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.