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Cardiothoracic Surgery, Medical College of Wisconsin, Children's Hospital of Wisconsin, 9000 W Wisconsin Ave, MS 715, Milwaukee, WI 53226
(Email: mmitchell{at}chw.org).
It was with great interest that I read this work by Lacour-Gayet and colleagues [1] outlining a proposed conformational change for the extracardiac Fontan coupled with an axial-flow pump as a strategy for optimizing hemodynamics during mechanical cavopulmonary assistance of the univentricular circulation, the "artificial right ventricle (ARV)."
The paradox of the Fontan is the presence of simultaneous systemic venous hypertension and pulmonary arterial hypotension [2]. This current work builds upon the first experiments outlining mechanical cavopulmonary assistance for failing univentricular circulation, published by Rodefeld and colleagues in 2003 [3], which assessed the use of axial-flow pumps positioned in both the superior and inferior vena cava in attempt to reduce systemic venous hypertension and improve pulmonary arterial perfusion [3].
This is a very interesting report and is clearly one potential solution to the major problem of ever-increasing numbers of failing Fontans. I applaud both the authors' ingenuity and their scientific method. The ARV approach has profound clinical and surgical implications.
My concern is somewhat simple minded. The proposed strategy, "designed to adapt to the need of the pump," requires major surgical revision at the time of mechanical support [1]. The authors propose Fontan revision to ARV configuration at the time of Fontan failure, requiring reoperative dissection and an additional cardiopulmonary bypass run in a patient with systemic venous hypertension and most likely a prebypass inflamed systemic state.
In the end, these efforts create an anatomy that suits the needs and limitations of the mechanical assist device, but which is suboptimal as a Fontan circuit alone. Clearly there would be little chance of successful weaning, and the ARV would be applicable only as either destination therapy or as a bridge to transplantation. The stakes will be very high if mechanical pump failure occurs in the context of a hemodynamically suboptimal Fontan circuit.
One could argue that instead of creating a novel anatomy to suit the needs of the existing pump, we should instead focus on creating a novel pump to suit the existing Fontan anatomy. Successful mechanical support of the failing Fontan is high risk; however, there have been reports of success using existing pumps [4, 5]. Combining Fontan revision with pump insertion might prove to be too high of a risk. Long-term destination cavopulmonary support may prove to be very challenging as well.
The authors are to be congratulated on their experiments. The conformation they propose better suits the current state of the art in mechanical assistance. The "ARV" concept is novel and successfully addresses the issue of retrograde superior vena cava flow. The experiments were run in model systems in which that group has previously reported. It is quite possible that when tested in forthcoming animal studies, the ARV axial-flow pump positioned as they describe will succeed in addressing the Fontan paradox by simultaneously lowering systemic venous pressure while raising flow to the pulmonary artery.
The authors do a careful job of addressing the limitations of their current computational and in vitro models and also the challenges of performing relevant animal studies. I am very eager to see their results, particularly their results in long-term animal experiments. They clearly have a fantastic team assembled to address these challenges.
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