Biomedical Engineering Reference
In-Depth Information
reported in the contour maps of relative stress variation (Fig.
6
b), between pre- and
post-operative models, this redistribution of mechanical stress along the free-margin
of the restored leaflet region (i.e. close to NCI insertion) proved to be technique-
dependent: passing from SN implantation to multiple NCI, mechanical stresses were
progressively redistributed on a larger region of leaflet and a lower peak stress was
noticed along the free margin of the leaflet.
Indeed, leaflet stress redistribution was combined with a different redistribution
of forces on ePTFE sutures, as a consequence of the different NCI set-up in terms of
number of NCIs. When considering multiple NCI, chordal tension was subdivided
on more ePTFE sutures than in SN configuration, where a single ePTFE supported
the entire tension. A different load subdivision was noticed for each NCI: 59 and
41% in DN simulation; 30, 30 and 40% in CL configuration and 32, 33 and 36% in
LNH simulation.
4 Discussion
In the last decades, ePTFE sutures have been more frequently used in the field of
MVP reconstructive surgery following the concept of preserving the posterior leaflet.
The surgical innovation of ePTFE sutures has supplanted earlier techniques, such as
chordal shortening, chordal transposition and, in particular, extensive leaflet resec-
tion which inevitably changes the anatomic and physiologic MV function. Indeed,
implantation of ePTFE sutures can restore the proper coaptation area, preserve
ventriculo-annular continuity and, minimize leaflet tension [
21
]. Moreover, a limited
tissue reactivity has been noticed: experimental tests have demonstrated that poten-
tial infections, due to ePTFE sutures, are comparable with that of other synthetic
sutures [
22
].
Hovewer, from the clinical point of view, MVP repair through ePTFE sutures is
still a challenging technique deserving continuous attention over time: the determi-
nation of suture length represents a key aspect and it is usually accomplished through
different techniques, as reported in literature [
23
]: the anatomic techniques evaluate
the length of ePTFE sutures having as a reference point a non-prolapsing scallop in
front of the prolapsing one; on the contrary, the functional techniques evaluate the
suture length filling the left ventricle with saline. In this study, the use of an auxil-
iary
Phy
model, was performed in order to numerically determine the proper suture
length reproducing, through the application of a pressure load on MV leaflets, the
same operative conditions of saline injection in functional techniques. As a matter
of facts, a neochordae that is too short will result in a restricted leaflet mobility (thus
inducing high concentrations of stresses on the leaflet); on the contrary, a neo-chordae
that is too long will be ineffective in controlling leaflet prolapse [
24
].
According to the aims of the study, different NCIs were simulated in order to
compare the effects of each repair technique on MV apparatus and infer systematic
differences between NCIs. Different groups have recently proposed non-standard
and innovative NCIs [
25
-
27
] in order to improve MV repair and increase the
