[Left-to-right shunt via the foramen ovale in the early neonatal period: evaluation by Doppler color flow mapping].

Serial two-dimensional Doppler echocardiography was performed in 22 normal neonates (2-9 hours after birth). A left-to-right shunt through the foramen ovale and a shunt through the ductus arteriosus were evaluated. Interatrial shunts were observed as transseptal jets in 16 of 22 neonates on initial examination and resolved nine to 26 hours after birth in 13 neonates. In the remaining three neonates the shunts were observed more than six days and resolved by two months of age. Shunts through the ductus arteriosus were observed in all neonates examined as diastolic or continuous flows toward the transducer in the main pulmonary artery at the initial examination. The ductal flow resolved simultaneously with (3/13) or after (10/13) the disappearance of interatrial flow. With two-dimensional echocardiography, the enlarged left atrium and rightward deviation of the interatrial septum were observed in the neonates with interatrial shunts. This was confirmed by the immobile septum primum and the increased ratio of the left atrial to aortic diameters (LA/Ao ratio) on the M-mode echo. The interatrial septum became mobile and the LA/Ao ratio decreased after disappearance of the interatrial shunts. It was speculated that in neonates with large ductal shunts, large pulmonary venous flow enters into the less compliant left ventricle and raises the left ventricular end-diastolic pressure. Then, increased left atrial pressure distends the interatrial septum and causes left-to-right interatrial shunts via the stretched foramen ovale. This shunt is considered one of the physiological phenomena occurring in the early neonatal period.