At the Cutting Edge

Corresponding Author

In this issue of JACC: Asia, Lu et al,¹ describe a classification system for commissural mitral regurgitation (MR). The ostensible goal for this was to facilitate a common understanding of commissural MR and guide the use of transcatheter edge-to-edge repair (TEER) techniques. Currently, there is no established classification system for types of commissural MR, especially with regards to TEER. However, Lu et al¹ are not the first to propose a classification system of commissural MR. In the context of planned TEER, Seo et al^2,3 had described their experience in which commissural MR may be treated by clipping the posterior or anterior leaflet to the commissure or clipping the commissure itself. The technique uses the “Stitch” artifact caused by respiratory movement when generating a 3-dimensional (3D) image. Seo et al also highlights that although 3D multiplanar reconstruction (MPR) can also be used to achieve the same results, the Stitch technique has better temporal and spatial technology, and is more widely available. However, with greater adoption of modern 3D MPR technology, the use of the Stitch artifact may no longer be necessary today. Furthermore, Seo et al’s classification, while intuitive, may not adequately consider other aspects of the commissural anatomy such as size of the commissure, the length of the posterior leaflet, or the extent of prolapse or flail commissure and/or that of the neighboring leaflets.

In this paper by Lu et al,¹ the investigators describe the prospective experience across 6 sites in China in which patients with commissural degenerative MR are evaluated with echocardiography, classified into 4 different types (Types I, II, IIIa, and IIIb) and then treated accordingly to a prespecified TEER protocol. Using the classification system and TEER strategy, the investigators describe an excellent technical success rate (100%) and excellent 1-year residual MR ≤2+ in 94.1%. These results are comparable with contemporary results from the EXPAND (A Contemporary, Prospective Study Evaluating Real-World Experience of Performance and Safety for the Next Generation of MitraClip® Devices) and PASCAL IID (Edwards PASCAL Transcatheter Valve Repair System Pivotal Clinical Trial) studies.^4,5 It should be noted that in this present study, only the MitraClip NTR and XTR systems (Abbott) were available and not the current G4 system. Lu et al’s classification system, meant for patients with degenerative MR, has several advantages and addresses some of the limitations of Seo et al’s. First the classification system was evaluated prospectively and utilized an independent echocardiographic core laboratory. Second, it can be used to guide TEER procedural outcomes with documented clinical procedural outcomes to validate the classification system and proposed clipping strategy. In particular, the Type II and IIIb types of degenerative commissural MR appear to present the greatest technical challenge and longest procedural time. It should be noted that the study excluded 7 patients (of 126) who had posterior leaflet <6 mm (Supplemental Figure 1¹). This suggests that the so-called Type IIIb patients would have posterior leaflet lengths of 6 to 7 mm. This detail does limit the utility of the Type IIIb category. The classification system also highlights the risks associated with TEER for Type II and IIIb anatomy with the greatest occurrence of valvular apparatus related complications (eg, single-leaflet attachment, leaflet injury, and chordal entanglement) in these patients. Experienced operators in TEER would identify with the challenges in treating the anatomy described. Indeed, given the small numbers in these 2 groups, it can be argued that the greater technical challenge is in the Barlow’s nature of the proposed Type II anatomy, and in the short posterior leaflet (<7 mm) in the Type IIIb anatomy. Third, this proposed classification system has the benefit of being utilized in 68 patients in 6 centers across China, with each site having a minimum TEER experience of 50 patients. This suggests that the classification system and technique can be adopted in reasonably experienced TEER centers.

Nonetheless, this classification system and treatment has several important limitations. First, the study described the experience of TEER in 68 of 126 patients with commissural MR. The numbers in each group were small, ranging from 11 to 21 patients. Given the importance of imaging and procedural technical expertise, the small numbers in each group will limit the interpretability of results. Second, the classification requires high-quality transesophageal echocardiography assessment. This is not always achievable given the variability in human anatomy, and the training and experience of the echocardiologist, especially with the use of 3D MPR. Third, the dimensions of the various leaflets including the commissural components are not dichotomous variables, and the relative sizes of the leaflets may complicate neat classification attempts. Third, the mitral apparatus is highly complicated, and the location of subvalvular apparatus (not easily visualized) and relevant chordal injury may also complicate TEER repair strategies. Fourth, indentations and clefts may not only complicate transesophageal echocardiography assessment but also influence the ability of the proceduralist to execute a TEER plan according to this classification. Fifth, the authors mentioned “restrictive,” “zipping,” “anchoring,” “integrating,” “simultaneous,” and “staged” clipping strategies in the text and in Figure 1.¹ Clarity in what these techniques entail may be helpful for non-experts to master these techniques. Sixth, although the described strategy may work, this study is descriptive in nature and does not compare alternative strategies. Lastly, this strategy utilizes only the MitraClip technology for TEER. With devices such as PASCAL (Edwards Lifesciences,) and Dragonfly (Valgen Medtech), potential technical considerations such as the presence of a spacer-like component may potentially complicate the strategy. At the same time, it is likely that the choices and technology improvements seen in the MitraClip G4 system may also translate to superior outcomes compared with the older-generation NTR and XTR systems in this present study.

For this proposed system to work, further research is required to validate its utility in other larger datasets or in a larger, perhaps international, prospective study. Nonetheless, this attempt by Lu et al¹ to classify commissural MR is an important and meaningful step forward because it recognizes the variability of commissural disease and the involvement of neighboring leaflet morphology and proposes a viable TEER strategy. While the results reported here are promising, it remains to be seen whether the experience described here can be replicated and if prospective use of this classification system will indeed lead to superior procedural outcomes.

Funding Support and Author Disclosures

Dr Yeo has received research support from Abbott Vascular and Boston Scientific; consults for Abbott Vascular, Boston Scientific, Medtronic, and Peijia Medical; has received speaker fees from Abbott Vascular, Biotronik, Boston Scientific, Edwards Lifesciences, Medtronic, MicroPort, Shockwave Medical, and Terumo; and is also co-founder and owns equity in Trisail for which OrbusNeich is an investor.