Mitral annular disjunction

Mitral annulus disjunction (MAD) is an anatomic abnormality involving the confluence of the left atrium, mitral valve annulus, and the base of the left ventricle. It is classically associated with the spectrum of myxomatous disease of the mitral valve and mitral valve prolapse (MVP). 

Epidemiology

Mitral annulus disjunction has been reported in 42-90% of patients with myxomatous mitral valve disease and mitral prolapse. The condition seems to be more common in women ¹.

Associations

Mitral annular disjunction has been associated with the following clinical conditions ^1-4:

• mitral valve prolapse (MVP)

  • particularly bileaflet prolapse ¹²

• myxomatous degeneration of mitral leaflets

• sudden cardiac death

  • ventricular ectopy and dysrhythmias

Clinical presentation

Patients may be asymptomatic with an incidental discovery or present with symptomatic dysrhythmias (palpitations, presyncope, dyspnea).
Sudden cardiac death (SCD) is a described presentation. 

Physical examination is non-specific, but may reveal findings of related anomalies such as MVP (mid-systolic auscultatory click ^1,4) or resultant pathologic sequelae such as a displaced point of maximal (apical) impulse with associated left ventricular dilation or a systolic murmur consistent with mitral regurgitation.  

Complications

Complications of mitral annular disjunction include the following conditions ^1-3:

• ventricular arrhythmias

• cardiac arrest

• sudden cardiac death

Pathology

The substrate for mitral annular disjunction (MAD) is a pathologic alteration of the anatomic relationship between the wall of the left atrium, the annulus fibrosus of the mitral valve, and the left ventricular myocardium. The pathognomonic feature is significant (usually exceeding 5 mm) displacement of the left atrial wall-mitral valvular junction which has become pathologically discontinuous from the corresponding basal left ventricular myocardium.

The saddle-shaped annulus of the mitral valve defines the insertion of the valve leaflets and defines the boundary between the the left atrium and left ventricle; in doing so it provides mechanical coupling of the atrium/valve apparatus and basal ventricular myocardium. Optimal annular structure and dynamic function, such as the early systolic contraction of annular dimensions and cyclical geometrical variation, is an important component of valvular competency. Left ventricular contraction and deformation is thought to drive the movement and structural rearrangement of the annulus (which lacks contractile fibers) during systole by "pulling" mechanically coupled adjacent segments ⁹. 

The presence of a discontinuity between the left ventricular myocardium and the left atrium-annulus continuum occurs in MAD with subsequent loss of mechanical coupling to the ventricle, resulting in such pathophysiologic derangements such as:

• tethering of the mitral annulus to left atrial wall motion with paradoxical systolic flattening, expansion and alteration in shape

  • loss of the usual systolic accentuation of "saddle-shaped" morphology ¹²

• hyper-mobility, with a high velocity outward "curling" of the annulus during mid systole and resultant deformation of the corresponding papillary muscle via the chordae tendinae ¹¹

These changes are thought to unfavorably change the distribution of mechanical stress on the mitral valve apparatus resulting in degeneration of the chordae and leaflets with a spectrum of multi-segmental leaflet prolapse and flail and increasingly severe mitral regurgitation ¹⁰.

The extent of mitral annular disjunction may be quantified by measuring the distance between the insertion of the leaflet at the left atrial wall and the left ventricular myocardium as well as the circumferential extension ^1-3. Increased severity of MAD has been found to correlate with:

• degree of mitral regurgitation ¹⁵

• number of valve segments with flail or prolapse

• increasing burden of ventricular dysrhythmias

Classification

A suggested classification for subgrouping MAD by measured degree of disjunction was proposed in 2013 by Konda et al. ^16,17:

• type I: excessive annular mobility with an absence of a visualized separation between annulus and basal left ventricular myocardium

• type II: annulus-ventricular separation (i.e. disjunction) of less than 5 mm

• type III: disjunction greater than 5 mm

Location

The annulus can be affected throughout its circumference, and may have multiple areas of discontinuous involvement. MAD most commonly occurs at the posterolateral annulus adjacent to the valvular scallops P1 and P2, affecting the posterior leaflet ¹². Involvement of both anterior and posterior leaflets is not uncommonly observed. The least common variant affects the anterior leaflet alone.

Radiographic features

Mitral annulus disjunction is most easily appreciable in systole when the detachment of the left inferolateral myocardial wall from the posterolateral portion of the mitral annulus can be demonstrated.

Likewise, the distance between the posterior mitral valvular leaflet insertion at the atrial wall and the connection of the left atrial wall to the myocardial free wall is measured in systole ^1-3.

Echocardiography

Echocardiography is considered is usually the first-line imaging modality for the evaluation of mitral valvular disorders ¹. A distance between the posterior mitral leaflet insertion and the left ventricular myocardium of ≥5 mm in transesophageal echocardiography is considered diagnostic ^1,5.

CT

Cardiac CT can identify and depict mitral annulus disjunction as a separation between the left atrial wall mitral valve leaflet junction and left ventricular wall along the mitral annular circumference ¹.

MRI

Cardiac MRI can detect and characterize the circumferential extent of mitral annulus disjunction and systolic curling. The separation distance has been described to vary between 1 and 15 mm ³. Moreover, cardiac MRI can assess myocardial fibrosis in the basal inferolateral free wall or papillary muscles, which can be depicted with T1 mapping or late gadolinium enhancement ^1,4.

Radiology report

The radiological report should include a description of the following features ¹:

• presence of absence of mitral annular disjunction

  • measured distance of leaflet insertion from left ventricular myocardium

• circumferential extent

• mitral valve prolapse

• myxomatous mitral valve leaflet thickening

• mitral regurgitation

• signs of replacement fibrosis

• basal left ventricular hypertrophy

Treatment and prognosis

Management apparently differs according to the experience in different centers. Medical therapy with beta-blockers is under consideration ².

Implantation of an implantable cardioverter-defibrillator (ICD) might be considered as secondary prevention in patients, who have experienced cardiac arrest and no underlying reversible cardiac disease ^1,2.

History and etymology

The term ‘mitral annular disjunction was first used by Bharati et al. in 1981 and later defined by Hutchins et al. in 1986 ^2,4-6.

Differential diagnosis

Conditions mimicking the imaging appearance of mitral valve disjunction include:

• mitral valve prolapse

• Anderson-Fabry disease