Does retrograde diastolic flow in the descending aorta signify impaired systemic perfusion in preterm infants?

High-volume systemic-to-pulmonary ductal shunting occurs frequently in preterm infants and is indicated by diastolic flow reversal in the descending aorta (DAo). We studied the relationship between ductal diameter, diastolic DAo reversal, and left ventricular output (LVO); and superior vena caval (SVC) flow (upper body perfusion) and DAo flow (lower body perfusion) in preterm (<31 wk) infants. Echocardiographic assessments were performed at 5, 12, 24, and 48 h postnatal age (80 infants, median gestation 28 wk, 1060 g). Incidence of ductal patency fell from 100% at 5 h to 72% at 48 h; incidence of pure systemic-to-pulmonary shunting increased from 66% to 95% of infants with patent ducts. In infants with duct diameter greater than the median, 35-48% of infants had DAo flow reversal. In infants with duct diameter greater than median, DAo reversal was associated with 23-29% increases in LVO at 5-48 h, and 35% decreases in DAo flow volume at 24-48 h, but no differences in SVC flow. In conclusion, a large duct with left-to-right shunting is common in preterm infants. Retrograde DAo flow is a marker of high-volume shunt, evidenced by increased LVO. Preterm infants with high-volume ductal shunt may have preserved upper body perfusion but reduced lower body perfusion.