Calculation
The overall and local 3D pathological anatomy of IMR is highly complex
and varies widely during patients. All patients with IMR have varying
degrees of annular dilatation and leaflet tethering, but the relative
contribution of these parameters to valve incompetence differs
significantly among patients. This implies that depending upon the
available reserve, the upper limit of the normal mitral annular diameter
is MV specific and perhaps region specific within the same MV.Mahmood Fet al. had made regional comparisons of 3D TEE data from
patients with IMR underwent MV surgery (n=66) and patients with normal
valvular and biventricular function (n=10)
to
identify measurements that reliably
differentiate normal from remodeled MVs. They found that extension of
the middle potion of the anterior annulus, larger nonplanarity angle,
and increased tenting angle of the posteromedial scallop of the
posterior leaflet were sufficient to distinguish IMR from the control
group. They thought specific 3D variations in the MV regional geometry
can be used to reliably identify a significantly remodeled valve
apparatus[74]. Cho E Jet al. suggested that
MA height likely to be a useful prognostic factor in choosing the timing
of surgery in patients with chronic primary MR. Annulus height/BSA can
provide supplementary information for predicting the postoperative LA
remodeling after successful MV repair[75].Bretschneider C et al. considered the presence of PM
infarction was not associated with IMR, because the severity of mitral
regurgitation was not increased compared with patients with partial or
no PM infarction[76].
For the unacceptably high risk of persistent or recurrent IMR after
reduction annuloplasty, what the “mitral valve reserve” can do to
predict the recurrence? Gogoladze Get al. had made a experiment
that regional coaptation sections were analyzed in cardiac surgery
patients with normal MVs (n=10) or with functional MR (n=10). They found
that the anterior leaflet coaptation length (CL) was greater than
posterior leaflet, the functional MR was associated with shorter leaflet
CLs, the biggest difference in CLs was in A2-P2, and coaptation depth
was higher in the functional MR group. They thought
there was a “anterior leaflet
reserve”for posterior movement of the coaptation line to compensate for
annular dilation and left ventricular enlargement so as to maintain
competency until the anterior leaflet CL was insufficient, followed by
the functional MR[77]. Wei Det al. had also
done a study about the association between the coaptation height of MV
and MR. They measured coaptation height of patients underwent
annuloplasty for mitral regurgitation (n=20). The results shown that
coaptation height had a significant negative correlation with the degree
of MR 12 months after operation. They made a point that MV annuloplasty
induced the morphologic change of the MV structure. The coaptation
height after MV repair may be one of the key factors in regulation of
MR[7]. And there were still other researchers
wanted to reveal the relationship between the “mitral valve reserve”
and the recurrence after mitral annuloplasty. Wijdh-den Hamer I
Jet al. performed 2D and 3D TEE on patients underwent undersized
annuloplasty due to IMR (n=50). They thought that MV replacement should
be strongly considered in patients with a preoperative P3 tethering
angle of ≥29.9° (especially when combined with basal
aneurysm/dyskinesis)[10].
A growing body of literature has documented an unacceptably high risk of
IMR recurrence after reduction annuloplasty, and a growing number of
researchers are interested in knowing the role of the “mitral valve
reserve” in predicting the recurrence. Some echocardiographic indices
derived from 2D TTE、TEE and 3D TEE modeling, have been collected in
several studies during the last decade[78-81]. The
most commonly used cut-offs points for determining the degree of MV
tethering and the risk of MV repair failure are as following: anterior
leaflet angle>25º, posterior leaflet angle
>45º, tenting height ≥11 mm, and the tenting area ≥2.5
cm2[10,14,82]. However, all of these cut-offs are
obtained from the integrity of MV. For remodeling of the MV apparatus in
IMR can be heterogeneous with a variable degree of reserve along the
line of coaptation, the upper limit of the MA diameter is MV specific
and perhaps region specific within the same MV. Maybe the cut-offs from
regional MV are more important in surgical dicision making. This is
worthy of further study and discussion.