Surgical Correction of the Posterior Mitral Annular Disjunction Associated With Structural Abnormalities of the Mitral Valve

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Mitral annular disjunction (MAD) is a structural abnormality characterized by the separation of the mitral valve annulus from the left atrial wall and the top of the left ventricular myocardium. 

MAD is frequently associated with mitral valve prolapse (MVP) and is more prevalent in myxomatous disease than in fibroelastic deficiency. The impact of MAD on long-term outcomes remains to be determined; however, incorrect positioning of the annuloplasty ring may contribute to the failure rate after mitral valve repair. 

Anatomy 

The annulus of the mitral valve (MV) is not a continuous fibrous structure. The anterior annulus is composed of densely collagenous fibers and is part of the fibrous skeleton of the heart, in conjunction with the aortic valve. Conversely, the posterior annulus is thinner and, in certain cases, shows discontinuity and direct attachment to the highly mobile crest of the left ventricle (LV) free myocardium. 

In 1986, Hutchins observed a separation between the left atrioventricular junction and the LV free wall, which he termed "disjunction" (1). The precise mechanism remains to be elucidated. The prevalence of MAD in the general population is about seven percent, with a higher incidence observed in young women and a significant correlation with LV systolic size. This condition can be considered a normal anatomical variant. 

Advanced myxomatous valve disease (Barlow's disease) with bileaflet involvement is independently associated with pathogenic MAD, typically observed in the central region of the posterior annulus, directly beneath the posterior mitral valve leaflet in the region of the P1 and P2 mitral valve scallops. A displacement distance of 3 mm or less is considered a benign finding, while distances greater than 8.5 mm are identified as strong predictors of ventricular tachycardia. The mean disjunction height over 5 mm has been shown in most patients with MVP. 

Diagnosis 

MAD can be visualized by echocardiography as the absence of myocardium during mid to late systole. Cardiac magnetic resonance (CMR) demonstrates superior resolution compared to echocardiography in detecting the presence, extent, and location of MAD. It also facilitates the differentiation between true MAD and pseudo-MAD, which is the apparent separation of the posterior MV leaflet that abuts the left atrium (LA) wall during systole. In addition, CMR has the advantage of assessing myocardial fibrosis. 

Discussion 

The recognition of MAD is crucial for the surgical planning of mitral valve surgery. The geometric restoration of the mitral annulus, with precise positioning of the ring or band, ensures immediate success, reproducibility, and the durability of the repair. 
 
The annuloplasty ring or prosthesis must be attached to the mitral annulus at the correct level to fill the gap caused by the disjunction, rather than being attached to the left atrial wall. Surgical MV repair is currently the standard of care for patients with MVP and MAD who suffer from ventricular arrhythmias. Transcatheter edge-to-edge MV repair cannot correct annular-myocardial separation. 
 
The Tirone David group has demonstrated the importance of annular reconstruction reinforcement for successful valve repair. They proposed a method that involves detaching and reducing the height of the posterior leaflet before reattaching to the LV's proximal musculature, followed by placement of the annuloplasty ring along the reconstructed area (8). 
 
Given the histology of the mitral annulus, which exhibits variability in its circumferential extent, the suturing technique should be tailored to the specific points. The posterior portion of the mitral annulus, which is sometimes absent, necessitates a distinct technical approach to the anterior portion, which is part of the heart's central fibrous skeleton. 
 
In this context, the surgeons opted to utilize pledget-reinforced sutures in the posterior annulus, aiming to address the fixation of the upper left ventricular muscle. The placement of the pledget in the ventricular portion was independent of whether the procedure involved repair or valve replacement, with total or partial preservation of the posterior cusp and corresponding tendinea chordae. 
 
In the anterior annulus, direct sutures were employed without pledgets, considering the preference for complete rings or sutures with pledgets on the atrial surface in cases of valve replacement. 
 
It is imperative to underscore those sutures reinforced with a pledget on the posterior annulus, which are intended to close the gap between the LA and the LV, must be fixed in its ventricular portion, even if the posterior cusp is preserved. If the pledget is placed carefully in this ventricular portion, it should not be affected by the presence of the posterior cusp and chordae tendineae. 

Future Directions 
 
The resolution of MAD has been demonstrated to reduce the arrhythmia burden in patients with MVP. This procedure has the potential to relieve the excessive stretch on the papillary muscles, thereby eliminating the trigger for ventricular arrhythmias. It may benefit patients with MAD who do not have a classical indication for MV surgery. However, prospective data are required to define the role of this treatment. 
 
Although the technique described was developed for the treatment of MVP with MAD, the surgeons currently treat the posterior mitral annulus in the same way regardless of the etiology of the mitral valve disease (i.e., rheumatic, myxomatous degeneration, or fibroelastic deficiency), even without the presence of MAD. This approach is believed to ensure that the ring or prosthesis is placed in the correct position, thus avoiding displacement into the atrium or any residual MAD. Studies with a greater number of patients and longer follow-up will show whether this technique will bring future benefits in terms of recurrences of mitral regurgitation or arrhythmias. 
 
Conclusion 

The recognition of mitral annular disjunction is relevant for the choice of the optimal surgical technique used for the mitral repair and might improve long-term durability. The annuloplasty ring or the prosthesis should be sutured to the mitral annulus at the correct level of the myocardium to obliterate the gap caused by the disjunction, rather than being attached to the left atrium wall. The pledget sutures placed at the top of the left ventricular muscle on the posterior annulus guarantee the correct attachment of the ring and close the gap after repair or even replacement of the mitral valve. 

References

1. Hutchins GM, Moore GW, Skoog DK. The association of floppy mitral valve with disjunction of the mitral annulus fibrosus. N Engl J Med 1986; 314:535-40.
2. Gaudiani V. The Full Anatomy and Physiology of the Mitral Valve Explained. August 2024. doi:10.25373/ctsnet.26784904
3. Bennett S, Thamman R, Griffith T, et al. Mitral annular disjunction: A systematic review of the literature. Echocardiography 2019; 00:1–10. https://doi. Org/10.1111/echo.14437
4. Van der Bijl PP, Stassen J, Haugaa KH, et all. Mitral Annular Disjunction in the Context of Mitral Valve Prolapse Identifying the At-Risk JACC Cardiovasc Imaging. 2024;17 (10):1229–1245.
5. Essayagh B, Sabbag A, Antoine C, et al. The mitral annular disjunction of mitral valve prolapse: presentation and outcome. JACC Cardiovasc Imaging. 2021; 14:2073–2087.
6. Souza AC, Carvalho MVSF, Sales MA, et all. Disjunção do Anel Mitral: Modalidades Diagnósticas, Implicações Clínicas e Evolução Prognóstica. Arq Bras Cardiol: Imagem cardiovasc. 2022;35(3): eabc300 doi: 10.47593/2675-312X/20223503eabc300
7. Zhua L, Chuaa YL. Mitral Annular Disjunction: Clinical Implications and Surgical Considerations. Cardiol Res. 2023;14(6):421-428. https://doi.org/10.14740/cr1584.
8. Newcomb AE, David TE, Lad VS, Bobiarski J, Armstrong S, Maganti M. Mitral valve repair for advanced myxomatous degeneration with posterior displacement of the mitral annulus J Thorac Cardiovasc Surg 2008; 136: 1503-9

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