NONINVASIVE ASSESSMENT OF MYOCARDIAL-CONTRACTILITY, PRELOAD, AND AFTERLOAD IN HEALTHY NEWBORN-INFANTS

Assessment of ventricular contractility in the newborn infant using st andard echocardiographic indexes con result in error due to the unique physiologic state that exists in the neonatal period. It has been sug gested from animal and human studies that maturational alterations in contractility occur with birth and continue throughout infancy. To fur ther investigate these developmental changes, 41 newborn infants aged 3 to 10 days and 37 children aged 3 to 18 years were evaluated with 2- dimensional and M-mode echocardiography. The rate-corrected velocity o f circumferential fiber shortening (VCFc)-end-systolic wall stress (ES WS) relation was used as a load-independent estimate of contractility. Preload, afterload, and ventricular mass were also measured. Despite similar shortening fractions, the infant group had significantly highe r mean VCFc and lower ESWS than the older age group (1.28 vs 1.08 circ /s and 30.2 vs 37.3 gm/m(2), respectively). An inverse linear relation between VCFc and ESWS was found in both age groups. The gamma-interce pt was higher in the infant group (p <0.01), and the slope of the mean regression line was steeper than in the older children (p <0.01). Ven tricular mass in relation to body surface area increased with age. We conclude that (1) newborn infants have a higher basal contractile stat e that cannot be accounted for by lower afterload, (2) myocardial perf ormance is more sensitive to afterload in the immature heart, and (3) shortening fraction may underestimate ventricular function in the newb orn.