Serial echocardiographic and Doppler evaluation of left ventricular diastolic filling in full-term neonates

Quantitative structural differences exist between fetal and adult myocardium.¹ In the fetus, noncontractile tissue constitutes about 70% of muscle mass in contrast to findings in the adult myocardium in which noncontractile elements represent only about 40% of muscle mass.¹ Friedman² studied isolated myocardium and showed that there was less active tension and higher passive stiffness in fetuses than in adult lambs, suggesting that fetal myocardium is less compliant than adult myocardium. Previous echocardiographic and Doppler studies in fetuses and neonates detected a pattern of mitral velocities showing a lower E-wave amplitude when compared with later normal mitral E peaks.^3,4 These studies detected less early left ventricular (LV) filling in fetuses and neonates that could be related to diminished relaxation and higher muscular stiffness. Previous investigators⁵ followed diastolic LV function in neonates up to the first 4 days of life and, therefore, did not determine the pattern of functional diastolic maturation. Further, prior studies of the neonate have not assessed LV isovolumic relaxation time by serial noninvasive measurement. Our study evaluates, by serial echocardiography and Doppler observations, the LV diastolic filling pattern in full-term neonates after birth and during the first 3 weeks of life to observe the natural evolution in LV diastolic function.