Teaching Case

A 10-year-old boy presented with complaints of multiple episodes of fainting and lightheadedness for a few months. There was no breathlessness or chest pain. No significant past medical history. Physical examination was unremarkable. 2D ECHO done elsewhere was suspicious for superior displacement of the mitral annulus junction.

Cardiac MRI (CMR) was performed with images obtained in the two-chambered, four-chambered, short-axis plane along with late gadolinium enhancement phase. There is a thickening of the mitral leaflets with myxomatous degeneration (Figure 1). There is a superior (atrial) attachment of the mitral annulus, away from the ventricular myocardium, suggestive of mitral annular disjunction (Figure 2). The length of the disjunction is 8.5mm. There is curling of the mitral annulus during systole. There is a jet towards the atrium during systole suggestive of mitral regurgitation (Figures 3a, 3b and 5). There is no late gadolinium enhancement in the myocardium or the papillary muscles to suggest fibrosis.

The mitral valve apparatus consists of the annulus, the leaflets, chordae tendineae and the papillary muscles [1,2]. The anterior annulus is in continuity with the aortic annulus. The posterior annulus is relatively mobile and is attached to the left atrial wall at its junction with the left ventricle [1,2].

Due to the specific anatomy, the mitral annulus contracts during systole and the leaflets are prevented from prolapsing into the atrium by the chordae tendineae due to papillary muscle contraction. However, in mitral annular disjunction (MAD), there is superior (atrial) displacement of the mitral annulus away from the ventricular myocardium (Figures 4a, 4b and 4c) [2]. Thus, MAD can contribute to or can be associated with mitral prolapse during systole. There can be outward curling of the annulus with the resultant increase in the diameter of the annulus. There can be associated myocardial stretching, myxomatous degeneration of the leaflets, abnormal tugging of the chordae tendineae with resultant papillary muscle hypertrophy, and, ultimately, fibrosis. Very rarely, there can be associated tricuspid annular disjunction [2].

MAD is frequently associated with mitral valve prolapse (MVP). However, it is unclear whether MAD is the cause or effect of MVP, or is an independent entity. It has been found that MAD is more commonly seen in younger individuals compared to MVP [3]. MAD is associated with arrhythmias and a risk of sudden cardiac death (SCD) [3,4]. Hence the emphasis on prompt and early recognition of the pathology.

Clinically, patients present with palpitations, syncope, or collapse due to arrhythmia. An electrocardiogram can pick up the ventricular arrhythmia. Echocardiography can detect the abnormal insertion of the mitral annulus, in the parasternal long axis plane. Cardiac CT is superior due to its multiplanar reconstruction and better anatomical delineation. However, cardiac MRI is considered the gold standard as it can also diagnose papillary muscle fibrosis (late gadolinium enhancement), and scar burden [2,4]. Dynamic imaging in the form of video images helps to differentiate it from pseudo-MAD, where the leaflet may be juxtaposed to the atrium, while the hinge is attached normally to the atrioventricular junction (Figures 4a, 4b and 4c) [2,4]. Although the disjunction itself is often more prominent in diastole, its effects are most noticeable in systole [5]. CMR can also provide an accurate quantification of mitral regurgitation, which is often associated with MAD and MVP.

The length of the annular disjunction is directly related to arrhythmogenicity, with a distance of more than 5mm considered significant [2]. The range of the circumferential extent of MAD involvement, presence of prolapse, ventricular hypertrophy, and status of the valves have to be mentioned.

Treatment includes anti-arrhythmic drugs (usually refractory), an implantable cardiac defibrillator, or mitral valve repair [4]. The choice of treatment depends on the severity of symptoms, associated mitral regurgitation, and the degree of ventricular arrhythmias.