The lower limit of the pulmonary artery index for the extracardiac Fontan circulation

ObjectiveIn the era of the staged Fontan operation, small pulmonary artery index (<250 mm2/m2) has not affected the early or midterm results. The lower limit of pulmonary artery index, however, has not yet been determined. We created numeric models of the Fontan circulation to investigate the lower limit of the pulmonary artery size.MethodsThe extracardiac Fontan geometries with pulmonary artery index, ranging from 50 to 200 mm2/m2 with every 10-mm2/m2 increase, were created from the postoperative angiographic data of 17 patients. The superior and inferior vena caval flow rates at rest and on 2 exercise levels (0.5 and 1.0 W/kg) were given by magnetic resonance imaging flow studies. Respiration-driven transient flow analysis was performed with a finite element solver. Energy loss and mean inferior vena caval pressure were obtained from the results.ResultsEnergy loss and mean inferior vena caval pressure were prominently increased in small pulmonary artery index models, especially during exercise. The pulmonary artery indices sufficient for mean inferior vena caval pressure less than 17 mm Hg were 80 mm2/m2 at rest, 100 mm2/m2 during 0.5-W/kg exercise, and 110 mm2/m2 during 1.0-W/kg exercise. With the increase of pulmonary arterial resistance, mean inferior vena caval pressure increased, but the flow pattern did not change.ConclusionsA small pulmonary artery causes a high pressure gradient and a high energy loss. The lower limit of pulmonary artery index, considering the exercise tolerance, was 110 mm2/m2.