Andersons pediatric cardiology 1867

Future Considerations Even the successful Fontan survivor faces a number of long-term challenges, including heart failure, thromboembolic complications, arrhythmias, residual cyanosis, chronic venous insufficiency, liver disease, renal disease, and abnormalities of lymphatic drainage including protein-losing enteropathy and plastic bronchitis The thoracic duct drains into the central venous system in the chest, and the elevation of central venous pressure that occurs with the Fontan will affect normal lymphatic drainage Advances in imaging of the lymphatic system have identified abnormal flow patterns, including retrograde flow in the thoracic duct and abnormal connections with the gut and lungs; these contribute to proteinlosing enteropathy and plastic bronchitis.320 Interventional strategies including lymphatic embolization have resulted in improvement in individual cases.321,322 Surgical thoracic duct decompression, achieved by anastomosis of the innominate vein to the pulmonary venous atrium, has also been performed for protein-losing enteropathy and chylous ascites.323 Modification of the lymphatic system by interventional or surgical means will likely increase as our ability to image and understand the lymphatic system's pathophysiology increases Heart transplantation may be the only option for patients with end-stage heart disease following the Fontan They may have congenital heart disease that includes abnormalities of cardiac position and venous anatomy They have had multiple previous cardiac procedures and as a consequence may be sensitized; they will have multiple collateral vessels and venous hypertension, all of which increase the risk of the transplant procedure.324,325 In addition, these Fontan survivors frequently have renal and hepatic dysfunction, which complicates their posttransplant course.326,327 The pulmonary vasculature of the surviving Fontan patient is abnormal due to altered flow distribution as well as the presence of aortopulmonary collaterals and pulmonary AVMs.328 Whereas it was once assumed that the Fontan survivor had low PVRs, the PVR may in fact be elevated, and this may be unmasked in the posttransplant patient Despite these challenges, recent experience demonstrates improved outcomes with heart transplantation in this population, with a 5-year posttransplant survival of greater than 70%.329–331 Mechanical circulatory support will likely play a greater role in the management of the failing Fontan patient due to the challenges of medical therapy, scarcity of organ donors, and improved outcomes of mechanical circulatory support in the noncongenital population.332–334 Short-term temporary extracorporeal devices such as the Centrimag or Rotaflow can be combined with typical bypass cannulas or Berlin Heart cannulas to provide temporary support as bridge to transplant Newer continuous-flow devices such as the HeartWare or HeartMate 3 are smaller and more adaptable to atypical anatomy and have been adapted for use in the fUVH population.335,336 There has been some experience using the Total Artificial Heart in the failing Fontan patient.337 Finally, devices designed to replace right ventricular function while preserving the Fontan pathway are in development.338 The entire field of mechanical circulatory support is rapidly advancing Although such support is currently used only as a bridge to transplant or decision, mechanical circulatory support will play a role as durable therapy for the failing Fontan patient in the near future The role of stem-cell therapy to treat ventricular dysfunction is being explored by several groups A phase 2 study using intracoronary injection of autologous cardiosphere-derived cells at the time of the SCPC or the Fontan procedure has shown a modest but significant improvement in single-right-ventricle ejection fraction as measured by MRI.339 Other groups are investigating umbilical cord– derived autologous cells in individuals with a prenatal diagnosis of fUVH.340 Finally, allogenic mesenchymal stem cells are being investigated.341 The extent and duration of benefit, ideal cell type, route of administration, and intracoronary versus direct myocardial injection remain to be determined Nevertheless the results are intriguing, and cell-based therapy may become a routine strategy to improve long-term function in patients with fUVH Closing Thoughts The pinnacle of vertebrate evolution is the development of the two ventricle circulation with dedicated pulmonary and systemic pumping chambers resulting in fully saturated hemoglobin that supports the high metabolic rate characteristic of birds and mammals Despite what would seem like an insurmountable limitation of the circulatory system, we have witnessed over a short, 75-year span the development of strategies to care for the patient with fUVH that restores in-series circulation and permits long-term survival The progress in the care of these individuals has impacted the care of every patient with congenital heart disease; much of our management strategies, especially in the area of critical care, are a consequence of the lessons learned from these most challenging patients For the individual with fUVH the fundamental problem of an impaired circulation persists throughout life Despite these limitations, survivors of palliation of fUVH are growing up, having families of their own, and inspiring us with their courage and tenacity Ongoing research provides hope for the future and will be focused on identifying the causes of cardiac maldevelopment, diagnosing earlier, improving fetal intervention, improving medical therapy, optimizing transplant outcomes, expanding the use of mechanical circulatory support, and improving functional outcomes, quality of life, and neurodevelopmental outcomes