By Michael H. Crawford, MD, Editor

SYNOPSIS: A patient cohort with mitral annular disjunction (MAD) identified by echo was characterized clinically and by MRI. Ventricular arrhythmias were common in MAD patients and related to the degree of MAD and papillary muscle fibrosis by MRI but not the presence of mitral valve prolapse.

SOURCES: Dejgaard LA, Skjølsvik ET, Lie ØH, et.al. The mitral annulus disjunction arrhythmic syndrome. J Am Coll Cardiol 2018;72:
1600-1609.

Basso C, Perazzolo Marra M. Mitral annulus disjunction: Emerging role of myocardial mechanical stretch in arrhythmogenesis. J Am Coll Cardiol 2018;72:1610-1612.

Displacement of the left ventricular (LV) basal wall from the mitral annulus or mitral annulus disjunction (MAD) is associated with mitral valve prolapse (MVP), papillary muscle fibrosis, and ventricular arrhythmias. However, these interrelationships are poorly understood. Dejgaard et al sought to clinically characterize patients with MAD and describe MAD anatomy by echocardiography and cardiac MRI.

In two hospitals in Norway, patients with MAD were identified in the echo lab and recruited into the study, which included a new echo, cardiac MRI, ECG, and clinical assessment. Patients with aborted cardiac arrest underwent a full evaluation for etiologies. Patients with a history of ventricular arrhythmias underwent ECG monitoring, exercise testing, or telemetry strips analysis. Of 122 patients identified during screening, protocol echo or MRI revealed the presence of MAD in 116 patients. A history of palpitation was common (71%), and 12% had experienced severe arrhythmic events. MAD longitudinal distance averaged 3 mm by MRI (range, 0-7.9 mm). Circumferential MAD averaged 150° (range, 30° to 240°). Also, MAD was confined to the annulus of the posterior leaflet.

MVP was present in 78% of MAD patients. A 24-hour ECG was obtained for 70% of all patients. Arrhythmia frequency was not different between those with and without MVP. An evaluation did not reveal another etiology for any of the 10 patients with cardiac arrest. In a multivariate analysis, longitudinal MAD distance and papillary muscle fibrosis by late gadolinium enhancement on MRI were associated with ventricular arrhythmias. Patients with severe arrhythmic events more frequently exhibited papillary muscle fibrosis than those without such events (36% vs. 9%; P = 0.03). The authors concluded that MAD, but not MVP, was associated with ventricular arrhythmic events.

COMMENTARY

Although known about for more than 30 years, MAD generally has been thought of as a subtype of MVP that increases the risk of ventricular arrhythmias. This study and others have shown that MAD can exist without MVP and carries a high risk of serious ventricular arrhythmias (31% in this select series). Paradoxically, this study shows when MVP is associated with MAD, arrhythmic risk is lower (7%). MAD leads to an abnormal curling motion of the basal posterior wall, which may result in increased wall stress and subsequent ventricular arrhythmias. If the individual also has MVP, this may reduce the wall stress, especially if there is mitral regurgitation, and decrease the incidence of VA. In support of this stress hypothesis, VAs also were associated with the presence of papillary muscle fibrosis on MRI. Further, some have hypothesized that MAD may be the initial lesion, and abnormal stress on the mitral apparatus leads to degeneration of the mitral valve apparatus. However, since there are many causes of MVP, this hypothesis (if true) would only explain a subgroup of MVP patients.

The major limitations to this study were the cross-sectional design with clinical events collected retrospectively and the selection bias of patients in whom an echo was ordered. Thus, the results may not apply to a general population. Also, ambulatory ECGs were not performed for all patients, nor were MRIs. In addition, without follow-up information, it is difficult to estimate the clinical impact of these findings.

Several clinical issues arise from this study. If one incidentally finds MAD in a patient imaged for nonarrhythmic reasons, should the clinician order an ambulatory ECG? If a patient is undergoing surgical mitral valve repair, should the surgeon correct the MAD? How should MAD-associated ventricular arrhythmias be treated: with drugs, ablation, or ICD? Since the MAD distance can vary along the mitral annulus and range from zero to several millimeters in the same patient, should all patients with MVP and no MAD detected undergo an MRI? Can some degree of MAD be a benign normal variant? These and other questions will await further studies of this interesting but potentially lethal condition.