In vivo evaluation of Fontan pathway flow dynamics by multidimensional phase-velocity magnetic resonance imaging

Background-Hemodynamic efficiency of Fontan circulation is believed to be a major determinant of outcome. Prior research on flow dynamics in different modifications of Fontan circulation used in vitro models and computer-base d simulation, This study was designed to compare in vivo flow dynamics in t he systemic venous pathway between patients with atriopulmonary anastomosis (APA) and those with total cavopulmonary connection (TCPC). Methods and Results-Multidimensional phase-velocity magnetic resonance imag ing (PV-MRI) studies were performed on 10 patients who had undergone a modi fied Fontan operation (5 with TCPC and 5 with APA) and were free of symptom s. The groups were comparable in terms of age and body surface area. The in terval since surgery was longer for APA than for TCPC subjects. In each sub ject, the phase-velocity data sets were used to generate dynamic velocity-v ector maps and to calculate quantitative flow indices describing the 3-dime nsional blood-flow patterns throughout the cardiac cycle at the widest diam eter of the Fontan pathway. Mean flow rate was comparable between groups. V elocity-vector maps showed areas of flow reversal, flow stagnation, and cir cular flow within APA but not TCPC pathways. Analysis of quantitative flow indices showed that compared with the APA group, flow velocities in the TCP C patients were significantly higher (mean velocity, 14+/-6 cm/s versus 5+/ -3 cm/s; P=0.02), less variable (coefficient of variation, 19+/-2% versus 3 7+/-3.5%; P<0.0001), and more unidirectional (degree of unidirectionality, 89+/-7% versus 71+/-12%; P=0.03). APA pathways were significantly more dila ted than were TCPC pathways (P<0.01) and showed a trend toward larger diame ter with increased interval since surgery (R-2=0.6, P=0.09). Fontan pathway dilatation correlated with flow velocity variability (R-2=0.57, P=0.01) an d inversely with flow unidirectionality (R-2=0.75, P=0.001). Conclusions-Blood flow patterns are more organized and uniform in TCPC than in APA pathways and are significantly influenced by pathway diameter. We s peculate that TCPC may result in a more hemodynamically efficient circulati on than APA because of differences in pathway dimension and uniformity.