Mitral annular disjunction has been scarcely mentioned in the literature. In a paper based on a review of 900 random histological mitral annulus exams at necropsy, Hutchins et al [1] describes a wide range of normal anatomic variation for this region. These authors observed mitral annulus disjunction in 65 (7%) hearts, 23 of them in association with floppy mitral valve. This abnormality was also seen in association with isolated calcified mitral annulus, and with otherwise normal hearts. Because patients with isolated annular disjunction were younger than those with associated floppy mitral valve it was suggested that the disjunction could play a role in the pathogenesis of myxomatous valve disease, through the increased mechanical stress induced by the excessive mobility of the mitral leaflets [1].
As for our results, the prevalence of annular disjunction in the setting of myxomatous valve disease is significantly high (55%). Although impressive, this proportion is nevertheless smaller than the 92% prevalence found by Hutchins et al [1], and the 98% prevalence found by Eriksson et al [2] with transoesophageal echocardiography in patients with advanced forms of myxomatous mitral valve disease. Both the reduced sensitivity of a transthoracic examination and the use of different diagnostic criteria may account for these discrepancies.
Real-time three-dimensional (3D) and 3D reconstruction transoesophageal echocardiography affords a better accuracy in patients with complex MV pathology when compared with 2D transoesophageal echocardiography.[6, 7] The complex structure of the mitral annulus makes it particularly suited to 3D assessment. MV may be viewed from either atrial or ventricular perspectives (en face) which permit a full length view of the mitral annulus contrasting with the segmental view offered by 2D assessment. This feature can enhance the sensitivity for the detection of mitral annular disjunction. However, the image quality using transthoracic echocardiography is sometimes poor weakening its advantage.
To the best of our knowledge, this is the first study where the recognition of mitral annular disjunction is described by transthoracic echocardiography. On intraoperative transoesophageal echocardiography, Eriksson et al described a significantly higher rate of mitral annular disjunction in patients with advanced versus mild or moderate mitral valve degeneration (98% vs 9%)[2]. In our series, there wasn't any relation between annular disjunction and other specific echocardiographic features, namely the degree of mitral valve regurgitation, atrial or ventricular enlargement and ventricular function.
Mitral annulus contractility contributes significantly to mitral valve function. Shortening of the annulus diameter during systole facilitates coaptation of the mitral leaflets [8–10]. Impairment of mitral annulus function is known to be associated with mitral regurgitation associated with myxomatous mitral valve disease, and has recently been implicated as a cause for valve repair failure [10, 11].
In the presence of annular disjunction, the valve insertion in the "atrial wall" is responsible for an increased diameter of the mitral valve circumference during systole, and hence impaired annular function due to coaptation deficit. Underestimating this abnormality during mitral valve repair can result in recurrent mitral regurgitation, since paradoxical systolic enlargement will persist [2].
The risk of sudden death is increased in patients with mitral regurgitation due to myxomatous mitral valve disease. Prior to surgery, the incidence of sudden death is 1.8% per year, accounting for one-fourth of the causes of death. Patients with severe symptoms, atrial fibrillation, and reduced LV systolic function are at higher risk. However, even asymptomatic patients in sinus rhythm with normal LV function are not exempt of risk, which occurs with an incidence of 0.8% per year [12–15]. Increased frequency of ventricular arrhythmias in myxomatous mitral valve disease may result from abnormal excessive traction on papillary muscles, generated by the parachuting closure of the mitral valve [16]. As proposed by Hutchins et al, the annular disjunction may, for itself, increase the tension over the mitral apparatus [1]. This mechanism could hypothetically predispose to ventricular arrhythmias. In our study, despite the absence of sustained ventricular arrhythmias, there was an increased frequency of ventricular extra beats and of non-sustained ventricular tachycardia in patients with greater lengths of annular disjunction.
The limitations of this study are its retrospective nature, the rather small population, and the performance of 24-hour Holter monitoring in a limited subset of patients. Larger and prospective studies are needed to validate our findings. Nevertheless, the novelty of the subject and the implications for both surgical management and for arrhythmic events remain of paramount importance.
