Is there an indication for mechanical prosthesis in Fallot patients?

This well-written and methodologically coherent original article in this issue of the journal nicely demonstrates non-superiority of mechanical prostheses over biological prostheses in pulmonary position, enhances the paucity of the literature on this subject and fills a gap in the current recommendations [1]. The current ESC guidelines report pulmonary valve replacement following Tetralogy of Fallot repair with a suggested durability of 10–15 years on average for tissue prostheses, and mentions concerns regarding thromboembolic events in mechanical prosthesis, without presenting evidence of durability of the valves themselves for this length of follow-up [2].

The current article by Dong-Hee Kim demonstrates problematic durability of mechanical valves in pulmonary position by isolating primary prosthesis failure, as defined by stenosis, regurgitation, endocarditis and need for reintervention, showing de facto inferiority of mechanical valves, when considering also the risk of thromboembolic and bleeding events.

Lifelong anticoagulation with coumadin, however, is accompanied by significant risks and quality-of-life impairment that must not be ignored. Thromboembolic complications occurred in 4 out of 43 study patients with mechanical prosthesis (9.3%). Bleeding complications were rare in this young population and were associated with INR measurements outside the here targeted therapeutic range of 2–3, representing a real-life data situation. A propensity of 0.6–1.5% is considered standard for thromboembolic and bleeding complications under coumadin therapy [3]. Considering the median age at implantation of 19 years, and a life expectancy of 79 years, this could result in a cumulative risk of 60% on average over a lifetime. Additionally, full anticoagulation often targeted between an international normalised ration (INR) 2.5 and 3.5 should be considered unfavourable in children and women in childbearing age. When this is considered alongside the endpoint of freedom of reintervention, the non-superiority of mechanical prostheses would be even more evident.

Size of the implant was also found to be of critical importance for prosthesis failure. The subgroup of >25 mm of both types of implants was associated with prolonged freedom of reintervention. According to the surgical description, an annuloplasty was performed in some patients in the biological group, to enable later valve-in-valve procedures. Eventually, this should be taken into consideration when planning a surgical procedure.

Considering the available literature, the freedom of reoperation at 10 years in the mechanical group was comparably low with 65.2% compared to 91% reported by Pragt et al. [4]. The various prostheses used, their size, model, age at implantation, body surface area (BSA), surgical aspects and target INR are all factors that potentially contributed to this seeming discrepancy.

The variation between different models of biological implants is another aspect to be considered. A review of the literature shows multiple comparative studies [5]. A study of Fiore et al. [6] from 2008 compared the early outcomes of different prostheses types. Amongst biological and mechanical valve prostheses, bovine prostheses followed by porcine ones were found as the most durable solution, compared to homograft prosthesis that showed a higher incidence of recurrent pulmonary valve regurgitation in this study. An earlier study of 1997 was able to show a freedom from reoperation of 86% after 10 years [7]. Since then a few of these prostheses have stopped being produced and newer generation biological valve have been introduced, all potentially influencing the reported performance and durability of these in pulmonary position. The options available for biological implants vary also by country and region, as for example homografts are available only in certain countries and biological valves may be restricted by resources or cultural regulations.

The optimal timing for intervention also remains a continuing topic for discussion [8], with classical indications either being symptoms, electrical parameters or functional and volumetric parameters e.g. indexed right ventricular end-diastolic volume (RVEDVi) or indexed right ventricular end systolic volume (RVESVi). Further refinement in decision-making tools is yet to be produced, but the TRIVIA study [9] might shed further clarity on this question in the future. Whereas previous guidelines were focussed on treating the symptomatic patient, recent experience has shown better outcomes with earlier intervention, demonstrating better protection from right ventricular failure, arrhythmias and sudden death.

Beyond the scope of this study are the outcomes of percutaneous valve-in-valve implantation and which valves are suited for this pathway. Whereas mechanical prostheses completely preclude this option, biological valves allow this to be a consideration. In situations where a percutaneous pulmonary valve implantation is technically feasible, it is now becoming a more commonly preferred first choice of treatment as current data are suggesting promising early- to medium-term results [10].

The long-term treatment of Tetralogy of Fallot repair patients will keep congenital cardiac surgeons and interventional cardiologists occupied for the foreseeable future, with an increasing number of patients and no solutions for an expected durability beyond 10–20 years. While the presented work reaffirms strongly that there is no benefit to be gained from implanting a mechanical prosthesis compared to a biological one, this has to be put in perspective into a time, when percutaneous pulmonary valve implantation is increasingly commonly a principal treatment option and can potentially significantly enhance the surgery-free interval, as no significant difference in freedom of reintervention has been found [10].

The improvements in durability of biological valve implants in both surgical valves and percutaneous valves are ongoing, and longer intervention-free intervals can be expected in the future. The place for mechanical prostheses in pulmonary position remains niche and advisable only in selected patients. We agree with the conclusion of the authors that this article may influence the next version of guidelines. The demonstrated low rate of freedom of reoperation and the additional risks associated with anticoagulation here reaffirms the role for mechanical valve prosthesis in pulmonary position being a very limited one and only advisable for patients with a very high surgical risk, already using anticoagulants for other reasons, no need for pulmonary artery work in the future.

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