitral annulus...
  

  Fig 9: Figure 1 and 2: Global longitudinal strain (GLS) in patients with mitral...
   

• Myxomatous degeneration of the leaflets due to their excessive mobility

  MVD is associated with Myxomatous disease of the mitral valve and Mitral valve prolapse (MVP).

  Complications of MVD include: Sudden cardiac death (SCD) and cardiac arrest.

  Patients are usually asymptomatic; although it may be found mid-systolic auscultatory click; if MVP is presented and displaced point of maximal (apical) impulse with associated left ventricular dilation or a systolic murmur consistent; if mitral regurgitation.

  Traction of the posteromedial papillary muscle in mesosystole by the prolapsed myxomatous leaflet generates dragging of the adjacent myocardium from the posterolateral region towards the apex.

1.3. Location

Can be affected throughout its circumference, but the most common is posterolateral involvement, adjacent to the P1 and P2 valvular scallops, where the annulus is adjacent to the myocardium (visible in 3C view).

Fig 10: Cardiac Magentic Resonance planes used for assessment of mitral AV junction....

Fig 11: 3C view showing a postero/ inferolateral disjunction. Severe mitral...

1.4. Clasification

• Type I: Hypermobility without any radiologically visible separation 
• Type II: Distance < 5 mm
• Type III: Distance > 5 mm

Increased severity of MAD has been found to correlate with:

• Degree of mitral regurgitation 
• Number of valve segments with flail or prolapse
• Increasing burden of ventricular dysrhythmias