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)