Objectives: Recent evidence suggests that conduits implanted in Fontan patients at the age of 2-4 years become undersized for adulthood. The objective of this study is to use computational fluid dynamic models to evaluate the effect of virtual expansion of the Fontan conduit on haemodynamics and energetics of the total cavopulmonary connection (TCPC) under resting conditions and increased flow conditions. Methods: Patient-specific, magnetic resonance imaging-based simulation models of the TCPC were performed during resting and increased flow conditions. The original 16-mm conduits were virtually enlarged to 3 new sizes. The proposed conduit sizes were defined based on magnetic resonance imaging-derived conduit flow in each patient. Flow efficiency was evaluated based on power loss, pressure drop and resistance and thrombosis risk was based on flow stagnation volume and relative residence time (RRT). Results: Models of 5 adult patients with a 16-mm extracardiac Fontan connection were simulated and subsequently virtually expanded to 24-32 mm depending on patient-specific conduit flow. Virtual expansion led to a 40-65% decrease in pressure gradient across the TCPC depending on virtual conduit size. Despite improved energetics of the entire TCPC, the pulmonary arteries remained a significant contributor to energy loss (60-73% of total loss) even after virtual surgery. Flow stagnation volume inside the virtual conduit and surface area in case of elevated RRT (>20/Pa) increased after conduit enlargement but remained negligible (flow stagnation <2% of conduit volume in rest, <0.5% with exercise and elevated RRT <3% in rest, <1% with exercise). Conclusions: Virtual expansion of 16-mm conduits to 24-32 mm, depending on patient-specific conduit flow, in Fontan patients significantly improves TCPC efficiency while thrombosis risk presumably remains low.

The causes and treatment solutions of congenital heart defects are difficult to address and discuss between patient and doctor. This is mainly due to the complex spatial nature of congenital cardiac defects, which makes it difficult for the patients to envision the defect without prior anatomical knowledge and renders the comprehension largely dependent on doctors' (variable) skills to describe the anomaly. To improve communication, 3D printed hearts have been developed, yet these are expensive, difficult to manage for the large collection of defects, and require substantial oral explanation. In addition, the correlation with cardiac function remains rather abstract. Instead, we propose an augmented reality solution, involving a see-through head-mounted display (HMD) extended with a built-in heart rate monitor. In order to increase the presence and the conversational power, the heartbeat of the patient is used to drive an animation of a supersized, floating heart visualisation; enabling the user to inspect a specific heart condition from all sides. To enable this, a universal add-on casing was developed for the HoloLens. Heuristic analysis and pilot tests with $6+15$ participants reveal limitations of the implementation and show that the solution does increase comprehension, although more has to be done to enable a robust system.