Haemodynamic comparison of a novel flow-divider Optiflo geometry and a traditional total cavopulmonary connection

Abstract

The total cavopulmonary connection (TCPC), the current palliation of choice for single-ventricle heart defects, is typically created with a single cylindrical tunnel or conduit routing inferior vena caval (IVC) flow to the pulmonary arteries. Previous studies have shown the haemodynamic efficiency of the TCPC to be sub-optimal due to the collision of vena caval flow, thus placing an extra energy burden on the single ventricle. The use of a bifurcated graft as the Fontan baffle (i.e. the 'Optiflo') has previously been proposed on the basis of theoretically improved flow efficiency; however, anatomical constraints may limit its effectiveness in some patients. In this study, an alternative approach to flow bifurcation is proposed, where a triangular insert is placed at the distal end of the IVC graft. The proof of concept for this design is demonstrated in two steps: first, determining the optimal insert size at a fixed Fontan graft size through a parametric study; then, characterizing the efficiency as a function of graft size when compared with a TCPC control. TCPC power loss and IVC flow distribution were the primary metrics of interest and were evaluated under both resting and simulated exercise conditions using an in-house computational fluid dynamics solver. Results demonstrated that there was an optimal insert size that improved efficiency compared with the TCPC. For an 18-mm Fontan baffle, TCPC power loss was 4.1 vs 3.7 mW with the optimal flow-divider. The optimal insert was then scaled up for a 20-mm graft, with a similar reduction in power loss observed. Flow distribution results were inconsistent, based on sensitivity to the placement of the insert within the baffle. This study demonstrated proof of concept that the flow-divider has the potential to reduce power loss and streamline IVC flow through the TCPC. An appropriate size for the insert in proportion to the Fontan baffle size was identified that reduced losses compared with a TCPC control under both resting and simulated exercise flow conditions.