M-mode ultrasound recording of perinatal geometry and dynamics of the cardiac interventricular septum.

Fetal and early neonatal cardiac interventricular septal geometry and dynamics were studied by the M-mode ultrasound technique in a cross-sectional study between 28 and 40 wk of gestation (n = 193) and a longitudinal antenatal-early neonatal study up until 48 h following delivery (n = 15). Antenatally the interventricular septal diameter shows a linear increase of about 30%. There is no measurable change in septal diameter during systole, suggesting no-involvement in the process of ventricular contraction. In over 50% of the fetuses no measureable septal motion during systole was observed. Paradoxical septal movement only occurred in about 10% of the cases studied. Postnatally there is a further increase in septal thickness of 46% during the end-systolic phase without any significant change during the end-diastolic phase of the cardiac cycle, indicating active involvement of the septum in ventricular contractility. The septal motion pattern is nearly always non-paradoxical.