Ventricular systolic time intervals by simultaneous echocardiographic recording of the semilunar valves during the first days of life: a study of normal newborn infants.

A modified ultrasonic method was used to image simultaneously the semilunar valves in order to study comparative neonatal right and left ventricular systolic time intervals (STI) and phasic respiration. We obtained 72 serial M-mode echocardiograms from 24 normal term infants during the first 3 days of life. Right and left ventricular pre-ejection period (RPEP, LPEP), ejection times (RVET, LVET), and STI ratios (RPEP/RVET, LPEP/LVET) did not vary with respiratory variation during the first days of life; aortic (Q-Ac) and pulmonic valve (Q-Pc) closure intervals were uninfluenced by respiration. Widening of Ac-Pc interval beyond 15 msec was present in 56% by day 3. The RPEP/LVET was greater than LPEP/LVET on the first day--a finding previously described in infants with dextro-transposition of the great arteries. Relatively fixed duration of right ventricular systole (Q-Pc) and the absence of inspiratory widening of the Ac-Pc interval, despite decreasing pulmonary vascular resistance, may be related to differences of right ventricular compliance and pulmonary vascular capacitance in the newborn infant.