Surgical implications
The concept of CC was addressed since the beginning to secondary MR, where chordal tethering was one of the most evident generating causes. However, even if excess of chordal tethering was considered a possible contraindication to MV repair, once accepted the concept of CC, the problem is to decide when CC has to be performed. In other words, is it necessary to cut always the second-order chordae or only in selected cases? This is an impossible question to answer. We can only speculate that the presence of chordal tethering is a possible cause of failure of MV repair, both in secondary and in primary MR, as causes at the basis of tethering are not only mechanical, but include metabolic changes that can make the process continue with time36.
In primary MR chordal tethering is a well known risk factor for MR return after repair for PL prolapse34,35. Then our advice is to cut the second-order chordae even if tethering is mild, irrespective from the leaflet that prolapse (fig. 3 and 4).
In case of secondary MR, chordal tethering is an uncontrolled variable that affects the long-term result. CC improves AL mobility, which favors coaptation. We think that in presence of unbalanced mitral plasticity (short AL and tethered chordae) we have to reproduce surgically what was the goal of plasticity, that is a long AL and elongated chordae. This procedure, by us called surgical mitral plasticity37, includes the augmentation of the AL and CC. When the AL is long enough to assure a good coaptation and the chordae are tethered, we prefer to cut them through an aortotomy (fig. 5). Persistence of chordal tethering after MRA is a risk factor for MR return (fig. 2).
The role of CC in MV repair, both primary and secondary, is not yet well defined. The suboptimal results of isolated MRA advice to expand the repair to valvular or subvalvular levels. CC, however, has not been included in any guideline, then its application depends on surgeon’s choice. The clinical experience in secondary MR, even if limited, since today is favourable, demonstrating a reduction of MR return without any negative effect on LV function. The marginal chordae are subjected to increased tension when PMs displace and, after CC, the further increase of tension is not enough to cause chordal rupture (the values of tension measured experimentally are 15- to 20-fold lower than the tension of rupture). The application of CC in primary MR is still episodic, but the adverse predictive effect of preoperative chordal tethering in prolapsing leaflets has been well studied in the literature.
CC is an effective and reproducible strategy that addresses an anatomical aspect that represent an uncontrollable variable (fig. 6) that can only worsen the surgical results.