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.