New insights but new questions as well in repaired tetralogy of Fallot management

Given a plethora of new knowledge on right ventricular outflow tract (RVOT) dysfunction in recent years, particularly in the area of new transcatheter device development, refinement in clinical decision-making as well as indications for pulmonary valve implantation, the present statement (1) by Geva et al is a welcome and timely addition. There is no disputing the burden of RVOT dysfunction anymore, be it post-tetralogy of Fallot (TOF) repair stenosis or pulmonary regurgitation (PR). As an aside, when I was in congenital heart surgery training 25 years ago, the morbidity of PR was widely disputed and often negated (2). In an era when transcatheter valve therapies had not been implemented yet, surgical pulmonary valve implantation (SPVR) was performed very rarely. In contrast, today, the long-term morbidity of chronic RVOT dysfunction is no longer contested, and SPVR is one of the most commonly performed congenital heart operations.

The present statement is comprehensive and well crafted. The overview of the available state-of-the-art device platform (both surgical and transcatheter) is excellent, and the focus on multi-disciplinary decision-making when deciding on which patients to intervene on cannot be overemphasized.   Figure 2 in particular provides a logical framework around which clinicians can articulate their decision-making regarding PVR, both surgical and transcatheter.    

There are still many areas in the long-term management of RVOT dysfunction in repaired TOF that remain unclear and could use data-driven decision making. One unanswered question will be whether the availability of midterm data on the recent self-expanding transcatheter pulmonary valve prostheses (designed expressly for patients with larger patched RVOTs) result in broadening of indications for PVR? Given the recent experience with transcatheter aortic valve replacement (TAVR) being increasingly utilized in younger and healthier patients, this seems likely.

On the surgical side, there is still uncertainty around which surgical prosthesis, pericardial or porcine prostheses, is best suited for the specific flow physiology of the right side of the heart, especially in the setting of the typically seen compensated RV chronic volume overload, increased end-diastolic pressures and decreased systolic function. In a recent propensity-matched study, we even found different outcomes not only between different valves, but also for valves implanted in native RVOTs as opposed to valves implanted in previously placed conduits (non-native outflow tracts). This strongly suggests that the local anatomic conditions, and even maybe the angle of valve placement have an important role to play (3). As a reminder, all of these prosthetic valves were developed for left-sided (aortic) implantation, and were never properly tested under right-sided conditions.

Another unknown is what type of prosthesis to use in a growing child, especially during the toddler to pre-teen period. This is not a very common occurrence, as PR is exceptionally well tolerated in children after TOF repair, but occasionally, a young patient might require a PVR due to out-of-norm RV dilation and/or dysfunction. Whether to use a conduit or a prosthetic valve in this setting is unclear. Finally, an ongoing controversy in surgical circles exists around the morbidity of a "standard" RVOT incision for primary TOF repair, as compared to the smaller RVOT incision used in the so-called transatrial-transpulmonary repair. The former requires a formal RVOT incision but very little to no muscle excision, while the latter requires either no RVOT incision or a minimal one, but much more extensive RVOT muscle bundles excision. Which one results in more RVOT dysfunction long term? Both camps have largely solidified their arguments and there is very little crossover. There is also no good available data to conclusively settle this question. And finally, as also noted in the manuscript, will the recent development towards living allogenic pulmonary valve transplantation result in a true "living" valve that grows with the patients and lasts longer than what we currently have? Time will tell.