In this study, 14 of 220 patients (6.4%) who underwent MV repair for DMR showed FMS. The FMS group showed a greater decrease in MV annulus area between pre- and post-MV repair than the group without FMS. MV annulus area change ratio between pre- and post-MV repair was predictive of FMS when the cut-off value was a 56.2% reduction in MV annulus area.

FMS following MV repair is known to be a poor prognostic factor after surgery, with an increased risk of postoperative congestive heart failure, atrial fibrillation, and pulmonary hypertension. [3]. In addition, FMS has been reported to cause impaired exercise tolerance, leading to decreased postoperative quality of life [9].

The importance of conducting a high-quality MV repair

The guidelines increasingly recommend early timing of MV repair, and avoidance of both FMS and residual regurgitation is an important issue in ensuring a good prognosis and valve function after MV repair. This study has shown that the pre-and postoperative valve ring area change ratio is more influential on FMS than the postoperative MV annulus area, In addition, the preoperative MVA did not differ between FMS and non-FMS, which showed that the effect of placing a smaller ring relative to the preoperative area was most strongly associated with FMS. Pre-operative recommendations on the minimum post-operative area that should be guaranteed to avoid FMS can lead surgeons away from the selection of relatively small rings. The post-operative MVA can be estimated to some extent for each product type and size, as presented in Table 3, and the values close to the published product information have been obtained, especially for semi-rigid type full rings such as Physio2. Concerning these values and the values given in the product information, the postoperative MVA values for each prosthetic valve ring used can be estimated preoperatively. Using these values to select a size that is not less than 56% of the preoperative MVA is useful to avoid FMS. It is important to carefully evaluate preoperative 3DTEE measurements and develop an appropriate surgical strategy.

Selection of prosthetic valve ring in MV repair

There are two factors to consider when selecting prosthetic valve ring size, avoidance of FMS and control of regurgitation. While a small prosthetic valve ring size has been reported as a risk factor for FMS [4], prosthetic valve ring size has not been reported to contribute to regurgitation control [10]. Accordingly, the main consideration when selecting prosthetic valve ring size should be the prevention of FMS. The improper treatment of valve leaflets, such as excessive leaflet resection or inappropriate artificial chordae implantation, results in short coaptation of leaflets. This in turn indicates the need to use a smaller-sized prosthetic valve ring to constrict the annulus for good leaflet coaptation. However, this increases the risk of FMS. A strategy based on the idea of repairing the valve leaflets to a form that can maintain sufficient coaptation even without the presence of a prosthetic valve ring and the use of a prosthetic valve ring to prevent future enlargement of the mitral valve annulus will allow the use of larger-sized valve rings.

Risk factors of postoperative TMPG elevation

Various factors have been reported regarding the risk of postoperative TMPG elevation, which can be divided into valve leaflet factors and valve annulus factors. The valve leaflet factor, including leaflet resection [11, 12] or the edge-to-edge technique [13], defines the postoperative MV orifice area. On the other hand, the valve annulus factors, including a small size ring [14] or full ring type [4] prosthetic valve ring, define the postoperative MV annulus area. Recent reports note that the valve annulus factors are more substantial contributors to FMS than the valve leaflet factors [4, 9, 14]. This may be due to recent changes in MV repair techniques. In the early days of MV repair (so-called ‘French correction’), the mainstay of the technique was to resect a large portion of the prolapse lesion for morphological repair of the mitral valve. In recent years, in contrast, the aim of the technique (so-called ‘American correction’) has been to repair the mitral valve functionally, with minimum leaflet resection and an artificial tendon cord [15]. The resulting reduction in leaflet area has less effect on MV orifice area, while the influence of prosthetic valve ring morphology on postoperative hemodynamics is thought to have increased.

Value of prosthetic valve ‘Ring Size’

It has been reported that small ring size contributes to FMS [4, 13]. These studies examined the size of the prosthetic valve ring using a ‘ring size’ specified for each product. This ‘ring size’ is defined differently for each product, however, and the area of the prosthetic valve ring differs for each product, even if the ‘ring size’ is the same. Multiple types of rings were used within these previous studies, and ‘ring size’ is hardly a uniform parameter of postoperative MV annulus size.

The usefulness of MV annulus area in MV repair

This study demonstrated a significant correlation between postoperative MV annular area and postoperative TMPG. Using MV annulus area rather than the conventional ‘ring size’ provides more universal evidence that a smaller prosthetic ring contributes to an increase in postoperative TMPG [3, 4].

A significant correlation was also shown between postoperative TMPG and the MV annulus area change ratio between pre- and post-MV repair. This suggests that preoperative evaluation of the MV annulus area on TEE may help lead to the appropriate postoperative valve ring area to avoid postoperative FMS. Determining the prosthetic valve ring size based on this case-specific value would allow for theory-based MV repair and could lead to good and durable repair, as follows:

1.

From our study, it was revealed that the pre-and postoperative mitral valve annulus area change ratio influences postoperative pressure differences and could be a predictive factor for FMS, with an optimal threshold of 56.2%.

2.

Since the postoperative mitral valve annular area is determined by the prosthetic valve ring during surgery, to avoid FMS it is advisable to use the preoperative valve area as a reference and refrain from selecting an overly small prosthetic valve ring.

Effect of using a full ring type prosthetic valve ring on MVP

In the present study, univariate analysis revealed that the use of a full ring type prosthetic valve ring was also a significant factor associated with FMS. The relationship between the use of a full ring type prosthetic valve ring and increased mitral pressure gradient has been reported in the past, especially about small ring sizes of 30 mm or less [4, 14]. Our present results also showed that the postoperative MV annulus area was significantly smaller in the FMS group, indicating that the use of small-size rings affected FMS. This is consistent with previous reports that the use of a full ring type and small-size rings affected increased TMPG. In contrast, the use of a full ring type prosthetic valve ring has been reported to reduce the risk of postoperative MR recurrence in MVP of anterior leaflet lesions compared to partial ring prostheses [9], and there are cases in which aggressive use of a full ring type prosthetic valve ring is considered in some lesions. Because the area of the full-ring prosthesis is defined for each product, the postoperative area of the full-ring prosthesis is easier to estimate preoperatively than that of a partial-ring prosthesis. Therefore, in cases where a full ring is used, the preoperative MV area can be used to calculate the postoperative valve ring area needed to avoid FMS, allowing for a preoperative strategy to determine the optimal prosthetic valve ring size for each case.

Limitations

There are several limitations in this study. First, the study was conducted under a retrospective design with a relatively small number of patients, and the power of all statistical analyses was insufficient. Second, MV repair in this study was conducted by several surgeons, which likely resulted in differences in technique in aspects other than prosthetic valve ring selection. Lastly, there were two groups of patients whose postoperative MV images were obtained using before-discharge TEE and intraoperative TEE. Images acquired from before-discharge TEE better assess MV annulus morphology under physiologically hemodynamic conditions than those acquired from intraoperative TEE. In cases evaluated with intraoperative TEE images, we attempted to obtain images in a maximally physiologically hemodynamic state wherever possible after cardiopulmonary withdrawal. The intraclass correlation coefficient (ICC) of the postoperative MV annulus area showed an excellent correlation (ICC 0.98) in 10 patients who underwent both before-discharge and intraoperative TEE, suggesting that the use of either image had little effect on the results.