EVOLUTION OF CARDIAC OUTPUT AND FUNCTION THROUGH PERINATAL TRANSITION

At birth, rapid and dramatic changes occur in the circulation as the newborn adapts to postnatal life. Cardiovascular function and adaption during this transition has not been well studied. We sought to investigate changes in cardiac output, cardiovascular function and myocardial mechanics from the late gestation fetus through the perinatal transition period. Nine healthy singleton pregnancies with no maternal or fetal pathology were prospectively recruited. Echocardiograms were performed in the fetus at ≥37 weeks gestational age and at 3 time intervals in the postnatal period between 4-6 hours, 20-24 hours, and 40-48 hours. Cardiac output (CO) was determined by pulse Doppler of the aortic and pulmonary valve and was reported as cc/kg/min for left (LVCO) and right (RVCO) ventricular output. Frame rate optimized left ventricle (LV) images were analyzed by speckle-tracking imaging. Tissue Doppler velocities, longitudinal and circumferential strain and strain rate (SR), peak rotation, twist and twisting rates were recorded. The combined CO (CCO) was similar between fetal and 4-6 hour neonatal time points; however, there was a significant increase in combined CO by 24 hours (mean 414± 76cc/kg/min vs. 341± 83 cc/kg/min at 4-6 hours, p=0.03). Although LVCO did not change significantly, RVCO was higher at 24 hours (mean 252± 65cc/kg/min, vs. 201± 59cc/kg/min at 4-6 hours, p=0.007). There was no further increase in CCO from 24 to 48 hours. LV shortening fraction, circumferential and apical strain were similar between time intervals. There was no difference in mitral inflow E/e’, however basal SR in diastole increased from 4-6 hours to 24 hours (mean SRE 1.97 ± 0.34, SRA 0.99± 0.4 at 4-6 hours vs. SRE 2.52± 0.5, SRA 1.51 ± 0.6 at 24 hours, p= 0.049 and 0.015, respectively). There was no difference in basal and apical rotation, twist and twisting rates between time points. Both the base and apex had more counter-clockwise rotation then clockwise rotation at all time intervals. Although the CCO does not acutely change immediately after birth, a significant increase occurs from 4-6 hours to 24 hours of life secondary to increasing RVCO. This may occur as a consequence of decreasing RV afterload and the impact of acutely increased LV afterload relative to fetal circulation, as well as atrial and ductal shunting. This is coupled with novel observations of increasing diastolic deformation and twist patterns showing similar rotational direction between base and apex at 24 hours.