Fluid mechanic assessment of the total cavopulmonary connection using magnetic resonance phase velocity mapping and digital particle image velocimetry

The total cavopulmonary connection (TCPC) is currently the most promising m odification of the Fontan surgical repair for single ventricle congenital h eart disease. The TCPC involves a surgical connection of the superior and i nferior vena cavae directly to the left and right pulmonary arteries, bypas sing the right heart. In the univentricular system, the ventricle experienc es a workload which may be reduced by optimizing the cavae-to-pulmonary ana stomosis. The hypothesis of this study was that the energetic efficiency of the connection is a consequence of the fluid dynamics which develop as a f unction of connection geometry. Magnetic resonance phase velocity mapping ( MRPVM) and digital particle image velocimetry (DPIV) were used to evaluate the flow patterns in vitro in three prototype glass models of the TCPC: har ed zero offset, flared 14 mm offset, and straight 21 mm offset. The flow fi eld velocity along the symmetry plane of each model was chosen to elucidate the fluid mechanics of the connection as a function of the connection geom etry and pulmonary artery flow split. The steady flow experiments were cond ucted at a physiologic cardiac output (4 L/min) over three left/right pulmo nary flow splits (70/30, 50/50, and 30/70) while keeping the superior/infer ior vena cavae flow ratio constant at 40/60. MRPVM, a noninvasive clinical technique for measuring how field velocities, was compared to DPIV, an esta blished in vitro fluid mechanic technique. A comparison between the results from both techniques showed agreement of large scale flow features, despit e some discrepancies in the detailed flow fields. The absence of caval offs et in the flared zero offset model resulted in significant caval flow colli sion at the connection site. In contrast, offsetting the cavae reduced the flow interaction and caused a vortex-like low velocity region between the c aval inlets as well as flow disturbance in the pulmonary artery with the le ast total flow. A positive correlation was also found between the direct ca val flow collision and increased power losses. MRPVM was able to elucidate these important fluid flow features, which may be important in future modif ications in TCPC surgical designs. Using MRPVM, two- and three-directional velocity fields in the TCPC could be quantified. Because of this, MRPVM has the potential to provide accurate velocity information clinically and, thu s, to become the in vivo tool for TCPC patient physiological/functional ass essment. (C) 2000 Biomedical Engineering Society. [S0090-6964(00)00610-X7].