The issue of the chordal length
Regardless of how to proceed to anchor the artificial chords to the PMs
or to the mitral leaflet, the real challenge that many surgeons have
taken on, giving rise to some very creative solutions, has been to
establish an adequate length of the chord.
Ibrahim et al29 tried to classify the different
methods in some groups: fixed length with or without caliper, anatomical
and adjustable length.
von Oppell and Mohr measured the length of the loop22,
taking into account the distance between the adjacent normal valve
segment and the respective PM tip. Once the length is established, the
surgeon constructs the loop using that fixed distance by means of a
caliper. Then, the loop is attached to ventricular face of the free edge
of the leaflet by means of a new Gore-Text suture passed inside the loop
itself, while the two arms of the suture are passed into the PM head and
knotted on two pledgets (Figure 1).
A different use of a caliper was proposed by Doi et
al.28 who passed the Gore-tex suture through the rough
zone of the leaflet, from atrial to ventricular face, and then through
the free edge of the leaflet. This leaves an adjustable loop, into which
surgeon introduces the caliper set at a distance already established
using preoperative transesophageal echocardiography. The loop is then
tied. (Figure 2)
Matsui et al30 introduced a new device consisting of
two small metallic tubes with distal tip, one sliding over the other, to
be used as a caliper. The exact length is established measuring the
distance between the leaflet edge and the site of implantation of the
artificial chords on the papillary muscle on the basis of a normal valve
adjacent segment. The Gore-Tex suture can be tied without knot
slipping.
Tam et al31 proposed a technique similar to the one
introduced by others22, rolling a 4-0 ePTFE suture
around a caliper at a fixed length and then the loops are fixed with a
5-0 ePTFE sutures and onto the PM tips using two pledgets.
Other authors suggested to determine the length of chords without using
a caliper, by means of a series of tight reverse knots corresponding to
a certain length32, or tying loops at a predetermined
length temporarily fixing them at a specific length using either a slit
tube33 (Figure 3) or a tourniquet34,
or fixing chordal length using a tube, that is after tying the chords to
the papillary muscle using a pledget, the arms of the suture are each
passed through plastic tubes cut to the required length. The sutures are
tied down over the tube. After tying, the tubes are cut-off the
chords35. Chan et al36 proposed to
mark the correct length (already established on the basis of the length
of a normal chord) with a marker pen and then a covered clip holds the
chords at the correct length, allowing them to be tied without movement
(Figure 4).
All the mentioned techniques foresee the measure of new chordal length
based on anatomically healthy chords, but it is important to bear in
mind that surgeons work on the mitral valve when the heart is arrested
in diastole, so this length could fail to replicate the required length
in the full, beating heart.
Indeed, to overcome this possible bias, Calafiore21proposed to pull the anterior leaflet (AL) with nerve hooks up to its
maximum length and then to tie the artificial chord adding 5 mm to the
border of the AL (Figure 5).
Other proposed alternatives are to tie the chords under LV loading
condition, that is after filling the left chamber with saline, using a
temporary Alfieri stitch37,38 or a
clip39 to hold the leaflets coapting.
Another key point to take in mind implanting artificial chords is the
issue of of knot slipping. Indeed, ePTFE sutures are very slippery, so
the final length of the new chords may change when surgeon ties the
knot. To avoid this possible mishap, some methods have been
proposed20,40.
Maselli et al40 proposed an adjustable loop technique
consisting of two parts: a papillary component with arrest knots at
constant intervals and a leaflet component with a reversible noose-lace
to fix the loop to one of the knots on the papillary component. After
implantation and coupling of the two components at a presumable optimal
length, a prosthetic ring is sutured in place. Hydrostatic testing is
then performed. Optimal chords length can be obtained by releasing the
noose-lace and sliding it over another fixing-knot. The adjustment can
be performed as often as required without placing stress on the anatomic
structures. The great advantage of this approach is that can be \soutto
be done without damaging the neochords anchors at the leaflet or
papillary component (Figure 6). Another approach to prevent
knot-slipping is tying multiple knots to a normal leaflet scallop so to
calculate the number of knots to be used in the prolapsing scallop,
tying the suture only after filling test20. (Figure 7)