Strategies for mitral valve disease in children: what, how and when

Brancaccio and colleagues report their single-centre experience with 115 patients (age < 18 years) who underwent mitral valve replacement (MVR) between 1982 and 2019. Analysed outcomes were freedom from redo-MVR and a composite freedom from death or transplant. Despite a large observational period of 37 years, median follow-up in the study was only 3.1 years [IQR 0.47–9.93] with a median interval to redo-MVR of 1.9 years. An increase of prosthesis size was only achieved in patients who underwent intra-annular MVR. The composite outcome death and/or transplant free was 77%±4 at 5 years and 72%±5 at 10 years. Not surprisingly the authors identified the use of biological prosthesis as a risk factor for reoperation, further they confirmed reports that a prostheses size/weight ratio >2 serves as an additional risk factor [1].

Regardless of the prosthesis choice, MVR is associated with worse outcomes in comparison to mitral valve repair (mostly for children <1 year) [2], underlining that mitral valve disease itself is not only an isolated valvar problem. It is rather a disease of the complete left ventricle and its function. Carpentier et al. [3] taught us that most mitral pathologies could be addressed by reconstructive techniques, which should be attempted whenever possible. New approaches, like dealing with an obstructing persistent left superior vena cava could be helpful in some cases of mitral stenosis and hypoplasia [4] and widen the spectrum of repairable pathologies. Nevertheless, dealing with parachute or Hammock valves, and complex subvalvar suspension and obstruction remains demanding. However, reconstruction attempts must be limited to a certain extent, remembering that mild regurgitation or stenosis could be well tolerated aiming to bridge the patient successfully to MVR in an older age [3].

Once reaching that point, choosing the right prosthesis remains difficult. Bioprostheses and mechanical valves have, of course, advantages and disadvantages. Biological prostheses are associated with a high rate of reoperations due to degeneration and formations of supraprosthetic pannus. Although mechanical prostheses have a greater durability [1, 5, 6], they carry an immanent risk of thromboembolism and bleeding. Paediatric patients may be less compliant in maintaining therapeutic anticoagulation levels later, when becoming teenagers.

MVR must therefore be reserved for ‘unrepairable’ cases, choice and size of prosthesis should be carefully evaluated based on the individual anatomy and risk factors. As Brancaccio and colleagues [1] have pointed out, in order to guarantee annular growth for later implantation of a larger prosthesis, it is recommended to implant the prosthesis in an intra-annular position.

All above-mentioned issues become even more problematic in case of very young patients, with a small mitral annulus. An ‘old rule’ wants to delay surgery to the latest possible date, in order to implant a rather large prosthesis, which is not always possible [3]. As reported by other authors [5], size of the mitral annulus in very young patients at surgery is a crucial factor in terms of mortality and the need for early reoperation. Smaller prostheses and left ventricular hypoplasia remain independent risk factors for redo-MVR. In particular, for a smaller annulus between 15 and 19 mm, mechanical prostheses are preferred, despite the need for anticoagulation. Recent introduction of surgically implanted Melody valves (Medtronic, Minnesota, USA) seems to be an interesting alternative especially in the presence of very small annuli (<15 mm) due to the option of percutaneous dilatation, thus postponing the need for reoperation [5]. Choi and colleagues [5] showed in a multivariable analysis no difference between Melody and mechanical valves in terms of durability. Predominant causes for failure were regurgitation, because of paravalvular leaks or leaflet perforations. Improved surgical techniques, including pericardial skirt creation, should help to prevent or reduce their incidence. Although Melody-prostheses may represent a valuable solution for patients with a very small annulus, it is necessary to remember that its design causes steric hindrance in the left ventricular outflow tract with possible dramatic impact on the haemodynamic performance of hypoplastic left ventricles (i.e. Shone-complex). In an ideal future world, surgeons would have more reconstructive options and dilatable low-profile-tissue-prostheses as substitutes.

Brancaccio et al. [1] scratched on the surface and confirmed well-proven facts like limited patient survival, better durability of mechanical valves and the negative impact of oversizing, however, we were missing a more ‘modern view’ on the complex topic offering new ideas and solutions. Instead of using historical indices for oversizing, we would recommend to report patient-prosthesis-mismatch by individual Z-scores. It was a surprise that only two patients received Melody valves, despite a very large surgical practice until 2019.

Future studies should rather be multicentric and investigate different treatment strategies in more uniform subpopulations regarding age and pathology. ‘Modern-MVR’ might need the skills of a joint cardiac-surgeon-cardiologist team combining the methological benefits of both therapeutic worlds.

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Author notes