Heart transplantation has become an effective therapy for patients with end stage heart failure. The success rate has now been translated to a median survival of close to eleven years. Considering patients with end stage heart failure have a mortality that is close to 100 per cent at one year, this is a fabulous achievement from science and medicine. It must also be noted that heart transplantation has had reasonable stable volumes for many years with less procedures than needed. It has only had a steady slight increase from 1993 to 2004 reaching an all-time high in 2015 with just over five thousand operations done worldwide. Not only does the heart failure population continue to grow overall, making heart transplant an even more precious resource, but there is also a patient population that has increased at an even higher proportion. This population is that of the patients with adult congenital heart disease who currently only represent approximately 3 per cent of the heart transplant operations done. Nevertheless, while that 3 per cent seems small, it represents a 40 per cent increase compared to the previous decade. This population is therefore likely to need wider representation in the near future.
Congenital heart disease is the most common cause of birth defects. The fact that this patient population is increasing is testament to the success of the surgical and medical management of the paediatric population. In the not too distant past, the more complex patients within this group of disorders used to end their lives in childhood. Thanks to breakthrough science, technology and medical improvements, the expected survival of these patients has improved dramatically. This has led to formal adult congenital heart disease programs that now care for these patients as they grow older.
As these patients grow older, they continue to require intense care. While it is true that the simpler and more common lesions such as an atrial septal defect rarely progress to end stage heart failure, the more complex cases such as those with tetralogy of Fallot, systemic right ventricle or the myriad of conditions that end up in single ventricle physiology do tend to continue to decline. Very notably, the main causes of death of the complex congenital heart disease population are by far due to cardiac reasons. Furthermore, within those potential cardiac causes of death which can include sudden cardiac death, ischemic heart disease or peri-procedural complications, the main cause is not the aforementioned but, indeed, end stage heart failure. If one keeps in mind that continued decline and refractory class IV symptoms are an indication for advanced therapies, such as cardiac transplantation, one can only expect that the number of patients with adult congenital heart disease that need a transplant will continue to increase. It must also be pointed out that this patient population is often ineligible to receive other forms of advanced therapies such as durable ventricular assist devices also known as mechanical circulatory support due to their specific anatomy and physiology. The latter comment means that, often heart transplantation is the only option despite the fact that some progress has been made with mechanical support and experience is being accumulated but so far the published data shows that there have been less than 200 durable mechanical devices in patients with congenital heart disease.
One of the most important reasons that the population in question merits its own chapter within the advanced heart failure subspecialty is that these patients carry more and very specific challenges. Some of these challenges are due to the fact that these patients have a higher incidence of entities such as chronic cyanosis (low oxygen levels in blood), multiple previous operations which means the tissue is harder to access and there is higher risk of bleeding; higher likelihood of kidney or liver impairment, higher incidence of pulmonary hypertension and the possibility of being sensitised immunologically. All these factors, alone or in combination mean that this kind of transplants are, in essence, higher risk transplants. Consequently, the mortality at thirty days and one year is significantly higher. Very notably, possibly due to the fact that this patient population tends to be younger than the overall cohort of adult heart transplants and that many of the challenges can slowly be overcome in the long-term after transplant, the mortality trend tends to be very similar at five years and, in fact, a higher proportion of patients with a history of congenital heart disease are alive compared to the rest of heart transplants. In other words, there is a higher up front risk but the long-term outcomes are better.
One subset of patients that warrants special attention is that of some of the most complex ones. These are the patients with single ventricle physiology or also commonly known as those who have had a Fontan procedure. What this means is that there is passive flow from the venous return into the pulmonary circulation without a ‘pump’ or right/subpulmonic ventricle. Blood passively flows through the pulmonary bed and returns to the single ventricle in order to be actively circulated systemically. While this is a life saving procedure, without which these patients would almost certainly die early in childhood, it has a large number of potential long-term complications, some of which add to the challenges seen at the time of requiring a heart transplant as the only choice to prolong life. Not only are there exclusive entities associated to the Fontan procedure which are protein losing enteropathy and Fontan-associated liver disease; but there is also an even higher incidence of arrhythmias, pulmonary hypertension, coagulopathy, congestion and allosensitisation. In addition, these patients have a tendency to develop collateral blood flow that is understood as a mechanism to compensate for the lack of a ‘right sided pump’. The problem with these collateral vessels is that they can represent a higher, and sometimes prohibitively risk of bleeding for thoracic surgery. Another point that is important to underline is that the chronic congestion can lead to liver failure requiring also a liver transplant in order to survive. Evidently, this further increases complexity. It has nevertheless been demonstrated that with adequate patient selection and management by a multidisciplinary team in a high volume centre, it is possible to have a successful dual heart and liver transplant programme for the failing Fontan patient.
It is not all bad news and challenging scenarios for the adult congenital heart disease population. In addition to the better long-term outcomes detailed above, some of the most complex patients that require a liver transplant can count with an immunologic advantage from the donated liver. In other words, in those patients whose immune system is sensitised against potential foreign tissue, the liver provides protection. These patients have lower incidence of rejection and when done carefully, can even afford some degree of incompatibility between the recipient and the donor. This effect is so prominent that the use of liver tissue has even been suggested as a strategy to successfully transplant sensitised patients.
In conclusion, heart transplantation is a formidable therapy for the adequate patient with all different sorts of end stage heart disease. One of this sort of diseases is that of the adult with congenital heart disease which is a patient population that continues to grow thanks to the paediatric successes. This is a special group of patients due to particular challenges that make their transplants higher risk. This risk is translated as higher short term mortality but overall better long-term outcomes. Further scientific and medical advancement is needed to further serve this growing population.