Fig. 13.1
Preoperative echocardiographic measurement of the coaptation depth and tenting area of the mitral valve in a patient with functional MR
From a technical point of view, an IABP is prophylactically inserted before skin incision in patients with severe LV dysfunction. We use this approach also in non-ischemic patients in whom the decreased afterload provided by the IABP can be helpful considering that those failing hearts, immediately after the operation, have to face the “afterload mismatch” produced by the newly competent repaired mitral valve.
The EE repair is carried out either through a conventional midline sternotomy or through a small right anterolateral thoracotomy following peripheral cannulation for cardiopulmonary bypass. The aorta is cross-clamped and the heart is arrested with a cardioplegic solution infused into the aortic root. The mitral valve is exposed through a conventional left atriotomy. In presence of particularly severe left ventricular dysfunction, the aortic clamping is avoided and the procedure is performed while the heart is beating. Since in functional MR the mitral valve is structurally normal, the intraoperative inspection does not provide additional information. The preoperative echocardiographic study, therefore, has literally to be used as a guide to identify the site of the approximating stitch which is chosen according to the echocardiographic location of the regurgitant jet. In case of central jet (between A2 and P2), a central edge-to-edge repair is performed leading to a double orifice mitral valve configuration. On the other hand, when the regurgitant jet is in correspondence of the posterior commissure, as in some cases of ischemic MR, a commissural edge-to-edge suture is applied, which results in a single orifice MV with a relatively smaller area. When more than one regurgitant jet is present, the edge-to-edge is applied on the largest one, relying on the undersized ring for the resolution of the others. The first stitch connecting the two leaflets at the regurgitation site is positioned in such a way that valve symmetry is respected and distortion is avoided. A continuous mattress suture of 4-0 polypropylene is used first followed by a second over-and-over continuous suture to stabilize the repair. Moreover the length of the suture is always kept as short as possible to minimize the risk of postoperative mitral valve stenosis: in most of the patients it is between a few millimetres and 1 cm (see Figs. 13.2 and 13.3). A complete rigid or semirigid prosthetic ring is invariably implanted. The annuloplasty ring is chosen according to the intertrigonal distance, to the surface area of the anterior leaflet and to the length of the EE suture. In the setting of functional mitral regurgitation it is usually one or two sizes smaller than the anterior leaflet surface. Most of the patients receive a ring number 28 (mean size 28.2 ± 2.3, range 26–31). Other concomitant procedures including myocardial revascularization, ablation of atrial fibrillation, resyncronization therapy and tricuspid annuloplasty are performed whenever indicated. At the end of the operation, the global mitral valve area is assessed by direct inspection and, in case of doubt, by introducing Hegar dilators into the valve orifices. In normal size patients a global valve area of more than 2–2.5 cm2 is usually accepted. After weaning from cardiopulmonary by-pass, the valve area is commonly assessed by a planimetric method using the transgastric, short-axis view (see Figs. 13.2 and 13.3). TEE echo-Doppler re-evaluation of the mitral valve typically shows no residual MR and no signs of mitral stenosis. In the central EE, leading to a double orifice mitral valve configuration, two diastolic flows can be visualized. At Doppler examination blood flow velocities are comparable in the two orifices. This finding is in accordance with computational model studies conducted by our group which demonstrated that the hemodynamic performance of a double-orifice mitral valve depends exclusively on the total valve area and on the cardiac output and not on the double orifice shape [18]. In double-orifice valve configuration, the velocity of the flow through each orifice is very similar to the one observed through a single orifice valve of area equal to the sum of the areas of the two orifices. Therefore, the flow velocities through the two orifices are exactly the same, even when the orifice sizes are significantly different, which means that the Doppler sampling of any of the two orifices is sufficient to assess the hemodynamic of the mitral valve.
Fig. 13.2
Postoperative echocardiographic view of a central edge-to-edge for functional MR: the length of the EE suture in this patient is only a few millimeters
Fig. 13.3
Postoperative echocardiographic view of a central edge-to-edge for functional MR: the length of the EE suture in this patient is about 1 cm
Results
Our method of combining the “edge-to-edge” technique with an undersized annuloplasty performed with a complete ring (preferentially rigid or semirigid), has resulted in a 3.7 % recurrence rate of 3 to 4+ MR at follow-up, which is 6-fold lower compared to that registered in our center with a restrictive annuloplasty alone (21.7 %) despite having, the EE patients, the more advanced degree of leaflet tethering [19]. Freedom from recurrence of severe MR at 1.5 years was 20 % higher in the edge-to-edge group (95 ± 3.3 % vs 77 ± 12.1 %, respectively). Moreover, the use of the edge-to-edge was identified as the only significant predictor of durability of MV repair (hazard ratio 4.7, P = 0.03). The ring size had no impact on the rate of failure of mitral repair [19]. By ensuring leaflet coaptation exactly where the tethering is more pronounced, the edge-to-edge approach could lead to early valve closure, abolishment of the “loitering effect” and prevention of MR recurrence. From a clinical point of view, NYHA functional class improved from a preoperative mean of 3.4 ± 0.4 to 1.4 ± 0.6 (P < 0.0001) [19].
Further analysis of our experience with mitral repair in functional MR [20] identified ischemic etiology, concomitant myocardial revascularization and successful simultaneous ablation of atrial fibrillation as univariate predictors of reverse LV remodeling. In addition, the longer the duration of the CHF history, the lower the likelihood of postoperative reverse remodeling to occur. At multivariable analysis only the duration of CHF history was significantly associated to the occurrence of reverse remodelling. Interestingly, the use of the edge-to-edge technique showed a trend towards favouring reverse LV remodeling compared to isolated annuloplasty (p = 0.08) [20]. This finding could be explained by the fact that the edge-to-edge technique, by anchoring the leaflets together, could exert a kind of “reins” effect on the LV chamber, counteracting the progression of the LV remodeling. This is extremely important considering that the occurrence of reverse remodeling is associated to longer repair durability and better clinical outcome [6, 20]. The potential restrictive effect at rest and during exercise of a valve submitted to the EE repair can be a matter of concern. In degenerative MR it has been demonstrated that functional mitral stenosis does not develop after the EE technique either at baseline or under exercise [21]. In the setting of functional MR, we measured the gradients at rest across the mitral valve after repair since the beginning of our experience. Both, immediately after surgery and at follow-up, they have been very low with no evidence of mitral stenosis. At hospital discharge, all patients with secondary MR treated with this approach had no or mild MR, with a mean MV area of 2.8 ± 0.6 cm2 (range 1.9–3.4 cm2) and a mean transmitral diastolic gradient of 3.8 ± 1.2 mmHg. About 2 years after surgery, those values had remained substantially unchanged being the mean MV area 2.8 ± 0.4 cm2 and the mean transmitral diastolic gradient 3.3 ± 2.1 mmHg. A clinically relevant mitral stenosis has never been observed in any of the patients with functional MR submitted to EE repair and annuloplasty. Certainly, experience and careful choice of the annuloplasty ring size, according to the surface of the anterior mitral leaflet and the length of the EE suture, are mandatory in order to avoid any significant postoperative MV stenosis. Of course the EE technique should be avoided in the rare instances where severe leaflet tethering is associated with only mild annular dilatation since, in those cases, this method of repair would lead to a significant restrictive effect due to the lack of preoperative dilatation of the mitral annulus (see Fig. 13.4).
