Left ventricular systolic time intervals in preterm infants with patent ductus arteriosus.

Left ventricular systolic time intervals were recorded by a non-invasive technique, from the axillary artery, in 13 preterm infants with patent ductus arteriosus. At the onset of clinical symptoms, consistent with a large left-to right ductal shunt, the preejection intervals were shorter than in a control group of nine preterm infants without a patent ductus. The most pronounced difference was found in the shortening of the isovolumic contraction time, 10.7 msec in the ductus group compared with 22.4 msec in the control group. Ductal closure normalized the isovolumic contraction time to 22.1 msec. The very short preejection intervals, associated with a large ductal shunt, are suggested to reflect a combination of reduced aortic diastolic pressure and increased left ventricular filling pressure. In spite of increased volume load to the left ventricle there were no detectable changes in the systolic time intervals indicating impaired left ventricular function. The left ventricle seems to be competent to handle increased volume load in the presence of reduced afterload in preterm infants with symptomatic left-to right ductal shunts.