Impact of upstream flow mixing on computational hemodynamic evaluation of total cavopulmonary connections

Hemodynamics in total cavopulmonary connections (TCPCs) are closely linked to patient outcomes. Previous studies have simplified assessments by focusing solely on the TCPC itself, overlooking the effects of upstream flow mixing. Consequently, the impact of upstream flow mixing on TCPC hemodynamics remains poorly understood. In this study, we quantified for the first time the effect of flow mixing from all vessels upstream of the TCPC. Hemodynamic metrics were obtained using a cutting-edge computational platform that considers patient-specific TCPC anatomy, peripheral vessels upstream of the TCPC, and corresponding flow data. Results showed that ignoring upstream flow mixing from the upper and lower body could lead to significant errors in calculating hepatic flow distribution—5.0% ± 5.9% and 14.4% ± 10.9%, respectively—but not in power loss (PL) or resistance throughout the TCPC. Interestingly, flow mixing from the upper body induces an additional 25.8 ± 16.8% PL beyond the losses within the TCPC itself, which could inspire innovative clinical treatments to improve patient outcomes. Our study underscores the critical need to account for upstream flow mixing from both the upper and lower body in TCPC hemodynamic assessments. Accurately simulating this mixing requires estimating the flow rates of peripheral vessels. We explored radius-based flow-splitting methods to achieve this, finding that the square law aligns most closely with patient data for lower-body vessels, while the fourth-power law yields satisfactory results for upper-body vessels. These findings could significantly impact clinical practices in Fontan hemodynamic assessment.