Undestanding Complications of Single Ventricle Circulation

Doctor Jacob Cao, University of Sydney

Postgraduate Scholarship

Years funded: 2026 - 2028

Some children are born with heart conditions so complex that they cannot develop the usual two-pump circulation. Instead, they undergo a series of operations to create a unique one-pump circulation called the Fontan circulation, where blood flows to the lungs without being ejected by the heart. While this allows survival into adulthood, the Fontan circulation is not a cure – it is a temporising procedure that places long-term strain on the body. Alarmingly, data from Australia and New Zealand suggest that nearly half of all patients with a Fontan circulation will experience a major complication, such as heart failure, stroke, or death, by the age of 30.

Thanks to improvements in surgical and medical care, survival has improved significantly, and most people with a Fontan circulation are now adults. In fact, the number of Fontan patients in Australia and New Zealand is expected to more than double by 2045 (compared to 2014), and their average age to increase from 18 to 31 years. As this population grows and ages, there is concern that we are heading towards a “tsunami” of complications, that the current healthcare system is unprepared to manage.

Despite the increasing number of Fontan patients, our understanding of their physiology remains poor. Much of what we know is based on childhood care. There is little consensus on how to monitor these patients, what tests to do, or how to treat early signs of decline. Many of the complications occur silently over time and are not picked up until it is too late to intervene.

One of the biggest and most concerning challenges is that a large proportion of Fontan patients, particularly during adolescence and early adulthood, are lost to medical follow-up. This can be due to many reasons: difficulty accessing specialist care, transitions between paediatric and adult health systems, or socioeconomic disadvantage. Studies have shown that 20-40% of people with complex congenital heart disease are lost to care, and this figure may be even higher in geographically large countries like Australia. Being lost to care is strongly linked with poor health outcomes and, tragically, preventable deaths.

My PhD aims to better understand the Fontan population – what causes the complications, how can we prevent them, and what can be done to ensure that everyone has access to appropriate, lifelong care.