Normal Fetal Foramen Flap and Transatrial Doppler Velocity Pattern

To define the normal size of the foramen ovale and the transatrial Doppler velocity pattern in the fetus, we examined foramen ovale size, foramen flap angle, and motion in 48 consecutive normal human fetal ultrasound studies. The maximal foramen diameter was similar in size to aortic root diameter at all gestational ages, differing by no more than 1.0 mm in any study. Attachment angle at the junction of the foramen with the rim of the foramen varied from 30 degrees to 50 degrees; at least a 30-degree angle was present at some point in the cardiac cycle in all studies. A redundant flap, defined as flap reaching greater than one half of the way across to the left atrial free wall, was observed in only three (6%) fetuses. Seventeen patients had transatrial Doppler velocities recorded with sample volume placed in the trough of the foramen flap on the left atrial side of the foramen ovale. A triphasic pattern was evident in systole with predominantly right-to-left flow in all fetuses. A biphasic pattern was present in diastole with bidirectional flow in all fetuses; this is toward the left atrium in early diastole and toward the right atrium in late diastole. Maximal right-to-left velocity ranged from 15 to 40 cm/sec (mean, 23 cm/sec) and was always less than or equal to mitral A wave velocity. Maximal left-to-right velocity ranged from 5 to 20 cm/sec (mean, 13 cm/sec). These data indicate that normal foramen ovale size is similar to aortic diameter, and foramen flap angle should reach 30 degrees or greater.(ABSTRACT TRUNCATED AT 250 WORDS)