Mitral valve (MV) repair for degenerative mitral regurgitation (MR) is achieved nowadays with a great success rate and a good survival, similar, in certain subgroups, to that of the normal population (1). The superiority of MV repair over replacement for degenerative MR has been consistently demonstrated (2). However, even if degenerative disease of the MV is a big umbrella which covers a lot of different pathologies, most of the techniques are addressed to correct the prolapse of one or both mitral leaflets, a widely diffused disease that interested cardiac surgeons since the early years. The first chapter in the huge book of MVr was however written by Carpentier et al. (3,4), who defined the terms and put the principles which, with some modifications, are still followed by many surgeons. His vision, together with the concept of annuloplasty (5) and the advent of artificial chords (6), are the pillars on which MVr surgery stands. There is no doubt that nowadays high percentage of repair can be achieved in specialized centers, but it is as well true that a huge variety of techniques are used to obtain a competent valve. Most of these have only midterm results, often very good, which justify the optimistic prevision for a high long-term patency rate.
The paper from Lapenna et al. (7) reports the long term outcome of a specific technique originally described by Carpentier et al. (4) to treat the prolapsing or flail posterior leaflet, applied in 142 patients from 1997 and 1998. Survival was 92%±2.3% at 10 years and 74%±3.7% at 20-year, 6 patients were reoperated on because of recurrent severe MR and the cumulative incidence function of MR ≥2+ with death as competing risk was 7%±2.1% at 10 years and 17%±3.2% at 19 years.
These superb results underline how MV repair can have a great success rate even in the long term and can change the natural history of the disease. Recent studies showed that strain for valves with organic disease is higher than for normal valves, globally and in each valve leaflet. It was postulated that reduction of strain is one of the component which affects durability of MV repair. Indeed, valve strain reduces after MVR, and it may be related to a smaller annular size, increased valve coaptation zone, a smaller exposed valve area, and the insertion of artificial chordae, each having been shown in various models to reduce strain (8). These observations provide a scientific basis to long term results after MV repair, independently from the technique used.
Results of Lapenna et al. (7) are in line with what previously reported in the literature (9-12), even if most reports deal with prolapse of one or both leaflets. The quality of the results, at least in terms of survival, is strictly related to the presence of preoperative risk factors, as atrial fibrillation or pulmonary hypertension or reduced ejection fraction. It is indubitable that better results can be achieved when patients are operated on in an early phase, without the late consequences of the disease (13,14).
However, in order to improve the outcome of MV repair, some complications, mostly technical, and the way of preventing them, have to be analyzed, as integral part of any surgical strategy.
Mitral stenosis (MS)
After MV repair for degenerative MV, the valve area decreases and the gradients increase, in general not in such a way to affect the functional capacity. However, this is an aspect intrinsic to the surgical technique, and its extent is not yet well defined. Although pannus ingrowth can develop over time reducing the MV orifice, other factors, as posterior leaflet surgery and complete annuloplasty rings, have been considered among the possible causes (15,16). The increase in transmitral pressures and inflow velocities, together with a change in the vortex pattern in the left ventricle (17), are indicative of functional MS of various degrees, dependent on the size of the device implanted and on the amount of tissue left inside the mitral orifice. This problem is not negligible in an era when mitral repair is proposed to asymptomatic patients, often young and active. MS can be a serious problem in the early period, reflecting the predominance of surgical techniques. It was cause of reoperation either in the operating theatre (OR) (10) or before hospital discharge (18).
It is difficult to clarify the exact prevalence of this complication. Chan et al. (15) reported 110 patients who had MV repair for MV prolapse and found a mean gradient across the valve >3 mmHg in 75 patients (68%). Most of the patients with higher gradients had complete rigid ring. In a further study with the same patients, the same authors (19) used the MV area calculated with the continuity equation. They found that 20% of the patients had a MV area ≤1.5 cm2, which was associated with worse intracardiac hemodynamics, lower exercise capacity and adverse outcomes. The MV area corresponded to a mean gradient of 5 mmHg. Kawamoto et al. (20) found that 8% of their patients (51/602) had a rest mean transmitral gradient ≥5 mmHg at discharge, mostly related to a smaller ring size. These patients had during the follow up increase of tricuspid regurgitation severity, of the pulmonary pressure and higher onset of atrial fibrillation than patients with lower gradients. Interestingly, even patients where the ring used was true sized can present severe MS. Doi et al. (21) found that 7 out of 20 patients who had stress echocardiography after MV repair with a semirigid ring showed peak gradients at effort ≥15 mmHg. The importance of pannus development was underlined by Suh et al. (22), who, in 45 patients who had a postoperative CT scan after at least 1 year from surgery, found a pannus in 29 of them (64.4%), significant in 10 (22.2%), with a prevalence in patients with Duran ring. In general, lacking prospective studies, we can speculate that 10% to 20% of the patients with a good repair re discharged with some significant mitral stenosis, which can affect the long-term outcome.
