Objective Exercise intolerance is common in total cavopulmonary connection (TCPC) patients. It has been suggested that power loss (Ploss) inside the TCPC plays a role in reduced exercise performance. Our objective is to establish the role of Ploss inside the TCPC during increased flow, simulating exercise in a patient-specific way.

Methods Cardiac MRI (CMR) was used to obtain flow rates from the caval veins during rest and increased flow, simulating exercise with dobutamine. A 3D reconstruction of the TCPC was created using CMR data. Computational fluid dynamics (CFD) simulations were performed to calculate Ploss inside the TCPC structure for rest and stress conditions. To reflect the flow distribution during exercise, a condition where inferior caval vein (IVC) flow was increased twofold compared with rest was added.

29 TCPC patients (15 intra-atrial lateral tunnel (ILT) and 14 extracardiac conduit (ECC)) were included.

Results Mean Ploss at rest was 1.36±0.94 (ILT) and 3.20±1.26 (ECC) mW/m² (p<0.001), 2.84±1.95 (ILT) and 8.41±3.77 (ECC) mW/m² (p<0.001) during dobutamine and 5.21±3.50 (ILT) and 15.28±8.30 (ECC) mW/m² (p=0.001) with twofold IVC flow. The correlation between cardiac index and Ploss was exponential (ILT: R²=0.811, p<0.001; ECC: R²=0.690, p<0.001).

Conclusions Ploss inside the TCPC structure is limited but increases with simulated exercise. This relates to the anatomy of TCPC and the surgical technique used. In all flow conditions, ILT patients have lower Ploss than ECC patients. We did not find a relationship between Ploss and exercise capacity.