Left and right ventricular systolic time intervals in the newborn. Usefulness and limitation in distinguishing respiratory disease from transposition of the great arteries.

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Abstract
To determine their usefulness in evaluating the cyanotic newborn, left and right ventricular systolic time intervals were determined by echocardiography in 67 neonates; 21 were normal, 25 had neonatal respiratory disease and 21 had dextro-transposition of the great arteries. The time intervals were measured from high-speed recordings of aortic and pulmonary valve motion. In normal newborns, the right ventricular pre-ejection period was shorter than the left ventricular pre-ejection period while right ventricular ejection time was longer than that of the left ventricle. The ratio of right ventricular pre-ejection period/ejection time was lower than the ratio of these intervals for the left ventricle in 15 of 21 infants (mean 0.33 .+-. 0.05 SD compared to 0.39 .+-. 0.06, P < 0.001). In patients with respiratory disease, the ratio of right ventricular pre-ejection period/ejection time was increased, primarily due to prolonged pre-ejection period. The ratio of right ventricular pre-ejection period/ejection time was greater than the left ventricular ratio in 15 of 25 patients and the ratios were equal in 8 (mean 0.44 .+-. 0.11 vs. 0.38 .+-. 0.08, P < 0.005). In infants with transposition of the great arteries, right ventricular pre-ejection period/ejection time was greater than left ventricular pre-ejection period/ejection time (0.42 .+-. 0.10 vs. 0.26 .+-. 0.06, P < 0.001), and the lowest values of left ventricular pre-ejection period/ejection time were recorded in this group. The pulmonary valve closed later than the aortic valve in 46(70%) of the subjects studied; simultaneous semilunar valve closure occurred in 19 (29%), and in 1 subject with respiratory disease the pulmonary valve closed before the aortic valve. The ratio of right ventricular pre-ejection period/ejection time was greater than the left ventricular ratio in neonatal respiratory disease and transposition of the great arteries. A very low left ventricular ratio (< 0.25) and delayed closure of the posterior semilunar valve suggest the latter diagnosis.