Discussion
Our case report deals with an obscure anatomic variation, probably a
congenital abnormality, of the mitral annulus in which there is still
little literature. For the first time, in a study of 900 hearts from
adult autopsies, Hutchins et al. in 1986 reported a strong association
between the mitral annular disjunction and the presence of MVP (92% of
typical floppy mitral valves showed MAD); they also found out that it
could be detected in approximately 6% of patients without MVP [1].
This feature was also clinically confirmed by Konda et al. in a study
performed in order to investigate frequencies and characteristics of
mitral annular disjunction in patients referred to an echocardiography
laboratory. They even found a significantly larger percentage of cases
(12%) with mitral annular disjunction but no floppy mitral valve
[2]. They also reported meaningfully larger distance of the mitral
annular disjunction in patients affected by MVP than in patients without
it and was not founded any relationship between mitral annular
disjunction and the degree of mitral regurgitation (MR).
An increased frequency of premature ventricular beats, chest pain and
non-sustained ventricular tachycardia was firstly demonstrated by Carmo
et al. in patients with MAD in the setting of MVP [4]; this was
subsequently proved by the examination of 116 patients with MAD by
Dejgaard et al. This is the first large clinical trial on patients with
MAD where the authors examined patients with MAD clinically and by
echocardiography and cardiac magnetic resonance (CMR), in order to
describe the clinical presentation, MAD morphology, association with MVP
and ventricular arrhythmias. The most important finding was, however,
the high occurrence of ventricular arrhythmias in patients with MAD,
independently of concomitant MVP, suggesting the existence of a novel
clinical syndrome: MAD arrhythmic syndrome. They also identified young
age, lower ejection fraction and papillary muscle fibrosis as markers
for severe arrhythmic events. Interestingly, MAD patients with MVP were
less likely to have experienced severe arrhythmic events, unlike other
papers [3].
The association between MAD and arrhythmic MVP was provided by Basso and
Perazzolo Marra. They postulated a cascade of events caused by MAD and
leading to electrical instability and also hypothesized papillary
muscle, inferobasal wall stretch and fibrosis as arrhythmogenic areas in
MVP. The reason of this postulation was the observation of premature
ventricular beats originating from these LV sites [5] [6].
Posterior systolic curling caused by MAD might create a mechanical
stretch of the inferobasal wall and papillary muscle (PM), leading to
myocardial hypertrophy and scarring [7]. The association between LV
fibrosis and ventricular arrhythmias in MAD was than confirmed by
Dejgaard et al. [3]. MAD itself, even independently from MVP, can
therefore account for mechanical stretch of the myocardium and
arrhythmogenesis [8].
The main instruments to detect MAD are echocardiography and cardiac
magnetic resonance. Absence of myocardium during systole between the
posterior mitral valve annulus and adjacent basal segments of the
ventricular wall is representative of MAD. On echocardiography, this is
most commonly seen in the parasternal long-axis view [9].
Studies focused on MAD, using CMR, confirmed that in patients with late
gadolinium enhancement (LGE), presence of LV fibrosis at level of
papillary muscle was more frequent in patient with MAD and, according to
other studies, showed that patients with MAD have the tendency to be
younger and with lower ejection fraction (LVEF), irrespectively of MR
severity [10].
A review of several studies showed up that the occurrence of ventricular
arrhythmias was higher with a greater extent of MAD distance and
circumferential area, highlighting the link between electrical
instability and extent of MAD [9]. A MAD with disjunction of
>8.5 mm was revealed to be prognostic of an increased risk
of ventricular arrhythmias [4].
Recently, since MAD has been suggested as a possible cause of
ventricular arrhythmias and sudden cardiac death, Scheirlynck et al.
carried out a study to explore the presence of soluble suppression of
tumorigenicity-2 (sST2) and transforming growth factor-β1 (TGFβ1) as
stretch-related and fibrosis-related biomarkers in MAD patients. They
found that circulating sST2 levels were higher in patients with MAD and
ventricular arrhythmias, compared with arrhythmia-free patients, while
TGFβ1 levels did not differ. Interestingly, they hypothesized that the
combination of sST2, LVEF and LGE assessment might detect high-risk
individuals [11].