Residual/recurrent MR after surgical correction is a constant and varies only as percentage. A residual MR in OR grade moderate or more needs always a second pump run. When MR is mild, it was demonstrated that there is no need of further corrections, as in more than 60% of the cases it even reduces during the follow up (23). The incidence of recurrent MR moderate or more is often reported as freedom from the event and has a great variability. It can be as low as 27.2%±8.6% at 7 years (24) or as high as 90.4% (CI: 89.3–91.4) at 10 years (11). In percentage of patients, incidence of MR moderate or more has a wide range: 25.9% after 10 years (25), 23.6% after 5 years (26), 13.3% at 13 years (27). There is general agreement that residual MR more than mild is a risk factor for MR moderate or more at follow up (25,27,28) and that correction of AL prolapse has a high rate of recurrent MR moderate or more at follow up than PL prolapse. Independently from the technical difficulties and from the possibility of further chordal elongation/rupture, a specific mechanism, in an era when chordal replacement is more and more frequent, is artificial chordal rupture. First reported in 2004 (29), its real incidence is not known. In the experience of Coutinho et al. (12) it represented the 26.1% (6/23) of the causes of reoperation and the 1.6% of the cases where artificial chordae were implanted. Another mechanism of recurrent MR, specific of the technique, is the dehiscence of the implanted device. The mitral annular biomechanics have been extensively studied. The strain is stronger in the commissural areas and in the anterior annulus, applying systolic torsion to a flat annuloplasty ring. This is in favor of saddle shaped rings, which present superior uniform annular distribution (30,31). The suture force maximums and their corresponding cyclic ranges (maximum to minimum) are greater along the anterior portion of the ring (32). As the collagen density of the anterior annulus is greater than the posterior annulus (33), the former can tolerate much higher tensile force, this would predispose to dehiscence along the posterior annulus, which is what is seen clinically, despite lower cyclic loading on posterior sutures. In other studies the posterior annulus, in particular at the intersection of the right commissural segment with the posterior segment, was found to be the weakest part of the mitral annulus (34). Incidence of the dehiscence of the ring/band varies in the different statistics. It represents 17% (35) to 42% (36) of the causes of reoperation, but its real incidence is not clear. In a recent series related to 475 patients operated on during 20 years ring dehiscence was the cause of reoperation in 21.6% of the cases (5/23), representing 1.1% of the total population (12).
Systolic anterior motion (SAM)
The prevalence of SAM after MV repair remained more or less constant during the last decades, being 9.1% in 1994 (37), 8.4% in 2007 (38) and 8.1% in 2017 (39). There is general agreement that the genesis of SAM is due to the movement of the coaptation point of the leaflets toward the septum, resulting in the extension of the residual AL beyond the coaptation point. Consequently, the AL tip strays into the left ventricular outflow tract (LVOT) and, as a consequence, the ejected blood flow force moves the AL more toward the LVOT. This causes both MR and LVOT obstruction. The displacement of the coaptation between leaflets toward the septum is related to an excess of movement of the PL. SAM seems to be more frequent when a rigid ring is used (40). In most cases the solution is medical (discontinuation of inotropes, increasing the filling of the LV). In some cases a second pump run is necessary, either to improve the correction or to increase the size of the ring or to perform other maneuvers [edge to edge (39) or resection of a bulging septum (41)] or to replace the mitral valve (42). However, SAM can persist at follow up. In the experience of Brown et al. (38) after 5 years from surgery 17 patients (9.8% of the patients who experienced SAM in OR and 0.8% of all patients who underwent MV repair) had persistent SAM with/out LVOT obstruction.
Long term results of MV repair for degenerative mitral regurgitation, in particular due to leaflets’ prolapse, are outstanding and the paper from Lapenna et al. (7) confirms the quality of the outcome. However, we think that reporting only survival and freedom from MR gives only a partial vision of the surgical results. Thromboembolic complication are as well present in this cohort of patients, representing, in the experience of David et al. (11), the 10% of his population during a follow up of 20 years. Even if there are only sparse reports, circumflex artery injury during MV repair has been described (43,44). Reporting our results must include all the possible information which can affect the quality of life of our patients. It is possible that in a relatively small number of cases, as those reported by Lapenna et al. (7), some particular complication did not occur. But, as we are proposing MV repair for prolapse of one or both MV leaflets to asymptomatic patients, we have to be aware of all the events that can affect the final results of our surgery.
Conflicts of Interest: The authors have no conflicts of interest to declare.
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