Ring sizing and coaptation length: creating the goldilocks mitral repair

The authors explore an underappreciated aspect of mitral repair, creating the ‘right’ coaptation length (CL) [1]. CL is the end result of the repair and key to a durable repair. Too little coaptation and there may be residual or recurrent mitral regurgitation (MR). Too much coaptation and the excess leaflet tissue in the left ventricle may develop systolic anterior motion (SAM), especially when the coaptation to septum distance (C-sept) is 25 mm or less.

This article highlights important questions that are rarely discussed: what is ‘normal’ CL; what should be the ‘target’ CL; and how do you modify the repair technique and ring size to achieve the ideal CL? There is a paucity of data about normal CL. If it is measured under general anaesthesia, as the references in this article, it is prone to errors from loading conditions. The authors chose 11 mm as the target CL based upon these data and their study. But, in conscious normal adults, the CL average is as low as 5 mm at A2 and 2 mm at A1 and A3 [2]. It would be helpful to have better studies of normal CL and ranges, using cohorts with a large distribution of ages, diversity and gender. That does not exist yet but could be assessed through 3D echo or computed tomography (CT) studies. Targeting a ‘normal’ 2–5-mm CL after repair for degenerative MR seems unwise, as myxomatous tissue is likely less efficient at sealing the orifice than normal tissue. Some moderate MR recurs over time in large series, likely from progression of the underlying disease, and a higher CL than normal post-repair intuitively will decrease late recurrence. At Northwestern, we targeted 5–10-mm CL, as per writings and discussions with Professor Carpentier [3, 4]. At 10 years, in a series of 1051 patients using a quantitative approach to repair, we reported a 0.3% reoperation rate, 1.4% more than moderate recurrent MR and 15.6% moderate at any time during follow-up [3]. The authors found that CL length of ‘less than’ 11 mm was associated with a higher recurrence of moderate or more MR at 5 years. Sasaki et al. [5] reported that a CL of <5.6 mm had a 78% sensitivity and 89% specificity for predicting recurrent MR. We did not find an association of recurrence of MR with CL [3]. If you routinely use small rings to create a high CL, especially in the setting of a C-Sept distance of 25 mm or less, the likelihood of SAM increases (as well as high gradients and possible stenosis). The authors had a patient with CL over 11 mm who required a reoperation at 1 month for SAM. In the Northwestern experience, SAM was only seen in 0.3% [3] with no reoperations for SAM. We think that is because we follow an algorithm using leaflet length, C-Sept, rules guiding leaflet reconstruction and proper ring size [3].

How do you modify the repair to achieve a desired CL, but not so much that SAM is created? Actually, it is simple. Repair and ring sizing is based on mathematics. The operative steps include measuring C-Sept and length of A2 with transoesophageal echocardiography. A2 length is confirmed by direct measurement. The posterior leaflet, involved in approximately 90%, is resected and reconstructed to half the height of A2, or a maximum of 15 mm. The height of the reconstructed posterior leaflet is remeasured. The total leaflet length is A2 and reconstructed posterior leaflet length. A ring is chosen with the desired AP diameter (the manufacturer can supply this). For example, a 28-mm A2 and 14-mm reconstructed posterior leaflet (42 mm when added together) will yield 7 mm of coaptation if a 28-mm AP diameter ring is used. (42–28 = 14; equal distribution of coaptation on each leaflet assuming there is no residual prolapse or restriction yields 7-mm coaptation on each leaflet). The CL can be created to the length the surgeon desires. You can achieve 11-mm coaptation by using a ring with a 20-mm AP diameter (42–20 = 22; divided in half is 11-mm CL). We have not used a ring ‘sizer’ in years. They are unnecessary if you know the numbers. If the C-Sept is <25 mm, then the surgeon can adjust 2 variables; make the posterior leaflet shorter or use a larger ring to achieve less CL (target 6 mm?). Should the target CL be 5.5 mm or more as in the Sasaki experience, or over 11 mm in this experience? We have routinely avoided SAM and recurrent MR targeting a range of 5–10 mm.

Transcatheter aortic valve replacement (TAVR) requires many CT and imaging measurements to guide, which commercial valve is chosen, what size, and the best landing zone. TAVR rapidly became very predictable and spread rapidly. Many believe that degenerative MR repair is very complex and only a handful of surgeons develop the experience and ‘art’ to create durable repairs. Mitral repair needs to move forward. We need to approach this like TAVR. We trained in science, not art.

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